The Micelle Formation of Some Alkyl Sulfates in a Dioxane-Water Mixture

The CMC values of three sodium alkyl sulfates with the number of carbon atoms 12, 14 and 16 in a dioxane-water mixture have been measured. The CMC-lowering effect of dioxane, especially appreciable in the case of sodium dodecyl sulfate, has been explained in terms of Shinoda’s equation. The CMC-raising effect of dioxane, which is the main effect in the case of sodium hexadecyl sulfate, has been explained by the decrease in the standard chemical potential, i. e., the free energy of transfer, ΔFtr, of the surfactant. An equation has been derived which expresses ΔFtr as a function of the dioxane concentration by applying Born’s equation and Hildebrand’s regular solution theory.