Girijavallabhan, C P; Radhakrishnan, P; Nampoori, V P N; Nibu, A George; George, A K(Applied Physics B Lasers and Optics, July 18, 2001)
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Abstract:
In this paper, we describe the use of an open cell
photoacoustic configuration for the evaluation of the thermal
effusivity of liquid crystals. The feasibility, precision and reliability
of the method are initially established by measuring
the thermal effusivities of water and glycerol, for which the
effusivity values are known accurately. In order to demonstrate
the use of the present method in the thermal characterization
of liquid crystals, we have measured the thermal
effusivity values in various mesophases of 4-cyano-4 -
octyloxybiphenyl (8OCB) and 4-cyano-4 -heptyloxybiphenyl
(7OCB) liquid crystals using a variable temperature open
photoacoustic cell. A comparison of the measured values for
the two liquid crystals shows that the thermal effusivities of
7OCB in the nematic and isotropic phases are slightly less
than those of 8OCB in the corresponding phases
Nampoori, V P N; Vallabhan, C P G; George, A K; Radhakrishnan, P; Rajasree, K; Vidyalal, V(Elsevier, July , 1998)
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Abstract:
he phenomenon of single beam mirage effect, otherwise known as photothermal deflection (PTD) effect using a He–Ne laser beam has been employed to detect phase transitions in some liquid crystals. It has been observed that anomalous changes in amplitude occur in the PTD signal level near the transition temperature. The experimental details and the results of measurements made in liquid crystals E8, M21 and M24 are given in this paper.
Girijavallabhan, C P; Radhakrishnan, P; V P N Nampoori; Nibu, A George; George, A K(Journal of Physics D : Applied Physics, October 13, 2000)
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Abstract:
We report on a laser induced photoacoustic study of the nematic-to-isotropic
transition in certain commercial nematic liquid crystal mixtures, namely BL001, BL002,
BL032 and BL035. A simple analysis of the experimental data using the
Rosencwaig–Gersho theory shows that the heat capacities of all these compounds exhibit a
sharp peak as the temperature of the sample is varied across the transition region. Also,
substantial differences in the photoacoustic signal amplitudes in nematic and isotropic phases
have been noticed for all the mixtures. The increased light scattering property of the nematic
phase may be the reason for the enhanced photoacoustic signal amplitude in this phase.