Adsorption from mixtures of cationic/non-ionic surfactants on to a polystyrene surface

The adsorption of cetyltrimethylammonium bromide (CTAB) and nonyl phenyl ethoxylates (NP-n, where n = 13, 20 and 30) on to polystyrene powder has been studied. Concentrations of surfactant solutions ranging from below CMC to well above CMC were investigated. In a single surfactant system, only the cationic surfactant (CTAB) was found to adsorb appreciably while nonionic surfactants showed negligible adsorption. In mixed surfactant systems, the cationic surfactant was found to induce significant co-adsorption of non-ionic surfactants. The increased adsorption of non-ionic surfactants has been attributed to the formation of non-ideal mixed hemimicelles due to intercomponent lateral interactions. However, non-ionic surfactants with longer hydrophilic chains did not form mixed hemimicelles with CTAB. In general, zeta potential measurements support the adsorption results.