热致相分离法制备乙烯-三氟氯乙烯共聚物微孔膜

通过热致相分离法制备了乙烯-三氟氯乙烯共聚物(ECTFE)微孔膜, 考察了ECTFE与不同溶剂的相互作用参数对ECTFE/溶剂体系的液液相区的影响, 通过相容性分析及对ECTFE微孔膜断面结构的观察, 筛选出能与ECTFE发生明显液液相分离的溶剂--邻苯二甲酸二乙酯(DEP). 热力学相图证明, ECTFE/DEP体系具有较宽的液液相分离区, 偏晶点所对应的ECTFE质量分数高达55%. 考察了冷却条件对\{ECTFE/DEP体系膜断面结构的影响, 结果表明, 膜断面孔径随着淬冷温度的降低而减小, 在淬冷温度为458 K时膜断面孔径随粗化时间的增加而增大.     

热致相分离法偏二氯乙烯-氯乙烯共聚物多孔膜的制备及性能

以偏二氯乙烯-氯乙烯共聚物[P(VDC-co-VC)]为成膜聚合物, 邻苯二甲酸二甲酯(DMP)为稀释剂, 采用热致相分离(TIPS)法制备了具有多孔结构的P(VDC-co-VC)膜. 通过聚合物-稀释剂二元体系相图、 场发射扫描电镜(FESEM)、 差示扫描量热仪(DSC)、 X射线衍射(XRD)、 原子力显微镜(AFM)、 纯水通量、 接触角、 孔径及其分布、 截留率及力学性能等研究了聚合物含量对P(VDC-co-VC)多孔膜结构和性能的影响. 结果表明, P(VDC-co-VC)-DMP二元体系成膜过程以液-液(L-L)分相为主, 随着聚合物含量增加, 膜的横截面由类花瓣状结构向胞腔状结构转变, 膜的孔连通性降低, 结构变得较为致密, 同时膜上表面孔隙率降低, 粗糙度增大. L-L分相时间和聚合物含量的变化, 导致膜结晶度先降低后增大. 聚合物含量的增加使膜上表面接触角、 断裂强度及蛋白截留率增加, 但膜的平均孔径、 孔隙率及纯水通量先增加后减小. 当聚合物质量分数为30%时, 所得膜通透性较优, 断裂强度可达7.5 MPa.     

热致相分离技术制备聚氨酯多孔膜的条件控制

采用自制的模具 ,利用热致相分离 (TIPS)的原理制备了聚氨酯 (PU)多孔膜 ,并重点研究了聚合物浓度对多孔膜的表面形貌、孔度大小、孔隙率和透湿率的影响 .在不同的聚合物浓度条件下制备的PU多孔膜的共同特征是底面 (与成膜平台接触面 )光滑平整 ,孔洞尺寸较小 ,为纳米级 ;而表面 (与空气接触的自由面 )的形貌结构较为复杂 ,但都有明显的孔洞出现 ,且孔洞的尺度大于底面 ,在微米级以上 .聚氨酯 1,4 二氧六环 (DO)形成的是上临界共溶温度 (UCST)体系 ,在发生相分离后底面与表面粗化时间的不同是导致形貌结构差异的主要原因 .改变冷台温度或调整DO H2 O的比例也会对PU多孔膜的孔度大小和形貌结构产生明显的影响     

热致相分离法制备聚苯硫醚微孔膜

采用热致相分离法,以己内酰胺为溶剂,制备得到了聚苯硫醚微孔膜并对薄膜性能表征.聚苯硫醚-己内酰胺体系制膜的优点之一是溶剂己内酰胺是水溶性的,可以采用纯水作为后处理的萃取剂.选择了合适的浓度,利用压制成型法制备聚苯硫醚平板膜;研究了体系冷却时的相行为,并考察了降温速率、聚合物浓度等因素对微孔形态与薄膜性能的影响.研究表明,聚苯硫醚-己内酰胺体系以固液分相为主,萃取后形成球晶状的微孔结构.降温速率对薄膜的微孔形态、孔径以及连通性有重要影响;当体系以较低降温速率冷却时,多孔形态为枝叶状,形成了更多的开孔结构并获得了更大的孔径,这是获得高通量微孔膜的主要原因.通过控制降温速率可以制备纯水通量大于100 L/m2h,孔径约4～5μm且连通性良好的聚苯硫醚微孔膜;研究了聚合物浓度的影响,薄膜的纯水通量随着聚合物浓度的增大而减小,并且当聚苯硫醚浓度>50 wt%时,由于大于临界浓度而失去渗透性.     

