SCALING OF TRANSIENT HYDRODYNAMIC INTERACTIONS IN CONCENTRATED SUSPENSIONS

The mean-square displacement [DELTA-r2(tau)] of particles in concentrated suspensions is measured at times sufficiently short to observe the transient nature of hydrodynamic interactions. For all volume fractions-phi, the velocity autocorrelation function decays as a power law R(tau) is similar to tau--3/2. A remarkable scaling with phi is observed for the time-dependent self-diffusion coefficient D(s)(tau) = [DELTA-r2(tau)]/6-tau: If D(s)(tau) is scaled by its asymptotic value and if time is scaled by a viscous time inversely proportional to the shear viscosity of the suspension, all the data fall onto a single master curve.