Flexoelectricity and competition of time scales in electroconvection

TL;DR

This paper investigates how flexoelectric effects influence electroconvection in nematic liquid crystals, revealing novel behaviors when director relaxation and driving frequency timescales are comparable, and providing theoretical explanations for observed phenomena.

Contribution

It introduces the role of flexoelectricity in electroconvection, explaining experimental results and extending theoretical models to account for new behaviors in nematic liquid crystals.

Findings

Flexoelectric effects explain quantitative behavior of conductive s-EC thresholds.

Nonstandard EC exhibits similar frequency dependence as dielectric s-EC.

Threshold voltages vary significantly with frequency depending on EC type.

Abstract

Novel behavior in electroconvection (EC) has been detected in nematic liquid crystals (NLCs) under the condition of comparable timescales of the director relaxation and the period of the driving ac voltage. The studied NLCs exhibit standard EC (s-EC) at the onset of the instability, except one compound in which nonstandard EC (ns-EC) has been detected. In the relevant frequency region, the threshold voltage for conductive s-EC bends down considerably, while for dielectric s-EC it bends up strongly with the decrease of the driving frequency. We show that inclusion of the flexoelectric effect into the theoretical description of conductive s-EC leads to quantitative agreement, while for dielectric s-EC a qualitative agreement is achieved. The frequency dependence of the threshold voltage for ns-EC strongly resembles that of the dielectric s-EC.