Pressure effect on the cholesteric – smectic A transition in cholestryl myristate

ABSTRACT

Cholesteryl myristate exhibits tricritical behavior under high pressures close to its cholesteric-smectic A (Ch/S_A) transition, as observed experimentally. We study here the thermodynamic properties of this liquid crystal by calculating the pressure dependence of the isothermal compressibility, thermal expansion and the specific heat close to the Ch/S_A transition. This calculation is performed at constant temperatures (80.8 and 105.0 °C) using the observed volume-pressure (V-P) data from the literature.

We find that the thermal expansion and the isothermal compressibility increase linearly, whereas the specific heat exhibits anomalous behaviour with increasing pressure close to the Ch/S_A transition in cholesteryl myristate. From the pressure dependence of the thermodynamic quantities studied, the Pippard relations are examined and their linear variations are obtained at various pressures at constant temperatures of 80.8 and 105.0°C for this liquid crystal close to the Ch/S_A transition. Our results also indicate that the tricritical point (TCP) is located at higher pressure (about 1 kbar) for the Ch/S_A transition in cholesteryl myristate, as suggested previously.

KEYWORDS:

• Cholesteric – smectic A transition
• cholesteryl myristate
• thermodynamic quantities
• pippard relations