Scaling of transient hydrodynamic interactions in concentrated suspensions

The mean-square displacemenf (Δr 2 (τ)) of particles in concentrated suspensions is measured at times sufficiently short to observe the transient nature of hydrodynamic interactions. For all volume fractions O, the velocity autocorrelation function decays as a power law R(τ)∼τ -3/2 . A remarkable scaling with O is observed for the time-dependent self-diffusion coefficient D s (τ)=(Δr 2 (τ))/6τ: If D s (τ) is scaled by its asymptotic value and if time is scaled by a viscous time inversely proportional to the shear viscosity of the suspension