Large anisotropy of orientational fluctuations in a lyotropic nematic liquid crystal

Abstract

Two hydrodynamic modes of the orientational fluctuations were investigated in a homeotropically aligned sample of a lyotropic uniaxial nematic mixture of potassium decanoate, potassium heptyloxybenzoate, potassium chloride, decanol and deuteriated water, which forms discotic micelles. The relaxation times, measured with a photon correlation light scattering technique, show a large anisotropy over the whole nematic range: the pure splay relaxation time is much larger than the pure twist and pure bend relaxation times. This is caused by the anisotropy of the effective viscosity, probably resulting from a backflow effect. The relaxation time exhibits an approximately exponential temperature dependence, caused by the temperature dependence of the viscosity coefficients, with activation energies 0·54eV and 0·40 eV for the deformations close to pure bend and pure splay.