(196z) Effect of Electric Field on the Structure and Dynamics of Model Ionomer Melts

Ionomers are polymers containing a small amount of charged groups attached to a relatively non-polar backbone, used in packaging and other applications. We consider a melt of ionomers and their counterions with no solvent, in which the aggregation of ions significantly impacts overall material properties. A prior coarse-grained model has been successful in capturing the low wavevector peak observed in x-ray scattering known as the ionomer peak, as well accurately predicting other structural and dynamic properties of these materials. This model represents poly(ethylene-co-acrylic) acid neutralized completely by sodium salt, using neutral monomer beads, charged beads that represent COO^– , and charged unbound beads that represent Na⁺. Commercially available ionomers however are only partially neutralized, with some COOH (carboxyl groups) along the backbone. These carboxyl groups play an important role in aggregate morphology and influence the overall properties of the polymer. Thus, in order to better model typical experimental systems that are partially neutralized, we use additional “sticker” groups that represent COOH. These stickers are similar to uncharged monomers but with adjusted short-range interaction strengths with each other and with ionic groups. Although sticker-sticker interactions are radially symmetric, aggregate morphologies obtained using the sticker-based model are in good agreement with prior atomistic simulation results. By including stickers, we can now more accurately represent Surlyn®, which is widely used commercially. To this modified model, we apply a static electric field. Aggregate morphology under the field was analyzed and compared with zero field morphology. Local and long range order of the aggregates was also studied. All analyses were performed on different chain architectures and neutralization levels.