Experimental investigation of phase inversion for stable emulsion formation.

Phase inversion refers to a phenomenon that occurs when an agitated oil in water emulsion, reverts quite suddenly to a water in oil and viceversa, due to a change of the spontaneous curvature of the surfactant(s) because of the temperature of the system or by changing the water volume fraction. This process is defined by some authors as a catastrophic event, because it appears to be a sudden and dramatic change in morphology caused by a gradual change in experimental conditions. Emulsification process is strongly affected by preparation method; very different particle size distribution could be achieved, which is strictly linked to the product stability. Phase inversion process leads to the formation of finely dispersed droplets in a continuous phase, unlike the classical emulsion preparation process, which consists in dissolving the surfactant in the continuous phase and to add the dispersed phase under appropriate agitation, by which macroemulsions could be formed. In this work an experimental investigation of phase inversion emulsification to produce stable samples has been performed. The emulsion morphology has been characterized in detail by direct observation in confocal and ESEM microscopy, the fluid rheological and electrical characterizations are also reported. In Fig. 1 the evolution of the system morphology as a function of the water content has been observed in confocal morphology. The water phase is coloured in red by adding a small concentration of rodamine, the oil phase is in black.