chapter  12
46 Pages

Microemulsions in Near-Critical and Supercritical Fluids

ByEric J. Beckman, John L. Fulton, Richard D. Smith

Although the discovery that micelles and microemulsion phases could be stabilized in supercritical fluid (SCF) solutions was made in the authors’ laboratory less than 5 years ago, our knowledge of these systems has progressed rapidly. The combination of the unique properties of SCFs (e.g., viscosity, diffusion rates, solvent properties, etc.) with those of a dispersed microemulsion (or reverse micelle) phase creates a whole new class of solvents. The microemulsion phase adds to the properties of the SCF what amounts to a second solvent environment, which is highly polar and which may be manipulated using pressure. This second phase can itself manifest a wide range of solvent properties. Although SCFs are very attractive for separation and reaction processes owing to their density-dependent properties, they are limited at moderate temperatures and pressure by their inability to appreciably solvate most moderately polar solutes and nearly all ionic materials. 1 The addition of a dispersed droplet phase (forming a microemulsion) provides a convenient means of solubilizing highly polar or ionic species into the low polarity environment of the SCF phase. Hence, the combination of supercritical solvents with microemulsion structures provides a new type of solvent with some unusual and important properties of potential interest to a range of technologies.