Flow-induced phase inversion in the intensive processing of concentrated emulsions

Flow-induced phase-inversion (FIPI) phenomenon is applied to the emulsification of highly viscous (polymeric) epoxide resins to obtain concentrated colloidal emulsions. It is shown that the phase inversion of a W/O emulsion can be achieved not only through changes in thermodynamic state variables but also by the imposition of ultra-high deformation (extensional) rates under constant thermodynamic conditions. Phase inversion is carried out using a model static mixer (multiple expansion contraction static mixer, MECSM) which is essentially a series of short capillaries with flow dividers; The degree of phase inversion is dependent on the rate of deformation and number of mixer units. The effects of temperature, surfactant concentration and composition and mean hydrophile-lipophile balance on phase inversion behaviour are investigated. The properties of the emulsions produced by this FIPI-emulsification are evaluated through particle size and viscosity measurements and optical and electron microscope studies. Mechanisms of phase inversion and subsequent emulsion droplet size reduction are proposed which are based on the behaviour of microstructured fluids under converging and diverging flows. The significance of the type of surfactant system used in the experiment is discussed in facilitating the flow-induced phase inversion and subsequent emulsion droplet size reduction, as well as emulsion stability. (C) 1997 Elsevier Science Ltd.