Molecular simulation of gas solution-diffusion in polyvinylamine/polyvinyl alcohol blend membranes

Polyvinylamine (PVAm)/polyvinyl alcohol (PVA) blend membranes have been drawing attention for their gas transport performance as carbon dioxide separating membranes. In PVAm/PVA blend membranes, carbon dioxide is selectively transported by taking advantage of its reactivity to amines. Carbon dioxide molecules diffuse through the membrane by binding and unbinding to the amines in side chains of PVAm molecules continuously, resulting in relatively high permeability and permselectivity against other types of gasses. In this study, molecular dynamics (MD) and grand canonical Monte Carlo (GCMC) simulations were conducted to analyze diffusivity and solubility of carbon dioxide and nitrogen molecules in assembled PVAm/PVA membrane models. We also constructed water-added membrane models to replicate humid environments. In the MD simulations, gas molecules inserted in the models with PVAm diffused less than those in models without PVAm. Additionally, insertion of water significantly enhanced the diffusion of both carbon dioxide and nitrogen molecules. In the GCMC simulations, insertion of PVAm chains leads to decrease in the number of inserted gas molecules. However, carbon dioxide maintained a solubility higher than that of nitrogen regardless of the proportion of PVA within the system.