Refractive Indices and Orientational Order Parameter of Five Liquid Crystals in Nematic Phase

Abstract

Abstract Refractive indices of bis-(4′-n-alkyloxy benzal)-2-chloro-1,4 phenylene diamine (alkyl = hexyl, octyl and decyl), RO-TN-101 and RO-CE-154 have been measured over the whole nematic ranges for different wave lengths. A prism method has been employed for these measurements. The samples were aligned by surface rubbing and by the application of magnetic field. For all the samples, the refractive index for the extra-ordinary ray (ne ) decreases and that for the ordinary ray (no) increases with increasing temperature. At the nematic isotropic transition there is a discontinuity in the refractive indices values. The principal molecular polarizabilities (αe and αo) for the samples have been calculated using Neugebauer's relation. The necessary density measurements have been made by us. The anisotropy of the molecular polarizabilities was calculated using Haller's extrapolation method. The orientational order parameters were calculated at different temperatures for the samples using principal polarizability and the molecular polarizability anisotropy values. The agreement with Maier-Saupe theory is quite good for all substances except RO-TN-101 which is a mixture.