Dynamics of a sheared twist bend nematic liquid crystal

TL;DR

This study investigates the flow behavior of twist-bend nematic liquid crystals under shear, revealing distinct stress responses, hysteresis, and dynamic oscillations, aligning with theoretical predictions for sheared nematogenic fluids.

Contribution

It provides the first detailed experimental characterization of shear stress responses and dynamic oscillations in twist-bend nematic liquid crystals, confirming theoretical models.

Findings

Three shear stress response regions identified

Hysteresis observed between regions II and III

Dynamic stress oscillations in the plateau region

Abstract

We study the flow behaviour of a twist-bend nematic $(N_{TB})$ liquid crystal. It shows three distinct shear stress ($\sigma$) responses in a certain range of temperatures and shear rates ($\dot{\gamma}$). In Region-I, $\sigma\sim\sqrt{\dot{\gamma}}$, in region-II, the stress shows a plateau, characterised by a power law $\sigma\sim{\dot{\gamma}}^{\alpha}$, where $\alpha\sim0.1-0.4$ and in region-III, $\sigma\sim\dot{\gamma}$. With increasing shear rate, $\sigma$ changes continuously from region-I to II, whereas it changes discontinuously with a hysteresis from region-II to III. In the plateau (region-II), we observe a dynamic stress fluctuations, exhibiting regular, periodic and quasiperiodic oscillations under the application of steady shear. The observed spatiotemporal dynamics in our experiments are close to those were predicted theoretically in sheared nematogenic fluids.