Depolarized Rayleigh scattering from binary mixtures composed of optically anisotropic molecules

Abstract

Total intensity depolarized Rayleigh light scattering measurements have been made on three liquids composed of cylindrically-symmetric anisotropic molecules, carbon disulphide, benzene and hexafluorobenzene. Measurements were made on mixtures of each of these liquids with the nearisotropic solvent, cyclohexane and on the three binary liquid pairs, carbon disulphide + benzene, carbon disulphide + hexfluorobenzene and benzene + hexafluorobenzene.

After the elimination of depolarized scattering due to molecular collisions the data on the cyclohexane mixtures have been analysed, using an expression due to Bothorel, to give values of G, the static orientational correlation function, for the pure anisotropic liquids. Carbon disulphide and hexafluorobenzene are found to exhibit a tendency for parallel orientation of neighbouring molecular axes (G > 1) whereas benzene appears to be orientationally random (G≃ 1). The unexpected difference between benzene and hexafluorobenzene, where the two molecules are of similar size and shape is, as yet, unexplained.

The experimental results on the three binary mixtures composed wholly of optically anisotropic molecules indicate that there are strong tendencies for parallel orientation of neighbouring unlike pairs in both benzene + hexafluorobenzene and carbon disulphide + hexafluorobenzene mixtures. In contrast carbon disulphide + benzene exhibits a tendency for perpendicular alignment of unlike pairs over most of the concentration range. It is felt that quadrupole–quadrupole interactions are the likely explanations of these gross structural differences.