动力学因素对热诱导相分离法制备亲水性乙烯-丙烯酸共聚物微孔膜结构的影响

选择 3种不同丙烯酸含量的乙烯 丙烯酸共聚物 (EAA)为原材料 ,二苯醚 (DPE)为稀释剂 ,研究了淬冷温度、粗化时间等影响液滴生长的动力学因素对热诱导相分离法 (TIPS)制备EAA DPE亲水性高分子微孔膜结构的影响 .淬冷温度的高低决定了EAA DPE体系是发生液 液相分离还是固 液相分离 ,而产生相分离的机理不同将影响稀释剂液滴的生长 ,最终影响微孔膜的孔径 .实验结果表明 ,在相同粗化时间的条件下 ,随着EAA1 41 0 DPE、EAA3 0 0 2 DPE、EAA3 0 0 3 DPE三体系冷却温度的逐渐升高 ,孔径逐渐变大 .在结晶温度以下 ( 0℃、3 0℃、60℃ )粗化时间相同时 ,温度对微孔膜的孔径影响较小 ,例如 0℃和 3 0℃的恒温条件粗化 1 0min,微孔膜的孔径在 1～ 3 μm之间 ;在 60℃的恒温条件粗化 1 0min ,微孔膜的孔径在 3～ 5 μm之间 .而在 90℃的恒温条件粗化相同的时间 ,由于体系始终处于结晶温度线以上 ,体系始终处在液 液相分离区域 ,最终得到微孔膜的孔径达到了 6～8μm .在结晶温度以下 ( 3 0℃ )进行恒温粗化 ,由于体系的过冷程度很大 ,液滴相的粗化过程被抑制住 ,所以粗化时间对微孔膜的孔径影响不大 ;而在结晶温度以上 ( 90℃ )进行恒温粗化时 ,则是随着粗化时间的延长 ,微孔膜的孔径逐渐变大     

Preparation of new membranes by complex formation of itaconic acid–acrylamide copolymer with polyvinylpyrrolidone: studies on gelation mechanism by light scattering

Mechanism of membrane formation by dipping a 10 wt% aqueous homogeneous polymer solution of poly(itaconic acid–co-acrylamide) (75:25 molar ratio)/polyvinylpyrrolidone (50/50) into acid solution was investigated by time-resolved light scattering and the pH effect of the acid solution to gelation mechanism during membrane formation was discussed. In the pH range 1.58–1.25, the gelation was governed by phase separation mechanism via the spinodal decomposition and then a membrane with regular pore size was obtained. The phase separation was caused by polymer–polymer complex formation between polymers. From an analysis based on Cahn's linearized theory of the spinodal decomposition, the apparent diffusion coefficient D_app of phase separation was smaller for lower pH. Because, at low pH there exists a lot of complex which dramatically reduces the chain mobility. The average pore size of membrane also depends on pH. When the pH was lower than 1.25, the liquid–liquid phase separation did not occur but the solution gelled homogeneously and a wrinkle-like morphology without pore was observed. FTIR analysis of the dried membranes showed that the complex formation had occurred by hydrogen bonding between the component polymers and its extent increased linearly with decreasing pH.     

高分子混合物薄膜的相分离行为

从高分子混合物薄膜的相分离行为的机理，相分离后期粗化动力微区尺寸与时间的标度关系，影响高分子混合物薄膜表面形态形成的因素等几个方面对近年来高分子混合物薄膜相行为的研究进展进行总结，概述了今后可能的发展趋势。     

Morphology and crystallization behavior of poly(vinylidene fluoride)/poly(methyl methacrylate)/methyl salicylate,and benzophenone systems via thermally induced phase separation

