Nuclear magnetic resonance studies of translational diffusion in thermotropic ionic liquid crystals

Abstract

The NMR methodologies employed for investigating translational diffusion in anisotropic fluids and the results of their applications to ionic liquid crystals are reviewed. Experiments on ionic liquid crystals are preferably performed using oriented samples and require magnetic field gradients in orthogonal directions. Diffusion experiments in anisotropic systems with broad NMR lines are performed using line narrowing techniques and by application of strong static or pulsed field gradients for efficient gradient encoding/decoding of the spatial locations of molecules. Self-diffusion studies on various thermotropic ion-conductive materials exhibiting smectic, cubic, and columnar phases have been reported. Diffusion rates and anisotropy characterise the translational dynamics of ions in nanostructures and reflect the molecular ordering and ion pairing/dissociation processes. Distinct diffusion behaviours were observed for cations and anions. The knowledge of molecular mobility in ionic liquid crystals is important for the understanding their dynamic properties and is, therefore, valuable for the development of anisotropic soft materials for ion transport.