The limitations of models of surfactant mixing at interfaces as revealed by neutron scattering

Understanding the nature of surfactant mixing at interfaces and in self-assembly is key to the successful and efficient exploitation of surfactant mixtures in a wide range of diverse applications. Phenomenological treatments often appear to give adequate explanations of some of the properties of straightforward mixtures, particularly the surface tension. However, the more detailed and direct information available from neutron reflectivity and small angle neutron scattering has identified several important situations in surfactant mixing where the phenomenological treatment and current theoretical models are inadequate. The focus of this article is to describe and discuss particular problems associated with such mixtures, but the issues discussed can also be considered as a paradigm for a wide class of mixtures.