Effect of surfactant on interfacial film and stability of highly concentrated emulsions stabilized by various binary surfactant mixtures

The interfacial properties of binary surfactant mixtures, prepared by mixing a poly(isobutenyl) succinic anhydride derivative with a series of non-ionic oil soluble (Spans) and water soluble (Tweens) compounds with varying structure (length, presence of double bonds, number of arms) hydrophobic tails, were investigated. The Rosen method was used to characterize the synergism between the two surfactants. The various surfactant compositions were used in the preparation of super-concentrated (92.4 wt%) water-in-oil emulsions. The properties of the interface layers were determined by the Wilhelmy method and correlated with the time to the start of crystallization of the oversaturated aqueous phase, stability with aging and resistance to shearing during emulsification and pumping. It was shown that synergism between the surfactant and co-surfactant is the main factor determining stability of the emulsions, and that it depends on the structure of the co-surfactant. Stability was found to be much more sensitive to the Span structure than to the Tween structure. Some of the Tweens family enables surfactant compositions that provide quite acceptable stability for different technological applications such as droplet refinement during production, an adequate long-term storage time and good pumping characteristics. (C) 2014 Elsevier B.V. All rights reserved.