Miao Du

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Name: DU, Miao; 杜淼

Organization: Zhejiang University , China

Department: Department of Polymer Science and Engineering

Title: Associate Professor(PhD)

TOPICS

Polymer

Chemicals
References

Boundary Lubrication by Associative Mucin

Co-reporter:Xiang Wang;Qiang Zheng;Yihu Song;Hongpeng Han

Langmuir April 28, 2015 Volume 31(Issue 16) pp:4733-4740

Publication Date(Web):2017-2-22

DOI:10.1021/acs.langmuir.5b00604

Mucus lubricants are widely distributed in living organisms. Such lubricants consist of a gel structure constructed by associative mucin. However, limited tribological studies exist on associative mucin fluids. The present research is the first to investigate the frictional behavior of a typical intact vertebrate mucin (loach skin mucin), which can recover the gel structure of mucus via hydrophobic association under physiological conditions (5–10 mg/mL loach skin mucin dissolved in water). Both rough hydrophobic and hydrophilic polydimethylsiloxane (PDMS) rubber plates were used as friction substrates. Up to 10 mg/mL loach skin mucin dissolved in water led to a 10-fold reduction in boundary friction of the two substrates. The boundary-lubricating ability for hydrophilic PDMS decreased with rubbing time, whereas that for hydrophobic PDMS remained constant. The boundary-lubricating abilities of the mucin on hydrophobic PDMS and hydrophilic PDMS showed almost similar responses toward changing concentration or sodium dodecyl sulfate (SDS). The mucin fluids reduced boundary friction coefficients (μ) only at concentrations (c) in which intermucin associations were formed, with a relationship shown as μ ∼ c–0.7. Destroying intermucin associations by SDS largely impaired the boundary-lubricating ability. Results reveal for the first time that intermolecular association of intact mucin in bulk solution largely enhances boundary lubrication, whereas tightly adsorbed layer plays a minor role in the lubrication. This study indicates that associated mucin should contribute considerably to the lubricating ability of biological mucus in vivo.

Revealing the three-dimensional filler structure in a rubber matrix based on fluorescein modified layered double hydroxides

Co-reporter:Weiyang Lv;Jianliang Xiao;Yihu Song;Qiang Zheng

RSC Advances (2011-Present) 2017 vol. 7(Issue 7) pp:4030-4038

Publication Date(Web):2017/01/09

DOI:10.1039/C6RA25496A

To gain insight into nonlinear viscoelastic behavior, e.g. the Payne effect, and in situ visualize the filler structure in a rubber matrix under strain, a methodology was developed to detect and track structural evolution based on fluorescent labeling. As a model system, layered double hydroxides (LDHs) with different lateral sizes (nanosheets and microsheets) were labeled with fluorescein (FLU) and then uniformly introduced into the rubber matrix through solution blending. The strain-induced deformation and destruction of the three-dimensional LDH filler structure were directly observed for the first time through laser scanning confocal microscopy (LSCM). The contributions of the breakdown of the filler network, strain softening of the glassy layer and macromolecular disentanglement to the Payne effect were qualitatively determined and analyzed in detail based on the structural information probed via LSCM together with transmission electron microscopy, rheometry and modulated differential scanning calorimetry. The primary mechanism for the Payne effect in this system was then proposed and the macromolecular disentanglement in the rubber matrix played a key role. Furthermore, the enhanced Payne effect with increasing LDH content was ascribed to the strain amplification effect induced by the filler network for the LDH nanosheet filled system and the chain sliding on orientated LDHs for microsheet filled compounds, respectively.

