Emulsification processes. Mechanisms of emulsion formation

Emulsions are liquid-liquid dispersions: single emulsions belong to two types: water-in-oil (W/O) or oil-in-water (O/W), and multiple (in fact double) emulsions to the W/O/W or O/W/O types. Variable in granulometry and kinetic stability, they inevitably evolve, albeit more or less rapidly, through various processes of droplet migration and/or enlargement, towards phase separation. They are found in a wide variety of fields, from foodstuffs to explosives, pharmaceuticals, cosmetics, textiles, lubricants, paper-making, paints, oil extraction and mineral processing. Their properties (type, viscosity, particle size, stability) depend on composition (formulation), temperature and manufacturing method (process). Apart from a few cases where emulsions are undesirable (e.g. in oil extraction), or temporarily desirable (e.g. during a chemical reaction or extraction process), the aim is to satisfy the criteria for preparing emulsions that are as stable as possible, so that they can be kept for a long time. After a brief review of emulsion formulation and characterization, this article looks at the energy involved in emulsification (viscous dissipation, droplet deformation, etc.) and presents the mechanisms involved in the process: droplet formation and break-up, effect of the emulsifier.

The following article [J 2 153] describes the main industrial preparation processes, their technology and the equipment required.