Archives of Acoustics, 30, 3, pp. , 2005

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

A. Balcerzak
Institute of Fundamental Technological Research, Polish Academy of Sciences

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.
Keywords: ultrasonic measurements; ultrasonic velocity and absorption; nematic-isotropic transition; adiabatic compressibility; thermal expansion
Full Text: PDF
Copyright © Polish Academy of Sciences & Institute of Fundamental Technological Research (IPPT PAN).