Influence of the surface interaction on threshold values in the cholesteric-nematic phase transition

Abstract

The threshold values for the field-induced cholesteric to nematic phase transition are described as crossover points of the free energy levels of the textures concerned. Known expressions for these energy levels as a function of an electric field are extended with a surface interaction term. By interpretation of experimental results in terms of the equations derived, the surface interaction energy is calculated both for planar and homeotropically aligned cholesteric liquid-crystal mixtures. Besides differences between planar and homeotropic wall alignment a difference between two types of planar wall alignment can now be understood, too. Additionally, the method appears very useful for calculating the twist elastic constant K22.