Emulsion inversion, which is the change in emulsion morphology from oil-in-water (O/W) to water-in-oil (W/O) or vice versa, is a handy alternative to produce fine and concentrated emulsions. It could result from the continuous stirring of an abnormal emulsion, in which case the external phase is not the one favored by the surfactant affinity but the one in higher volume proportion.

The inversion mechanism associated with continuous stirring often involves the formation of a multiple emulsion (w/O/W), in which a portion of the (W) external phase is continuously included as (w) droplets in the dispersed (O) phase drops. This inclusion is eventually opposed by droplet escape from the drops. When both phenomena are in dynamic equilibrium, the inversion cannot take place, but if the inclusion dominates over the escape, the apparent volume of the dispersed phase increases until a critical value is reached and the inversion is triggered.

In the nonionic-brine-kerosene system studied, the balance between the inclusion and escape is found to be affected by the formulation (as the hydrophilic-lipophilic-deviation HLD) and by the alcohol concentration. The interface composition influences the stability of both inner w/O and outer O/W emulsions, thus determining the kinetics of inclusion and the stirring time required to trigger the inversion into the W/O final morphology.