On the nature of the acoustic mechanism of domain formation in a cholesteric liquid crystal

The dual nature of the acoustic mechanism of destabilizing the planar texture of a cholesteric liquid crystal is confirmed experimentally. This destabilization manifests itself in the formation of a system of two-dimensional domains in the frequency range where the wavelength exceeds the cholesteric-helix pitch. A criterion for identifying two independent acoustic mechanisms (vortex and relaxation ones) is suggested and experimentally verified by analyzing the measured dependence of the critical compression amplitude on the cholesteric-helix pitch in the 40-, 120-, and 240-μm-thick mesophase layers for frequencies of 2.95 and 14.5 MHz, which are respectively lower and higher than the reciprocal relaxation time of the orientational order parameter of the cholesteric liquid crystal.