title: Stokes-Einstein diffusion of colloids in nematics.
abstract: We report the experimental observation of anisotropic diffusion of polystyrene particles immersed in a lyotropic liquid crystal with two different anchoring conditions. Diffusion is shown to obey the Stokes-Einstein law for particle diameters ranging from 190 nm up to 2 μm. In the case of prolate micelles, the beads diffuse four times faster along the director than in perpendicular directions, D||/D[Symbol: see text] ≈ 4. In the theory part we present a perturbative approach to the Leslie-Ericksen equations and relate the diffusion coefficients to the Miesovicz viscosity parameters η(i). We provide explicit formulas for the cases of uniform director field and planar anchoring conditions which are then discussed in view of the data. As a general rule, we find that the inequalities η(b) <η(a) <η(c), satisfied by various liquid crystals of rodlike molecules, imply D||>D[Symbol: see text].
authors.affiliation: Centre de Recherche Paul Pascal, Université de Bordeaux and CNRS, 33600 Pessac, France.
authors.forename: Frédéric
authors.initials: F
authors.lastname: Mondiot
authors.forename: Jean-Christophe
authors.initials: JC
authors.lastname: Loudet
authors.forename: Olivier
authors.initials: O
authors.lastname: Mondain-Monval
authors.forename: Patrick
authors.initials: P
authors.lastname: Snabre
authors.forename: Alexandre
authors.initials: A
authors.lastname: Vilquin
authors.forename: Alois
authors.initials: A
authors.lastname: Würger
mesh_terms: D003102:Colloids / Q000737:chemistry*; D003198:Computer Simulation; D004058:Diffusion; D050866:Liquid Crystals / Q000737:chemistry*; D008956:Models, Chemical; D014783:Viscosity
chemical_list: D003102:Colloids