Temporal response to harmonic driving in electroconvection

TL;DR

This study investigates the temporal dynamics of electroconvection patterns in nematic liquid crystals under harmonic driving, confirming theoretical predictions and revealing how traveling patterns and anisotropy types influence pattern evolution.

Contribution

It provides experimental validation of theoretical models for electroconvection patterns and explores the effects of traveling patterns and anisotropy on temporal behavior.

Findings

Stationary s-EC and ns-EC patterns match theoretical predictions.

Traveling conductive EC patterns show altered temporal evolution depending on Hopf frequency.

Patterns with positive anisotropies develop and decay faster than the driving period.

Abstract

The temporal evolution of the spatially periodic electroconvection (EC) patterns has been studied within the period of the driving ac voltage by monitoring the light intensity diffracted from the pattern. Measurements have been carried out on a variety of nematic systems, including those with negative dielectric and positive conductivity anisotropy, exhibiting "standard EC" (s-EC), those with both anisotropies negative exhibiting "non-standard EC" (ns-EC), as well as those with the two anisotropies positive. Theoretical predictions have been confirmed for stationary s-EC and ns-EC patterns. Transitions with Hopf bifurcation have also been studied. While traveling had no effect on the temporal evolution of dielectric s-EC, traveling conductive s-EC and ns-EC patterns exhibited a substantially altered temporal behavior with a dependence on the Hopf frequency. It has also been shown that in nematics with both anisotropies positive, the pattern develops and decays within an interval much shorter than the period, even at relatively large driving frequencies.