Metallic nanoparticles production and processing using supercritical carbon dioxide and carbon dioxide gas-expanded liquids as tunable solvents

Nanoparticles have gained attention of late for their potential application in catalysts, sensors, semiconductors, optical materials and numerous other areas. Respectful of this burgeoning field, this preliminary dissertation focuses on the use of supercritical fluids and CO2 gas-expanded liquids as tunable solvent systems to direct the synthesis and manipulation of nanoparticles.; The research in this dissertation extends particle synthesis in reverse micelles to systems using supercritical carbon dioxide as the bulk solvent. Carbon dioxide has a supercritical region which is reached at relatively mild temperatures and pressures but it is also nontoxic, inexpensive, nonflammable, environmentally friendly, and possesses low viscosity, high diffusivity, and no surface tension, thus making it a very desirable processing fluid. Newly discovered CO2-philic surfactants (i.e., perfluoropolyether ammonium carboxylate (PFPE-NH4)) were utilized and found to result in stabilized silver intermediates which are stabilized by the surfactant and evidenced by multiple UV-Vis absorption bands. A series of experiments were performed where buffering, elimination of the water core, and formation of reverse micelles in a hydrofluoroether solvent using the PFPE surfactant revealed the nature of the intermediate stabilization as an ionic interaction arising between the PFPE surfactant and the silver intermediates.; In order to overcome limitations associated with reverse micelle synthesis such as intermediate formation and low yield, metal particles were subsequently synthesized in a continuous flow apparatus using only CO2 solvent. Fluorinated ligands were used to stabilize metal particles formed from reduced CO2 soluble metal complexes. The synthesis routine decreases the difficulties associated with particle synthesis in CO2 while providing for future application to the continuous production of metallic nanoparticles.; A significant amount of supercritical CO2 knowledge can be transferred to CO2 gas-expanded liquids as tunable solvents. As such, these gas expanded liquid system were used to deposit ligand stabilized particles from organic solution using CO2 as the antisolvent. It was found that thin, low-defect films of these particles can be deposited on surfaces by CO2 pressurization and processed supercritically to avoid the wetting instabilities common to traditional liquid solvents. Slower CO2 pressurization and smaller ligand stabilized particles were shown to produce higher quality films.; These CO2 gas-expanded liquids were also used as tunable solvents for the size selection of ligand stabilized nanoparticles. It is shown that from an initial polydisperse solution (sigma = 30%), precise nanoparticle fractions having sigma = 10.1% can be recovered. Furthermore, multiple fractions were rapidly separated from an initial solution by adjusting only CO2 pressure. This new technique facilitates a significant reduction in process time and liquid solvent usage.