Twist, splay, and uniform domains in ferroelectric nematic liquid crystals

TL;DR

This paper explores the complex defect phenomena and domain structures in ferroelectric nematic liquid crystals, analyzing how electrostatic, elastic, and surface effects influence domain formation and size.

Contribution

It provides new insights into the interplay of electrostatic, elastic, and surface effects on domain structures in ferroelectric nematic liquid crystals, supported by experiments and calculations.

Findings

Electrostatic interactions shrink domain size.

Elastic and surface effects promote larger domains.

Ionic screening suppresses domain formation.

Abstract

The newly-discovered ferroelectric nematic liquid crystal exhibits a variety of unique defect phenomena. The depolarization field in the material favors spontaneous spatial variations in polarization, manifesting in diverse forms such as bulk twists and arrangements of alternating polarization domains. The configuration of these domains is governed by a balance between depolarization field reduction and molecular alignment at interfaces. We investigate a ferroelectric nematic confined in a thin cell with apolar surface anchoring, patterned using photoalignment. Under uniform planar alignment, the system forms stripes, while a radial +1 defect pattern results in pie-slice domains. Neighboring domains show either opposite directions of uniform polarization (thin cells) or opposite handedness of the spontaneous twist (thick cells). Our calculations and experiments demonstrate that electrostatic interactions tend to shrink domain size, whereas elastic and surface anchoring effects promote larger domains. In this work, we make predictions and measurements of the domain size as a function of cell thickness, and show that ionic screening suppresses domain formation.