ZETA POTENTIALS OF CUTTING-OIL WATER EMULSIONS: INFLUENCE OF INORGANIC SALTS

ABSTRACT

Electrophoretic light scattering (ELS) is used to determine the zeta potential of O/W emulsions of five commercial cutting oils. AlCl₃, MgCl₂, CaCl₂ and NaCl were added as electrolytes to the emulsions at concentrations varying from 10⁻⁴ mol/dm³ to 10⁻¹ mol/dm³ in order to study the influence of electrolyte concentration and cation charge on the zeta potential of the emulsions and to explain their stability.

A decrease of the absolute value of the zeta potential was observed when the electrolytes were added to the emulsions, except for low NaCl concentrations where the zeta potential increased due to the adsorption of the Cl⁻ ions on the droplet surface while AlCl₃ cancelled the zeta potential of the droplets at very low concentrations. The effect of added electrolytes agrees well with the Schulze-Hardy rule.

The tendency of the dispersed oils to coagulate is discussed using the Derjaguin-Landau-Verwey-Overbeek (DLVO) theory.

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Notes on contributors

J. Coca

Author to whom correspondence should be addressed