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Review date: July 24, 2003
PNNL-SA-27883

Synthesizing and Dipsersing Silver Nanoparticles in a Water-in-Supercritical Carbon Dioxide Microemulsion

M. Ji, X. Chen, C. M. Wai, J. L. Fulton, J. Am. Chem. Soc., 121, 2631-2632, (1999).

Abstract: Reverse micelles and microemulsions formed in liquid and supercritical carbon dioxide (CO2) allow highly polar or polarizable compounds to be dispersed in this non-polar fluid. However, since the polarizability per unit volume of dense CO2 is quite low, it is difficult to overcome the strong Van der Waals attractive interactions between particles in order to stably suspend macromolecular species. Conventional surfacants by themselves do not form reverse micelles or microemulsions in CO2 because the Van der Waals inter-droplet attractions are too high. The use of surfactants or cosurfactants with fluorinated tails provides a layer of a weakly attractive compound covering the highly attractive droplet cores thus preventing their short-range interactions that would destabilize the system. Using this strategy, we describe a method to synthesize and stabilize metallic silver nanoparticles having diameters from 5 to 15 nm in supercritical CO2 using an optically transparent, water-in-CO2 microemulsion.