Polymerized ionic liquids (polyILs) are touted as the ideal solid-state electrolyte materials for electrochemical devices due to enhanced mechanical characteristics of polymer nature and unique physico-chemical properties inherent from ionic liquids. PolyILs offer great flexibility in designing the task specific media through judicious choosing component cations, anions and polymer structures for a wide range of energy conversion and storage applications, such as dye-sensitized solar cells, lithium ion rechargeable batteries, and alkaline fuel cells. While polyILs enjoy many favorable properties such as low flammability, high thermal/chemical/electrochemical stability, and mechanical strength, they inevitably suffer from the retarded ionic conductivity, one of the detrimental shortcomings in electrochemical applications.  PolyILs usually have elevated glass transition temperature Tg and subsequently several orders of magnitude decrease in ionic conductivity with respect to their molecular IL counterparts. Most of previous research involve in finding the optimal polyILs to achieve the maximum accessible ionic conductivity. It is generally accepted that ionic conductivity of polyILs depends on the complex correlations between chemical nature of polymer backbone and counter-ions, glass transition temperature, mesophase morphology, temperature and pressure. Therefore, a molecular-level understanding of the relationship between chemical structure, morphology and ion transport will promote the rational design of polyILs for electrochemical applications.

In present work, we use atomistic molecular dynamics simulations to investigate structural properties of model system poly(1-n-alkyl-3vinylimidzolium bistrifluoromethylsulfonylimide) poly(nVim Tf2N) . X-ray scattering measurement on structural properties of polyILs is elusive. The detailed simulations provide a direct quantitative picture for understanding the structure/morphology of polyILs on the atomic scale. In particular, we present the first direct comparison of structure factors obtained from X-ray scattering and simulations for various alkyl chain length of poly(nVim Tf2N). Excellent agreement is found between the experimental and simulated scattering profiles in terms of peak position and shape, which provides proper validation of our simulation methods.  All characteristic distances (backbone-to-backbone, anion-to-anion and pendant-to-pendant) are well reproduced. As the alkyl chain length increases, the backbone-to-backbone peak becomes stronger, moving to larger distance, the anion-to-anion separation slightly increases with vanishing intensity, and the pendant-to-pendant peak hardly changes. This quantitative comparison of X-ray scattering and atomistic simulations is expected to lead to a molecular-level predictive understanding in structure and morphology of polyILs and paves a substantive step towards the rational design of future polyILs for electrochemical devices.