SEPARATIONS Phase Separation of Liquid Mixtures in the Presence of Surfactants

The presence of surface-active compounds does not influence the settling time of a partially miscible liquid mixture as it phase separates. On the other hand, when the same mixture is agitated isothermally while in its two-phase state, its settling time greatly increases if surfactants are added. This phenomenon is monitored microscopically through a series of direct visualizations and is explained theoretically by applying the model H, showing that phase separation is governed by the convective motion due to capillary forces. These forces induce a net attraction between droplets which greatly dominates the repulsive forces due to the presence of surfactants.