Microscopic Insights on Shear Rheology of Polyampholyte Ionomers via Molecular Simulations

Abstract

Ionomers are polymers that contain a small fraction of charged groups. The ionic attraction of charged groups allows ionomers to act similarly to crosslinked polymers. Depending on the strength of electrostatic interactions and structure of the ionomers, different dynamics and rheological responses can be observed. With moderate attraction between ions, these noncovalent crosslinks can be broken when heated, allowing ionomers to flow and show the strength of a crosslinked network at low temperatures. Nonequilibrium molecular dynamics (NEMD) simulations will be performed under shear in the xy-plane and the macroscopic rheology and conformation of the polyampholyte ionomer will be determined. The bead-spring model with the inclusion of charged particles will be implemented to mimic the behavior of ionomers in a melt state. The data obtained will be the stress-strain behavior, shear viscosity, and chain conformation. The microscopic and macroscopic chain alignment with the flow field will be used to identify the flow mechanisms and structure disruption of polyampholyte ionomers formed with different charge distributions, namely random and precise. Furthermore, the effect of dielectric constant and the extent of gelation on the rheological properties will be characterized. The results will be compared with those for a control system without any charged groups