Investigation of abnormal thermoresponsive PVDF membranes on casting solution, membrane morphology and filtration performance

Abstract

An interesting PVDF membrane with unusual thermoresponsive behavior was prepared by the incorporation of P(OEGMA-co-VTMOS). The P(OEGMA-co-VTMOS) copolymer was first in situ synthesized in a PVDF/triethyl phosphate (TEP) casting solution. A P(OEGMA-co-VTMOS) network was assembled in the PVDF membrane through hydrolysis and condensation during phase inversion. PVDF/P(OEGMA-co-VTMOS) in organic solvent demonstrated a typical LCST around 35 °C, reflecting the reversible transition of the coil-to-globule conformation. Microphase separation was responsible for the appearance of turbidity of the casting solution. FTIR, XPS, TGA and SEM confirmed the surface enrichment of the copolymer, especially in the membrane bottom. The hydrophilicity and protein anti adsorption were improved despite the temperature variation. In particular, AFM in aqueous media was conducted to determine the reversible morphology and water channel variation under heating and cooling. Different from common thermoresponsive membranes, the so-modified PVDF membranes exhibit a reversible abnormal change of pure water flux and BSA rejection with temperature. The intriguing thermoresponsive behavior and mechanism of the modified PVDF membrane was thoroughly investigated from the aspects of PVDF/TEP casting solution, membrane morphology in aqueous media and water/BSA filtration performance.