A general strategy for the synthesis of layered double hydroxide nanoscrolls on arbitrary substrates: its formation and multifunction

Co-reporter:Weiyang Lv;Qingqing Mei;Huakang Fu;Jianliang Xiao;Qiang Zheng

Journal of Materials Chemistry A 2017 vol. 5(Issue 36) pp:19079-19090

Publication Date(Web):2017/09/19

DOI:10.1039/C7TA05556K

Synthesis of structure-controlled nanocrystals on target substrates presents an enticing prospect for fabricating multifunctional devices. Herein, layered double hydroxides (LDHs) with different morphologies were fabricated via hydrothermal treatment on various substrate surfaces. The morphology of the LDH nanostructures from ultrathin nanosheets, parallel aligned nanoscrolls and vertically aligned nanoscrolls could be finely tuned by adjusting the reaction time, temperature and metal–salt concentration. A speculative model was proposed to illustrate the reaction process where the LDH growth units interacted with the modified surface at first, then gradually formed the nanosheets and finally developed into nanoscrolls upon termination of the reaction. The investigation confirmed that amino groups and a positively charged surface play key roles in the formation of well-defined LDH nanoscrolls. Benefiting from the unique hierarchical structure and high LDH loading, the hybrid nanofiber membranes with vertically aligned LDH nanoscrolls exhibited excellent adsorption capability toward methyl orange and Cu2+ and could effectively separate a surfactant stabilized oil-in-water emulsion solely by gravity, with high flux and oil rejection. Meanwhile, these hybrid membranes have shown great potential as highly efficient catalysts for degradation of organic pollutants, making them versatile and comprehensive materials for water remediation.

3D Multiscale Superhydrophilic Sponges with Delicately Designed Pore Size for Ultrafast Oil/Water Separation

Co-reporter:Weiyang Lv;Qingqing Mei;Jianliang Xiao;Qiang Zheng

Advanced Functional Materials 2017 Volume 27(Issue 48) pp:

Publication Date(Web):2017/12/01

DOI:10.1002/adfm.201704293

AbstractDeveloping novel filtering materials with both high permeation flux and rejection rate presents an enticing prospect for oil/water separation. In this paper, robust porous poly(melamine formaldehyde) (PMF) sponges with superwettability and controlled pore sizes through introducing layered double hydroxides (LDH) and SiO2 electrospun nanofibers are reported. The LDH nanoscrolls endow the sponge with inherent superhydrophilicity and the SiO2 nanofibers act as pore size regulators by overlapping the PMF mainframe. This approach allows the intrinsic large pores in the pristine sponge to decrease quickly from 109.50 to 23.35 µm, while maintaining porosity above 97.8%. The resulting modified sponges with varied pore sizes can effectively separate a wide range of oil/water mixtures, including the surfactant-stabilized emulsions, solely by gravity, with ultrahigh permeation flux (maximum of 3 × 105 L m−2 h−1 bar−1) and satisfactory oil rejection (above 99.46%). Moreover, separation of emulsions stabilized by different surfactants, such as anionic, nonionic, and cationic surfactants has been investigated for further practical evaluation. It is expected that such a pore size tuning technology can provide a low cost and easily scaled-up method to construct a series of filtering materials for high-efficient separation of target oil/water mixtures.

Morphological control of poly(vinylidene fluoride)@layered double hydroxide composite fibers using metal salt anions and their enhanced performance for dye removal

Co-reporter:Qingqing Mei;Weiyang Lv;Qiang Zheng

RSC Advances (2011-Present) 2017 vol. 7(Issue 74) pp:46576-46588

Publication Date(Web):2017/10/02

DOI:10.1039/C7RA08282G

Self-standing membranes of poly(vinylidene fluoride)@layered double hydroxide (PVDF@LDH) composite fibers were fabricated by using metal salts with different anions (NO3−, Cl−, SO42−) as the reactants through a combination of electrospinning and hydrothermal treatment. The anions have a significant effect on the morphology and loading amount of LDHs anchored onto the surface of PVDF nanofibers. In a monovalent anion (such as nitrate) system, small crystal nuclei were formed. Only a small proportion with a large size grew up to well-defined hexagonal LDH layered nanocrystals with large thicknesses. However in a divalent anion sulfate system, large crystal nuclei were generated first and most of them could grow up to thin and curly LDH layered nanocrystals owing to the serious steric hindrance. Well-defined PVDF@CoAl-LDH composite fibers with a hierarchical structure and uniform core/sheath morphology could only be obtained in the sulfate system, which could act as an excellent adsorbent for treating dye solutions. The obtained PVDF@CoAl-LDH core/sheath fibers present a maximum adsorption capacity of 621.17 mg g−1 for methyl orange (MO). Moreover, benefiting from the perfect properties and stable form, the composite fiber membrane could be used directly in membrane filtration with high removal efficiency and cycling stability. The MO removal rate of the membrane remained above 93% with a maximum flux of 140 L (m2 h)−1 despite three times of regeneration, indicating its practical application for the efficient treatment of dye pollution.

