Effect of Electrolytes and Correlations for Salinities at the Optimum Formulation of Sodium Dodecyl Benzene Sulfonate Microemulsions

The influences of different kinds of electrolytes on sodium dodecyl benzene sulfonate microemulsions were investigated in this work. Electrolyte cations had a strong influence on the microemulsion phase behavior. The higher the valence of the cation was, the stronger the influence of the electrolyte on the microemulsion phase inversion and the higher the optimum solubilization parameters, ordered as AlCl₃ > MgCl₂ > NH₄Cl > KCl > NaCl. The anion in electrolytes showed a relatively weak influence. The influences of anions with equal valence are almost the same for sodium salts, and a lower valence had a stronger impact on microemulsion phase inversion, ordered as Cl^? > CO₃^2? = SO₄^2? > PO₄^3?. The change of anions in sodium salts had little influence on the optimum solubilization parameters , all in the range of 5.301 ± 0.105 g_oil/g_surfactant. The efficiency ratio of electrolytes was defined based on the cationic charge concentration in mol/l. The efficiency ratios for electrolytes with monovalent cations were inversely proportional to (1 + Z_i), where Z_i is the anion valence, but this was not true for electrolytes with higher valence cations. For a microemulsion using electrolyte mixtures, the efficiency ratio shows a linear relationship with that of the component salts and the composition of the mixture.