Local Structure and Dynamics in Melts and Glasses of Polyzwitterions

Abstract

Polyzwitterions are a class of polyampholytes containing equal numbers of positive and negative charges bonded together within each repeating monomer. The electrostatic interactions and the chain connectivity are believed to be the most important factors in affecting local ordering and dynamics in the melts and glasses of polyzwitterions, leading to their high glass transition temperatures and low fragilities. In this study, we use coarse-grained molecular dynamics (CGMD) simulations with explicit charges on side groups to study the effects of electrostatic interactions and chain architecture on the static structure factor, the glass transition temperature (Tg), segmental dynamics, fragility index, and temperature- and frequency-dependent dielectric responses of polyzwitterions. Comparisons of the results obtained for polyzwitterions containing zwitterions on the side groups with additional simulations of uncharged linear chains and polymers bearing uncharged side groups reveal a key role played by the chain architecture in affecting the local packing. However, the electrostatic interactions are found to dominate the dynamic behavior, as evidenced by the elevated Tg, slower segmental and dipole relaxation dynamics, and reduced fragility indices. Finally, we construct the dielectric spectra from simulations to assist in the interpretation of experimental measurements.