Preparation And Characterization Of High Performance Polyvinylidene Fluoride Film By Thermally Induced Phase (TIPS) Method

This paper focused on the modification of PVDF membrane via TIPS, which concentrated on the influence of the different preparation methods and additive content on the membrane structure and performance. The paper mainly includes three aspects.First, Graphene and its derivatives（such as Graphene Oxide, GO） as the promising filler materials have been employed in many fields included membrane via NIPS, yet still not found the blended membrane via TIPS in literatures and papers. Utilizing in situ hydrolysis and condensation of TEOS on the surfaces of graphene oxide（SiO₂@GO） to modify the PVDF membrane via TIPS and then paying attention to the effect of additive content on membrane structure and performance in details, the PVDF/SiO₂@GO membranes were obtained and characterized. The results demonstrate that the membranes induced by the mechanism of liquid-liquid phase separation exhibit the bi-continuous sponge-like structure of cross-sectional morphologies and shows varied performances with different additive loading, but polymorphism of PVDF domains α-phase induced high temperature. At low concentration of SiO₂@GO, the top surface of modified membrane turns denser compared to the net membrane, which results in even BSA retain to 91.7% and lower water flux. Nevertheless overhigh additive triggers in the adverse trend. The phenomena can be explained by the combined actions of nucleation and growth of PVDF and viscosity increase of cast solution due to the addition SiO₂@GO nanohybrid.Second, according to the impact of PVDF crystallinity on membrane structure and performance via NIPS in other reports, the salt-induced TIPS was proposed to fabricate the PVDF flat membrane in the paper. It turns out the salt content can produce the transformation of structure and permeation performance. At low lever of salt, the top surface of membrane in comparison with control membrane emerges more porous and regular, and present macro pores indeed with the content increase. Upon the limit of salt saturation, the membrane pore becomes smaller and uniform, leading to flux decline instead. The two competitive factors of nucleation and growth of PVDF are responsible for the structure change.Third, on the basis of previous sections, the diluent system of DBP and crystalline DMSO₂ was aimed to explore the effect of diluent ratio on the flat membrane structure and performance. The results show that compared to the control membrane, the modified membranes appear the tubular-like pores in the cross section, spherulites at the bottom surface. The crystalline properties of PVDF from the α-phase to β-phase prove the mechanism change. As a result, the top surface of modified membranes becomes denser than the control membrane and presents smaller pore, which brings about the improvement of BSA retain.