DROPLET BREAK-UP IN A STIRRED WATER-IN-OIL EMULSION IN THE PRESENCE OF EMULSIFIERS

Scaling laws for droplet break-up in stirred emulsifier-containing wat er-in-oil emulsions with dispersed volume fractions up to 70% were eva luated. The emulsions were stirred with a standard turbine impeller an d the droplet diameters were determined as a function of time both mic roscopically and via turbidity measurements. The droplet size was foun d to decrease very slowly: a steady state was reached after 1-2 h. In emulsions without emulsifier the steady state droplet diameters were f ound to be in agreement with predicted values. Emulsions with emulsifi er showed a bimodal size distribution with a very large number of very small droplets. The average diameter of the ''coarse part'' of the si ze distribution could be described reasonably well with the droplet br eak-up relationships provided that the equilibrium interfacial tension was applied, indicating that the transport of emulsifier was sufficie ntly fast to maintain (nearly) equilibrium adsorption during the defor mation of the droplet. The very small droplets could possibly be forme d by tip streaming: the flow pushes the emulsifier to the tips of the droplet, resulting in a very low interfacial tension locally which lea ds to a stream of very small droplets.