Experimental investigations on ultrasonic velocity and behavior of thermodynamic parameters of four members of no.m series

摘要

Ultrasonic velocity measurements are carried out on four nOm compounds viz., N-(p-n-methoxy and ethoxy benzylidene)-p-n-dodecyl and tetradecyl anilines, 1O.12, 1O.14, 2O.12 and 2O.14. The first three compounds exhibit mono variant nematic phase while the last compound exhibits nematic and smectic-A phases with variable thermal ranges. The temperature dependence of sound velocity, U shows minima at the isotropic-nematic and nematic-smectic-A transitions. In conjunction with the density data of these compounds, the thermo acoustic parameters such as adiabatic compressibility (β_(ad)), the molar sound velocity (Rao's number) (R_n), molar compressibility (W), molecular free length (L_f) and available volume (V_a) are estimated. In addition the intermolecular free length (L_f) is estimated in three different ways employing density and ultrasonic velocity data. The results are compared with the data available in literature of other compounds.