Collective diffusion of charged spheres in the presence of hydrodynamic interaction

Abstract

The short-time behavior of the scattering intensity, which can be measured by dynamic light scattering, is investigated theoretically. We consider a monodisperse system of charged hard spheres and study the combined effects of electrostatic repulsion and hydrodynamic interactions. The electrostatic repulsion determines the static properties, which are calculated from the thermodynamically consistent Rogers-Young scheme. For comparison, some results obtained within the rescaled mean spherical approximation (RMSA) are shown as well. Many-body hydrodynamic interaction is treated within the renormalization approach due to Beenakker. We compare results depending on the scattering vector to experimental data. Further, we show various trends for the collective diffusion coefficient, which is obtained as the long wavelength limit of the collective diffusion function, when volume fraction of spheres, salinity, and charge of the spheres are changed. The results are aimed at the interpretation of dynamic light scattering properties of systems of weakly charged spheres, which could be ionic micelies or macromolecules at moderate concentrations.