Single- and two-step emulsification to prepare a persistent multiple emulsion with a surfactant-polymer mixture

The regions corresponding to different emulsion morphology occurrences have been clearly identified on a bidimensional formulation-composition map. Multiple emulsions spontaneously form when there is a conflict between the formulation and composition effects. In such systems the most external emulsion is found to be unstable when the formulation effect is produced by a single surfactant. The use of a proper surfactant-polymer mixture allows one to strongly inhibit the mass transfer and to considerably lengthen the equilibration between interfaces. As a consequence, the multiple emulsion can be stable enough to be used in encapsulation and controlled-release applications. The area where multiple emulsions occur and their characteristics (conductivity and amount of encapsulated external phase) are reported for a system containing a sorbitan ester lipophilic surfactant and a diblock poly(ethylene oxide)-poly(propylene oxide) hydrophilic polymer, as a function of the formulation and composition, for a single-step process in which a specific amount of mechanical energy is supplied. An increase in the oil viscosity is found to alter the map and to modify the multiple emulsion characteristics. The application of the results to emulsion-making technology is discussed.