非溶剂添加剂对PES/NMP铸膜液性质的影响

Effect of nonsolvent additives on the properties of PES/NMP membrane-forming systems

依据文献报道的PES/NMP(聚醚砜 /N -甲基吡咯烷酮 )制膜体系的浊点数据和特性粘数 ,从传统的宏观热力学和铸膜液中高分子的构象两方面讨论了非溶剂添加剂的种类和加入量 (邻近比 )对PES/NMP铸膜液性质的影响 .非溶剂添加剂改变了PES/NMP铸膜液的热力学性质和PES分子的构象 .这种效应依非溶剂种类的不同而显著不同 .非溶剂添加剂对铸膜液性质的影响不仅表现在种类的差别上 ,也和无因次量———邻近比密切相关 .邻近比可以表征铸膜液的热力学状态和混合溶剂的质量 .铸膜液的邻近比增大 ,混合溶剂的质量下降 ,铸膜液的热力学稳定性降低 ,PES分子的构象也由舒展状态逐渐收缩 .聚合物分子的构象对成膜过程的影响十分显著 ,研究成膜机理不能忽视非溶剂添加剂对铸膜液中高分子构象的影响 .

The effect of nonsolvent additives on the properties of PES/NMP membrane-forming systems was investigated based on the cloud point data and intrinsic viscosities reported in the literature. Nonsolvent additives not only change the thermodynamic state of the membrane-forming systems but also alter the polymer conformation in solution. The effect varies with the type of nonsolvent additive, which is macroscopically reflected by the close relationship between the values of χ 13 , g 12 and the position of the cloud point curve in the triangle phase diagram. In addition, the effect can be demonstrated by the different dropping rate of the intrinsic viscosities caused by various nonsolvent additives. The value of χ 13 characterizes the strength of the nonsolvent additive and its ability to alter the polymer conformation in solution. The value of χ 13 combined with that of g 12 largely determines the position of the cloud point curve in the triangle phase diagram. The effect of nonsolvent additives on the polymer conformation also varies significantly with the type of nonsolvent additive. Besides the type of nonsolvent additive, the amount of nonsolvent additive can alter the properties of the PES/NMP membrane-forming systems. The latter is characterized by a dimensionless parameter, the approaching ratio, which describes the thermodynamic state of the membrane-forming system and the quality of the solvent mixture. With increasing approaching ratio, the quality of the mixed solvent decreases and the membrane-forming system becomes unstable. In addition, the polymer conformation in solution varies with increasing approaching ratio. The polymer conformation in solution has a significant effect on membrane formation, and so the influence of nonsolvent additives on the polymer conformation in solution cannot be neglected in the investigation of the mechanism of membrane formation.