(608a) Environmentally Benign Nanomixing by Sonication in Supercritical CO2

Due to increased use of nanocomposites and nanomaterials, mixing at nanoscale has become important. Conventional dry mixing is not effective in achieving mixing at nanoscale, and wet mixing suffers from different disadvantages including the need for a non-solubilizing and wetting liquid, and the removal of the liquid after mixing. To overcome the disadvantages, we propose to replace the liquids by supercritical carbon dioxide, which is environmentally benign, non flammable, non toxic, low viscous and inexpensive fluid. In the proposed method, ultrasound is applied to the suspension of agglomerated nanoparticles in supercritical carbon dioxide. Due to the high enough molar density and low viscosity of carbon dioxide, high impact collisions are created during sonication. These collisions are strong enough to provide a good mixing, and the final mixture is obtained by simple depressurization. The method was tested for binary mixtures of alumina/silica, silica/titania, MWCNT (multiwalled carbon nanotubes)/silica, and MWCNT/titania. The effects of sonication intensity and pressure (e.g., molar density of carbon dioxide) on the degree of mixing are studied. Comparative study was also done with liquid hexane as a media for mixing. Quantitative characterization (e.g., composition standard deviation, degree of homogeneity) of mixing of alumina/silica and silica/titania was done with energy dispersive x-ray spectroscopy. The qualitative characterization of binary mixing of MWCNT/silica and MWCNT/titania was done using field emission scanning electron microscope and day light illumination spectrophotometer. Results show that mixing in carbon dioxide and at higher ultrasound amplitude was as good as in liquid hexane. And the final mixed product does not contain any residual media as in the case of liquid hexane in conventional method.