Bistable anchoring of nematics on rough substrates

TL;DR

This paper investigates how rough substrates influence the anchoring behavior of nematic liquid crystals, revealing conditions for bistability and transitions between different orientations.

Contribution

It provides a detailed phase diagram for nematic anchoring on disordered substrates, highlighting regimes of coupled and decoupled wetting and anchoring transitions.

Findings

Identification of two regimes: strongly coupled and weakly coupled.

Anchoring transition is first order, switching between homeotropic and planar.

Surfaces can be engineered to produce bistable nematic orientations.

Abstract

We analyze the interplay between wetting and anchoring of nematic liquid crystals on disordering, e.g., rough substrates in the framework of the Landau-de Gennes theory, in situations of competing homeotropic and planar easy axes on the substrate and the nematic-isotropic (NI) interface. The phase diagram for azimuthally symmetric substrates is calculated. We identify two regimes - a strongly coupled regime, where the wetting transition coincides with an anchoring transition, and a weakly coupled regime, where the two are separated. The anchoring transition is first order and switches between homeotropic and planar anchoring. The two competing orientations are metastable over a broad parameter range. Hence such surfaces can be used to generate bistable surfaces.