Phase behaviour of propane- and scCO(2)-microemulsions and their prominent role for the recently proposed foaming procedure POSME (Principle of Supercritical Microemulsion Expansion).

In this study we present a systematic investigation of the phase behaviour of microemulsions containing near- or supercritical solvents. The starting point of this study are microemulsions of the type water/NaCl-propane-polyethyleneglycol mono-n-alkyl ether at a pressure of p = 220 bar. Replacing propane stepwise by supercritical carbon dioxide the typical phase behavior of microemulsions systems can still be observed using scCO(2) as the only nonpolar solvent. Thus, increasing the temperature a phase inversion from a CO(2)-in-water to a water-in-CO(2) microemulsion via a balanced CO(2) microemulsion is found for the first time. Such mixtures of water and scCO(2) are expected to be versatile solvents in green chemistry. In addition, the formulation of supercritical microemulsions is the initial step in the Principle Of Supercritical Microemulsion Expansion (POSME) (DE Pat., 102 60 815 B4, 2008), which is a promising new approach for the production of low-cost nanocellular foams. In contrast to conventional foaming procedures, this approach suggests the formation of nanofoams by expanding micelles swollen with a supercritical blowing agent, thereby ensuring the unhindered formation and growth of bubbles without mass transport.