On the Mechanism of the Inversion of Emulsions

In the inversion process of an emulsion in a stirred vessel, a certain effective volume fraction is required in order to initiate inversion. During continuous stirring, this effective volume fraction can be generated by enclo sing the continuous phase into the droplets of the dispersed phase. This enclosure occurs as a result of the coalescence of droplets of the dispersed phase. However, the enclosed droplets can also ‘disappear’, either by dissolution or by escape to the continuous phase. The effective volume fraction of the dispersed phase continues to increase as long as the inclusion dominates over the escape. It is possible that a steady-state is reached in which the rate of inclusion balances the rate of ‘disappearance’. In this case inversion will not be obtained. This increase of the effective volume fraction is a gradual process, which takes the largest part of the inversion process time. The actual inversion process starts when the effective volume fraction required for inversion is approached. At that stage the droplet size increases strongly and inversion occurs subsequently. These very large droplets can only be formed when there is such a large coalescence frequency that the increase in diameter due to coalescence can no longer be completely compensated by droplet break-up events, which results in a rapidly increasing droplet diameter.