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

TL;DR

This study investigates how hydrodynamic interactions influence many-particle diffusion in 2D colloidal suspensions using a novel simulation method, revealing that hydrodynamics significantly affect collective diffusion but not single-particle diffusion at certain conditions.

Contribution

It introduces a new mesoscopic simulation technique to analyze hydrodynamic effects on diffusion in colloidal suspensions, highlighting differences in collective versus single-particle diffusion behaviors.

Findings

Hydrodynamics has little effect on single-particle diffusion at low Schmidt numbers.

At higher Schmidt numbers, single-particle diffusion is slightly enhanced by hydrodynamics.

Collective diffusion is strongly affected by hydrodynamics and differs from purely dissipative models.

Abstract

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 $D_C(\rho) / D_0$, where $D_0$ is the single-particle diffusion coefficient, as a function of the density of the colloids $\rho$. At low Schmidt numbers $Sc={\cal O}(1)$, we find that hydrodynamics has essentially no effect on the behaviour of $D_T(\rho)/D_0$. At larger $Sc$, $D_T(\rho)/D_0$ is enhanced at all densities, although the differences compared to the case without hydrodynamics are 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.