STRUCTURE AND SHORT-TIME DYNAMICS OF POLYDISPERSE CHARGE-STABILIZED SUSPENSIONS

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