STABILITY OF NONAQUEOUS EMULSIONS

We examined the stability of emulsions of oil in several nonaqueous po lar liquids using commercially available nonionic surfactants. Stable nonaqueous emulsions were only obtained with formamide and dimethylsul foxide. Hydrogen bonding, and not polarity, appears to be the importan t factor determining the emulsifying power of a solvent. Ostwald ripen ing plays a much more important role in the stability of these nonaque ous emulsions than in the corresponding aqueous systems. This destabil izing process can be prevented, however, by addition to the oil phase of a small amount (1%) of an oil that has a very low solubility in the continuous phase. Furthermore, a larger size of the surfactant molecu le protects emulsions against droplet coalescence. Thus, emulsions in formamide and dimethylsulfoxide did not show any breakdown when stabil ized with a triblock copolymer of polyoxyethylene-polyoxypropylene-pol yoxyethylene. (C) 1997 Academic Press.