Topology and Bistability in liquid crystal devices

TL;DR

This paper investigates the topological configurations and bistability mechanisms in nematic liquid crystal devices, specifically the PABN cell, using continuum modeling, numerical simulations, and experimental comparisons.

Contribution

It identifies four distinct topologies in the PABN cell and constructs initial configurations to explore their energetics and stability, revealing a topological basis for bistability.

Findings

Four topologies identified in PABN cell

Numerical solutions agree with experimental morphologies

Topological mechanism proposed for bistability

Abstract

We study nematic liquid crystal configurations in a prototype bistable device - the Post Aligned Bistable Nematic (PABN) cell. Working within the Oseen-Frank continuum model, we describe the liquid crystal configuration by a unit-vector field, in a model version of the PABN cell. Firstly, we identify four distinct topologies in this geometry. We explicitly construct trial configurations with these topologies which are used as initial conditions for a numerical solver, based on the finite-element method. The morphologies and energetics of the corresponding numerical solutions qualitatively agree with experimental observations and suggest a topological mechanism for bistability in the PABN cell geometry.