"Matière et Systèmes Complexes"
4 février 2010 à 10h
Bâtiment Condorcet, 4ème étage, salle 454 A.
Ellipsoidal Inclusions in Lyotropic Nematic Liquid
F. Mondiot, S.P. Chandran, J.-C. Loudet, O. Mondain-Monval
We study the behavior of colloidal particles dispersed in nematic liquid crystals. We focus on the influence of the particles shape on their interactions when introduced into the liquid crystal matrix, which are solutions of rodlike (calamitic phase) or disklike (discotic phase) micelles. Micrometer-sized ellipsoids are prepared by uniaxial mechanical stretching of polystyrene spheres  of controllable aspect ratio. Contrary to theoretical predictions  and spheres which form anisotropic structures that depend on the shape of the surrounding micelles , ellipsoids with an aspect ratio k higher than a critical value remain surprisingly well-dispersed in the lyotropic nematic phases. Our observations (using optical microscopy and dynamic light scattering) therefore suggest the existence of a critical aspect ratio above which elastic deformations (and consequently elastic interactions) do not propagate over a certain length scale. We also evidence the different anchoring geometries that are shown to depend on the shape of micelles. We present a simple model that can account for the observed results .
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