Boundary lubricating properties of hydrophobically modified polyacrylamide

Co-reporter:Heng Su, Xiang Wang, Miao Du, Yihu Song and Qiang Zheng

RSC Advances 2016 vol. 6(Issue 7) pp:5695-5702

Publication Date(Web):07 Jan 2016

DOI:10.1039/C5RA24777B

Boundary lubrication has been studied in many associative bio-systems, including synovial fluids, phosphatidylcholine vesicles and mucus. However, comprehensive tribological investigations on synthetic associative polymers have not received sufficient attention. In this paper, we investigated the frictional behavior of polydimethylsiloxane (PDMS) rubber substrates lubricated with a universal and typical synthetic hydrophobically modified polyacrylamide (PAM) aqueous solution. Boundary lubrication was only observed at high concentrations above which intermolecular association was strong while adsorption mass and conformation were constant. Direct dilution with excessive water and replacement of concentrated solution with water both gave the PDMS the same boundary friction coefficient as that of lubrication only with water. Addition of surfactant that could disrupt the interchain association evidently destroyed the boundary lubrication of the hydrophobically modified PAM aqueous solution. Results revealed that interchain association, rather than the robust adsorption layer, plays a significant role in boundary lubrication of compliant PDMS–PDMS contact. This finding may provide new insight into the understanding of the boundary lubrication mechanism and developing novel boundary lubricants for artificial cartilage or consumer industry.

Interaction between Poly(vinyl alcohol) and Layered Double Hydroxide (LDH) Particles with Different Topological Shape and Their Application in Electrospinning

Co-reporter:Weiyang Lv

The Journal of Physical Chemistry C 2016 Volume 120(Issue 26) pp:14435-14443

Publication Date(Web):June 17, 2016

DOI:10.1021/acs.jpcc.6b04783

To explore the influence of filler topological shape on the rheological behavior of poly(vinyl alcohol) (PVA) aqueous solution, three kinds (nanosized layered crystals, microsized layered crystals, and nanoscrolls) of layered double hydroxides (LDHs) were synthesized. Except for nanosized layered crystals, both LDH microsized layered crystals and nanoscrolls filled system showed distinct “N” shape viscosity curves with increasing LDH loadings. Notably, the one-dimensional LDH nanoscrolls could increase or decrease the viscosity of PVA solution by only changing the loadings. With combined theoretical calculation with dynamic mechanical analyses, the adsorbed state of PVA chains on surface of the three LDH particles was proposed, in which PVA chains exhibited various adsorbed states due to different interactions between PVA chains and LDH particles with disparate topological shape. Taking the advantage of remarkable rheological modulation and adsorption capacity, LDH nanoscrolls were introduced into PVA aqueous solution to broaden effectively its electrospinnable concentration window from 8.5–11.3 wt % to 6.5–18.0 wt %. More importantly, the adsorption capacity of LDH nanoscrolls was well preserved in the as-electrospun composite nanofibers, implying a superior adsorbent for methyl orange from wastewater was obtained.

Dopamine/Silica Nanoparticle Assembled, Microscale Porous Structure for Versatile Superamphiphobic Coating

