Electro-optical effects in room temperature blue phases (BP) with positive dielectric anisotropy have been studied. It is shown that the maximum wavelength of the Bragg reflection of blue phases, BP II and BP I, shifts to longer wavelength with increasing electric field. The electric field influences more strongly on BP II: a reversible shift of (lambda) 0 up to 80 nm was observed.
The color 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 colored texture with unusual properties was observed for pitch values of P approximately 0.8 micrometers 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 electrified dependencies of the spectral characteristics indicate that this state possesses diffractive grating properties. A voltage controlled color shift and a laser beam deflection were investigated.
A new electro-optic effect in an optically active nematic chiral structure beyond Mauguin's region has been studied. This structure rotates the polarization plane of incident light, and a liquid crystal with positive dielectric anisotropy sandwiched between crossed polarizers is switched from transparent into dark state in electric field. The characteristic features of this structure are: (a) the absence of oscillations in the transmission-voltage characteristics, (b) low demands on surface conditions (including nonrubbed cells), (c) the ability to function in any position between crossed polarizers, and (d) wide viewing angle.
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