Orientational diffusivities in a disk-like lyotropic nematic phase : a strong backflow effect

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Abstract
We have studied the disk-like lyotropic nematic phase of a K-Laurate/Decanol/D 2O mixture by Rayleigh scattering. The decay time of the director thermal fluctuations, obtained by light-beating techniques, is measured as a function of the wave vector. The employed geometrical configuration allows to determine the splay and twist diffusivities. The observed large ratio between these two quantities is interpreted in terms of the anisotropy between their associated viscosities, due to the backflow. This splay-twist anisotropy for disk-like (lyotropic) nematics appears similar to the well-known bend-twist anisotropy for rod-like (thermotropic) nematics