Co-reporter:Fang Li, Miao Du, and Qiang Zheng

ACS Nano 2016 Volume 10(Issue 2) pp:2910

Publication Date(Web):February 1, 2016

DOI:10.1021/acsnano.6b00036

Artificial superamphiphobic surfaces, which could repel both water and low surface tension organic liquids, have been limited to particular kinds of materials or surfaces thus far. In this work, a kind of microscale porous coating was developed. Taking dopamine and hydrophilic fumed silica nanoparticles as initial building blocks, microscale porous coating was constructed via ice templation. Polydopamine bound silica nanoparticles together to form a porous structure network and rendered the coating to have potential for further postfunctionalization. After two-step CVD, the microscale porous coating changes from superhydrophilic to superamphiphobic, exhibiting super-repellency to droplets with surface tension of 73–23 mN/m. The influences of concentration of initial dopamine, hydrophilic fumed silica nanoparticles, and dry conditions on the formation of the porous structure have been studied to optimize the conditions. Coatings with different pore sizes and pore heights have been fabricated to discover the relationship between the structure parameters and the repellency of the porous coatings. Only with optimal pore size and pore height can the porous coating display superamphiphobicity. Compared with nanoscale, the microscale structure favors the achievement of superamphiphobicity. Given the outstanding adhesive ability of polydopamine, the superamphiphobic coatings have been successfully applied to various materials including artificial materials and natural materials.Keywords: dopamine; ice templation; porous structure; superamphiphobic coating; various substrates;

The formation mechanism of layered double hydroxide nanoscrolls by facile trinal-phase hydrothermal treatment and their adsorption properties

Co-reporter:Weiyang Lv, Miao Du, Weijuan Ye and Qiang Zheng

Journal of Materials Chemistry A 2015 vol. 3(Issue 46) pp:23395-23402

Publication Date(Web):09 Oct 2015

DOI:10.1039/C5TA05218A

The formation mechanism of layered double hydroxide (LDH) nanoscrolls via a trinal-phase hydrothermal system has been investigated via powder X-ray diffraction and transmission electron microscopy (TEM) at different reaction temperatures and times. LDH nanosheets formed at first and subsequently developed into nanoscrolls. Notably, the investigation confirmed that urea and pressure played key roles in the formation of the one-dimensional LDH structure. Further observations by scanning electron microscopy and high-resolution TEM indicated that the nanoscrolls with apparent hollow cores were derived from nanosheets through a roll-up process, rather than through the control of the crystal growth in one particular direction. A detailed model was also proposed to describe the reaction process based on the assumption that the LDH growth units are anion coordination octahedra. Furthermore, owing to the increased specific surface area and novel structure, the nanoscrolls exhibit high adsorption capacity and excellent reusability in the adsorption of methyl orange in aqueous solution.

Rheological behavior of hydrophobically modified polysulfobetaine methacrylate aqueous solution

Co-reporter:Miao Du, Yanjie Ma, Heng Su, Xiang Wang and Qiang Zheng

RSC Advances 2015 vol. 5(Issue 43) pp:33905-33913

Publication Date(Web):02 Apr 2015

DOI:10.1039/C5RA05017K

Polysulfobetaine methacrylate (PSBMA) that was hydrophobically modified with methacrylic acid 2,3-epoxypropyl ester (GMA) was synthesized via the micellar copolymerization method. Basic properties of the obtained copolymer were investigated via fluorescence, transmission electron microscopy (TEM), dynamic light scattering (DLS), zeta-potential analyzer, etc. The rheological properties of polymer (or copolymer) solutions were determined as a function of shear rate, temperature, NaCl concentration, etc. Hydrophobically modified PSBMA were capable of forming micelles even at extremely low concentrations (0.001 g L−1), and the micelle sizes increased upon increasing concentration. Hydrophobic interactions were observed within the system and were enhanced with increasing copolymer concentration. Both PSBMA with and without hydrophobic modification exhibited negative zeta-potential and increased with increasing polymer concentration. The viscosity of the P(SBMA–GMA) aqueous solution showed features that are different from those of typical polymer solutions. In addition, the rheological behavior of hydrophobically modified PSBMA aqueous solution had an unusual relationship with temperature because of hydrophobic association and epoxy groups. The viscosity of hydrophobically modified PSBMA solution was sensitive to the added salt concentration, i.e., the viscosity initially decreased and subsequently increased upon the addition of salt.

