Influence of Parameters on Flexoelectro-Optic Effect in Cholesteric Liquid Crystals

M. Buczkowska Institute of Physics, Lodz University of Technology, Wólczańska 219, 90-924 Łódź, Poland

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The deformations of a cholesteric liquid crystal layer with a helical axis parallel to the layer plane are investigated numerically. When such a layer, called the Uniform Lying Helix texture, is placed between crossed polarizers, then the system gives an interesting linear electro-optic effect provided that the cholesteric possesses flexoelectric properties. Namely, the electric field perpendicular to the layer plane rotates the optical axis of the liquid crystal around the layer normal by an angle nearly proportional to the field strength. As a result, the optical transmission of the system is controlled by the bias voltage. The present study is devoted to numerical simulations of the Uniform Lying Helix layers. The director distributions in the layers were calculated by means of minimizing the free energy of the system. The voltage dependence of the rotation angle and of the pitch, occurring at various system parameters, was determined. The influence of parameters on efficiency of the flexoelectro-optic effect expressed by the derivative of the rotation angle with respect to bias voltage was studied. The results showed that high efficiency is favoured by long pitch, small sum of bend and splay elastic constants, large difference between splay and bend flexoelectric coefficients, zero dielectric anisotropy and thin layer which confirmed the earlier theoretical predictions.

DOI:10.12693/APhysPolA.140.258 topics: flexoelectro-optic effect, cholesterics, director deformations