Investigation of the effects of methanol presence on characteristics of sulfonated aromatic electrolyte membranes: Molecular dynamics simulations

Effects of methanol solvent on characteristics of water-methanol solvated sulfonated poly(2,6-dimethyl-1,4-phenylene oxide) (SPPO) membranes were investigated at different methanol concentrations and temperatures using molecular dynamics simulations. Simulation results showed phase segregation of membrane on the uptake of methanol. Analysis of S-S RDFs revealed that the distance between sulfonic acid groups increased by increasing methanol concentration. Using RDFs of SPPO chains to solvent molecules, it was found that sulfonic acid groups were more solvated with water while aromatic backbone of SPPO exhibited stronger affinity toward methanol. From cluster size distribution examination, it was understood that larger solvent clusters formed at lower methanol concentrations. Diffusivity of water molecules decreased and that of methanol enhanced with an increase in methanol uptake. Calculated methanol diffusion coefficients were smaller in SPPO compared with Nafion, in agreement with experimental observations. Furthermore, increasing the temperature improved diffusivities for all permeants.