ULTRASONIC STUDIES IN CHOLESTERYL MYRISTATE-CHOLESTERYL PROPIONATE LIQUID CRYSTALLINE MIXTURES.

Mixtures of Cholesteryl Myristate (CM) and Cholesteryl Propionate (CP) were studied at four different concentrations. CM exhibits smectic, cholesteric and blue phases, while CP is a cholesteric liquid crystal. Addition of CP to CM disrupts the smectic phase while it enhances the cholesteric and blue phases. Ultrasonic velocity (V) was measured in all the mixtures besides the pure ones using fixed path double crystal interferometer at a frequency of 2 MHz. Specific volume ( nu ) was measured using a special dilatometer designed for the study of liquid crystals. The parameters, viz. , adiabatic compressibility (K//a//d) and molar sound velocity (R) were also estimated. Anomalous behavior was observed in all the parameters, viz. , V, nu , K//a//d and R. The results are interpreted on the basis of McMillan's and Lee's theories. The mean interaction parameter was estimated for different mixtures and found to decrease with increasing concentration of CP in the mixture. It was observed that the cholesteric-smectic A transition becomes second order when the mean interaction parameter equals 0. 78 which is in agreement with McMillan's predictions.