Self-Assembly of Faceted Colloidal Particles

Abstract

A colloidal dispersion consists of insoluble microscopic particles that are suspended in a solvent. Typically, a colloid is a particle for which at least one of its dimension is within the size range of a nanometer to a micron. Due to collisions with much smaller solvent molecules, colloids perform Brownian motion, which allows them to explore all possible configurations available to them. Colloidal particles suspended in a fluid interact with each other in addition to the background interaction with the solvent atoms/molecules. As a result colloids can exhibit rich phase behavior similar to that of atomic and molecular systems. For example, colloids can self-assemble, not only into gas, liquid, solid phases, but also nematic, smectic, biaxial, hexatic phases. The type of phases that can emerge in a colloidal system depends not only on the interaction potential between the colloidal particles but also on the shape of the colloidal particle itself. In this thesis we study the effect of colloid shape on its phase behavior. In particular, we investigate the phase behavior of experimentally available polyhedral particles using Monte Carlo simulations and free-energy calculations both in bulk and at an interface. In Chapter 2, we present our study on the phase behavior of a family of truncated cubes. In addition to the phase behavior, we also study and compute the equilibrium vacancy concentration of these truncated cubes in Chapter 3. Then we proceed to study the phase behavior of superballs in Chapter 4. We then describe the phase behavior of hexagonal bi-pyramids and hexagonal bi-frustums adhered at a liquid-air interface and compare our results to the experimentally obtained structures in Chapter 5. In Chapter 6 we study the phase behavior of equilateral and right-angled isosceles triangles in 2D. Finally, in Chapter 7 we compute the dispersion relations for colloidal crystals which exhibit diffusion using a recently developed theoretical technique.