Quantifying the concept of physico-chemical formulation in surfactant-oil-water systems — State of the art

Abstract

The properties of surfactant-oil-water systems either at equilibrium or in dispersed state depend upon a large number of formulation variables that include not only the nature of the three components, but also the influence of electrolytes, alcohols and other additives (type and concentration), as well as temperature and pressure. These variables contribute to an overall affinity balance at interface, a fact that was recognized in Winsor’s pioneering work as an attempt to interpret the experimental results rendered by the use of Banckoft’s rule or Griffin’s HLB. Then, Shinoda introduced the Phase Inversion Temperature (PIT), a characterization parameter that relies on an easily attainable experimental situation, whereas Beerbower and Hill proposed the Cohesive-Energy-Ratio (CER) approach as an attempt to develop a theoretical concept that could be easily linked with experimental results. In the 1970s, the Enhanced Oil Recovery research drive resulted in an extensive amount of experimental work dedicated to the development of multivariate empirical correlations for the attainment of three-phase behavior, a very well defined physico-chemical situation. The correlations contain a numerical contribution of the effect of each formulation variable that was later identified as an energy contribution to the surfactant affinity difference (SAD), a generalized formulation variable. The straightforward use of the correlations motivated experimentalists to extend its validity to very different systems, far beyond the original oil recovery scope. On the other hand, the surfactant partition coefficient between oil and water, an early measurement of the physico-chemical match, has been recently reinstated to a prominent place thanks to enhanced analytical methods; this approach is shown to lead to the same kind of quantitative description as the SAD, with a partial contribution of each group to the overall balance.