Acoustical analog of the Fréedericksz transition in liquid crystals

A nonlinear relaxation model describing thresholdlike variation in the symmetry of a homeotropic orientational structure of a nematic liquid crystal (NLC) layer in an ultrasonic wave field has been constructed in the nonlinear hydrodynamics framework based on a molecular micromodel representing all processes in the mesophase proceeding from the behavior of a separate LC molecule. The relationship between the threshold characteristics and the ultrasound frequency, NLC mesophase layer thickness and material parameters, temperature, and parameters of the molecular micromodel is determined. The results of calculations for the frequency range containing the relaxation frequency of the NLC orientational order parameter are compared to the obtained experimental data.