Co-reporter:Lan Ma, Hui Tang, and Peiyi Wu
Langmuir October 31, 2017 Volume 33(Issue 43) pp:12326-12326
Publication Date(Web):October 3, 2017
DOI:10.1021/acs.langmuir.7b02884
The microdynamic volume phase transition mechanism of poly[di(ethylene glycol)ethyl ether acrylate] (PDEGA)-based microgels with newly developed thermoresponsive polyionic liquid (PIL) (poly(tetrabutylphosphonium styrenesulfonate) P[P4,4,4,4][SS]) moieties was studied by applying temperature-variable Fourier transform infrared (FTIR) spectroscopy in combination with two-dimensional correlation spectroscopy (2Dcos) and the perturbation correlation moving window (PCMW) technique. It can be found that the content of hydrophilic PIL moieties plays a significant role in the thermally induced phase transition behavior of microgel systems; namely, the microgels containing fewer PIL moieties present a sharp transition behavior and a gel-like state (10%, w/v) in water whereas the microgels with more PIL moieties undergo a slightly broad phase transition process and a flowable solution state. Herein, the C═O···D2O-PIL hydrogen bonds as the interaction between PDEGA and P[P4,4,4,4][SS] moieties result in a complete dehydration process for the microgels with fewer PIL moieties and the dehydrated behavior of SO3– groups acts as the driving force during the phase transition. As for the microgels with more PIL moieties, the whole transition process is dominated by the hydrophobic interaction of C–H groups. Even though the intermolecular hydrogen bonds (C═O···D2O-PIL) appear as well, the more remarkable effect of the Coulombic repulsive force of PIL restrains the water molecules from breaking away, thus causing a gradual and incomplete dehydration process during heating.
Co-reporter:Huazhen Sun, Beibei Tang, and Peiyi Wu
ACS Applied Materials & Interfaces October 11, 2017 Volume 9(Issue 40) pp:35075-35075
Publication Date(Web):September 27, 2017
DOI:10.1021/acsami.7b13013
Metal–organic framework (MOF)/polymer composite proton exchange membranes (PEMs) are being intensively investigated due to their potentials for the systematic design of proton-conducting properties. However, the development of MOF/polymer composite PEMs possessing high selectivity remains exceedingly desirable and challenging for practical application. Herein, two-dimensional (2D) zeolitic imidazolate framework (ZIF-8)/carbon nanotube (CNT) hybrid cross-linked networks (ZCN) were synthesized via the rational design of the physical form of ZIF-8, and then a series of composite PEMs were prepared by hybridizing ZCN with sulfonated poly(ether ether ketone) (SPEEK) matrix. The effect of the incorporation of zero-dimensional (0D) raw ZIF-8 nanoparticles and 2D ZCN on the proton conduction and methanol permeability of the composite membranes was systemically studied. Benefiting from the morphological and compositional advantages of ZCN, the SPEEK/ZCN composite membranes displayed a significant enhancement in proton conductivity under various conditions. In particular, the proton conductivity of SPEEK/ZCN-2.5 membrane was up to 50.24 mS cm–1 at 120 °C-30% RH, which was 11.2 times that of the recast SPEEK membrane (4.50 mS cm–1) and 2.1 times that of SPEEK/ZIF membrane (24.1 mS cm–1) under the same condition. Meanwhile, the methanol permeability of the SPEEK/ZCN composite membranes was greatly reduced. Therefore, novel MOF/polymer composite PEMs with high selectivity were obtained. Our investigation results reveal that the proton conductivity and methanol permeability of the MOF/polymer composite membranes can be effectively tailored via creating more elaborate superstructures of MOFs rather than altering the chemical component. This effective strategy may provide a useful guideline to integrate with other interesting MOFs to design MOF/polymer composite membranes.Keywords: ionic nanochannels; metal−organic framework; methanol permeability; proton conduction; proton exchange membrane; superstructure;
Co-reporter:Wenhui Sun, Zesheng An, and Peiyi Wu
Macromolecules March 14, 2017 Volume 50(Issue 5) pp:2175-2175
Publication Date(Web):March 2, 2017
DOI:10.1021/acs.macromol.7b00020
Copolymerization has been widely used to tune the thermoresponsive behavior of water-soluble polymers. However, the observation of both upper and lower critical solution temperature (UCST and LCST) from the same type of copolymer comprising only one monomer whose homopolymer is thermosensitive and the other monomer whose homopolymer is nonthermosensitive has not been reported. In this work, well-defined thermoresponsive copolymers with tunable compositions have been synthesized by copolymerization of N-acryloylglycinamide (NAGA) and diacetone acrylamide (DAAM) via reversible addition–fragmentation chain transfer (RAFT) polymerization. The thermal transitions of these copolymers are investigated using a combination of turbidimetry, dynamic light scattering (DLS), proton nuclear magnetic resonance (1H NMR), and Fourier transform infrared (FTIR) spectroscopy. The solubility of these copolymers shows a distinct dependence on the composition. While copolymers with up to 30 mol % NAGA are essentially insoluble, copolymers with 35–55 mol % NAGA or 90–100 mol % NAGA have either LCST- or UCST-type transitions respectively, and soluble copolymers are obtained with 60–85 mol % NAGA. The LCST- and UCST-type transitions are tunable with respect to composition, degree of polymerization, polymer concentration, isotope effect and the presence of electrolyte. Insights from variable-temperature 1H NMR and FTIR spectroscopies reveal the key role of hydrogen-bonding between the NAGA and DAAM units in determining the thermal transitions.
Co-reporter:Zhouyue Lei, Shengtong Sun, and Peiyi Wu
ACS Sustainable Chemistry & Engineering June 5, 2017 Volume 5(Issue 6) pp:4499-4499
Publication Date(Web):May 1, 2017
DOI:10.1021/acssuschemeng.7b00313
As important precursors of crystalline phases, amorphous phases of minerals, especially carbonate-based minerals, have been attracting more and more interest in fundamental research and materials chemistry, as well as industrial applications. However, it is still challenging to largely and rapidly synthesize stable amorphous carbonate minerals without the assistance of stabilizers. In this paper, we report an ultrafast method for the high-yield, scale-up synthesis of amorphous carbonate mineral nanoparticles (CaCO3, MgCO3, SrCO3, and their hybrids) within 1 min through the fast diffusion of high-pressure carbon dioxide into ethanol. The present strategy not only allows for the massive production of pure and stable amorphous carbonates but also shows great potential in industrial uses like water treatment.Keywords: Amorphous carbonate minerals; Biomineralization; High-pressure carbon dioxide; Massive production; Water treatment;
Co-reporter:Xiongwei Wang and Peiyi Wu
ACS Applied Materials & Interfaces June 14, 2017 Volume 9(Issue 23) pp:19934-19934
Publication Date(Web):May 23, 2017
DOI:10.1021/acsami.7b04768
Rational distribution and orientation of boron nitride nanosheets (BNNSs) are very significant for a polymer/BNNS composite to obtain a high thermal conductivity at low filler content. In this paper, a high-performance thermal interface material based on exfoliated BNNSs and polystyrene (PS) microspheres was fabricated by latex blending and subsequent compression molding. In this case, BNNSs and PS microspheres first self-assembled to form the complex microspheres via strong electrostatic interactions between them. The as-prepared complex microspheres were further hot-pressed around the glass transition temperature, which brought the selective distribution of BNNSs at the interface of the deformed PS microspheres. As a consequence, a polymer composite with homogeneous dispersion and high in-plane orientation of BNNSs in PS matrix was obtained. Benefitted from this unique structure, the resultant composite exhibits a significant thermal conductivity enhancement of 8.0 W m–1 K–1 at a low filler content of 13.4 vol %. This facile method provides a new strategy to design and fabricate highly thermally conductive composites.Keywords: boron nitride; electrostatic interaction; orientation; polymer composite; polystyrene microspheres; thermal conductivity;
Co-reporter:Wei Jia, Beibei Tang, and Peiyi Wu
ACS Applied Materials & Interfaces July 12, 2017 Volume 9(Issue 27) pp:22620-22620
Publication Date(Web):June 14, 2017
DOI:10.1021/acsami.7b06117
A facile method to prepare high-performance Nafion slightly reduced graphene oxide membranes (N-srGOMs) via vacuum filtration is proposed. The long-range connected ionic nanochannels in the membrane are constructed via the concentration-dependent self-assembling of the amphiphilic Nafion and the hydrophilic–hydrophobic interaction between graphene oxide (GO) and Nafion in water. The obtained N-srGOM possesses high proton conductivity, and low methanol permeability benefitted from the constructed unique interior structures. The proton conductivity of N-srGOM reaches as high as 0.58 S cm–1 at 80 °C and 95%RH, which is near 4-fold of the commercialized Nafion 117 membrane under the same condition. The methanol permeability of N-srGOM is 2.0 × 10–9 cm2 s–1, two-magnitude lower than that of Nafion 117. This novel membrane fabrication strategy has proved to be highly efficient in overcoming the “trade-off” effect between proton conductivity and methanol resistance and displays great potential in DMFC application.Keywords: long-range ionic nanochannel; Nafion; proton exchange membrane; self-assembling; slightly reduced graphene oxide membranes(srGOM);
Co-reporter:Zhuang Rao, Beibei Tang, and Peiyi Wu
ACS Applied Materials & Interfaces July 12, 2017 Volume 9(Issue 27) pp:22597-22597
Publication Date(Web):June 16, 2017
DOI:10.1021/acsami.7b05969
In this study, two functionalized metal–organic frameworks (MOFs), UiO-66-SO3H and UiO-66-NH2, were synthesized. Then, different composite proton exchange membranes (PEMs) were prepared by single doping and codoping of these two MOFs, respectively. It was found that codoping of these two MOFs with suitable sizes was more conducive to the proton conductivity enhancement of the composite PEM. A synergistic effect between these two MOFs led to the the formation of more consecutive hydration channels in the composite PEM. It further greatly promoted the proton conductivity of the composite PEM. The proton conductivity of the codoped PEM reached up to 0.256 S/cm under 90 °C, 95% RH, which was ∼1.17 times higher than that of the recast Nafion (0.118 S/cm). Besides, the methanol permeability of the codoped PEM was prominently decreased owing to the methanol trapping effect of the pores of these two MOFs. Meanwhile, the high water and thermal stabilities of these two MOFs were beneficial to the high proton conductivity stability of the codoped PEM under high humidity and high temperature. The proton conductivity of the codoped PEM was almost unchanged throughout 3000 min of testing under 90 °C, 95% RH. This work provides a valuable reference for designing different functionalized MOFs to synergistically promote the proton conductivities of PEMs.Keywords: codoping; metal−organic frameworks; proton conductivity; proton exchange membrane; synergistic effect;
Co-reporter:Huazhen Sun, Beibei Tang, and Peiyi Wu
ACS Applied Materials & Interfaces August 9, 2017 Volume 9(Issue 31) pp:26077-26077
Publication Date(Web):July 17, 2017
DOI:10.1021/acsami.7b07651
Metal–organic frameworks (MOFs) are being intensively explored as filler materials for polymeric proton exchange membranes (PEMs) due to their potentials for the systematic design and modification of proton-conducting properties. S-UiO-66, a stable MOF with functional groups of −SO3H in its ligands, was selected here to prepare S-UiO-66@graphene oxide (GO) hybrid nanosheets via a facile in situ growth procedure, and then a series of composite PEMs were prepared by hybridizing S-UiO-66@GO and sulfonated poly(ether ether ketone) (SPEEK). The resultant hybrid nanosheets not only possessed abundant −SO3H groups derived from the ligands of S-UiO-66 but also yielded a uniform dispersion of S-UiO-66 onto GO nanosheets, thus effectively eliminating the agglomeration of S-UiO-66 in the membrane matrix. Thanks to the well-tailored chemical composition and nanostructure of S-UiO-66@GO, the as-prepared SPEEK/S-UiO-66@GO composite PEMs present a significant increase in their proton conductivity under various conditions. In particular, the proton conductivity of the SPEEK/S-UiO-66@GO-10 membrane was up to 0.268 S·cm–1 and 16.57 mS·cm–1 at 70 °C-95% RH and 100 °C-40% RH (2.6 and 6.0 times that of recast SPEEK under the same condition), respectively. Moreover, the mechanical property of composite membranes was substantially strengthened and the methanol penetration was well-suppressed. Our investigation indicates the great potential of S-UiO-66@GO in fabricating composite PEMs and also reveals that the high proton conductivity of MOFs can be fully utilized by means of MOF/polymer composite membranes.Keywords: in situ growth; metal−organic framework; optimized ionic nanochannels; proton conduction; proton exchange membrane;
Co-reporter:Yuanyuan Zhou;Hui Tang
Physical Chemistry Chemical Physics 2017 vol. 19(Issue 9) pp:6626-6635
Publication Date(Web):2017/03/01
DOI:10.1039/C6CP08574A
Temperature-induced phase transition together with the liquid–liquid phase separation (LLPS) phenomenon of poly(oligo(2-isopropyl-2-oxazoline)methacrylate) with the comb-shaped architecture (comb-PiPOx) in aqueous solution has been discussed at the molecular level. Differing from linear poly(2-isopropyl-2-oxazoline) (linear-PiPOx), polymer-rich liquid droplets appear at higher temperature compared with the phase transition determined by differential scanning calorimetry (DSC) in comb-PiPOx solution. As investigated using variable-temperature Fourier transform infrared (FTIR) spectra analysis, the densely grafted architecture gives rise to an intra-molecular interaction (hydrophobic interaction of alkyl groups and H-bond of carbonyl groups) dominating the dehydration process of comb-PiPOx. With temperature increment, most of the water within hydrated polymers is expelled to the outer water phase through intra-molecular association, corresponding to the transition temperature. Afterwards, the dehydration of methyl groups on side chain ends reflects the massive aggregation of polymer chains through inter-molecular association, accompanied by hysteretic LLPS.
Co-reporter:Zhuang Rao, Kai Feng, Beibei Tang, and Peiyi Wu
ACS Applied Materials & Interfaces 2017 Volume 9(Issue 3) pp:
Publication Date(Web):December 30, 2016
DOI:10.1021/acsami.6b15873
A new metal–organic framework/graphene oxide composite (IRMOF-3/GO) with high adsorption capacity of copper(II) (maximal adsorption amount = 254.14 mg/g at pH 5.0 and 25 °C) was prepared. Novel and highly efficient nanofiltration (NF) membrane can be facilely fabricated via surface decoration of IRMOF-3/GO onto polydopamine (PDA)-coated polysulfone (PSF) substrate. After decoration of IRMOF-3/GO, membrane surface potential increased from 6.7 to 13.1 mV at pH 5.0 and 25 °C. Due to the adsorption effect of IRMOF-3/GO and the enhancement of membrane surface potential, the prepared NF membrane (the loading amount of IRMOF-3/GO is ca. 13.6 g/m2) exhibits a highly efficient rejection of copper(II). The copper(II) rejection reaches up to ∼90%, while maintaining a relatively high flux of ∼31 L/m2/h at the pressure of 0.7 MPa and pH 5.0. Moreover, the membrane also presents an outstanding stability throughout the 2000 min NF testing period. Thus, the newly developed NF membrane shows a promising potential for water cleaning. This work provides a worthy reference for designing highly efficient NF membranes modified by metal–organic framework (MOF) relevant materials.Keywords: IRMOF-3/GO; nanofiltration; polydopamine; rejection; water cleaning;
Co-reporter:Sheng-tong Sun 孙胜童;Pei-yi Wu 武培怡
Chinese Journal of Polymer Science 2017 Volume 35( Issue 6) pp:700-712
Publication Date(Web):23 April 2017
DOI:10.1007/s10118-017-1938-1
Generalized two-dimensional correlation spectroscopy (2DCOS) and its derivate technique, perturbation correlation moving window (PCMW), have found great potential in studying a series of physico-chemical phenomena in stimuli-responsive polymeric systems. By spreading peaks along a second dimension, 2DCOS can significantly enhance spectral resolution and discern the sequence of group dynamics applicable to various external perturbation-induced spectroscopic changes, especially in infrared (IR), near-infrared (NIR) and Raman spectroscopy. On the basis of 2DCOS synchronous power spectra changing, PCMW proves to be a powerful tool to monitor complicated spectral variations and to find transition points and ranges. This article reviews the recent work of our research group in the application of 2DCOS and PCMW in thermoresponsive polymers, mainly focused on liquid crystalline polymers and lower critical solution temperature (LCST)-type polymers. Details of group motions and chain conformational changes upon temperature perturbation can thus be elucidated at the molecular level, which contribute to the understanding of their phase transition nature.
Co-reporter:Xiongwei Wang, Yong Liu, Peiyi Wu
Chemical Engineering Journal 2017 Volume 328(Volume 328) pp:
Publication Date(Web):15 November 2017
DOI:10.1016/j.cej.2017.07.064
•Water-soluble PIL microgel was used as a soft template and phosphorus dopant.•Nitrogen, phosphorus co-doped mesoporous graphene framework was obtained.•Its specific area and pore structure could be adjusted with microgel content.•High capacitance and excellent ORR catalytic activity were achieved.In this work, we endowed the hydrophobic triphenylphosphine (TPP) with vinyl group as a new copolymerization monomer to synthesize water-soluble microgels, in which the hydrophilic and positively charged TPP-derived chain segments are mainly located at the surface. These synthesized microgel is simultaneously used as a soft template and phosphorus dopant to fabricate nitrogen, phosphorus co-doped mesoporous graphene framework (NP-PG) via a facile hydrothermal process containing graphene oxide and ammonia. Self-assembly of graphene oxide sheets and microgels induced by their electrostatic interaction enable a tight contact between them, which would confine the phosphorus doping mostly in the pore walls. The obtained NP-PG, as a metal-free electrocatalyst for oxygen reduction, shows a comparable electrocatalytic activity to commercial Pt/C catalyst with a peak potential of −0.18 V (vs. Ag/AgCl) and long-term durability. Additionally, it can also be used as a supercapacitor electrode to achieve a high specific capacitance of 245 F g−1 at 0.5 A g−1 and 95% of capacitance retention even after 3000 cycles at 5 A g−1.Download high-res image (109KB)Download full-size image
Co-reporter:Yalei Ren, Yinyu Zhang, Wenhui Sun, Fei Gao, Weigui Fu, Peiyi Wu, Wenguang Liu
Polymer 2017 Volume 126(Volume 126) pp:
Publication Date(Web):22 September 2017
DOI:10.1016/j.polymer.2017.08.016
•Methyl influences dramatically the hydrogen bonding interactions•An automatic rapid healing is achieved in PMNAGA hydrogel•The mechanical properties of hydrogel can be tuned by methylPoly(N-acryloyl glycinamide) (PNAGA) with a protein-like thermoresponsive gelation behavior in water has been developed as a high strength self-healable supramolecular polymer(SP) hydrogels recently. However, harsh conditions, such as high temperature treatment and long waiting time, were required for achieving the complete healing due to strong dual amide hydrogen bonding interactions. In this study, to create an autonomic rapid self-healing SP hydrogel, we deliberately introduced a methyl into the opposite side to dual amide to synthesize N-methacryloyl glycinamide (MNAGA) monomer. Rheological analysis, dynamic light scattering(DLS), Fourier transform infrared (FTIR) spectroscopy, and Gaussian calculation revealed that one substitution methyl caused a considerable perturbation to the hydrogen bonding interaction, thus leading to the increased starting gelling concentration and pronounced decrease in mechanical properties of PMNAGA hydrogel compared to PNAGA hydrogel. The PMNAGA hydrogel was shown to exhibit rapid autonomic reparability without any external intervention, and dynamic swelling measurement indicated this PMNAGA hydrogel could evolve from permanent to transient network due to the metastable hydrogen bonding crosslinkage, depending on its environmental temperature. This intriguing robust, autonomous healing and autolytic PMNAGA hydrogel holds great potential as a short-term embolic agent for blocking blood vessel and artificial tears for moistening eyes.Download high-res image (287KB)Download full-size image
Co-reporter:Yuanyuan Zhou, Lei Hou, Hongyu Chen, Rudi Steenbakkers, Kalyan Sehanobish, Peiyi Wu, Qing Shi
Polymer 2017 Volume 130(Volume 130) pp:
Publication Date(Web):9 November 2017
DOI:10.1016/j.polymer.2017.10.001
•Effects of temperature, EO chain length and resin type on diffusivity are studied.•The molar mass dependence of diffusivity is described by a power law (D=bMn−a).•Two Eyring-type models involved in effects of temperature and EO number are given.A migration kinetics study of a series of oligo (oxyethylene) fatty acid esters of various chain lengths in polyethylene film was studied using Fourier transform infrared (FT-IR) spectroscopy. Diffusion coefficients (D) were determined as a function of temperature, ethylene oxide (EO) chain length and base resin type. The activation energy of diffusion (Ea) for each oligo (oxyethylene) fatty acid ester was determined using the Arrhenius plot of D dependence on inverse temperature. The correlation between obtained D and the number-averaged molecular weight Mn of oligo (oxyethylene) fatty acid ester was described well by a power law expression (D=bMn−a), and the parameters a and b were determined from experimental data. Two other models, which have the form of an Eyring expression, were derived to express the effects of temperature and EO chain length on the diffusion process of oligo (oxyethylene) fatty acid esters. Diffusivity of oligo (oxyethylene) fatty acid ester in linear low density polyethylene (LLDPE) was higher than in high density polyethylene (HDPE) and low density polyethylene (LDPE).Download high-res image (216KB)Download full-size image
Co-reporter:Zhuang Rao, Kai Feng, Beibei Tang, Peiyi Wu
Journal of Membrane Science 2017 Volume 533(Volume 533) pp:
Publication Date(Web):1 July 2017
DOI:10.1016/j.memsci.2017.03.031
•Well interconnected MOF structures were constructed for proton conduction.•Proton conductivity of PEM was greatly improved by MOF structures.•Methanol permeability was reduced by barrier and trapping effects.•PEM exhibited excellent stability in proton conductivity even after 3250 min.To obtain proton exchange membrane (PEM) with high proton conductivities under both high humidity and anhydrous condition, interconnected UiO-66-NH2 was tethered onto graphene oxide (GO) surfaces, and then incorporated into Nafion matrix. Thanks to tethering effect of GO surfaces and interconnection among MOF grains, well interconnected metal-organic framework (MOF) structures (GO@UiO-66-NH2) were constructed. The structural advantage and mechanism of GO@UiO-66-NH2 in proton conduction were explored. It was found the synergistic effect between GO and UiO-66-NH2 with suitable particle size was especially important for promoting proton transfer. Such interconnected structure of MOF on GO also made acid/base pair pathways between –SO3H of Nafion and –NH2 of GO@UiO-66-NH2 more consecutive. This was favorable to proton conduction via both vehicle mechanism and Grotthuss mechanism. The proton conductivity of the as-prepared composite membrane reached up to 0.303 S/cm under 90 °C, 95% RH, and 3.403×10−3 S/cm under anhydrous condition, which was about 1.57 and 1.88 times higher than that of the recast Nafion (0.118 S/cm and 1.182×10−3 S/cm), respectively. Furthermore, the composite membrane showed a reduced methanol permeability, which was attributed to the barrier effect of the two-dimensional GO and the trapping of methanol by UiO-66-NH2 pores.Download high-res image (184KB)Download full-size image
Co-reporter:Wenhui Sun
Physical Chemistry Chemical Physics 2017 vol. 19(Issue 1) pp:127-134
Publication Date(Web):2016/12/21
DOI:10.1039/C6CP06862F
In this paper, we investigated the internal structure and the volume phase transition (VPT) behavior of poly(N-vinylcaprolactam-co-vinylimidazole)/polymerizable carbon nanodot (P(VCL-co-VIM)/PCND) microgels with different amounts of PCNDs. Our study shows that compared to the pure P(VCL-co-VIM) microgel, the hybrid microgels undergo a two-step VPT as the temperature increases and a core–shell(–corona) structure of the hybrid microgels is formed by copolymerization with PCNDs. A change in the amount of PCNDs has effects on both of the volume phase transition temperature and internal structure of microgels. Moreover, based on FT-IR in combination with perturbation correlation moving window (PCMW) and two-dimensional correlation spectral (2Dcos) analyses, the difference in VPT behavior between the shell and the core (corona) structure of the hybrid microgels at the molecular level is elucidated. The core/shell of the hybrid microgels fixed with hydrophilic PCNDs has a higher transition temperature during heating and a more compact structure due to the additional crosslinkers PCNDs.
Co-reporter:Wenhui Sun;Zesheng An
Physical Chemistry Chemical Physics 2017 vol. 19(Issue 37) pp:25746-25753
Publication Date(Web):2017/09/27
DOI:10.1039/C7CP05084D
The distinct thermal transition behavior of thermoresponsive block polymers based on poly(ethylene glycol)methyl ether acrylate (PEGA) and their corresponding disulfide-cross-linked nanogels was studied by using FTIR measurements in combination with two-dimensional correlation spectroscopy (2Dcos). Spectral analysis clearly reveals that the sharp thermal transition of the precursor polymer is accompanied by a forced hydration process induced by the formation of hydrogen bonds between the entrapped water molecules and the CO groups, while the nanogel with a relatively continuous thermal transition is related to the existence of various dehydrating states of the CO groups. The C–H groups in the pyridyl disulfide (PDS) units exhibit a distinct change in the thermoresponsive profile of the precursor and the nanogel to show the effect of the polymer architecture on the thermal transition behavior. Additionally, a portion of the poly(N,N-dimethylacrylamide) (PDMA) segments is entrapped in the nanogel core, indicating that the thiol–disulfide exchange reaction occurs rapidly within the nanogels.
Co-reporter:Yalan Dai
Physical Chemistry Chemical Physics 2017 vol. 19(Issue 28) pp:18556-18564
Publication Date(Web):2017/07/19
DOI:10.1039/C7CP02942J
A new LCST-type thermoresponsive polyelectrolyte P[P4,4,4,4][SS], poly(tetrabutyl phosphonium styrene sulfonate), was introduced to PMEO2MA (poly(2-(2-methoxyethoxy)ethyl methacrylate)) via RAFT polymerization, in order to explore the transition behavior of the block copolymer PMEO2MA-b-P[P4,4,4,4][SS] with two distinct LCST-type segments. A relatively sharp LCST-type phase transition with only one transition point is observed in the turbidity curves, while the whole phase transition is completely different from the micro perspective. The phase transition temperature range is relatively broad, according to the unsynchronized changes of different protons of the two blocks in the temperature-variable 1H NMR analysis. From PCMW analysis, it is found that there exists an obvious two-step phase transition behavior, especially in the region of the C–H groups. Accordingly, we divided the whole transition process into two subregions: 20–40 °C and 40–55 °C in 2Dcos analysis. At the first stage of 20–40 °C, the CH3 groups mainly belonging to the backbones of PMEO2MA blocks have the earliest response to the heating and drive the first step of the dehydration process of PMEO2MA-b-P[P4,4,4,4][SS], resulting in the formation of an intermediate micelle state composed of the collapsed PMEO2MA core and hydrophilic P[P4,4,4,4][SS] corona. In particular, the conformational changes and the more compact structures due to the interaction between the CO groups and P[P4,4,4,4][SS] segments (ν(CO⋯D2O-PILs)) were observed using IR analysis. With the continual increase of the temperature, when the second temperature range of 40–55 °C is reached, the P[P4,4,4,4][SS] segments start to collapse and expel the water molecules, driven by the anions of the poly(ionic liquid)s, with the phosphonium cations being distributed over the relatively hydrophilic outside.
Co-reporter:Yingna Zhang;Hui Tang
Physical Chemistry Chemical Physics 2017 vol. 19(Issue 45) pp:30804-30813
Publication Date(Web):2017/11/22
DOI:10.1039/C7CP05846B
The effect of multiple interactions including anion–macromolecule interaction, water-mediated ion–macromolecule interaction and hydrophobic interaction on the phase transition behaviors of random copolymers P(OEGMA-co-BVIm[X]) comprising oligo(ethylene glycol)methacrylate (OEGMA) and imidazolium-based ionic liquids is investigated in the present study. Temperature-variable 1H NMR and FT-IR investigations demonstrated that the hydration of CH2 side chains in P(OEGMA-co-BVIm[SCN]) was enhanced due to the anion–dipole interaction between a chaotropic anion SCN− and CH2 groups, and dehydration of CO groups served as the driving force of phase transition. In particular, the formation of CO⋯D2O–PIL hydrogen bonds was preferred in P(OEGMA-co-BVIm[SCN]) during the phase transition process considering the interaction of IL–D2O associations and CO groups. This water-mediated ion–macromolecule interaction acted as a “linkage” among polymers, resulting in the gradual dehydration of copolymers and the formation of stable small size micelles. As for P(OEGMA-co-BVIm[NTf2]), water molecules were sequentially squeezed out of the polymer chains upon heating and the self-aggregation of polymer chains was carried out through hydrophobic interaction between OEGMA side chains with IL segments wrapped in the aggregates.
Co-reporter:Zhouyue Lei;Quankang Wang
Materials Horizons (2014-Present) 2017 vol. 4(Issue 4) pp:694-700
Publication Date(Web):2017/07/03
DOI:10.1039/C7MH00262A
An effective and general strategy is developed to prepare a multifunctional and mechanically compliant skin-like sensor by incorporating a 3D printed thermo-responsive hydrogel into a capacitor circuit. The prepared intelligent skin shows a sensitive and stable capacitance–temperature response, and also exhibits very high pressure sensitivity within 1 kPa, allowing it to sense body temperature, gentle finger touches and finger bending motion. This work not only demonstrates that stimuli-responsive hydrogels are promising candidates for artificially intelligent skins, but might also enrich the design of skin-like sensors for future artificial intelligence, wearable devices and human/machine interaction applications.
