ANISOTROPY OF DIFFUSION-COEFFICIENTS IN H EXAGONAL DISCOTIC LIQUID-CRYSTALS

The diffusion constants of dyes in several hexagonal discotic liquid c rystals are measured and discussed. For all the liquid crystals studie d, these constants are anisotropic : the diffusion in the direction pa rallel to the columns is faster than that in the perpendicular plane ( D(parallel-to)/D(perpendicular-to) > 1). The effects of the length and shape of the chains bound to the triphenylene discs are shown. The ef fect of the dye molecular size is also described. The study of the dif fusion coefficients of hexapentoxytriphenylene (C5HET) as a function o f temperature has shown that the activation energies along the columns and perpendicular to the columns are comparable. The main features of dye diffusion in the hexagonal columnar liquid crystals studied are s imilar to those reported in nematic phases.