Defect structures in nematic liquid crystals around charged particles

TL;DR

This study uses numerical simulations to explore how charged particles influence defect structures in nematic liquid crystals, revealing new defect types and alignment behaviors depending on dielectric anisotropy and anchoring effects.

Contribution

It introduces a Ginzburg-Landau model incorporating inhomogeneous electric fields to analyze defect formations around charged particles in nematic liquid crystals, identifying novel defect structures and alignment preferences.

Findings

Saturn ring defects form for positive dielectric anisotropy.

Novel

Ansa

Abstract

We numerically study the orientation deformations in nematic liquid crystals around charged particles. We set up a Ginzburg-Landau theory with inhomogeneous electric field. If the dielectric anisotropy varepsilon_1 is positive, Saturn ring defects are formed around the particles. For varepsilon_1<0, novel "ansa" defects appear, which are disclination lines with their ends on the particle surface. We find unique defect structures around two charged particles. To lower the free energy, oppositely charged particle pairs tend to be aligned in the parallel direction for varepsilon_1>0 and in the perpendicular plane for varepsilon_1<0 with respect to the background director . For identically charged pairs the preferred directions for varepsilon_1>0 and varepsilon_1<0 are exchanged. We also examie competition between the charge-induced anchoring and the short-range anchoring. If the short-range anchoring is sufficiently strong, it can be effective in the vicinity of the surface, while the director orientation is governed by the long-range electrostatic interaction far from the surface.