聚合物微观结构对聚合物电解质膜性能的影响

聚合物的微观结构是设计具有优异的电化学性能的聚合物电解质膜(PEMs)的基础.在电解质膜中,相分离结构形成的离子簇和离子通道可以影响膜在高温低湿度条件下的离子传导和水的传输,这种结构形成的形貌也可以影响膜的吸水率、溶胀度、碱稳定性等性能.近几年来,人们对于具有微观相分离形貌的PEMs的合成和形貌开展了很多研究.本文主要...     

填料对聚合物共混物相分离行为的影响

近年来,由于粒子填充聚合物共混物的广泛运用,复合材料的结构研究具有重要意义.除了研究粒子在聚合物中的分散外,关于粒子对聚合物共混物的相分离影响也做了大量工作.研究结果表明粒子的尺寸,粒子的表面处理以及粒子含量对聚合物共混物相分离热力学以及动力学有重要影响.由于粒子对聚合物组分的选择吸附、聚合物分子对粒子的润湿作用、填料对聚合物相区生长的阻碍导致了聚合物共混物-填料体系相行为的复杂性.本文扼要地综述了聚合物共混物-填料体系相分离的理论基础以及实验结果,介绍了粒子对相分离的影响因素,并展望了该领域的研究趋势和前景.     

聚酰亚胺多层膜的制备及其在非线性光学中的应用

报道了一种通过旋涂制备NLO聚合物多层膜的方法.紫外-可见吸收光谱及膜的厚度表征说明,在所得多层膜的结构中,聚合物单层膜的厚度可以较好地控制在100~200nm之间,所得含有5个双层的NLO多层膜(厚度1.6μm)具有良好的结构均一性,光学显微镜下没有观察到明显的结构缺陷.与单层具有较大厚度的NLO聚合物薄膜(如2~4μm)相比,所得聚合物多层膜可以允许掺杂更多的发色团而不发生相分离.     

燃料电池用聚合物质子交换膜的研究进展

质子交换膜（PEM）是质子交换膜燃料电池的核心组件之一,具有隔绝阴阳极、提供质子传递通道和阻止燃料渗透的作用. 商业化应用的全氟磺酸PEM存在燃料渗透严重、高温条件下导电性差和成本高的问题,开发性能优良的聚合物PEM显得很有必要. 本文讨论了近年来聚合物PEM的研究进展,分别从聚合物的主链、支链和交联结构角度介绍了分子结构对薄膜相分离、质子导电性、稳定性和电池性能等性能的影响,并讨论了聚合物分子结构设计方面存在的问题,最后对燃料电池用聚合物PEM在未来的发展方向进行了展望.     

液晶聚合物/柔性链聚合物共混体系相分离形态

利用元胞动力学方法在二维情况下对浓度、取向序参量的含时Ginzberg-Landau方程进行数值求解,研究了液晶聚合物/柔性链聚合物共混体系的相分离动力学,考察了浓度、取向有序过程的耦合对相分离形态的影响.结果表明,此耦合作用对相分离的时间进程以及相分离图样的空间排布都有影响.液晶聚合物的取向有序相当于增加了两组分间的不相容性而促进两相分离;两个序参量在热力学方面的耦合使液晶聚合物趋向于沿着界面方向取向,而动力学方面的耦合使液晶聚合物分子沿着其取向方向扩散,相分离图样的空间排布由这两种效应共同决定通过极化率张量的定义用数值方法模拟得到了相分离体系的小角光散射图样,结果表明,散射强度分布具有方位角依赖性,它是由浓度、取向序参量的空间变化共同决定的.     

亚表面引发原子转移自由基聚合构筑温度响应型纳米纤维油水分离膜

亚表面引发聚合是一种用于制备共价嵌入型聚合物刷的新型改性策略. 该方法在发展高稳定性聚合物刷功能化表界面材料方面具有显著的优势. 本工作利用亚表面引发原子转移自由基聚合(sSI-ATRP)对静电纺丝聚丙烯腈(PAN)基纳米纤维膜进行亚表面改性, 通过接枝聚N-异丙基丙烯酰胺(PNIPAM)制备了温度响应型纳米纤维油水分离膜(PAN-sg-PNIPAM). 当温度低于低临界溶解温度(LCST)时, PNIPAM链与水分子之间的强氢键作用使得聚合物链完全伸展, 分离膜表面亲水且对油滴具有非常低的粘附力, 对油水乳液具有非常高的分离效率(达98.7%); 当温度高于LCST时, PNIPAM链失水收缩, 膜表面变得更加疏水且对油滴的粘附力显著增加, 其油水乳液分离效率显著降低, 仅为9.1%. 此外, 由于共价嵌入聚合物刷的高稳定性, 该分离膜在4 kPa压力下, 20 ℃和45 ℃之间可逆切换10个循环后, 仍能保持非常稳定的渗透通量. 本研究为发展高稳定性的智能型油水分离膜提供了一种新方法.     