Co-reporter:Xiongwei Wang;Ludan Zhang
Inorganic Chemistry Frontiers 2017 vol. 4(Issue 4) pp:683-691
Publication Date(Web):2017/04/11
DOI:10.1039/C7QI00009J
In this work, a novel nanocomposite with few-layered ultrasmall MoS2 nanosheets uniformly anchored on a three-dimensional (3D) flower-like carbon (FC) was designed and prepared, where zinc oxide was used as a sacrificial template to prepare a biomass-based FC skeleton by a hydrothermal method and subsequent high-temperature carbonization. When evaluated as an anode material for lithium ion batteries (LIBs), the three-dimensional FC matrix can not only improve the electronic conductivity of the hybrid, but also enable fast electrolyte diffusion to MoS2. The FC–MoS2 hybrid exhibits a high second reversible capacity of 1033 mA h g−1 at 0.2 A g−1, excellent cycling stability with negligible capacity loss after 200 cycles at 1.6 A g−1, and good rate performance. Additionally, the hybrid also shows enhanced electrocatalytic performance for hydrogen evolution. We believe that our method may provide a cost-effective and eco-friendly route to prepare 3D biomass-based composites for energy generation or storage.
Co-reporter:Xiongwei Wang;Ludan Zhang;Congcong Zhang
Inorganic Chemistry Frontiers 2017 vol. 4(Issue 5) pp:889-897
Publication Date(Web):2017/05/16
DOI:10.1039/C7QI00057J
The huge volume variation and poor electronic conductivity of tin oxide (SnO2) during the discharge/charge process greatly limit its practical application in lithium ion batteries (LIBs). Hybridization with graphene is a widely-used method to improve its electrochemical performance, but it still faces some limitations. In this work, we integrate carbon encapsulation with graphene hybridization to synthesize a sandwich-like carbon-coated SnO2/graphene composite via a flexible method. In this case, a mesoporous graphene/carbon framework (MCF) derived from acid etching of an as-prepared graphene@Fe3O4@C composite was used as a robust matrix for the embedment of SnO2. When evaluated as an anode material for LIBs, the resultant MCF@SnO2 composite exhibits a high second reversible capacity of 1205 mA h g−1 at 0.2 A g−1, excellent cycling performance with 668 mA h g−1 capacity retention after 200 cycles at 1.0 A g−1, and a good rate capability. This facile strategy could be further extended to embed other metal oxide nanoparticles into the mesoporous carbon framework for applications in energy conversion and storage.
Co-reporter:Zhouyue Lei;Quankang Wang;Shengtong Sun;Wencheng Zhu
Advanced Materials 2017 Volume 29(Issue 22) pp:
Publication Date(Web):2017/06/01
DOI:10.1002/adma.201700321
In the past two decades, artificial skin-like materials have received increasing research interests for their broad applications in artificial intelligence, wearable devices, and soft robotics. However, profound challenges remain in terms of imitating human skin because of its unique combination of mechanical and sensory properties. In this work, a bioinspired mineral hydrogel is developed to fabricate a novel type of mechanically adaptable ionic skin sensor. Due to its unique viscoelastic properties, the hydrogel-based capacitive sensor is compliant, self-healable, and can sense subtle pressure changes, such as a gentle finger touch, human motion, or even small water droplets. It might not only show great potential in applications such as artificial intelligence, human/machine interactions, personal healthcare, and wearable devices, but also promote the development of next-generation mechanically adaptable intelligent skin-like devices.
Co-reporter:Zhouyue Lei, Shengjie Xu, Jiaxun Wan and Peiyi Wu
Nanoscale 2016 vol. 8(Issue 4) pp:2219-2226
Publication Date(Web):22 Dec 2015
DOI:10.1039/C5NR07335A
In this study, uniform nitrogen-doped carbon quantum dots (N-CDs) were synthesized through a one-step solvothermal process of cyclic and nitrogen-rich solvents, such as N-methyl-2-pyrrolidone (NMP) and dimethyl-imidazolidinone (DMEU), under mild conditions. The products exhibited strong light blue fluorescence, good cell permeability and low cytotoxicity. Moreover, after a facile post-thermal treatment, it developed a lotus seedpod surface-like structure of seed-like N-CDs decorating on the surface of carbon layers with a high proportion of quaternary nitrogen moieties that exhibited excellent electrocatalytic activity and long-term durability towards the oxygen reduction reaction (ORR). The peak potential was −160 mV, which was comparable to or even lower than commercial Pt/C catalysts. Therefore, this study provides an alternative facile approach to the synthesis of versatile carbon quantum dots (CDs) with widespread commercial application prospects, not only as bioimaging probes but also as promising electrocatalysts for the metal-free ORR.
Co-reporter:Kai Feng, Lei Liu, Beibei Tang, Nanwen Li, and Peiyi Wu
ACS Applied Materials & Interfaces 2016 Volume 8(Issue 18) pp:11516
Publication Date(Web):April 14, 2016
DOI:10.1021/acsami.6b02248
Nafion is one of the most widely investigated materials applied in proton exchange membranes. Interestingly, it was found that Nafion could serve as a macroinitiator to induce atom transfer radical polymerization (ATRP) on its C–F sites. In this study, poly(1-vinylimidazole) was selectively bonded on the side chains of Nafion via the Nafion-initiated ATRP process, which was confirmed by the measurements of 1H/19F nuclear magnetic resonance spectra, Fourier transform infrared spectroscopy, X-ray photoelectron spectroscopy, differential scanning calorimeter and matrix-assisted laser desorption ionization-time-of-flight/time-of-flight mass spectrometry. The as-prepared Nafion-co-poly(1-vinylimidazole) (Nafion-PVIm) membranes, with tunable loading amount of imidazole rings, presented greatly enhanced proton conductivity and methanol resistivity due to their well-controlled chemical structures. Especially, chemically bonding PVIm with Nafion chains endowed the Nafion-PVIm membranes with high stability in proton conductivity. For the first time, we revealed the great potentials of the Nafion-initiated ATRP process in developing high-performance proton exchange membranes.Keywords: atom transfer radical polymerization; fuel cell; imidazole; Nafion; proton exchange membrane
Co-reporter:Zhouyue Lei, Wencheng Zhu, Shengjie Xu, Jian Ding, Jiaxun Wan, and Peiyi Wu
ACS Applied Materials & Interfaces 2016 Volume 8(Issue 32) pp:20900
Publication Date(Web):July 28, 2016
DOI:10.1021/acsami.6b07326
A facile poly(vinylpyrrolidone) (PVP)-assisted exfoliation method is utilized to simultaneously exfoliate and noncovalently modify MoSe2 nanosheets. The resultant hydrophilic nanosheets are shown to be promising candidates for biocompatible photothermal therapy (PTT) agents, and they could also be encapsulated into a hydrogel matrix for some intelligent devices. This work not only provides novel insights into exfoliation and modification of transition metal dichalcogenide (TMD) nanosheets but also might spark more research into engineering multifunctional TMD-related nanocomposites, which is in favor of further exploiting the attractive properties of these emerging layered two-dimensional (2D) nanomaterials.Keywords: dual-responsive; photothermal therapy; polymer-assisted exfoliation; smart device; transition metal dichalcogenide
Co-reporter:Wei Jia, Beibei Tang, and Peiyi Wu
ACS Applied Materials & Interfaces 2016 Volume 8(Issue 42) pp:28955
Publication Date(Web):October 5, 2016
DOI:10.1021/acsami.6b07467
In the current study, carbon nanotube/graphene oxide nanoribbon (CNT/GONR) composites were obtained via a chemical “unzipping” method. Then novel CNT/GONR Nafion composite proton exchange membranes (PEMs) were prepared via a blending method. The CNT/GONR nanocomposites induce the adjustment of (—SO3–)n ionic clusters in Nafion matrix to construct long-range ionic nanochannels and keep the activity of ionic clusters at the same time. This dramatically promotes the proton transport of the CNT/GONR Nafion composite PEMs at low humidity and high temperature. The proton conductivity of the composite PEM with 0.5 wt % CNT/GONR is as high as 0.18 S·cm–1 at 120 °C and 40%RH, nine times of recast Nafion (0.02 S·cm–1) at the same conditions. The 1D/2D nanostructure of CNT/GONR nanocomposite also contributes to restrain the methanol permeability of CNT/GONR Nafion. The composite PEM shows a one-order-of-magnitude decrease (2.84 × 10–09 cm2·s–1) in methanol permeability at 40 °C. Therefore, incorporation of this 1D/2D nanocomposite into Nafion PEM is a feasible pathway to conquer the trade-off effect between proton conductivity and methanol resistance.Keywords: 1D/2D; CNT/GONR nanocomposite; ionic nanochannel; Nafion; PEM
Co-reporter:Xiongwei Wang, Ludan Zhang, Zehui Zhang, Aishui Yu and Peiyi Wu
Physical Chemistry Chemical Physics 2016 vol. 18(Issue 5) pp:3893-3899
Publication Date(Web):08 Jan 2016
DOI:10.1039/C5CP06903C
Nickel oxide (NiO) as one of the anode electrode materials for lithium ion batteries (LIBs) has attracted considerable research attention. However, the poor electron conductivity and bad capacity retention performance greatly hinder its wide application. Herein, we prepared a novel three-dimensional (3D) hierarchical porous graphene@NiO@carbon composite via a simple solvothermal process, in which the graphene sheets were uniformly wrapped by porous NiO@carbon nanoflakes. In this case, nickelocene was creatively used as the precursor for both NiO and amorphous carbon, while graphene oxide sheets were employed as a template for the two-dimensional nanostructure and the conductive graphene backbone. The resultant composites possess high surface area (196 m2 g−1) and large pore volume (0.46 cm3 g−1). When it is applied as an anode for LIBs, the carbon outer-layer can effectively suppress the large volume change and serious aggregation of NiO nanoparticles during the charge–discharge process. Therefore, the graphene@NiO@carbon composites show a high reversible capacity of 1042 mA h g−1 at a current density of 200 mA g−1, an excellent rate performance and long cycle life. We believe that our method provides a new route for the fabrication of novel transition metal oxide composites.
Co-reporter:Lei Hou, Qijing Chen, Zesheng An and Peiyi Wu
Soft Matter 2016 vol. 12(Issue 8) pp:2473-2480
Publication Date(Web):19 Jan 2016
DOI:10.1039/C5SM03054D
The lower critical solution temperature (LCST) transition in water and the upper critical solution temperature (UCST) transition in ethanol of poly(oligo(ethylene glycol) acrylate) (POEGA)-based core cross-linked star (CCS) polymers have been investigated and compared by employing turbidity, dynamic light scattering (DLS), 1H NMR and FTIR measurements. Macroscopic phase transitions in water and in ethanol were observed to occur when passing through the transition temperature, as revealed by DLS and turbidity measurements. Analysis by IR indicated that the interactions between the polymer chains and solvent molecules in water are stronger than those in ethanol such that the CCS polymer arm chains in water adopt more extended conformations. Moreover, hydrophobic interaction among the aliphatic groups plays a predominant role in the LCST-type transition in water whereas weak solvation of the polymer chains results in the UCST-type transition in ethanol. Additionally, the LCST-type transition in water was observed to be much more abrupt and complete than the UCST-type transition in ethanol, as suggested by 1H NMR and IR at the molecular level. Finally, an abnormal “forced hydration” phenomenon was observed during the LCST transition upon heating. This study provides a detailed understanding of the subtle distinctions between the thermal transitions of CCS polymers in two commonly used solvents, which may be useful to guide future materials design for a wide range of applications.
Co-reporter:Ge Wang and Peiyi Wu
Soft Matter 2016 vol. 12(Issue 3) pp:925-933
Publication Date(Web):05 Nov 2015
DOI:10.1039/C5SM02032H
The influence of two thermoresponsive polymers, poly(N-isopropylacrylamide) (PNIPAM) and poly(N-vinylcaprolactam) (PVCL), on the phase transition behavior of a thermoresponsive ionic liquid, tributylhexylphosphonium 3-sulfopropylmethacrylate ([P4,4,4,6][MC3S]), was investigated. An obvious distinction was observed in the LCSTs and morphologies of [P4,4,4,6][MC3S]–PNIPAM and [P4,4,4,6][MC3S]–PVCL aqueous solutions, indicating their large differences in dynamic transition processes. In general, PNIPAM can “break” the water structure of [P4,4,4,6][MC3S] to decrease the transition temperature, while PVCL can “make” the water structure to increase it. Surprisingly, [P4,4,4,6][MC3S] has an unusual over-hydration behavior before dehydration while PNIPAM experiences a two-step transition process in [P4,4,4,6][MC3S]–PNIPAM aqueous solution, which has never been reported so far. Further studies revealed that the formation of strong intra-/inter-molecular hydrogen bonds CO⋯D–N in PNIPAM is the driving force for the LCST phenomenon of [P4,4,4,6][MC3S]–PNIPAM solution, while it is the [P4,4,4,6][MC3S] that dominates the phase separation of [P4,4,4,6][MC3S]–PVCL solution.
Co-reporter:Yalan Dai and Peiyi Wu
Physical Chemistry Chemical Physics 2016 vol. 18(Issue 31) pp:21360-21370
Publication Date(Web):07 Jul 2016
DOI:10.1039/C6CP04286D
The assembly properties, thermal phase behavior and microdynamics of well-defined P(MEO2MA-co-OEGMA)-b-P4VP, (poly(2-(2-methoxyethoxy)ethylmethacrylate)-co-poly(oligo(ethylene glycol) methacrylate))-b-poly(4-vinyl pyridine), in aqueous solution during heating are investigated in detail by dynamic light scattering (DLS), turbidity measurements, temperature-variable 1H NMR and FTIR spectroscopy in combination with two-dimensional correlation spectroscopy (2Dcos) and the perturbation correlation moving window (PCMW) technique. It is observed that the chain length of the relatively hydrophobic P4VP segment strongly affects the temperature-induced phase transition behavior of the block copolymers: the copolymers with shorter P4VP7/10 segments exhibit an abrupt phase transition process, while the copolymer with longer P4VP19 blocks presents a relatively gradual transition behavior. Moreover, the two systems with different P4VP segment lengths have different morphologies in aqueous solution: a single-chain globule for shorter P4VP7/10 systems and a core–shell micelle consisting of a relatively hydrophobic P4VP core and a hydrophilic POEGMA-based shell for the longer P4VP19 system. Analysis of spectral results clearly illustrates that the dehydration of the CO groups at the linkages between backbones and pendant chains predominates the sharp phase transition of P(MEO2MA-co-OEGMA)-b-P4VP10, while the dehydration of hydrophobic C–H groups on the side chains in P(MEO2MA-co-OEGMA)-b-P4VP19 leads to the continuous increase of the hydrodynamic diameter (Dh) upon heating.
Co-reporter:Kai Feng, Beibei Tang and Peiyi Wu
Physical Chemistry Chemical Physics 2016 vol. 18(Issue 28) pp:19440-19450
Publication Date(Web):23 Jun 2016
DOI:10.1039/C6CP03176E
Ex situ characterizations based on TGA and XRD techniques revealed that MeOH vapor had little influence on the Nafion microstructures. To reveal the underlying mechanism, in this study, we designed new FTIR-based equipment to track in situ the microstructural changes of a bulk Nafion membrane in MeOH-saturated air. First, an interesting MeOH-breathing phenomenon was found in the ionic domains of Nafion. It demonstrated that there existed a dynamic equilibrium between the sorption and desorption processes of MeOH vapor in Nafion. Second, the FTIR results also detected the high stability of the hydrophobic regions of Nafion in MeOH vapor. The super-acid –CF2–SO3H always retained a small quantity of bonded H2O (H+(H2O)n) inside the Nafion membrane. MeOH vapor was absorbed first into the hydrophilic regions, however, the interactions between –CF2–SO3H and MeOH vapor were much weaker than those between –CF2–SO3H and H+(H2O)n. Therefore, a protective layer composed of residual water formed in the lumen of the hydrophilic ionic domains of Nafion, which protected its hydrophobic regions from the MeOH attack. Hereby, the self-protection ability of Nafion in MeOH vapor was detected for the first time. This work gave a new insight into the complex interplay between Nafion and MeOH vapor.
Co-reporter:Lei Hou and Peiyi Wu
Physical Chemistry Chemical Physics 2016 vol. 18(Issue 23) pp:15593-15601
Publication Date(Web):11 May 2016
DOI:10.1039/C6CP01244B
Turbidity, DLS and FTIR measurements in combination with the perturbation correlation moving window (PCMW) technique and 2D correlation spectroscopy (2Dcos) analysis have been utilized to investigate the LCST-type transition of a oligo ethylene glycol acrylate-based copolymer (POEGA) in aqueous solutions in this work. As demonstrated in turbidity and DLS curves, the macroscopic phase separation was sharp and slightly concentration dependent. Moreover, individual chemical groups along polymer chains also display abrupt changes in temperature-variable IR spectra. However, according to conventional IR analysis, the C–H groups present obvious dehydration, whereas CO and C–O–C groups exhibit anomalous “forced hydration” during the steep phase transition. From these analyses together with the PCMW and 2Dcos results, it has been confirmed that the hydrophobic interaction among polymer chains drove the chain collapse and dominated the phase transition. In addition, the unexpected enhanced hydration behavior of CO and C–O–C groups was induced by forced hydrogen bonding between polar groups along polymer chains and entrapped water molecules in the aggregates, which originated from the special chemical structure of POEGA.
Co-reporter:Zhouyue Lei, Shengjie Xu and Peiyi Wu
Physical Chemistry Chemical Physics 2016 vol. 18(Issue 1) pp:70-74
Publication Date(Web):12 Nov 2015
DOI:10.1039/C5CP06483J
In this study, ultra-thin and porous molybdenum selenide (MoSe2) nanosheets were prepared through a modified liquid exfoliation method as efficient electrocatalysts for the hydrogen evolution reaction (HER). This novel structure enables the exposure of more catalytically active sites and moreover maintains effective electron transport, resulting in a small peak potential of ∼75 mV as well as long-term durability. In addition, due to the facile and economical preparation method as well as its eco-friendly synthetic conditions, this study provides a high-performance HER catalyst with promising commercial application prospects.
Co-reporter:Ge Wang and Peiyi Wu
Langmuir 2016 Volume 32(Issue 15) pp:3728-3736
Publication Date(Web):March 29, 2016
DOI:10.1021/acs.langmuir.6b00392
In this paper, one LCST-type thermoresponsive poly(ionic liquid) (PIL), poly(tetrabutylphosphonium styrenesulfonate) (P[P4,4,4,4][SS]), was introduced to poly(N-isopropylacrylamide) (PNIPAM) by two different ways, mixing and copolymerization. Interestingly, they show distinct thermoresponsive phase transition behaviors, evidenced by temperature-variable 1H nuclear magnetic resonance and Fourier transform infrared in combination with the perturbation correlation moving window (PCMW) technique. The PNIPAM/P[P4,4,4,4][SS] mixture exhibits a sharp and drastic phase transition, similar to that of pure PNIPAM. In the statistical copolymer, PNIPAM-co-P[P4,4,4,4][SS], the thermosensitivity of P[P4,4,4,4][SS] is largely suppressed, resulting in a linear, mild, and incomplete phase transition, which has never been reported before. This abnormal phenomenon is shown to arise from the outstanding hydration ability of P[P4,4,4,4][SS]. Our findings should be conducive to improving our understanding of the interaction between LCST-type polymers with distinct structures and provide a new perspective for preparing thermoresponsive materials with linear phase transition behavior.
Co-reporter:Lei Hou and Peiyi Wu
Macromolecules 2016 Volume 49(Issue 16) pp:6095-6100
Publication Date(Web):August 11, 2016
DOI:10.1021/acs.macromol.6b01359
A newly developed poly(2-methoxyethyl acrylate-co-oligo(ethylene glycol) methyl ether acrylate) (P(MEA-co-OEGA) microgel, synthesized by free radical precipitation copolymerization, displays a linear volume phase transition in water upon heating in a wide range of temperature. Varying cross-linking density in the microgels does not interrupt the linear thermosensitivity. By changing the feeding molar ratio of MEA and OEGA, the linear thermosensitive temperature range can be adjusted, where higher OEGA content results in higher plateau starting temperature. Furthermore, temperature- and pH-sensitive microgels could be achieved by adding another comonomer, acrylic acid (AA). The resulting P(MEA-co-OEGA-co-AA) microgels are ideal candidates to prepare hybrid microgels by in situ formation of silver nanoparticles (AgNPs).
Co-reporter:Qiuwen Wang;Hui Tang
Journal of Polymer Science Part B: Polymer Physics 2016 Volume 54( Issue 3) pp:385-396
Publication Date(Web):
DOI:10.1002/polb.23896
ABSTRACT
Dynamic phase transition and self-assembly mechanism of thermosensitive poly(ethylene oxide)-b-poly(N-vinylcaprolactam) (PEO-b-PVCL) copolymer are explored deeply. A gradual dehydration process with predominated hydrophobic interactions among copolymer chains in the phase transition process distinguishes the copolymer from homopolymer. PVCL in the inner zone is restricted and counter-balanced by the PEO segments based on the sequence order of representative groups during the heating-cooling cycles. Remarkably, PEO shell experiences unusual hydration process, which is first discovered. This hydrophilic shell plays as water absorption sponge layer and captures expelled water from PVCL core, accompanied by gradient distribution of water existed in the assembly structures. Peculiarly, pseudo-linear changes of the integral area of free CO are presented compared with inflection point in the hydrated CO integral area, which propose that a part of hydrated CO forms incomplete dehydrated states. During the cooling process, perfect reversibility is observed without obvious hysteresis. © 2015 Wiley Periodicals, Inc. J. Polym. Sci., Part B: Polym. Phys. 2016, 54, 385–396
Co-reporter:Zhangxin Ye, Youcheng Li, Zesheng An, and Peiyi Wu
Langmuir 2016 Volume 32(Issue 26) pp:6691-6700
Publication Date(Web):June 14, 2016
DOI:10.1021/acs.langmuir.6b01785
Understanding of phase transition mechanism of thermoresponsive polymers is the basis for the rational design of smart materials with predictable properties. Linear ABC triblock terpolymer poly(di(ethylene glycol)ethyl ether acrylate)-b-poly(N,N-dimethylacrylamide)-b-poly(N-vinylcaprolactam) (PDEGA-b-PDMA-b-PVCL) was synthesized by reversible addition–fragmentation chain transfer (RAFT) polymerization. The doubly thermal phase transition of PDEGA-b-PDMA-b-PVCL in aqueous solution was investigated by a combination of nuclear magnetic resonance (NMR), differential scanning calorimetry (DSC), turbidimetry, and dynamic light scattering (DLS). The terpolymer self-assembles into micelles with PDEGA being the core-forming block during the first lower critical solution temperature (LCST) transition corresponding to PDEGA, which is followed by a second LCST transition corresponding to PVCL, resulting in the formation of micellar aggregates. The PDMA middle segment plays an important role as an isolation zone to prevent cooperative dehydration of the PDEGA and PVCL segments, and therefore, two independent LCST transitions corresponding to PDEGA and PVCL were observed. Furthermore, FT-IR with perturbation correlation moving window (PCMW) and two-dimensional spectroscopy (2DCOS) was applied to elucidate the two-step phase transition mechanism of this terpolymer. It was observed that the CH, ester carbonyl, and ether groups of PDEGA change prior to the CH and amide carbonyl groups of PVCL, further supporting that the two phase transitions corresponding to PDEGA and PVCL indeed occur without mutual interferences.
Co-reporter:Shengjie Xu;Dian Li
Advanced Functional Materials 2015 Volume 25( Issue 7) pp:1127-1136
Publication Date(Web):
DOI:10.1002/adfm.201403863
In this work, uniform molybdenum disulfide (MoS2)/tungsten disulfide (WS2) quantum dots are synthesized by the combination of sonication and solvothermal treatment of bulk MoS2/WS2 at a mild temperature. The resulting products possess monolayer thickness with an average size about 3 nm. The highly exfoliated and defect-rich structure renders these quantum dots plentiful active sites for the catalysis of hydrogen evolution reaction (HER). The MoS2 quantum dots exhibit a small HER overpotential of ≈120 mV and long-term durability. Moreover, the strong fluorescence, good cell permeability, and low cytotoxicity make them promising and biocompatible probes for in vitro imaging. In addition, this work may provide an alternative facile approach to synthesize the quantum dots of transition metal dichalcogenides or other layered materials on a large scale.
Co-reporter:Zhouyue Lei, Shengjie Xu, Jiaxun Wan and Peiyi Wu
Nanoscale 2015 vol. 7(Issue 45) pp:18902-18907
Publication Date(Web):26 Oct 2015
DOI:10.1039/C5NR05960G
Boron nitride quantum dots are obtained by a facile sonication–solvothermal technique. They are proven to be promising fluorescent bioimaging probes for bioimaging with remarkably low cytotoxicity and easily integrated into high-performance proton exchange membranes. This work will probably trigger research interest in BN and its new applications in a variety of fields.
Co-reporter:Kai Feng, Beibei Tang and Peiyi Wu
Journal of Materials Chemistry A 2015 vol. 3(Issue 36) pp:18546-18556
Publication Date(Web):03 Aug 2015
DOI:10.1039/C5TA04916D
For a proton exchange membrane (PEM), the ratio of its proton conductivity to its fuel permeability usually defines the membrane selectivity. Generally, a highly selective PEM is preferred for application in direct methanol fuel cells. Herein, sulfonated SiO2@polystyrene core–shell (SiO2@sPS) nanoparticles were synthesized and then imbedded into a Nafion membrane by a blending–casting method. SiO2@sPS partakes in strong interactions with the Nafion polymer, which benefits its dispersion in the membrane matrix. The as-prepared SiO2@sPS + Nafion composite PEM presents a large increase in its proton conductivity owing to the introduction of additional –SO3H groups and hence has optimized channels for proton transport. Meanwhile, a reduced methanol crossover was also observed for the SiO2@sPS + Nafion composite PEM because of the formation of obstructed transport channels for bulk methanol. Besides this, a deep investigation on further enhancement of the membrane’s performance was conducted by etching the SiO2 core and hence forming well-dispersed uniform hollow spheres inside the membrane matrix. The intact hollow sulfonated PS spheres (h-sPS) acted as water reservoirs which in turn could gradually release water to hydrate the membrane under high-temperature and low-humidity conditions. Therefore, compared to the SiO2@sPS + Nafion membrane, the h-sPS + Nafion one presented a further increased proton conductivity at 100 °C under 40% RH. Meanwhile, h-sPS further suppressed methanol penetration by trapping it inside the hollow spheres. Herein, a “H2O donating/methanol accepting” mechanism was proposed for the first time, providing a promising platform to alleviate critical disadvantages of Nafion membranes and thereby fabricate highly selective Nafion-based PEMs.
Co-reporter:Shengjie Xu, Zhouyue Lei and Peiyi Wu
Journal of Materials Chemistry A 2015 vol. 3(Issue 31) pp:16337-16347
Publication Date(Web):03 Jul 2015
DOI:10.1039/C5TA02637G
In this paper, 3D porous MoS2/MoSe2 nanosheet–graphene networks were successfully prepared by a simple mixing solvothermal treatment. The resulting products possessed highly conductive graphene networks on which highly exfoliated MoS2/MoSe2 nanosheets were decorated. This hybrid 3D architecture facilitated loading of 2D nanosheets (including some 0D quantum dots), exposure of active sites, and improvement of electron transfer between the electrode and the catalysts. The highly exfoliated and defect-rich structure of MoS2/MoSe2 nanosheets endowed these composites with plentiful active sites for the electrocatalysis of the hydrogen evolution reaction (HER). The MoSe2 sample exhibited remarkable activity for the HER with a very small overpotential of approximately 70 mV and a low Tafel slope of 61 mV per dec, as well as excellent long-term durability. Moreover, due to the facile and relatively low-cost preparation method, our work might develop promising candidates for Pt-free HER catalysts for future commercial applications and provide an alternative facile approach to fabricate other layered materials confined in graphene hybrid 3D networks on a large scale.
Co-reporter:Lijia Yang, Beibei Tang and Peiyi Wu
Journal of Materials Chemistry A 2015 vol. 3(Issue 31) pp:15838-15842
Publication Date(Web):26 Jun 2015
DOI:10.1039/C5TA03507D
This work studies Nafion based proton exchange membranes (PEMs) modified by a metal–organic framework–graphene oxide composite (ZIF-8@GO). The ZIF-8@GO/Nafion hybrid membrane displays a proton conductivity as high as 0.28 S cm−1 at 120 °C and 40% RH, resulting from a synergetic effect of ZIF-8 and GO.
Co-reporter:Wei Jia, Kai Feng, Beibei Tang and Peiyi Wu
Journal of Materials Chemistry A 2015 vol. 3(Issue 30) pp:15607-15615
Publication Date(Web):18 Jun 2015
DOI:10.1039/C5TA03381K
In the current study, a composite proton exchange membrane (PEM) was prepared by incorporating β-cyclodextrin (β-CD) modified silica nanoparticles (SN-β-CD) into a Nafion matrix. Due to the decoration of β-CD on the SN surface, SN-β-CD possesses excellent compatibility with the Nafion polymer, resulting in a good dispersibility inside the membrane matrix. SN-β-CD brings a better water retention capability for the composite PEM and hence significantly improves the proton conductivity of the composite PEM. Simultaneously, the barrier effect of SN-β-CD which increases the tortuosity of transport channels for bulk methanol leads to an evident reduction in methanol permeability. Herein, a nearly two-order-of-magnitude promotion in membrane selectivity (i.e. the ratio of proton conductivity to membrane permeability) was achieved even under crucial conditions at elevated temperatures or high methanol concentrations.
