Co-reporter:Junzhe Song, Jinbao Xu, Stergios Pispas and Guangzhao Zhang
RSC Advances 2015 vol. 5(Issue 48) pp:38243-38247
Publication Date(Web):22 Apr 2015
DOI:10.1039/C4RA17202G
By using 1,8-diazabicyclo-[5.4.0]undec-7-ene (DBU) as both the atom transfer radical polymerization (ATRP) ligand and ring-opening polymerization (ROP) catalyst, we have combined copper-catalyzed ATRP and organo-catalyzed ROP in one-pot, and successfully synthesized poly(L-lactide)-b-poly(methyl methacrylate) (PLA-b-PMMA) diblock copolymers. The structure of the block copolymers is confirmed by nuclear magnetic resonance (NMR), size exclusion chromatography (SEC) and differential scanning calorimetry (DSC).
Co-reporter:Jinbao Xu, Junzhe Song, Stergios Pispas and Guangzhao Zhang
Polymer Chemistry 2014 vol. 5(Issue 16) pp:4726-4733
Publication Date(Web):17 Apr 2014
DOI:10.1039/C4PY00342J
Narrowly distributed poly(ε-caprolactone) (PCL) was synthesized by the ring-opening polymerization (ROP) of ε-caprolactone (CL) using tris(pentafluorophenyl)borane (B(C6F5)3) as an acidic catalyst and benzyl alcohol (BnOH) as the initiator in bulk at 80 °C. The use of functional initiators such as 2-hydroxyethyl methacrylate (HEMA), propargyl alcohol (PGA), 6-azido-1-hexanol (AHA) and methoxy poly(ethylene glycol) (mPEG) leads to end-functionalized PCLs. 1H NMR, SEC and MALDI-TOF MS measurements clearly indicate the presence of an initiator residue at the chain end of the obtained PCL homopolymers. The study on polymerization kinetics confirms the controlled/living nature of the B(C6F5)3-catalyzed ROP of CL. Accordingly, the block copolymerization of CL with δ-valerolactone (VL) and trimethylene carbonate (TMC) successfully proceeded to give PCL-b-PVL and PCL-b-PTMC copolymers. Macrocyclic PCL was also prepared by the intramolecular click reaction of the heterotelechelic α-azido,ω-ethynyl-PCL.
Co-reporter:Hongjun Yang, Jun Ge, Wenyan Huang, Xiaoqiang Xue, Jianhai Chen, Bibiao Jiang and Guangzhao Zhang
RSC Advances 2014 vol. 4(Issue 45) pp:23377-23381
Publication Date(Web):13 May 2014
DOI:10.1039/C4RA00829D
Biodegradable polymers have been used in environmental and biomedical engineering, but the lack of functional groups limits their applications. In the present work, we report a facile approach to synthesize a biodegradable and clickable polymer consisting of ε-caprolactone (CL) and allyl methacrylate (AMA) with phosphazene base as the catalyst via hybrid copolymerization, where AMA is selectively copolymerized leaving the allylic groups for the click reaction. The facile and efficient approach can be used to functionalize biodegradable polymers and synthesize some new polymers under mild conditions.
Co-reporter:Jinbao Xu;Junzhe Song;Stergios Pispas
Journal of Polymer Science Part A: Polymer Chemistry 2014 Volume 52( Issue 8) pp:1185-1192
Publication Date(Web):
DOI:10.1002/pola.27104
ABSTRACT
Ring-opening polymerization (ROP) of ε-caprolactone (CL) using salicylic acid (SAA) as the organocatalyst and benzyl alcohol as the initiator in bulk at 80 °C successfully proceeded to give a narrowly distributed poly(ε-caprolactone) (PCL). In addition, 2-hydroxyethyl methacrylate, propargyl alcohol, 6-azido-1-hexanol, and methoxy poly(ethylene glycol) were also used as functional initiators. The 1H NMR, SEC, and MALDI-TOF MS measurements of the PCL clearly indicate the presence of the initiator residue at the chain end, implying that the SAA-catalyzed ROP of CL was through the activated monomer mechanism. The kinetic experiments confirmed the controlled/living nature of the SAA-catalyzed ROP of CL. Furthermore, the block copolymerization of CL and δ-valerolactone successfully proceeded to give poly(ε-caprolactone)-block-poly(δ-valerolactone). © 2014 Wiley Periodicals, Inc. J. Polym. Sci., Part A: Polym. Chem. 2014, 52, 1185–1192
Co-reporter:Zhonglin Cao, Guangzhao Zhang
Polymer 2014 Volume 55(Issue 26) pp:6789-6794
Publication Date(Web):15 December 2014
DOI:10.1016/j.polymer.2014.10.046
•A combination of LLS and AUC is used to study polyelectrolytes solutions.•The slow mode arises from the temporal aggregates due to long range interactions.•The fast mode is related to the coupling diffusion of macroions and counterions.•The behaviors of polyelectrolytes are affected by the electrostatic interactions.We have investigated the dynamics of xanthan aqueous solutions with and without added salt (NaCl) by using laser light scattering (LLS) and analytical ultracentrifugation (AUC) via sedimentation velocity (SV). The fast and slow modes are observed in salt-free and low-salt xanthan solutions by dynamic light scattering (DLS). The scattering ratio (KC/Rs(q)) and apparent diffusion coefficient (Ds,app(q)) of the slow mode is linearly related to scattering vector (q2), indicating that it is related to the diffusion of scattering objects. The intensity contribution (αs) of the slow mode is independent of scattering angles, indicating that the slow mode is not related to some scattering objects larger than the LLS observation length. However, the slow mode disappears in SV experiments, indicating that it arises from the temporal aggregates due to long range electrostatic interactions between chains, which can be destroyed in centrifugal field. The diffusion coefficient measured by SV is close to that of the fast mode in DLS measurements, indicating that it is the coupling diffusion of macroions and counterions. The present studies also demonstrate that the chain stiffness does not change the characteristics of the dynamics of polyelectrolyte in solutions.
