Micellization of mixed nonionic surface active agents

A theory is developed for micellization in systems of mixed nonionic surfactants. Assumptions of ideal mixing in the micellel and of a simple phase separation model enable the concentration of each monomeric species and hence the micellar composition to be calculated as a function of total concentration (c). For mixtures of homologous surfactants the surface tension (γ) at the air-water interface is calculated by assuming the mixed monolayer to be in equilibrium with the monomers in solution. The γ against log c curve in such a system is predicted to have a minimum. Comparison with γ against log c curves obtained experimentally shows excellent agreement with theory over the whole concentration range both below and above the c.m.c.