双层刮膜中分层／粘结和开孔结构形成机理研究

Origin of delamination/adhesion in co-casting and the open structure

以PEI与PSf为对象,研究了双层刮膜过程中两种高分子分层的原因,考察了PSf膜表面开孔结构的形成原理.考察了两层制膜液间的凝胶值之差、膜的收缩率以及添加剂PVPK-90等热力学和动力学参数对分层/粘结性的影响.研究发现,凝胶值作为一个热力学参数不能单独作为高分子分层/粘结的标准;同时发现,通过提高凝胶浴温度减少PEI膜与PSf膜之间的收缩率差别可以促进粘结.研究还发现,PVPK-90起到了促进膜层间粘结性的作用.采用含不同量溶剂的凝胶浴,证明了双层刮膜过程中PSf膜的表面开孔结构是由于PEI膜为支撑层提供了一个近似富含溶剂的凝胶浴得到的.

PEI and PSf polymer solutions were used for co-casting. Mechanisms for delamination/adhesion were investigated. It was found that the contribution of the coagulation values of membrane solutions is insignificant to the adhesion of two layers. Instead, membrane shrinkage appears to play a significant role because composite membranes were obtained by minimising their shrinkage difference at the thickness direction by the increase of the coagulant temperature. In addition, the PVP in PSf solution also improves the adhesion between PEI and PSf layer. The open structure formation mechanism of PSf membrane was ascribed to a solvent enriched environment caused by the presence of PEI coating layer, which was confirmed by addition of a large amount of solvent into water coagulant. Finally, the concave defects forma- tion on PSf surface was proposed as the impact of the growth of finger-like macrovoids in PEI layer. The results provides a solid theoretical basis for the expanding the application of co-casting technique.