Calcium effect on the solubility of sodium dodecyl sulfate in sodium chloride solutions

• Published in: Journal of colloid and interface science 1983-01, Vol.92 (2), p.580-583
• Main Authors: Baviere, Marc, Bazin, Brigitte, Aude, Robert
• Format: Article
• Language: English
• ISSN: 0021-9797; 1095-7103
• DOI: 10.1016/0021-9797(83)90179-0

Below its critical micelle concentration (CMC), the solubility of sodium dodecyl sulfate as a function of the calcium ion concentration is governed by the solubility product of calcium dodecyl sulfate. Some data in the literature show that, above the CMC, the tolerance of sodium dodecyl sulfate to calcium ions increases with surfactant concentration. This is usually explained as resulting from an association between calcium ions and micelles. The increase in calcium tolerance, however, occurs at a surfactant concentration higher than the CMC. This difference is assumed to be due to competition between precipitation, which follows the solubility product rule, and the calcium-micelle association. Moreover, the higher the initial sodium chloride concentration, the larger the difference. This relationship results from a strong decrease in CMC. The addition of sodium chloride increases tolerance toward calcium by causing this reduction of the CMC value. It is suggested that, at low NaCl contents, the increase in tolerance is mainly due to the adsorption of calcium ions on the micelles, whereas at high NaCl concentrations, tolerance results primarily from a decrease in the monomer concentration.