Channel morphologies and aqueous dynamics in simulations of anion exchange membranes

Anion exchange membranes (AEMs) are candidate materials for applications in alkaline fuel cells, although more understanding of the hydroxide dynamics is required. Building upon prior work investigating a fluorine-free polyethylene-like polymer with phenyl sulfonic acid groups on every fifth backbone carbon, we present atomistic molecular dynamics simulations of two polymers with pendant quaternary nitrogen groups on every fifth backbone carbon. At various levels of hydration, we investigate system morphology and the dynamics of hydroxide and water. Specifically, we quantify how increasing water content swells water channels and enhances both water and counterion diffusion, as well as how the shape of the quaternary pendant group dictates the structure of the polymer matrix and dynamics within the water channel. These results point towards fundamental physics dictating the properties of hydrated polymer membranes at the nanoscale, an important step towards informed and improved material design.