Near-Wall Dynamics of Concentrated Hard-Sphere Suspensions: Comparison of Evanescent Wave DLS Experiments, Virial Approximation and Simulations

TL;DR

This study compares experimental near-wall dynamics of concentrated colloidal hard spheres with virial approximation and simulations, revealing the diminishing of many-particle hydrodynamic interactions near the wall and proposing a new assessment method.

Contribution

It introduces a virial-based approach for analyzing near-wall particle diffusion up to moderate densities and proposes a new method for assessing near-wall self-diffusion at high densities.

Findings

Virial approximation describes data well up to φ=0.25.

Hydrodynamic interactions are reduced near the wall at higher densities.

Diminishment of interactions differs for normal and parallel motions.

Abstract

In this article we report on a study of the near-wall dynamics of suspended colloidal hard spheres over a broad range of volume fractions. We present a thorough comparison of experimental data with predictions based on a virial approximation and simulation results. We find that the virial approach describes the experimental data reasonably well up to a volume fraction of $\phi=0.25$ which provides us with a fast and non-costly tool for the analysis and prediction of Evanescent Wave DLS data. Based on this we propose a new method to assess the near-wall self-diffusion at elevated density. Here, we qualitatively confirm earlier results [Michailidou et al., Phys. Rev. Lett., 2009, 102, 068302], which indicate that many-particle hydrodynamic interactions are diminished by the presence of the wall at increasing volume fractions as compared to bulk dynamics. Beyond this finding we show that this diminishment is different for the particle motion normal and parallel to the wall.