A Novel Polar Electro-Optic Effect in Thin Large-Pitch Cholesteric Films

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Abstract
Left-handed or right-handed spiral patterns have been observed in thin large-pitch cholesteric-nematic mixtures under the long time application of a DC voltage. The handedness of the winding of the spiral patterns was dependent on the polarity of the voltage, the type of the cholesteric-nematic mixture under study and the thickness of the cells. Their formation has been accounted for by the gradient flexoelectric splaytwist-bend deformation of point singularities formed in the electrode region. The gradient in the electric field was created by the accumulation of injected charges near the two electrodes. It was surprisingly observed that the adding of a small amount of a cholesteric to nematics favours very much the injection from the electrodes. This polar effect might be an important tool for the investigation of the gradient flexoelectric or injection phenomena in the thin large-pitch cholesterics.