Co-reporter:Kai Feng, Beibei Tang and Peiyi Wu
Journal of Materials Chemistry A 2015 vol. 3(Issue 24) pp:12609-12615
Publication Date(Web):14 May 2015
DOI:10.1039/C5TA02855H
For the first time, dehydrofluorination reaction was detected between PVDF and Nafion in the presence of ammonia. Cross-linked networks were hence formed in the ammonia-modified Nafion + PVDF composite proton exchange membrane (PEM). They significantly enhanced the fuel resistance, thermal and mechanical stabilities, as well as the structural maintenance of the composite PEM. Meanwhile, at 80 °C, a slight increase in the proton conductivity of the composite PEM was also observed due to its improved water retention capability and the newly formed oxygen-containing functional groups. More importantly, such a highly selective Nafion-based PEM may have strong cost competitiveness in the market of commercial PEMs by virtue of the extremely low cost of PVDF (a dosage of up to 30–50 wt%) and ammonia.
Co-reporter:Ying Tang, Beibei Tang and Peiyi Wu
Journal of Materials Chemistry A 2015 vol. 3(Issue 23) pp:12367-12376
Publication Date(Web):27 Apr 2015
DOI:10.1039/C5TA01823D
In this work, we report a novel method to prepare a positively charged nanofiltration (NF) membrane by rapid counter-ion exchange of a poly(ionic liquid) (PIL) in aqueous solution, which transforms from being hydrophilic to hydrophobic. A thin PIL layer is deposited on the supporting membrane via a phase separation process induced by an ion exchange reaction along with a self-inhibiting effect, and a series of positively charged NF membranes are obtained. The membrane formation process is mainly dominated by the concentration of the hydrophilic PIL and its counter-ions. In brief, the density of the top layer is predominated both by the PIL and its aqueous counter-ion, and the thickness of the surface layer is mainly determined by the aqueous counter-ion. A streaming potential measurement confirmed that the resultant membrane is positively charged when the pH range is below 11. The pure water flux (PWF) was up to 45.3 L m−2 h−1 under the operating pressure of 0.6 MPa. The rejection to MgCl2 of the membrane reached 84% and decreased in the order of MgCl2, NaCl, MgSO4, and Na2SO4. It also shows a high rejection of about 90% to heavy metallic salts such as CuCl2, NiCl2 and CoCl2. The method based on the hydrophilic–hydrophobic transformation of the PIL provides an alternative way to prepare a charged membrane with high performance.
Co-reporter:Ying Tang, Beibei Tang and Peiyi Wu
Journal of Materials Chemistry A 2015 vol. 3(Issue 15) pp:7919-7928
Publication Date(Web):04 Mar 2015
DOI:10.1039/C5TA00212E
A temperature-responsive composite membrane with tunable responsive behavior was prepared by covalently grafting a polymeric ionic liquid (PIL) functionalized temperature-responsive copolymer onto the brominated poly(2,6-dimethyl-1,4-phenylene oxide) (BPPO) supporting membrane. The “switch” effect of the composite membrane can be facilely adjusted by tuning the counter-ion of PIL units of the grafted copolymer based on the transformation between hydrophilicity and hydrophobicity of PIL. The response temperature of the composite membrane was decreased with increasing the content of hydrophobic PIL units. Both the pure water flux and rejection of dyes and polyethylene glycol (PEG) of the composite membrane show a good responsiveness with changing the temperature. The study provides an easily available, flexible and effective method for the design and preparation of a temperature-responsive membrane with tunable responsive behavior to satisfy various applications.
Co-reporter:Zehui Zhang, Fei Wang, Qiao An, Wei Li and Peiyi Wu
Journal of Materials Chemistry A 2015 vol. 3(Issue 13) pp:7036-7043
Publication Date(Web):11 Feb 2015
DOI:10.1039/C4TA06910B
Development of anode materials with high capacity and long cycle life, while maintaining low production cost is crucial for achieving high-performance lithium-ion batteries (LIBs). Herein, we report a simple and cost-effective one-pot solvothermal method to synthesize graphene@Fe3O4@C core–shell nanosheets as a LIB anode with improved electrochemical performances. In this case, ferrocene was used as the precursor for both Fe3O4 and carbon, while graphene oxide was used as a template for the resultant two-dimensional nanostructure and conductive graphene backbone. The obtained graphene@Fe3O4@C core–shell nanosheets have a unique core–shell nanostructure, ultrasmall Fe3O4 nanoparticles (∼6 nm), and a high surface area of ∼136 m2 g−1, as well as show a high reversible capacity of ∼1468 mA h g−1, an excellent rate capability and long cycle life, which reflects the ability of graphene backbone to enhance the conductivity and carbon coating to prevent agglomeration of iron oxide nanoparticles. These findings provide a new approach to the design and synthesis of high-performance anode materials.
Co-reporter:Zehui Zhang, Ludan Zhang, Wei Li, Aishui Yu, and Peiyi Wu
ACS Applied Materials & Interfaces 2015 Volume 7(Issue 19) pp:10395
Publication Date(Web):April 30, 2015
DOI:10.1021/acsami.5b01450
Graphene-based hybrids have been well studied as advanced catalysts and high-performance electrode materials. In this Article, we have fabricated a novel graphene@mesoporous TiO2 nanocrystals@carbon nanosheet by a simple one-step solvothermal method. We have found that titanocene dichloride can act as an extraordinary source with multiple roles for forming TiO2 nanocrystals, ultrathin carbon outer shells, and cross-linkers to binding TiO2 nanocrystals on graphene surface. Moreover, it also serves as a controlling agent to produce mesoporous structure on TiO2 nanocrystals. The loading-concentration of mesoporous TiO2 nanocrystals on graphene sheets can be well controlled by adjusting the initial content of titanocene dichloride. The as-obtained graphene@mTiO2@carbon nanosheets possess a uniform sandwich-like structure, highly crystalline mesoporous TiO2 nanocrystals, a high surface area of ∼209 m2/g, and a large pore volume of ∼0.68 cm3 g–1. When used as anodes for LIBs, the resultant nanosheets show a high reversible capacity (∼145 mAh/g), good rate capability, and long cycling life (capacity remains 110 mAh/g after 100 cycles at a current density of 0.2 A/g). We believe that our method represents a new path way to synthesize novel nanostructured graphene-based hybrids for future applications.Keywords: carbon; graphene; lithium-ion batteries; mesoporous; TiO2 nanocrystals;
Co-reporter:Shengjie Xu, Zhangxin Ye, and Peiyi Wu
ACS Sustainable Chemistry & Engineering 2015 Volume 3(Issue 8) pp:1810
Publication Date(Web):June 18, 2015
DOI:10.1021/acssuschemeng.5b00387
In this work, uniform calcium carbonate (CaCO3) and barium carbonate (BaCO3) crystals were synthesized under the control of poly(2-methacryloyloxyethylphosphorylcholine) (PMPC) via a simple gas–liquid diffusion reaction. Spherical CaCO3 particles with six smooth facets symmetrically distributed on the surface were prepared and systemically characterized by means of TEM, SEM, XRD, Raman, TGA, and FTIR. Time-resolved experiments showed the spherical calcite crystals were transformed from amorphous calcium carbonate (ACC) in the early stage and underwent a dissolution–recrystallization process in the later stage. For BaCO3, dumbbell-shaped crystals that were formed by the dendritic aggregation of rod-like subunits with six sides were generated. Both the morphologies of CaCO3 and BaCO3 crystals could be effectively tuned by changing the crystallization time and concentration of PMPC. Finally, a possible crystallization mechanism for the formation of CaCO3 and BaCO3 particles under the control of PMPC was proposed based on the experiments.Keywords: Dendritic BaCO3; Poly(2-methacryloyloxyethylphosphorylcholine); Spherical calcite with six planes; Time-resolved experiments; Zwitterionic
Co-reporter:Zehui Zhang, Wenhui Sun, and Peiyi Wu
ACS Sustainable Chemistry & Engineering 2015 Volume 3(Issue 7) pp:1412
Publication Date(Web):June 2, 2015
DOI:10.1021/acssuschemeng.5b00156
Carbon dots, which are superior fluorescent nanomaterials with low photobleaching, low toxicity, excellent biocompatibility, and low environmental hazard, have presented exciting opportunities in many fields. However, a better strategy to synthesize fluorescent carbon dots with high quantum yield and further developing their potential applications is still needed. Herein, a one-step hydrothermal strategy was proposed to prepare carbon dots from egg white. The as-prepared CDs, with a diameter of 2.1 nm, were well-dispersed in aqueous solution and showed excellent pH stability. During the hydrothermal reaction, the carbonization, N-doping, and surface functionalization were realized at the same time. With a high quantum yield of 61%, the CDs were used as a probe for detecting metal ions and in living cell imaging. Additionally, multifunctional nanocomposites were also prepared with novel thermosensitive photoluminescent properties.Keywords: Cell imaging; Hydrothermal carbonization; Ions detecting; Multi-stimuli-responsive nanocomposites; Nitrogen-doped fluorescent carbon nanoparticles
Co-reporter:Ge Wang and Peiyi Wu
Soft Matter 2015 vol. 11(Issue 26) pp:5253-5264
Publication Date(Web):19 May 2015
DOI:10.1039/C5SM00603A
The temperature-induced phase transition behaviors of a thermoresponsive ionic liquid (tributylhexylphosphonium 3-sulfopropylmethacrylate, [P4,4,4,6][MC3S]) and its polymer (poly-tributylhexylphosphonium 3-sulfopropylmethacrylate, P[P4,4,4,6][MC3S]) have been investigated using DSC, optical microscopy, temperature-variable 1H NMR, and FT-IR in combination with two-dimensional analysis methods, including perturbation correlation moving window (PCMW) and two-dimensional correlation spectroscopy (2Dcos). We found that there exists a distribution gradient of water molecules in P[P4,4,4,6][MC3S] ranging from hydrophobic backbones to hydrophilic sulfonates. Linked together by covalent bonds, P[P4,4,4,6][MC3S] would form an “urchin-like” structure, which can improve its stability and strengthen the gradient distribution of water. Finally, 2Dcos was employed to elucidate the sequential order of chemical group motions during heating. It is concluded that both [P4,4,4,6][MC3S] and P[P4,4,4,6][MC3S] experience the anionic dominated phase transition process. Moreover, the driving force for the phase transitions is shown to be the dehydration of hydrophobic ester carbonyls.
Co-reporter:Lei Hou and Peiyi Wu
Soft Matter 2015 vol. 11(Issue 35) pp:7059-7065
Publication Date(Web):28 Jul 2015
DOI:10.1039/C5SM01745A
The UCST-type transition of poly(acrylamide-co-acrylonitrile) (P(AAm-co-AN)) (molar fraction of AN: 13.3%; PDI = 3.2) in H2O and D2O is explored and compared by applying turbidity, DLS as well as FTIR measurements. The transition temperature of P(AAm-co-AN) in D2O is observed to be almost 10 °C higher than that in H2O at the same concentration, demonstrating a dramatic solvent isotope effect. Such a phenomenon could be rooted from a stronger interaction among polymer chains in D2O than in H2O, as indicated from DLS results. It is also observed in second-derivative analysis of FTIR spectra in the ν(CO) region, where all CO groups participate in the formation of inter-/intra-chain hydrogen bonds (CO⋯H–N) in D2O while there is still part of relatively “free” CO groups in H2O. Moreover, we find in the temperature-dependent FTIR spectra that CN groups exhibit hydrating behavior while CO groups present increased inter-/intra-molecular hydrogen bonding interaction (CO⋯H–N) upon cooling, revealing the later process to be the driving force of the UCST-type transition.
Co-reporter:Tianjiao Li, Hui Tang and Peiyi Wu
Soft Matter 2015 vol. 11(Issue 15) pp:3046-3055
Publication Date(Web):27 Feb 2015
DOI:10.1039/C5SM00186B
Detailed phase transition processes of poly(2-isopropyl-2-oxazoline) (PIPOZ)/poly(N-isopropylacrylamide) (PNIPAM) and PIPOZ/poly(N-vinylcaprolactam) (PVCL) mixtures in aqueous solution were investigated by DSC, temperature-variable 1H-NMR, optical microscopy and FT-IR spectroscopy measurements accompanied with two-dimensional correlation spectroscopy (2Dcos) and perturbation correlation moving window (PCMW) analytical methods. Through the comparison of these two systems, it is revealed that PVCL chains can interact with PIPOZ chains directly through the polymer–water–polymer cross-linking hydrogen bonds (CO⋯D–O–D⋯OC), which induce their transition process as one. However, in the PIPOZ/PNIPAM mixture, the phase transition of the given component (PNIPAM or PIPOZ) is indirectly affected by the presence of the second component, because the strong hydrogen bonds CO⋯D–N in PNIPAM components forbid the direct connection with PIPOZ, which induces two phase transition processes separately with no liquid–liquid phase separation (LLPS). Additionally, the formation of polymer–water–polymer hydrogen bonds (CO⋯D–O–D⋯OC) is highlighted as the key process in macroscopic LLPS.
Co-reporter:Lei Hou and Peiyi Wu
Soft Matter 2015 vol. 11(Issue 14) pp:2771-2781
Publication Date(Web):10 Feb 2015
DOI:10.1039/C5SM00026B
The LCST-transitions of linear, well-defined polymers of N-isopropylacrylamide (NIPAM) and N-vinylcaprolactam (VCL), including a homopolymer mixture, diblock and statistical copolymers, in water are explored and compared by applying turbidity and FTIR measurements in combination with two-dimensional correlation spectroscopy (2Dcos). Only one transition is observed in all polymer systems, suggesting a dependent aggregation of poly(N-isopropylacrylamide) (PNIPAM) and poly(N-vinylcaprolactam) (PVCL) parts in the phase transition processes. With the help of 2Dcos analysis, it is discovered that the hydrophobic interaction among C–H groups is the driving force for simultaneous collapse of the two distinct thermo-responsive segments. Additionally, the delicate differences within the LCST-transitions thereof have been emphasized, where the phase separation temperatures of the homopolymer mixture and the diblock copolymer are close while that of the statistical copolymer is relatively higher. Moreover, both diblock and statistical copolymers exhibit rather sharp phase transitions while the homopolymer mixture demonstrates a moderately continuous one.
Co-reporter:Tianjiao Li, Hui Tang and Peiyi Wu
Soft Matter 2015 vol. 11(Issue 10) pp:1911-1918
Publication Date(Web):09 Jan 2015
DOI:10.1039/C4SM02812K
The deswelling and swelling behaviors of poly(2-isopropyl-2-oxazoline)-based hydrogel synthesized by a one-pot microwave-assisted solvent-free reaction were investigated. A distinct hydrophobic collapse of the hydrogel compared with the corresponding aqueous solution was observed by FT-IR spectroscopy combined with two-dimensional correlation spectroscopy (2DCOS) and perturbation–correlation moving-window (PCMW) analyses. The volume phase transition (VPT) temperature of 35 °C during heating and the transition temperature range of 41–30 °C during cooling were determined, indicating different dynamic transition mechanisms during heating and cooling. Water expulsion starting from the benzene ring-centered hydrophobic spots to the surroundings was revealed during deswelling. However, during swelling, although the rebuilding of cross-linking hydrogen bond bridges provided a channel-like microstructure to reswell the hydrogel gradually, a slow, unusual recovery of the amide hydrogen bonds to water molecules was observed.
Co-reporter:Shengtong Sun and Peiyi Wu
Physical Chemistry Chemical Physics 2015 vol. 17(Issue 48) pp:32232-32240
Publication Date(Web):06 Nov 2015
DOI:10.1039/C5CP05626H
One easy strategy to comprehend the complex folding/crystallization behaviors of proteins is to study the self-assembly process of their synthetic polymeric analogues with similar properties owing to their simple structures and easy access to molecular design. Poly(2-isopropyl-2-oxazoline) (PIPOZ) is often regarded as an ideal pseudopeptide with similar two-step crystallization behavior to proteins, whose aqueous solution experiences successive lower critical solution temperature (LCST)-type liquid–liquid phase separation upon heating and irreversible crystallization when annealed above LCST for several hours. In this paper, by microscopic observations, IR and Raman spectroscopy in combination with 2D correlation analysis, we show that the second step of PIPOZ crystallization in hot water can be further divided into two apparent stages, i.e., nucleation and crystal growth, and perfect crystalline PIPOZ chains are found to only develop in the second stage. While all the groups exhibit changes in initial nucleation, only methylene groups on the backbone participate in the crystal growth stage. During nucleation, a group motion transfer is found from the side chain to the backbone, and nucleation is assumed to be mainly driven by the cleavage of bridging CO⋯D–O–D⋯OC hydrogen bonds followed by chain arrangement due to amide dipolar orientation. Nevertheless, during crystal growth, a further chain ordering process occurs resulting in the final formation of crystalline PIPOZ chains with partial trans conformation of backbones and alternative side chains on the two sides. The underlying crystallization mechanism of PIPOZ in hot water we present here may provide very useful information for understanding the crystallization of biomacromolecules in biological systems.
Co-reporter:Shengtong Sun and Peiyi Wu
Physical Chemistry Chemical Physics 2015 vol. 17(Issue 46) pp:31084-31092
Publication Date(Web):30 Oct 2015
DOI:10.1039/C5CP05719A
Poly(2-isopropyl-2-oxazoline) (PIPOZ) with an isomeric structure of poly(N-isopropylacrylamide) (PNIPAM) represents an important class of stimuli-responsive synthetic polymers. Unlike PNIPAM, PIPOZ exhibits an unusual heat-induced crystallization behaviour at around 120 °C in the solid state, whose dynamic mechanism involving all group motions and conformational changes is still poorly understood. In this paper, IR spectroscopy in combination with two-dimensional analysis methods – the perturbation correlation moving window (PCMW) and two-dimensional correlation spectroscopy (2DCOS) – was used to monitor and study the conformational changes in the crystallization of PIPOZ in the solid state. The incorporated water molecules are found to be not necessary to assist the solid-state crystallization of the PIPOZ film. PCMW and 2DCOS analyses reveal that following the breaking of minor CH3⋯OC hydrogen bonds, all the group moieties exhibit highly synergetic motions during crystallization, and methylene groups on the backbone do not show significant changes throughout the crystallization process. Raman spectroscopic and molecular dynamics simulation results further support this conclusion. The chain alignment of PIPOZ chains is shown to be mainly achieved by the lateral distortion of coplanar side chains or the ordered chain arrangement of amide dipoles together with the torsion of the backbone through C–N linkages. Upon heating, gauche conformations of methylene groups on the backbone are always dominating, resulting in an ordered PIPOZ chain with alternate side chains and a slightly distorted backbone.
Co-reporter:Kai Feng, Lei Hou, Beibei Tang and Peiyi Wu
Physical Chemistry Chemical Physics 2015 vol. 17(Issue 14) pp:9106-9115
Publication Date(Web):03 Mar 2015
DOI:10.1039/C5CP00203F
Investigating the dehydration process of a Nafion membrane helps to understand the mechanism of the decrease in its proton conductivity under high-temperature and low-humidity conditions. Herein, the influence of thermal treatment on a H2O-saturated Nafion membrane was in situ studied by FTIR spectroscopy. With the aid of generalized two-dimensional correlation spectroscopy (2Dcos), the microstructural changes during the thermal treatment were discussed in detail. In short, side-chain regions first lost H2O, followed by the H2O loss in ionic cluster domains. It resulted in shrunken ionic channels in the Nafion membrane, which exhibited a negative influence on its proton conduction. The immediate aftermath was the crystallization of amorphous backbone regions. All these results were confirmed by TGA and XRD techniques, and the 2Dcos method was first applied in TGA and XRD results in this field.
Co-reporter:Qiuwen Wang, Hui Tang, and Peiyi Wu
Langmuir 2015 Volume 31(Issue 23) pp:6497-6506
Publication Date(Web):May 26, 2015
DOI:10.1021/acs.langmuir.5b00878
Detailed phase transition and conformational changes taking place as a function of temperature in poly(ethylene oxide)-b-poly(N-isopropylacrylamide) (PEO-b-PNIPAM) semidiluted aqueous solutions are elucidated in the present study. By the use of elaborate vibrational spectroscopy techniques in combination with two-dimensional correlation spectroscopy (2Dcos), three transition regions including respective rich domains (<29 °C), loose aggregations (30–36 °C), and dense sphere micelles (>37 °C) are depicted. In particular, subtle variations of hydrogen bonds are detected even under the lower critical solution temperature (LCST), and the respective rich domain regime is marked with strong participation from hydrogen bonding at different concentrations and compositions. Both the formation of intermolecular hydrogen bonds and the less hydration degrees of PNIPAM segments compared with PNIPAM homopolymer at elevated temperatures verify the evolution of PNIPAM from their own domains to loose aggregations with PEO shells. Dense micelles are formed beyond the LCST of PNIPAM, while the outmost PEOs act as buffer layers and postpone the shrinkage of PNIPAM chains. Due to the existence of a buffer layer, higher phase transition temperatures compared with PNIPAM homopolymer are observed.
Co-reporter:Tianjiao Li, Hui Tang, and Peiyi Wu
Langmuir 2015 Volume 31(Issue 24) pp:6870-6878
Publication Date(Web):May 29, 2015
DOI:10.1021/acs.langmuir.5b01009
A detailed phase transition process of poly(2-isopropyl-2-oxazoline) (PIPOZ) in aqueous solution was investigated by means of DSC, temperature-variable 1H NMR, Raman, optical micrographs, and FT-IR spectroscopy measurements. Gradual phase separation accompanied by large dehydration degree and big conformational changes above the lower critical solution temperature (LCST) and facile reversibility were identified. Based on the two-dimensional correlation (2Dcos) and perturbation correlation moving window (PCMW) analyses, the sequence order of chemical group motions in phase transition process was elucidated. Additionally, a newly assigned CH3···O═C intermolecular hydrogen bond at 3008 cm–1 in the PIPOZ system provides extra information on the interactions between C–H and C═O groups. The formation of cross-linking “bridging” hydrogen bonds C═O···D–O–D···O═C (1631 cm–1) is proposed as the key process to induce the liquid–liquid phase separation and polymer-rich phase formation of PIPOZ solution. With slow heating, more and more “bridging” hydrogen bonds were formed and D2O were expelled with an ordered and mostly all-trans conformation adopted in the PIPOZ chains. On the basis of these observations, a physical picture on the molecular evolution of PIPOZ solution during the phase transition process has been derived.
Co-reporter:Lijia Yang, Beibei Tang and Peiyi Wu
Journal of Materials Chemistry A 2014 vol. 2(Issue 43) pp:18562-18573
Publication Date(Web):05 Sep 2014
DOI:10.1039/C4TA03790A
In this work, graphene oxide (GO) was first functionalized with branched polyethyleneimine (PEI). The obtained PEI–GO was incorporated into a brominated poly(2,6-dimethyl-1,4-phenylene oxide) (BPPO) matrix by a covalent bond interaction to form a cross-linking network. Then, a novel ultrafiltration (UF) membrane was prepared via casting and phase-inversion methods. The PEI–GO/BPPO membrane showed highly improved water flux, which was almost 6 times higher than that of the pristine BPPO membrane and 2.5 times higher than that of the GO/BPPO membrane, whereas the rejection of PEI–GO/BPPO membrane was still maintained at a high level. The improvement of membrane performance could be attributed to the special property of PEI–GO and the interactions between PEI–GO and the BPPO matrix. First, a cross-linking network of PEI–GO/BPPO membrane was formed because of the reaction between PEI–GO and the BPPO matrix to provide passageways for water rapidly passing through. Second, the high hydrophilicity of PEI–GO could accelerate the exchange rate between solvent and non-solvent, resulting in a rougher and more hydrophilic surface, higher porosity and a more porous structure. Third, the good dispersion and compatibility of PEI–GO promoted the formation of a uniform structure with fewer defects. Proper molecular weight of PEI was very important for the modification of GO, subsequently resulting in an overall enhancement in membrane performance. Anti-fouling experiments and stability tests of the membranes were also conducted. All of these results were confirmed by various characterizations, such as SEM, TEM, AFM and, etc.
Co-reporter:Kai Feng, Beibei Tang and Peiyi Wu
Journal of Materials Chemistry A 2014 vol. 2(Issue 38) pp:16083-16092
Publication Date(Web):25 Jul 2014
DOI:10.1039/C4TA03207A
In the current study, sulfonated graphene oxide–silica (S-GO–SiO2) nanohybrid particles were obtained first. The FTIR, TGA, XRD, Raman, AFM, FE-SEM and EDX characterizations were employed to confirm the successful decoration of SiO2 onto GO surface and the attachment of sulfonic acid groups onto the GO–SiO2 surface. Then, S-GO–SiO2/Nafion proton exchange membranes (PEMs) were prepared via solution casting. S-GO–SiO2 had a good dispersibility inside the membrane matrix. The increased water uptake and the incorporated –SO3H groups bestowed a large increase in proton conductivity upon these composite PEMs. Meanwhile, the barrier effect of two-dimensional S-GO–SiO2 contributed to the obvious reduction in methanol permeability of the composite PEMs, as a result of the increased tortuosity of the transport channels. Therefore, novel S-GO–SiO2/Nafion PEMs with enhanced selectivity (the ratio of proton conductivity to methanol permeability) were obtained. Even under harsh conditions, such as high methanol concentration and/or increased temperature, the membrane selectivity of S-GO–SiO2/Nafion composite membranes was still nearly two-orders-of-magnitude higher than that of the recast Nafion membrane. It renders this type of composite PEMs a very promising candidate for the application in DMFC. All the conclusions were demonstrated by various characterizations, such as (FE-) SEM, TEM, AFM, FTIR, TGA, water uptake, etc.
Co-reporter:Shengjie Xu and Peiyi Wu
Journal of Materials Chemistry A 2014 vol. 2(Issue 33) pp:13682-13690
Publication Date(Web):24 Jun 2014
DOI:10.1039/C4TA01417K
In this work, a well-dispersed Au cluster/reduced graphene oxide (RGO) composite was synthesized using citric acid (CA) as a reducing and binding agent. The as-prepared composite was systemically characterized by TEM, XPS, TGA and FTIR. TEM image showed Au clusters uniformly distributed on the RGO sheet with an average size of 1.8 nm. The Au clusters/RGO composite exhibited excellent catalytic performance for the oxygen reduction reaction (ORR). Moreover, the electrocatalytic comparison indicated that the long-term durability and methanol tolerance of this composite was superior to the commercial Pt/C catalyst. Therefore, such a composite might be an alternative and more promising non-Pt electrocatalyst for fuel cells.
Co-reporter:Wenlong Li and Peiyi Wu
Polymer Chemistry 2014 vol. 5(Issue 3) pp:761-770
Publication Date(Web):09 Sep 2013
DOI:10.1039/C3PY01104F
The influence of different Ionic Liquids (ILs) on the phase transition behavior of poly(N-vinylcaprolactam) (PVCL) solution is investigated by differential scanning calorimetry (DSC) and turbidity measurements, in combination with FT-IR spectroscopy. The DSC and turbidity results reveal that hydrophilic ILs at a concentration of 0.25 mol L−1 only slightly change the transition temperature. The LCST experiences an increase while the phase separation behavior disappears gradually as the concentration of 1-butyl-3-methylimidazolium tetrafluoroborate ([BMIM][BF4]) increases from 0 to 1.0 mol L−1. In contrast, the addition of hydrophobic ILs, especially 1-ethyl-3-methylimidazolium bis(trifluoromethylsulfonyl) imide ([EMIM][NTf2]), even at a low concentration, greatly raises the LCST, indicating the possibility of hydrogen bonding between [EMIM][NTf2] and PVCL. Finally, temperature-dependent FTIR spectra are employed to elucidate the dynamic mechanism of the different influences on the phase transition of PVCL. The hydrophilic ILs can change the state of the PVCL chains indirectly by varying their interaction with water molecules. For comparison, the formation of hydrogen bonds between the unsaturated C–H of [EMIM][NTf2] and the CO of PVCL results in a higher temperature and more energy to complete the phase transition. However, with the continual increasing of the concentration, extra [EMIM][NTf2] can not be well dispersed in water due to its hydrophobicity, so the LCST undergoes a decrease and finally reaches an equilibrium. Additionally, hydrophilic ILs tend to distribute in the solution, while hydrophobic ILs, especially [EMIM][NTf2], are prone to be wrapped in polymer chains of the aggregates after phase separation. Furthermore, both types of IL experience the process of hydrogen bond disruption and chain aggregation.
Co-reporter:Guijun Yu and Peiyi Wu
Polymer Chemistry 2014 vol. 5(Issue 1) pp:96-104
Publication Date(Web):31 Jul 2013
DOI:10.1039/C3PY00878A
In this study, methylenedianiline-modified graphene oxide (GO-MDA) was incorporated into the diglycidyl ether of a bisphenol A/polyetherimide (DGEBA/PEI) binary system to regulate the Cure-Reaction Induced Phase Separation (CRIPS) behaviour. After the cure-reaction was completed, the fractured surfaces of DGEBA/PEI/GO-MDA composites were etched and observed by SEM measurement to determine the final morphology. Rheological and DSC measurements were used to analyze the effect of GO-MDA on the CRIPS behaviour of the composites. It was found that the CRIPS behaviour of the DGEBA/PEI system, with or without GO-MDA, all followed a spinodal decomposition mechanism. The introduction of GO-MDA increased the complex viscosity and cure-reaction rate of the DGEBA/PEI/GO-MDA composites, which significantly suppressed the development of phase separation and helped freeze the final morphology of the composites at an earlier stage of co-continuous structure. The toughness and modulus of the composites were improved by adding GO-MDA according to DMA measurement and tensile tests, while TGA results showed little decrease in the thermal stability of the composites.
