New optical method for studying anisotropic diffusion in liquid crystals

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Abstract
A new approach to studying diffusion in liquid crystals is described in which the optically observable textural changes in a nematic phase caused by a cholesteric diffusant gives direct visualization of the concentration gradient. Utilizing either homeotropic of homogeneous alignments under different boundary conditions, and with and without an applied magnetic field, the parallel and perpendicular components of the diffusivity have been determined for a cholesteryl ester diffusing into N‐(p ‐methoxybenzylidene)‐p ‐n ‐butylaniline as a function of temperature. The diffusion coefficients in the isotropic phase can also be determined by annealing at a high temperature and quenching to room temperature, whereupon the cholesteric texture is again developed. Values of the diffusion coefficients and the activation energies of the diffusion process are discussed and compared to other available data.