Influence of hydrodynamics on many-particle diffusion in 2D colloidal suspensions

We study many-particle diffusion in 2D colloidal suspensions with full hydrodynamic interactions through a novel mesoscopic simulation technique. We focus on the behaviour of the effective scaled tracer and collective-diffusion coefficients D-T(rho)/D-0 and D-C(rho)/D-0, respectively, where D-0 is the single-particle diffusion coefficient, as a function of the density of the colloids rho. At low Schmidt numbers Scsimilar to1, we find that hydrodynamics has essentially no effect on the behaviour of D-T(rho)/D-0. At larger Sc, D-T(rho)/D-0 seems to be enhanced at all densities, although the differences compared to the case without hydrodynamics are rather minor. The collective-diffusion coefficient, on the other hand, is much more strongly coupled to hydrodynamical conservation laws and is distinctly different from the purely dissipative case without hydrodynamic interactions.