Co-reporter:Jinbao Xu, Xuelin Fan, Jinxian Yang, Chunfeng Ma, Xiaodong Ye, Guangzhao Zhang
Colloids and Surfaces B: Biointerfaces 2014 Volume 116() pp:531-536
Publication Date(Web):1 April 2014
DOI:10.1016/j.colsurfb.2014.01.047
•We have synthesized a polymer with both biodegradation and protein resistance.•Quartz crystal microbalance with dissipation (QCM-D) and surface plasmon resonance (SPR) studies demonstrate that the polymers exhibit protein resistance depending on their composition.•In vitro cytotoxicity test reveals the copolymer has low cytotoxicity.We have synthesized poly(l-lactide-co-2-(2-methoxyethoxy)ethyl methacrylate) (LA-co-MEO2MA) containing both degradable and protein resistant units via hybrid copolymerization with (1-tert-butyl-4,4,4-tris(dimethylamino)-2,2-bis[tris(dimethylamino)phophoranylidenamino]-2Λ5,Λ5-catenadi(phosphazene) (t-BuP4) as the catalyst. Nuclear magnetic resonance (NMR) and differential scanning calorimetry (DSC) show that LA-co-MEO2MA is a random copolymer. The studies of quartz crystal microbalance with dissipation (QCM-D) demonstrate that the copolymer enzymaticlly degrades much faster than poly(l-lactide) (PLA) homopolymer due to its lower crystallinity. We have also investigated the adsorption of bovine serum albumin (BSA), lysozyme or fibrinogen on a LA-co-MEO2MA surface in real time by use of QCM-D and surface plasmon resonance (SPR). Our studies reveal that the polymer is protein resistant depending on MEO2MA content. 3-(4,5-Dimethylthiazol-2-yl)-2,5-diphenyl tetrazolium bromide (MTT) assay experiments demonstrate that the polymer has a low cytotoxicity.
Co-reporter:Xin-ming Xing;Guang-ming Liu;Yan-wei Ding
Chinese Journal of Polymer Science 2014 Volume 32( Issue 5) pp:531-539
Publication Date(Web):2014/05/01
DOI:10.1007/s10118-014-1440-y
The lower critical solution temperature (LCST) behavior of poly(acrylamide-co-diacetone acrylamide) (poly(AM-co-DAM)) copolymer in aqueous solutions was studied. The results demonstrate the LCST linearly decreases as the molar fraction of DAM (fDAM) increases. In the range of fDAM < 0.36, the transmittance increases as fDAM decreases because the more hydrophilic copolymer chains can form looser aggregates with a lower refractive index. The transmittance exhibits a minimum when fDAM is less than 0.28 as the chains form micelle-like structure with a size smaller than the wavelength. The LCST decreases with the initial polymer concentration, but it levels off when the polymer concentration is high enough. Moreover, no hysteresis can be observed in the change of transmittance during the heating-cooling process because no additional hydrogen bonds are formed in the collapsed state due to the steric hindrance of the large side groups in DAM units.
Co-reporter:Chunfeng Ma, Xiaobo Bi, To Ngai and Guangzhao Zhang
Journal of Materials Chemistry A 2013 vol. 1(Issue 17) pp:5353-5360
Publication Date(Web):28 Feb 2013
DOI:10.1039/C3TA00123G
Well-defined polyurethane (PU)-based grafted copolymers with poly(2-(dimethylamino)ethyl methacrylate) (PDEM) side chains were prepared by a combination of radical polymerization and condensation reaction. They can self-assemble in water to form nanoparticles with PU as the core and hydrophilic PDEM chains as the shell. Tuning the pH value of the solutions allowed these nanoparticles to stabilize either oil-in-water (O/W) or water-in-oil (W/O) Pickering emulsions. Stable O/W emulsions were obtained with PU-based nanoparticles in the pH 3–5 or pH 11–12 range due to their better affinity to the aqueous phase. In contrast, changing the pH value to the range of 8–9 significantly changed the stabilizing behavior of the nanoparticles, leading to the formation of stable W/O emulsions. Additionally, the effect of oil polarity on the emulsification behavior of the PU-based nanoparticles was investigated. For highly non-polar oil like n-hexane, only O/W emulsions were generated and the resulting emulsions showed no response to pH change.
Co-reporter:Chunfeng Ma, Liguo Xu, Wentao Xu and Guangzhao Zhang
Journal of Materials Chemistry A 2013 vol. 1(Issue 24) pp:3099-3106
Publication Date(Web):01 May 2013
DOI:10.1039/C3TB20454E
Degradable polyurethane (PU) with copolyester oligomer consisting of ε-caprolactone (CL) and glycolide (GA) as the soft segments has been prepared by a combination of ring-opening polymerization and condensation reaction. Enzymatic and hydrolytic degradation experiments demonstrate that the PU can degrade in seawater. Such a polyurethane exhibit a more rapid degradation in comparison with that with poly(ε-caprolactone) (PCL) soft segments because the introduction of GA can reduce the crystallinity, as revealed by differential scanning calorimetry (DSC) and polarizing optical microscope (POM). Marine field tests show that the degradable polyurethane has good antifouling ability due to its self-renewal property. Besides, such polyurethane can serve as a carrier and controlled release system for an antifoulant, and the incorporation of an antifoulant in the polyurethane can significantly improve the antifouling ability and duration.
Co-reporter:Yijie Lu, Cong Meng, Hongwei Xia, Guangzhao Zhang and Chi Wu
Journal of Materials Chemistry A 2013 vol. 1(Issue 38) pp:6107-6111
Publication Date(Web):04 Jan 2013
DOI:10.1039/C2TC00747A
We have developed electrically driven photonic crystals (PCs) from a quaternized polystyrene-b-poly(2-vinyl pyridine) (PS-b-P2VP) block copolymer which can form a one dimensional periodic lamellar structure. The variation of applied voltage from −4.50 to +2.36 V on the PCs can lead to color display over the entire visible region with a sub-second fast response, where the periodic structure swells from 4.3 to 7 times that at dry state. The fast response is attributed to the charging of the P2VP block. Besides, the photonic crystal exhibits a reverse volatility behavior, that is, as the applied voltage increases, the reflective peak wavelength decreases. Such fast switching PCs are facilely prepared with low driving voltage and good durability. The PCs are expected to find applications in information technologies.
Co-reporter:Hongli Xu, Wenli Zhang, Zaijun Lu and Guangzhao Zhang
RSC Advances 2013 vol. 3(Issue 11) pp:3677-3682
Publication Date(Web):10 Jan 2013
DOI:10.1039/C3RA22247K
The difunctional urushiol-based benzoxazine (U-da) was synthesized by utilizing urushiol, 4,4′-diaminodiphenyl methane (DDM) and formaldehyde. The 3,3′-phenylmethanebis(3,4-dihydro-2H-1,3-benzoxazine) (P-da) was prepared by the similar procedure with DDM, phenol and formaldehyde. The U-da and P-da were cured into hybrid polybenzoxazine with different U-da fractions, where the alkyl chains in urushiol can improve the ductility of the polybenzoxazines. Fourier transform infrared (FTIR) spectroscopy and differential scanning calorimetry (DSC) studies demonstrate that the thermally activated ring-opening polymerization can happen at a relatively low temperature (∼180 °C) without addition of catalyst. The hybrid polybenzoxazines were measured by thermal gravimetric analysis (TGA). It shows the temperatures corresponding to the 5% and 10% weight loss are slightly affected by the U-da content whereas the residual weight at 800 °C increases with P-da content. Dynamic mechanical analysis (DMA) studies indicate that the hybrid polybenzoxazine with U-da content of 50 wt% has a relatively high elongation (10%) and stress (101 MPa) at break. The properties of the hybrid polybenzoxazine can be tuned by the composition.
