Microemulsions formation carbon dioxide

The environmentally benign, nontoxic, and nonflammable fluids water and carbon dioxide (C02) are the two most abundant and inexpensive solvents on Earth. Water-in-C02 (w/c) or C02-in-water (c/w) dispersions in the form of microemulsions and emulsions offer new possibilities in waste minimization for the replacement of organic solvents in separations, reactions, and materials formation processes. Whereas the solvent strength of C02 is limited, these dispersions have the ability to function as a universal solvent medium by solubilizing high concentrations of polar, ionic, and nonpolar molecules within their dispersed and continuous phases. These emulsions may be phase-separated easily for product recovery (unlike the case for conventional emulsions) simply by depressurization. 

Fremgen DE, Smotkin ES, Gerald RE, Klinger RJ, Rathke JW. Microemulsions of water in supercritical carbon dioxide an in-situ NMR investigation of micelle formation and structure. J Supercrit Fluids 2001 19 287-298. 

Lee CT, Psathas PA, Zielger KJ, Johnston KP, Daib HJ, Cochran HD, Melnichenko YB, Wignall GD. Formation of water-in-carbon dioxide microemulsions with a cationic surfactant a small-angle neutron scattering study. J Phys Chem B 2000 104 11094-11102. 

So far we can generate supercritical carbon dioxide microemulsions with varying mi-crostructures under a pressure of p = 220 bar. The next step is to find appropriate surfactants for an efficient solubilisation of C02 as today over 48 wt.% surfactant is required to formulate a one-phase region in the system H20/NaCl-C02-Lutensol XL70 (see Fig.ll.3).Good amphiphilic candidates with C02 -philic parts are fluorinated surfactants. Once a more efficient surfactant has been identified, the formation of microemulsions under pressure has to be studied. 

Nanoparticle Formation in Rapid Expansion of Water-in-Carbon Dioxide Microemulsion into Liquid... 

Thurecht, K., Hill, D. and Whittaker, A. (2006). Investigation of spontaneous microemulsion formation in supercritical carbon dioxide using high-pressure NMR, J. Supercrit. Fluid, 38,... 

The uses of fluorosurfactants to stabilize water-in-carbon dioxide (w/c) microemulsions are reviewed. A systematic study with fluorosuccinate surfactants of the effects of the extent of fluorination of hydrophobic chains on the stability and structures of these w/c phases is described. Therefore, it has been possible to delineate a structure-function relationship for these fluorosurfactants with reference to their efficiency of water-in-carbon dioxide microemulsion formation. An important finding is that one of these surfactants, namely sodium bis(l//,l//-perfluoropentyl)-2-sulfosuccinate (di-CF4), is able to stabilize w/c microemulsions close to the bottle pressure of a normal CO2 cylinder. Such efficient surfactants of this kind have obvious advantages for potential practical applications of CO2. 

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