A Facile, Multifunctional, Transparent, and Superhydrophobic Coating Based on a Nanoscale Porous Structure Spontaneously Assembled from Branched Silica Nanoparticles

Co-reporter:Fang Li;Zhong Zheng;Yihu Song ;Qiang Zheng

Advanced Materials Interfaces 2015 Volume 2( Issue 13) pp:

Publication Date(Web):

DOI:10.1002/admi.201500201

Transparent and durable SiO2-containing superhydrophobic coatings on glass

Co-reporter:Fang Li;Qiang Zheng

Journal of Applied Polymer Science 2015 Volume 132( Issue 8) pp:

Publication Date(Web):

DOI:10.1002/app.41500

ABSTRACT

We fabricated novel superhydrophobic coatings based on SiO₂ nanoparticles combined with NH₂-terminated silicone (SN₂) or SN₂-modified polyurethane (SN₂-prePU) by alternately spin-coating them onto glass slides. The final fabricated surface contained SN₂/SiO₂ or SN₂-prePU/SiO₂ bilayers. The conditions of spin-coating method were also explored. SN₂-prePU with different SN₂/prePU molar ratios were synthesized to study the influence of SN₂ ratio on the water contact angles of ultimate spin-coated surfaces. The surface was found to be tunable from hydrophobic to superhydrophobic by choosing SN₂-prePU with different SN₂/prePU molar ratios or SN₂ content. Water droplets easily rolled off on these superhydrophobic surfaces. Surfaces coated with SN₂/SiO₂ bilayers showed better transparency, whereas surfaces coated with SN₂-prePU(2 : 1)/SiO₂ bilayers exhibited better durability. Droplets of varied pH were prepared to test the anti-wettability of the coatings. Results showed that the as-coated surfaces had stable superhydrophobicity to droplets with pH values ranging from 1 to 14. © 2014 Wiley Periodicals, Inc. J. Appl. Polym. Sci. 2015, 132, 41500.

Fabrication of high-performance poly(vinyl alcohol)/MgAl-layered double hydroxide nanocomposites

Co-reporter:Miao Du, Weijuan Ye, Weiyang Lv, Huakang Fu, Qiang Zheng

European Polymer Journal 2014 Volume 61() pp:300-308

Publication Date(Web):December 2014

DOI:10.1016/j.eurpolymj.2014.11.002

•A high-performance PVA film is fabricated.•Charging sequence should be controlled during fabricating PVA/LDH nanocomposites.•Hydration number of PVA is calculated basing on DSC measurement.•Optimum mechanical property is gained with the LDH content of 1.0 wt%.•The mechanism explains the achievement of high-performance.High-performance poly(vinyl alcohol) (PVA)/MgAl-layered double hydroxide (LDH) nanocomposite films were fabricated by directly dispersing PVA particles into LDH aqueous suspension. Compared with the simple mixing of PVA dispersion with LDH suspension, the method described in this paper enabled uniform dispersion of LDH nanoplatelets in PVA matrix based on scanning electron microscopy and transmission electron microscopy observations. Exfoliated structures of LDH nanoplatelets were observed in the LDH content (ΦLDH) of 1.0 wt%. Thus, the corresponding PVA/LDH nanocomposite films exhibited mechanical properties that are extremely superior to those of neat PVA films. A simple model was proposed to describe the interaction mechanism during dispersion and the ultimate morphology of PVA/LDH nanocomposites with various LDH contents. The lowest hydration number of PVA/LDH suspension with ΦLDH = 1.0 wt% indicated the strongest interaction between PVA chains and LDH nanoplatelets. The PVA/LDH nanocomposite films also exhibited high transparency and water resistance, which could be potentially used in the packaging industry.

Negative velocity dependence of friction for poly(2-Acrylamido-2-methyl propanesulfonic acid) hydrogel sliding against a glass surface in the low-velocity region

Co-reporter:Miao Du;Yan Zhang;Yihu Song ;Qiang Zheng

Journal of Polymer Science Part B: Polymer Physics 2014 Volume 52( Issue 11) pp:765-772

Publication Date(Web):

