INTERFACIAL PROPERTIES AND STABILITY OF OIL-IN-WATER EMULSIONS STABILIZED WITH BINARY-MIXTURES OF SURFACTANTS

The effect of sodium dodecyl sulfate (SDS) on ζ-potential of oil-in-water emulsions stabilized with a nonionic surfactant (Tween 80) at two different concentrations, one above and one below its CMC, has been studied. Adsorption of SDS causes an increase in ζ-potential. An estimate of the free energy of adsorption can be made from the ζ-potential versus log concentration SDS plot. The demulsification rates of the emulsions are evaluated by counting the droplet number with time hemocytometrically. Flocculation is considered the main factor of instability. Electrostatic forces, as well as steric stabilization factors, are considered to be responsible for the stability in some cases, depending on Tween 80 concentration and the time of SDS addition. The adsorption behavior of SDS in the presence of Tween 80 is also discussed and the amount of SDS adsorbed per unit area of the interface is calculated with the help of the Gibbs equation. © 1990.