Air-water interfacial studies with mixtures of linear and branched analogue give rise to surprising and unexpected behavior: apparently a strong interfacial partitioning of branched chain surfactant at the expense of the linear chain relative (non-idealities). This behavior is not predicted by the established theories, where it is believed that surfactants bearing the same headgroup type and similar chains (hydrocarbons) mix ideally: i.e. it is straightforward to predict physico-chemcial properties based on those of the individual compounds, and the known mixture composition. These trends are also seen in water-in-oil (w/o) microemulsion phase stabilities and aqueous solubility measurements.

Neutron reflectivity (NR), small angle neutron scattering (SANS), surface tension (ST), phase behavior and aqueous solubilities have been used to interrogate these mixed surfactant systems (comprising a homologous series of di-alkyl anionic surfactants based on Aerosol-OT (AOT, sodium bis(2-ethyl-1-hexyl)sulfosuccinate - linear and branched alkyl chains).

The understanding of complex surface chemistry and bulk behavior of mixtures of surfactants from a homologous series is important for a wide range of applications such as detergents, drug delivery systems and tertiary oil recovery. This is because mixtures provide synergistic enhancement of properties, or because commercial surfactants are naturally a distribution of molecular masses.