Poly(vinylidene fluoride) (PVDF) blend microporous membranes were prepared by PVDF/poly(methyl methacrylate) blend (with mass ratio = 70/30) via thermally induced phase separation. Benzophenone (BP) and methyl salicylate (MS) were used as diluents. The phase diagram calculations were carried out in terms of a pseudobinary system, considering the PVDF blend to be one component. The crytallization behaviors of PVDF in the dilutions were detected by differential scanning calorimetry measurement. In these two systems, the melting and crystallization temperatures leveled off in the low polymer concentration (<40 wt %), but shifted to a higher temperature when the polymer concentration >40 wt %. The calculated crystallinity of PVDF for samples with low polymer concentrations was greater than those with high polymer concentrations, because of the limited mobility of polymer chains at a high polymer concentration. The membrane structure as determined by scanning electron microscopy depended on the phase separation mechanism. The quenched samples mainly illustrated the occurrence of crystallization on the same time scale as the liquid–liquid phase separated, resulting in the obvious spherulitic structure with small pores in the spherulites. As the polymer concentration increased, the size of the spherulites and pores within the spherulite was decreased. The evaluated porosity for BP diluted system was higher than that for MS diluted system, and decreased with the increased polymer concentration. © 2008 Wiley Periodicals, Inc. J Polym Sci Part B: Polym Phys 47: 248–260, 2009     

Computer Simulations on the Channel Membrane Formation by Nonsolvent Induced Phase Separation

The formation of channel membrane of polystyrene‐block‐poly(4‐vinyl pyridine) block copolymer is studied by computer simulations with the nonsolvent induced phase separation (SNIPS) method. Dissipative particle dynamics is employed to study the microphase separation process and the SNIPS mechanism. Simulation results indicate that polymer concentration has a significant effect on the membrane structure. Channel membranes form in the copolymer concentration range of 44–58%. Block ratio plays an important role in shaping the membrane structure. Solvent exchange rate also affects the degree of microphase separation at each evolution stage of simulation. The time evolution of morphologies shows that the microphase separation processes happen with the following sequences: the polymer self‐assembled and many small pores appear, then they form irregular cavities and cross‐link gradually, finally the channel membrane forms. These results throw light on the formation mechanism of polymer membranes and provide insightful guidance for future membrane design and preparation.     

Formation of porous flat membrane by phase separation with supercritical CO2

Microporous polystyrene membranes were prepared by the phase separation process using the supercritical CO₂ as a nonsolvent for the polymer solution. The thin polymer solution in a laboratory dish was located inside a cell and the supercritical CO₂ was introduced to induce the phase separation. The dry flat microporous membranes were obtained without collapse of the structure after the CO₂ pressure was diminished. Effects of the experimental conditions such as the CO₂ pressure, the polymer concentration and the temperature on the average pore size and membrane porosity were investigated.     

An experimental investigation of evaporation time and the relative humidity on a novel positively charged ultrafiltration membrane via dry–wet phase inversion

In this paper, a novel positively charged asymmetrical membrane was manufactured from brominated polyphenylene oxide (BPPO)/N-methyl-2-pyrrolidone (NMP)/H₂O via in situ amination with triethanolamine (TEOA) and a dry–wet phase inversion. The casting solution was exposed to the humid surroundings before immersing into the coagulation bath. The positive charge character of the membrane surface was examined by streaming potential and the effect of the evaporation time and the relative humidity (RH) on the membrane properties and microstructure were investigated, respectively. It was interestingly found that the role of evaporation time and the relative humidity on the membrane performance and morphologies for a positively charged casting system was different from the conventional rule. This was mainly due to the competition of two influence factors, i.e., evaporation of solvent and water absorption of the casting solution. The results were conformed to SEM observation and pore size distribution. Furthermore, the process of water absorption of the casting solution was monitored by attenuated total reflectance infrared (ATR-FTIR) spectroscopy technique. Additionally, in order to compare to the dry–wet phase inversion method, the membranes were obtained by prolonging the exposure time to more than 12 h (which was similar to vapor-induced phase inversion) at different RH. Polymer nodules on the membrane surface and a symmetrical morphology were observed by SEM.     

