Short-time transport properties of bidisperse suspensions and porous media: a Stokesian Dynamics study

TL;DR

This study uses Stokesian Dynamics to analyze the short-time transport properties of bidisperse colloidal suspensions and porous media, covering various particle size ratios and volume fractions, and compares results with existing theories.

Contribution

It provides a comprehensive computational analysis of bidisperse suspensions and porous media, evaluating the accuracy of SD and approximation schemes across different densities.

Findings

SD accurately predicts short-time transport properties.

Pairwise Additive approximations have limited validity at high densities.

Hydrodynamic interactions significantly influence dense bidisperse systems.

Abstract

We present a comprehensive computational study of the short-time transport properties of bidisperse neutral colloidal suspensions and the corresponding porous media. Our study covers bidisperse particle size ratios up to $4$, and total volume fractions up to and beyond the monodisperse hard-sphere close packing limit. The many-body hydrodynamic interactions are computed using conventional Stokesian Dynamics (SD) via a Monte-Carlo approach. We address suspension properties including the short-time translational and rotational self-diffusivities, the instantaneous sedimentation velocity, the wavenumber-dependent partial hydrodynamic functions, and the high-frequency shear and bulk viscosities; and porous media properties including the permeability and the translational and rotational hindered diffusivities. We carefully compare the SD computations with existing theoretical and numerical results. For suspensions, we also explore the range of validity of various approximation schemes, notably the Pairwise Additive (PA) approximations with the Percus-Yevick structural input. We critically assess the strengths and weaknesses of the SD algorithm for various transport properties. For very dense systems, we discuss in detail the interplay between the hydrodynamic interactions and the structures due to the presence of a second species of a different size.