Metallic Nanoparticle Synthesis within Reverse Micellar Microemulsion Systems

Abstract

The synthesis of metallic nanoparticles is integral for the advancement of the field of nanotechnology. Solution based nanomaterial synthesis is an effective method for the production of nanomaterials, particularly with the use of surfactants and other materials for directed assembly allowing control over the nanomaterials’ physical properties. This dissertation presents research performed to study the synthesis of metallic nanoparticles within reverse micelle systems. A fundamental approach has been taken to carefully examine the role of each component of the reverse micelle system, specifically the surfactant, bulk solvent, and the aqueous micelle core. The role of the sodium bis(2-ethylhexyl) sulfosuccinate (AOT) surfactant is two fold. Initially, the surfactant forms reverse micelles, nano-sized water pools dispersed within the bulk organic solvent which act as nano-reactors for the chemical reduction of the metallic precursors and metallic nanoparticle synthesis. The surfactant also acts as a stabilizing agent, effectively dispersing synthesized particles in solution, preventing agglomeration. Previously it was thought that spherical reverse micelles acted as templates for nanoparticle synthesis despite the negligible effect of the initial micelle diameter on the on the diameter of nanoparticles synthesized. Rather the initial micelle diameter influences the nanoparticle growth rate. In contrast, the properties of the bulk organic solvent do influence the nanoparticle diameter. The nature of solvent interactions with the AOT surfactant tails in various liquid alkane solvents, compressed propane, and supercritical ethane demonstrates that steric stabilization of the metallic nanoparticles by the AOT surfactant determines the particle sizes synthesized, rather than the previously accepted templating effect. Time resolved UV-vis spectroscopy was used to study the kinetics of particle synthesis, Neutron Spin Echo spectroscopy and Small Angle Neutron Scattering were used to determine the bending elasticity of the reverse micelle AOT monolayer as a measure of the micelle rigidity, a total interaction energy model was developed to determine the thermophysical effects by predicting the synthesized particle diameters and electron microscopy was used to analyze the synthesized particles. The nature of anionic interactions on metallic nanoparticle synthesis was also investigated with impacts on microemulsion stability and nanoparticle surface properties. The presence of chloride ions within compressed propane results in the formation of diamond-shaped copper nanoparticle assemblies. Compressed and supercritical fluids have been demonstrated as effective media for the production of nanomaterials by taking advantage of their novel, tunable properties. This investigation of metallic nanoparticle synthesis within the AOT reverse micelle system has provided an increased understanding of the controlling factors of microemulsion based nanoparticle synthesis with applications in the production of novel yet practical nanomaterials and the advancement of nanotechnology.