Adsorption of the Nonionic Surfactant Triton X-405 on Polystyrene Latex Particles As Monitored by Small-Angle X-ray Scattering

An investigation of the adsorption of the nonionic surfactant Triton X-405 on a polystyrene latex by use of small-angle X-ray scattering (SAXS) is given. Since the latex particles only have a low contrast toward water whereas the electron density of the added surfactant is rather high, the gradual buildup of the surfactant layer on the particles can be monitored with good sensitivity. The contrast of the particles can be matched by adding glycerol or sucrose to the dispersion medium. Thus, a detailed study of the adsorbed layer by contrast variation is possible. Small differences in the scattering patterns depending on the nature of the contrast agent (glycerol and sucrose) could be observed and are discussed. It is shown that the adsorbed Triton molecules form a thin, dense layer of approximately 1−3 nm thickness on the latex spheres. After maximum coverage of the surface is reached, the additional surfactant forms free micelles which give a distinct scattering contribution in the region of wider angles.