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arXiv · 1806.05000

Importance of reorientational dynamics for the charge transport in ionic liquids

P. Sippel·S. Krohns·D. Reuter·P. Lunkenheimer·A. Loidl
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Abstract

Most ionic liquids contain at least one rather complex ion species exhibiting a dipolar moment. In the present work, we provide a thorough evaluation of broadband dielectric spectra of 12 ionic liquids taking into account the often neglected reorientational dynamics of these ions. We confirm that this dynamics leads to a clear relaxational signature in the spectra, a fact that so far only was considered in few previous works. The obtained reorientational relaxation times are well consistent with earlier inelastic light-scattering and high-frequency dielectric investigations. Evaluating our dielectric spectra in terms of reorientational motions reveals a close coupling of the ion-rotation dynamics to the ionic charge transport in a broad temperature range from the low-viscosity liquid above room temperature deep into the high-viscosity supercooled state close to Tg. This coupling does not seem to be mediated by the viscosity but probably is of more direct nature, pointing to a revolving-door mechanism as also considered for plastic-crystalline ionic conductors. Our results show that the reorientational motion of the dipolar ions plays a significant and so far widely overlooked role for the ionic charge transport in ionic liquids.

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P. Sippel, S. Krohns, D. Reuter, P. Lunkenheimer, A. Loidl. 2018-08-10. Importance of reorientational dynamics for the charge transport in ionic liquids. https://doi.org/10.1103/physreve.98.052605

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