Alternating-Current-Field Induced Cholesteric–Nematic Phase Transitions

Abstract

In order to determine whether interaction between the permanent or the induced molecular dipole moments of a cholesteric liquid crystal and an applied electric field is responsible for inducing a transition to a nematic phase, ac‐field measurements were performed. In a mixture of cholesteryl chloride and cholesteryl myristate, phase transitions can be induced by an ac field of a frequency up to a threshold value $f_{\mathrm{pt}}{\mathrm{;\; f}}_{\mathrm{pt}}$ is approximately equal to the relaxation frequency for rotation of cholesteryl chloride molecules around a short molecular axis which has recently been determined by dielectric measurements. A relation between the rms field and $f_{\mathrm{pt}}$ is derived and experimentally verified. The absence of ferroelectric ordering in the induced and aligned nematic phase is demonstrated.