Dynamical behaviour of phase transitions in liquid crystals under ultrasound field

Abstract

The study investigates the influence of an acoustic field on the process of interface formation, phase boundary propagation kinetics, and isotropic phase nucleation in a nematic liquid crystal (NLC) during the NLC → isotropic liquid (IL) phase transition. Experimental studies were conducted using acoustically "rigid" drops and both "rigid" and "soft" cells of sandwich type, with one substrate being a piezo quartz’s X-cut plate. The thickness of the investigated LC layers with planar and homotropic orientations was 20, 50, and 100 μm. The frequency of the ultrasonic field ranged from 3.77 to 4 MHz. Additionally, we computed the values of isotropic germ’s radius in NLC during the NLC → IL phase transition both without and under the ultrasonic field. The obtained data indicate an increased probability of forming a germ of an isotropic phase during the NLC → IL phase transition under the influence of ultrasound. These findings align well with the experimentally observed trends in the changes of phase transition temperature, specifically with the depression of the NLC → IL phase transition temperature in the presence of an ultrasound field.