Pore formation in graphene/poly(vinylidene fluoride-co hexafluopropylene) nanocomposite thin film membranes

Abstract

A new facile process—filler regulated phase separation was introduced to prepare Poly(vinylidene fluoride-co hexafluoropropylene) (PVDF-HFP) porous membranes by using graphene (GN) with its typical shape and size to regulate solvent evaporation and induce PVDF-HFP precipitating into a porous polymeric structure. An interesting resultant hierarchical porous structure composed of micropores and nanopores has been obtained for the first time. Corresponding to a dramatic change of surface morphology and structure of PVDF-HFP/GN membranes, a unique "switch-like" behavior of hydrophobicity was observed when the GN concentration of PVDF-HFP exceeded a critical value (around 0.6-0.7 wt %), where the water contact angle of the membrane increased by 45 degrees. However, such phenomenon is not observed when carbon nanotube was used in a comparative study. This proposed new process is a promising way to tailor polymer membrane structure and even membrane wettability for specific applications such as membrane contactors, membrane distillation, and supported liquid membrane etc. Surface morphology, crystal structure and thermal stability of these membranes were characterized by SEM, FTIR and DSC respectively.