Formation mechanisms of low-biofouling PVDF/F127 membranes prepared by VIPS process

Abstract

Research on the preparation by in-situ modification of antifouling membranes has grown exponentially. Yet, little is known on their formation mechanisms and dedicated studies could help at improving the fine control of their structure. Our purpose here was to investigate the formation of PVDF/F127 membranes (PEG-type PVDF membranes). F127 was blended with PVDF and vapor-induced phase separation process applied to form the membranes. Like for virgin PVDF membranes, morphology of PVDF/F127 membranes is dependent on the dissolution temperature of the casting solution. The thermodynamic and kinetic effects of copolymer were investigated through the establishment of phase diagram and diffusion kinetics of non-solvent during phase separation. In the conditions tested, solutions containing PVDF and F127 are less viscous than those only containing PVDF. Also, as F127 enhances the chemical affinity of the blend with water, it eventually promotes non-solvent diffusion. Additionally, it reduces the stability of the system. However, despite a major role of copolymer on thermodynamic and kinetic of phase separation, crystallization (size of nodules, nature of polymorphs) is unaffected by F127. The morphology and arising bulk properties of low-biofouling PVDF/F127 membranes is only dependent on the initial nucleation density of crystals prior to phase separation, controlled by the dissolving temperature.