Emulsion Catastrophic Inversion from Abnormal to Normal Morphology. 5. Effect of the Water-to-Oil Ratio and Surfactant Concentration on the Inversion Produced by Continuous Stirring

When the emulsion inversion from abnormal to normal morphology is induced by continuous stirring only, the required duration and the kinetics of the process are found to be related to the water-to-oil ratio of the initial emulsion. The emulsion inversion from O/W to W/O occurs through the formation of a w/O/W multiple emulsion, in which water from the external phase is continuously included as droplets in the dispersed oil phase drops until a critical dispersed phase value is reached and the inversion takes place. For intermediate, initial, continuous phase content (0.6 and 0.7 water phase fraction), the water inclusion is found to take place throughout the entire process. In contrast, at high-water, continuous phase content (0.8 water phase fraction), this inclusion process appears to be delayed, and the filling of the oil drops takes place suddenly just before the inversion occurrence. The influence of the surfactant concentration is related to the initial water content, too. At fw = 0.6, the inversion time is the same whatever the surfactant concentration is, but at fw 0.7 and 0.8, there is an optimal surfactant concentration at which the inversion time is minimal. For systems with a given hydrophilic−lipophilic balance (HLB = 6) and 7 wt % of surfactant concentration, there is, according to conductivity measurements, a unique, critical dispersed phase content at which inversion is triggered, no matter the initial WOR.