Co-reporter:Hongjun Yang, Jinbao Xu, Stergios Pispas and Guangzhao Zhang
RSC Advances 2013 vol. 3(Issue 19) pp:6853-6858
Publication Date(Web):27 Feb 2013
DOI:10.1039/C3RA23422C
Hyperbranched poly(ε-caprolactone) (h-PCL) is synthesized via hybrid copolymerization of ε-caprolactone (CL) with glycidyl methacrylate (GMA) as the branching agent and (1-tert-butyl-4,4,4-tris(dimethylamino)-2,2-bis[tris(dimethylamino)phophoranylidenamino]-2Λ5,Λ5-catenadi(phosphazene) (t-BuP4) as the catalyst in one step. Proton nuclear magnetic resonance (1H NMR) and Fourier transform infrared (FTIR) spectroscopy show that the polymerization regarding the double bonds and ring-opening take place simultaneously. Size exclusion chromatography measurements with light scattering and viscosity detection indicate that the resultant polymer has a hyperbranched structure.
Co-reporter:Jinbao Xu;Hongjun Yang
Macromolecular Chemistry and Physics 2013 Volume 214( Issue 3) pp:378-385
Publication Date(Web):
DOI:10.1002/macp.201200510
Abstract
Poly(ϵ-caprolactone-co-tert-butyl methacrylate) (CL-co-BMA) random copolymer is synthesized via hybrid copolymerization with 1-tert-butyl-4,4,4-tris(dimethylamino)-2,2-bis[tris(dimethylamino)phophoranylidenamino]-2Λ5,4Λ5-catenadi(phosphazene) (t-BuP4) as the catalyst. The copolymer is hydrolyzed into poly(ϵ-caprolactone-co-methacrylic acid) (CL-co-MAA), a charged copolymer. Nuclear magnetic resonance, Fourier transform infrared spectroscopy, differential scanning calorimetry, and thermogravimetric analysis measurements indicate that cyclic ester and vinyl monomer form a random copolymer. The degradation of the copolymers has also been studied by use of quartz crystal microbalance with dissipation.
Co-reporter:Chunfeng Ma, Bo Wu, Guangzhao Zhang
Colloids and Surfaces B: Biointerfaces 2013 Volume 104() pp:5-10
Publication Date(Web):1 April 2013
DOI:10.1016/j.colsurfb.2012.11.043
By use of quartz crystal microbalance with dissipation (QCM-D), we have investigated the adsorption of proteins such as fibrinogen, bovine serum albumin or lysozyme on the surface of soy protein film in PBS buffer solution in real time. Our studies demonstrate that the proteins can be adsorbed on soy protein film at a pH between the isoelectric point (pIsp) of soy protein film and that (pIfp) of the foreign protein, where the adsorption decreases with the concentration of added salt. Beyond the pH range, soy protein generally resists the adsorption of the foreign protein due to electrostatic repulsion, which is slightly affected by the concentration of the added salt in the range we investigated. At a pH close to pIsp or pIfp, the proteins can also be adsorbed on soy protein film due to hydrophobic interactions. The present study reveals that the protein resistance of soy protein film is determined by electrostatic interactions, hydrophobic interactions and hydrogen bonding between the foreign protein and soy protein.Graphical abstractHighlights► The soy protein surface can reduce the adsorption of other proteins. ► The protein adsorption or resistance is examined by use of quartz crystal microbalance with dissipation (QCM-D). ► The protein resistance of soy protein film is determined by electrostatic interactions and hydrophobic interactions.
Co-reporter:Zhenli Luo, Xiaoyan Wang and Guangzhao Zhang
Physical Chemistry Chemical Physics 2012 vol. 14(Issue 19) pp:6812-6816
Publication Date(Web):21 Mar 2012
DOI:10.1039/C2CP40077D
The sedimentation of quaternized poly(4-vinyl pyridine) (QP4VP) or poly(N-methyl 4-vinyl pyridine iodide) in aqueous solution has been investigated by using an analytical ultracentrifuge (AUC) via sedimentation velocity (SV). When NaI is introduced, either the sedimentation coefficient (s) or apparent molar mass (Mw) of QP4VP increases with NaI concentration because the polyelectrolyte chains aggregate or even form precipitates due to hydrophobic interaction. Upon addition of NaCl, either s or Mw exhibits a maximum as NaCl concentration increases. The sedimentation in NaBr solution falls in between. Besides, the diffusion coefficient (D) shows a minimum as the added salt concentration increases when either of the salts is added. Isothermal titration calorimetry (ITC) measurements show that the enthalpy change increases from NaI over NaBr to NaCl when each of them is mixed with QP4VP, revealing that the order of the strength of the anion–pyridinium interaction is I− > Br− > Cl−. When I− ions are added, they only screen the electrostatic interaction and no counterion competition happens. Upon addition of Cl− or Br− ions, the original counterions (I−) win the competition at low Cl− or Br− concentration, so that the added anions only screen the electrostatic interaction. When the concentration of Cl− or Br− ions is high enough, they replace I− ions to interact with the polyelectrolyte chains due to osmotic pressure. The present study demonstrates that the complex dynamics of the polyelectrolyte is greatly influenced by the ion-specific effect.
Co-reporter:Hongli Xu, Zaijun Lu and Guangzhao Zhang
RSC Advances 2012 vol. 2(Issue 7) pp:2768-2772
Publication Date(Web):08 Feb 2012
DOI:10.1039/C2RA00829G
We have synthesized a novel benzoxazine monomer and polybenzoxazine thermosetting resin based on urushiol, a natural product. Fourier transform infrared (FTIR) spectroscopy and differential scanning calorimetry (DSC) studies demonstrate that the thermally activated ring opening polymerization of the benzoxazine occurs at around 210 °C without addition of catalyst. Thermal gravimetric analysis (TGA) measurements show the temperatures corresponding to 5% and 10% weight loss are 325 °C and 357 °C, respectively, with a char yield of 22% at 600 °C. Dynamic mechanical analysis (DMA) studies indicate the urushiol-based polybenzoxazine exhibits excellent toughness with a storage modulus (G′) of 606 MPa at room temperature and an elongation at break of 17.4%.