Co-reporter:Wenlong Li and Peiyi Wu
Polymer Chemistry 2014 vol. 5(Issue 19) pp:5578-5590
Publication Date(Web):16 May 2014
DOI:10.1039/C4PY00593G
Dynamic thermal phase transition behavior of a well-defined thermoresponsive ionic liquid (IL), [P4,4,4,4][SS], and its polymer, poly(ionic liquid) (PIL), P[P4,4,4,4][SS], synthesized by modified free radical polymerization was investigated by means of DSC, turbidity, temperature-variable 1H NMR, FT-IR spectroscopy measurements, in combination with perturbation correlation moving window (PCMW) and two-dimensional correlation (2Dcos) analysis. Obvious distinction was observed between the LCST of monomer and polymer solutions indicating their largely different dynamic transition process. Further studies revealed that the aggregation of [P4,4,4,4][SS] is mainly driven by the synergetic variations of cations and anions while the separation process of the P[P4,4,4,4][SS] solution is found to be dominated by conformation changes of anions. Finally, 2Dcos was employed to elucidate the sequence order of chemical group motion during heating. It is concluded that synergetic variations of cations and anions in the [P4,4,4,4][SS] solution resulted in the randomly aggregated structure of globules during separation. In contrast, in the P[P4,4,4,4][SS] solution, anions of repeated units tend to be wrapped into the aggregated globules while cations would distribute at the periphery of globules after transition. Additionally, several unusual phenomena were also interpreted, such as the different varying tendency in LCST of monomer and polymer solutions with increasing concentration, their distinction in the final transmittance and their rather different LCST at the same concentration.
Co-reporter:Bo Zhang, Hui Tang and Peiyi Wu
Polymer Chemistry 2014 vol. 5(Issue 20) pp:5967-5977
Publication Date(Web):19 Jun 2014
DOI:10.1039/C4PY00653D
Dynamic thermal phase transition behavior of a well-defined poly(N-isopropylacrylamide)–poly(2-hydroxyethyl methacrylate) (PNIPAM–PHEMA) interpenetrating polymer network (IPN) microgel in D2O synthesized by two-step precipitation polymerization was studied by means of IR spectroscopy in combination with the perturbation correlation moving window (PCMW) technique and two-dimensional correlation spectroscopy (2Dcos) analysis. Due to the hydrophobic and non-thermo-responsive properties of PHEMA and the special IPN structure, the IPN microgel exhibited an unusual thermally induced collapse process. The introduction of PHEMA would lower the volume phase transition temperature (VPTT) and the volume phase transition degree. 2Dcos was finally employed to discern the sequence order of all the group motion during heating and cooling processes. PHEMA plays different roles in different stages during the volume phase transition. Additionally, as PHEMA exhibits only a slight response to temperature, it would provide the PNIPAM–PHEMA IPN microgel with good reversibility.
Co-reporter:Shengjie Xu and Peiyi Wu
CrystEngComm 2014 vol. 16(Issue 7) pp:1311-1321
Publication Date(Web):31 Oct 2013
DOI:10.1039/C3CE41888J
In this work, a series of metal carbonate minerals such as BaCO3, SrCO3, MnCO3, PbCO3 and CdCO3 with uniform and well-defined morphology were synthesized via the combination of regenerated silk fibroin (RSF) and compressed CO2. The as-prepared samples were systemically characterized by means of TEM, SEM, XRD, TGA and FTIR. The results showed the size, morphology, and nanostructure of crystals could be well controlled by altering the RSF concentration and crystallization time. Based on the time-resolved experiments, we found a spherical BaCO3 superstructure was formed by RSF chains induced stacking of needle-like units, following a “rod-to-dumbbell-to-twined sphere-to-sphere” morphological evolution process. In addition, both amorphous phase and a dissolution–recrystallization process of BaCO3 were observed in crystallization. Finally, a probable crystallization mechanism for the formation of spherical BaCO3 aggregates was proposed based on the experiments.
Co-reporter:Wenlong Li and Peiyi Wu
Soft Matter 2014 vol. 10(Issue 33) pp:6161-6171
Publication Date(Web):13 Jun 2014
DOI:10.1039/C4SM00941J
Influence of bovine serum albumin on the phase transition behavior of the synthetic ionic liquid tetrabutylphosphonium styrenesulfonate ([P4,4,4,4][SS]) together with the interactions between [P4,4,4,4][SS] and bovine serum albumin (BSA) was investigated by differential scanning calorimetry (DSC), turbidity measurements, FT-IR, in combination with perturbation correlation moving window (PCMW) and two-dimensional correlation spectroscopy (2DCOS). Our results reveal that the addition of BSA would increase the phase transition temperature but weaken the transition behavior of [P4,4,4,4][SS] solution. DSC and turbidity data show us that the transition temperature of a ternary system with 20 wt% BSA added is 3 °C higher than that with 20% (w/v) [P4,4,4,4][SS] solution. Interactions between [P4,4,4,4][SS] and BSA together with the phase transition behavior of [P4,4,4,4][SS] are responsible for the denaturation of BSA upon heating. PCMW determined the obvious distinctions in LCST of different chemical groups manifesting their various response sequences in the phase separation and denaturation upon heating. Finally, 2DCOS was employed to elucidate the sequential order of chemical group motions during heating. It is worth noting that the appearance of the isosbestic point in the CO groups of FTIR spectra indicates the direct transformation of the conformation of α-helix, random coil to β-sheet and β-turn without an intermediate transition state. Additionally, the phase separation process of ionic liquid is able to recover to the original state before heating while the denaturation of BSA is irreversible after a cooling process.
Co-reporter:Lei Hou and Peiyi Wu
Soft Matter 2014 vol. 10(Issue 20) pp:3578-3586
Publication Date(Web):20 Feb 2014
DOI:10.1039/C4SM00282B
The self-aggregation behavior of poly(N-isopropylacrylamide)-b-poly(N-vinylcaprolactam) (PNIPAM-b-PVCL) during the thermal-induced phase transition in water was explored by a combination of calorimetric, turbidity, dynamic light scattering (DLS) and FTIR measurements. Only one transition can be observed via all detecting methods, revealing the cooperative aggregation of the two distinct temperature-sensitive segments. What is more, the combination of strong hydrophobic interactions among the entire polymer chains and hydrogen bonds of CO…H–N within PNIPAM segments results in the sharp variations at the LCST and gradual variations above the LCST during the phase transition of PNIPAM-b-PVCL aqueous solution upon heating. Additional analysis by perturbation correlation moving window (PCMW) and two-dimensional correlation spectroscopy (2Dcos) indicates that the hydrophobic C–H groups have an earlier response than the relatively hydrophilic CO groups during the LCST transition.
Co-reporter:Zehui Zhang and Peiyi Wu
RSC Advances 2014 vol. 4(Issue 85) pp:45619-45624
Publication Date(Web):15 Sep 2014
DOI:10.1039/C4RA08945F
3D graphene aerogel-based microporous N-doped carbon composites can be prepared by hydrothermal assembly of graphene oxide with chitosan. A large amount of chitosan added into the system acts as a coating to adhere to the graphene sheets and separate the graphene. During the hydrothermal reaction, the GO is reduced and forms 3D graphene-based frameworks which provide the 3D template for the efficient growth of N-doped carbon on the graphene surface, and the chitosan, which went through a dehydration and carbonization process, forms N-doped carbon strongly adhered to the graphene sheets due to the π–π stacking interactions which effectively solve the aggregation problems between the graphene layers. Furthermore, the resulting microporous N-doped carbon composites show enhanced supercapacitive performance and high efficiency as metal-free catalysts for oxygen reduction reaction.
Co-reporter:Lei Hou and Peiyi Wu
RSC Advances 2014 vol. 4(Issue 74) pp:39231-39241
Publication Date(Web):19 Aug 2014
DOI:10.1039/C4RA06471B
The volume phase transition (VPT) behavior of poly(N-vinylcaprolactam-co-4-vinylpyridine) P(VCL-co-4VP) microgels and their hybrid counterparts containing Au nanoparticles (AuNPs) is explored and compared by FTIR measurements in combination with the perturbation correlation moving window (PCMW) technique and two-dimensional correlation spectroscopy (2Dcos) analysis. It is demonstrated that the incorporation of AuNPs inside the microgels cause a slight dehydration effect on the microgels in the swollen state and an increase of the VPT temperature. Moreover, the interaction between CO and AuNPs can be confirmed by combining the conventional IR and 2Dcos analysis. It is with the help of the additional cross-links between AuNPs and the polymer chains (CO and pyridine groups) in the microgel network and the tendency of AuNPs to aggregate that the hybrid microgels exhibit a much greater dehydration during the VPT, as compared with the nonhybrid ones.
Co-reporter:Yong Liu, Wenlong Li, Lei Hou and Peiyi Wu
RSC Advances 2014 vol. 4(Issue 46) pp:24263-24271
Publication Date(Web):12 May 2014
DOI:10.1039/C4RA02242D
A thermosensitive hyperbranched polyethylenimine (HPEI) partially substituted with N-isopropylacrylamide (NIPAM) monomer (HPEI-pNIPAM) was obtained and its thermodynamic properties were compared with the previously reported fully substituted hyperbranched HPEI-NIPAM polymer using calorimetric and turbidity measurements and one- and two-dimensional correlation infrared spectroscopy. With fewer NIPAM units embedded in the interior of the HPEI backbone, more hydrogen bonds between CO and D2O in the HPEI-pNIPAM polymer could be transformed into CO/D–N bonds and fewer CO related intermediates were formed during heating. During both the heating and cooling of HPEI-pNIPAM, collapse and restoration of the branched backbone occurred first, followed by the formation and debonding of self-associated CO/D–N hydrogen bonds in the same process; all of these processes might be due to a lower conformational confinement effect in the interior backbone leading to the formation of weaker hydrophobic–hydrophobic interactions. The residual NH groups in the hyperbranched thermosensitive HPEI-pNIPAM polymer could be used to bind to graphene oxide by the reaction of NH with epoxyl and carboxyl groups; it could also serve as a blocking reagent to prevent the aggregation of graphene during the preparation process. The new thermosensitive graphene composite obtained has a good potential for use in various biomedical or biosensor applications and provides opportunities for other similar hyperbranched polymers to be developed with responsive effects to multi-stimuli.
Co-reporter:Huiqing Wu, Beibei Tang, Peiyi Wu
Journal of Membrane Science 2014 451() pp: 94-102
Publication Date(Web):
DOI:10.1016/j.memsci.2013.09.018
Co-reporter:Lei Hou;Kai Feng;Hao Gao
Cellulose 2014 Volume 21( Issue 6) pp:4009-4017
Publication Date(Web):2014 December
DOI:10.1007/s10570-014-0458-1
Two-dimensional correlation spectroscopy (2Dcos) analysis on the time-resolved attenuated total reflectance Fourier transform infrared spectroscopy has been employed to investigate the diffusion behavior of water in ethyl cellulose/triethyl citrate (EC/TEC) films with varied TEC content. The diffusion coefficients of water in the EC-based films are calculated from the diffusion curves according to the Fickian Diffusion Model. And they are observed to increase with TEC content, possibly caused by the increased free volume in the film matrix. In the 2Dcos analysis, the broad O–H stretching vibration region is split into at least four bands, which can be assigned to four different states of water molecules, that is, bulk water, cluster water, relatively free water and free water. Moreover, it is found that as water molecules disperse into the EC-based films, cluster water with moderate hydrogen bonds diffuses faster than bulk water with strong hydrogen bonds. The relatively free water and free water are formed during the diffusion process due to their interactions with the films matrix, which makes water molecules confined and restricted in limited space.
Co-reporter:Lijia Yang, Beibei Tang, Peiyi Wu
Journal of Membrane Science 2014 467() pp: 236-243
Publication Date(Web):
DOI:10.1016/j.memsci.2014.05.033
Co-reporter:Lei Hou, Kai Ma, Zesheng An, and Peiyi Wu
Macromolecules 2014 Volume 47(Issue 3) pp:1144-1154
Publication Date(Web):January 23, 2014
DOI:10.1021/ma4021906
The volume phase transition behavior of well-defined thermally responsive poly(2-methoxyethyl acrylate-co-poly(ethylene glycol) methyl ether acrylate)/poly(N,N′-dimethylacrylamide) (P(MEA-co-PEGA)/PDMA) and poly(N-isopropylacrylamide)/poly(N,N′-dimethylacrylamide) (PNIPAM/PDMA) core–shell nanogels, synthesized via reversible addition–fragmentation chain transfer (RAFT) mediated aqueous dispersion polymerization, is studied and compared by applying FTIR measurements in combination with two-dimensional correlation spectroscopy (2Dcos). Analysis through spectral insights clearly illustrates that the continuous dehydration of the C═O groups in the P(MEA-co-PEGA)/PDMA nanogel core predominates the linear volume phase transition while the hydrogen bonding transformation in the PNIPAM/PDMA nanogel core leads to the abrupt decrease in nanogel size on heating. Additionally, considering the core and the shell separately, the data shows that, for both nanogels, the inner core contributes much more to the volume phase transition and the outer shell only undergoes slight dehydration following the core on heating.
Co-reporter:Bo Zhang, Hui Tang, and Peiyi Wu
Macromolecules 2014 Volume 47(Issue 14) pp:4728-4737
Publication Date(Web):July 7, 2014
DOI:10.1021/ma500774g
Dynamic thermal phase transition behavior of a thermoresponsive copolymer P(MEO2MA-co-PEGMA2080) synthesized by ATRP random copolymerization of 2-(2-methoxyethoxy)ethyl methacrylate(MEO2MA, Mn = 188 g/mol) and poly(ethylene glycol) methyl ether methacrylate (PEGMA, Mn= 2080 g/mol) in D2O was studied by means of infrared spectroscopy in combination with two-dimensional correlation analysis (2Dcos). Because of the absence of strong intermolecular hydrogen bonding interactions between polymer chains and the amphiphilic property of PEGMA2080 with long ethylene glycol segments, this copolymer exhibited an unusual thermally induced multistep aggregation process. In general, the change of hydrophilic side chain takes place before carbonyl groups and backbones during the whole process and thus the driving force of this phase transition process of P(MEO2MA-co-PEGMA2080) should be hydration changes of side chains. 2Dcos was finally employed to discern the sequence order of all the group motions during heating process in different temperature regions. It is concluded that during the phase transition P(MEO2MA-co-PEGMA2080) chains successively experience “unimers–clusters–micelles– aggregates” four consecutive conformation changes.
Co-reporter:Kai Feng, Beibei Tang, and Peiyi Wu
ACS Applied Materials & Interfaces 2013 Volume 5(Issue 24) pp:13042
Publication Date(Web):November 27, 2013
DOI:10.1021/am403946z
Proton conductivity and methanol permeability are the most important transport properties of proton exchange membranes (PEMs). The ratio of proton conductivity to methanol permeability is usually called selectivity. Herein, a novel strategy of in situ growth of MoS2 is employed to prepare MoS2/Nafion composite membranes for highly selective PEM. The strong interactions between the Mo precursor ((NH4)2MoS4) and Nafion’s sulfonic groups in a suitable solvent environment (DMF) probably lead to a selective growth of MoS2 flakes mainly around the ionic clusters of the resultant MoS2/Nafion composite membrane. Therefore, it would significantly promote the aggregation and hence lead to a better connectivity of these ionic clusters, which favors the increase in proton conductivity. Meanwhile, the existence of MoS2 in the ionic channels effectively prevents methanol transporting through the PEM, contributing to the dramatic decrease in the methanol permeability. Consequently, the MoS2/Nafion composite membranes exhibit greatly increased selectivity. Under some severe conditions, such as 50 °C with 80 v/v% of methanol concentration, an increase in the membrane selectivity by nearly 2 orders of magnitude compared with that of the recast Nafion membrane could be achieved here, proving our method as a very promising way to prepare high-performance PEMs. All these conclusions are confirmed by various characterizations, such as (FE-) SEM, TEM, AFM, IR, Raman, TGA, XRD, etc.Keywords: high selectivity; molybdenum disulfide; Nafion; proton exchange membrane; selective growth;
Co-reporter:Shengjie Xu, Liu Yong, and Peiyi Wu
ACS Applied Materials & Interfaces 2013 Volume 5(Issue 3) pp:654
Publication Date(Web):January 16, 2013
DOI:10.1021/am302076x
Flowerlike gold nanoparticles (Au NPs)/reduced graphene oxide (RGO) composites were fabricated by a facile, one-pot, environmentally friendly method in the presence of regenerated silk fibroin (RSF). The influences of reaction time, temperature, and HAuCl4: RGO ratio on the morphology of Au NPs loaded on RGO sheets were discussed and a tentative mechanism for the formation of flowerlike Au NPs/RGO composite was proposed. In addition, the flowerlike Au NPs/RGO composite showed superior catalytic performance for oxygen reduction reaction (ORR) to Au/RGO composites with other morphologies. Our work provides an alternative facile and green approach to synthesize functional metal/RGO composites.Keywords: electro-catalysis; flowerlike Au NPs; graphene; oxygen reduction; regenerated silk fibroin;
Co-reporter:Kai Feng, Beibei Tang, and Peiyi Wu
ACS Applied Materials & Interfaces 2013 Volume 5(Issue 4) pp:1481
Publication Date(Web):January 21, 2013
DOI:10.1021/am302995c
In the present work, we prepare rolled up graphene oxide sheets (GOSs) by “evaporating” GOSs from their dispersion to a remote aluminum foil surface. The topological structure of the rolled up GOSs on the aluminum foil surface, which is determined by the quantity of the formed Al3+ ions from the reaction between the alumina on the aluminum foil surface and the weak acidic condensed vapor of the GOS dispersion, can be easily controlled via simply changing the H2O content in the original GOS dispersion. Meanwhile, a GO/Nafion composite membrane for proton exchange membrane fuel cell is successfully prepared utilizing the as-obtained hole-like self-assembled structure of the rolled-up GOSs as a supporting material. The resultant composite membrane exhibits excellent proton conductivity compared to that of the recast Nafion membrane, especially under low-humidity conditions. An increase in proton conductivity by several times could be easily observed here, which is mainly attributed to the rearrangement of the microstructures of Nafion matrix to significantly facilitate the proton transport with rolled up GOSs being independently incorporated. The method reported here offers new degrees of freedom to achieve such transformations among the allotropic forms of carbon and/or develop new carbon material/polymer composite materials with excellent properties.Keywords: carbon nanoscroll; evaporation; graphene oxide; Nafion; porous supporting material; proton exchange membrane; topological transformation;
Co-reporter:Shengtong Sun and Peiyi Wu
ACS Applied Materials & Interfaces 2013 Volume 5(Issue 8) pp:3481
Publication Date(Web):March 22, 2013
DOI:10.1021/am400703v
We demonstrate a facile new and environmentally friendly strategy to fabricate monolithic macroporous gold (MPG) films using graphene sheets as a sacrificial template. Gold nanoparticle (AuNP) decorated graphene sheets were prepared by a one-pot simultaneous reduction of graphene oxide (GO) and gold precursor (HAuCl4) by sodium citrate. Two thermal annealing methods, direct thermal annealing in air and a two-step thermal treatment (in N2 first and subsequently in air), were then employed to remove the template (graphene sheets), which can both produce macroporous structures, but with distinctly different morphologies. We additionally investigated the porosity evolution mechanism as well as the effect of graphene/Au weight ratio and annealing temperature on the nanoarchitecture. The two-step treatment has a more significant templating effect than direct thermal annealing to fabricate MPG films because of the existence of a preaggregation process of AuNPs assisted by graphene sheets in N2. Moreover, the resulting MPG films were found to exhibit excellent surface-enhanced Raman scattering (SERS) activity. Our method can be hopefully extended to the synthesis of other porous materials (such as Ag, Cu, Pt, and ceramic) and much wider applications.Keywords: gold nanoparticles; graphene; macroporous gold; surface-enhanced Raman scattering; templating; thermal annealing;
Co-reporter:Yong Liu and Peiyi Wu
ACS Applied Materials & Interfaces 2013 Volume 5(Issue 8) pp:3362
Publication Date(Web):March 26, 2013
DOI:10.1021/am400415t
The doping of heteroatoms into graphene quantum dot nanostructures provides an efficient way to tune the electronic structures and make more active sites for electro-catalysis, photovoltaic, or light emitting applications. Other than the modification of chemical composition, novel architecture is very desirable to enrich the research area and provides a wide range of choices for the diverse applications. Herein, we show a novel lotus seedpod surface-like pattern of zero-dimension (0D) seed-like N-GODs of ca.3 nm embedded on the surface of a two-dimension (2D) N-GQD sheet of ca.35 nm. It is demonstrated that different photoluminescence (PL) could be tuned easily, and the novel multidimensional structure displays excellent performance toward oxygen reduction reaction in alkaline solutions. Thus, the fabricated N-GQD hybrids show bright perspective in biomedical imaging, biosensors, and conversion and storage of energy.Keywords: graphene quantum dots; architecture; oxygen reduction reaction; photoluminescence;
Co-reporter:Shengtong Sun, Zehui Zhang, and Peiyi Wu
ACS Applied Materials & Interfaces 2013 Volume 5(Issue 11) pp:5085
Publication Date(Web):May 2, 2013
DOI:10.1021/am400938z
Graphene, especially few-layer graphene solid film, has been found to strongly suppress fluorescence and enhance Raman signals of probe molecules. In this paper, we attempt to explore the possibility of using graphene nanocolloids as potential substrates for the enhancement of Raman scattering. Graphene nanocolloids chemically produced from the reduction of graphene oxide by sodium citrate are nearly all monolayers in solution and are also found to exhibit certain surface-enhanced Raman scattering (SERS) activity to common aromatic probe molecules. Interestingly, largely different from few-layer graphene solid film, graphene nanocolloids show maximal SERS activity only when the probe molecules are at resonant laser excitation. According to our analysis, this phenomenon should arise from a combined effect of fluorescence quenching of graphene and a photoinduced charge transfer mechanism, in which the strong charge transfer accounts for the main contribution from close coupling between graphenes and probe molecules photoinduced by resonant excitation as well as the desolvation of graphene sheets and probe molecules.Keywords: desolvation; graphene nanocolloids; photoinduced charge transfer; probe molecules; resonant excitation; surface coupling; surface-enhanced Raman scattering;
Co-reporter:Ying Jing, Hui Tang and Peiyi Wu
Polymer Chemistry 2013 vol. 4(Issue 24) pp:5768-5775
Publication Date(Web):16 Jul 2013
DOI:10.1039/C3PY00764B
Temperature-resolved FTIR spectroscopy in combination with two-dimensional correlation spectroscopy (2Dcos) was employed to elucidate the dynamic mesophase transition behavior of poly{2,5-bis[(4-methoxyphenyl)oxycarbonyl]styrene} (PMPCS) blended with PMPCS grafted graphene oxide (GO-PMPCS) nanofiller. After integration with 2.0 wt% nanofiller, the columnar nematic phase of polymer nanocomposites was retained while deviation of the mesophase transition temperature was identified, which was ascribed to the π–π stacking interactions and charge transfer effect between polymer and GO sheets revealed by Raman and X-ray photoelectron spectroscopy. Based on 2Dcos analysis, a sequential group motion from aromatic rings to carbonyl groups and main chains was discerned at the early stage of the phase transition. It was concluded that surface-tethering of the PMPCS matrix onto GO sheets may be preferred before the mesophase development. A two-step mesophase transition process defined as a physical adsorption process and a mesophase development process under physical cross-linking was illustrated.
Co-reporter:Hengjie Lai and Peiyi Wu
Polymer Chemistry 2013 vol. 4(Issue 11) pp:3323-3332
Publication Date(Web):13 Mar 2013
DOI:10.1039/C3PY00239J
Poly(3-(2-methoxyethyl)-N-vinyl-2-pyrrolidone) (MeOE-PVP), a potential material in the pharmaceutical industry, is an amphiphilic polymer with hydrophobic CH groups and two different hydrophilic groups (CO and C–O), and readily absorbs water vapor from humid environments. In this work, the hydration capabilities and structures of different chemical groups in MeOE-PVP film during water vapor sorption and desorption process are investigated by in situ FTIR spectroscopy, two-dimensional (2D) correlation analysis and density functional theory (DFT) calculations. When the film is tested in a stable humid environment, the changes of the CO group are more sensitive to water vapor than those of the C–O group, which is further verified by 2DIR maps, with much more hydrated structures of the CO group being formed after moisture absorption. Compared with MeOE-PVP in aqueous solution, it is believed that C–O group is a relatively stable hydrophilic group from which is difficult to lose water molecules once it is at the hydrated state. In addition, combined with DFT calculations, it is observed that CO and C–O groups of MeOE-PVP are inclined to interact with water molecules in the form of CO⋯H2O and CO⋯H2O⋯H2O, but as CO⋯(H2O)2, probably due to limited absorption concentration and contact area in the MeOE-PVP film.
Co-reporter:Ying Jing, Hui Tang, Guijun Yu and Peiyi Wu
Polymer Chemistry 2013 vol. 4(Issue 8) pp:2598-2607
Publication Date(Web):14 Feb 2013
DOI:10.1039/C3PY00126A
In our work, graphene oxide (GO) was covalently functionalized with propargyl alcohol to obtain alkyne terminated graphene oxide. These alkyne groups on graphene oxide sheets further reacted with a kind of azido-functionalized liquid crystalline polymer via click chemistry, which was found to be a facile and effective method to graft the liquid crystalline polymer onto GO sheets. The liquid crystalline polymer introduced here was a side-chain liquid crystalline polymer – poly{2,5-bis[(4-methoxyphenyl)oxycarbonyl]styrene} (PMPCS). Azido-functionalized PMPCS was prepared beforehand by atom transfer polymerization to obtain polymers with designed molecular weight. The successful introduction of functional PMPCS chains onto GO sheets was confirmed by FTIR, TEM and AFM characterizations. Thermogravimetric analysis was used to calculate the graft efficiency. Raman and X-ray photoelectron spectroscopies revealed that functional PMPCS had more profound π–π stacking interactions and charge transfer effect with GO sheets after liquid crystalline phase transition. Therefore, the as-prepared GO–PMPCS composite had potential applications in improving the mechanical properties of liquid crystalline PMPCS matrix as had been investigated by rheological measurements.
Co-reporter:Shengtong Sun, Hongna Wang and Peiyi Wu
Soft Matter 2013 vol. 9(Issue 10) pp:2878-2888
Publication Date(Web):28 Jan 2013
DOI:10.1039/C2SM27544A
Hyperbranched polyethylenimine (HPEI) has been modified with N-isopropylacrylamide (NIPAM) by Michael addition to obtain a series of LCST-type thermoresponsive HPEI–NIPAMs. According to turbidity and calorimetric measurements, the phase transition temperature of HPEI–NIPAM shows negative correlations with both the substitution degree of NIPAM groups and concentration (75 to 38 °C from 0.2 to 10 mg mL−1). From FT-IR spectra, two kinds of carbonyl groups are found to exist in the amide I region for HPEI–NIPAM, along with the gradual emergence of a rather small band at 1648 cm−1 due to the lower conformational freedom of amide groups compared to linear PNIPAM. The absence of isosbestic points for C–H and CO groups in the heating-and-cooling cycle also suggests that HPEI–NIPAM has a much more restricted structure. Moreover, two-dimensional correlation infrared spectroscopy was employed to study the thermodynamic self-aggregation and disaggregation behavior of HPEI–NIPAM. A two-step dynamic mechanism was identified during both heating and cooling by distinguishing the sequence order among the hydrogen bond changes, chain collapse and revival as well as water diffusion. Wherein, the formation and breakage of self-associated CO⋯D–N hydrogen bonds are found to be always dominating in the phase transition in close relation to the chain aggregation of HPEI–NIPAM unimers and disaggregation of micelles respectively.
Co-reporter:Bo Zhang, Shengtong Sun and Peiyi Wu
Soft Matter 2013 vol. 9(Issue 5) pp:1678-1684
Publication Date(Web):14 Dec 2012
DOI:10.1039/C2SM27355A
The poly(N-isopropylacrylamide)–poly(2-hydroxyethyl methacrylate) (PNIPAM–PHEMA) interpenetrating polymer network (IPN) microgel was synthesized for the first time. FT-IR, AFM and DLS were used to help propose the mechanism of formation of the IPN microgel. Due to the hydrogen bonds between the NIPAM and HEMA monomers, polymerization of HEMA takes place earlier inside the PNIPAM microgel than on the outside. We also focus our research on the volume phase transition temperature (VPTT) of the IPN microgels obtained at different reaction times during polymerization. Due to the incorporation of the PHEMA chains, the VPTT of the IPN microgel exhibits a decreasing trend with increasing reaction time, which is unusual for an IPN microgel.
Co-reporter:Shengjie Xu and Peiyi Wu
CrystEngComm 2013 vol. 15(Issue 25) pp:5179-5188
Publication Date(Web):30 Apr 2013
DOI:10.1039/C3CE40181B
In this paper, spherical calcium carbonate (CaCO3) with ordered lamella nanostructure was prepared by using regenerated silk fibroin (RSF) as a crystal modifier via compressed CO2. The crystal morphology could be tuned from lens-like to spherical by altering RSF concentration, reaction time, and temperature. Time-resolved experiments showed that the lamellas were formed by several nanoparticles’ aggregation and orientation. Amorphous calcium carbonate (ACC) was seized in the early stage, which would transform to vaterite in a short period. And the dissolution–recrystallization process of CaCO3 was found in a later stage, which was consistent with Ostwald ripening, resulting in the decrease of lamella thickness and the release of RSF that was absorbed in the crystal. Finally, a possible mechanism for the formation of spherical CaCO3 crystal was proposed.
