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

E. Falck; J. M. Lahtinen; I. Vattulainen; T. Ala-Nissila

doi:10.1140/epje/i2003-10075-9

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Soft Matter and Biological Physics

Eur. Phys. J. E (2004) 13: 267-275
https://doi.org/10.1140/epje/i2003-10075-9

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

E. Falck¹^,2^*, J. M. Lahtinen¹, I. Vattulainen¹^,2 and T. Ala-Nissila¹^,3

¹ Laboratory of Physics - Helsinki University of Technology, P.O. Box 1100, FIN-02015 HUT, Finland
² Helsinki Institute of Physics - Helsinki University of Technology, P.O. Box 1100, FIN-02015 HUT, Finland
³ Department of Physics, Brown University, Box 1843, RI 02912-1843, Providence, USA

^* e-mail: efalck@cc.hut.fi

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 $D_{\rm T}(\rho) / D_0$ and $D_{\rm C}(\rho) / D_0$ , respectively, where D ₀ is the single-particle diffusion coefficient, as a function of the density of the colloids $\rho$ . At low Schmidt numbers $Sc \sim 1$ , we find that hydrodynamics has essentially no effect on the behaviour of $D_{\rm T}(\rho) / D_0$ . At larger Sc, $D_{\rm T}(\rho) / D_0$ 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.