Preparation of a stable double emulsion: Study of the factors affecting the stability of the system (W1/O/W2)

The primary objective of the research was to prepare double emulsions of the type W1/O/W2 and investigate the factors affecting the mechanism of formation and the emulsions' stability respectively. A review of the literature indicates that stability of double emulsions requires a balance between Laplace and the osmotic pressure between W1 droplets in oil and between W1 droplets and the external aqueous phase W2. It was assumed a priori that the different interfacial films, W1/O and O/W2, were completely stable.; The study focused mainly on the formulation of two different systems: (1) the formulation of a stable W1/O/W2 emulsion using mineral oil with a concentration of over 12% of surfactant in the outer aqueous phase; (2) the formulation of a stable edible multiple emulsion using soybean oil. A stable emulsion (W1/O) is a critical first step to achieve before preparing a stable W1/O/W2 double emulsion. Consequently, we initially focused on the preparation of the primary emulsion, W1/O, and investigated the role of the W1/O film on the stability of the emulsion. Among the different classes of primary surfactants (low Hydrophile-Lipophile Balance) that we tested, only cetyl dimethicone copolyol (Abil Em90), A-B-A block copolymer (Arlacel P135), and polyglycerol ester of ricinoleic acid (Grinstead PGR90) produced a stable W/O emulsion.; The mechanical and electrical surface properties of these surfactants were also investigated using a monolayer technique. These three surfactants showed the following similar surface properties: (1) stable compressible and reversibly expandable monolayer; (2) irreversible adsorption at the interface; (3) high elasticity; and (4) high surface potential. The high values obtained for film elasticity give the interfacial film strong resiliency during stress. According to the high surface potential observed, the surfactant molecules appear to lie flat at the oil/water interface. In the case of polyglycerol ester of ricinoleic acid, the -OH groups on the fatty acid chains seem to serve as anchors at the O/W interface and are responsible for the high surface potential.; We also found that the presence of a thickener is necessary in the outer aqueous phase in order to reach a viscosity ratio of about 1 with W1/O. This allows the dispersion of the viscous primary emulsion into the W2 aqueous phase. The presence of the thickener also prevents phase separation due to its thixotropic property. However, the thickener must be compatible with the surfactants. Finally, another factor that needs to be considered is the interaction between the low and high HLB emulsifiers. In order to prevent destabilization of the films, the addition of the high HLB surfactant in W2 should not interact by displacement with the low HLB surfactant at the O/W2 interface.