Ultrasonic measurements in the 1-(trans-4-hexylcyclohexyl)-4-isothiocyanatobenzene near the nematic-isotropic transition

The absorption and velocity of ultrasonic longitudinal
waves in the nematic liquid crystal
1-(trans-4-hexylcyclohexyl)-4-isothiocyanatobenzene (6CHBT) have been measured
as a function of temperature between 24oC and 55oC at 5.2 MHz. The temperature
dependence of ultrasonic absorption has a sharp maximum, whereas that dependence
of velocity shows a local minimum in the region of the nematic-isotropic (N-I)
phase transition. Additional temperature measurements of density have been done
to calculate the thermal coefficient of expansion and the temperature
coefficient of adiabatic compressibility. Both these parameters exhibit critical
behaviour at the transition which has been analysed. The values of the exponent
determining the growth of the order fluctuations have been calculated and
compared with references.