MECHANISMS FOR LOWERING OF INTERFACIAL-TENSION IN ALKALI ACIDIC OIL SYSTEMS - EFFECT OF ADDED SURFACTANT

Experiment al studies are conducted in order to determine the physicochemical mechanisms responsible for lowering of interfacial tension in alkali, surfactant, and surfactant-enhanced alkali/acidic oil systems. A well-defined model oil is chosen to examine the influence of various surfactants and surfactant mixtures, such as oleic acid and its ionic counterpart, sodium dodecyl sulfate, petroleum sulfonate, and isobutanol, on equilibrium interfacial tension. With added surfactant alone, the interfacial tension goes through an ultralow minimum with increasing acid concentration. Thus proves for the first time that the un-ionized acid species plays a major role in affecting interfacial tension, and appears to be the key element in the synergistic process taking place between the added surfactant and the ionized acid species. The un-ionized acid species partitions the added surfactant out of the aqueous phase, and the minimum in interfacial tension occurs when the partition coefficient is about unity. When alkali is added, the low interfacial tension is not lost, but actually shifts to different acid concentrations in a systematic way.