Eur. Phys. J. E (2009) 30: 55-64
https://doi.org/10.1140/epje/i2009-10506-7

Regular Article

Defect structures in nematic liquid crystals around charged particles

¹ Department of Physics, Kyoto University, 606-8502, Sakyo-ku, Kyoto, Japan
² Institute of Industrial Science, University of Tokyo, 153-8505, Meguro-ku, Tokyo, Japan

^* e-mail: araki@scphys.kyoto-u.ac.jp

Received: 28 January 2009
Revised: 27 May 2009
Accepted: 5 August 2009
Published online: 15 September 2009

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 is positive, Saturn-ring defects are formed around the particles. For < 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 > 0 and in the perpendicular plane for < 0 with respect to the background director. For identically charged pairs the preferred directions for > 0 and < 0 are exchanged. We also examine 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.