Dynamics of Ionic Liquids in Confinement by Means of NMR Relaxometry-EMIM-FSI in a Silica Matrix as an Example.

Danuta Kruk,Malgorzata Florek-Wojciechowska,Rajendra Kumar Singh,Milosz Wojciechowski

doi:10.3390/ma13194351

Danuta Kruk, Malgorzata Florek-Wojciechowska + Show 2 more

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https://doi.org/10.3390/ma13194351

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Abstract

1H and 19F spin–lattice relaxation studies for 1-ethyl-3-methylimidazolium bis(fluorosulfonyl)imide in bulk and mesoporous MCM-41 silica matrix confinement were performed under varying temperatures in a broad range of magnetic fields, corresponding to 1H resonance frequency from 5Hz to 30MHz.A thorough analysis of the relaxation data revealed a three-dimensional translation diffusion of the ions in the bulk liquid and two-dimensional diffusion in the vicinity of the confining walls in the confinement. Parameters describing the translation dynamics were determined and compared. The rotational motion of both kinds of ions in the confinement was described by two correlation times that might be attributed to anisotropic reorientation of these species.

Highlights

The dynamical properties of ionic liquids in confinement are of high interest from the point of view of fundamental as well as applied science
Conclusions and 19 F spin–lattice relaxation studies were performed for EMIM-FSI in bulk and mesoporous
The 3D character of the ionic diffusion in bulk was confirmed by revealing the linear dependencies of the 1 H and 19 F spin–lattice relaxation rates on a squared root of the corresponding resonance frequencies

Summary

Introduction

The dynamical properties of ionic liquids in confinement are of high interest from the point of view of fundamental as well as applied science. In both cases, the underlying question concerns the influence of the interactions with the confining walls on the translational and rotational diffusion of the ions. Attempt to gain this type of information is to measure the translation diffusion coefficient using nuclear magnetic resonance (NMR) gradient methods. This concept is based on differences in the resonance frequencies of NMR active nuclei (nuclei possessing a spin) caused by the diffusion in a magnetic field with controlled inhomogeneity (a magnetic field gradient) [1,2]. This concept sounds attractive because one is approaching the ionic dynamics on the atomistic level by probing the time scale of the fluctuations of spin interactions

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Conclusion