浸没沉淀相转化法制备结晶性聚合物微孔膜的研究进展

综述了近期关于结晶性聚合物浸没沉淀相转化法制备微孔膜的成膜机理和实验研究工作.对制膜体系的热力学、相分离、成膜机理进行了分析和总结,并依此解析了结晶性聚合物膜中常见的结构形态,最后从热力学和动力学两个方面对影响膜结构形态的因素如聚合物的浓度、铸膜液的组成、凝固浴的组成等进行了详细的讨论.     

聚甲苯胺蓝-(多壁碳纳米管/PDDA)n杂化膜修饰电极的制备及其对NADH的催化氧化

导电聚合物修饰电极由于聚合物结构致密,限制了底物在聚合物膜中的渗透,且随着膜厚的增加其导电能力逐渐减弱.碳纳米管在导电聚合物中的掺杂明显改善了导电聚合物的导电性~([1]).但是碳纳米管的水溶性差及纳米尺寸带来的聚集效应,使得通过主体聚合制备杂化膜的过程中容易出现相分离进而影响到杂化膜的性质~([2]).     

直链淀粉交联氨基酸酯取代聚膦腈杂化材料的制备

利用直链淀粉与甘/丙氨酸乙酯共取代聚膦腈交联, 制得了一种具有网络结构的新型杂化材料. 实验结果表明, 淀粉衍生物上的羟基转变为醇钠后, 可与聚膦腈分子链上的P-Cl键发生亲核取代反应; 所得聚合物膜无明显相分离, 力学性能优于具有相似组成的直链淀粉/聚膦腈共混膜, 表面亲水性和吸水率与对应的共混膜接近, 且均高于纯聚膦腈膜. 因此, 该聚合物可作为杂化生物材料用于药物控制释放和组织工程方面的研究.     

三维骨架聚合物的孔径调控及其滤光效应

利用二阶段相分离控制方法制备不同孔径的三维骨架聚合物及配位聚合物材料.在第一阶段的反应诱导相分离中,通过加入十二烷基苯磺酸作为相分离抑制剂,控制了环氧树脂在聚乙二醇介质中固化反应的相分离速率和程度;在第二阶段,将处于亚稳状态的聚合物用ZnSO4或CdSO4水溶液处理,在配合作用的推动下发生二次相分离,并稳定三维骨架结构,最终实现了在1~2μm范围内调节孔径大小.研究了三维连续孔道在充满二乙烯基苯高折射液体后的滤光特性,通过引入金属离子改变固体材料折射率的方法,验证了光在高折射液相中的全反射效应,并从定性角度建立三维骨架材料的孔径及分布与透射光波长范围之间的关系,对新光学现象给出了初步解释.     

A Brush‐Gel/Metal‐Nanoparticle Hybrid Film as an Efficient Supported Catalyst in Glass Microreactors

A polymer‐brush‐based material was applied for the formation and in situ immobilization of silver and palladium nanoparticles, as a catalytic coating on the inner wall of glass microreactors. The brush film was grown directly on the microchannel interior by means of atom‐transfer radical polymerization (ATRP), which allows control over the polymer film thickness and therefore permits the tuning of the number of nanoparticles formed on the channel walls. The wide applicability of the catalytic devices is demonstrated for the reduction of 4‐nitrophenol and for the Heck reaction.     

Monolayer and multilayer compact film formations on different substrates by physical deposition

Dissipative particle dynamics simulations are applied to investigate the monolayer and multilayer film formations on different solid substrates by physical deposition. The influences of the polymer concentration, the polymer chain length, the solvent quality, and the interactions between the polymer solution and the solid substrate surface on the film formation dynamics and the mechanism are studied in detail. The results are analyzed in terms of the thickness and the shape of the deposited film, the kinetics of phase separation in the polymer solution, and the contact angle formed between the polymer aggregations and the substrate surface. Moreover, we suggest two strategies, designing a deposition process analogous to “chemical titration” and physically blocking interlayer diffusion by a simple crosslinked network barrier, to deposit the compact monolayer and multilayer films with better quality, respectively. © 2009 Wiley Periodicals, Inc. J Polym Sci Part B: Polym Phys 47: 353–365, 2009     

Phase equilibria in ternary polymer blends

The phase states and rheological properties of blends of three polymers??polystyrene, poly(methyl methacrylate), and the styrene-acrylonitrile copolymer??in the common solvent chloroform are studied. The phase diagrams are constructed and the positions of spinodals are determined via the method of turbidity points. The effect of the third polymer on the compatibility of the binary blend obeys Prigogine??s rule; that is, it is determined by the solubility of the added polymer in the first two components. The extremum composition dependence of rheological properties of ternary polymer systems in the vicinity of the separation point (the metastable region) is found. Through the method of convex-shell construction, the phase diagrams are calculated.     

