STABILITY OF EMULSIONS UNDER EQUILIBRIUM AND DYNAMIC CONDITIONS

In the present article we analyse the influence of various factors, bo th thermodynamic and hydrodynamic, on the stability of emulsion system s. The effect of the droplet size on the droplet lifetime in an emulsi on cream is quantified. The comparative importance of kinetic factors such as surface and bulk diffusion fluxes, or viscous and elastic surf ace stresses, is investigated. The fact that the emulsion films drain much more slowly when the surfactant is dissolved in the continuous ph ase (rather than in the disperse phase) provides a new understanding o f the Bancroft rule and the process of chemical demulsification. New t hermodynamic aspects of emulsion stability are also discussed. One of them is the relatively high surface electric potential of pure oil-wat er interfaces and adsorption monolayers of nonionic surfactants. Anoth er aspect is the role of non-DLVO surface forces, such as the hydratio n repulsion, oscillatory structural and depletion forces due to the pr esence of surfactant micelles. A criterion of emulsion stability is fo rmulated synthesizing the effects of the major factors. Finally we con sider the importance of the kinetic phenomena in emulsions formed from non-pre-equilibrated phases. (C) 1997 Elsevier Science B.V.