Multiscale NMR investigation of mesogenic ionic-liquid electrolytes with strong anisotropic orientational and diffusional behaviour

Abstract

A new class of mesogenic ionic-liquid electrolytes made of long-chain imidazolium cations mixed with lithium salts is described. Fast, homogeneous and uniform orientational alignment of these systems can be obtained by cooling the mixture from the isotropic melt under magnetic constraint (magnetic fields of 9.4 and 14.1 T). The local orientational behaviour of the different species inside the electrolyte and the ionic diffusional properties in oriented phases of these new materials are investigated by NMR of ²H, ⁷Li and ¹¹B quadrupolar nuclei and PFG-NMR measurements, respectively. Interestingly, the local orientation of C–H internuclear directions along the alkyl chains of the imidazolium cations is examined using natural abundance deuterium (NAD) 2D-NMR spectroscopy, thus avoiding any isotopic enrichment of material. The large anisotropy of self-diffusion coefficients measured from mobile ions (Li⁺ and BF₄⁻) evidences the long-range alignment of ionic slabs of these materials.