The Zeta Potential Op Droplets Prepared from a Self-Emulsifying Oil

The zeta potential of droplets formed by the self emulsification of compositions of n-hexane, phosphated nonylphenol ethoxylate and phosphated fatty alcohol ethoxylate has been determined in water and aqueous electrolyte solutions over a pH range of 3-11. Anomalies may be noted as a function of the n-hexane concentration of the surfactant/oil composition added to water. This, it is suggested, may be related to the mesomorphic systems that occur in bulk composition/water mixtures and could form at the interface of the droplets in water.

Effects on the electrophoretic/mobility observed in the presence of sodium, lithium, calcium or magnesium may be explained by the relative size of the sphere of hydration around the cat ion that controls the depth of penetration through the surface layers of the droplets.

Aluminum ions appear to react completely with the surfactant phosphate moiety, precipitating directly onto the droplet surface. The droplet surface charge always remains negative and below 30 mV except in the presence of aluminum ions. The maximum charge is obtained at the pH of 5.5 which approximates to the pKa₁ Df the surfactant mixture.