Simulated preparation and hydration property of a new-generation zwitterionic modified PVDF membrane

Improving the surface hydrophilicity of the membrane can effectively deal with the membrane fouling problem in the water treatment process. In this work, the molecular dynamics (MD) simulation method was adopted to simulate the vapor induced phase separation (VIPS) process in the preparation of trimethylamine oxide-derived zwitterionic polymer-grafted polyvinylidene fluoride (PVDF-g-PTMAO) membrane. PTMAO is a new-generation zwitterionic material with zero-length carbon spacer length (CSL), which exclude the hydrophobic effect of the CSL. The hydration properties of the formed zwitterionic membrane were investigated. The effect of grafting ratio of PTMAO:PVDF on the membrane surface morphology and hydration ability were explored. The simulation results show that the zwitterionic segments are enriched at membrane surface due to the attraction of water vapor and a stable hydration layer is formed on the membrane surface. As the grafting ratio increases from 5% to 15%, the number of hydrogen bonds between membrane and water molecules boosts and their interaction is strengthened, while water diffusion along the membrane surface is reduced, as a result of significantly enhanced hydration of PVDF-g-PTMAO membrane. This work helps investigate the migration behavior of the zwitterionic polymer in a PVDF-based membrane during the VIPS process and provides a better understanding of the antifouling mechanism of zwitterionic membrane as well as gives a guidance for designing new antifouling materials.