溶剂浓度对PVDF相转换膜大孔结构的影响

提出决定大孔能否发展的初始分相点处溶剂浓度临界点的概念 ,认为初始分相点处较高的溶剂浓度有利于大孔的发展 ,溶剂浓度低于一定的界限后 ,大孔停止发展 ,转为海绵状结构 .实验考察了不同凝胶液组成下制得的PVDF中空膜的结构 ,建立了相应的传质模型 ,模拟不同制膜条件下初生态膜内的组成分布情况 ,根据初始分相点处溶剂浓度临界点的概念 ,预测膜的形态结构 .模拟结果与相应制膜条件下的电镜照片有很好的对应关系 ,证明了上述大孔形成机理的正确性 .

EFFECT OF SOLVENT CONCENTRATION ON DEVELOPMENT OF MACROVOIDS OF PVDF PHASE-INVERSION MEMBRANES

A conception of critical solvent concentration (CSC) at the onset of phase separation was proposed.The macrovoid-formation mechanism came up with this conception.It was considered that a higher solvent concentration at the onset of phase separation than that critical value is required for the development of macrovoids in phase-inversion membranes.When the solvent concentration at the onset of phase separation is smaller than the critcal value,the macrovoids development stops and a sponge-like structure is formed.The polyvinylidene difluoride(PVDF)hollow fiber membranes by using PVDF(18%)-PEG1000(5%)-DMAc(77%)casting solutions and different inner coagulation baths.A mass transfer model was established to simulate the composition variation of nascent hollow fiber during the PVDF hollow fiber formation process under the corresponding technical condition.The solvent concentration at the onset of phase separation was calculated.The membrane morphological structures were predicted according to the conception of CSC at the onset of phase separation,the macrovoids formation mechanism and the simulation results.SEM observations of the membranes prepared in various inner coagulation baths show that the predicted results coincide well with the membrane morphological structre and verify the macrovid-formation mechanism.