Adsorption of SDS and PVP at the air/water interface

Abstract

The technique of specular reflection of neutrons has been used to investigate the adsorption from polyvinylpyrrolidone/sodium dodecyl sulphate (PVP/SDSI) solutions at the air/water interface. Isotropic substitution was used to highlight features of the adsorbed layer and to distinguish between solvent and solute in this layer. At low SDS concentrations the presence of the polymer causes an increase in the adsorption of surfactant (at 1 × 10 −4 M SDS, the area per molecule of SDS is 227A˚ 2 in the absence of polymer, 100A˚ 2 in 0.5% PVP and 85A˚ 2 in 2.0% PVP). On increasing the surfactant concentration this difference is reduced unit, at high SDS concentrations, the surface concentration of surfactant is higher in the absence of PVP (at 0.01 M SDS, the area per SDS molecule is 42A˚ 2, and 46a˚ 2 at 0%, 0.5% and 2.0% PVP respectively).