Polarization Field and Molecular Order in Nematic Liquid Crystals

Abstract

Abstract In the smectic A and B mesophases, the polarization field is anisotropic and the extraordinary and ordinary refractive indices n e and n o are related to the effective polarizabilities αe and αo and the internal field constants γe and γo by the Neugebauer's relations. The Neugebauer relations lead to the Born relation which is valid to a high degree of accuracy particularly for the long wavelengths. The paper presents a method for calculating the anisotropic internal field constants and the ratio of αe to αo, even if density data are not available. The birefringence data reported by Pelzl and Sackmann for six cinnamates which exhibit both smectic A and B mesophases are discussed in terms of the theory and results are presented with regard to the internal field constants and the ratio of αe to αo at different temperatures. Their variations are explained as due to mainly the rotational isomerism exhibited by the alkyl and alkoxy endgroups in the different compounds.