Chain dynamics and conductivity of polymerized ionic liquids: Effects of electrostatic correlation and chain length

Abstract

Polymerized ionic liquids (PILs) exhibit complex ion transport dynamics that are central to advancing energy storage design. In this work, we employ coarse-grained molecular dynamics simulations with smeared electrostatics and mass to isolate the role of electrostatic correlations and chain length on ion transport in solvent-free PILs. This model enables access to long chain lengths and entangled regimes and is constructed such that it eliminates glassy slowdown. We find that introducing electrostatics slightly stiffens the polymer chains, slows their relaxation, and reduces diffusivity. Nevertheless, the charged system retains ideal chain statistics and exhibits the same Rouse-to-reptation crossover observed in the analogous uncharged system. Moreover, although polyanion diffusivity decreases sharply with chain length, the ion conductivity remains nearly constant. Analysis of the Onsager transport coefficients reveals that this behavior arises from a competition between the slowdown of polymer diffusion and enhanced interchain correlations. This competition and the resulting conductivity behavior persist even in the absence of electrostatic interactions, highlighting the role of melt incompressibility rather than charge-mediated effects. These findings reveal an intrinsic decoupling between charge transport and chain relaxation that does not rely on glass transition, suggesting that mechanical properties can, in principle, be tuned via the chain length without compromising conductivity.