Modification of Krafft temperature or solubility of surfactants using surfactant mixtures

Krafft temperatures of anionic/anionic, anionic/nonionic, and anionic/anion ic/nonionic surfactant mixtures were studied at various surfactant composit ions and salt concentrations. The Krafft temperature of a binary mixture of anionic surfactants can be less than that of any single surfactant. Additi on of a nonionic surfactant to an anionic surfactant can cause further Kraf ft temperature depression. Addition of a monovalent counterion to each syst em decreases the critical micelle concentration (CMC), but increases the Kr afft temperature of anionic surfactants or their mixtures. A simple model b ased on the pseudo-phase separation approach can successfully predict the m ixture Krafft temperatures based on pure surfactant behavior and interactio ns in mixed micelles. Predictions from the model are very sensitive to the solubility products and CMC parameters.