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

Balcerzak A.

Molecular and Quantum Acoustics

2005

Vol. 26

7-13

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.

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

Balcerzak A.

Archives of Acoustics

2005

Vol. 30, No. 3

373-378

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 24°C and 55°C 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.

Results of Ultrasonic Velocity and Density Investigations of the Nematic Liquid Crystal

Balcerzak A.

Molecular and Quantum Acoustics

2004

Vol. 25

17-22

Velocity of ultrasonic longitudinal waves in the nematic liquid crystal 1-(trans-4- hexylcyclohexyl)-4-isothiocyanatobenzene (6CHBT) has been measured as a function of temperature between 24oC and 55oC at 5.2 MHz. The temperature dependence of velocity shows a local minimum in the region of the nematicisotropic (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.