Co-reporter:Wei Li;Zehui Zhang;Biao Kong;Shanshan Feng;Dr. Jinxiu Wang;Dr. Lingzhi Wang;Jianping Yang;Dr. Fan Zhang;Dr. Peiyi Wu;Dr. Dongyuan Zhao
Angewandte Chemie 2013 Volume 125( Issue 31) pp:8309-8313
Publication Date(Web):
DOI:10.1002/ange.201303927
Co-reporter:Huiqing Wu, Beibei Tang, Peiyi Wu
Journal of Membrane Science 2013 428() pp: 341-348
Publication Date(Web):
DOI:10.1016/j.memsci.2012.10.053
Co-reporter:Huiqing Wu, Beibei Tang, Peiyi Wu
Journal of Membrane Science 2013 428() pp: 425-433
Publication Date(Web):
DOI:10.1016/j.memsci.2012.10.042
Co-reporter:Huiqing Wu, Beibei Tang, Peiyi Wu
Journal of Membrane Science 2013 428() pp: 301-308
Publication Date(Web):
DOI:10.1016/j.memsci.2012.09.063
Co-reporter:Ying Jing
Cellulose 2013 Volume 20( Issue 1) pp:67-81
Publication Date(Web):2013 February
DOI:10.1007/s10570-012-9816-z
In this paper, it was discovered that during the heating process from 35 to 63 °C, hydroxypropyl cellulose (HPC) concentrated aqueous solution (20 wt%) would first go through coil-to-globule transition and then sol–gel transition with temperature elevation. The microdynamic mechanisms of the two phase transitions were thoroughly illustrated using mid and near infrared spectroscopy in combination with two-dimensional correlation spectroscopy (2Dcos) and perturbation correlation moving window (PCMW) technique. Mid infrared spectroscopy is an effective way to study the hydrophobic interactions in HPC molecules. And near infrared spectroscopy is a potent method to study hydrogen bonds between HPC molecules and water molecules. Boltzmann fitting and PCMW could help determine the exact transition temperatures of each involving functional groups in the two processes. Moreover, 2Dcos was used to discern the sequential moving orders of the functional groups during the two phase transitions. Depending on the structure of HPC and the thermodynamic conditions, the dominating associative elements in either process might vary. During the coil-to-globule transition, HPC molecules precipitated to form an opaque system with mobility.It was discovered that the driving force of the coil-to-globule transition process in microdynamics could only be the dehydration and hydrophobic interactions of C–H groups. However, in the sol–gel transition, the system crosslinked to form a physical network with no mobility. The driving force of this process in microdynamics was primarily the self-assembly behavior of O–H groups in HPC “active molecules”.
Co-reporter:Shengtong Sun and Peiyi Wu
Macromolecules 2013 Volume 46(Issue 1) pp:
Publication Date(Web):December 27, 2012
DOI:10.1021/ma3022376
Dynamic thermally reversible hydration behavior of a well-defined thermoresponsive copolymer P(MEO2MA-co-OEGMA475) in D2O synthesized by ATRP random copolymerization of 2-(2-methoxyethoxy)ethyl methacrylate (MEO2MA) and oligo(ethylene glycol) methacrylate (Mn = 475 g/mol) was studied by means of IR spectroscopy in combination with perturbation correlation moving window (PCMW) technique and two-dimensional correlation spectroscopy (2DCOS). Largely different from poly(N-isopropylacrylamide) (PNIPAM), P(MEO2MA-co-OEGMA475) exhibits a sharp change below LCST and a gradual change above LCST due to the absence of strong intermolecular hydrogen bonding interactions between polymer chains, and the apparent phase transition is mainly arising from the multiple chain aggregation without a precontraction process of individual polymer chains. Additionally, the self-aggregation process of P(MEO2MA-co-OEGMA475) is found to be mainly dominated or driven by the conformation changes of oxyethylene side chains, which collapse first to get close to the hydrophobic backbones and then distort to expose hydrophilic ether oxygen groups to the “outer shell” of polymer chains as much as possible. On the other hand, PCMW easily determined the phase transition temperature to be ca. 32.5 °C during heating and ca. 31 °C during cooling as well as the transition temperature range to be 28.5–37 °C. 2DCOS was finally employed to discern the sequence order of all the group motions during heating and cooling. It is concluded that during the phase transition P(MEO2MA-co-OEGMA475) chains successively experience “hydrated chains–dehydrated chains–loosely aggregated micelles–densely aggregated micelles” four consecutive conformation changes. The results were further confirmed by temperature-variable 1H NMR analysis and molecular dynamics simulation.
Co-reporter:Wei Li;Zehui Zhang;Biao Kong;Shanshan Feng;Dr. Jinxiu Wang;Dr. Lingzhi Wang;Jianping Yang;Dr. Fan Zhang;Dr. Peiyi Wu;Dr. Dongyuan Zhao
Angewandte Chemie International Edition 2013 Volume 52( Issue 31) pp:8151-8155
Publication Date(Web):
DOI:10.1002/anie.201303927
Co-reporter:Shengjie Xu;Danping Shen
Journal of Nanoparticle Research 2013 Volume 15( Issue 4) pp:
Publication Date(Web):2013 April
DOI:10.1007/s11051-013-1577-6
Hematite nanoparticle-coated magnetic composite fiber was prepared in supercritical carbon dioxide (scCO2). With the help of scCO2, cellulose did not need to be dissolved and regenerated and it could be in any form (e.g., cotton wool, filter paper, textile, etc.). The penetrating and swelling effect of scCO2, the slowing reaction rate of weak alkalis, and the template effect of cellulose fibers were discovered to be the key factors for the fabrication of ordered cellulose/Fe2O3 composite fibers. The structures of the composite fibers as well as the layers of Fe2O3 particles were characterized by means of scanning/transmission electron microscopy, X-ray diffraction, X-ray photoelectron spectroscopy, and Raman investigation. It was found that α-Fe2O3 granules which ranged from 30 to 85 nm with average diameter around 55 nm would be generated on the surface of cellulose fibers via potassium acetate, while irregular square prisms (ranged from 200 to 600 nm) which were composed of smaller nanoparticles (~10 nm) would be fabricated via urea. And, the obtained composite was highly water repellent with superparamagnetic or ferromagnetic properties.
Co-reporter:Kai Feng, Yewen Cao and Peiyi Wu
Journal of Materials Chemistry A 2012 vol. 22(Issue 23) pp:11455-11457
Publication Date(Web):18 Apr 2012
DOI:10.1039/C2JM31713C
Graphene oxide (GO) can “evaporate” and then transform into quasi-carbon nanotubes on the aluminium foil surface placed 4 cm above an evaporating aqueous GO dispersion. The resulting self-assembly behavior of GO can be easily tailored by varying evaporation time and/or temperature, providing new approaches for preparing new large-area graphene-based materials.
Co-reporter:Zhangwei Wang, Hengjie Lai and Peiyi Wu
Soft Matter 2012 vol. 8(Issue 46) pp:11644-11653
Publication Date(Web):01 Oct 2012
DOI:10.1039/C2SM26172C
The assembly properties, thermal phase behavior and microdynamics of poly(NIPAM-b-BVImBr), poly(N-isopropylacrylamide)-b-poly(1-butyl-3-vinylimidazolium bromide), in aqueous solution are investigated by dynamic light scattering (DLS), turbidity measurements and FTIR spectroscopy in combination with two-dimensional correlation spectroscopy (2Dcos) and the perturbation correlation moving window (PCMW) technique. In particular, the influence of the introduction of the poly(BVImBr) segment on the solution properties of the block copolymer has attracted our attention: a core–shell micelle structure forms, consisting of a relatively hydrophobic core of poly(BVImBr) and a hydrophilic shell of PNIPAM; the phase transition temperature increases, due to one more step in the dehydration process originating from the alkyl side chains of the poly(1-butyl-3-vinylimidazolium bromide) (PIL) segment; what's more, a stronger hysteresis during the heating–cooling cycle, closely related to the recovery process, is observed. It reveals that the hydrogen bonds of CO⋯D–N among the micelles formed during heating are harder to remove, thus, the reconstruction of the CO⋯D–O–D hydrogen bonding and the recovery hydration process for the C–H groups during cooling are prevented due to the compact and regular micelle structure. More interestingly, the CO groups interact with the N–D groups at room temperature because of the existence of the micelle structure, which is regarded as intra-micelle hydrogen bonding; above the LCST, hydrogen bonds of the CO⋯D–N among the aggregated micelles called inter-micelle hydrogen bonding occur.
Co-reporter:Zehui Zhang and Peiyi Wu
CrystEngComm 2012 vol. 14(Issue 21) pp:7149-7152
Publication Date(Web):24 Aug 2012
DOI:10.1039/C2CE26117K
A facile one-step hydrothermal method with NH3 as a passivation agent was developed for the preparation of polycrystalline graphite quantum dots (GQDs). The prepared GQDs exhibited high crystallinity, a uniform size of 3.8 nm and blue photoluminescence at 402 nm. Moreover, a hydrothermal aggregation induced crystallization mechanism was proposed to explain the formation of the GQDs.
Co-reporter:Shengtong Sun, Weidong Zhang, Wei Zhang, Peiyi Wu and Xiulin Zhu
Soft Matter 2012 vol. 8(Issue 14) pp:3980-3987
Publication Date(Web):29 Feb 2012
DOI:10.1039/C2SM06908C
IR spectroscopy in combination with the perturbation correlation moving window (PCMW) technique and 2D correlation spectroscopy (2DCOS) is employed to elucidate the dynamic self-aggregation behavior of a novel miktoarm star PNIPAM-based multihydrophilic block copolymer, poly(N-isopropylacrylamide)2–[poly(N-vinylpyrrolidone)-b-poly(acrylic acid)]2 ((PNIPAM)2–(PVP-b-PAA)2). At pH = 8, (PNIPAM)2–(PVP-b-PAA)2 tends to self-assemble into micelles with PNIPAM in the core and ionized PAA segments in the shell during heating. IR investigation shows that the AA segments exhibit a similar “phase transition” behavior to the PNIPAM segments, which can be ascribed to the indirect influence through the drastic content changes of water molecules along with the hydrophilic-to-hydrophobic transformation of PNIPAM segments. Boltzmann fitting and PCMW easily determine the transition temperature to be ca. 33 °C and the transition temperature range to be 29.5–35 °C. Moreover, 2DCOS discerns a sequential group motion from PNIPAM to PVP and PAA segments. It is concluded that the three polymeric segments have relatively independent phase behavior during the formation of PNIPAM-core micelles, and the chain conformation adjustment induced by hydrophilic-to-hydrophobic transformation of PNIPAM segments should be the driving force of the whole self-aggregation process. The dynamic self-aggregation process we proposed can be further confirmed by dynamic laser scattering (DLS) and zeta potential measurements.
Co-reporter:Hengjie Lai, Zhangwei Wang, Peiyi Wu, Bharat Indu Chaudhary, Saurav S Sengupta, Jeffrey M Cogen, and Bin Li
Industrial & Engineering Chemistry Research 2012 Volume 51(Issue 27) pp:9365-9375
Publication Date(Web):June 15, 2012
DOI:10.1021/ie300007m
Tri-2-ethylhexyltrimellitate (TOTM) is one of the commercially used plasticizers for poly(vinyl chloride) (PVC). In this work, the diffusion behavior of TOTM in PVC films is investigated through real-time ATR-IR spectroscopy at 25, 40, and 70 °C, and the ratio changes of three C═O structures of TOTM are plotted as a function of diffusion time. TOTM itself is composed of two types of C═O structures: one C═O structure represents a free state and the other represents an aggregated C═O state formed by dipolar–dipolar interactions, as confirmed by the second derivative of FTIR and density functional theory (DFT). Furthermore, another new band related to C═O groups of TOTM was observed during diffusion experiments in PVC at different temperatures, which can be assigned to dipolar–dipolar interactions between TOTM and PVC (interacting C═O structure). These results show that the diffusion coefficients of TOTM in PVC increase with temperature. Conversely, the equilibrium concentrations of TOTM in PVC films decrease significantly with temperature due to rapid molecular movements and less interacting C═O structures. Moreover, it is also found that free C═O structures more easily interact with C–Cl groups of PVC at 25 °C, while aggregated C═O structures show prior contribution at 40 °C, which is effectively confirmed by two-dimensional (2D) correlation infrared spectroscopy. At 70 °C, however, free and aggregated C═O structures can reach an equilibrium much more quickly, but the content of interacting C═O structures has to keep a lower level because of higher temperature.
Co-reporter:Hengjie Lai, Zhangwei Wang and Peiyi Wu
RSC Advances 2012 vol. 2(Issue 31) pp:11850-11857
Publication Date(Web):29 Oct 2012
DOI:10.1039/C2RA21288A
The structural evolution of payload transfer in biphasic systems is significant but difficult to accurately follow over the whole process. The dynamic transfer of homopolymer poly(N-isopropylacrylamide) (PNIPAM) from water to a hydrophobic IL (1-ethyl-3-methylimidazolium bis(trifluoromethylsulfonyl)imide, [C2MIM][NTf2]) phase was investigated by in situ react infrared (IR) spectroscopy to reveal the detailed transfer process and structural changes of PNIPAM, water and [C2MIM][NTf2]. Compared with the corresponding binary systems, this work summarizes the four-step transfer behavior and the interactions among the components according to IR spectroscopy and multivariate curve resolution (MCR). At the initial stage, only some water diffuses into the hydrophobic IL in the form of a symmetric 1:2-type hydrogen bonded (anion⋯H2O⋯anion) species while most of the PNIPAM molecules are preserved in the water layer in the form of aggregates. Afterwards, the water molecules are bonded with PNIPAM in the aggregated state and they start to transfer together into the IL layer in the second stage where PNIPAM is changed into unfolding structures with complex interactions such as H2O⋯PNIPAM⋯anion, and meanwhile water structures of anion⋯(H2O)n⋯anion form due to further diffusion of water. After these stages, water molecules continue to dissolve in the IL although the polymer transfer is completed, and they are inclined to form further water clusters (H2O)n as deduced from the increase of OH region (3500–3300 cm−1) absorption. Finally, all of the components (PNIPAM, water and IL) coexist in the homogeneous IL phase with the aid of complex hydrogen bond and electric charge interactions.
Co-reporter:Zhangwei Wang and Peiyi Wu
RSC Advances 2012 vol. 2(Issue 18) pp:7099-7108
Publication Date(Web):06 Jul 2012
DOI:10.1039/C2RA01349E
The role of ionic liquid, 1-butyl-3-methylimidazolium tetrafluoroborate ([Bmim][BF4]), on the phase transition behavior of concentrated PNIPAM solutions was investigated by FTIR spectroscopy in combination with two-dimensional correlation spectroscopy (2Dcos) and the perturbation correlation moving window (PCMW) technique for the first time. At low IL concentrations, the Tp of the PNIPAM solution decreases with increases in the IL concentration, due to the destabilization of the hydrated macromolecule structure via preferential interactions between IL and water molecules. However, at higher IL concentrations, unexpectedly, the phase transition behavior disappears. This has been attributed to the formation of a stable interaction network via intra- and intermolecular hydrogen bonding. Furthermore, two changes can be observed in the ν(C–H) region for the sample with 0.4 mol L−1 [Bmim][BF4]. The first change is related to the phase separation of the PNIPAM solution, while the second step is attributed to an IL–D2O association, which takes part in the globule construction, probably interacting with hydrophilic groups of PNIPAM. Thus, the role of ILs on the phase behavior of PNIPAM is embodied in two opposite aspects, the “destroyer” and the “constructer”.
Co-reporter:Jiatao Yan;Xiaoqian Zhang;Xiuqiang Zhang;Kun Liu;Wen Li;Afang Zhang
Macromolecular Chemistry and Physics 2012 Volume 213( Issue 19) pp:2003-2010
Publication Date(Web):
DOI:10.1002/macp.201200320
Abstract
A series of first- and second-generation supramolecular dendrimers (SDs) was prepared via host–guest interaction from the cyclodextrin trimer and oligoethylene glycol (OEG)-based threefold dendritic guests. These SDs are water soluble at room temperature but show characteristic thermoresponsive behavior at elevated temperatures. Their thermoresponsiveness was investigated by UV–Vis spectroscopy and dynamic light scattering measurements. Supramolecular complexation from a mixture of two dendritic guests with different hydrophilicity was performed to check the feasibility to tune the phase transition temperatures of codendrimers. Based on temperature-varied 1H NMR spectra, it was found that the SDs start to decompose when the OEG units are dehydrated.
Co-reporter:Jiatao Yan;Xiaoqian Zhang;Xiuqiang Zhang;Kun Liu;Wen Li;Afang Zhang
Macromolecular Chemistry and Physics 2012 Volume 213( Issue 19) pp:
Publication Date(Web):
DOI:10.1002/macp.201290060
Co-reporter:Huiqing Wu ; Beibei Tang
The Journal of Physical Chemistry C 2012 Volume 116(Issue 3) pp:2246-2252
Publication Date(Web):December 21, 2011
DOI:10.1021/jp2073045
A novel hybrid ultrafiltration membrane was prepared by incorporating hollow mesoporous silica spheres (HMSS) into a polymer matrix of brominated polyphenylene oxide (BPPO) using triethanolamine as the amination agent. The hybrid membrane exhibits improved water permeability, thermal stability, and water content, while the rejection to egg albumin maintaining at a high level (>90%). Especially when the addition of HMSS is 1.0 wt %, the water flux of the hybrid membrane reaches a maximum that is almost two times that of the BPPO membrane. The unique properties of HMSS and good interaction between HMSS and polymer contribute to the improvement of membrane performance. The effect of the structures of silica particles on the membrane performance was also investigated, and the results suggest that HMSS with moderate wall thickness is more suitable for the optimization of hybrid membrane properties.
Co-reporter:Yewen Cao, Zuliang Lai, Jiachun Feng and Peiyi Wu
Journal of Materials Chemistry A 2011 vol. 21(Issue 25) pp:9271-9278
Publication Date(Web):19 May 2011
DOI:10.1039/C1JM10420A
Herein, by taking advantage of click chemistry, we propose a general and effective methodology to covalently functionalize graphene oxide sheets (GOSs) with block copolymers, namely poly(styrene-b-ethylene-co-butylene-b-styrene) (SEBS) triblock copolymers as an example in this study. The covalent attachment of SEBS to GOSs, as well as the individual nature of the hybrids, was confirmed by detailed investigations. For the potential applications of the block copolymer-clicked GOSs, they were incorporated into polystyrene (PS) as reinforcing fillers. The SEBS-clicked GOSs showed excellent compatibility with a PS matrix, and as a consequence, remarkably improved mechanical properties and thermal stability of the resulting composite films were achieved. This protocol is believed to offer possibilities to fully combine the extraordinary performances of GOSs with the multifunctional properties of block copolymers, and thus be useful in a variety of technological fields.
Co-reporter:Shengtong Sun and Peiyi Wu
Journal of Materials Chemistry A 2011 vol. 21(Issue 12) pp:4095-4097
Publication Date(Web):22 Feb 2011
DOI:10.1039/C1JM10276A
A facile one-step strategy for graphene oxide interpenetrating PNIPAM hydrogel networks is developed by covalently bonding GO sheets and PNIPAM-co-AA microgels directly in water, which exhibit dual thermal and pH response with good reversibility.
Co-reporter:Yewen Cao, Tao Yang, Jiachun Feng, Peiyi Wu
Carbon 2011 Volume 49(Issue 4) pp:1502-1504
Publication Date(Web):April 2011
DOI:10.1016/j.carbon.2010.11.014
Graphene oxide sheets (GOSs) functionalized with rare-earth (RE) complexes were prepared using a noncovalent approach. The adsorption of RE complexes onto GOSs, as well as the individual nature of the hybrids, was confirmed. The GOS–RE complex hybrids and their dispersion can emit bright red luminescence, which makes them useful in many practical fields, such as biological labeling and anti-counterfeiting.
Co-reporter:Shengtong Sun and Peiyi Wu
Physical Chemistry Chemical Physics 2011 vol. 13(Issue 47) pp:21116-21120
Publication Date(Web):21 Oct 2011
DOI:10.1039/C1CP22727K
Herein, noble metal nanoparticle (Au or Ag NP) decorated graphene sheets, fabricated according to a facile one-pot environmentally friendly method, are used as good substrates for the investigation of the combined surface-enhanced Raman scattering (SERS) effect, where both the electromagnetic mechanism and the chemical mechanism effects coexist among the Au or Ag NPs, graphene sheets and the absorbed analytes. Our results show that, in aqueous solution, the SERS effect of both the Au and Ag NPs on the absorbed probe molecules and on graphene is competitive, which varies dependent on the species and the concentration of the absorbed probe molecule. By a detailed comparison of three probe molecules (rhodamine 6G, nile blue A, and 4-aminobenzenethiol) with different coupling abilities to the graphene sheets, we finally attribute this phenomenon to the result of the strong suppressing effect of the macrocyclic probe molecules on the SERS of graphene, induced by charge transfer, as the probe molecules are coupled to the graphene sheets. This competitive effect is a non-ignorable phenomenon when graphene/Au or Ag nanocomposites are used as SERS substrates, and our study may deepen our understanding of the SERS mechanism.
Co-reporter:Shengtong Sun and Peiyi Wu
Soft Matter 2011 vol. 7(Issue 16) pp:7526-7531
Publication Date(Web):07 Jul 2011
DOI:10.1039/C1SM05459G
Highly branched poly(N-isopropylacrylamide) (PNIPAM) was first synthesized by self-condensing atom transfer radical copolymerization (SCATRCP) catalyzed by CuBr/tris[2-(dimethylamino)ethyl]amine (Me6TREN) complex in isopropanol at room temperature. This method showed good control over chain morphology and lower critical solution temperature (LCST) type phase transition behavior of PNIPAM by varying reaction time and monomer/inimer feed ratios. On the basis of GPC, FTIR, 1HNMR and DSC results, four stages were discerned during the polymerization procedure, at which chain architectures experienced “linear – comblike – slightly branched – highly branched” transformations. Additionally, the synthesized highly branched PNIPAM chains were found to be able to self-assemble into hollow spheres in alcohols such as methanol and ethanol, which arise from the presence of large amounts of hydrophobic branched points inside polymer chains.
Co-reporter:Shengtong Sun and Peiyi Wu
Soft Matter 2011 vol. 7(Issue 14) pp:6451-6456
Publication Date(Web):08 Jun 2011
DOI:10.1039/C1SM05548H
Near infrared spectroscopy in combination with two-dimensional correlation spectroscopy (2Dcos) and perturbation correlation moving window (PCMW) technique is employed to illustrate the gelation microdynamic mechanism of hydrogelator N-octyl-D-gluconamide (8-GA), which can rapidly self-agglomerate into helical bilayer micellar fibers upon cooling from spherical micelles. Boltzmann fitting and PCMW easily determined the gelation temperature to be ca. 72 °C and the transition temperature range to be 70–75 °C. Moreover, band shifting and splitting phenomena can be observed for CH-related overtones, indicating the formation of much ordered and tight hydrophobic core from octyl tails. On the other hand, 2Dcos was used to discern the sequential orders during the gelation process and concluded that all the group motions have a continuous transfer from the octyl tail to the chiral carbohydrate head followed by the final immobilization of the solvent, which meanwhile, is actually a continuous dehydration process from the hydrophobic core to the outer hydrophilic chiral head. The driving force of the gelation process in microdynamics can only be the dehydration process of hydrophobic octyl chains, but with final helical superstructures being stabilized by amide-associated hydrogen bonding and the “chiral bilayer effect” of carbohydrate heads.
Co-reporter:Jiwen Wu, Hui Tang and Peiyi Wu
Soft Matter 2011 vol. 7(Issue 9) pp:4166-4169
Publication Date(Web):30 Mar 2011
DOI:10.1039/C1SM05085K
Owing to the peculiarity of its molecular architecture, dendritic-linear copolymer consisting of Percec type dendron molecules and a relatively stiff poly{2,5-bis[(4′-methoxyphenyl)oxycarbonyl]styrene} (PMPCS) chain could self-assemble into hollow spherical particles in common solvent. This type of self-assembly offers a new convenient route for obtaining hollow vesicles in copolymer systems without secondary bonding. And vesicular structures and micro-spherical compound micelles can be obtained in selective solvents. Additionally, under moisture-rich conditions, solution-cast films of dendron-b-PMPCS can form well-defined honey-comb patterns.
Co-reporter:Shengtong Sun, Jun Hu, Hui Tang and Peiyi Wu
Physical Chemistry Chemical Physics 2011 vol. 13(Issue 11) pp:5061-5067
Publication Date(Web):03 Feb 2011
DOI:10.1039/C0CP01939A
The thermally induced volume phase transition process of poly(N-isopropylacrylamide-co-acrylic acid) (PNIPAM-co-AA) hydrogel is studied using FT-IR spectroscopy in combination with the perturbation correlation moving window (PCMW) technique and two-dimensional correlation spectroscopy (2Dcos) analysis. According to PCMW spectra analysis, an elevation of volume phase transition temperature (VPTT) due to an extra equilibrium of repulsive electrostatic interactions of acrylic acid moieties in hydrogel from 34 °C to ca. physiological temperature (37 °C) is determined. 2Dcos helps us to conclude that the dehydration of hydrogel responds earlier in the process of network collapse than hydrogen bond variations of AA and NIPAM moieties during heating, while the hydrogen bonds of NIPAM and AA moieties change before the network swelling in the cooling process. Furthermore, relatively stable inner hydrogen bonds of AA moieties restrict the complete expansion of PNIPAM-co-AA hydrogel, resulting in a unique irreversible recovery during cooling.
Co-reporter:Jiwen Wu, Hui Tang and Peiyi Wu
Soft Matter 2011 vol. 7(Issue 3) pp:1185-1191
Publication Date(Web):06 Dec 2010
DOI:10.1039/C0SM00934B
Novel dendron–liquid crystalline (dendron–LC) block copolymers integrating Percec type (alkoxy benzyl ether) dendron molecules and liquid crystalline polymer blocks were prepared by atom transfer radical polymerization (yields ca. 80%, molecular weights were in the range of 15000–50000). Poly{2,5-bis[(4-methoxyphenyl)oxycarbonyl]styrene} (PMPCS), of which the thermotropic mesomorphic behavior strongly relied on its molecular weight, was utilized as the liquid crystalline polymer block. Thermal property investigation of the copolymers revealed that only the glass transition temperature (111–119 °C) belonging to the PMPCS block was observed, indicating that the dendron molecule and the liquid crystalline polymer block were immiscible and the phase transition of the dendron molecule was restrained. The subtle interplay between the thermotropic mesomorphic behaviors of PMPCS and the microphase structure in these dendron–LC copolymers was discussed. With increasing molecular weight of the PMPCS block, a morphological evolution from bilayer to interdigitated lamellar structure was proposed based on the small-angle X-ray scattering (SAXS) examination. More importantly, a less-ordered columnar nematic phase instead of a hexatic columnar nematic phase which should be stabilized in the PMPCS block was identified by in situwide-angle X-ray scattering (WAXS) experiments. The degradation of the hierarchical packing of PMPCS chain was attributed to the confinement effect originating from the interdigitated microphase structure.
Co-reporter:Mengyin Wang, Peiyi Wu, Saurav S. Sengupta, Bharat Indu. Chadhary, Jeffrey M. Cogen, and Bin Li
Industrial & Engineering Chemistry Research 2011 Volume 50(Issue 10) pp:6447-6454
Publication Date(Web):April 6, 2011
DOI:10.1021/ie102221a
Water diffusion through low density polyethylene (LDPE) film was investigated by attenuated total reflectance Fourier transform infrared (ATR-FTIR) spectroscopy and two-dimensional correlation spectroscopy (2DCOS) over a temperature range of 25–80 °C. The 2DCOS spectra of water diffusion in LDPE at different temperatures were very similar. The broad OH stretching vibration (ν(OH)) was split into four bands assigned to three different types of water molecules, namely, bulk water, cluster water, and free water, which will be defined. It appeared that as water molecules disperse in LDPE, cluster water with moderate hydrogen bonds diffused faster than bulk water with strong hydrogen bonds. Additionally, the hydrogen bonds between water molecules may have been further weakened or even broken to form free water, possibly due to limited free volume. On the basis of a Fickian model, the diffusion coefficients could be calculated from overall, fast and slow diffusion process, respectively. The diffusion coefficients were observed to increase with temperature, possibly due to increased swelling of molecular chain, more free volume, and reduced size of the penetrants.
Co-reporter:Bingjie Sun, Hengjie Lai, and Peiyi Wu
The Journal of Physical Chemistry B 2011 Volume 115(Issue 6) pp:1335-1346
Publication Date(Web):January 24, 2011
DOI:10.1021/jp1066007
The thermal behavior of a poly(vinyl methyl ether) (PVME) aqueous solution (30 wt %) during a heating-and-cooling cycle is studied using FTIR spectroscopy in combination with 2D correlation analysis. The FTIR spectral data of O−H, CH3−O, and C−H stretching vibration regions provide detailed changes of hydrophilic and hydrophobic groups of PVME. Hydrogen bonds between hydrophilic groups and water and hydration interactions between hydrophobic groups and water are confirmed to be completely reversible in the heating-and-cooling cycle. Two-dimensional correlation method helps us to understand the microdynamics mechanism of phase separation behavior of PVME 30 wt % aqueous solution. During the heating process, the initially hydrated CH3 groups start to dehydrate as the first action of phase separation, and the initially hydrated CH2 groups follow to start their dehydration; interestingly, water molecules leave CH2 groups very fast, and the whole dehydration process of CH2 groups finishes even earlier than that of CH3. After hydrophobic groups finish their dehydrations, hydrogen bonds between hydrophilic group and water start to dissociate. 1:2 adducts formed between PVME and water dissociate first and transfer to the 1:1 adducts, whereas with further heating, 1:1 adducts eventually dissociate and release free water and free CH3−O. PCMW method is used as supplement to determine changing conditions of various chemical structures. During the phase separation, O−H hydrogen bond in 1:2 adduct is found to dissociate between 35.5 and 39 °C in a style, whereas the 1:1 adduct (also considered as free water) increases between 35.5 and 39 °C in a style. Moreover, dehydration conditions of hydrophobic groups are also found. Both of the dehydrated states CH3 and CH2 increase like .
