Patterns driven by combined AC and DC electric fields in nematic liquid crystals

TL;DR

This paper investigates how combined ac and dc electric fields influence pattern formation in nematic liquid crystals, using a theoretical model and experiments to understand the conditions that enhance or suppress electroconvection and flexoelectric patterns.

Contribution

It introduces an extended model for electro-hydrodynamic instabilities under combined ac and dc fields and compares theoretical predictions with experimental results.

Findings

Combined ac and dc fields can either promote or inhibit pattern formation.

Theoretical predictions generally match experimental observations.

Discrepancies suggest the need for further model refinement.

Abstract

The effect of superimposed ac and dc electric fields on the formation of electroconvection and flexoelectric patterns in nematic liquid crystals was studied. For selected ac frequencies an extended standard model of the electro-hydrodynamic instabilities was used to characterize the onset of pattern formation in the two-dimensional parameter space of the magnitudes of the ac and dc electric field components. Numerical as well as approximate analytical calculations demonstrate that depending on the type of patterns and on the ac frequency, the combined action of ac and dc fields may either enhance or suppress the formation of patterns. The theoretical predictions are qualitatively confirmed by experiments in most cases. Some discrepancies, however, seem to indicate the need to extend the theoretical description.