Decoupling Conductivity and Segmental Motion in Polymerized Ionic Liquids*

We characterize diffusion trends in polymerized ionic liquids using atomistic molecular dynamics simulations of a number of anion species and imidazolium cations, both tethered to and implanted in poly-alkyl backbones, to develop design guidelines for polymerized ionic liquids with highly decoupled conductivity and polymer segmental dynamics. We use glass-transition-normalized temperature to compare conductivity for similar segmental dynamics behavior across a variety of chemical species. Results suggest that ion mobility decoupling depends on two distinct modes: 1) a small-ion ion-pairing mode where conduction relies heavily on an ion-hopping mechanism that has been explored previously, and 2) a large-ion free-volume diffusion mode that utilizes large, interconnected gaps in the polymer matrix for diffusion in the absence of segmental motion.