Electrically assisted light-induced gliding of nematic liquid-crystal easy axis at varying polarization azimuth of reorienting light: model and experiment

TL;DR

This paper extends a torque balance model to analyze how the nematic liquid crystal easy axis reorients under combined electric field and polarized UV light, supported by experiments showing polarization azimuth effects.

Contribution

The study generalizes the torque balance model to include varying polarization azimuth and validates it with experimental data on liquid crystal reorientation.

Findings

Reorientation occurs outside interelectrode gaps at non-zero polarization azimuth.

Reorientation dynamics slow down with increasing azimuth angle.

Sense of easy axis rotation is independent of azimuth sign.

Abstract

The phenomenological torque balance model previously introduced to describe the electrically assisted light-induced gliding is generalized to study the reorientation dynamics of the nematic liquid crystal easy axis at photoaligned azo-dye films under the combined action of in-plane electric field and reorienting UV light linearly polarized at varying polarization azimuth, $\varphi_p$. We systematically examine the general properties of the torque balance model by performing analysis of the bifurcations of equilibria at different values of the polarization azimuth and apply the model to interpret the experimental results. In our experiments, it is found that, in contrast to the case where $\varphi_p=0$ and the light polarization vector is parallel to the initial easy axis, at $\varphi_p\ne 0$, the pronounced purely photoinduced reorientation occurs outside the interelectrode gaps. It is also observed that, in the regions between electrodes with non-zero electric field, the dynamics of reorientation slows down with $\varphi_p$ and the sense of easy axis rotation is independent of the sign of $\varphi_p$.