Electromechanical effect in cholesteric liquid crystals with fixed boundary conditions

Abstract

We describe a number of experiments to demonstrate the electromechanical effect in cholesteric liquid crystals. The Lehmann rotation phenomenon of drops with stress free boundary conditions is the most convincing effect produced by this coupling. In samples with fixed boundary conditions, the cross coupling produces a distortion of the profile of the azimuthal angles of the director. We have used a conoscopic technique to demonstrate this distortion in thick samples containing negative dielectric anisotropy materials. A strong linear electrooptic effect of electromechanical origin is produced in materials with a weak positive dielectric anisotropy. We provide an evidence that a twisted nematic cell without any chiral molecules also exhibits the electromechanical effect, due to the macroscopic chirality of the medium in such a cell.