Temperature dependence of the enthalpy and the heat capacity of the liquid-crystal octylcyanobiphenyl (8CB)

J. Thoen, H. Marynissen, and W. Van Dael
Phys. Rev. A 26, 2886 – Published 1 November 1982
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Abstract

An adiabatic scanning calorimeter has been used to study the thermal behavior of the liquid-crystal octylcyanobiphenyl (8CB) in the temperature range between 10 and 50°C. The solid—to—smectic-A (KA), the smectic-A—to—nematic (AN), as well as the nematic-to-isotropic (NI) phase transitions, which fall in this temperature range, have been investigated in great detail. From our measuring procedure the enthalpy behavior (including latent heats) as well as the heat capacity have been obtained. For the KA transition the latent heat was 25.7±1.0 kJ/mol and for the NI transition it was 612±5 J/mol. Within the resolution of our experiment we find that the AN transition is a continuous one. For the latent heat, if any, we arrive at an upper limit of 0.4 J/mol (or 1.4×103 J/g). The observed anomaly in the heat capacity for the AN transition is not consistent with a nearly logarithmic singularity as predicted by the XY model, instead we obtain a critical exponent α=α=0.31±0.03. This result is consistent with the anisotropic scaling relation ν+2ν=2α. The pretransitional effects near the NI transition are in qualitative agreement with the hypothesis of quasitricritical behavior.

  • Received 14 June 1982

DOI:https://doi.org/10.1103/PhysRevA.26.2886

©1982 American Physical Society

Authors & Affiliations

J. Thoen, H. Marynissen, and W. Van Dael

  • Laboratorium voor Molekuulfysika, Katholieke Universiteit Leuven, B-3030 Leuven, Belgium

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Vol. 26, Iss. 5 — November 1982

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