Carbon dioxide/water, water/carbon dioxide emulsions and double emulsions stabilized with a nonionic biocompatible surfactant.

Whereas microemulsions and emulsions of water and carbon dioxide have been reported for various surfactants with fluorocarbon surfactants, relatively few studies have been successful in forming these emulsions with hydrocarbon surfactants. Stable CO(2)/water and water/CO(2) emulsions with droplets smaller than 1 microm were formed at high shear with the nonionic surfactant polysorbate 80 (Tween 80). In order to understand the emulsion phase behavior at high shear, low shear phase behavior experiments were performed at the same temperature and pressure. For pressures up to 250 bar and temperatures of 25-60 degrees C, C/W emulsions were formed for water concentrations as low as 10%, as the surfactant is highly hydrophilic with limited CO(2)-philicity. However, with added NaCl, the surfactant partitioned away from water toward CO(2), and W/C emulsions were formed with droplet sizes from a few 100 nm to a few mum in diameter, which were stable for at least 24 h. In addition C/W/C double emulsions are reported for the first time, as well as W/C/W/C triple emulsions. The ability to form emulsions with environmentally benign solvents, CO(2) and water, and biocompatible surfactants is desirable for green reaction and separation processes, as well as production of materials including pharmaceutical particles and composites.