Hydrodynamic effects in polydisperse charged colloidal suspensions at short times

The effect of combined intrinsic size and charge polydispersity and hydrodynamic interaction on the short-time dynamics in unimodal and bimodal suspensions of charged macroparticles is investigated. The first cumulant of the dynamic-scattering function is calculated based on a bimodal Schulz distribution for the particle sizes and charges. The influence of the solvent-mediated hydrodynamic interaction between the macroparticles is approximately described by a far-field expansion in terms of reciprocal distance ${\mathit{r}}^{\mathrm{-}1}$, including terms up to order ${\mathit{r}}^{\mathrm{-}11}$. The partial static-structure functions, which are required as an input, are obtained using the multicomponent-hypernetted-chain approximation. Our results are compared with data from dynamic-light-scattering experiments on binary mixtures of polystyrene spheres and on unimodal suspensions of charged silica particles. It is shown that both the intrinsic polydispersity and the hydrodynamic interaction significantly affect the measured first cumulant.