Preparation of new membranes by complex formation of itaconic acid–acrylamide copolymer with polyvinylpyrrolidone: studies on gelation mechanism by light scattering

Abstract

Mechanism of membrane formation by dipping a 10 wt% aqueous homogeneous polymer solution of poly(itaconic acid– co-acrylamide) (75:25 molar ratio)/polyvinylpyrrolidone (50/50) into acid solution was investigated by time-resolved light scattering and the pH effect of the acid solution to gelation mechanism during membrane formation was discussed. In the pH range 1.58–1.25, the gelation was governed by phase separation mechanism via the spinodal decomposition and then a membrane with regular pore size was obtained. The phase separation was caused by polymer–polymer complex formation between polymers. From an analysis based on Cahn's linearized theory of the spinodal decomposition, the apparent diffusion coefficient D app of phase separation was smaller for lower pH. Because, at low pH there exists a lot of complex which dramatically reduces the chain mobility. The average pore size of membrane also depends on pH. When the pH was lower than 1.25, the liquid–liquid phase separation did not occur but the solution gelled homogeneously and a wrinkle-like morphology without pore was observed. FTIR analysis of the dried membranes showed that the complex formation had occurred by hydrogen bonding between the component polymers and its extent increased linearly with decreasing pH.