Diffusion and interaction of emulsifiers in double emulsions and their effect on the release of encapsulated substances

Double emulsions show great potential regarding the encapsulation of hydrophilic components in food, cosmetics and pharmaceuticals. Thereby, an active substance is dissolved in a water phase (W1), which is emulsified in the oil phase (O) protecting the active. The inner emulsion again is emulsified in the outer water phase (W2) for aqueous applications. Due to stability issues, only few products currently exist. During storage, the inner water phase and consequently the active ingredient is lost.
In W1/O/W2 double emulsions, a lipophilic emulsifier stabilizes the encapsulated inner water droplets. A hydrophilic emulsifier prevents the coalescence of the oil droplets with each other. To produce double emulsions, the emulsifiers are added separately to different phases. The hydrophilic emulsifier dissolves in the outer water phase, the lipophilic emulsifier in the oil phase. By diffusion, however, the emulsifiers can distribute over time at both interfaces. This can lead to interactions between the emulsifiers, which can strongly decrease the stability of the double emulsion. These interactions are difficult to isolate and describe in double emulsions.
... mehr
In this work, the interfaces in double emulsions are investigated in simplified model systems. In these models, the diffusion and interaction of the emulsifiers is measured and the resulting stability of the emulsion is determined. With the “Diffusion and Coalescence Time Analyzer” (DCTA) the behavior of single drops at the interface can be characterized [1]. In this setup, drops of the W1 phase are placed at a quasi-planar O-W2 interface and their stability against coalescence is measured (see Figure 1). Additionally, the diffusion of the hydrophilic emulsifier to the inner interface is examined. This method gives the opportunity to find emulsifier pairings that show no negative interaction and are therefore suitable for the production of stable double emulsions [2].