| A unifying theme in my work is the theoretical treatment of the self-assembly of colloidal particles in solution. An underlying theme to all of our approaches is our belief that basic ideas in complex fluids have wide-ranging applications.;Part 1. Self-assembly of metal nanoparticles and arrays. In recent years, there has been tremendous interest in nanoparticle synthesis and the fabrication of ordered arrays of particles, because of their potential uses in electronic devices, optics, catalysis, ceramics, photographic materials, and magnetic storage. Our research has focused on metal nanoparticle synthesis, and their 2D ordered arrays. We prepare the particles via a two-phase synthesis, where the nanoparticles formed are thermodynamic products, with average size (1-6nm diameter) controlled by composition: for fixed metal ion concentrations, higher amounts of added thiol produce smaller particles. We then investigate the 2D structures which form when a drop of dilute organic solution of nanoparticles is placed on a carbon substrate. After the solvent evaporates, the resulting sub-monolayer structures of particles are either size-segregated, compact domains or annular rings, depending on the average size and polydispersity of the sample. We discuss the role of size-dependent dispersional attractions in compact, size-segregated domain formation. We also present a mechanism for ring vs. compact structure formation, where rings are explained in terms of the evaporation of--and hole nucleation in--wetting thin liquid films, and the subsequent pinning of hole rims. Ideas are tested via a dynamic Monte Carlo simulation, which illustrates the effect of the time scales of fluid flow and evaporation on the resulting configurations.;Part 2. Phase behavior of disklike micellar dispersions. Micellar self-assembly is a primary field of study in complex fluids. The surfactant molecules that comprise micelles, after all, are the basic building blocks for biological structures. We investigated the phase behavior of model disklike micelles. Specifically, we studied the isotropic (randomly oriented) to nematic (aligned) phase transition of disklike micelles in solution, for varying surfactant lengths. We developed a statistical thermodynamic description that treated self-assembly of disklike micelles and hard particle interactions. |
