For the production of nanofoams, which have very small heat conductivity and special optical properties, Strey et al developed the new procedure: Principle Of Supercritical Microemulsion Expansion (POSME). The principle is based on the formulation of supercritical microemulsions containing nano-sized spherical micelles swollen by a supercritical fluid. In this study we used the non-toxic and non-flammable carbon dioxide. Staying above the critical parameters, T_c = 31°C and p_c = 72 bar, allows to continuously expand the CO₂-swollen micelles in a supercritical state. This work examines whether the well-known properties of microemulsions at atmospheric pressure are also found at increased pressure. We studied the temperature dependent phase behaviour of systems of the type H₂O/NaCl - CO₂ - technical non-ionic surfactant at a pressure of p = 220 bar. For the first time the typical phase inversion of a non-ionic surfactant system from a CO₂ - in - water to a water - in - CO₂ microemulsion is found. It turned out that a hydrocarbon-type surfactant could solubilize supercritical CO₂ only inefficiently. The addition of a perfluorinated surfactant led to an improved efficiency and could be the key for an efficient solubilisation of supercritical CO₂. Having determined the phase behaviour systematically, we performed small angle neutron scattering (SANS) experiments on these scCO₂-microemulsions to elucidate the microstructure and their variation with pressure. To this end we built a new high pressure cell with variable volume which is suitable for SANS experiments under pressures up to p = 250 bar. First results are presented.