Mass Transfers Within Emulsions Studied by Differential Scanning Calorimetry (DSC) - Application to Composition Ripening and Solid Ripening

Abstract

In this chapter mass transfer within simple, mixed and multiple emulsions will be considered. Simple emulsions are made of either water droplets dispersed within an oil phase (W/O) or oil droplets dispersed within an aqueous phase (O/W). Mixed emulsions are obtained by mixing gently to avoid coalescence, two simple emulsions the composition of the droplets being different. Finally, multiple or double emulsions are obtained by dispersing either a simple emulsion (W/O) in an aqueous phase to get what is referred as W/O/W emulsion or by dispersing a simple emulsion (O/W) in an oil phase to get an O/W/O emulsion. These systems are known to be instable and their evolution towards bulk separated phases is the result of coalescence of the droplets due to different main mechanisms as Ostwald ripening, flotation, aggregation, sedimentation or creaming. This evolution can be considerably reduced by adding in their formulations either surfactants or/and particles. Thus, kinetic stability can be obtained. In that case other mechanisms can be studied, mechanisms that traduce an evolution of the systems as well but breakdown of the emulsions is not the result of the evolution understudy. It is this kind of evolution due to mass transfer that will be studied in this chapter. The bibliography will be done in each part dealing with the different kinds of emulsions considered. First mass transfer in simple emulsions will be described. For these systems a not very well known mass transfer can be the result of the coexistence of still liquid droplets and yet solid ones at a temperature below the solid/liquid equilibrium temperature. This situation is the result of nucleation phenomena that create a delay for the formation of a solid germ that will induce the solidification of the droplets at different temperatures during the regular cooling of the emulsion. Another phenomenon leading to mass transfer in these systems is obtained by adding a material in the oil phase in a W/O emulsion, material that will diffuse and react