Co-reporter:Chunfeng Ma, Hongjun Yang, Xi Zhou, Bo Wu, Guangzhao Zhang
Colloids and Surfaces B: Biointerfaces 2012 100() pp: 31-35
Publication Date(Web):
DOI:10.1016/j.colsurfb.2012.04.045
Co-reporter:Hongjun Yang, Junpeng Zhao, Manqing Yan, Stergios Pispas and Guangzhao Zhang
Polymer Chemistry 2011 vol. 2(Issue 12) pp:2888-2892
Publication Date(Web):19 Oct 2011
DOI:10.1039/C1PY00334H
We have synthesized nylon 3 via ring opening polymerization of 2-azetidinone (β-lactam) with 1-tert-butyl-4,4,4-tris(dimethylamino)-2,2-bis[tris(dimethylamino)- phosphoranylidenamino]-2Λ5,4Λ5-catenadi(phosphazene) (t-BuP4) as the catalyst in a mixture of dimethylacetamide (DMAc) and LiCl. The polymers have been characterized by nuclear magnetic resonance spectroscopy (NMR), Fourier transform infrared spectroscopy (FTIR), X-ray diffraction (XRD), laser light scattering (LLS) and viscometry. The synthesized nylon 3 is a linear and crystalline polymer with a molecular weight as high as 105 g mol−1. The intrinsic viscosity ([η]) relates to the weight average molecular weight (Mw) as [η] = 1.02 × 10−4Mw0.91. The effects of solvent, temperature and catalyst concentration on the polymerization have been examined. The molecular weight and yield increases with the amount of LiCl in the polymerization mixture, but both of them decrease with temperature at a temperature above 50 °C. As the catalyst concentration increases, the yield and the molecular weight of nylon 3 decrease. The possible mechanism for the initiation of polymerization is discussed.
Co-reporter:Hongwei Xia, Junpeng Zhao, Cong Meng, Ying Wu, Yijie Lu, Jingxia Wang, Yanlin Song, Lei Jiang and Guangzhao Zhang
Soft Matter 2011 vol. 7(Issue 9) pp:4156-4159
Publication Date(Web):30 Mar 2011
DOI:10.1039/C1SM05065F
Amphoteric one-dimensional photonic crystal (PC) based on polystyrene-b-poly(2-vinyl pyridine) (PS-b-P2VP) block copolymer was developed by intercalation polymerization of acrylic acid and 2-hydroxyethyl methacrylate in the partly quaternized P2VP (QP2VP) layers. The amphoteric PC reversibly exhibits a high first Bragg peak position (λmax > 700 nm) at both acidic and basic pH values where the QP2VP layers are positively and negatively charged respectively. The minimum λmax (300 nm) at pH 5.5 can be observed due to charge screening. The PC with a U-shaped pH response also shows good durability.
Co-reporter:Yi Hou, Guangming Liu, Ying Wu and Guangzhao Zhang
Physical Chemistry Chemical Physics 2011 vol. 13(Issue 7) pp:2880-2886
Publication Date(Web):16 Dec 2010
DOI:10.1039/C0CP01994A
Poly(sodium styrenesulfonate) (PSSNa) chains have been grafted onto a SiO2-coated resonator surface. The conformational changes of grafted chains have been investigated using a quartz crystal microbalance with dissipation (QCM-D) in the presence of monovalent or multivalent salts as a function of ionic strength. In the case of monovalent counterions, the changes in frequency (Δf) and dissipation (ΔD) indicate that the highly extended PSSNa chains first shrink into a loose and inhomogeneous layer as the ionic strength increases. As the ionic strength increases further, the chains will collapse and form a denser and more homogeneous layer. In the case of divalent or trivalent counterions, the grafted PSSNa chains also collapse into a dense layer as the ionic strength increases. However, when the ionic strength is above a critical value, the chains would re-expand so that the layer becomes partially extended due to the charge inversion. Additionally, the effect of ion-specificity on the conformational changes of the chains has also been examined.
Co-reporter:Hongjun Yang;Manqing Yan;Stergios Pispas
Macromolecular Chemistry and Physics 2011 Volume 212( Issue 23) pp:2589-2593
Publication Date(Web):
DOI:10.1002/macp.201100391
Abstract
Poly[(ethylene carbonate)-co-(ethylene oxide)] is synthesized by ROP of 1,3-dioxolan-2-one using 1-tert-butyl-4,4,4-tris(dimethylamino)-2,2-bis[tris(dimethylamino)phosphoranylidenamino]-2Λ5,Λ5-catenadiphosphazene as the catalyst. NMR spectroscopy shows that the copolymer chain consists of EO-EC-EO-EO sequences. GPC measurements indicate a PDI of 1.43–1.66 and show that the molecular weight increases with monomer conversion. Thermal analysis demonstrates that the copolymer is amorphous with a glass transition temperature of about –42 °C and an onset decomposition temperature of about 200 °C.
Co-reporter:Zhuo Ao ; Guangming Liu
The Journal of Physical Chemistry C 2011 Volume 115(Issue 5) pp:2284-2289
Publication Date(Web):January 11, 2011
DOI:10.1021/jp110782g
We have investigated the ion specificity at low salt concentrations in view of surface force by use of total internal reflection microscopy (TIRM). The polystyrene (PS) particle−glass slide interaction potential energies in different salt solutions have been measured as a function of the concentration of each salt, and the separation distance (hm) corresponding to the minimum potential energy as well as the Debye length (κ−1) are obtained from the potential profiles. In the case of cation specificity, a V-shaped cation series is observed in terms of hm, which is attributed to the difference in the direct interactions between the cations and the sulfate groups on the particle surface on the basis of the law of matching water affinities. The cation specificity of κ−1 indicates that the effective double layer thickness increases with the effective size of hydrated counterions. In the case of anion specificity, the anion sequence in terms of hm also exhibits a V-shaped series due to the accumulation or exclusion of anions near the particle surface. Moreover, the anion specificity of κ−1 is more complex than the cation specificity because the distribution of anions in the electrical double layer is influenced by both the anion−surface and anion−cation interactions.
Co-reporter:Zhenli Luo, Guangzhao Zhang
Polymer 2011 Volume 52(Issue 25) pp:5846-5850
Publication Date(Web):28 November 2011
DOI:10.1016/j.polymer.2011.10.010
Sedimentation of poly(sodium styrenesulfonate) (PSSNa) in aqueous solutions with or without added salt (NaCl) has been investigated by use of analytical ultracentrifuge (AUC) via sedimentation velocity (SV). In a solution without added salt or a low salt solution, as PSSNa concentration (Cp) increases, the sedimentation coefficient (s) decreases and exhibits two transitions corresponding to the overlap concentration (C*) and entanglement concentration (Ce). On the other hand, either C∗ or Ce increases with salt concentration (Cs). When the salt concentration is high enough, the interchain electrostatic interactions are screened, and s slightly varies with Cp at Cp < C∗. However, s decreases with Cp at Cp > C∗ with s ∼ Cp-α, where the scaling index α has dependence on the salt concentration but not on PSSNa molar mass.