DOI:10.1002/polb.23480

ABSTRACT

The frictional behavior of poly(2-acrylamido-2-methylpropanesulfonic acid) (PAMPS) hydrogel sliding against a glass substrate in water over a wide sliding velocity (v) region has been investigated. The results showed that the frictional behavior of PAMPS gel conformed to a hydrodynamic lubrication mechanism only at relatively high sliding velocities. At low sliding velocities, a “negative” velocity dependence of friction was observed, which we believe not to be attributable to the experimental friction-measuring mode used. This wider and weak mixed region at low sliding velocities is in contrast to the extremely narrow mixed region in the case of solid friction with a lubricant. The area of the PAMPS hydrogel surface subject to shearing decreased with increasing sliding velocity, and this would seem to be responsible for the weakly negative dependence of friction on velocity. In addition, the friction was found to increase with increasing the compressive modulus (E) of the gels attributing to the shearing exerted on the gel surface, in which the shear stress increased with E. The hydration layer between the sliding surfaces also contributes to the friction and weakens the dependence of friction on E to some extent. © 2014 Wiley Periodicals, Inc. J. Polym. Sci., Part B: Polym. Phys. 2014, 52, 765–772

Mucin from loach skin mucus and its interfacial behavior on gold surface

Co-reporter:Xiang Wang 杜淼;Yi-hu Song 宋义虎;Qiang Zheng

Chinese Journal of Polymer Science 2014 Volume 32( Issue 10) pp:1381-1389

Publication Date(Web):2014 October

DOI:10.1007/s10118-014-1524-8

Loach skin mucin was isolated from loach skin mucus and found to be similar to mammalian mucins in many aspects, i.e., low amino acid residue content, high molecular weight, presence of hydrophobic blocks and gel-forming characteristics in water. However, loach skin mucin can form a weak gel in water at a much lower concentration (3 mg/mL) than mammalian mucins, indicating its good hydrophilicity. Loach skin mucin can also form a stable adsorption layer on gold surface in aqueous environment, owing to the existence of hydrophobic blocks within mucin. The nature of high hydrophilicity and interfacial behavior give loach skin mucin potential as excellent material for use in solid-water interfaces for antifouling and lubrication, and should be crucial to the versatile functions of loach skin mucus.

Relaxation behavior of layered double hydroxides filled dangling chain-based polyurethane/polymethyl methacrylate nanocomposites

Co-reporter:Wenwen Yu, Miao Du, Weijuan Ye, Weiyang Lv, Qiang Zheng

Polymer 2014 Volume 55(Issue 10) pp:2455-2463

Publication Date(Web):13 May 2014

DOI:10.1016/j.polymer.2014.03.039

A series of dangling chain based-polyurethane/poly(methyl methacrylate) (DPU/PMMA) filled with exfoliated layered double hydroxides (LDH) were synthesized by methyl methacrylate in-situ intercalative polymerization. The dangling chains were introduced by using vegetable oils as chain extender. The effect of dangling chain and the contents of LDH on the molecular dynamics of DPU/PMMA was investigated by a combination of dynamic mechanical analysis and broadband dielectric relaxation spectroscopy. Compared with polyurethane/poly(methyl methacrylate) (PU/PMMA) without dangling chain, the glass transition temperature (Tg) of DPU/PMMA shifts to lower temperature and the segmental dynamics becomes faster. A plateau with a high loss factor value above Tg significantly broadens the damping temperature range due to the synergy effect between the dangling chains and LDH layers. In DPU/PMMA/LDH nanocomposites, the α-relaxation associated with the glass transition of the polymer matrix becomes slower with the increase of LDH content, which indicates a restricted molecular mobility in the interfacial regions between polymer and LDH. However, the local relaxations at relatively low temperature remain unaffected by dangling chain or the addition of LDH. When the LDH content increases, Maxwell–Wagner–Sillars (MWS) interfacial polarization process caused by charge accumulation at interfaces becomes faster because of the smaller mean distance d between the exfoliated LDH layers.

Role of graded length side chains up to 18 carbons in length on the damping behavior of polyurethane/epoxy interpenetrating polymer networks

