CREAMING AND RHEOLOGY OF EMULSIONS CONTAINING POLYSACCHARIDE AND NONIONIC OR ANIONIC SURFACTANTS

The influence of the anionic polysaccharide rhamsan on the kinetics of creaming of concentrated oil-in-water emulsions (30 wt.% mineral oil, 1 wt.% surfactant, pH 7) has been monitored visually and by ultrasound velocity scanning. The rate and extent of serum separation was found to depend not only on the polysaccharide concentration but on whether the emulsifier was a non-ionic surfactant (polyoxyethylene (20) sorbitan monolaurate (Tween 20)) or an anionic surfactant (sodium dodecyl sulphate (SDS)). Creep rheological measurements have been made on the same emulsions over the shear stress range 10(-2)-10 Pa. There is a good correlation between the difference in the limiting low-stress apparent shear viscosity of Tween 20 and SDS emulsions containing 0.1 wt.% rhamsan and the difference in the creaming stability of the same emulsions. These results demonstrate the importance of surfactant-biopolymer interactions in controlling the stability of emulsions.