TIME-DEPENDENT COLLECTIVE DIFFUSION OF COLLOIDAL PARTICLES

We use a combination of numerical simulations and laboratory experiments to study the time-dependent collective diffusion coefficient D(q, t) in concentrated colloidal suspensions. At short times, the particle configuration is frozen, and D(q, t) probes the temporal and spatial evolution of hydrodynamic interactions, via their effects on the particle velocities. We find that D(q, t) exhibits a surprising scaling behavior, with a single, q-dependent relaxation time, suggesting that the suspension behaves as an effective medium for hydrodynamic interactions over a wide range of length scales and time scales. © 1995 The American Physical Society.