Refractive Indices and Optical Anisotropy of Homologous Liquid Crystals

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Abstract
We have measured as functions of temperature the refractive indices and linear birefringence of seven homologous compounds of p, [pacute]-di-n-alkoxy-azoxybenzenes in the nematic phase. Using the Vuks' model of local-field correction, we have deduced from our results both the microscopic and the macroscopic order parameters. The former agree well with those determined by Pines et al from the NMR results. The variations of the various microscopic parameters with the increase of the alkyl chain length are discussed. It is shown that addition of CH2 groups to the alkyl chain increases the average polarizability much faster than the polarizability anisotropy. Contributions to the polarizability anisotropy from the core and from the alkyl chains respectively are found.