Co-reporter:Yijie Lu, Kejin Zhou, Yanwei Ding, Guangzhao Zhang and Chi Wu
Physical Chemistry Chemical Physics 2010 vol. 12(Issue 13) pp:3188-3194
Publication Date(Web):10 Feb 2010
DOI:10.1039/B918969F
By choosing poly(N,N-diethylacrylamide) which lacks the possibility to form intra- or inter-chain hydrogen bonds, we studied its chain association and dissociation in water by using laser light scattering (LLS), ultrasensitive differential scanning calorimetry (US-DSC) and Fourier transform infrared spectroscopy (FTIR). As the solution temperature increases, the average hydrodynamic radius (〈Rh〉) and average radius of gyration (〈Rg〉) decrease, indicating the intrachain shrinking. When the temperature is higher than its lower critical solution temperature (LCST, ∼30 °C), the apparent weight-average molar mass (Mw,app) increases, reflecting the interchain association. At the same time, FTIR study reveals that as the temperature increases, the area ratio of two absorption peaks, respectively, associated to one hydrogen bonded carbonyl >CO⋯H–O–H and free carbonyl >CO groups increases, while that related to two hydrated hydrogen bonded carbonyl groups decreases, indicating heating-induced dehydration. In the reversible cooling process, 〈Rh〉, 〈Rg〉, Mw,app and area ratios of the absorption peak are similar to those in the heating process for each given temperature, indicating that there is no hysteresis in the interchain association and dissociation. This present study confirms that the hysteresis previously observed for a sister polymer, poly(N-isopropylacrylamide), is due to the formation of some additional hydrogen bonds in its collapsed state at temperatures higher than the LCST.
Co-reporter:Fei Hong, Yijie Lu, Junfang Li, Wenjing Shi, Guangzhao Zhang, Chi Wu
Polymer 2010 Volume 51(Issue 6) pp:1413-1417
Publication Date(Web):11 March 2010
DOI:10.1016/j.polymer.2010.01.034
Co-reporter:Chunfeng Ma;Guoying Zhou
Journal of Polymer Science Part B: Polymer Physics 2010 Volume 48( Issue 18) pp:1987-1993
Publication Date(Web):
DOI:10.1002/polb.22077
Abstract
Polyurethane (PU) containing poly(propylene glycol) (PPG) or poly(tetramethylene oxide) (PTMG) soft segments have been prepared by two-step condensation polymerization. The former (PPG-PU) with a lower critical solution temperature (LCST) at ∼21 °C can change from hydrophilic to hydrophobic, whereas the latter (PTMG-PU) is hydrophobic at a temperature above 0 °C. The adsorption of fibrinogen, bovine serum albumin, or lysozyme on such a PU surface in aqueous solution has been investigated by use of quartz crystal microbalance with dissipation (QCM-D) and surface plasmon resonance (SPR) in real time. PPG-PU surface exhibits protein resistance at a temperature below the LCST of PPG, but it significantly adsorbs proteins at a temperature above the LCST. On the other hand, the hydrophobic PTMG-PU surface adsorb the proteins at any temperatures investigated, in contrast with the hydrated poly(ethylene glycol) exhibiting excellent protein resistance. The hydration and dehydration of the polymers at different temperatures were confirmed by Raman spectroscopy. Our study demonstrates that the protein resistance of polymers is determined by their hydration. © 2010 Wiley Periodicals, Inc. J Polym Sci Part B: Polym Phys 48: 1987–1993, 2010
Co-reporter:Zhenli Luo and Guangzhao Zhang
Macromolecules 2010 Volume 43(Issue 23) pp:10038-10044
Publication Date(Web):November 17, 2010
DOI:10.1021/ma101324j
We have investigated the dynamics of poly(sodium styrenesulfonate) (PSSNa) in aqueous solutions with and without added salt (NaCl) by use of analytical ultracentrifuge (AUC) via sedimentation velocity (SV) as a function of NaCl concentration (Cs) or PSSNa concentration (Cp). As Cs increases, the sedimentation coefficient monotonically increases, whereas the diffusion coefficient shows a minimum. On the other hand, as Cp increases, the sedimentation coefficient decreases while the diffusion coefficient exhibits a minimum at Cs < 1.0 × 10−3 M. However, they linearly vary with Cp at Cs > 1.0 × 10−3 M. The scaling relation between the molar mass and sedimentation coefficient or diffusion coefficient at infinite dilution indicates that PSSNa chain changes from an extended conformation to a random coil as NaCl concentration increases. Our experiments demonstrate that the dynamics of polyelectrolyte chains is mediated by interchain electrostatic repulsion, hydrodynamic interactions, and intrinsic excluded volume effect.
Co-reporter:Guangming Liu, Yi Hou, Xiao Xiao and Guangzhao Zhang
The Journal of Physical Chemistry B 2010 Volume 114(Issue 31) pp:9987-9993
Publication Date(Web):July 21, 2010
DOI:10.1021/jp1018263
The specific anion effects on the deposition of a multilayer formed by poly(sodium 4-styrene sulfonate) (PSS) and poly(diallyldimethylammonium chloride) (PDDA) have been investigated by use of quartz crystal microbalance with dissipation (QCM-D) in single and mixed electrolyte solutions. In the case of single electrolyte solutions, the frequency change (−Δf) demonstrates that the multilayer in NaBr, NaClO3, and NaCl solutions grows in a nonlinear mode, which is dominated by the penetration of PSS. In NaF, CH3COONa, NaH2PO4, and Na2SO4 solutions, the multilayer growth mainly determined by the conformation of PDDA chains exhibits a linear mode. The growth shows a mode in between in NaHCO3 solution. The dissipation change (ΔD) has slight dependence on anion species except in the cases of Br−, HCO3−, and SO42−. ΔD remarkably increases with layer number in NaHCO3 solution, indicating the formation of a relatively loose multilayer. In a mixed electrolyte solution containing chaotropic and kosmotropic anions, the multilayer growth is dominated by the chaotropic anions due to the anion competition effects. The effects of anions on the deposition of multilayer are nonadditive.
