Permeation and copermeation behavior of methanol and acetate in cation exchange membranes*

The permeation of solutes, molecules and ions, through hydrated polymer membranes is of critical importance for many applications. We utilize in situ ATR FTIR spectroscopy to quantify the multicomponent transport of molecules and polyatomic ions through ion exchange membranes. We examine the individual and co-permeation of methanol and acetate across commercially available membranes, Nafion 117, and synthesized polyether-based membranes of varied and tunable ion content and charge type. Membrane permeability and selectivity calculated from single component permeation experiments are compared to those calculated for solutes in multicomponent permeation experiments. In Nafion 117 and model cation exchange membranes we find distinct differences in transport behavior of the acetate anion while the behavior of methanol remains unchanged. We also find no difference in transport behavior for these solutes in uncharged polyether membranes. We attribute this emergent transport behavior of the acetate anion to specific solute-solute-membrane interactions which likely emerge from the electrostatic screening of interactions between the acetate anion and membrane-bound anions.