SMALL-ANGLE X-RAY-SCATTERING ON LATEXES

Small-angle X-ray scattering (SAXS) is a tool which allows the study o f the structure and the interaction of polymer latexes with great accu racy. The low electron density of the polymers used for the synthesis of latex particles as e.g. polystyrene allows the matching of the cont rast by adding sucrose to the serum. Thus, scattering intensities meas ured at different contrast, i.e., at different excess electron densiti es can be evaluated (contrast variation). This yields precise informat ion on the radial electron density of the particles. In this article r ecent SAXS-investigations on latex particles are reviewed It is demons trated that core-shell latexes can be analyzed precisely by contrast v ariation. The same method can be applied to swollen latex particles to examine the polymer concentration near the boundary to the water phas e. Here it is shown that the depletion of the polymer molecules near t his boundary is very small which points to a minute wall-repulsion eff ect. Since the excess electron density of polystyrene latex particles in water is very small, the scattering from adsorbed layers of surfact ants dominates tile measured intensity in this particular system. Ther efore the adsorption equilibrium of a given surfactant as well as the competitive adsorption of two different surfactants on a polystyrene l atex can be assessed by SAXS.