Double emulsions stabilized by macromolecular surfactants

Multiple emulsions are emulsions within emulsions, stabilized traditionally by monomeric emulsifiers both at the inner and outer interface. Double emulsions are thermodynamically unstable and fast coalescence, as well as fast release of markers and drugs, have been the main drawbacks of this technology. Polymeric synthetic emulsifiers, as well as natural macromolecules in combination with monomeric emulsifiers, have recently been studied and evaluated. The review brings new results on the use of amphiphilic proteins such as BSA and casein along with monomeric emulsifiers in relation to improved stability and release properties. Kinetic results are brought to demonstrate the role of BSA as the inner emulsifier and the outer emulsifier. Diffusion controlled mechanisms are suggested. Synthetic block copolymers based on silicon backbones and polyethylene oxide side-chains have also been studied. Double emulsions with relatively small droplets (5 μm) are formed and excellent stability (to storage, sheer and dilution) is obtained. Release data indicates that the newly designed double emulsions have longer shelf-life and very slow rates of release of markers. Such emulsions are good candidates for agricultural formulations.