Single ion diffusive transport within a Poly(styrene sulfonate) polymer brush matrix probed by fluorescence correlation spectroscopy

Diffusive transport within complex environments is a critical piece of the chemistry occurring in such diverse membrane systems as proton exchange and bilayer lipid membranes. In the present study, fluorescence correlation spectroscopy was used to evaluate diffusive charge transport within a strong polyelectrolyte polymer brush. The fluorescent cation rhodamine-6G was used as a counterion probe molecule, and the strong polyelectrolyte poly(styrene sulfonate) was the polymer brush. Such strong polyelectrolyte brushes show promise for charge storage applications, and thus it is important to understand and tune their transport efficiencies. The polymer brush demonstrated preferential solvation of the probe counterion as compared to solvation by the aqueous solvent phase. Additionally, diffusion within the polymer brush was strongly inhibited, as evidenced by a decrease in diffusion constant of 4 orders of magnitude. It also proved possible to tune the transport characteristics by controlling the solvent pH, and thus the ionic strength of the solvent. The diffusion characteristics within the charged brush system depend on the brush density as well as the effective interaction potential between the probe ions and the brush. In response to changes in ionic strength of the solution, it was found that these two properties act in opposition to each other within this strong polyelectrolyte polymer brush environment. A stochastic random walk model was developed to simulate interaction of a diffusing charged particle with a periodic potential, to show the response of characteristic diffusion times to electrostatic field strengths. The combined results of the experiments and simulations demonstrate that responsive diffusion characteristics in this brush system are dominated by changes in Coulombic interactions rather than changes in brush density. More generally, these results support the use of FCS to evaluate local charge transport properties within polyelectrolyte brush systems, and demonstrate that the technique shows promise in the development of novel polyelectrolyte films for charge storage/transport materials.     

Behavior of a polymer chain immersed in a binary mixture of solvents

The behavior of a polymer chain immersed in a binary solvent mixture is investigated via a single-polymer simulation using an effective Hamiltonian, where the solvent effects are taken into account through a density-functional theory for polymer-solvent admixtures. The liquid-liquid phase separation of the binary solvent mixture is modeled as that of a Lennard-Jones binary fluid mixture with weakly attractive interactions between the different components. Two types of energetic preferences of the polymer chain for the better solvent-(A) no preferential solvophilicity and (B) strong preferential solvophilicity-are employed as polymer-solvent interaction models. The radius of gyration and the polymer-solvent radial distribution functions are determined from the simulations of various molar fractions along an isotherm slightly above the critical temperature of the liquid-liquid phase separation. These quantities near the critical point conspicuously depend on the strength of the preferential solvophilicity. In the case where the polymer exhibits a strong preferential solvophilicity, a remarkable expansion of the polymer chain is observed near the critical point. On the other hand, in the case where the polymer has no preferential solvophilicity, no characteristic variation of the polymer conformation is observed even near the critical point. These results indicate that the expansion of a polymer chain enhances the local phase separation around it, acting as a nucleus of demixing in the vicinity of the critical point. This phenomenon in binary solvents near the liquid-liquid critical point is similar to the expansion of the polymer chain in one-component supercritical solvents near the liquid-vapor critical point, which we have reported [T. Sumi and H. Sekino J. Chem. Phys. 122, 194910 (2005)].     

Polymer brushes in solvents of variable quality: molecular dynamics simulations using explicit solvent

The structure and thermodynamic properties of a system of end-grafted flexible polymer chains grafted to a flat substrate and exposed to a solvent of variable quality are studied by molecular dynamics methods. The macromolecules are described by a coarse-grained bead-spring model, and the solvent molecules by pointlike particles, assuming Lennard-Jones-type interactions between pairs of monomers (epsilon(pp)), solvent molecules (epsilon(ss)), and solvent monomer (epsilon(ps)), respectively. Varying the grafting density sigma(g) and some of these energy parameters, we obtain density profiles of solvent particles and monomers, study structural properties of the chain (gyration radius components, bond orientational parameters, etc.), and examine also the profile of the lateral pressure P( parallel)(z), keeping in the simulation the normal pressure P( perpendicular) constant. From these data, the reduction of the surface tension between solvent and wall as a function of the grafting density of the brush has been obtained. Further results include the stretching force on the monomer adjacent to the grafting site and its variation with solvent quality and grafting density, and dynamic characteristics such as mobility profiles and chain relaxation times. Possible phase transitions (vertical phase separation of the solvent versus lateral segregation of the polymers into "clusters," etc.) are discussed, and a comparison to previous work using implicit solvent models is made. The variation of the brush height and the interfacial width of the transition zone between the pure solvent and the brush agrees qualitatively very well with corresponding experiments.     

