The Effect of Electrolytes on O/W Emulsions Stabilized by Alkyl Phosphoric Surfactants

Abstract

The effect of electrolytes on the viscosity of the emulsions of liquid paraffin stabilized by a series of alkyl ethoxy phosphates have been investigated.
It is a well known fact that the viscosity of emulsions is changed by the addition of electrolytes. Our experiments showed that the viscosiy of the emulsions decreased as the added electrolytes increased and it began to rise again after passing through a minimum point of viscosity. The viscosity of the emulsions stabilized by trilauryl ethoxy phosphate decreased most remarkably by the addition of electrolytes. By using this surfactant we obtained the following facts.
The minimum points of viscosity were included in the concentration range between 20 and 60m equiv./1 of the electrolytes and they had no relation to the valence of ions or their characteristics: and anions of electrolytes exert influenec on the decrease of the viscosity while cations have the reincreasing effect. However, the above-mentioned principles are not applicable to salts such as Na₂CO₃ or Na₃PO₄, which are hydrolized in aqueous solutions to make them alkaline.
Friling et al. recently reported that a latex emulsion stabilized by soap is obtained in the form of gel when the concentration of electrolyte is low. But when the concentration of elecrolyte increased, the viscosity of emulsion was decreased. The reasons are as follows: the droplets are surrounded by the water layer which is more highly viscous than ordinary liquid water, and these hydrated particles approach the state of close packing. Supposedly, the effective volume concentration was decided by the volume of the polymer plus the volume of the charged double layer which prevented the particles from approaching one another.
According to our data, it may be assumed that not only the electrical double layer but also the hydration layer on the surface of droplets exert effect on the change of the viscosity.