Co-reporter:Wenwen Yu, Dezhi Zhang, Miao Du, Qiang Zheng

European Polymer Journal 2013 Volume 49(Issue 6) pp:1731-1741

Publication Date(Web):June 2013

DOI:10.1016/j.eurpolymj.2013.03.024

•Introduction of graded length side chains improved significantly the damping peak of PU/EP IPNs.•The damping temperature range depended on the interaction between the side chain and PU segments not the side chain length.•The side chain with ester group enhanced H-bond interaction within the hard segments.•The IPNs with side chain carrying ester group exhibited microphase separation structure with relatively large-sized domain.•The mechanical properties of IPNs were significantly affected not by the side chain length but by the side chain content.A series of novel polyurethane (PU)/epoxy resin (EP) graft interpenetrating polymer network (IPN) composites with graded length side chains were prepared from toluene diisocyanate (TDI), polytetrahydrofuran glycol (PTMG), EP, trimethylolpropane (TMP), and diol chain extenders. The effects of the side chain lengths, content, and groups on the damping properties and mechanical properties were investigated. Two damping peaks were observed in the PU/EP IPN system, indicating that the peak damping factor (tan δ) increased with increased side chain length at low temperatures. The introduction of an apolar side chain slightly narrowed the damping range. However, the side chain carrying polar groups broadened the damping temperature range. The strong H-bond interaction between the ester group of side chain and the NH of hard segments in PU was believed to favor microphase separation to form a larger-sized domain and induce the appearance of the relaxation peak at high temperatures. Consequently, the effective damping temperature range was broadened. The side chain content tethered in the hard segment remarkably influenced the damping properties of PU/EP IPNs both at low and high temperatures. The width and intensity of the tan δ peaks of PU/EP IPNs increased with increased side chain content. The mechanical properties (tensile strength and elongation at break) were significantly affected by the side chain content. Thus, an important method of improving the mechanical damping of elastomers by controlling the side chain molecular structure was established.

Influence of Dangling Chains on Molecular Dynamics of Polyurethanes

Co-reporter:Wenwen Yu, Miao Du, Dezhi Zhang, Yu Lin, and Qiang Zheng

Macromolecules 2013 Volume 46(Issue 18) pp:7341-7351

Publication Date(Web):September 3, 2013

DOI:10.1021/ma401260d

The effect of dangling chains on phase-separated microstructure and molecular dynamics for polyurethanes (PUs) was investigated. PUs with different dangling chain lengths and polar groups were prepared through changing the types of diol extender. The molecular dynamics was studied by a combination of dynamic mechanical analysis (DMA) and broadband dielectric relaxation spectroscopy (BDRS). Four relaxations (processes), namely, a secondary relaxation (β), the soft phase segmental relaxation (α), the I process associated with hydrogen bond, and Maxwell–Wagner–Sillars (MWS) interfacial polarization process caused by charge accumulation at hard/soft phase interfaces, were detected. The I process occurred in temperatures lower than that of MWS process but higher than α relaxation in general. The β relaxation remains unaffected with changing dangling chain lengths or polar groups. However, the glass transition temperature (Tg) of the soft phase shifts to lower temperature, and the segmental motion becomes faster with increasing dangling chain length, while the introduction of a polar ester group into the dangling chains makes it slow down, corresponding to a higher Tg, and results in a higher fragility. On the other hand, there is an absence of I process, and the MWS process shifts to higher frequencies when longer dangling chain is introduced. In the case of increasing the hard segment content, the I process reappears and the MWS process slows down. It is suggested that these results are related to the H-bond interactions within hard segments and the micromorphologies of PUs.

Effect of Iron Concentration on the Growth of Carbon Nanotubes on Clay Surface

Co-reporter:Fu Huakang, Du Miao, and Zheng Qiang

ACS Applied Materials & Interfaces 2012 Volume 4(Issue 4) pp:1981

Publication Date(Web):March 16, 2012

DOI:10.1021/am201804p

The successful growth of carbon nanotubes (CNTs) on montmorillonite (MMT) precursors treated with different concentrations of ferric nitrate at 50 °C (MMT(Fe)-50) and 100 °C (MMT(Fe)-100) was achieved via the in situ chemical vapor deposition (CVD) of acetylene. The as-obtained MMT-CNTs composites were characterized using X-ray diffraction, inductively coupled plasma emission spectrometry, scanning electron microscopy, and transmission electron microscopy. All Fe3+ ions were intercalated into the MMT interlayers at either 50 or 100 °C in the case of [Fe3+]/[clay] = 1. However, the iron content in MMT(Fe)-100 increased rapidly with the amount of ferric nitrate added, whereas the iron content in MMT(Fe)-50 did not exhibit significant changes. On the other hand, the physical and chemical adsorption of Fe3+ onto the MMT surface was believed to be responsible for the great diversity of iron contents in MMT(Fe)-50 and MMT(Fe)-100 at the same [Fe3+]/[clay] ratios. Moreover, the CNT yield showed variation similar to the iron content because the CNTs yield depends primarily on the amount of catalyst available. The CNTs embedded onto MMT(Fe)-100 exhibited narrower diameter distributions than those on the MMT(Fe)-50 precursors, with more CNTs with diameters less than 50 nm on the former. It is suggested that a porous structure with many pores formed by iron species and MMT laminas is related to the morphology and structure of CNTs embedded on the surface of MMT.Keywords: adsorption; carbon nanotubes; in situ growth; interlayer; iron concentration; montmorillonite;

