Particle stabilized water in water emulsions

Food products often contain mixtures of incompatible water soluble macromolecules such as proteins and polysaccharides. When two aqueous solutions of incompatible macromolecules are mixed they separate into two phases each enriched in one of the two macromolecules. Contrary to oil-water (O/W) emulsions, water/water (W/W) emulsions cannot be stabilized by addition of surfactants and in food applications macroscopic phase separation is avoided by gelling one or both phases. However, recently it was shown that W/W emulsions can be stabilized to varying extents by addition of particles. Such particle stabilized emulsions are also known as Pickering emulsions and have been studied extensively for O/W emulsions. Here the literature on particle stabilization of W/W emulsions is reviewed. The behavior of particle stabilized W/W emulsions is found to be quite different from that of O/W emulsions due to the much smaller interfacial tension and the much larger length scale at which the interface expresses itself. Besides the particle size, interaction of the particles with the macromolecules in the mixture and with each other at the interface appears to play a decisive role for stabilization.