Microscopic theory of activated ion relaxation in polymerized ionic liquids

We study the structural correlations in model polymerized ionic liquids with small ions using the polymer integral equation theory to understand how ions and polymers affect each other's dynamics. The equilibrium structures are influenced by interaction strength, ion size, polymer chain rigidity, and dielectric constant, which together govern ion and segmental dynamics. While it’s known that interaction strength impacts the structural properties of ions and monomers differently, we extend this understanding to their dynamics. Interestingly, interaction strength has minimal effect on polymer dynamics but plays a key role in ion-level dynamics, as shown through self-consistent cooperative hopping theory.

Our study confirms that ions move faster when interaction strength is reduced. We also observe a nonlinear rise in the energy barrier with increasing interaction strength and a new onset of the barrier for small ions at negligible strength. Modifying polymer chemistry to alter dielectric constants can tune interaction strength, thereby controlling the temperature-dependent dynamics of ions around the vitrification point. Additionally, we find that the thermal expansion coefficient significantly impacts polymer segmental dynamics more than ion dynamics.