Evaluation of stability ratio in oil-in-water emulsions

The kinetics for emulsion coagulation retarded by the electrostatic repulsion between droplets in the micron size range was studied. The rather high electrokinetic potential is provided by the presence of 10(-3) M NaOH. The enormous discrepancy between theory and experiment is shown to be analogous to that of solid suspensions. It was shown that Fuchs theory is invalid for emulsions where the existence of surface roughness or heterogeneity is completely excluded. To ensure that the electrostatic barrier is the single reason for the coagulation retardation, the use of ionic surfactant adsorption was avoided. This necessary condition causes an increase of the critical thickness h(cr) at which spontaneous disruption of the thin emulsion him occurs. The condition h(cr) < h(max) is formulated as necessary for the examination of slow coagulation theory on emulsions, where h(max)is the distance between the surface and the electrostatic energy maximum. For micron size droplets the predominance of Brownian coagulation over gravitational coagulation was ensured by the use of a dichlorodecane emulsion.