Electric double-layer repulsion, related stability

The theory has certain practical limitations. It is useful for o/w (oil-in-water) emulsions but for w/o (water-in-oil) systems DLVO theory must be applied with extreme caution (16). The essential use of the DLVO theory for emulsion technology lies in its ability to relate the stability of an o/w emulsion to the salt content of the continuous phase. In brief, the theory says that electric double-layer repulsion will stabilize an emulsion, when the electrolyte concentration in the continuous phase is less than a certain value. 

As a related matter it is easily understood that addition of salts at a certain concentration destabilizes an emulsion. It may be concluded that if an emulsion remains stable at electrolyte contents higher than those cited in the preceding paragraphs, the stability is not the result of electric double-layer repulsion, which may be useful information to find the optimum manner for destabilization. 

Ionic compounds such as halides, carboxylates or polyoxoanions, dissolved in (generally aqueous) solution can generate electrostatic stabilization. The adsorption of these compounds and their related counter ions on the metallic surface will generate an electrical double-layer around the particles (Fig. 1). The result is a coulombic repulsion between the particles. If the electric potential associated with the double layer is high enough, then the electrostatic repulsion will prevent particle aggregation [27,30]. 

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