Advances in adsorption of surfactants and their mixtures at solid/solution interfaces

Surfactants and their mixtures can drastically change the interfacial properties and hence are used in many industrial processes such as dispersion/flocculation, flotation, emulsification, corrosion inhibition, cosmetics, drug delivery, chemical mechanical polishing, enhanced oil recovery, and nanolithography. A review of studies on adsorption of single surfactant as well as mixtures of various types (anionic–cationic, anionic–nonionic, cationic–nonionic, cationic–zwitterionic and nonionic–nonionic) is presented here along with mechanisms involved. Results obtained using techniques such as zeta potential, flotation, AFM, specular neutron reflectivity, small angle neutron scattering, fluorescence, ESR, Raman spectroscopy, ellipsometry, HPLC and ATR-IR are reviewed along with those from traditional techniques to elucidate the mechanisms of adsorption and particularly to understand synergistic/antagonistic interactions at solution/liquid interfaces and nanostructures of surface aggregates. In addition, adsorption of several mixed surfactant systems is considered due to their industrial relevance. Finally an attempt is made to derive structure–property relationships to provide a solid foundation for the design and use of surfactant formulations for industrial applications.