Reactive Force-Field Molecular Dynamics and Experimental FTIR Analyses of the Impact of State-of-Hydration on Nafion Morphology

Abstract

For any average value of H2O/exchange-site (λave) for a hydrated Nafion membrane, we show that there exists a wide distribution of local (λlocal) values at any instant. These distributions can be quantified by site-by-site analyses of exchange site environments characterized by molecular dynamics. Reactive force field molecular dynamics (ReaxFF MD) enables consideration of bond breaking events (sulfonic acid dissociation) that occur at λlocal values of 4 or greater. We use ReaxFF MD to predict the distribution λlocal values at any λave, and show how the dynamics elucidate water-rich, hydrophobic and interphasial regions of hydrated membranes. Each λlocal contributes to the vibrational spectrum of the polymer. The overall spectrum of the polymer electrolyte is correlated to the distribution of λlocal. Figure 1