8th Liquid Matter Conference September 6-10, 2011 Wien, Austria ...

P5.146Wed 711:10-14:00Interplay of anisotropy and interactions in chargedcolloidal plateletsJabbari-Farouji Sara, 1 Weis Jean-Jacques, 2 and Trizac Emmanuel 11 Le Laboratoire de Physique Théorique et Modèles Statistiques (LPTMS), 15 rue GeorgesClémenceau, 91405, Orsay cedex, France2 Laboratoire de Physique Theorique d’Orsay, Orsay cedex, FranceSpherical colloids have provided us with a fundamental insight about equilibrium and nonequilibriumstates of matter. Given that particles of a variety of materials have an anisotropicnature, it is important to understand the role of anisotropy in shape and interactions of particlesin the phase behavior of matter. To this end, we have systematically studied both equilibrium andnon-equilibrium phases in a model system of thin charged platelets that has direct implications forthe system of clays found both in natural and industrial forms. We model the electrostatic interactionsbetween charged colloids in the electrolyte medium by means of an orientation-dependentYukawa-type potential. This potential consistently accounts for the range and anisotropy of interactionsthat depend continuously on tunable parameters such as ionic strength. We have performedextensive Monte-Carlo simulations to study the phase behavior of the system as a function of colloidsdensity and ionic strength and to characterize the dynamics of the system, we have developeda dynamic Monte-Carlo scheme. We identify four distinct phases: isotropic fluid, nematic fluid,plastic solid and orientationally solid, similar to phases found for oblate spheroids. We find thatthe competition between orientational and packing entropy and orientational interactions leadsto emergence of a number of interesting features in phase behavior. For a wide range of ionicstrengths the isotropic-nematic transition is inhibited due to formation of solid-like structures andfor the ionic strengths that the isotropic-nematic transition is observed, it is shifted towards higherdensities. In the light of these results, we discuss the experimental data on clays.146