水蒸汽诱导法成膜过程研究

在用水蒸汽诱导法制备聚偏氟乙烯(PVDF)微孔膜时,利用光学显微镜对初生态膜在水蒸汽中凝胶过程进行动态观察,结合膜在不同湿度下质量变化和表面液滴层的红外光谱图,研究了蒸汽诱导法成膜的具体过程.结果表明,蒸汽诱导法制备PVDF膜的成膜过程存在着溶剂和非溶剂的迁移,刚开始是非溶剂水的迁入占主导地位,膜质量增加;此后,溶剂与非溶剂的挥发逐渐占主导地位,膜质量在达到最大值后逐渐减少,最终稳定.湿度较高时,溶剂与非溶剂扩散速度较快,膜的凝胶速度较快;湿度较低时,膜凝胶速度则较慢.膜表面和断面电镜照片表明,随着膜在蒸汽中停留时间的延长,蒸汽诱导法最终形成的膜为粗糙多孔表面及对称的断面结构.

Research on the Process of Membrane Formation via Water-vapor Induced Phase Separation

The specific process of membrane formation via water-vapor induced phase separation method was investigated through observing the gelation process of polyvinylidene fluoride(PVDF)casting-solution in vapor under optical microscope,combining mass variation of the membrane solution under different humidity and infrared spectra of the liquid drop layer on the film surface.The results showed that there existed transfer between solvent and non-solvent during the membrane formation.The film quality increased in the beginning due to the absorption of non-solvent water as dominant.Afterwards,film quality reached a maximum value,then decreased gradually to be steady owing to the volatilization of the solvent and non-solvent as dominant.The gelation rate in the high humidity was faster than that in the low humidity because of the faster exchange between the solvent and non-solvent.According to the SEM images of the PVDF membrane surface and cross-section,the final membrane structure for rough and porous surface was formed with the longer exposure time in vapor while the symmetrical cross-section formed.