Self-emulsification of surfactant-oil mixtures produced by diffusion and chemical reaction

Drops having diameters of order 100 pin and containing various combinations of oils, surfactants, and in some cases alcohols were injected into water or aqueous salt or buffer solutions. The resulting dynamic behavior was observed by videomicroscopy. Spontaneous emulsification yielding oil droplets a few microns in diameter was seen in a variety of systems when diffusion and/or chemical reaction caused inversion of the drop from an oil-continuous to a water-continuous phase leading to local supersaturation in oil. Surfactants used included nonionic (C12E6), anionic (Aerosol-OT). and zwitterionic (tetradecyldimethylamine oxide). In some experiments inversion occurred because a lipophilic surfactant was converted to a hydrophilic surfactant, e.g., a double-chain phospholipid to two single-chain surfactants.