Formation of polyethersulfone membranes via nonsolvent induced phase separation process from dissipative particle dynamics simulations

Abstract

Dissipative particle dynamics (DPD), a coarse-grained simulation method, was used to investigate the formation of polyethersulfone (PES) membranes via the nonsolvent induced phase separation (NIPS) process with N-methyl-2-pyrrolidone (NMP) as the solvent and water as the nonsolvent coagulant. The effects of PES polymer concentration (8–16% (v/v)) and molecular weight (chain length with degree of polymerization of 60, 90, 135) on the membrane structure and morphology were investigated. The formation of asymmetric nanostructures with polymer-lean (liquid-rich) and polymer-rich domains was observed. A thin but dense polymer top layer at the liquid-polymer interface, with a more porous sub-layer, evolved over time. The effect of polymer concentration on membrane structure is more significant than that of the molecular weight of the PES polymer. As the polymer concentration increases from 8 to 16% (v/v), the surface layer becomes significantly denser, which is in agreement with experimental observations. Furthermore, high molecular weight PES leads to a slightly more porous membrane structure.