The field-induced cholesteric-nematic phase transition and its dependence on layer thickness, boundary conditions, and temperature

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Abstract
Chiral-nematic liquid-crystal layers which have a short pitch, homeotropic boundary conditions, and bistable properties are investigated with respect to the temperature dependence of their field-induced cholesteric-nematic phase transition. Hereto the threshold field needed for the transition is studied as a function of the layer thickness. This is done for various temperatures. The threshold field hardly depends on the layer thickness. Moreover, it sharply rises below −5 °C. Both the value of the threshold field and its temperature dependence can be fully described in terms of liquid-crystal bulk material parameters, the conditions at the homeotropic boundary layer used do not play a role. From the threshold field data the twist elastic constant is determined as a function of temperature. This temperature dependence is compared to the temperature dependence as determined from the square of the long range order parameter calculated from temperature dependent refractive index data. A good correlation is found between both data sets of the twist elastic constant.