Surface and interface characterization of smart membranes

Abstract

Multistimuli-responsive microfiltration (MF) membranes were fabricated from blends of poly(N-isopropylacrylamide) (PNIPAm) and poly(vinylidene fluoride) (PVDF) grafted with poly(acrylic acid) (PAAc) and poly(4-vinylpyridine) (P4VP) side-chains (PVDF-g-PAAc/PNIPAm and PVDF-g-P4VP/PNIPAm, respectively) by phase inversion in aqueous media. Elemental and XPS analyses indicated that both the bulk and surface concentration of PNIPAm in the PVDF-g-PAAc/PNIPAm and PVDF-g-P4VP/PNIPAm blend membranes increased with increasing PNIPAm concentration in the blend used for the casting solution. Surface enrichment of the PNIPAm chains occurred in both types of membrane, leading to a surface concentration ten times that of the bulk. SEM results showed that the porous morphology of the membranes could be regulated by the pH and temperature of the coagulation bath. Actual measurements revealed that the pore size of the PVDF-g-P4VP/PNIPAm blend membranes increased with the increase in temperature and the decrease in pH of the aqueous casting bath. The flux through the PVDF-g-PAAc/PNIPAm and PVDF-g-P4VP/PNIPAm blend membranes exhibited simultaneously temperature- and pH-dependent behaviour. Copyright © 2004 John Wiley & Sons, Ltd.