Electrically Switchable Multi‐Stable Topological States Enabled by Surface‐Induced Frustration in Nematic Liquid Crystal Cells

Abstract

In liquid crystal (LC) cells, the surface patterning directs the self‐assembly of the uniaxial building blocks in the bulk, enabling the design of stimuli‐response optical devices with various functionalities. The combination of different anchoring patterns at both substrates can lead to surface induced frustration, preventing a purely planar and defect‐free configuration. In cells with crossed assembly of rotating anchoring patterns, elastic deformations allow to obtain a defect‐free bulk configuration, but an electrical stimulus can induce disclination lines. The disclination network is preserved without applied voltage. Depending on the electric field treatment and geometrical parameters, different multi‐stable states with and without disclinations are obtained. This is demonstrated with the help of dual‐frequency LCs, for which the frequency dependent dielectric properties allow repeatable switching between multi‐stable states. Topological protection and the associated energy barrier between different states explains the observed metastability. The obtained configurations are retrieved with Q‐tensor simulations and the validity is confirmed by matching optical simulations with experimentally obtained microscopy images. The realized multi‐stable topological states interact differently with light, resulting in distinct optical properties. Optimization allows to switch between a highly transparent state and an opaque state, opening up opportunities for smart windows with low energy consumption.