Aggregate formation of binary nonionic surfactant mixtures on hydrophilic surfaces

Adsorption of surfactant mixtures on hydrophilic solid surfaces is of considerable theoretical and practical importance. Cooperative adsorption of nonionic surfactant mixtures of nonyl phenol ethoxylated decyl ether (NP-10) and n-dodecyl-beta-d-maltoside (DM) on silica and alumina was investigated in this study with a view to elucidate the nanostructures of their aggregates. In the mixed system, DM is identified to be the "active" component and NP-10 is the "passive" one for the process of adsorption on alumina, while their roles are reversed for silica. The difference in the adsorptive interactions of the surfactants with the above minerals is attributed to the differences in the molecular structures of the surfactants. To better understand the interaction between surfactants at solid/solution interface from a molecular structure point of view, the nanostructures of mixed surface aggregates have been quantitatively predicted for the first time using a modified packing parameter: the structures are spherical or cylindrical on silica and those on alumina undergo a spherical-to-cylindrical-to-bilayer transition with the addition of the active component. This work offers a new way for developing of structure-performance relationships.