Towards Nematic Phases in Ionic Liquid Crystals – A Simulation Study

Abstract

Ionic liquid crystals (ILCs) are soft matter materials with broad liquid crystalline phases and intrinsic electric conductivity. They typically consist of a rod-shaped mesogenic ion and a smaller spherical counter-ion. Their mesomorphic properties can be easily tuned by exchanging the counter ion. ILCs show a strong tendency to form smectic A phases due to the segregation of ionic and the non-ionic molecular segments. Nematic phases are therefore extremely rare in ILCs and the question of why nematic phases are so exceptional in existing ILCs, and how nematic ILCs might be obtained in the future is of vital interest for both the fundamental understanding and the potential applications of ILCs. Here, we present the result of a simulation study, which highlights the crucial role of the location of the ionic charge on the rod-like mesogenic ions in the phase behaviour of ILCs. We find that shifting the charge from the ends towards the centre of the mesogenic ion destabilizes the liquid crystalline state and induces a change from smectic A to nematic phases.

Amphiphilic salts as single-component, solvent-free, lithium electrolytes

“…Recent coarse-grained simulations suggest that ionic liquid crystals with the charge located at the center of the mesogen may form nematics while in the amphiphilic case like we are concerned with here, the smectic is the only LC phase observed with direct transition to the isotropic. 46 Either way, whether the broad scattering in each LiC10TFSI and LiC18TFSI is from the isotropic or nematic phase, the ion clusters in those phases must be relatively disordered much like in an ionic liquid. Upon cooling of LiC10TFSI from 160 ℃ to 130 ℃, below the small DSC peak observed at 149 ℃, there was little immediate change to the scattering profile.…”

Phase behaviour of mixtures of charged soft disks and spheres

“…mixtures of charged hard spherocylinders and hard spheres 11 or mixtures of soft Gay-Berne ellipsoids and Lennard-Jones spheres. [12][13][14][15][16][17] On the other hand, ionic discotic systems have been less studied, using highly coarse-grained models, with some notable exceptions of colloidal suspensions of platelet particles using Monte Carlo simulations. 18,19 However, to the best of our knowledge, there are no reports in the literature of simulations of mixtures of oppositely charged discotic and spherical soft particles as models of discotic ILCs.…”

“…mixtures of charged hard spherocylinders and hard spheres 11 or mixtures of soft Gay-Berne ellipsoids and Lennard-Jones spheres. 12–17…”