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 (SA XS) is given. Since the latex particles only have a low contrast towar d water whereas the electron density of the added surfactant is rather high, the gradual buildup of the surfactant layer on the particles ca n be monitored with good sensitivity. The contrast of the particles ca n be matched by adding glycerol or sucrose to the dispersion medium, T hus, a detailed study of the adsorbed layer by contrast variation is p ossible. 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 for m a thin, dense layer of approximately 1-3 nm thickness on the latex s pheres. After maximum coverage of the surface is reached,the additiona l surfactant forms free micelles which give a distinct scattering cont ribution in the region of wider angles.