(413h) Effect of Nanoparticle on the Structure and Dynamics of Model Peaa Ionomers from Molecular Dynamics Simulations

Ionomers are polymers that contain a small fraction of ionic groups covalently bound to a non-polar backbone. These bound ions along with free counterions tend to aggregate strongly, holding the polymer chains together as temporary crosslinks. This gives rise to interesting properties different from the parent, uncharged polymer. Ionomers are used in dental fixtures, fuel cell membranes and packaging, among other applications. We consider a dense melt of ionomers and unbound counterions, with no solvent and above the glass transition temperature. Prior work established a useful coarse-grained model for acetic acid based ionomers, but considered only fully neutralized materials. To allow clearer mapping to typical experimental systems, we developed a new model that includes unneutralized acid groups with adjusted Lennard-Jones interaction strengths with each other and with ionic groups. Using this modified model, we simulate a single spherical nanoparticle (whose diameter is ten times that of a monomer bead) surrounded by partially neutralized ionomers, and we consider two different nanoparticle – monomer and nanoparticle – ion interaction strengths. Detailed aggregate morphologies were calculated and compared with similar systems without nanoparticles. These analyses were done systematically for differing mole content of ions and different levels of neutralization. We find that aggregates are depleted near the nanoparticle surface, increasing the segmental dynamics near the surface relative to the bulk.