(521a) Structure and Dynamics in Sulfonated Polyphenylenes from Atomistic and Coarse-Grained Simulations

Proton exchange membranes are critical for a variety of energy applications, including fuel cells and flow batteries. Proton conduction in hydrated, proton-conducting polymer membranes is highly affected by hydration level and membrane morphology. Here we examine morphology and dynamics in a promising proton-conducting polymer, a sulfonated Diels-Alder polyphenylene (SDAPP). We performed atomistic molecular dynamics (MD) simulations on a series of sulfonated polyphenylenes, systematically varying the degree of sulfonation and water content to determine their effect on the nanoscale structure, particularly for the hydrophilic domains formed by the ionic groups and water molecules. The static structure factors calculated from simulation are in good agreement with X-ray scattering data. We characterize the morphology of the ionic domains employing two complementary clustering algorithms. At low sulfonation and hydration levels, clusters are more elongated in shape and poorly connected throughout the system. As the degree of sulfonation and water content are increased, the clusters became more spherical, and a fully percolated ionic domain is formed. The relation between the nanoscale morphology and experimental measures of water diffusion and conductivity will be discussed. Additionally, we have derived a coarse-grained model from the atomistic simulations using inverse Boltzmann iteration. We simulate the coarse-grained model using DPD simulations. Following Neimark et al. [M.-T. Lee, A. Vishnyakov, and A.V. Neimark, J Chem Theory Comput 11, 4395 (2015)], we include a Morse potential between explicit protons and water molecules to mimic the Grotthuss hopping mechanism of the protons. The coarse-grained model also shows percolated water domains. We will discuss the relation between morphology and proton and water dynamics from the DPD simulations, and relate these to experimental measures of water diffusion from NMR pulse-field-gradient measurements.

Sandia National Laboratories is a multimission laboratory managed and operated by National Technology & Engineering Solutions of Sandia, LLC, a wholly owned subsidiary of Honeywell International Inc., for the U.S. Department of Energy’s National Nuclear Security Administration under contract DE-NA0003525.