Physical studies of nematic azoxybenzenes. II. Refractive indices and the internal field

The ordinary refractive index and the birefringence are reported for two homologous series of nematic liquid crystals, the p,p′-di-n-alkyl and p,p′-di-n-alkoxy azoxybenzenes. It is found that the high-frequency dielectric anisotropy is proportional to the anisotropy of the magnetic susceptibility. For axially symmetric molecules this proportionality allows a simplification of the intricate problem of the internal field, which can be taken as independent of the anisotropy of the surroundings of a molecule. Representing a molecule by a homogeneously polarizable spheroid, an equation is derived which relates the anisotropic high-frequency dielectric permittivity to the anisotropic molecular polarizability, and which gives consistent results for both the solid state and the nematic phase.