Emulsion catastrophic inversion from abnormal to normal morphology. 7. Emulsion evolution produced by continuous stirring to generate a very high internal phase ratio emulsion

Abstract

When emulsion inversion is produced by continuous stirring, from an abnormal water-in-oil-in-water (w/O/-W) system to a normal water-in-oil (W/O) morphology, to create a very high internal phase ratio emulsion (water fraction fw >0.85), the main mechanism is the continuous inclusion of the initial W external phase as w droplets into the dispersed O drops, which results in an increase of the dispersed (w + O) volume. Once a critical dispersed volume fraction is reached and a local inversion is detected, an additional stirring time, referred as &propagation time&, is required in order to complete the inversion of the system into a W/O morphology, instead of the usual behavior which is an almost instant culmination. This time is related to the energy input necessary to overcome the Laplace pressure involved in the change of the interfacial curvature. The present work shows how this propagation time is affected by the formulation, the composition, and the stirring conditions. © 2008 American Chemical Society.