Orientational order parameter of two cyano nematogens by optical spectroscopy

Abstract

Refractive index and density measurements of two cyano nematogens, namely p-hexyloxybenzylidene p-aminobenzonitrile and p-octyloxybenzylidene p-aminobenzonitrile have been carried out. From these data, orientational order parameter S has been estimated using different methods. Principal polarizabilities have been calculated using the well-known Vuks isotropic and Neugebauer anisotropic models. Polarizability anisotropy has been estimated using Lippincott δ-function, molecular vibration, Haller's extrapolation and Vuks scaling methods. Using these values, the orientational order parameter S has been estimated at different temperatures in their nematic phases. The values obtained have been compared and discussed. Further, using the experimental refractive index data, the nematic crossover temperatures have also been estimated for these compounds.