Prewavy instability-originated dielectric chevrons of electroconvection in nematic liquid crystals

Abstract

This paper reports the pattern formation and evolution in a high-frequency dielectric regime observed in the AC-driven electroconvection of nematic liquid crystals (NLCs). It is determined that prewavy (PW) instability is essential for the formation and evolution. Specifically, in a twisted-aligned NLC cell, we observe a unique pattern that is comparable to the dielectric chevrons (DCVs) typically observed in a conventional planarly aligned pattern. It is determined to be a combined PW pattern with dielectric normal rolls (DNRs). Moreover, the power indices (alpha(PW), alpha(DNR), and alpha(DCV)) are determined from the frequency-dependent thresholds (V-th alpha f(alpha)) of PW, DNR, and DCV. By taking into account the appearance of PW and the different power indices, the pattern evolution scenarios for DCV are proposed, which can well explain the previous experimental results. Specifically, the PW-originated DCV2 clearly differs from the defect-mediated DCV1, which is known as a typical pattern evolution.