Micromechanical cantilever technique: a tool for investigating the swelling of polymer brushes

Polymer brush coatings are well-known for their ability to tailor surface properties in a wide range of applications from colloid stabilization to medicine. In most cases, the brushes are used in solution. Consequently, efforts were expended to experimentally investigate or theoretically predict the swelling behavior of the brushes in solvents of different qualities. Here, we show that the micromechanical cantilever (MC) sensor technique is a tool to perform time-resolved physicochemical investigations of thin layers such as polymer brushes. Complementary to scattering techniques, which measure the thickness, the MC sensor technique provides information about changes in the internal pressure of the brushes during a swelling and deswelling process. We show that the kinetics of both swelling and deswelling are dependent on solvent quality. Comparing the measured data with its thickness evolution, which was calculated based on the Flory-Huggins theory, we found that only the first 10% of the thickness increase of the polymer brush results in a significant pressure increase inside the polymer brush layer.     

Stimuli-responsive mixed grafted polymer films with gradually changing properties: direct determination of chemical composition

Infrared spectroscopic ellipsometry (IRSE) and visible monochromatic ellipsometry (VISE) approaches were applied to investigate the chemical structure and thickness of ultrathin polymer films. Mixed polystyrene-poly(2-vinylpyridine) and polystyrene-poly(tert-butyl acrylate) polymer grafted films (mixed brushes) with gradually changing composition (1D gradient mixed brush) along the sample were prepared on a temperature gradient stage via two subsequent "grafting to" reactions. The films were characterized by high-precision mapping VISE at a single wavelength (632.8 nm) and IRSE. The set of 1D IRSE spectra of the polymer brush films obtained by mapping the 1D gradient brush were used to estimate the thickness and the local composition of the film and to construct the 1D map of the film in terms of the chemical composition of the brush. The results were compared with the data obtained using monochromatic ellipsometry where the brush composition was estimated from the results of two subsequent measurements followed each grafting step. The measurements of the brush thickness and composition with both methods were found to be in gratifying agreement. The results demonstrate the high potential of IRSE methods for the one-step characterization (by thickness and chemical composition) of ultrathin polymer films of complex composition.     

Temperature-responsive chromatography for the separation of biomolecules

Temperature-responsive chromatography for the separation of biomolecules utilizing poly(N-isopropylacrylamide) (PNIPAAm) and its copolymer-modified stationary phase is performed with an aqueous mobile phase without using organic solvent. The surface properties and function of the stationary phase are controlled by external temperature changes without changing the mobile-phase composition. This analytical system is based on nonspecific adsorption by the reversible transition of a hydrophilic-hydrophobic PNIPAAm-grafted surface. The driving force for retention is hydrophobic interaction between the solute molecules and the hydrophobized polymer chains on the stationary phase surface. The separation of the biomolecules, such as nucleotides and proteins was achieved by a dual temperature- and pH-responsive chromatography system. The electrostatic and hydrophobic interactions could be modulated simultaneously with the temperature in an aqueous mobile phase, thus the separation system would have potential applications in the separation of biomolecules. Additionally, chromatographic matrices prepared by a surface-initiated atom transfer radical polymerization (ATRP) exhibit a strong interaction with analytes, because the polymerization procedure forms a densely packed polymer, called a polymer brush, on the surfaces. The copolymer brush grafted surfaces prepared by ATRP was an effective tool for separating basic biomolecules by modulating the electrostatic and hydrophobic interactions. Applications of thermally responsive columns for the separations of biomolecules are reviewed here.     

Role of solvent in the compatibility of a vinylchloride–vinylacetate–maleic acid terpolymer and nitrocellulose blends

The compatibility of cast films of a vinylchloride–vinylacetate–maleic acid terpolymer (VMCH) and nitrocellulose (NC) blends is influenced by solvents. Transparent films of VMCH/NC blends are obtained when cast from solvents such as tetrahydrofuran or cyclohexanone, whereas hazy films are obtained when cast from solvents such as acetone or ethylacetate. Visible spectroscopy and phase morphology were used to analyse the compatibility–incompatibility of the blend. Differential scanning calorimetry (DSC) studies demonstrate that the transparent film is compatible, but the hazy film is incompatible. Fourier transform infra-red (FTIR) studies establish that a greater interaction is observed between the polymer pair in case of the compatible blend than in the case of the incompatible blend. A solvent dependency of blend compatibility is reflected in this study. The conformational state of the polymers in solution, which is responsible for the compatibility phenomena, may depend on the donor number and/or Taft-β value of the solvent. The greater the donor number and/or the Taft-β value, the higher may be the level of interaction between the solvent and the polymer molecules, which in turn may give a compatible blend after removal of the solvent.