Molecular Simulations of Nafion Membranes in the Presence of Polar Solvents

Abstract

We describe molecular dynamics computer simulations coupled with quantum chemical calculations of relevant geometries and interaction constants for studying the detailed behavior of solvent-containing Nafion(R) membranes. Our attention here is focused on the effect of different solvent additives on the equilibrium structure of micellar aggregates. Taking into account the practical importance of methanol membrane fuel cells, methanol-containing systems are the subject of our primary interest. Also, we study mixed aggregates containing alcohols H(CH2)(n)OH with longer hydrocarbon chain, up to n = 7. In the case of the bicomponent solvent-containing aggregates we have suggested how events occurring at the molecular level produce polymorphic transitions in these mixed aggregates from spherical structures toward cylindrical and rather exotic toroidal micelle structures, stabilized by a more uniform compact packing of the hydrophobic groups in the micelle exterior. These transitions predicted in the present study illustrate how intermolecular forces such as solvation as well as solvent chain length can affect overall aggregate structure and result in polymorphism.