Studies of optical texture, birefringence, order parameter, normalized polarizability and validation of the four-parameter model of a thermotropic mesogen 7OAOB

Abstract

Study of optical texture of different mesophases and phase transition temperatures of the liquid crystal compound 4,4′-di-n-heptyloxy-azoxy benzene has been carried out by using optical polarizing microscope. Enthalpy values and the phase transition temperatures have also been conducted by DSC studies. The variation of refractive indices with temperature has been measured by a thin prism technique using He–Ne laser and temperature dependent birefringence is calculated which shows a moderate value. Validation of the modified four-parameter model based on Vuks approximation has been carried out and reported in this article. The most important characteristics of LC compound namely macroscopic and microscopic order parameter have been evaluated by using direct extrapolation method and modified Vuks method based on Haller's extrapolation respectively. Temperature gradients of refractive indices have also been calculated. Further the normalized polarizabilities for extraordinary and ordinary rays and their ratio have been reported in this paper.