(28c) Quantitative Structure Analysis of Polymerized Ionic Liquids with Atomistic Molecular Simulations

The design of solid-state electrolytes for electrochemical applications that utilize polymerized ionic liquids (polyiLs) would require the elucidation of molecular-level understanding of structure-property relationships. Atomistic molecular dynamics simulations are used to investigate the structural properties of a homologous series of poly(n­alkyl-vinylimidzolium bistrifluoromethylsulfonylimide) poly(CnVim Tf2N) and present the direct S(q) comparison with experiment. Excellent agreement is found in terms of peak position and shape. The quantitative cluster analysis along with color-coded snapshots vividly demonstrates that discrete nonpolar islands first form within the continuo polar network, then nonpolar domains grow beyond the percolation threshold, finally interconnect with the polar network into a bicontinuous 'sponge-like' nanostructure. Moreover, we exploit the selective labeling technique of neutron scattering using hydrogen/deuterium substitution to afford further insight into the morphology of poly(CnVi Tf2N). The neutron scattering profiles markedly depend on the isotopic substitution pattern. The total neutron structure factors of the backbone deuterated samples reveal the most noticeable low-q peak and are much more intense than those observed in single isotope neutron scattering. We also investigate a model ammonium based polyiLs and anion effect. We hope these insights will lead to a fundamental understanding into the structure and morphology of polylls and pave a path forward towards the rational design of future polyiLs for electrochemical devices.