STATICS AND TRACER-DIFFUSION IN BINARY SUSPENSIONS OF POLYSTYRENE SPHERES - EXPERIMENT VS THEORY

Extensive measurements of the static and dynamic field autocorrelation function of dilute bidisperse suspensions of charged polystyrene spheres, obtained by static and dynamic light scattering experiments, are discussed in terms of the two-component macroion fluid model. The suspensions under study consist of a small amount of large spheres immersed in a system of small spheres. For these suspensions the self-scattering function at short and intermediate times can be determined by dynamic light scattering (DLS), performed at large wavenumbers. The self-scattering function contains information on the tracer-diffusion of both small and large spheres. The experimentally observed self-scattering functions of the binary mixtures are compared with theoretical calculations based on the so-called single exponential approximation (SEXP). The SEXP is based on the exact short-time behavior of the single particle dynamics and within it the dynamic properties are entirely expressed in terms of the partial static structure functions. The latter are calculated using the extended rescaled mean spherical approximation (RMSA) for colloidal mixtures. Good agreement between experimental data and the SEXP theory has been found.