Formation of Poroas Membrane by Phase soparation with Supercritica/CO_2

以超临界CO_2为非溶剂，采用相分离法制备了聚苯乙烯微孔膜。将实验室培养皿中的聚合物溶液置于细胞内，引入超临界CO_2诱导相分离。在降低CO_2压力的条件下，得到了干燥的扁平微孔膜，膜的结构没有发生坍塌。考察了CO_2压力、聚合物浓度和温度等实验条件对膜平均孔径和膜孔隙率的影响。在超临界CO_2相分离法制备多孔醋酸纤维素膜的过程中，采用了5种稀释剂，考察了稀释剂对膜结构和性能的影响。随着稀释剂与超临界CO_2相互亲和力的降低，膜的孔隙率和中心位置附近的平均孔径增大，上表面形成较厚的皮层。在所有情况下，虽然CO_2的引入会瞬间发生相分离，但都没有形成大空洞。这与以水为非溶剂的瞬时相分离条件下形成的大孔隙形成形成对比。对制备的多孔膜进行了溶质抑制系数和透水性等性能测试。

Microporous polystyrene membranes were prepared by the phase separation process using the supercritical CO_2 as a nonsolvent for the polymer solution. The thin polymer solution in a laboratory dish was located inside a cell and the supercritical CO_2 was introduced to induce the phase separation. The dry flat microporous membranes were obtained without collapse of the structure after the CO_2 pressure was diminished. Effects of the experimental conditions such as the CO_2 pressure, the polymer concentration and the temperature on the average pore size and membrane porosity were investigated.In the preparation of porous cellulose acetate membrane by phase separation with supercritical CO_2, five kinds of diluents were used and effect of the diluent on the membrane structure and performance was investigated. As the mutual affinity between diluent and supercritical CO_2 decreased, the membrane porosity and the average pore size near the center position increased and the thicker skin layer was formed at the top surface. In all cases, macrovoid was not formed, although the phase separation occurred instantaneously after CO_2 was introduced. This was a contrast to the macrovoid formation in the condition of instantaneous phase separation using water as nonsolvent. The membrane performances such as the solute rejection coefficient and the water permeability were measured for the obtained porous membranes.