Binary Mass Diffusion Constants in Nematic Liquid Crystals Studied by Forced Rayleigh Scattering

The binary mass diffusion constants of methyl red in the nematogens MBBA and 5CB were measured by forced Rayleigh scattering (FRS). The diffusion constants in the direction parallel to the director orientation, D//, are always larger than those perpendicular to it, D⊥; D///D⊥=1.6 for both MBBA and 5CB at room temperature. The temperature dependence is of the Arrhenius type except near the phase transition temperature of 5CB, where the values tend to deviate downwards. A comparison between the results obtained by other methods and those obtained by the present method suggests that the binary mass diffusion constant of methyl red obtained by FRS is a good measure of the self-diffusion constant.