Co-reporter:Yijie Lu, Hongwei Xia, Guangzhao Zhang and Chi Wu
Journal of Materials Chemistry A 2009 vol. 19(Issue 33) pp:5952-5955
Publication Date(Web):30 Jun 2009
DOI:10.1039/B905760A
Electrically tunable full color display photonic crystals (PCs) made of a thin film of block copolymer, polystyrene-b-poly(2-vinyl pyridine) (PS-b-P2VP), have been developed. The phase separation of PS and P2VP blocks leads to a one-dimensional periodic lamellar structure parallel to the surface of the thin film. In a solvent mixture of water and ethanol, each P2VP layer is swollen and partially charged. Applying a low voltage (<2.5 V) to such a thin film can lead to the repeatable expansion or contraction of each P2VP layer, depending on the direction and strength of the electrical potential. Such a variation of the lamellar periodicity leads to a full color display over a wide range from ultraviolet to near infrared. The advantages of such PCs are their facile preparation, low driving voltage and good durability, which make them potentially useful in information technologies.
Co-reporter:Guangzhao Zhang;Chi Wu
Macromolecular Rapid Communications 2009 Volume 30( Issue 4-5) pp:328-335
Publication Date(Web):
DOI:10.1002/marc.200800611
Co-reporter:YanWei Ding
Science Bulletin 2009 Volume 54( Issue 11) pp:1908-1911
Publication Date(Web):2009 June
DOI:10.1007/s11434-009-0278-0
Using an ultra-sensitive differential scanning calorimetry (US-DSC), we have investigated the folding and aggregation behaviors of poly(N-isopropylacrylamide) (PNIPAM) chains in dilute and semidilute solutions. In the heating process, the intrachain folding and interchain aggregation simultaneously occur in the dilute solutions, and the ratio of intrachain folding increases with decreasing concentration. In the semidilute solutions, PNIPAM chains show limited interchain aggregation with elevated temperature, because most of the PNIPAM chains have been collapsed at lower temperature. In an extremely dilute solution, PNIPAM chains undergo a single folding transition in the heating process. By extrapolating heating rate and concentration to zero, we have obtained the phase transition temperature (TS) and enthalpy change (ΔHS) of the single chain folding. ΔHS is higher than that for a phase transition involving intrachain collapse and interchain aggregation, indicating that a single chain folding can not be taken to be a macroscopic phase transition.
Co-reporter:Guangming Liu, Li Fu and Guangzhao Zhang
The Journal of Physical Chemistry B 2009 Volume 113(Issue 11) pp:3365-3369
Publication Date(Web):February 19, 2009
DOI:10.1021/jp810304f
We have investigated the adsorption of poly(ethylene glycol) (PEG) with different end groups onto phospholipid membranes at the liquid/solid interface by use of a quartz crystal microbalance with dissipation in real time. On a SiO2-coated surface, the adsorption of lipid vesicles results in a solid-supported lipid bilayer. Our experiments demonstrate that PEG chains with enough hydrophobic end groups (PEG-C18H37) can insert in the bilayer and form aggregates on the membrane surface. On the other hand, the adsorbed vesicles are intact on a gold surface. When the end group of PEG chain is not hydrophobic enough, PEG chains do not interact with the vesicles so that they have slight effect on the vesicle stability. However, PEG-C18H37 chains with enough hydrophobic end groups lead to a vesicle-to-bilayer transition because of the insertion of the chains and their aggregation on the membrane surface. In addition, the studies on effect of polymer concentration show that PEG-C18H37 can readily induce the rupture of vesicles at a concentration above the critical micelle concentration.
Co-reporter:Zhenli Luo and Guangzhao Zhang
The Journal of Physical Chemistry B 2009 Volume 113(Issue 37) pp:12462-12465
Publication Date(Web):August 26, 2009
DOI:10.1021/jp906468n
The sedimentation and diffusion of poly(ethylene glycol) (PEG) with weight average molecular weight (Mw) from 5 × 102 to 2 × 105 g/mol have been investigated by use of an analytical ultracentrifuge (AUC). The sedimentation velocity analysis based on the Lamm equation gives the sedimentation coefficient (s) and diffusion coefficient (D). Our study reveals that the sedimentation coefficient (s0) and diffusion coefficient (D0) at infinite dilution scale to molecular weight (Mw), namely, s0 = KsMwα, with Ks = 6.14 × 10−3 and α = 0.469 ± 0.008, and D0 = KDMw−β, with KD = 1.43 × 10−8 and β = 0.576 ± 0.007.
Co-reporter:Guangming Liu and Guangzhao Zhang
The Journal of Physical Chemistry B 2008 Volume 112(Issue 33) pp:10137-10141
Publication Date(Web):July 29, 2008
DOI:10.1021/jp801533r
Poly(acrylic acid) (PAA) chains exhibit conformational change in response to pH, whereas bromate−sulfite−ferrocyanide (BSF) solution shows pH oscillation between 3.2 and 6.6. By use of quartz crystal microbalance with dissipation (QCM-D), we have investigated the pH induced conformational change of PAA brushes under a continuous flow of BSF solution in real time. The changes in frequency and dissipation clearly indicate the periodic swelling and collapse of brushes with pH oscillation. The changes in thickness, viscosity, and elastic modulus further indicate the oscillation of the interface.
Co-reporter:Yi Hou, Jing Ye, Zhou Gui and Guangzhao Zhang
Langmuir 2008 Volume 24(Issue 17) pp:9682-9685
Publication Date(Web):July 19, 2008
DOI:10.1021/la800312u
Cadmium sulfide (CdS) quantum dots (QDs) grafted with thermoresponsive poly(N-isopropylacrylamide) chains have been prepared. As the temperature increases, PNIPAM chains shrink and aggregate so that the QDs exhibit enhanced fluorescence emission. At a temperature around the lower critical solution temperature (LCST) of PNIPAM, the fluorescence exhibits a maximum intensity. Our experiments reveal that the fluorescence emission is determined by the interactions between QDs as a function of the interdot distance. The optical interdot distance for the maximum luminescence intensity is ∼10 nm. The chain length of PNIPAM also has an effect on the luminescence. Short PNIPAM chains are difficult to associate, leading to a large interdot distance, so that the luminescence intensity changes slightly with temperature.
Co-reporter:F. Xia;H. Ge;L. Chen;L. Jiang;G. Zhang;T. Sun;Y. Hou
Advanced Materials 2007 Volume 19(Issue 18) pp:2520-2524
Publication Date(Web):22 AUG 2007
DOI:10.1002/adma.200602334
Surfaces that respond to multiple stimuli may be well-suited for drug delivery applications. Here, such a surface is prepared by coating a silicon wafer with a block copolymer comprising a pH/glucose- and a temperature-sensitive block. The figure shows how the multiresponsive surfaces work in response to glucose concentration at pH 7.4 and at a temperature of 26 °C. Under these conditions the surface shows a reversible change from superhydrophobic to superhydrophilic.
