Weak Anchoring Effects in Nematic Liquid Crystals

Abstract

We consider a twisted nematic liquid crystal confined by two parallel boundary plates. The nematic is subject to an in-plane magnetic field applied in a direction parallel to the plates. At the lower plate the director is strongly anchored so that the director twist is fixed. On the upper surface we introduce an easy direction for the director. Although the director prefers to align with the easy direction, the actual twist exhibited at the upper surface may differ from the easy direction twist. This is due to the competition between elastic, magnetic and anchoring effects. We examine and compare two surface energies that model the weak anchoring at the upper plate. For both energies, equilibrium twist profiles for the director within the sample have been obtained by minimizing the total free energy for the system.

Influence of weak anchoring upon the alignment of smectic A liquid crystals with surface pretilt

“…In many of these instances there will be a surface twist of the director in addition to the surface tilt that is described here. Recent work on weak anchoring for surface twist with no director tilt has been carried out on nematics by McKay et al [24], based on the work of Rapini-Papoular [14] and Belyakov et al [25], and these results will provide motivation for examining the problems discussed here in the context of more involved boundary phenomena. Although the aforementioned details are in the context of ferroelectric smectics, they are directly relevant to the understanding of the induced SmC phase discussed here for SmA samples.…”