You are not logged in to this journal. Log in    |   Subscription Information

Phys. Rev. E 74, 031402 (2006) [29 pages]

Hydrodynamic interactions and Brownian forces in colloidal suspensions: Coarse-graining over time and length scales

J. T. Padding1,2,3 and A. A. Louis1
1Department of Chemistry, Cambridge University, Lensfield Road, Cambridge CB2 1EW, United Kingdom
2Schlumberger Cambridge Research, High Cross, Madingley Road, Cambridge CB3 0EL, United Kingdom
3Computational Biophysics, University of Twente, P.O. Box 217, 7500 AE, Enschede, The Netherlands

Received 13 March 2006; published 8 September 2006

We describe in detail how to implement a coarse-grained hybrid molecular dynamics and stochastic rotation dynamics simulation technique that captures the combined effects of Brownian and hydrodynamic forces in colloidal suspensions. The importance of carefully tuning the simulation parameters to correctly resolve the multiple time and length scales of this problem is emphasized. We systematically analyze how our coarse-graining scheme resolves dimensionless hydrodynamic numbers such as the Reynolds number Re, which indicates the importance of inertial effects, the Schmidt number Sc, which indicates whether momentum transport is liquidlike or gaslike, the Mach number, which measures compressibility effects, the Knudsen number, which describes the importance of noncontinuum molecular effects, and the Peclet number, which describes the relative effects of convective and diffusive transport. With these dimensionless numbers in the correct regime the many Brownian and hydrodynamic time scales can be telescoped together to maximize computational efficiency while still correctly resolving the physically relevant processes. We also show how to control a number of numerical artifacts, such as finite-size effects and solvent-induced attractive depletion interactions. When all these considerations are properly taken into account, the measured colloidal velocity autocorrelation functions and related self-diffusion and friction coefficients compare quantitatively with theoretical calculations. By contrast, these calculations demonstrate that, notwithstanding its seductive simplicity, the basic Langevin equation does a remarkably poor job of capturing the decay rate of the velocity autocorrelation function in the colloidal regime, strongly underestimating it at short times and strongly overestimating it at long times. Finally, we discuss in detail how to map the parameters of our method onto physical systems and from this extract more general lessons—keeping in mind that there is no such thing as a free lunch—that may be relevant for other coarse-graining schemes such as lattice Boltzmann or dissipative particle dynamics.

©2006 The American Physical Society

URL: http://link.aps.org/doi/10.1103/PhysRevE.74.031402
DOI: 10.1103/PhysRevE.74.031402
PACS: 82.70.Dd; 05.40.-a; 47.11.-j; 47.20.Bp
  • 82.70.Dd
    Colloids
  • 05.40.-a
    Fluctuation phenomena, random processes, noise, and Brownian motion
  • 47.11.-j
    Computational methods in fluid dynamics
  • 47.20.Bp
    Buoyancy-driven hydrodynamic instability
  • YEAR: 2006
KEYWORDS: colloids, suspensions, hydrodynamics, flow simulation, Monte Carlo methods, compressibility, self-diffusion, friction, convection, Brownian motion

REFERENCES (102)

For access to fully linked references, you need to log in. For access to fully linked references, you need to Log in.

CITING ARTICLES

For access to citing articles, you need to log in.
For access to citing articles, you need to Log in.



A new free weekly publication from APS

Physics - A new free weekly publication from APS
Please visit physics.aps.org
 
Article Tools