Co-reporter:Changdao Mu;Defu Li;Wei Lin;Yanwei Ding
Biopolymers 2007 Volume 86(Issue 4) pp:
Publication Date(Web):12 APR 2007
DOI:10.1002/bip.20742
The denaturation of collagen solution in acetic acid has been investigated by using ultra-sensitive differential scanning calorimetry (US-DSC), circular dichroism (CD), and laser light scattering (LLS). US-DSC measurements reveal that the collagen exhibits a bimodal transition, i.e., there exists a shoulder transition before the major transition. Such a shoulder transition can recover from a cooling when the collagen is heated to a temperature below 35°C. However, when the heating temperature is above 37°C, both the shoulder and major transitions are irreversible. CD measurements demonstrate the content of triple helix slowly decreases with temperature at a temperature below 35°C, but it drastically decreases at a higher temperature. Our experiments suggest that the shoulder transition and major transition arise from the defibrillation and denaturation of collagen, respectively. LLS measurements show the average hydrodynamic radius 〈Rh〉, radius of gyration 〈Rg〉of the collagen gradually decrease before a sharp decrease at a higher temperature. Meanwhile, the ratio 〈Rg〉/〈Rh〉 gradually increases at a temperature below ∼ 34°C and drastically increases in the range 34–40°C, further indicating the defibrillation of collagen before the denaturation. © 2007 Wiley Periodicals, Inc. Biopolymers 86: 282–287, 2007.
This article was originally published online as an accepted preprint. The “Published Online” date corresponds to the preprint version. You can request a copy of the preprint by emailing the Biopolymers editorial office at biopolymers@wiley.com
Co-reporter:He Cheng;Guangming Liu;Chengqing Wang;Chi Wu
Journal of Polymer Science Part B: Polymer Physics 2006 Volume 44(Issue 4) pp:770-778
Publication Date(Web):12 JAN 2006
DOI:10.1002/polb.20734
Poly(N-isopropylacrylamide-co-sodium acrylate) copolymer brushes grafted on SiO2-coated quartz crystal surface were prepared with a surface-immobilized initiator. The collapse and swelling of the thermally sensitive copolymer brushes in water were studied with quartz crystal microbalance in situ. The frequency and dissipation changes with the temperature increasing in the range 20–38 °C indicate that the brushes undergo a continuous collapse transition. Our results show that the copolymer brushes collapse to a state where the brushes were prepared. A hysteresis was observed in the cooling process. Fourier transform infrared (FTIR) results revealed that the formation of some additional hydrogen bonds within the copolymer chains at their collapsed state is responsible for the hysteresis. © 2006 Wiley Periodicals, Inc. J Polym Sci Part B: Polym Phys 44: 770–778, 2006
Co-reporter:Yi Hou, Guangming Liu, Ying Wu and Guangzhao Zhang
Physical Chemistry Chemical Physics 2011 - vol. 13(Issue 7) pp:NaN2886-2886
Publication Date(Web):2010/12/16
DOI:10.1039/C0CP01994A
Poly(sodium styrenesulfonate) (PSSNa) chains have been grafted onto a SiO2-coated resonator surface. The conformational changes of grafted chains have been investigated using a quartz crystal microbalance with dissipation (QCM-D) in the presence of monovalent or multivalent salts as a function of ionic strength. In the case of monovalent counterions, the changes in frequency (Δf) and dissipation (ΔD) indicate that the highly extended PSSNa chains first shrink into a loose and inhomogeneous layer as the ionic strength increases. As the ionic strength increases further, the chains will collapse and form a denser and more homogeneous layer. In the case of divalent or trivalent counterions, the grafted PSSNa chains also collapse into a dense layer as the ionic strength increases. However, when the ionic strength is above a critical value, the chains would re-expand so that the layer becomes partially extended due to the charge inversion. Additionally, the effect of ion-specificity on the conformational changes of the chains has also been examined.
Co-reporter:Chunfeng Ma, Xiaobo Bi, To Ngai and Guangzhao Zhang
Journal of Materials Chemistry A 2013 - vol. 1(Issue 17) pp:NaN5360-5360
Publication Date(Web):2013/02/28
DOI:10.1039/C3TA00123G
Well-defined polyurethane (PU)-based grafted copolymers with poly(2-(dimethylamino)ethyl methacrylate) (PDEM) side chains were prepared by a combination of radical polymerization and condensation reaction. They can self-assemble in water to form nanoparticles with PU as the core and hydrophilic PDEM chains as the shell. Tuning the pH value of the solutions allowed these nanoparticles to stabilize either oil-in-water (O/W) or water-in-oil (W/O) Pickering emulsions. Stable O/W emulsions were obtained with PU-based nanoparticles in the pH 3–5 or pH 11–12 range due to their better affinity to the aqueous phase. In contrast, changing the pH value to the range of 8–9 significantly changed the stabilizing behavior of the nanoparticles, leading to the formation of stable W/O emulsions. Additionally, the effect of oil polarity on the emulsification behavior of the PU-based nanoparticles was investigated. For highly non-polar oil like n-hexane, only O/W emulsions were generated and the resulting emulsions showed no response to pH change.
Co-reporter:Yijie Lu, Kejin Zhou, Yanwei Ding, Guangzhao Zhang and Chi Wu
Physical Chemistry Chemical Physics 2010 - vol. 12(Issue 13) pp:NaN3194-3194
Publication Date(Web):2010/02/10
DOI:10.1039/B918969F
By choosing poly(N,N-diethylacrylamide) which lacks the possibility to form intra- or inter-chain hydrogen bonds, we studied its chain association and dissociation in water by using laser light scattering (LLS), ultrasensitive differential scanning calorimetry (US-DSC) and Fourier transform infrared spectroscopy (FTIR). As the solution temperature increases, the average hydrodynamic radius (〈Rh〉) and average radius of gyration (〈Rg〉) decrease, indicating the intrachain shrinking. When the temperature is higher than its lower critical solution temperature (LCST, ∼30 °C), the apparent weight-average molar mass (Mw,app) increases, reflecting the interchain association. At the same time, FTIR study reveals that as the temperature increases, the area ratio of two absorption peaks, respectively, associated to one hydrogen bonded carbonyl >CO⋯H–O–H and free carbonyl >CO groups increases, while that related to two hydrated hydrogen bonded carbonyl groups decreases, indicating heating-induced dehydration. In the reversible cooling process, 〈Rh〉, 〈Rg〉, Mw,app and area ratios of the absorption peak are similar to those in the heating process for each given temperature, indicating that there is no hysteresis in the interchain association and dissociation. This present study confirms that the hysteresis previously observed for a sister polymer, poly(N-isopropylacrylamide), is due to the formation of some additional hydrogen bonds in its collapsed state at temperatures higher than the LCST.
