Stability of nonaqueous emulsions

We examined the stability of emulsions of oil in several nonaqueous polar liquids using commercially available nonionic surfactants. Stable nonaqueous emulsions were only obtained with formamide and dimethylsulfoxide. Hydrogen bonding, and not polarity, appears to be the important factor determining the emulsifying power of a solvent. Ostwald ripening plays a much more important role in the stability of these nonaqueous emulsions than in the corresponding aqueous systems. This destabilizing 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 molecule protects emulsions against droplet coalescence. Thus, emulsions in formamide and dimethylsulfoxide did not show any breakdown when stabilized with a triblock copolymer of polyoxyethylene-polyoxypropylene-polyoxyethylene.