Issue 5, 2017

Nanostructuration of ionic liquids: impact on the cation mobility. A multi-scale study

Abstract

When probed at the macroscopic scale, Ionic Liquids (ILs) behave as highly dissociated (i.e. strong) electrolytes while, at the molecular scale, they show clear characteristics of weak ionic solutions. The multi-scale analysis we report in this paper reconciles these apparently at odds behaviors. We investigate by quasi-elastic neutron scattering (QENS) and neutron spin-echo (NSE), the nanometer/nanosecond dynamics of OMIM-BF4, an imidazolium-based IL showing strong nanostructuration. We also probe the same IL on the microscopic (μm and ms) scale by pulsed field gradient NMR. To interpret the neutron data, we introduce a new physical model to account for the dynamics of the side-chains and for the diffusion of the whole molecule. This model describes the observables over the whole and unprecedented investigated spatial ([0.15–1.65] Å−1) and time ([0.5–2000] ps) ranges. We arrive at a coherent and unified structural/dynamical description of the local cation dynamics: a localized motion within the IL nanometric domains is combined with a genuine long-range translational motion. The QENS, NSE and NMR experiments describe the same long-range translational process, but probed at different scales. The associated diffusion coefficients are more than one order of magnitude different. We show how this apparent discrepancy is a manifestation of the IL nanostructuration.

Graphical abstract: Nanostructuration of ionic liquids: impact on the cation mobility. A multi-scale study

Supplementary files

Article information

Article type
Paper
Submitted
27 sep. 2016
Accepted
20 des. 2016
First published
23 des. 2016

Nanoscale, 2017,9, 1901-1908

Nanostructuration of ionic liquids: impact on the cation mobility. A multi-scale study

F. Ferdeghini, Q. Berrod, J. Zanotti, P. Judeinstein, V. G. Sakai, O. Czakkel, P. Fouquet and D. Constantin, Nanoscale, 2017, 9, 1901 DOI: 10.1039/C6NR07604A

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