Co-reporter:Hongna Wang, Shengtong Sun, and Peiyi Wu
The Journal of Physical Chemistry B 2011 Volume 115(Issue 28) pp:8832-8844
Publication Date(Web):June 9, 2011
DOI:10.1021/jp2008682
The thermodynamic behavior of hyperbranched poly(ethylenimine) with isobutyramide groups (HPEI-IBAm) during thermal-induced phase transition in water was investigated by turbidity measurement, calorimetric measurements (DSC), FT-IR, and dynamic light scattering (DLS). Both turbidity and calorimetric measurements indicated a recoverable phase transition with a small hysteresis. Detailed FT-IR investigation gave an insight into its molecular mechanism about detailed group interaction during the heating–cooling process. The second derivative and Gaussian fit were carried out to separate three components of ν(C═O): 1648, 1625, and 1600 cm–1, which are assigned to C═O···D—N H-bonds, single and double H-bonded carbonyl groups with water molecules, respectively. Quantitative analysis of amide I groups indicates a better revival compared to PNIPAM. The isosbestic point determination and 2D correlation analysis together with dynamic light scattering were applied to draw out the mechanism. Thermosensitive HPEI-IBAm dissolves in water exhibits small particles of ca. 3 nm at room temperature at first. As temperature increases, the polymer begins to shrink and water is driven out from the polymer. Finally, the polymer results in a hydrophobic sphere, which aggregates further for a relative stable state upon heating. Above LCST, C═O···D—N hydrogen bonds form with the disassociation of C═O···D2O, which helps in the dehydration of CH groups. Upon cooling, the driven force of the transition is the hydration of CH groups. Compared with linear-PNIPAM, the globule-like hyperbranched polymer has a high specific area which endows the groups with a high degree of freedom and more sufficient interaction with water.
Co-reporter:Zhangwei Wang and Peiyi Wu
The Journal of Physical Chemistry B 2011 Volume 115(Issue 36) pp:10604-10614
Publication Date(Web):August 11, 2011
DOI:10.1021/jp205650h
The gelation microdynamic mechanism of PNIPAM in a ionic liquid, 1-ethyl-3-methylimidazolium bis(trifluoromethylsulfonyl)imide ([C2mim][NTf2]), is investigated by FTIR spectroscopy in combination with two-dimensional correlation spectroscopy (2Dcos) and perturbation correlation moving window (PCMW) technique for the first time. Appreciable changes in band frequencies and shapes are observed in the ν(N–H) and ν(C═O) regions, indicating the formation of new interactions between the ionic liquid and PNIPAM and the transformation of interior interaction between polymer chains during gelation. In particular, the variation of the ion environment with the relative change of the isolated and associated components of [C2mim][NTf2] on the sol-to-gel transition of PNIPAM is revealed by 2DIR analysis to the ν(C–H) region of imidazole ring. Upon cooling, the side chains of PNIPAM experience a changing process from dissociation of the interaction with ionic liquid to formation of N–H···O═C hydrogen bonding, then polymer shrinks from the side chains to backbone, followed by the final immobilization of the associated species in polymer network. Meanwhile, the gelation is actually a desolvation process upon the variation of ion environment.
Co-reporter:Jiatao Yan;Dr. Wen Li;Kun Liu;Dalin Wu;Feng Chen; Peiyi Wu; Afang Zhang
Chemistry – An Asian Journal 2011 Volume 6( Issue 12) pp:3260-3269
Publication Date(Web):
DOI:10.1002/asia.201100528
Abstract
Combining the concepts of supramolecular polymers and dendronized polymers provides the opportunity to create bulky polymers with easy structural modification and tunable properties. In the present work, a novel class of side-chain supramolecular dendronized polymethacrylates is prepared through the host–guest interaction. The host is a linear polymethacrylate (as the backbone) attached in each repeat unit with a β-cyclodextrin (β-CD) moiety, and the guest is constituted with three-fold branched oligoethylene glycol (OEG)-based first- (G1) and second-generation (G2) dendrons with an adamantyl group core. The host and guest interaction in aqueous solution leads to the formation of the supramolecular polymers, which is supported with 1H NMR spectroscopy and dynamic light scattering measurements. The supramolecular formation was also examined at different host/guest ratios. The water solubility of hosts and guests increases upon supramolecular formation. The supramolecular polymers show good solubility in water at room temperature, but exhibit thermoresponsive behavior at elevated temperatures. Their thermoresponsiveness is thus investigated with UV/Vis and 1H NMR spectroscopy, and compared with their counterparts formed from individual β-CD and the OEG dendritic guest. The effect of polymer concentration and molar ratio of host/guest was examined. It is found that the polar interior of the supramolecules contribute significantly to the thermally-induced phase transitions for the G1 polymer, but this effect is negligible for the G2 polymer. Based on the temperature-varied proton NMR spectra, it is found that the host–guest complex starts to decompose during the aggregation process upon heating to its dehydration temperature, and this decomposition is enhanced with an increase of solution temperature.
Co-reporter:Shengtong Sun and Peiyi Wu
The Journal of Physical Chemistry B 2011 Volume 115(Issue 40) pp:11609-11618
Publication Date(Web):September 7, 2011
DOI:10.1021/jp2071056
IR spectroscopy in combination with two-dimensional correlation spectroscopy (2DCOS) and the perturbation correlation moving window (PCMW) technique is employed to illustrate the dynamic hydration behavior of poly(N-vinylcaprolactam) (PVCL) in water, which exhibits a typical type I continuous lower critical solution temperature (LCST) behavior. PCMW easily determined the transition temperature to be ca. 43.5 °C during heating and ca. 42.5 °C during cooling and the transition temperature range to be 39.5–45 °C. On the other hand, 2DCOS was used to discern the sequence order of different species in PVCL and concluded that hydrogen bonding transformation predominates at the first stage below LCST while hydrophobic interaction predominates at the second stage above LCST. In combination with molecular dynamics simulation results, we find that there exists a distribution gradient of water molecules in PVCL mesoglobules ranging from a hydrophobic core to a hydrophilic surface. Due to the absence of self-associated hydrogen bonds and topological constraints, PVCL mesoglobules would form a “sponge-like” structure which can further continuously expel water molecules upon increasing temperature, while poly(N-isopropylacrylamide) (PNIPAM) with self-associated hydrogen bonds forms mesoglobules with a “cotton-ball-like” structure without an apparent distribution gradient of water molecules and does not change much upon increasing temperature.
Co-reporter:Mengyin Wang, Peiyi Wu
Polymer 2011 Volume 52(Issue 3) pp:769-777
Publication Date(Web):3 February 2011
DOI:10.1016/j.polymer.2010.12.051
Two dimensional correlation spectroscopy (2DCOS) is a powerful technique which can enhance spectral resolution and probe a certain sequential order of spectral variations under external perturbation. However, in asynchronous 2D contour maps which provide richer valuable information than synchronous ones, some effects other than real asynchronicity (called spectral effects), such as position shift, band width change and band overlapping, may generate interfering cross peaks. In this paper, we performed a simulation in the region of OH stretching vibration of water to evaluate the contributions of spectral effects on a highly overlapped band and study the dynamic changes of water during diffusion process in poly(ɛ-caprolactone) (PCL) matrix. From the comparison between experimental and simulated asynchronous 2D correlation spectra, the detailed information on water diffusion process in PCL film can be extracted. It is demonstrated that artificial asynchronous cross peaks in the region of 3670–3570 cm−1 are induced by band overlapping and the bound and free water in PCL matrix change simultaneously.
Co-reporter:Shengtong Sun, Yewen Cao, Jiachun Feng and Peiyi Wu
Journal of Materials Chemistry A 2010 vol. 20(Issue 27) pp:5605-5607
Publication Date(Web):10 Jun 2010
DOI:10.1039/C0JM01269F
A facile methodology has been developed to immobilize well-defined polymers onto graphene sheets using “click” chemistry; upon polystyrene coupling, the resulting sheets can be well dispersed and fully exfoliated in common organic media.
Co-reporter:Huiqing Wu, Beibei Tang, Peiyi Wu
Journal of Membrane Science 2010 Volume 362(1–2) pp:374-383
Publication Date(Web):15 October 2010
DOI:10.1016/j.memsci.2010.06.064
Novel ultrafiltration membranes were prepared by incorporating multi-walled carbon nanotubes (MWNTs) into a matrix of brominated polyphenylene oxide (BPPO) and using triethanolamine (TEOA) as the crosslinking agent. The membranes exhibited not only high permeability and hydrophilicity but also excellent separation performance and chemical stability. Furthermore, the water permeability increased as the weight fraction of MWNTs increased, reaching a maximum of 487 L/m2 h at 5 wt% of MWNTs, while maintaining a 94% membrane rejection rate to egg albumin. The addition of TEOA into the BPPO/MWNTs casting solution might result in an increase in water permeation rate of membrane if the amount of TEOA exceeded a threshold value; however, the membrane rejection rate was essentially constant despite increasing the molar fraction of TEOA in the casting solution. Using an adequate amount of MWNTs and a proper TEOA/BPPO ratio, it is feasible to make MWNTs/polymer ultrafiltration membranes with both high permeation flux and excellent selectivity.Research highlights▶ MWNTs/BPPOqua membranes were prepared by in situ amination with triethanolamine (TEOA), which crosslinked MWNTs and polymer (BPPO). ▶ Hydrophilic zwitterions containing the quaternary ammonium group and MWNT-carboxylate are formed in the membrane. ▶ The permeation flux of the MWNTs/BPPOqua membrane can be improved and the selectivity can be simultaneously maintained well. ▶ A synergy between MWNTs and TEOA contributes to the better membrane performance.
Co-reporter:BeiBei Tang, Cheng Zou, Peiyi Wu
Journal of Membrane Science 2010 Volume 365(1–2) pp:276-285
Publication Date(Web):1 December 2010
DOI:10.1016/j.memsci.2010.09.015
Composite membranes were prepared by interfacial polymerization of trimesoyl chloride (TMC) with (i) triethanolamine (TEOA), and (ii) N-methyl-diethanolamine (MDEOA) on addition of various contents of LiBr in aqueous phase. The influence of LiBr in aqueous phase on the composite membrane performance and surface morphologies was investigated. For monomer TEOA, the pure water flux of composite membrane enhanced as the LiBr content increased and it reached a maximum at 3% of LiBr, then decreased. However, the extreme value of the salt rejection functioned with the content of LiBr changed to 1% (a turning point), at which the membrane displayed a lowest salt rejection. The change in performance of the composite membrane with the content of LiBr was due to the competition of two factors. One was the interaction of Li+ ion with the hydroxyl oxygen atom of alcohol amine, which could induce an increase in the density and reactivity of OH groups in the aqueous phase, forming a dense skin layer of the composite membrane as a result. The other factor was the complexation of Li+ ion with the carbonyl in TMC, causing the acid chloride group of TMC preferring to hydrolyze which could induce to construct a hydrophilic and loose surface layer. The role of LiBr in the formation of the composite membrane was further testified by investigating another monomer MDEOA. The analysis of the composite membrane formation in the presence of LiBr was validated by reaction coefficient, contact angle, streaming potential, SEM, and AFM.Research highlights▶ Inorganic salt can adjust the performance of thin-film composite membrane. ▶ The role of LiBr during membrane formation attributes to two competed factors. ▶ LiBr affects the effective density and reactivity of monomer in aqueous phase. ▶ LiBr promotes the hydrolyzation of monomer in organic phase.
Co-reporter:Wei Li, Shengtong Sun, Qisi Yu and Peiyi Wu
Crystal Growth & Design 2010 Volume 10(Issue 6) pp:2685
Publication Date(Web):April 22, 2010
DOI:10.1021/cg100159k
Inspired by mineralization in biological organisms, fabrication of higher ordered inorganic crystals induced by polymer chains has received much attention. In our present work, we made use of a widely used industrial material, carboxymethyl cellulose (CMC), to mediate the nucleation and growth of barium carbonate (BaCO3). We calculated the interactions between CMC chains and crystalline needle-like units of BaCO3 by molecular dynamic simulation, concluding that the (111) face of crystalline units is the most favorable face for CMC chains to attach onto. Based on the simulation results and the time-resolved experiments, we suggested the dumbbell-like BaCO3 aggregates formed via polymer induced stacking of needle-like units. More importantly, we realized control over the morphology of aggregates from dumbbell-like to spherical particles by simply adjusting the polymer concentration. By clarifying the aggregation mechanism mediated by polymer chains, we demonstrate here not only a simple method to fabricate BaCO3 particles with controllable morphologies but also a reference work which may serve the exploration of the mechanism in biomineralization.
Co-reporter:Jingya Shi, Peiyi Wu and Feng Yan
Langmuir 2010 Volume 26(Issue 13) pp:11427-11434
Publication Date(Web):June 10, 2010
DOI:10.1021/la1009225
The intermolecular interaction and distribution of components in [Bmim][BF4]-based polystyrene composite membrane which is composed of 1-butyl-3-methylimidazolium tetrafluoroborate ([Bmim][BF4]), poly(1-(2-methyl acryloyloxyundecyl)-3-methylimidazolium bromide) (poly(MAUM-Br)) and polystyrene is investigated by in situ Fourier transform infrared spectroscopy (FTIR) and two-dimensional correlation infrared spectroscopy (2DIR) in this study. A proposed model about the structure of this composite material is presented, and a sketch map about the local distributions of components is provided. In this model, alkyl chains in [Bmim][BF4], poly(MAUM-Br), and polystyrene in this system were supposed to form a polymeric network through aggregation or copolymerization. Cations of ionic liquids separate into the polymer network, while anions are kept mainly through the Coulomb force and partially by the hydrogen bonding between cations and anions. To support this model, FTIR has provided some hints on the π−π interaction existing in this complex material between the imidazole ring of ionic liquids and the benzene ring of polystyrene, based on the discovery of the shifts of IR absorption bands assigned to the C−C stretching vibrational mode. The sequential order of the responses from different chemical groups toward the variation of temperature is calculated by 2DIR, and the results suggest how different components distributed in this [Bmim][BF4]-based polystyrene composite membrane.
Co-reporter:Huiqing Wu ; Beibei Tang
The Journal of Physical Chemistry C 2010 Volume 114(Issue 39) pp:16395-16400
Publication Date(Web):September 9, 2010
DOI:10.1021/jp107280m
An improved process to prepare MWNTs/polyester thin film nanocomposite membranes was initiated by interfacial polymerization of trimesoyl chloride (TMC) and triethanolamine (TEOA) solution containing MWNTs. The improved process was facilely done by immersing the support membrane into the organic phase before the conventional process of interfacial polymerization. The TEM images showed that the MWNTs were embedded throughout the polyester thin film layer. The MWNTs/polyester thin film nanocomposite membrane prepared via the improved process exhibited both high permeability and excellent selectivity when compared with the thin film composite membrane without MWNTs and the MWNTs/polyester thin film nanocomposite membrane prepared via the conventional process. The water permeability increased upon an increase of reaction time of TMC-saturated support membrane immersed into aqueous phase (step-1), reaching a maximum of 4.7 L/m2 h at 25 min, while the membrane rejection rate kept increasing. The role of step-1 played a positive role in the performance and the morphology of the thin film composite membrane. It was found that the process of step-1 produced a low degree of cross-linking thin layer with high amount of hydrophilic and negatively charged carboxyl groups. This improved process of interfacial polymerization to prepare MWNTs/polymer thin film nanocomposite membranes provides a new approach to overcome the trade-off effect between permeability and selectivity.
Co-reporter:Shengtong Sun, Hui Tang and Peiyi Wu
The Journal of Physical Chemistry B 2010 Volume 114(Issue 10) pp:3439-3448
Publication Date(Web):February 23, 2010
DOI:10.1021/jp908951c
A combination method of spectral analysis and molecular simulation was employed to interpret the carbonyl band splitting phenomenon of poly[di(butyl)vinylterephthalate] (PDBVT), a novel thermotropic liquid crystalline polymer, which can self-assembly into a two-dimensional hexagonal, columnar (2D ΦH) phase without conventional mesogens. Two-dimensional correlation infrared spectroscopy results of PDBVT during heating showed four splitting bands at 1707, 1712, 1731, and 1741 cm−1. Accordingly, four PDBVT conformers were classified on the basis of carbonyls rotating in a π-electron resonance system. Detailed spectral comparison and molecular dynamics (MD) simulation for the columnar phase of PDBVT were carried out to make a clear assignment of splitting bands to different conformers. The internal self-assembly nature of PDBVT can be concluded that the rotation of carbonyls at the 2-position (close to backbone) of the phenylenes would take place, along with the formation of the 2D ΦH phase. Meanwhile, the consecutive motions of PDBVT backbones with a distortion and extension in the mesophase formation and preparation processes have also been examined and reproduced by MD simulation. Finally, a good simulated conformity of the side chain size dependence of the liquid crystallinity of PDAVTs with experimental observations was achieved. This work combining spectral analysis and molecular simulation may bring some new insight into a better understanding of various physical chemical phenomena unintelligible before.
Co-reporter:Shengtong Sun, Jun Hu, Hui Tang and Peiyi Wu
The Journal of Physical Chemistry B 2010 Volume 114(Issue 30) pp:9761-9770
Publication Date(Web):July 13, 2010
DOI:10.1021/jp103818c
Two-dimensional correlation infrared spectroscopy (2DIR) and a newly developed perturbation correlation moving window (PCMW) technique were employed to study the precise chain collapse and revival thermodynamic mechanism of poly(N-isopropylacrylamide) (PNIPAM) hydrogel. Both Boltzmann fitting and PCMW had figured out the volume phase transition temperature for heating and cooling processes to be about 35 and 33.5 °C, respectively, close to the results obtained from DSC. Furthermore, determination of the isosbestic points for v(CH3) and v(C═O) overlaid spectra showed that the chain collapse of PNIPAM hydrogel took place along with some intermediate states or a completely continuous phase transition while the chain revival occurred with only conversion between two single states. Finally, 2Dcos discerned all the sequence of group motions of PNIPAM hydrogel, indicating that in the heating process, PNIPAM hydrogel occurred to collapse along the backbone before water molecules were expelled outside the network, while in the sequential cooling process, PNIPAM hydrogel had water molecules diffusing into the network first before the chain revival along the backbone occurred.
Co-reporter:Shengtong Sun and Peiyi Wu
The Journal of Physical Chemistry A 2010 Volume 114(Issue 32) pp:8331-8336
Publication Date(Web):July 26, 2010
DOI:10.1021/jp105034m
A designed ligand-accelerated Cu(I)-catalyzed cycloaddition (CuAAC) reaction was monitored for the first time by real time infrared analysis technique based on ATR-FTIR principles. Principal components analysis (PCA) and two-dimensional correlation spectroscopy (2Dcos) results showed that the consumption of alkyne and azide took place successively followed by the formation of the product 1,2,3-triazole, and a 1:1 complex of two reactants would be formed in the reaction process. The rate-determining step of the CuAAC reaction was also experimentally confirmed for the first time to be the transition of azide−alkyne 1:1 complex to the preproduct 1,2,3-triazole. Our results are in good conformity with the current catalytic mechanism proposed by Sharpless et al. according to DFT calculation results.
Co-reporter:Hui Tang, Shengtong Sun, Jiwen Wu, Peiyi Wu, Xinhua Wan
Polymer 2010 Volume 51(Issue 23) pp:5482-5489
Publication Date(Web):29 October 2010
DOI:10.1016/j.polymer.2010.09.036
Raman spectroscopy was applied to study the conformational changes of poly[di(alkyl) vinylterephthalate] (alkyl = n-butyl and sec-butyl). Spectral regions assigned to C–H, C–C and ester carbonyl stretching modes were utilized to provide information on the molecular motion, the relative content of trans and gauche conformers, and the specific interactions existed in the mesophase formation process of these novel thermotropic liquid crystalline polymers. Both the experimental results and the conformational analysis suggested that the aliphatic side groups do have a significant impact on the formation of stable liquid crystalline phase. Based on the van’t Hoff relation, the thermodynamic parameters in the phase transition of poly[di(n-butyl) vinylterephthalate] were estimated (ΔH = 5.52 kJ mol−1, ΔS = 14.02 J mol−1 K−1), which were much smaller than the typical values generally obtained in first-order phase transition. Based on generalized two-dimensional correlation Raman analysis, specific interaction among the phenyl-ring in the mesophase development process was elucidated.
Co-reporter:Hengjie Lai, Peiyi Wu
Polymer 2010 Volume 51(Issue 6) pp:1404-1412
Publication Date(Web):11 March 2010
DOI:10.1016/j.polymer.2010.01.036
FTIR in combination with perturbation correlation moving window (PCMW) technique was applied to study the phase transition of concentrated aqueous solutions of Poly(N-isopropylacrylamide) (PNIPAM) and its small molecular model compound N-isopropylpropionamide(NIPPA). It was found that lower critical solution temperature (LSCT) of 40% NIPPA/D2O solution was 39 °C which was higher by ca. 8 °C than that of PNIPAM, and that NIPPA exhibited much wider temperature ranges of phase transition from 30 to 50 °C while PNIPAM underwent the phase separation in a narrow temperature range (29.1–33.1 °C). Moreover, we utilized two-dimensional correlation infrared spectroscopy (2DIR) analysis to reveal that the presence of main chains didn't affect the sensitivity and changing sequence of different groups, but did have a strong effect on the size of aggregation and formation of hydrogen bonds between carbonyl groups and water molecules. Without the interference of hydrophobic main chains, the carbonyls of NIPPA (1600 cm−1) could interact with more water than those of PNIPAM (1627 cm−1) below LSCT, which was the reason of the slower and milder phase transition taking place in NIPPA system.
Co-reporter:Bingjie Sun and Peiyi Wu
The Journal of Physical Chemistry B 2010 Volume 114(Issue 28) pp:9209-9219
Publication Date(Web):June 25, 2010
DOI:10.1021/jp1041525
The thermally induced evolution mechanisms of various interactions in ionic liquids (1-butyl-3-methylimidazolium tetrafluoroborate, bmimBF4) and water mixtures have been investigated in this paper. In the near-infrared (NIR) spectroscopy, we focus mainly on ν(OH) and ν(CH) overtone regions. During heating of bmimBF4 and water mixtures, the ν(OH) overtone peak shows a significant blue shift, and the area of this peak shows different changes in three heating regions. By using the perturbation correlation moving window (PCMW) method, we have ascertained the critical temperatures of these three regions: 25−100, 105−160, and 165−190 °C, and we have accordingly performed 2D correlation NIR analysis in three parts. On the basis of 2D study results, we find several types of O−H involved hydrogen bonds (H-B’s) in a bmimBF4 and water (15 mol %) mixture and arrive at their evolution mechanisms in each heating region. During heating at 25−100 °C, strong H-B’s, such as BF4−···water···BF4− and BF4−···cyclic water dimer···BF4−, transform into weaker H-B’s with simpler structures; at 105−160 °C, the remaining BF4−···water···BF4− continues to dissociate, and cation···water H-B’s start to dissociate, and a large amount of released free water evaporates; whereas in the final heating region of 165−190 °C, BF4−···water···BF4− still exists and continues to dissociate, and in the study of the ν(CH) overtone region, we have found that the concentration of water in bmimBF4 affects interactions between cations and anions. In the mixture of bmimBF4 with more water (15 mol %), H-B’s between water and bmimBF4 cannot be completely destroyed, even at very high temperature; therefore, only limited new electrostatic interactions would be formed between cations and anions during heating, but in a mixture of bmimBF4 with less water (15 mol %), cations and anions are able to form new electrostatic interactions during the heating process. However, the intensity of these interactions is smaller than that in the 80 °C isothermal process due to the low contacting possibilities among ions at high temperatures.
Co-reporter:Shengtong Sun and Peiyi Wu
Macromolecules 2010 Volume 43(Issue 22) pp:9501-9510
Publication Date(Web):October 28, 2010
DOI:10.1021/ma1016693
The role of water/methanol clustering dynamics on thermosensitivity of poly(N-isopropylacrylamide) (PNIPAM) chains in concentrated solutions (10 wt %) is investigated by turbidity, FT-IR and calorimetric measurements through point-by-point comparison. FT-IR spectral variations show that PNIPAM−methanol interactions are largely weakened and PNIPAM chains are more collapsed in water/methanol mixture (methanol volume fraction xm = 0.17) than in pure water because of the formation of large water/methanol clusters, which, meanwhile, causes the decrease of hydration sites. On the other hand, weak hysteresis and excess recovery phenomena in the phase transition process can also be observed with addition of methanol to PNIPAM aqueous solution due to the existence of water/methanol clustering dynamics. Two-dimensional infrared correlation spectroscopy and calorimetric analysis finally conclude that the role of water/methanol clustering dynamics is mainly embodied in the inhibition of the hydration process of PNIPAM chains which shows a faster thermal response than hydrogen bonding association.
Co-reporter:Wei Li, Qisi Yu and Peiyi Wu
Green Chemistry 2009 vol. 11(Issue 10) pp:1541-1549
Publication Date(Web):06 Aug 2009
DOI:10.1039/B914787J
The preparation of biominerals based on CO2 fixation and regulatory effect of organic macromolecules has attracted more and more interests in recent years, inspired by the increase in technological interests in bio-inspired materials science and fabrication of useful products via an environmentally friendly process. In this paper, submicronic CaCO3 particles with ellipsoidal morphology were synthesized using compressed or supercritical CO2 with sodium salt of carboxymethyl cellulose (NaCMC) as a template. By regulating some experimental parameters, including the concentration and molecular weight of NaCMC, as well as the CO2 pressure and temperature, the morphology and size of the CaCO3 particles could be effectively controlled. Besides, in contrast to the effective results of another additive, Polyacrylic Acid (PAA), our research suggested that the morphology of the synthesized particles was strongly related to the flexibility of the polymer chains, namely, the relatively rigid chains induce the formation of ellipsoidal particles while the more flexible chains would result in the spherical ones. In addition, amorphous calcium carbonate was traced as an intermediate phase during the crystallization process. Based on the experimental results, we discussed the formation mechanism of such particles: the polymer chains serve as the skeletons, then the ions attach along the chains to grow. The final morphology of CaCO3 aggregates is tailored by the flexibility of the polymer chain, while the size of the particles is related with the chain length of the polymer. In comparison with the traditional mineralization methods, here we provide a highly efficient and versatile approach to integrate the fixation of CO2 and the regulating effect of different polymer chains, to produce submicroscopic CaCO3 particles and further control their morphology and size distribution. Such an approach is facile and of potential importance as an environmentally benign industrial route to synthesize biomaterials, and it may also serve to shed light on the study of the mechanism of biomimetic mineralization.
Co-reporter:Li Gao, Beibei Tang, Peiyi Wu
Journal of Membrane Science 2009 Volume 326(Issue 1) pp:168-177
Publication Date(Web):5 January 2009
DOI:10.1016/j.memsci.2008.09.048
In this paper, a novel positively charged asymmetrical membrane was manufactured from brominated polyphenylene oxide (BPPO)/N-methyl-2-pyrrolidone (NMP)/H2O via in situ amination with triethanolamine (TEOA) and a dry–wet phase inversion. The casting solution was exposed to the humid surroundings before immersing into the coagulation bath. The positive charge character of the membrane surface was examined by streaming potential and the effect of the evaporation time and the relative humidity (RH) on the membrane properties and microstructure were investigated, respectively. It was interestingly found that the role of evaporation time and the relative humidity on the membrane performance and morphologies for a positively charged casting system was different from the conventional rule. This was mainly due to the competition of two influence factors, i.e., evaporation of solvent and water absorption of the casting solution. The results were conformed to SEM observation and pore size distribution. Furthermore, the process of water absorption of the casting solution was monitored by attenuated total reflectance infrared (ATR-FTIR) spectroscopy technique. Additionally, in order to compare to the dry–wet phase inversion method, the membranes were obtained by prolonging the exposure time to more than 12 h (which was similar to vapor-induced phase inversion) at different RH. Polymer nodules on the membrane surface and a symmetrical morphology were observed by SEM.
Co-reporter:Wei Li, Bingjie Sun, Peiyi Wu
Carbohydrate Polymers 2009 Volume 78(Issue 3) pp:454-461
Publication Date(Web):15 October 2009
DOI:10.1016/j.carbpol.2009.05.002
Carboxymethyl cellulose is widely used in many industrial aspects and also in laboratory due to its good biocompatibility. However, special researches on infrared especially aiming at the hydrogen bonds structure of carboxymethyl cellulose were relatively poor. We demonstrate here a full view of infrared spectroscopy in the temperature range of 40–220 °C, mainly aiming at the hydrogen bonds in the NaCMC film. The two important transition points was defined with DSC and together with Infrared analysis, that is, 100 °C corresponding to the complete loss of water molecules and 170 °C to the starting temperature point the O6H6 being oxidized. The series of IR spectra during heating from 40 to 220 °C was analyzed by the two-dimensional correlation method. We found that the water molecules bound with CO groups and OH groups. With the evaporating of water molecules, the hydrated CO groups gradually transited into non-hydrated CO groups. As the temperature continued to increase, the intrachain hydrogen bonds were weakened and transited into weak hydrogen bonds. When the temperature was higher than 170 °C, the O6H6 groups were gradually oxidized and thus the interchain hydrogen bonds formed between CH2COONa groups and O6H6 were weakened. In summary, we defined the main sorts of hydrogen bonds in carboxymethyl cellulose and pictured the changes of the hydrogen bonds structure during heating process, which may provide for the further application in both industry aspects and laboratory use.
Co-reporter:Shengtong Sun, Hui Tang, Peiyi Wu and Xinhua Wan
Physical Chemistry Chemical Physics 2009 vol. 11(Issue 42) pp:9861-9870
Publication Date(Web):04 Aug 2009
DOI:10.1039/B909914J
Two-dimensional correlation infrared spectroscopy (2DIR) and a newly developed perturbation correlation moving window (PCMW) technique was employed to study the precise supramolecular self-assembly nature of poly[di(butyl)vinyl terephthalate] (PDBVT), a novel thermotropic liquid crystalline polymer which can self-assemble into a two-dimensional hexagonal columnar (2D ΦH) phase without conventional mesogens. PCMW had found the weak phase transition temperature to be about 85 °C, and further divided the “S or anti-S” shaped spectral variations into three evolving stages. 2DIR results indicated that carbonyl groups acted as the starting point of molecular motions upon heating, and had a significant influence on the formation of the 2D ΦH phase. Based on the additional motion sequence of symmetric and asymmetric C–H stretching vibrations, the whole self-assembly process of PDBVT on the mesoscale, whose backbones experienced “extension–distortion–slight extension” consecutive motions was elucidated.