Effect of precursors on the growth of carbon filaments onto clay surface

Co-reporter:Huakang Fu, Miao Du, Qiang Zheng

Applied Surface Science 2011 Volume 257(Issue 21) pp:8981-8984

Publication Date(Web):15 August 2011

DOI:10.1016/j.apsusc.2011.05.076

Abstract

The successful growth of carbon filaments on two different precursors, i.e., the pristine sodium-montmorillonite (Na⁺MMT), which undergoes reflux at 100 °C (r-MMT), and the Na⁺MMT exchanged with Fe³⁺ ions (MMT(Fe)), was attained through chemical vapor deposition (CVD). The products obtained were characterized by X-ray diffraction, thermogravimetry, scanning electron microscopy, and transmission electron microscopy. Refluxing can make the Fe³⁺ ions in the octahedral layer of Na⁺MMT migrate to the interlayer and exchange with Na⁺ ions. Furthermore, through calcination at 500 °C, the Fe³⁺ ions migrate again to the surface of the clay layer and form iron oxides, which can serve as precursors for the deposition of carbon. Although r-MMT contained less iron than the MMT(Fe), the ultimate yield of carbon components grown was almost the same, indicating that the iron species in r-MMT possess higher catalytic activity. However, on the surface of r-MMT, CVD hardly generated carbon nanotubes with a clear hollow structure but that those with a carbon fiber structure instead.

Viscoelastic relaxation of styrenebutadienestyrene block copolymers with different topological structures

Co-reporter:Miao Du;Qiuming Yu;Yi Lu;Qiang Zheng

Journal of Applied Polymer Science 2011 Volume 120( Issue 5) pp:2962-2970

Publication Date(Web):

DOI:10.1002/app.33376

Abstract

The viscoelastic relaxation of linear styrene–butadiene–styrene triblock copolymer (l-SBS) and star styrene–butadiene–styrene triblock copolymer (s-SBS) with four arms were investigated with differential scanning calorimetry and dynamic rheological measurements. Three characteristic viscoelastic responses of l-SBS and s-SBS in the plot of the loss tangent (tan δ) and temperature at different frequencies (ω's), which corresponded to the relaxation of the polybutadiene (PB) block (peak I), the glass transition of the polystyrene (PS) phase (peak II), and the mutual diffusion between the PB blocks and PS blocks (peak III), respectively, were observed in the experimental range. Although ω was 0.1 rad/s, a noticeable peak III was gained for both l-SBS and s-SBS. The dynamic storage modulus (G′) of l-SBS showed two distinct types of behavior, depending on the temperature. At temperature (T) < T₂ (where T₂ is the temperature corresponding to peak II), G′ of l-SBS displayed a very weak ω dependency. In contrast, at T > T₂, G′ decayed much more rapidly. However, G′ of s-SBS displayed a very weak ω dependency at both T<T₂ and T > T₂. Only near T₂ did s-SBS decay with ω a little sharply. These indicated, in contrast to l-SBS, that s-SBS still exhibited more elasticity even at T > T₂ because of its crosslinking point between the PB blocks (the star structure). In the lower ω range, l-SBS exhibited a stronger peak III than s-SBS despite the same styrene content for l-SBS and s-SBS. The high tan δ value of peak III for l-SBS was considered to be related to the internal friction among the PB blocks or the whole l-SBS chain, not the PS blocks. © 2011 Wiley Periodicals, Inc. J Appl Polym Sci, 2011