Twist-bend heliconical chiral nematic liquid crystal phase of an achiral rigid bent-core mesogen

TL;DR

This paper reports the discovery of a twist-bend heliconical nematic phase in an achiral bent-core liquid crystal, showing nanoscale modulation and chiral domain formation under an electric field.

Contribution

It demonstrates the existence of a twist-bend nematic phase in an achiral, rigid bent-core mesogen, expanding understanding of chiral nematic phases beyond chiral molecules.

Findings

Nanoscale periodic modulation with a pitch of ~14 nm.

Formation of macroscopic focal-conic textures.

Observation of chiral domains under electric field.

Abstract

The chiral, heliconical (twist-bend) nematic ground state is reported in an achiral, rigid, bent-core mesogen (UD68). Similar to the nematic twist-bend (NTB) phase observed in bent molecular dimers, the NTB phase of UD68 forms macroscopic, smectic-like focal-conic textures and exhibits nanoscale, periodic modulation with no associated modulation of the electron density, i.e., without a detectable lamellar x-ray reflection peak. The NTB helical pitch is pTB ~ 14 nm. When an electric field is applied normal to the helix axis, a weak electroclinic effect is observed, revealing 50 um-scale left- and right-handed domains in a chiral conglomerate.