Influence of Surfactant and Humidity on Sol-Gel Macroporous Organosilicate Coatings

In the preparation of macroporous hydrophobic organosilicate films using methyltriethoxysilane (MTES) as precursor, the effects of surfactant addition, surfactant properties and atmospheric humidity were explored. As films dried, preferential evaporation of the ethanol resulted in an increase of the relative water content. This led to development of phase separation between the hydrophobic gel and the aqueous liquid and ultimately the formation of macropores. In the presence of surfactant, surfactant adsorption at the aqueous phase/gel interface affected the extent of phase separation therefore the resulting pores. Span 20 surfactant (HLB = 8.6) has lower compatibility with the aqueous phase than Tween 20 (HLB = 16.7) and effectively increases the hydrophobicity of the gel phase leading to the formation of larger pores. An increase in Span 20 content from 2 wt.% to 5 wt.% also increased pore size. Film porosity also increased significantly with humidity inside the coating chamber. It would appear that the increased porosity is a result of increased phase separation caused by reduced water evaporation at the higher humidity. Highly macroporous (up to 80% porosity), reproducible and uniform films were obtained by incorporating Span 20 surfactant into the coating solutions and performing dip coating at 80% relative humidity.     

Breath figure patterns prepared by spin coating in a dry environment

We introduce a novel method for fabricating breath figure patterns on a homopolymer film by spin coating of polymer solutions with various solvents. The homopolymers employed in this study were cellulose acetate butyrate, monocarboxylated end-functional polystyrene, and poly(methyl methacrylate). Breath figure patterns were generated even when a water-miscible solvent such as tetrahydrofuran (THF) was used as a solvent. We even succeeded in generating breath figure patterns by spin coating even under a dry environment (relative humidity less than 30%), when water was directly added into THF solution. With the combination of the spin coating method, pores with a few hundred nanometers to several micrometers have been generated. We found that the pore size becomes larger with increasing water content in THF solution and decreasing rotating speed. This is equivalent to increasing humidity and decreasing evaporation speed, respectively, in the conventional method, which is direct solvent evaporation under a humid environment. Thus, compared with the conventional method for making breath figure patterns, this method would be very convenient for fabricating large-scale films with various pore sizes.     

Effects of polymer chain length and stiffness on phase separation dynamics of semidilute polymer solution

Three-dimensional dissipative particle dynamics (DPD) simulations were performed to investigate the phase separation dynamics of semidilute polymer solutions with different polymer chain length and stiffness. For the polymer solution composed of shorter and more flexible chains, a crossover of the domain growth exponent from 1/3 to 2/3 was observed during the course of phase separation, indicating that the growth mechanism altered from diffusion to interfacial-tension driven flow. When the chain flexibility was kept the same but the chain was lengthened to allow for the chain entanglement to occur, the growth exponent changed to 1/4 in the diffusion-dominating coarsening regime while the growth exponent remained 2/3 in the flow-dominating regime. When the chain length was kept short but the stiffness was increased, the growth exponent became 1/6 in the diffusion-dominating regime and little effect was observed in the flow-dominating coarsening regime. The slow down of the phase separation dynamics in the diffusion-dominating coarsening could be explained by that the polymer chains could only perform wormlike movement when chain entanglements occurred or when the chain motion was limited by chain stiffness during phase separation. Moreover, when both the effects of chain length and stiffness were enhanced, polymer networks composed of longer and stiffer chains appeared and imposed an energy barrier for phase separation to occur. As a result, the polymer solution with stiffer and longer chains required a larger quench depth to initiate the phase separation and caused the delay in crossover of the coarsening mechanism from diffusion to flow.     

Effect of cooling baths on EVOH microporous membrane structures in thermally induced phase separation

The purpose of this work is to investigate the effect of cooling bath on the membrane preparation of crystalline polymer/diluent system via thermally induced phase separation (TIPS), when the cooling bath is compatible with the diluent. In this work, poly(ethylene-co-vinyl alcohol) (EVOH)/PEG300 system with water and methanol as the cooling baths was proposed. Results showed that when water was used as the cooling bath, the membrane presented an asymmetric structure consisting of a porous skin, macrovoids near the top and lacy structures near the bottom. In contrast, when cooled in the bath of methanol, it showed particulate morphology on the top surface and cellular pores near the bottom. The lacy and cellular structures were the typical structures resulted from liquid–liquid thermally induced phase separation, the novel macrovoids and particulate morphology were then supposed to be induced by the mutual diffusion between the diluent and the cooling bath. In the case of water, the diluent's outflow was comparative with the water's inflow into the membrane, so the penetrated water acted as a strong nonsolvent and induced macrovoids near the top. In the bath of methanol, the diluent's outflow was much faster than the methanol's inflow, which changed the solution composition from a liquid–liquid phase separation region to a solid–liquid phase separation region and resulted in particulate morphology near the top.     

