In-situ measurements of twist and bend elastic constants in oblique helicoidal cholesteric

TL;DR

This paper reports direct in-situ measurements of twist and bend elastic constants in oblique helicoidal cholesteric liquid crystals, revealing their temperature dependence and implications for optical device development.

Contribution

It introduces a method to measure elastic constants directly in the cholesteric phase using electric field response, advancing understanding of ChOH properties.

Findings

Measured K22 and K33 elastic constants directly in ChOH.

Determined temperature dependence of elastic constants.

Explored electric tunability of the ChOH pitch.

Abstract

Unique electro-optical properties of the oblique helicoidal cholesteric (ChOH) stem from its heliconical director structure. An applied electric field preserves the single harmonic modulation of the director while tuning the ChOH period and the corresponding Bragg peak wavelength within a broad spectral range. We use the response of ChOH to the electric field to measure the elastic constants of twist K22 and bend K33 directly in the cholesteric phase. The temperature dependencies of K22 and K33 allow us to determine the range of the electric tunability of the ChOH pitch and the heliconical angle. The data are important for understanding how molecular composition and chirality influence macroscopic elastic properties of the chiral liquid crystals and for the development of ChOH-based optical devices.