Anisotropic diffusion in nematic liquid crystals and in ferrofluids

A unified, mean-field kinetic theory approach to the anisotropic translational diffusion observed in liquid crystals and in ferrofluids is proposed. In the dilute regime, unified expressions for the parallel as well as for the perpendicular diffusion coefficient in terms of orientational order parameters are found that apply for liquid crystals as well as for ferrofluids. This result explains the common origin of the anisotropic diffusion found in liquid crystals and in ferrofluids. Differences between the two liquids appear in the semi-dilute regime, where the diffusion coefficients depend on the specific interaction potentials. Explicit expressions for the diffusion coefficients are worked out also in this regime within a mean-field approximation. Comparisons with previous theoretical and experimental results are performed, showing satisfactory agreement to the present results.