Precipitation of Surfactants and Surfactant Mixtures in Aqueous Solutions

摘要

The precipitation of an anionic surfactant by several different counterions is examined. The counterions include: Na sup + , Ca sup +2 ; and a monovalent counterion which is a cationic surfactant. At concentrations below the CMC(critical micelle concentration), surfactant precipitation is similar to precipitation of any simple salt and can be described by a solubility product relationship. Above the CMC, when micelles are present, the solubility product must be written between the anionic surfactant monomer concentration and the unbound (unassociated) counterion concentration. A model has been developed for each system that successfully predicts the counterion concentration required to cause precipitation. The primary goal of this work is to understand the changes in anionic surfactant precipitation brought about by adding nonionic surfactant and/or NaCl. In anionic-nonionic surfactant mixtures, monomer-micelle equilibrium is described using a pseudo-phase approach combined with a regular solution theory assumption for the micelles. 100 refs., 40 figs., 7 tabs. (ERA citation 13:015531)