UC San Diego

Development of fine and sophisticated nanosized composite colloidal particles has been intensively studied due to their huge potential to solve a lot of problems in a variety of fields. To have higher degree of freedom in designing nano-architecture on colloidal particles and controlling their unique properties, a more detailed understanding of chemical and physical phenomena in colloidal suspension is required. This dissertation discusses new mathematical approaches to describe in detail the behaviors of silica nanoparticle deposition and gold coating on submicron polystyrene (PS) colloidal particles in terms of colloidal science including surface chemistry and surface physics. To consider realistic phenomena inside the colloidal suspension, the proposed models for these two topics are based on the non-linear relationship between surface charge density and surface potential which are regulated by free ions. Chapter 1 presents the numerical analysis for the deposition behavior of monodispersed silica nanoparticles onto PS particles by using modified pairwise DLVO (Derjaguin, Landau, Verwey, and Overbeek) interaction force at different pH. This model includes an improved nonlinear charge regulation model considering redistribution of ions. To vindicate the model, silanol-terminated silica nanoparticles and L-lysine covered silica nanoparticles were separately deposited on polyallylamine hydrochloride-covered polystyrene (PAH/PS) particles. The morphological analysis of the experimental results shows that this modified DLVO force well describe the deposition behavior of the silica nanoparticles onto the PAH/PS particles. Chapter 2 discusses the computational models to elucidate the gold coating behavior on the positively charged PAH/PS particles at different concentration of L-ascorbic acid in terms of the initial nucleation stage. This analysis focuses on the initial generation rate gradient of Au(I) complex ions and the Casimir-Lifshitz interaction force between particles under the potential gradient. To justify our models, a direct gold coating method was performed on the PAH/PS particles with a constant concentration of HAuCl4 and various concentrations of L-ascorbic acid. The morphological analysis of the variation of gold coating shows that the computational results properly describe the morphological difference in gold coating by the trend of nucleation of gold along with the distance away from the PAH/PS particles.