Moderate the adsorption of cationic surfactant on gold surface by mixing with sparingly soluble anionic surfactant

Surfactants with amine groups are often used in the nanoparticle synthesis due to the high affinity with Au atoms. The match of charges of a capping reagent with Au has significant influence on structures in nanoparticle synthesis. Thus we studied the adsorption of a catanionic surfactant system on Au surface. The surfactants used in the study are bis[[(amidoethyl)carbamoyl]ethyl]octadecylamine (C18N3) and arachidic acid. Three combinations of the surfactants were studied with regard to the protonation state of the amine groups and the match of charges of the surfactant headgroup. The morphology of the surfactant mixtures changes from high-curvature aggregates to low-curvature with increasing the molar ratio of arachidic acid in the mixtures or the pH of the surfactant solutions. The adsorption of the mixed surfactant systems was studied by means of scanning electron microscopy (SEM), quartz crystal microbalance (QCM) and cyclic voltammetry (CV). The results revealed that the homogeneity and the compactness of the adsorbed layer on a gold surface were increased with the molar ratio of arachidic acid in the complexes. Furthermore, we may obtain the construction of the film of the mixed surfactant on gold surface using the result obtained by QCM.