Effect of Neutralization on the Structure and Dynamics of Model Ionomer Melts

Using coarse-grained molecular dynamics simulations, we investigate how ionomer behavior depends on ion and acid content. Our coarse-grained model builds on a prior model that was successful in capturing the low wavevector ionomer peak observed in X-ray scattering. As in prior work, we consider a linear backbone of neutral monomer beads with charged pendant beads and unbound counterions; we now also include "stickers" pendant to the backbone to represent unneutralized acid groups. These stickers are similar to backbone monomers but have higher cohesive interaction strength with each other and with the ionic groups, chosen to approximately match structural features of prior atomistic simulations. This allows us to simulate partially neutralized materials over longer time and length scales than is possible atomistically. We find that stickers can aid in ionic aggregate rearrangements such that samples containing sticker groups can show a lower viscosity than samples with the same ion content but without stickers; this agrees with experimental results of analogous materials.