(648d) Atomistic Molecular Dynamics Simulations of Model Ionomers

Ionomers are polymers that contain a small fraction of ionic groups. Due to their unique electrical properties, ionomers are being investigated as potential solid electrolytes in mobile battery applications. However, the relationships between ionomer chemistry, morphology and ion transport are poorly understood, which has hindered the development of ionomer-based batteries. To this end, we report atomistic molecular dynamics (MD) simulations of a model ionomer (polyethylene-co-acrylic acid) neutralized with different ions at various neutralization levels. The structure factor computed from the simulations is in good agreement with experimental X-ray scattering data, which provides strong validation of the simulation methods. Our simulations provide additional insight into the shape and size distribution of ionic clusters, which suggests the need for a novel interpretation of scattering data. In particular, we observe large networks of string-like clusters, and report quantitative features of these structures as a function of ionic group spacing in the polymer backbone, counterion type and neutralization level. We also report detailed structural information pertaining to local structures around ions, which is difficult to obtain experimentally and may have important consequences for ion transport properties. Overall, we show that the structural properties of ionomers are amenable to atomistic simulations, which provide a valuable complement to experimental investigations.