AC Electric-Field-Induced Cholesteric-Nematic Phase Transition in Mixed Liquid Crystal Films

Abstract

The electric-field-induced cholesteric-nematic phase transition is investigated in mixed liquid crystals consisting of p-n-butoxybenzylidene-p'-cyanoaniline, p-methylbenzylidene-p'-n-butyl-aniline, and cholesteryl oleyl carbonate. The relaxation transient of mixed liquid crystal films from a transparent nematic state back to a cloudy cholesteric state is studied by measuring the transmission of plane-polarized monochromatic light through the films. Optical rotation occurs in the early stage of the relaxation, followed by the formation of small birefringent regions randomly oriented with respect to each other. It is found that the optical rotation is due to the inverse process of cholesteric-to-nematic transition induced by the electric field parallel to a helical axis. An ac bias field above a certain value has an effect of prolonging the relaxation time. An interpretation of the results is presented.