Understanding Segmental Dynamics in Polymer Electrolytes: A Computer Study

TL;DR

This study uses microscopic simulations to analyze the segmental dynamics of poly(ethylene oxide) in both neat and electrolyte forms, verifying Rouse theory applicability and revealing effects of cation interactions on polymer mobility.

Contribution

It demonstrates the applicability of Rouse theory to polymer electrolytes and elucidates how cation-polymer interactions influence segmental dynamics and heterogeneities.

Findings

Rouse modes are orthogonal despite non-exponential relaxation.

Cation binding increases local friction, slowing segmental dynamics.

Rouse predictions match well for electrolyte segments except at very short times.

Abstract

We study the segmental dynamics of poly(ethylene oxide) (PEO) from microscopic simulations in the neat polymer and a polymer electrolyte (PEO/LiBF$_4$) by analyzing the normal modes. We verify the applicability of the Rouse theory, specifically for the polymer electrolyte where dynamic heterogeneities, arising from cation-polymer interactions, alter the mobility non-uniformly along the chains. We find that the Rouse modes for both the systems are orthogonal despite the presence of non-exponential relaxation of the modes and violation of the Gaussian self-similarity of the chains. The slowdown of the segmental dynamics in the polymer electrolyte is rationalised by an order of magnitude increase in the friction coefficient for those monomers which are bound by cations. In general, for the electrolyte the Rouse predictions for the dynamics of segments (both free and/or bound) agree well except for very short times.