Nanoparticles and nanocomposites offer unique properties that arise from their small size, large surface area, and the interactions of phases at their interfaces, and are attractive for their potential to improve performance of drugs, biomaterials, catalysts and other high-value-added materials. However, a major problem in utilizing nanoparticles is that they often lose their high surface area due to grain growth. Creating nanostrauctured composites where two or more nanosized constituents are intimately mixed can prevent this loss in surface area, but in order to obtain homogeneous mixing, de-agglomeration of the individual nanoparticle constituents is necessary. The presented work concerns the overall problem of nanoparticle deagglomeration, mixing and characterization. The experimental study involves measurements of the degree of deagglomeration as a result of the applied deagglomerating forces. Four different environmentally benign nanoparticle mixing methods are also being investigated, one of which is a unique approach in which, a supercritical fluid (SCF), such as supercritical carbon dioxide is used as an ideal medium for the purpose of intimately mixing nanoparticles. Supercritical carbon dioxide is used due to its beneficial properties such as a liquid-like density and solubility, yet gas-like diffusivity and viscosity, nonflammability, low toxicity and environmentally benign nature. Our method of nanoparticle deagglomeration and mixing currently under investigation is the rapid expansion of supercritical suspensions (RESS). In this process two types of nanoparticles are mixed together in a 1-liter high pressure tank. Rapid depressurization to atmospheric conditions, through a micron sized capillary nozzle results in deagglomeration and mixing. The exiting nanoparticles enter a collection box that will allow for the sampling of the aerosolized particles from the exiting jet stream. The sampling methods allow for characterization of the size distribution and degree of mixing at axial and radial distances from nozzle. The other mixing methods include use of high-impact mechanical blending as well as nano-powder fluidization through external agitations.

The sizing methods use the Aerosizer and the Scanning Mobility Particle Sizer (SMPS) by TSI, Inc. Mixing is characterized my multiple methods of electron microscopy. These include electron dispersive x-ray spectroscopy (EDX) on the scanning electron microscope (SEM) for micron scale characterization and elemental electron loss spectroscopy (EELS) on the transmission electron microscope (TEM). The results for degree of deagglomeration and mixing are presented.