Stokesian dynamics study of quasi-two-dimensional suspensions confined between two parallel walls

Abstract

We present a Stokesian dynamics (SD) computer simulation study of the static and dynamical properties of a monolayer of spherical colloidal particles restricted to diffuse in the midplane between two parallel walls. SD simulations account for hydrodynamic interactions (HI's) among the particles, and between particles and walls. Three different types of systems are studied: first, a monolayer of neutral spheres and neutral hard walls; second, particles interacting by a repulsive Yukawa-type potential of range depending on the wall separation. As a third system, the interesting case of charged particles between charged parallel walls with a longer-range attractive part in the pair potential is investigated, using the experimentally determined effective pair potential of Acuna-Campa et al. [Phys. Rev. Lett. 80, 5802 (1998)]. Various measurable quantities are calculated in dependence of the particle concentration and the wall distance: short- and long-time self-diffusion coefficients, radial distribution functions and static structure factors, hydrodynamic functions, mean squared displacements, and van Hove real-space correlation functions. We assess the importance of HI's by comparing our results with simulation results where HI's are fully or partially disregarded. Some of our results are also compared with experimental data, and good agreement is found. Remarkable effects are investigated, like the hydrodynamic enhancement of self-diffusion for the case of strongly charged particles, and the strong increase of the hydrodynamic function at small wave numbers.