Thermodynamic and acoustical parameters of some nematic liquid crystals

Ultrasonic and density measurements on solutes in dilute solutions are used to obtain thermodynamic and acoustical parameters and their excess values. The physical parameters that can be obtained such as molar sound velocity or Rao's number (R), molar compressility or Wada's constant (B), characteristic acoustic impedance (Z), intermolecular or free length (L-f), free volume (V-f), available volume (V-a) and adiabatic compressibility (beta) play an important role in the phenomenon of sound transmission. For example, the parameter Z determined by the product of density (d) and ultrasonic velocity (c) has a greater significance as a characteristic property than density or velocity. In the case of sound transmission the parameter of more concern is the molar sound volume (V-m) rather than molar sound velocity or Rao's number. Such studies on pure liquid crystals around phase transition temperature yield important information. In view of the above facts, the ultrasonic velocity and density measurements on pure samples of nematics, namely, 4,4'-azoxy anisole and 4,4'-dibutoxy azoxy benzene in dilute solutions were taken up. The results of this work is presented in this paper and discussed. (c) 2006 Elsevier B.V. All rights reserved.