Adsorption of sodium dodecyl sulfate to a polystyrene/ water interface studied by neutron reflection and attenuated total reflection infrared spectroscopy

Spun-cast layers of polystyrene have been transferred to large silicon crys tals as substrates for neutron reflectivity studies and to prisms for infra red-attenuated total reflection measurements of surfactant adsorption. This paper describes an investigation of the adsorption from aqueous solutions of sodium dodecyl sulfate (SDS) to this interface of aqueous solution and p olystyrene. The structure and amount of adsorbate is described and discusse d. The adsorption isotherm shows that both the thickness and volume fractio n of the SDS layer increase to plateau values above the critical micelle co ncentration (cmc) where the area per molecule is approximately 42 Angstrom( 2). Above the cmc, there is a decrease in the total amount of adsorbed mate rial unless SDS of very high purity is used. This unusual behavior is expla ined by the presence of dodecan-1-ol from hydrolysis of SDS which is highly surface active but can be solubilized in micelles of SDS.