Self-diffusion of colloidal particles in a two-dimensional suspension: Are deviations from Fick’s law experimentally observable?

Simulations of a colloidal particle suspended in a two-dimensional fluid are reported. The dissipative and fluctuating hydrodynamic forces acting on the particle are modeled by a lattice gas. Our results indicate that large long-time tails are present in both the translational and the rotational velocity correlation functions; these are the first observations of a rotational long-time tail. The strong translational tail leads to an observable renormalization of the diffusion coefficient; our results suggest that experimental observation of the latter effect is possible.