Effect of the Polar Substituents on the Optical Parameters of Binary Mixtures of 4-Substituted-phenyl-4-hexyloxybenzoates

Abstract

The refractive indices as a function of temperature were measured for the individual components of 4-substituted-phenyl-4-hexyloxybenzoates as well as their binary mixtures. In these components one terminal substitution is C 6 H 13 O and the other terminal is either the methoxy (CH 3 O), methyl (CH 3 ), cyano (CN), or nitro (NO 2 ) group. Refractive index data were used to estimate the molecular order parameter (S) and the length-to-breadth ratio (k) for all samples investigated. The entropy change (Ds c ) at the nematic-isotropic transition temperatures (T c ) was also calculated from differential scanning calorimetry data (DSC). The results were thoroughly analyzed and compared.

Crossover temperature (TCO) and temperature gradient of refractive indices and length to breadth ratio of 4O.m mesomorphic compounds – an optical study

“…In the estimation of the length to breadth ratio, k, the procedure adopted by Roushdy [11] and the equations of Palffy-Muhoray and Balzarini [12] are used. Palffy-Muhoray and Balzarini [12] have given that the local field η zz for LC molecules is nearly proportional to the order parameter and the slope of that plot is equal to ½À4ðk À 1Þ=½5ðk þ 2Þ.…”