Reactions and Synthesis in Microemulsions and Emulsions in Carbon Dioxide

I. INTRODUCTION The environmentally benign, nontoxic, and nonflammable fluids water and carbon dioxide (CO2) are the two most abundant and inexpensive solvents on earth. Recently discovered water/CO2 (W/C) and CO2/water (C/W) microemulsions [1,2] and emulsions [3,4] offer new possibilities in waste minimization by replacing organic solvents in separations, reactions, and materials formation processes. Microemulsion droplets 2 to 10 nm in diameter are optically transparent and thermodynamically stable, whereas kinetically stable emulsions and latexes in the range of 200 nm to 10 m are opaque and thermodynamically unstable. These studies in CO2 result from a foundation that was built for water/oil microemulsions [5,6] and polymer latexes [7] in ethane and propane as reviewed [8-10]. Because CO2 is nonpolar (unlike water) and has weak van der Waals forces (unlike lipophilic phases), it may be considered a third type of condensed phase. Consequently, polymers with low cohesive energy densities and thus low surface tensions are the most soluble in CO2 (e.g., fluoroacrylates [11], fluorocarbons, fluoroethers [12], siloxanes, and to a lesser extent propylene oxide).