Séminaires
MSC
"Matière et Systèmes Complexes"
Jeudi
4 février 2010 à 10h
Bâtiment Condorcet, 4ème
étage, salle 454 A.
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 [1] of controllable aspect ratio.
Contrary to theoretical predictions [2] and spheres which form anisotropic
structures that depend on the shape of the surrounding micelles [3], 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 [4].
[1] Champion et al., PNAS, Vol. 104, No 29, 11901-11904 (2007).
[2] Andrienko et al., PRE (2002) ; F. R. Hung et al., PRE74, 011711 (2006).
[3] P. Poulin, N. Francès, and O. Mondain-Monval, PRE 59, 4384 (1999).
[4] F. Mondiot et al, PRL 103, 238303 (2009)