Coalescence of Inner Water Droplets in Double Emulsions Due to Surfactant Transport through Oil

Double emulsions of the water-in-oil-in-water type are promising encapsulation and delivery systems containing at least one hydrophilic and one lipophilic surfactant. Currently, there are still very few implementations on the market, as these systems are subject to extreme stability problems. This study focuses on stability problems induced by the transport of hydrophilic surfactant molecules through the lipophilic phase to the encapsulated inner water droplets. In particular, a model system was developed to quantify surfactant transport and resulting effects on the coalescence of encapsulated water droplets. Changes in stability of the inner water droplets are demonstrated for different surfactants and compared to the stability of the inner water-in-oil emulsions and corresponding double emulsions.