Co-reporter:Yijie Lu, Cong Meng, Hongwei Xia, Guangzhao Zhang and Chi Wu
Journal of Materials Chemistry A 2013 - vol. 1(Issue 38) pp:NaN6111-6111
Publication Date(Web):2013/01/04
DOI:10.1039/C2TC00747A
We have developed electrically driven photonic crystals (PCs) from a quaternized polystyrene-b-poly(2-vinyl pyridine) (PS-b-P2VP) block copolymer which can form a one dimensional periodic lamellar structure. The variation of applied voltage from −4.50 to +2.36 V on the PCs can lead to color display over the entire visible region with a sub-second fast response, where the periodic structure swells from 4.3 to 7 times that at dry state. The fast response is attributed to the charging of the P2VP block. Besides, the photonic crystal exhibits a reverse volatility behavior, that is, as the applied voltage increases, the reflective peak wavelength decreases. Such fast switching PCs are facilely prepared with low driving voltage and good durability. The PCs are expected to find applications in information technologies.
Co-reporter:Yijie Lu, Hongwei Xia, Guangzhao Zhang and Chi Wu
Journal of Materials Chemistry A 2009 - vol. 19(Issue 33) pp:NaN5955-5955
Publication Date(Web):2009/06/30
DOI:10.1039/B905760A
Electrically tunable full color display photonic crystals (PCs) made of a thin film of block copolymer, polystyrene-b-poly(2-vinyl pyridine) (PS-b-P2VP), have been developed. The phase separation of PS and P2VP blocks leads to a one-dimensional periodic lamellar structure parallel to the surface of the thin film. In a solvent mixture of water and ethanol, each P2VP layer is swollen and partially charged. Applying a low voltage (<2.5 V) to such a thin film can lead to the repeatable expansion or contraction of each P2VP layer, depending on the direction and strength of the electrical potential. Such a variation of the lamellar periodicity leads to a full color display over a wide range from ultraviolet to near infrared. The advantages of such PCs are their facile preparation, low driving voltage and good durability, which make them potentially useful in information technologies.
Co-reporter:Chunfeng Ma, Liguo Xu, Wentao Xu and Guangzhao Zhang
Journal of Materials Chemistry A 2013 - vol. 1(Issue 24) pp:NaN3106-3106
Publication Date(Web):2013/05/01
DOI:10.1039/C3TB20454E
Degradable polyurethane (PU) with copolyester oligomer consisting of ε-caprolactone (CL) and glycolide (GA) as the soft segments has been prepared by a combination of ring-opening polymerization and condensation reaction. Enzymatic and hydrolytic degradation experiments demonstrate that the PU can degrade in seawater. Such a polyurethane exhibit a more rapid degradation in comparison with that with poly(ε-caprolactone) (PCL) soft segments because the introduction of GA can reduce the crystallinity, as revealed by differential scanning calorimetry (DSC) and polarizing optical microscope (POM). Marine field tests show that the degradable polyurethane has good antifouling ability due to its self-renewal property. Besides, such polyurethane can serve as a carrier and controlled release system for an antifoulant, and the incorporation of an antifoulant in the polyurethane can significantly improve the antifouling ability and duration.
Co-reporter:Yecang Tang ; Yanwei Ding
The Journal of Physical Chemistry B () pp:
Publication Date(Web):June 26, 2008
DOI:10.1021/jp711581h
Poly(N-isopropylmethacrylamide) (PiPMA) has one more methyl group at each monomeric unit than poly(N-isopropylacrylamide) (PiPA). By use of laser light scattering (LLS) and ultrasensitive differential scanning calorimetry (US-DSC) we have investigated the association and dissociation of PiPMA chains in water. LLS studies reveal that PiPMA chains form larger aggregates at a temperature above its lower critical solution temperature (LCST) as the chain molar mass (Mw) decreases. In comparison with PiPA aggregates, PiPMA aggregates show a larger ratio of average radius of gyration to average hydrodynamic radius (⟨Rg⟩/⟨Rh⟩), indicating that PiPMA aggregates are looser. US-DSC studies show PiPMA chains have smaller enthalpy change (ΔH) and entropy change (ΔS) than PiPA chains during the phase transition, indicating that PiPMA chains have smaller conformational change. Our experiments demonstrate that the additional methyl groups in PiPMA chains restrain the intrachain collapse and interchain association, leading the phase transition to occur at a higher temperature.
Co-reporter:Zhenli Luo, Xiaoyan Wang and Guangzhao Zhang
Physical Chemistry Chemical Physics 2012 - vol. 14(Issue 19) pp:NaN6816-6816
Publication Date(Web):2012/03/21
DOI:10.1039/C2CP40077D
The sedimentation of quaternized poly(4-vinyl pyridine) (QP4VP) or poly(N-methyl 4-vinyl pyridine iodide) in aqueous solution has been investigated by using an analytical ultracentrifuge (AUC) via sedimentation velocity (SV). When NaI is introduced, either the sedimentation coefficient (s) or apparent molar mass (Mw) of QP4VP increases with NaI concentration because the polyelectrolyte chains aggregate or even form precipitates due to hydrophobic interaction. Upon addition of NaCl, either s or Mw exhibits a maximum as NaCl concentration increases. The sedimentation in NaBr solution falls in between. Besides, the diffusion coefficient (D) shows a minimum as the added salt concentration increases when either of the salts is added. Isothermal titration calorimetry (ITC) measurements show that the enthalpy change increases from NaI over NaBr to NaCl when each of them is mixed with QP4VP, revealing that the order of the strength of the anion–pyridinium interaction is I− > Br− > Cl−. When I− ions are added, they only screen the electrostatic interaction and no counterion competition happens. Upon addition of Cl− or Br− ions, the original counterions (I−) win the competition at low Cl− or Br− concentration, so that the added anions only screen the electrostatic interaction. When the concentration of Cl− or Br− ions is high enough, they replace I− ions to interact with the polyelectrolyte chains due to osmotic pressure. The present study demonstrates that the complex dynamics of the polyelectrolyte is greatly influenced by the ion-specific effect.
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![1-Propanaminium, N,N-dimethyl-N-[3-[(2-methyl-1-oxo-2-propen-1-yl)amino]propyl]-3-sulfo-, inner salt, homopolymer](/data/chemimg/128300/117829-14-8_b.png)
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![1-Propanaminium, N,N-dimethyl-3-[(2-methyl-1-oxo-2-propen-1-yl)amino]-N-(2-sulfoethyl)-, inner salt](/data/chemimg/2071100/93981-95-4_b.png)
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