Co-reporter:Shengtong Sun, Hui Tang and Peiyi Wu
Physical Chemistry Chemical Physics 2009 vol. 11(Issue 35) pp:7611-7618
Publication Date(Web):26 Jun 2009
DOI:10.1039/B906773F
Near infrared spectroscopy (NIR) and two-dimensional correlation spectroscopy (2Dcos) were employed to study the dynamic self-disassociation behavior of hydrogen bonds in neat liquid pyrrole during heating. Two regions (7000–6430 cm−1 for NH-related vibrational overtones and 6200–6100 cm−1 for CH-related vibrational overtones and combination modes) are the focus of this paper, whose integral absorption temperature dependence exhibited a continuous convex variation. Two-dimensional correlation analysis has discerned the sequence of change of different aggregated species of pyrrole. Additionally, we carefully investigated the band shift phenomenon of N–H⋯π hydrogen bonding in pyrrole dimers, and assigned this band shift as the result of the transformation of pyrrole dimers from T-shaped geometry to antiparallel geometry.
Co-reporter:Wei Li and Peiyi Wu
CrystEngComm 2009 vol. 11(Issue 11) pp:2466-2474
Publication Date(Web):30 Jul 2009
DOI:10.1039/B901580A
Carboxymethyl cellulose (CMC) is systematically investigated for the first time in regulating the CaCO3crystallization using a biomimetic gas-diffusion method. Monodisperse rosette-like calcite spherules in uniform size with their surfaces composed of rhombohedral subunits were synthesized in certain conditions. According to time-resolved experiment, the evolution of the crystal morphology was traced and the possible route in which rosette-like spherules form is suggested. We propose that the amorphous calcium carbonate precursors form initially and act as secondary nuclei, followed by the stacking of rhombohedral subunits in partial rather than complete superposition between each other due to the electrostatic repulsive interactions between the polyanion chains adsorbed on the blocks, which results in the final rosette-like morphology. Mineralization experiments in CMC solutions with different concentrations were also carried out and the results obtained at no higher than 1 g L−1 further prove the above mechanism from the fact that the extent of the polymer influence decreases proportionally with concentration, i.e. the degree of superposition of the building blocks becomes larger by decreasing the CMC concentration. In contrast, in a higher polymer concentration of 5 g L−1, another aggregation way from nanoparticles is adopted. In addition, the influence of the initial calcium ion concentration and the chain length of CMC on the crystal morphology were also investigated. The present investigation on the influence of CMC on CaCO3crystallization not only provides for the formation mechanisms of the rosette-like calcite spherules but also leads to a new possible route to fabricate new materials which can be used in many industrial areas.
Co-reporter:Beibei Tang, Peiyi Wu
Vibrational Spectroscopy 2009 Volume 51(Issue 1) pp:65-71
Publication Date(Web):18 September 2009
DOI:10.1016/j.vibspec.2008.10.005
In the study, the diffusion process of water and CaCl2 aqueous solution in polyacrylonitrile (PAN) membrane have been investigated using attenuated total reflection Fourier transform infrared (ATR-FTIR) spectroscopy and two-dimensional (2D) correlation analysis. In 2D ATR-FTIR spectra, the water ν(OH) band in PAN membrane during both water and CaCl2 solution diffusion is split into three separate bands. However, the OH band appearing from bound water which forms hydrogen-bonding of CaCl2 solution diffusion has a considerably lower wavenumber than that of pure water diffusion, which is due to association between Ca2+ ions and the CN groups in PAN. The sequential orders of the intensity changes for water and CaCl2 solution diffusion in the region of ν(OH) and ν(CN) bands reveal the diffusion process and interaction of water and electrolyte in PAN membrane. That is, in the process of water diffusion in PAN membrane, water molecules first interact with –CN group in PAN to form weak hydrogen bond, then the moderate hydrogen-bonding interactions start gradually, and finally, the strong hydrogen-bonding interactions may be formed. When CaCl2 solution diffuses in PAN membrane, the CN groups in PAN first associate with Ca2+ ions and then interact with water molecules to form hydrogen bond that grows gradually from weak to strong. Furthermore, the results are validated further by band fitting to calculate the ratio of each component band area and the proportion of component band to ν(OH) water band.
Co-reporter:Bing-Jie Sun, Wei-Hui Shang, Qiu Jin, Qian-Wei Xu, Pei-Yi Wu
Vibrational Spectroscopy 2009 Volume 51(Issue 1) pp:93-99
Publication Date(Web):18 September 2009
DOI:10.1016/j.vibspec.2008.10.017
Pyromellitic dimethacrylate (PMDM), a dental adhesive functional monomer has been investigated by FTIR and two-dimensional infrared spectroscopy (2D-IR) methods. With the comparison of the curing processes among three samples (Base-Resin, PMDM and monomethacrylate monomer 4-methacryloxyethyl trimellitic anhydride (4-META)), better properties and faster curing of newly used PMDM has been found. Assignments of Base-Resin, PMDM and 4-META in the mid-infrared (MIR) and near-infrared (NIR) regions are ascertained detailedly. According to the high resolution of 2D-NIR maps, assignments of the dental adhesive functional monomers are further validated and the mechanism of the curing process has been accurately concluded as well; similar 2D-NIR spectra of all three samples show the same transformation process from the double-bonds to the single-bonds during visible-light curing.
Co-reporter:Zuliang Lai, Peng Xu, Peiyi Wu
Journal of Molecular Structure 2009 Volume 917(2–3) pp:84-92
Publication Date(Web):15 January 2009
DOI:10.1016/j.molstruc.2008.06.029
Multi-steps infrared spectroscopic methods, including conventional Fourier transform infrared spectroscopy (FT-IR), second derivative spectroscopy and two-dimensional infrared (2D-IR) correlation spectroscopy, have been proved to be effective methods to examine complicated mixture system such as Chinese herbal medicine. The focus of this paper is the investigation on the effect of flowering on the pharmaceutical components of Cistanche tubulosa by using the Multi-steps infrared spectroscopic method. Power-spectrum analysis is applied to improve the resolution of 2D-IR contour maps and much more details of overlapped peaks are detected. According to the results of FT-IR and second derivative spectra, the peak at 1732 cm−1 assigned to CO is stronger before flowering than that after flowering in the stem, while more CO groups are found in the top after flowering. The spectra of root change a lot in the process of flowering for the reason that many peaks shift and disappear after flowering. Seven peaks in the spectra of stem, which are assigned to different kinds of glycoside components, are distinguished by Power-spectra in the range of 900–1200 cm−1. The results provide a scientific explanation to the traditional experience that flowering consumes the pharmaceutical components in stem and the seeds absorb some nutrients of stem after flowering. In conclusion, the Multi-steps infrared spectroscopic method combined with Power-spectra is a promising method to investigate the flowering process of C. tubulosa and discriminate various parts of the herbal medicine.
Co-reporter:Jingya Shi, Peiyi Wu, Lei Li, Tao Liu, Ling Zhao
Polymer 2009 50(23) pp: 5598-5604
Publication Date(Web):
DOI:10.1016/j.polymer.2009.09.078
Co-reporter:Qisi Yu, Peiyi Wu, Peng Xu, Lei Li, Tao Liu and Ling Zhao
Green Chemistry 2008 vol. 10(Issue 10) pp:1061-1067
Publication Date(Web):19 Aug 2008
DOI:10.1039/B806094K
The modifications and applications of natural cellulose have attracted more and more interest in recent years, sparked by the progressive shortage of the fossil energy resources and increase in the technological interests in sustainable and renewable raw materials. In this paper, a novel approach for preparation of cellulose/titanium dioxide hybrids was achieved by utilizing supercritical carbon dioxide-assisted impregnation. The hybrids, with a very small scale in length, suggest that the titania particles were not only coating on the external surface but also penetrating into the micro-cavity structure of the cellulose fibers. The penetrating and swelling effect of supercritical carbon dioxide, with a colsovent of ethanol, on the cellulose was also investigated. It was found that such actions of carbon dioxide in the supercritical state influenced the interactions between the molecular chains of cellulose. The titania particles were facilitated by the effect of supercritical carbon dioxide to access and impregnate into the crystalline structure of cellulose fibers by formation and stabilization of hydrogen bonds with abundant hydroxyl groups of cellulose, resulting in a change of its thermal stability in pyrolysis. This preparative procedure is facile and environmentally friendly, and provides a simple approach for the synthesis of useful materials in various applications.
Co-reporter:Yi Shen, Peiyi Wu
Journal of Molecular Structure 2008 Volume 886(1–3) pp:72-76
Publication Date(Web):27 August 2008
DOI:10.1016/j.molstruc.2007.10.037
Temperature-dependent variation of N-ethylcarbazole chromium tricarbonyl complex by itself without the solid support has been studied by carefully examining their IR spectra with the aid of two-dimensional correlation analysis. Two obvious stages have been observed during the heating process. In the first stage, the crystalline ECzC undergoes a slow process to change into the amorphous form due to the strong interactions of the hydrogen bonding. In the second stage, ECzC gradually decomposes, which results in the formation of Cr(CO)6. The results suggest that the interaction between the organometallics and its solid support may not have direct influence to the final product generated under the thermal treatment.
Co-reporter:Yilu Guo, Peiyi Wu
Journal of Molecular Structure 2008 Volumes 883–884() pp:31-37
Publication Date(Web):30 July 2008
DOI:10.1016/j.molstruc.2007.11.009
The state of acrylamide (AM) confined within the hydrophilic core of sodium bis(2-ethylhexyl) sulfosuccinate (AOT) reversed micelles has been investigated by Fourier transform infrared spectroscopy with an attenuated total reflection (ATR) accessory. 2D correlation spectroscopy and curve fitting revealed that the acrylamide molecule was carried into the micellar core by one of the two long tails of the AOT through H-bonding between the amide group and the carbonyl group of AOT. The acrylamide tended to stick at the interface of the inverse emulsion at lower acrylamide-to-AOT molar ratio value (X); when X increased to some higher values, the acrylamide would tend to congregate in the micellar core. Therefore, it is important to choose the suitable initiator for the inverse emulsion polymerization under different experimental conditions.
Co-reporter:Yilu Guo, Yun Peng, Peiyi Wu
Journal of Molecular Structure 2008 Volume 875(1–3) pp:486-492
Publication Date(Web):17 March 2008
DOI:10.1016/j.molstruc.2007.05.023
Thermosensitive phase transition behavior of poly(vinyl methyl ether) (PVME) in an aqueous solution during heating was investigated by Fourier transform infrared (FTIR) spectroscopy with attenuated total reflection (ATR) accessory. ATR-IR spectra of PVME in an aqueous solution change dramatically in the vicinity of the lower critical solution temperature (LCST). Heating of the solution above LCST leads to the lower wavenumber shifts of C–H stretching bands, which result from the hydration of polymer chains. Two-dimensional infrared (2D IR) analysis results indicate that hydrated C–H groups change prior to dehydrated C–H groups with increasing temperature around the phase transition. Furthermore, the CH2 groups in the main chain dehydrate more slowly than the side chain methyl groups. When 0.5 M KCl was added into a PVME aqueous solution, IR spectra showed that the phase transition temperature was reduced, and the phase separation proceeded in two successive steps. On the other hand, features of 2D IR spectra did not change compared to PVME aqueous solution in the absence of KCl. The result indicates that the underlying phase transition mechanism itself was not altered by the presence of KCl, although the transition temperature is shifted.
Co-reporter:Zuliang Lai, Peiyi Wu
Journal of Molecular Structure 2008 Volumes 883–884() pp:236-241
Publication Date(Web):30 July 2008
DOI:10.1016/j.molstruc.2008.01.017
The carbonyl groups of sodium bis(2-ethylhexyl) sulfosuccinate (AOT) in the water-in-oil (W/O) microemulsions of AOT/tetrachloromethane/water were investigated by using two-dimensional attenuated total reflection Fourier transform infrared (2D-ATR-FTIR) correlation spectroscopy under a perturbation of temperature. The results of a traditional curve fitting method were compared with the 2D correlation spectra results. The peaks at 1718 and 1736 cm−1 were assigned to different carbonyl groups in trans conformation and gauche conformation of AOT molecules, respectively. With the increase of temperature, the trans conformation increased quickly at the lower temperature below 35 °C and decreased slowly at the higher temperature. The special phenomenon owed to the composition and decomposition of the hydrogen bonding between water of the inner polar core and carbonyl groups of AOT molecules. Two new peaks at 1707 and 1747 cm−1 in the 2D correlation spectra implied the process of the transition of AOT molecule conformation and the deviation of correlation coefficients of curve fitting method. 2D-ATR-FTIR correlation spectroscopy exhibited the superiority over the traditional curve fitting method.
Co-reporter:Bingjie Sun, Qiu Jin, Lisha Tan, Peiyi Wu and Feng Yan
The Journal of Physical Chemistry B 2008 Volume 112(Issue 45) pp:14251-14259
Publication Date(Web):October 17, 2008
DOI:10.1021/jp806805r
The mixture of ionic liquid (1-butyl-3-methylimidazolium tetrafluoroborate, bmimBF4) and water (2.5%, molar fraction) under isothermal conditions at 80 °C was investigated by FTIR spectroscopy and two-dimensional correlation infrared spectroscopy (2D-IR) methods. Three regions were focused: the OH stretching band of water (3755−3300 cm−1), the stretching band of CH on the imidazole ring (3300−3020 cm−1), and the BF stretching band of anions (1310−1260 cm−1). During this process, water was gradually evaporated as time passed, which produced influences on the interactions among cations, anions, and water molecules. In the FTIR analysis, we found an interesting “V”-shaped changing trend in peak areas of the C−H on the imidazole ring and the B−F stretching band; the inflection of the system was 913 s, gained through the “moving window” method. A two-step variation was accordingly found during this process. Hydrogen bonds formed by water molecules with cations or water molecules with anions were destroyed by the reduction of water, making a fall in the former period of “V” process, while electrostatic interactions newly formed between anions and cations leading to a rise during the latter period of this course. In this paper, various conformations formed among cations, anions, and water molecules were clearly assigned, and we managed to trace the whole dynamic mechanism of this isothermal process by 2D-IR techniques.
Co-reporter:Yilu Guo, Bingjie Sun and Peiyi Wu
Langmuir 2008 Volume 24(Issue 10) pp:5521-5526
Publication Date(Web):April 25, 2008
DOI:10.1021/la7038398
The thermosensitive phase separation of poly(vinyl methyl ether) (PVME) aqueous solutions has been investigated using near-infrared spectroscopy in combination with two-dimensional correlation analysis, and a two-step phase separation mechanism during gradual heating has been established. Two-dimensional near-infrared (2D NIR) analysis results indicate that during this two-step process the dehydration of CH2 groups occurs earlier than that of CH3 groups. This result suggests that it is the change of the hydrophobic hydrocarbon chain conformation induced by heating that indirectly leads to the dehydration of the hydrophilic ether oxygen side groups.
Co-reporter:Yan Xu, Peiyi Wu
Journal of Molecular Structure 2007 Volume 833(1–3) pp:145-149
Publication Date(Web):15 May 2007
DOI:10.1016/j.molstruc.2006.09.016
The dehydration progress of nylon 6 was investigated at two different temperatures, using near-infrared (NIR) spectroscopy. The two-dimensional (2D) correlation technique was applied to analyse the experimental data. In the region of the O–H combination band (5350–5000 cm−1), the asynchronous spectra of the two temperatures resolve the complex band into three component bands centered at 5280, 5230, and 5140 cm−1, respectively, indicating the existence of three species of water molecules in different states of hydrogen bonding. From the study of the 2D correlation analysis at two temperatures, we have suggested different dehydration mechanisms of the polyamide 6 soaked with water for 50 and 80 °C.
Co-reporter:Weizhen Li
Macromolecular Chemistry and Physics 2004 Volume 205(Issue 10) pp:1338-1342
Publication Date(Web):18 JUN 2004
DOI:10.1002/macp.200400123
Summary: A novel experimental approach, that is, two-dimensional (2D) correlation analysis based on time-resolved attenuated total reflection (ATR) FT-IR spectroscopy, has been used to study the diffusion behavior of ethylene glycol molecules into EP and EPB (novolac epoxy resins cured with novolac resin or novolac butyrate resin, respectively). The diffusion behavior of ethylene glycol into these systems is discussed and compared with that of water. Ethylene glycol absorbed in EP can be classified into two types (free and bound types), while in EPB a third type (referred to as “specific” type) is also observed, which differs from water sorption behavior. In particular, it is interesting to find that the hydrogen bonding of specific ethylene glycol involves two hydroxyl groups rather than one hydroxyl group and polar group in epoxy networks (carbonyl group), a similar example of which has not been previously observed. In addition, in both EP and EPB, bound ethylene glycol molecules diffuse faster than any other types.
Co-reporter:Peiyi Wu, H.W. Siesler
Chemical Physics Letters 2003 Volume 374(1–2) pp:74-78
Publication Date(Web):4 June 2003
DOI:10.1016/S0009-2614(03)00691-2
The water diffusion process in a novolac epoxy resin (EP) was studied by 2D ATR-FTIR spectroscopy, the originally broad water OH bands in 1D-IR spectra can be effectively differentiated into three bands, located at 3610, 3460 and 3240 cm−1, respectively. The bands at 3460 cm−1 (antisymmetric) and 3240 cm−1 (symmetric) are assigned to the OH stretching vibration of water fully hydrogen-bonded with other water molecules, while the 3610 cm−1 band could be attributed to the stretching vibration of water partially hydrogen-bonded with epoxy resin. The mechanism of the water diffusion process in EP is also discussed.
Co-reporter:Yan Jiang, Yi Shen, Peiyi Wu
Journal of Colloid and Interface Science (15 March 2008) Volume 319(Issue 2) pp:398-405
Publication Date(Web):15 March 2008
DOI:10.1016/j.jcis.2007.12.020
Polymer/Au nanoparticle multilayer ultrathin films are fabricated via hydrogen-bonding interaction by a layer-by-layer technique. The Au nanoparticles surface-modified with pyridine groups of poly(4-vinylpyridine) (PVP) are prepared in dimethyl formamide (DMF). Transmission electron microscopy (TEM) image shows that uniform nanoparticles are dispersed in the PVP chains. Poly(3-thiophene acetic acid) (PTAA) and poly(acrylic acid) (PAA) are utilized to form hydrogen bonds with PVP, respectively. Considering the pH-sensitive dissociation behavior of PTAA and PAA, we investigate the release behavior of the Au-containing multilayers at different pH values in this work. UV–vis spectroscopy and atomic force microscopy (AFM) are employed to monitor the buildup and the release of the multilayers. The results indicate that in the films assembled with gold nanoparticles, the polymers are difficult to be removed from the substrate. The interaction between the gold particles and the neighboring PVP chains is responsible for the phenomenon. Gold particles act as physical cross-link points in the multilayers. Due to the additional interaction caused by the gold nanoparticles in the films except the hydrogen-bonding interaction between PTAA (or PAA) and PVP, the stability of the Au-containing multilayer film is ensured even though the changes in pH values may result in the break of the hydrogen bonds.The interaction between the adjacent bilayers induced by the gold nanoparticles serves to maintain the stability of the Au-containing multilayer film.Download full-size image
Co-reporter:Wenhui Sun and Peiyi Wu
Physical Chemistry Chemical Physics 2017 - vol. 19(Issue 1) pp:NaN134-134
Publication Date(Web):2016/11/22
DOI:10.1039/C6CP06862F
In this paper, we investigated the internal structure and the volume phase transition (VPT) behavior of poly(N-vinylcaprolactam-co-vinylimidazole)/polymerizable carbon nanodot (P(VCL-co-VIM)/PCND) microgels with different amounts of PCNDs. Our study shows that compared to the pure P(VCL-co-VIM) microgel, the hybrid microgels undergo a two-step VPT as the temperature increases and a core–shell(–corona) structure of the hybrid microgels is formed by copolymerization with PCNDs. A change in the amount of PCNDs has effects on both of the volume phase transition temperature and internal structure of microgels. Moreover, based on FT-IR in combination with perturbation correlation moving window (PCMW) and two-dimensional correlation spectral (2Dcos) analyses, the difference in VPT behavior between the shell and the core (corona) structure of the hybrid microgels at the molecular level is elucidated. The core/shell of the hybrid microgels fixed with hydrophilic PCNDs has a higher transition temperature during heating and a more compact structure due to the additional crosslinkers PCNDs.
Co-reporter:Shengtong Sun and Peiyi Wu
Physical Chemistry Chemical Physics 2011 - vol. 13(Issue 47) pp:NaN21120-21120
Publication Date(Web):2011/10/21
DOI:10.1039/C1CP22727K
Herein, noble metal nanoparticle (Au or Ag NP) decorated graphene sheets, fabricated according to a facile one-pot environmentally friendly method, are used as good substrates for the investigation of the combined surface-enhanced Raman scattering (SERS) effect, where both the electromagnetic mechanism and the chemical mechanism effects coexist among the Au or Ag NPs, graphene sheets and the absorbed analytes. Our results show that, in aqueous solution, the SERS effect of both the Au and Ag NPs on the absorbed probe molecules and on graphene is competitive, which varies dependent on the species and the concentration of the absorbed probe molecule. By a detailed comparison of three probe molecules (rhodamine 6G, nile blue A, and 4-aminobenzenethiol) with different coupling abilities to the graphene sheets, we finally attribute this phenomenon to the result of the strong suppressing effect of the macrocyclic probe molecules on the SERS of graphene, induced by charge transfer, as the probe molecules are coupled to the graphene sheets. This competitive effect is a non-ignorable phenomenon when graphene/Au or Ag nanocomposites are used as SERS substrates, and our study may deepen our understanding of the SERS mechanism.
Co-reporter:Xiongwei Wang, Ludan Zhang, Congcong Zhang and Peiyi Wu
Inorganic Chemistry Frontiers 2017 - vol. 4(Issue 5) pp:NaN897-897
Publication Date(Web):2017/03/16
DOI:10.1039/C7QI00057J
The huge volume variation and poor electronic conductivity of tin oxide (SnO2) during the discharge/charge process greatly limit its practical application in lithium ion batteries (LIBs). Hybridization with graphene is a widely-used method to improve its electrochemical performance, but it still faces some limitations. In this work, we integrate carbon encapsulation with graphene hybridization to synthesize a sandwich-like carbon-coated SnO2/graphene composite via a flexible method. In this case, a mesoporous graphene/carbon framework (MCF) derived from acid etching of an as-prepared graphene@Fe3O4@C composite was used as a robust matrix for the embedment of SnO2. When evaluated as an anode material for LIBs, the resultant MCF@SnO2 composite exhibits a high second reversible capacity of 1205 mA h g−1 at 0.2 A g−1, excellent cycling performance with 668 mA h g−1 capacity retention after 200 cycles at 1.0 A g−1, and a good rate capability. This facile strategy could be further extended to embed other metal oxide nanoparticles into the mesoporous carbon framework for applications in energy conversion and storage.
Co-reporter:Yalan Dai and Peiyi Wu
Physical Chemistry Chemical Physics 2017 - vol. 19(Issue 28) pp:NaN18564-18564
Publication Date(Web):2017/06/28
DOI:10.1039/C7CP02942J
A new LCST-type thermoresponsive polyelectrolyte P[P4,4,4,4][SS], poly(tetrabutyl phosphonium styrene sulfonate), was introduced to PMEO2MA (poly(2-(2-methoxyethoxy)ethyl methacrylate)) via RAFT polymerization, in order to explore the transition behavior of the block copolymer PMEO2MA-b-P[P4,4,4,4][SS] with two distinct LCST-type segments. A relatively sharp LCST-type phase transition with only one transition point is observed in the turbidity curves, while the whole phase transition is completely different from the micro perspective. The phase transition temperature range is relatively broad, according to the unsynchronized changes of different protons of the two blocks in the temperature-variable 1H NMR analysis. From PCMW analysis, it is found that there exists an obvious two-step phase transition behavior, especially in the region of the C–H groups. Accordingly, we divided the whole transition process into two subregions: 20–40 °C and 40–55 °C in 2Dcos analysis. At the first stage of 20–40 °C, the CH3 groups mainly belonging to the backbones of PMEO2MA blocks have the earliest response to the heating and drive the first step of the dehydration process of PMEO2MA-b-P[P4,4,4,4][SS], resulting in the formation of an intermediate micelle state composed of the collapsed PMEO2MA core and hydrophilic P[P4,4,4,4][SS] corona. In particular, the conformational changes and the more compact structures due to the interaction between the CO groups and P[P4,4,4,4][SS] segments (ν(CO⋯D2O-PILs)) were observed using IR analysis. With the continual increase of the temperature, when the second temperature range of 40–55 °C is reached, the P[P4,4,4,4][SS] segments start to collapse and expel the water molecules, driven by the anions of the poly(ionic liquid)s, with the phosphonium cations being distributed over the relatively hydrophilic outside.
Co-reporter:Yuanyuan Zhou, Hui Tang and Peiyi Wu
Physical Chemistry Chemical Physics 2017 - vol. 19(Issue 9) pp:NaN6635-6635
Publication Date(Web):2017/02/03
DOI:10.1039/C6CP08574A
Temperature-induced phase transition together with the liquid–liquid phase separation (LLPS) phenomenon of poly(oligo(2-isopropyl-2-oxazoline)methacrylate) with the comb-shaped architecture (comb-PiPOx) in aqueous solution has been discussed at the molecular level. Differing from linear poly(2-isopropyl-2-oxazoline) (linear-PiPOx), polymer-rich liquid droplets appear at higher temperature compared with the phase transition determined by differential scanning calorimetry (DSC) in comb-PiPOx solution. As investigated using variable-temperature Fourier transform infrared (FTIR) spectra analysis, the densely grafted architecture gives rise to an intra-molecular interaction (hydrophobic interaction of alkyl groups and H-bond of carbonyl groups) dominating the dehydration process of comb-PiPOx. With temperature increment, most of the water within hydrated polymers is expelled to the outer water phase through intra-molecular association, corresponding to the transition temperature. Afterwards, the dehydration of methyl groups on side chain ends reflects the massive aggregation of polymer chains through inter-molecular association, accompanied by hysteretic LLPS.
Co-reporter:Xiongwei Wang, Ludan Zhang and Peiyi Wu
Inorganic Chemistry Frontiers 2017 - vol. 4(Issue 4) pp:NaN691-691
Publication Date(Web):2017/02/07
DOI:10.1039/C7QI00009J
In this work, a novel nanocomposite with few-layered ultrasmall MoS2 nanosheets uniformly anchored on a three-dimensional (3D) flower-like carbon (FC) was designed and prepared, where zinc oxide was used as a sacrificial template to prepare a biomass-based FC skeleton by a hydrothermal method and subsequent high-temperature carbonization. When evaluated as an anode material for lithium ion batteries (LIBs), the three-dimensional FC matrix can not only improve the electronic conductivity of the hybrid, but also enable fast electrolyte diffusion to MoS2. The FC–MoS2 hybrid exhibits a high second reversible capacity of 1033 mA h g−1 at 0.2 A g−1, excellent cycling stability with negligible capacity loss after 200 cycles at 1.6 A g−1, and good rate performance. Additionally, the hybrid also shows enhanced electrocatalytic performance for hydrogen evolution. We believe that our method may provide a cost-effective and eco-friendly route to prepare 3D biomass-based composites for energy generation or storage.
Co-reporter:Ying Tang, Beibei Tang and Peiyi Wu
Journal of Materials Chemistry A 2015 - vol. 3(Issue 23) pp:NaN12376-12376
Publication Date(Web):2015/04/27
DOI:10.1039/C5TA01823D
In this work, we report a novel method to prepare a positively charged nanofiltration (NF) membrane by rapid counter-ion exchange of a poly(ionic liquid) (PIL) in aqueous solution, which transforms from being hydrophilic to hydrophobic. A thin PIL layer is deposited on the supporting membrane via a phase separation process induced by an ion exchange reaction along with a self-inhibiting effect, and a series of positively charged NF membranes are obtained. The membrane formation process is mainly dominated by the concentration of the hydrophilic PIL and its counter-ions. In brief, the density of the top layer is predominated both by the PIL and its aqueous counter-ion, and the thickness of the surface layer is mainly determined by the aqueous counter-ion. A streaming potential measurement confirmed that the resultant membrane is positively charged when the pH range is below 11. The pure water flux (PWF) was up to 45.3 L m−2 h−1 under the operating pressure of 0.6 MPa. The rejection to MgCl2 of the membrane reached 84% and decreased in the order of MgCl2, NaCl, MgSO4, and Na2SO4. It also shows a high rejection of about 90% to heavy metallic salts such as CuCl2, NiCl2 and CoCl2. The method based on the hydrophilic–hydrophobic transformation of the PIL provides an alternative way to prepare a charged membrane with high performance.
