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 (SA) and B (SB) phases, the anisotropy D///D⊥ drastically changes from 0.028 to 1.67 with the phase sequence through SB, SA and nematic (N). In SB, D// is much smaller than D⊥, while D// gets larger than D⊥ in SA near the phase transition temperature to N, TAN. The anomalous behavior at TAN is also discussed.