Quantifying proton diffusion in acid-functionalized chitosan membranes

Abstract

We explore proton diffusion in hydrated, maleic-acid-functionalized chitosan membranes using ab initio molecular dynamics (AIMD) simulations. Our simulations show that more frequent proton hopping between water molecules leads to an increase in the proton diffusion coefficient at higher water content in membranes based on 50 and 100% de-acetylated maleic chitosan. Moreover, mobile protons interact with the oxygen atoms of the 50% de-acetylated polymer’s acetyl groups, making them susceptible to protonation. The maleic acid group’s three oxygen atoms hydrogen-bond to water molecules in the membrane channels and are protonated less frequently than the acetyl groups.