Assessment of the stability of water in water emulsions using analytical centrifugation

Abstract

Water in water (W/W) emulsions were prepared by mixing aqueous dextran and polyethylene oxide (PEO) solutions. Addition of different amounts of the polysaccharide chitosan inhibited coalescence of dispersed droplets of the dextran phase in the continuous PEO phase to different extents depending on the concentration and pH. Transmission profiles were measured during centrifugation and analysed. It is shown that the evolution of the transmission profile is determined by the relative rates of coalescence and sedimentation of the droplets. The rate of coalescence of the sedimented droplets into a continuous dextran phase depends on the resistance of the protective chitosan layer to compression by centrifugation. It is concluded that the efficacy of stabilization of W/W emulsions can rapidly be quantitatively assessed, but it is difficult to deduce the behaviour under gravity from that observed during centrifugation.