(Invited) Chemical and Structural Factors Affecting the Hydrated Morphology of Anion Exchange Membranes

Abstract

The hydrated morphology of ion containing polymers is a critically important property affecting ion and water transport. Anion exchange membranes (AEMs) are increasingly of interest as the electrolyte in energy and conversion devices due, in part, to their suitability with non-noble metal catalysts. However, the rather low chemical stability under alkali conditions and only meager ionic conductivity present difficulties in their application. A promising strategy to enhance the conductivity of these materials may be through tailoring of the phase segregation of the polymer. Recently, AEMs based on the triblock copolymer, polystyrene-b-poly(ethylene-co-butylene)-b-polystyrene (SEBS), and functionalized with various cationic groups have shown satisfactory chemical stability. We are continuing an extensive investigation to understand how various molecular features (degree of functionalization, placement of alkyl spacer(s) on the side chain, choice of the cationic group, and the associated anion) determine the hydrated morphology of functionalized SEBS ionomers. With this goal we are utilizing dissipative dynamics (DPD) simulations, a meso-scale technique, to probe relatively large time and length scales and thereby elucidate the morphology of the polymer systems. The optimized structure and the interaction parameters used in these DPD simulations were calculated using a recently developed methodology employing DFT based electronic structure calculations. The morphology was determined over a broad range of hydration and our results underscore the complexity of the effects of these parameters.