Structure and short-time dynamics of polydisperse charge-stabilized suspensions

In this work we investigate the equilibrium structure and short-time dynamics of moderately concentrated suspensions of polydisperse charged silica particles immersed in a nearly optically matched solvent. We measure the static structure factor S-M(q) and the first cumulant of the intensity autocorrelation function with static and dynamic light-scattering techniques. From these two quantities we obtain the hydrodynamic function H-M(q) containing the configuration-averaged effects of the hydrodynamic interactions on the short-time dynamics. The experimental results for HM(q) compare favorably with theoretical calculations based on recent work by Nagele et al. [Phys. Rev. E 47, 2562 (1993); Phys. Rep. (to be published)]. We show that both hydrodynamic interactions and polydispersity significantly affect the short-time dynamics even at small volume fractions. At small wave numbers hydrodynamic interactions slow the initial decay of the intensity autocorrelation function, whereas near the position of the principal peak of S-M(q) the decay rate is enhanced.