Entropy Driven Ordering in Colloidal Suspensions

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w:\awards\awards97\fraden5336.doc 9705336 Fraden The objective of this new project is to develop fundamental understanding of (1) liquid crystal ordering of colloids, and (2) the phase behavior of mixtures of rodlike and spherical colloids. These inter-related projects involve understanding of the physics of colloids at three levels, the microscopic level of the particles and their interaction, the mesoscopic level of ordered phase formation, and the macroscopic level of materials properties. The interparticle potentials of the colloids we study are dominated by steric and short-range repulsive interactions, and thus serve as experimental models of hard particle suspensions, where phase behavior is determined solely by entropy. The colloids are well characterized, uniform particles and since there is an established theoretical framework for understanding their phase behavior, what we learn about these particular systems has implications for the fundamental understanding of liquid crystals, colloid - polymer mixtures, protein crystallization, and the biophysics of the intracellular environment, as well as the design of composite materials where molecular ordering and self-assembly is important. %%% This new project will carry out a series of studies of the structure, dynamics, and phase behavior of two systems, (1) colloidal mixtures of rods and spheres, and (2) colloidal suspensions of rods. The interparticle potentials of the colloids we study are dominated by steric and short-range repulsive interactions, and thus serve as experimental models of hard particle suspensions, where phase behavior is solely determined by entropy. Hard particle theories serve as a basis for the understanding of all fluids, and in particular capture essential features of the phase behavior of colloidal suspensions. The colloids w e study are well characterized, uniform particles and since there is an established theoretical framework for understanding their phase behavior, what we learn about these particular systems has implications for the understanding of fundamental properties of liquid crystals, colloid - polymer mixtures, protein crystallization, and the biological cellular environment, as well as for the design of novel materials where molecular self- assembly is important. ***