Preparation, characterization and effect of annealing on performance of cellulose acetate/sulfonated polysulfone and cellulose acetate/epoxy resin blend ultrafiltration membranes

Polymeric membranes based on cellulose acetate (CA)--sulfonated polysulfone blends at three different polymer compositions were prepared by solution blending and phase inversion technique, characterized and subjected to annealing at 70, 80 and 90 °C. The permeate water flux, separation of bovine serum albumin and its flux by the blend membranes before and after thermal treatment, have been compared and discussed. Similarly, CA and epoxy resin (diglycidyl ether of bisphenol-A) were blended in various compositions, in the presence and in the absence of polyethyleneglycol 600 as non-solvent additive, using N,N^′-dimethylformamide as solvent, and used for preparing ultraflltration membranes by phase inversion technique. The polymer blend composition, additive concentration, casting and gelation conditions were optimized. Blend membranes were characterized in terms of compaction, pure water flux, water content and membrane resistance. The effects of polymer blend composition and additive concentration on the above parameters were determined and the results are discussed.     

High density polyethylene-grafted-maleic anhydride low-k porous films prepared via thermally induced phase separation

Low dielectric constant (low-k) porous films of high density polyethylene-grafted-maleic anhydride were prepared via thermally induced phase separation (TIPS) using di-n-octyl phthalate as the solvent and methanol as the extractant. The results show that, for the process of TIPS, cellular structures of spherical pores were obtained. Lower polymer concentration and lower cooling rate induced larger pores and higher porosity. For the dielectric constant, the introduction of pores considerably reduced the dielectric constant from 2.60 to 1.56 at most. Pore size showed little effect on dielectric constant in our experiment, but porosity was found to be the key influential factor. The relationship between dielectric constant and porosity was found to be best fit to Rayleigh model.     

水辅助法制备聚醚酰亚胺微孔膜

通过水辅助法采用聚醚酰亚胺的氯仿溶液制备了聚醚酰亚胺微孔膜, 并研究了环境相对湿度和聚合物浓度对孔形貌的影响. 研究结果表明, 在优化条件下, 可以制备规则均一的聚醚酰亚胺(Ultem 1010)微孔膜, 而且微孔膜的热稳定性、耐腐蚀性以及力学性能表现优异.     

Characterization of SAPO-34 membranes by water adsorption

The effects of humidity on gas permeation were studied for five SAPO-34 membranes with different fractions of permeation through non-SAPO pores. Membranes with high CO₂/CH₄ separation selectivities (>20) were stable in humidified gases, but degradation was seen for some membranes after months of exposure to the laboratory atmosphere. Once the membranes started to degrade, the rate of degradation appeared to accelerate. The degradation created non-SAPO pores that were larger than the SAPO-34 pores, as indicated by i-C₄H₁₀ permeance, CO₂/CH₄ selectivity, and CO₂ flux dependence on pressure. The effect of humidity on gas permeance correlated with these indicators of non-SAPO pores. Adsorbed water appeared to completely block the SAPO pores, but permeation through non-SAPO pores increased with humidity. Therefore, water adsorption can be used to determine membrane quality and the fraction of transport through non-SAPO pores.     

两相聚合物熔体中相区粗化过程的格子Boltzmann研究

在自由能格子Boltzmann方法的基础上, 采用附加的作用力项描述非理想流体作用, 得到了改进自由能形式的格子Boltzmann模型. 对于高分子共混体系, 采用了Flory-Huggins自由能函数形式, 对两相聚合物熔体中的相区粗化过程进行了模拟. 首先通过格子Boltzmann方法计算得到了聚合物共混物的相分离曲线, 该曲线与两相共存曲线的解析值吻合得较好. 应用此模型, 研究了聚合物共混体系不稳分相机理的相区粗化过程. 在此基础上, 探讨了分相后期相区尺寸随时间的增长指数与高分子链长和Flory-Huggins相互作用参数的关系. 模拟结果表明, 相区的后期增长机理与高分子链长和Flory-Huggins相互作用参数关系不大, 而流体的粘度决定了相区的后期增长机理, 是影响相区后期增长指数的重要因素.