Optimized frequency regime for the electrohydrodynamic induction of a uniformly lying helix structure

Abstract

This study specifies the optimal frequency regime for the uniformly lying helix (ULH) alignment induced by the electrohydrodynamic (EHD) effect in a cholesteric liquid crystal with positive dielectric anisotropy. Based on the transport behavior of ionic charges in response to the externally applied ac electric field, four frequency regimes, divided by three critical frequencies (i.e., f (L), f (R), and f (H)), are identified by means of dielectric spectroscopy. By discussing the voltage-dependent cholesteric textural changes in each frequency regime in terms of the voltageand frequency-dependent transmission spectra and optical textures, our results suggest that the designated frequency regime f (L), < f < f (R), where electrical charges can effectively oscillate in the bulk of the cell with less ion accumulation on the electrode surfaces, is most adequate for the generation of well-structured ULH via effective induction of the EHD flow by the external voltage. As a result, this study provides a pathway to determination of the optimal frequency regime for generating the EHD-induced ULH state prior to voltage treatment. (C) 2016 Chinese Laser Press