Influence of molecular weight on ion-transport properties of polymeric ionic liquids
JR Keith and S Mogurampelly and F Aldukhi and BK Wheatle and V Ganesan, PHYSICAL CHEMISTRY CHEMICAL PHYSICS, 19, 29134-29145 (2017).
We report the results of atomistic molecular dynamics simulations on polymerized 1-butyl-3-vinylimidazolium-hexafluorophosphate ionic liquids, studying the influence of the polymer molecular weight on the ion mobilities and the mechanisms underlying ion transport, including ion-association dynamics, ion hopping, and ion-polymer coordinations. With an increase in polymer molecular weight, the diffusivity of the hexafluorophosphate (PF6-) counterion decreases and plateaus above seven repeat units. The diffusivity is seen to correlate well with the ion- association structural relaxation time for pure ionic liquids, but becomes more correlated with ion-association lifetimes for larger molecular weight polymers. By analyzing the diffusivity of ions based on coordination structure, we unearth a transport mechanism in which the PF6- moves by "climbing the ladder'' while associated with four polymeric cations from two different polymers.
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