Understanding structure and transport characteristics in hydrated sulfonated poly(ether ether ketone)–sulfonated poly(ether sulfone) blend membranes using molecular dynamics simulations

Abstract

Polymeric acid–acid blend membranes comprising of sulfonated poly(ether ether ketone) and sulfonated poly(ether sulfone) were studied at varied water contents ranging from λ=3 to λ=15 using MD simulations. Based on the obtained simulation results, blend membranes were found to swell against hydration. With increase in hydration, sulfonic acid groups were observed to become increasingly hydrated which led to increased average distance of sulfur–sulfur, and decreased hydronium ion coordination number around the sulfonic acid groups. By analyzing the water coordination number to water molecules, less developed water phase and less phase separated structure were found for the blend membrane compared to that of Nafion. Furthermore, using cluster size distribution analysis for water molecules, it has been understood that large spanning water clusters encompassing all molecules were formed at higher hydrations, which resulted in improved water and hydronium ion transport properties. In comparison with Nafion, the simulated diffusion coefficients were smaller in blend membrane.