Anisotropy of Binary Mass Diffusion Constants in Nematic, Smectic A and Smectic B Phases Studied by Forced Rayleigh Scattering

The binary mass diffusion constants of methyl red in p -butoxybenzylidene- n -octylaniline have been measured by forced Rayleigh scattering. Because of the different activation energies between the diffusion constants D // and D ⊥ in the smectic A (S A ) and B (S B ) phases, the anisotropy D // / D ⊥ drastically changes from 0.028 to 1.67 with the phase sequence through S B , S A and nematic (N). In S B , D // is much smaller than D ⊥ , while D // gets larger than D ⊥ in S A near the phase transition temperature to N, T AN . The anomalous behavior at T AN is also discussed.