Direct Comparison of Atomistic Molecular Dynamics Simulations and X-ray Scattering of Polymerized Ionic Liquids

The design of solid-state electrolytes for electrochemical applications that utilize polymerized ionic liquids (polyILs) would greatly benefit from a molecular-level understanding of structure-function relationships. We herein use atomistic molecular dynamics simulations to investigate the structural properties of a homologous series of poly(n-alkyl-vinylimidzolium bistrifluoromethylsulfonylimide) poly(nVim Tf2N) and present the first direct comparison of the structure factors obtained from X-ray scattering and simulations. Excellent agreement is found in terms of peak position and shape. The backbone-to-backbone correlation length increases at a rate of 1 Å/CH₂. The longer alkyl chains lead to the longer backbone-to-backbone separation and the larger nonpolar nanodomains. This quantitative comparison of atomistic simulations to X-ray scattering will lead to a fundamental understanding in structure and morphology of polyILs and pave a path forward toward the rational design of future polyILs for electrochemical devices.