Investigation of Dynamics in BMIM TFSA Ionic Liquid through Variable Temperature and Pressure NMR Relaxometry and Diffusometry

Abstract

A comprehensive variable temperature, pressure and frequency multinuclear (1H, 2H, and 19F) magnetic resonance study was undertaken on selectively deuterated 1-butyl-3-methylimidazolium bis(trifluoromethylsulfonyl)amide (BMIM TFSA) ionic liquid isotopologues. This study builds on our earlier investigation of the effects of increasing alkyl chain length on diffusion and dynamics in imidazolium-based TFSA ionic liquids. Fast field cycling 1H T1 data revealed multiple modes of motion. Through calculation of diffusion coefficient (D) values and activation energies, the low- and high-field regimes were assigned to the translational and reorientation dynamics respectively. Variable-pressure 2H T1 measurements reveal site-dependent interactions in the cation with strengths in the order MD3 > CD3 > CD2, indicating dissimilarities in the electric field gradients along the alkyl chain, with the CD2 sites having the largest gradient. Additionally, the α saturation effect in T1 vs. P was observed for all three sites, suggesting significant reduction of the short-range rapid reorientational dynamics. This reduction was also deduced from the variable pressure 1H T1 data, which showed an approach to saturation for both the methyl and butyl group terminal methyl sites. Pressure-dependent D measurements show independent motions for both cations and anions, with the cations having greater D values over the entire pressure range.

Application of proton field‐cyclingNMRrelaxometry for studying translational diffusion in simple liquids and polymer melts

“…In recent years, so‐called room temperature ionic liquids with both cations and anions bearing organic groups have gained broad interest. Often several NMR‐active nuclei such as fluorine or phosphorus in addition to protons are present, and one can exploit the selectivity of NMR: performing FC experiments on different nuclei . However, increasing the number of different spin species makes the relaxation analysis rather involved.…”

Relationship between Translational and Rotational Dynamics of Alkyltriethylammonium-Based Ionic Liquids

“…Much less studies have been performed for ionic liquids. There is, however, a growing awareness that NMR relaxometry is a very valuable source of information about ionic dynamics, both the cation and the anion, in bulk ionic liquids and in confinement [22][23][24][25][26][27][28][29]. One should also point out that Electron Spin Resonance gives a highly valuable insight into dynamical properties of ionic liquids by investigating the performance of paramagnetic probes placed in ionic liquids [30][31][32][33][34].…”

Reorientation dynamics and ion diffusivity of neat dimethylimidazolium dimethylphosphate probed by NMR spectroscopy

“…48,86 We wish to point out that eld-cycling NMR relaxometry is successfully employed to investigate the dynamics of ILs recently. 26,45,47,63,[87][88][89][90][91][92] Although from a theoretical point of view similar in size, the [C 1 C 1 IM] + cation and the [(CH 3 ) 2 PO 4 ] À anion reveal different reorientation mobilities and diffusivities. The [(CH 3 ) 2 PO 4 ] À anion shows a three to ve times faster reorientation at room temperature compared to the cation.…”