Dissolution of nonionic surfactant mixtures

Videomicroscopy was used to observe dissolution in water of drops of neat commercial nonionic surfactants and mixtures of pure nonionic surfactants. The time required for complete dissolution of such drops was greater at temperatures slightly below their cloud points than at lower temperatures, in contrast to behavior found for pure nonionic surfactants. Moreover, emulsification within and/or at the surfaces of surfactant drops was often observed at temperatures just below their cloud points. During the latter part of the dissolution process for these conditions, the rate of dissolution slowed, and drops became elongated and formed conical projections, apparently of the lamellar liquid crystalline phase. In some experiments, the projections emitted jets of small droplets or particles. While aspects of these intriguing phenomena are not completely understood, some interpretation is given, which makes use of relevant ternary phase diagrams.