Relaxation Phenomena In The Nematic Phase of Liquid Crystal Near Phase Transition

Absorption of ultrasonic longitudinal waves in the nematic liquid crystal 1-(trans- 4-hexylcyclohexyl)-4-isothiocyanatobenzene (6CHBT) was measured in the temperature (24-56oC) and frequency (3.2-100 MHz) ranges. In the region of the phase transition the anomalous absorption has been observed. This absorption rapidly increases when the frequency of the ultrasonic wave decreases. The experimental results for the nematic phase were analysed and two relaxation processes have been found. Relaxation parameters for both processes were calculated. The process with the longer relaxation time is connected with the order parameter changes. The isomeric changes in the hexyl chain of the 6CHBT molecule is the origin of the process characterized by the shorter relaxation time.