A study on thermodynamic and sound parameters of some nematics

Abstract

Measurements of ultrasonic velocity and density of solutes in dilute solutions as a function of concentration and temperature can be used to obtain several thermodynamic and acoustical parameters and their excess adiabatic compressibility. The physical parameters that can be determined through these are: molar sound velocity or Rao's number (R), molar compressibility 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 (β). These parameters play an important role in the phenomenon associated with intermolecular interaction and hence in sound transmission. For example, the parameter Z that is determined by the product of density (d) and ultrasonic velocity (c) has a greater significance as a characteristic property of the medium than does either the density or velocity individually so also in case of sound transmission the parameter of more concern is the molar sound volume (V m) rather than molar sound velocity or Rao’ number. Such studies on liquid crystals around phase transition temperature in their pure state yield important information and so also in their dilute solutions. In view of above facts, the ultrasonic velocity with density measurement studies on pure samples of nematics, namely, Butyl-p-(p-ethoxy phenoxy carbonyl)phenyl carbonate, p-(p-ethoxy phenyl azo)phenyl undecylenate and p-[N-(p-methoxy benzylidene)amino]phenyl benzoate in dilute solutions was taken up both as a function of mole fraction (in benzene) and temperature. The results of the above work is presented in this article and discussed.