Field-induced motion of nematic disclinations

TL;DR

This paper investigates how external magnetic fields influence the motion and interactions of disclinations in nematic liquid crystals, revealing a velocity scaling law and the potential to control defect annihilation.

Contribution

It provides a theoretical analysis of disclination dynamics under external fields, including velocity scaling and defect interaction modifications, which was not previously detailed.

Findings

Disclination velocity scales as H/|log H| with field strength.

External fields can prevent disclination annihilation.

The dynamics of defect pairs are significantly altered by applied fields.

Abstract

An individual defect in a nematic liquid crystal moves not only in response to its interaction with other defects but also in response to an external field. We analyze the motion of a wedge disclination in the presence of an applied field of strength $H$. We neglect backflow and seek steadily travelling patterns. The stationary picture yields a semi-infinite wall of strength $\pi$, bounded by the defect line. We find that the disclination advances into the region containing the wall at velocity $v(H)$, where $v$ scales as $H/|\log H|$ as long as the magnetic coherence length is greater than the core radius. When the external field is applied in the presence of a pair of disclinations, their dynamics is strongly influenced. We compute the expected relative velocity of the disclinations as a function of distance and field. The natural tendency for the disclinations to annihilate each other can be overcome by a sufficiently strong field suitably directed.