Co-reporter:Kai Feng, Beibei Tang and Peiyi Wu
Journal of Materials Chemistry A 2014 - vol. 2(Issue 38) pp:NaN16092-16092
Publication Date(Web):2014/07/25
DOI:10.1039/C4TA03207A
In the current study, sulfonated graphene oxide–silica (S-GO–SiO2) nanohybrid particles were obtained first. The FTIR, TGA, XRD, Raman, AFM, FE-SEM and EDX characterizations were employed to confirm the successful decoration of SiO2 onto GO surface and the attachment of sulfonic acid groups onto the GO–SiO2 surface. Then, S-GO–SiO2/Nafion proton exchange membranes (PEMs) were prepared via solution casting. S-GO–SiO2 had a good dispersibility inside the membrane matrix. The increased water uptake and the incorporated –SO3H groups bestowed a large increase in proton conductivity upon these composite PEMs. Meanwhile, the barrier effect of two-dimensional S-GO–SiO2 contributed to the obvious reduction in methanol permeability of the composite PEMs, as a result of the increased tortuosity of the transport channels. Therefore, novel S-GO–SiO2/Nafion PEMs with enhanced selectivity (the ratio of proton conductivity to methanol permeability) were obtained. Even under harsh conditions, such as high methanol concentration and/or increased temperature, the membrane selectivity of S-GO–SiO2/Nafion composite membranes was still nearly two-orders-of-magnitude higher than that of the recast Nafion membrane. It renders this type of composite PEMs a very promising candidate for the application in DMFC. All the conclusions were demonstrated by various characterizations, such as (FE-) SEM, TEM, AFM, FTIR, TGA, water uptake, etc.
Co-reporter:Shengjie Xu and Peiyi Wu
Journal of Materials Chemistry A 2014 - vol. 2(Issue 33) pp:NaN13690-13690
Publication Date(Web):2014/06/24
DOI:10.1039/C4TA01417K
In this work, a well-dispersed Au cluster/reduced graphene oxide (RGO) composite was synthesized using citric acid (CA) as a reducing and binding agent. The as-prepared composite was systemically characterized by TEM, XPS, TGA and FTIR. TEM image showed Au clusters uniformly distributed on the RGO sheet with an average size of 1.8 nm. The Au clusters/RGO composite exhibited excellent catalytic performance for the oxygen reduction reaction (ORR). Moreover, the electrocatalytic comparison indicated that the long-term durability and methanol tolerance of this composite was superior to the commercial Pt/C catalyst. Therefore, such a composite might be an alternative and more promising non-Pt electrocatalyst for fuel cells.
Co-reporter:Shengtong Sun and Peiyi Wu
Journal of Materials Chemistry A 2011 - vol. 21(Issue 12) pp:NaN4097-4097
Publication Date(Web):2011/02/22
DOI:10.1039/C1JM10276A
A facile one-step strategy for graphene oxide interpenetrating PNIPAM hydrogel networks is developed by covalently bonding GO sheets and PNIPAM-co-AA microgels directly in water, which exhibit dual thermal and pH response with good reversibility.
Co-reporter:Yewen Cao, Zuliang Lai, Jiachun Feng and Peiyi Wu
Journal of Materials Chemistry A 2011 - vol. 21(Issue 25) pp:NaN9278-9278
Publication Date(Web):2011/05/19
DOI:10.1039/C1JM10420A
Herein, by taking advantage of click chemistry, we propose a general and effective methodology to covalently functionalize graphene oxide sheets (GOSs) with block copolymers, namely poly(styrene-b-ethylene-co-butylene-b-styrene) (SEBS) triblock copolymers as an example in this study. The covalent attachment of SEBS to GOSs, as well as the individual nature of the hybrids, was confirmed by detailed investigations. For the potential applications of the block copolymer-clicked GOSs, they were incorporated into polystyrene (PS) as reinforcing fillers. The SEBS-clicked GOSs showed excellent compatibility with a PS matrix, and as a consequence, remarkably improved mechanical properties and thermal stability of the resulting composite films were achieved. This protocol is believed to offer possibilities to fully combine the extraordinary performances of GOSs with the multifunctional properties of block copolymers, and thus be useful in a variety of technological fields.
Co-reporter:Yalan Dai and Peiyi Wu
Physical Chemistry Chemical Physics 2016 - vol. 18(Issue 31) pp:NaN21370-21370
Publication Date(Web):2016/07/07
DOI:10.1039/C6CP04286D
The assembly properties, thermal phase behavior and microdynamics of well-defined P(MEO2MA-co-OEGMA)-b-P4VP, (poly(2-(2-methoxyethoxy)ethylmethacrylate)-co-poly(oligo(ethylene glycol) methacrylate))-b-poly(4-vinyl pyridine), in aqueous solution during heating are investigated in detail by dynamic light scattering (DLS), turbidity measurements, temperature-variable 1H NMR and FTIR spectroscopy in combination with two-dimensional correlation spectroscopy (2Dcos) and the perturbation correlation moving window (PCMW) technique. It is observed that the chain length of the relatively hydrophobic P4VP segment strongly affects the temperature-induced phase transition behavior of the block copolymers: the copolymers with shorter P4VP7/10 segments exhibit an abrupt phase transition process, while the copolymer with longer P4VP19 blocks presents a relatively gradual transition behavior. Moreover, the two systems with different P4VP segment lengths have different morphologies in aqueous solution: a single-chain globule for shorter P4VP7/10 systems and a core–shell micelle consisting of a relatively hydrophobic P4VP core and a hydrophilic POEGMA-based shell for the longer P4VP19 system. Analysis of spectral results clearly illustrates that the dehydration of the CO groups at the linkages between backbones and pendant chains predominates the sharp phase transition of P(MEO2MA-co-OEGMA)-b-P4VP10, while the dehydration of hydrophobic C–H groups on the side chains in P(MEO2MA-co-OEGMA)-b-P4VP19 leads to the continuous increase of the hydrodynamic diameter (Dh) upon heating.
Co-reporter:Shengtong Sun, Hui Tang, Peiyi Wu and Xinhua Wan
Physical Chemistry Chemical Physics 2009 - vol. 11(Issue 42) pp:NaN9870-9870
Publication Date(Web):2009/08/04
DOI:10.1039/B909914J
Two-dimensional correlation infrared spectroscopy (2DIR) and a newly developed perturbation correlation moving window (PCMW) technique was employed to study the precise supramolecular self-assembly nature of poly[di(butyl)vinyl terephthalate] (PDBVT), a novel thermotropic liquid crystalline polymer which can self-assemble into a two-dimensional hexagonal columnar (2D ΦH) phase without conventional mesogens. PCMW had found the weak phase transition temperature to be about 85 °C, and further divided the “S or anti-S” shaped spectral variations into three evolving stages. 2DIR results indicated that carbonyl groups acted as the starting point of molecular motions upon heating, and had a significant influence on the formation of the 2D ΦH phase. Based on the additional motion sequence of symmetric and asymmetric C–H stretching vibrations, the whole self-assembly process of PDBVT on the mesoscale, whose backbones experienced “extension–distortion–slight extension” consecutive motions was elucidated.
Co-reporter:Shengtong Sun, Hui Tang and Peiyi Wu
Physical Chemistry Chemical Physics 2009 - vol. 11(Issue 35) pp:NaN7618-7618
Publication Date(Web):2009/06/26
DOI:10.1039/B906773F
Near infrared spectroscopy (NIR) and two-dimensional correlation spectroscopy (2Dcos) were employed to study the dynamic self-disassociation behavior of hydrogen bonds in neat liquid pyrrole during heating. Two regions (7000–6430 cm−1 for NH-related vibrational overtones and 6200–6100 cm−1 for CH-related vibrational overtones and combination modes) are the focus of this paper, whose integral absorption temperature dependence exhibited a continuous convex variation. Two-dimensional correlation analysis has discerned the sequence of change of different aggregated species of pyrrole. Additionally, we carefully investigated the band shift phenomenon of N–H⋯π hydrogen bonding in pyrrole dimers, and assigned this band shift as the result of the transformation of pyrrole dimers from T-shaped geometry to antiparallel geometry.
Co-reporter:Shengtong Sun, Jun Hu, Hui Tang and Peiyi Wu
Physical Chemistry Chemical Physics 2011 - vol. 13(Issue 11) pp:NaN5067-5067
Publication Date(Web):2011/02/03
DOI:10.1039/C0CP01939A
The thermally induced volume phase transition process of poly(N-isopropylacrylamide-co-acrylic acid) (PNIPAM-co-AA) hydrogel is studied using FT-IR spectroscopy in combination with the perturbation correlation moving window (PCMW) technique and two-dimensional correlation spectroscopy (2Dcos) analysis. According to PCMW spectra analysis, an elevation of volume phase transition temperature (VPTT) due to an extra equilibrium of repulsive electrostatic interactions of acrylic acid moieties in hydrogel from 34 °C to ca. physiological temperature (37 °C) is determined. 2Dcos helps us to conclude that the dehydration of hydrogel responds earlier in the process of network collapse than hydrogen bond variations of AA and NIPAM moieties during heating, while the hydrogen bonds of NIPAM and AA moieties change before the network swelling in the cooling process. Furthermore, relatively stable inner hydrogen bonds of AA moieties restrict the complete expansion of PNIPAM-co-AA hydrogel, resulting in a unique irreversible recovery during cooling.
Co-reporter:Shengtong Sun and Peiyi Wu
Physical Chemistry Chemical Physics 2015 - vol. 17(Issue 46) pp:NaN31092-31092
Publication Date(Web):2015/10/30
DOI:10.1039/C5CP05719A
Poly(2-isopropyl-2-oxazoline) (PIPOZ) with an isomeric structure of poly(N-isopropylacrylamide) (PNIPAM) represents an important class of stimuli-responsive synthetic polymers. Unlike PNIPAM, PIPOZ exhibits an unusual heat-induced crystallization behaviour at around 120 °C in the solid state, whose dynamic mechanism involving all group motions and conformational changes is still poorly understood. In this paper, IR spectroscopy in combination with two-dimensional analysis methods – the perturbation correlation moving window (PCMW) and two-dimensional correlation spectroscopy (2DCOS) – was used to monitor and study the conformational changes in the crystallization of PIPOZ in the solid state. The incorporated water molecules are found to be not necessary to assist the solid-state crystallization of the PIPOZ film. PCMW and 2DCOS analyses reveal that following the breaking of minor CH3⋯OC hydrogen bonds, all the group moieties exhibit highly synergetic motions during crystallization, and methylene groups on the backbone do not show significant changes throughout the crystallization process. Raman spectroscopic and molecular dynamics simulation results further support this conclusion. The chain alignment of PIPOZ chains is shown to be mainly achieved by the lateral distortion of coplanar side chains or the ordered chain arrangement of amide dipoles together with the torsion of the backbone through C–N linkages. Upon heating, gauche conformations of methylene groups on the backbone are always dominating, resulting in an ordered PIPOZ chain with alternate side chains and a slightly distorted backbone.
Co-reporter:Shengtong Sun and Peiyi Wu
Physical Chemistry Chemical Physics 2015 - vol. 17(Issue 48) pp:NaN32240-32240
Publication Date(Web):2015/11/06
DOI:10.1039/C5CP05626H
One easy strategy to comprehend the complex folding/crystallization behaviors of proteins is to study the self-assembly process of their synthetic polymeric analogues with similar properties owing to their simple structures and easy access to molecular design. Poly(2-isopropyl-2-oxazoline) (PIPOZ) is often regarded as an ideal pseudopeptide with similar two-step crystallization behavior to proteins, whose aqueous solution experiences successive lower critical solution temperature (LCST)-type liquid–liquid phase separation upon heating and irreversible crystallization when annealed above LCST for several hours. In this paper, by microscopic observations, IR and Raman spectroscopy in combination with 2D correlation analysis, we show that the second step of PIPOZ crystallization in hot water can be further divided into two apparent stages, i.e., nucleation and crystal growth, and perfect crystalline PIPOZ chains are found to only develop in the second stage. While all the groups exhibit changes in initial nucleation, only methylene groups on the backbone participate in the crystal growth stage. During nucleation, a group motion transfer is found from the side chain to the backbone, and nucleation is assumed to be mainly driven by the cleavage of bridging CO⋯D–O–D⋯OC hydrogen bonds followed by chain arrangement due to amide dipolar orientation. Nevertheless, during crystal growth, a further chain ordering process occurs resulting in the final formation of crystalline PIPOZ chains with partial trans conformation of backbones and alternative side chains on the two sides. The underlying crystallization mechanism of PIPOZ in hot water we present here may provide very useful information for understanding the crystallization of biomacromolecules in biological systems.
Co-reporter:Kai Feng, Beibei Tang and Peiyi Wu
Physical Chemistry Chemical Physics 2016 - vol. 18(Issue 28) pp:NaN19450-19450
Publication Date(Web):2016/06/23
DOI:10.1039/C6CP03176E
Ex situ characterizations based on TGA and XRD techniques revealed that MeOH vapor had little influence on the Nafion microstructures. To reveal the underlying mechanism, in this study, we designed new FTIR-based equipment to track in situ the microstructural changes of a bulk Nafion membrane in MeOH-saturated air. First, an interesting MeOH-breathing phenomenon was found in the ionic domains of Nafion. It demonstrated that there existed a dynamic equilibrium between the sorption and desorption processes of MeOH vapor in Nafion. Second, the FTIR results also detected the high stability of the hydrophobic regions of Nafion in MeOH vapor. The super-acid –CF2–SO3H always retained a small quantity of bonded H2O (H+(H2O)n) inside the Nafion membrane. MeOH vapor was absorbed first into the hydrophilic regions, however, the interactions between –CF2–SO3H and MeOH vapor were much weaker than those between –CF2–SO3H and H+(H2O)n. Therefore, a protective layer composed of residual water formed in the lumen of the hydrophilic ionic domains of Nafion, which protected its hydrophobic regions from the MeOH attack. Hereby, the self-protection ability of Nafion in MeOH vapor was detected for the first time. This work gave a new insight into the complex interplay between Nafion and MeOH vapor.
Co-reporter:Kai Feng, Lei Hou, Beibei Tang and Peiyi Wu
Physical Chemistry Chemical Physics 2015 - vol. 17(Issue 14) pp:NaN9115-9115
Publication Date(Web):2015/03/03
DOI:10.1039/C5CP00203F
Investigating the dehydration process of a Nafion membrane helps to understand the mechanism of the decrease in its proton conductivity under high-temperature and low-humidity conditions. Herein, the influence of thermal treatment on a H2O-saturated Nafion membrane was in situ studied by FTIR spectroscopy. With the aid of generalized two-dimensional correlation spectroscopy (2Dcos), the microstructural changes during the thermal treatment were discussed in detail. In short, side-chain regions first lost H2O, followed by the H2O loss in ionic cluster domains. It resulted in shrunken ionic channels in the Nafion membrane, which exhibited a negative influence on its proton conduction. The immediate aftermath was the crystallization of amorphous backbone regions. All these results were confirmed by TGA and XRD techniques, and the 2Dcos method was first applied in TGA and XRD results in this field.
Co-reporter:Lei Hou and Peiyi Wu
Physical Chemistry Chemical Physics 2016 - vol. 18(Issue 23) pp:NaN15601-15601
Publication Date(Web):2016/05/11
DOI:10.1039/C6CP01244B
Turbidity, DLS and FTIR measurements in combination with the perturbation correlation moving window (PCMW) technique and 2D correlation spectroscopy (2Dcos) analysis have been utilized to investigate the LCST-type transition of a oligo ethylene glycol acrylate-based copolymer (POEGA) in aqueous solutions in this work. As demonstrated in turbidity and DLS curves, the macroscopic phase separation was sharp and slightly concentration dependent. Moreover, individual chemical groups along polymer chains also display abrupt changes in temperature-variable IR spectra. However, according to conventional IR analysis, the C–H groups present obvious dehydration, whereas CO and C–O–C groups exhibit anomalous “forced hydration” during the steep phase transition. From these analyses together with the PCMW and 2Dcos results, it has been confirmed that the hydrophobic interaction among polymer chains drove the chain collapse and dominated the phase transition. In addition, the unexpected enhanced hydration behavior of CO and C–O–C groups was induced by forced hydrogen bonding between polar groups along polymer chains and entrapped water molecules in the aggregates, which originated from the special chemical structure of POEGA.
Co-reporter:Xiongwei Wang, Ludan Zhang, Zehui Zhang, Aishui Yu and Peiyi Wu
Physical Chemistry Chemical Physics 2016 - vol. 18(Issue 5) pp:NaN3899-3899
Publication Date(Web):2016/01/08
DOI:10.1039/C5CP06903C
Nickel oxide (NiO) as one of the anode electrode materials for lithium ion batteries (LIBs) has attracted considerable research attention. However, the poor electron conductivity and bad capacity retention performance greatly hinder its wide application. Herein, we prepared a novel three-dimensional (3D) hierarchical porous graphene@NiO@carbon composite via a simple solvothermal process, in which the graphene sheets were uniformly wrapped by porous NiO@carbon nanoflakes. In this case, nickelocene was creatively used as the precursor for both NiO and amorphous carbon, while graphene oxide sheets were employed as a template for the two-dimensional nanostructure and the conductive graphene backbone. The resultant composites possess high surface area (196 m2 g−1) and large pore volume (0.46 cm3 g−1). When it is applied as an anode for LIBs, the carbon outer-layer can effectively suppress the large volume change and serious aggregation of NiO nanoparticles during the charge–discharge process. Therefore, the graphene@NiO@carbon composites show a high reversible capacity of 1042 mA h g−1 at a current density of 200 mA g−1, an excellent rate performance and long cycle life. We believe that our method provides a new route for the fabrication of novel transition metal oxide composites.
Co-reporter:Zhouyue Lei, Shengjie Xu and Peiyi Wu
Physical Chemistry Chemical Physics 2016 - vol. 18(Issue 1) pp:NaN74-74
Publication Date(Web):2015/11/12
DOI:10.1039/C5CP06483J
In this study, ultra-thin and porous molybdenum selenide (MoSe2) nanosheets were prepared through a modified liquid exfoliation method as efficient electrocatalysts for the hydrogen evolution reaction (HER). This novel structure enables the exposure of more catalytically active sites and moreover maintains effective electron transport, resulting in a small peak potential of ∼75 mV as well as long-term durability. In addition, due to the facile and economical preparation method as well as its eco-friendly synthetic conditions, this study provides a high-performance HER catalyst with promising commercial application prospects.
Co-reporter:Shengtong Sun, Yewen Cao, Jiachun Feng and Peiyi Wu
Journal of Materials Chemistry A 2010 - vol. 20(Issue 27) pp:NaN5607-5607
Publication Date(Web):2010/06/10
DOI:10.1039/C0JM01269F
A facile methodology has been developed to immobilize well-defined polymers onto graphene sheets using “click” chemistry; upon polystyrene coupling, the resulting sheets can be well dispersed and fully exfoliated in common organic media.
Co-reporter:Kai Feng, Yewen Cao and Peiyi Wu
Journal of Materials Chemistry A 2012 - vol. 22(Issue 23) pp:NaN11457-11457
Publication Date(Web):2012/04/18
DOI:10.1039/C2JM31713C
Graphene oxide (GO) can “evaporate” and then transform into quasi-carbon nanotubes on the aluminium foil surface placed 4 cm above an evaporating aqueous GO dispersion. The resulting self-assembly behavior of GO can be easily tailored by varying evaporation time and/or temperature, providing new approaches for preparing new large-area graphene-based materials.
Co-reporter:Lijia Yang, Beibei Tang and Peiyi Wu
Journal of Materials Chemistry A 2014 - vol. 2(Issue 43) pp:NaN18573-18573
Publication Date(Web):2014/09/05
DOI:10.1039/C4TA03790A
In this work, graphene oxide (GO) was first functionalized with branched polyethyleneimine (PEI). The obtained PEI–GO was incorporated into a brominated poly(2,6-dimethyl-1,4-phenylene oxide) (BPPO) matrix by a covalent bond interaction to form a cross-linking network. Then, a novel ultrafiltration (UF) membrane was prepared via casting and phase-inversion methods. The PEI–GO/BPPO membrane showed highly improved water flux, which was almost 6 times higher than that of the pristine BPPO membrane and 2.5 times higher than that of the GO/BPPO membrane, whereas the rejection of PEI–GO/BPPO membrane was still maintained at a high level. The improvement of membrane performance could be attributed to the special property of PEI–GO and the interactions between PEI–GO and the BPPO matrix. First, a cross-linking network of PEI–GO/BPPO membrane was formed because of the reaction between PEI–GO and the BPPO matrix to provide passageways for water rapidly passing through. Second, the high hydrophilicity of PEI–GO could accelerate the exchange rate between solvent and non-solvent, resulting in a rougher and more hydrophilic surface, higher porosity and a more porous structure. Third, the good dispersion and compatibility of PEI–GO promoted the formation of a uniform structure with fewer defects. Proper molecular weight of PEI was very important for the modification of GO, subsequently resulting in an overall enhancement in membrane performance. Anti-fouling experiments and stability tests of the membranes were also conducted. All of these results were confirmed by various characterizations, such as SEM, TEM, AFM and, etc.
Co-reporter:Lijia Yang, Beibei Tang and Peiyi Wu
Journal of Materials Chemistry A 2015 - vol. 3(Issue 31) pp:NaN15842-15842
Publication Date(Web):2015/06/26
DOI:10.1039/C5TA03507D
This work studies Nafion based proton exchange membranes (PEMs) modified by a metal–organic framework–graphene oxide composite (ZIF-8@GO). The ZIF-8@GO/Nafion hybrid membrane displays a proton conductivity as high as 0.28 S cm−1 at 120 °C and 40% RH, resulting from a synergetic effect of ZIF-8 and GO.
Co-reporter:Wei Jia, Kai Feng, Beibei Tang and Peiyi Wu
Journal of Materials Chemistry A 2015 - vol. 3(Issue 30) pp:NaN15615-15615
Publication Date(Web):2015/06/18
DOI:10.1039/C5TA03381K
In the current study, a composite proton exchange membrane (PEM) was prepared by incorporating β-cyclodextrin (β-CD) modified silica nanoparticles (SN-β-CD) into a Nafion matrix. Due to the decoration of β-CD on the SN surface, SN-β-CD possesses excellent compatibility with the Nafion polymer, resulting in a good dispersibility inside the membrane matrix. SN-β-CD brings a better water retention capability for the composite PEM and hence significantly improves the proton conductivity of the composite PEM. Simultaneously, the barrier effect of SN-β-CD which increases the tortuosity of transport channels for bulk methanol leads to an evident reduction in methanol permeability. Herein, a nearly two-order-of-magnitude promotion in membrane selectivity (i.e. the ratio of proton conductivity to membrane permeability) was achieved even under crucial conditions at elevated temperatures or high methanol concentrations.
Co-reporter:Kai Feng, Beibei Tang and Peiyi Wu
Journal of Materials Chemistry A 2015 - vol. 3(Issue 36) pp:NaN18556-18556
Publication Date(Web):2015/08/03
DOI:10.1039/C5TA04916D
For a proton exchange membrane (PEM), the ratio of its proton conductivity to its fuel permeability usually defines the membrane selectivity. Generally, a highly selective PEM is preferred for application in direct methanol fuel cells. Herein, sulfonated SiO2@polystyrene core–shell (SiO2@sPS) nanoparticles were synthesized and then imbedded into a Nafion membrane by a blending–casting method. SiO2@sPS partakes in strong interactions with the Nafion polymer, which benefits its dispersion in the membrane matrix. The as-prepared SiO2@sPS + Nafion composite PEM presents a large increase in its proton conductivity owing to the introduction of additional –SO3H groups and hence has optimized channels for proton transport. Meanwhile, a reduced methanol crossover was also observed for the SiO2@sPS + Nafion composite PEM because of the formation of obstructed transport channels for bulk methanol. Besides this, a deep investigation on further enhancement of the membrane’s performance was conducted by etching the SiO2 core and hence forming well-dispersed uniform hollow spheres inside the membrane matrix. The intact hollow sulfonated PS spheres (h-sPS) acted as water reservoirs which in turn could gradually release water to hydrate the membrane under high-temperature and low-humidity conditions. Therefore, compared to the SiO2@sPS + Nafion membrane, the h-sPS + Nafion one presented a further increased proton conductivity at 100 °C under 40% RH. Meanwhile, h-sPS further suppressed methanol penetration by trapping it inside the hollow spheres. Herein, a “H2O donating/methanol accepting” mechanism was proposed for the first time, providing a promising platform to alleviate critical disadvantages of Nafion membranes and thereby fabricate highly selective Nafion-based PEMs.
Co-reporter:Zehui Zhang, Fei Wang, Qiao An, Wei Li and Peiyi Wu
Journal of Materials Chemistry A 2015 - vol. 3(Issue 13) pp:NaN7043-7043
Publication Date(Web):2015/02/11
DOI:10.1039/C4TA06910B
Development of anode materials with high capacity and long cycle life, while maintaining low production cost is crucial for achieving high-performance lithium-ion batteries (LIBs). Herein, we report a simple and cost-effective one-pot solvothermal method to synthesize graphene@Fe3O4@C core–shell nanosheets as a LIB anode with improved electrochemical performances. In this case, ferrocene was used as the precursor for both Fe3O4 and carbon, while graphene oxide was used as a template for the resultant two-dimensional nanostructure and conductive graphene backbone. The obtained graphene@Fe3O4@C core–shell nanosheets have a unique core–shell nanostructure, ultrasmall Fe3O4 nanoparticles (∼6 nm), and a high surface area of ∼136 m2 g−1, as well as show a high reversible capacity of ∼1468 mA h g−1, an excellent rate capability and long cycle life, which reflects the ability of graphene backbone to enhance the conductivity and carbon coating to prevent agglomeration of iron oxide nanoparticles. These findings provide a new approach to the design and synthesis of high-performance anode materials.
Co-reporter:Shengjie Xu, Zhouyue Lei and Peiyi Wu
Journal of Materials Chemistry A 2015 - vol. 3(Issue 31) pp:NaN16347-16347
Publication Date(Web):2015/07/03
DOI:10.1039/C5TA02637G
In this paper, 3D porous MoS2/MoSe2 nanosheet–graphene networks were successfully prepared by a simple mixing solvothermal treatment. The resulting products possessed highly conductive graphene networks on which highly exfoliated MoS2/MoSe2 nanosheets were decorated. This hybrid 3D architecture facilitated loading of 2D nanosheets (including some 0D quantum dots), exposure of active sites, and improvement of electron transfer between the electrode and the catalysts. The highly exfoliated and defect-rich structure of MoS2/MoSe2 nanosheets endowed these composites with plentiful active sites for the electrocatalysis of the hydrogen evolution reaction (HER). The MoSe2 sample exhibited remarkable activity for the HER with a very small overpotential of approximately 70 mV and a low Tafel slope of 61 mV per dec, as well as excellent long-term durability. Moreover, due to the facile and relatively low-cost preparation method, our work might develop promising candidates for Pt-free HER catalysts for future commercial applications and provide an alternative facile approach to fabricate other layered materials confined in graphene hybrid 3D networks on a large scale.
Co-reporter:Kai Feng, Beibei Tang and Peiyi Wu
Journal of Materials Chemistry A 2015 - vol. 3(Issue 24) pp:NaN12615-12615
Publication Date(Web):2015/05/14
DOI:10.1039/C5TA02855H
For the first time, dehydrofluorination reaction was detected between PVDF and Nafion in the presence of ammonia. Cross-linked networks were hence formed in the ammonia-modified Nafion + PVDF composite proton exchange membrane (PEM). They significantly enhanced the fuel resistance, thermal and mechanical stabilities, as well as the structural maintenance of the composite PEM. Meanwhile, at 80 °C, a slight increase in the proton conductivity of the composite PEM was also observed due to its improved water retention capability and the newly formed oxygen-containing functional groups. More importantly, such a highly selective Nafion-based PEM may have strong cost competitiveness in the market of commercial PEMs by virtue of the extremely low cost of PVDF (a dosage of up to 30–50 wt%) and ammonia.
Co-reporter:Ying Tang, Beibei Tang and Peiyi Wu
Journal of Materials Chemistry A 2015 - vol. 3(Issue 15) pp:NaN7928-7928
Publication Date(Web):2015/03/04
DOI:10.1039/C5TA00212E
A temperature-responsive composite membrane with tunable responsive behavior was prepared by covalently grafting a polymeric ionic liquid (PIL) functionalized temperature-responsive copolymer onto the brominated poly(2,6-dimethyl-1,4-phenylene oxide) (BPPO) supporting membrane. The “switch” effect of the composite membrane can be facilely adjusted by tuning the counter-ion of PIL units of the grafted copolymer based on the transformation between hydrophilicity and hydrophobicity of PIL. The response temperature of the composite membrane was decreased with increasing the content of hydrophobic PIL units. Both the pure water flux and rejection of dyes and polyethylene glycol (PEG) of the composite membrane show a good responsiveness with changing the temperature. The study provides an easily available, flexible and effective method for the design and preparation of a temperature-responsive membrane with tunable responsive behavior to satisfy various applications.
![2-Propenamide, N,N-dimethyl-, polymer with N,N'-methylenebis[2-propenamide] and oxirane, graft](/data/chemimg/3781800/2001117-43-5.png)
![2-Propenamide, N,N-dimethyl-, polymer with N,N'-methylenebis[2-propenamide] and oxirane, graft](/data/chemimg/3781800/2001117-43-5_b.png)
![Propanoic acid, 2-[[(ethylthio)thioxomethyl]thio]-, methyl ester](/data/chemimg/3730200/1636131-17-3.png)
![Propanoic acid, 2-[[(ethylthio)thioxomethyl]thio]-, methyl ester](/data/chemimg/3730200/1636131-17-3_b.png)
![Poly[oxy(2,6-dimethyl-1,4-phenylene)]](http://img.cochemist.com/ccimg/25000/24938-67-8.png)
![Poly[oxy(2,6-dimethyl-1,4-phenylene)]](http://img.cochemist.com/ccimg/25000/24938-67-8_b.png)
![Poly[[(2-methyl-1-oxopropyl)imino]-1,2-ethanediyl]](http://img.cochemist.com/ccimg/25900/25821-80-1.png)
![Poly[[(2-methyl-1-oxopropyl)imino]-1,2-ethanediyl]](http://img.cochemist.com/ccimg/25900/25821-80-1_b.png)
