Emulsification

Abstract

The aim of emulsification is to produce an interface between two immiscible fluids and to increase its area. However, the amount of energy needed is quite small. For example, to transform one liter of a 50/50 water/oil mixture with an interfacial tension of 10mN/m into one-micrometer drops, an energy of 15 J is necessary, which corresponds to the energy consumed by a 60 W light bulb in 0.25 s. In practice, however, a lot of energy is lost during emulsification through heating, either because of viscous dissipation for a mechanical energy supply or through diffusion or convection for a chemical energy supply. Reduction of this high amount of lost energy is a real challenge in industrial emulsion production. From a more fundamental point of view, the mixture obtained is in a metastable state and therefore the properties of an emulsion depend not only on the state variables (temperature and composition), as in the case of a thermodynamic system, but also on the preparation method. For this reason, emulsification is of the utmost importance. Different emulsification routes can be distinguished. After a quick review of the existing emulsification methods, we shall focus on one particular emulsification technique, which consists in shearing a crude, macroscopically homogeneous mixture [2], because in this case, the flow can be controlled and therefore some information can be extracted as to the fragmentation mechanism and the conditions required to obtain either calibrated or polydisperse emulsions.