Interfacial behavior of oil/oil and oil/water soluble binary surfactants and their effect on stability of highly concentrated W/O emulsions

Instability of highly concentrated water-in-oil emulsions which contain a metastable inorganic salt solution in a form of drops arises from the crystallization of salt in the dispersed phase, both on the shelf and under high shear. In this work the interfacial properties of two binary mixtures of oil/oil soluble and oil/water soluble surfactants with different molar ratios were studied to determine their effect on the stability of manufactured emulsions. The two mixed surfactants used were mainly poly (isobutenyl) succinic anhydride (PIBSA)-based surfactant with either sorbitan monooleate (SMO) (oil/oil soluble) or with polyoxyethylene sorbitan monooleate (Tween 80) (oil/water soluble). Interfacial studies showed completely opposite behavior of these two mixtures with changing concentration of polymeric surfactant. A synergetic effect between PIBSA-Mea and Tween 80 molecules was evident. PIBSA/Tween 80 emulsions exhibited better shelf stability than the PIBSA-Mea/SMO mixtures due to the efficiently packed interfacial film produced by this synergetic binary surfactant mixture. In addition, a significant improvement in stability under high shear conditions was achieved with the oil/water soluble PIBSA/Tween 80 mixture. The results showed that the interfacial study are important for the understanding of instability due to crystallization in emulsions with an oversaturated dispersed phase.