HYDRODYNAMIC EFFECTS IN POLYDISPERSE CHARGED COLLOIDAL SUSPENSIONS ATSHORT TIMES

The effect of combined intrinsic size and charge polydispersity and hy drodynamic interaction on the short-time dynamics in unimodal and bimo dal suspensions of charged macroparticles is investigated. The first c umulant of the dynamic-scattering function is calculated based on a bi modal Schulz distribution for the particle sizes and charges. The infl uence of the solvent-mediated hydrodynamic interaction between the mac roparticles is approximately described by a far-field expansion in ter ms of reciprocal distance r-1, including terms up to order r-11. The p artial static-structure functions, which are required as an input, are obtained using the multicomponent-hypernetted-chain approximation. Ou r results are compared with data from dynamic-light-scattering experim ents on binary mixtures of polystyrene spheres and on unimodal suspens ions of charged silica particles. It is shown that both the intrinsic polydispersity and the hydrodynamic interaction significantly affect t he measured first cumulant.