Phase Behavior and Salt Partitioning in Two- and Three-Phase Anionic Surfactant Microemulsion Systems: Part II, Partitioning of Salt

✍ Scribed by Morten Gunnar Aarra; Harald Høiland; Arne Skauge

• Publisher: Elsevier Science
• Year: 1999
• Tongue: English
• Weight: 126 KB
• Volume: 215
• Category: Article
• ISSN: 0021-9797
• DOI: 10.1006/jcis.1999.6228

✦ Synopsis

The partitioning of salt (chlorides of Na, K, Ca, Mg) between an excess water phase and a microemulsion phase were studied for two five-component anionic microemulsion systems at 20°C. Three-phase microemulsions contain two phases that include inorganic salts, that is, excess brine and the microemulsion phase. The aim of the investigation was to describe the partitioning of Na ؉ , K ؉ , Ca ؉؉ , Mg ؉؉ , and Cl ؊ between water in the microemulsion phase and water in the excess water phase. Both surfactant systems were anionic with Na ؉ as counterion. It was found that Na ؉ and Cl ؊ partitioned more strongly toward the excess water phase while K ؉ , Ca ؉؉ , and Mg ؉؉ show more preference for the microemulsion phase. The validity of considering (NaCl ؉ water) as pseudo-component brine has been examined. Including a chloride depleted region, caused by electrostatic repulsion from the negatively charged surfactant layer, in the surfactant pseudocomponent, is found to describe the NaCl partitioning. When discussing partitioning of K ؉ , Ca ؉؉ , and Mg ؉؉ between the microemulsion phase and the excess water phase in these systems, it is important to consider that there are two cations in the solutions, Na ؉ as counterion for the surfactant and either K ؉ , Ca ؉؉ , or Mg ؉؉ for the electrolyte. The preferential partitioning toward the microemulsion phase for K ؉ , Ca ؉؉ , and Mg ؉؉ seems to be caused by an ion exchange of Na ؉ in the surfactant layer.