Cholesteric liquid crystals in applied electric fields: structural transformations and applications

The colour change electrooptic effect in dual frequency addressable cholesteric liquid crystals (LCs) with an initial planar orientation was investigated. A field induced increase of the pitch was observed for the switching between low and high frequency fields. The investigations allow new conclusions on the origin of blue and red shift observed in an electric field applied parallel to the helix axis. In cholesteric LCs and polymer-dispersed cholesteric LCs with positive dielectric anisotropy, a coloured texture with unusual properties was observed for pitch values of P similar to 0.8 mu m and under certain conditions. This texture appears after the reduction of the electric field during the transition from the homeotropic nematic structure into the cholesteric one. The angular and the electric field dependencies of the spectral characteristics indicate that this state possesses diffractive grating properties. A voltage controlled colour shift and a laser beam deflection were investigated.