Amphiphilic polyelectrolyte for stabilization of multiple emulsions

Multiple emulsions are complex thermodynamically unstable systems where both types of emulsion coexist. We investigated the stability behaviour of water-in-oil-in-water (W/O/W) emulsions formulated with a hydrophobically modified poly(sodium acrylate) emulsifier at the outer interface and a monomeric surfactant (span 80) at the inner interface. Their stability was tested through release kinetics of a marker (NaCl) initially encapsulated in the aqueous droplets, and by rheology. Slow release rates and remarkably long shelf-life were obtained compared to typical multiple emulsions stabilized by two commonly used surfactants (span 80 and tween 20). In addition, we prepared stable highly concentrated multiple emulsions. Their rheological behaviour indicated that the internal interface was essentially covered with span 80. Thus, transportation of the polymer across the oil phase is limited, which in turn explains, at least partially, the stability improvement in the presence of the polymeric emulsifier. Finally, the long lifetime of the emulsions allowed study by diffusing wave spectroscopy of the interactions between the droplets and the globule surface which are important for understanding the destruction mechanisms of multiple emulsions. (C) 2003 Society of Chemical Industry.