Short-time Rheology and Diffusion in Suspensions of Yukawa-type Colloidal Particles

TL;DR

This study evaluates analytical models for short-time colloidal particle dynamics, comparing them with simulations, and finds the hybrid method offers accurate, efficient predictions across concentrations, revealing limitations of the generalized Stokes-Einstein relation.

Contribution

The paper introduces and validates a hybrid analytical scheme combining elta and pairwise additive methods for predicting colloidal dynamics, demonstrating its accuracy across a wide concentration range.

Findings

Hybrid method matches simulation data well at all concentrations.

Pairwise additive scheme is accurate up to 10-20% volume fraction.

Generalized Stokes-Einstein relation is violated in low salinity systems.

Abstract

A comprehensive study is presented on the short-time dynamics in suspensions of charged colloidal spheres. The explored parameter space covers the major part of the fluid-state regime, with colloid concentrations extending up to the freezing transition. The particles are assumed to interact directly by a hard-core plus screened Coulomb potential, and indirectly by solvent-mediated hydrodynamic interactions (HIs). By comparison with accurate accelerated Stokesian Dynamics (ASD) simulations of the hydrodynamic function H(q), and the high-frequency viscosity, we investigate the accuracy of two fast and easy-to-implement analytical schemes. The first scheme, referred to as the pairwise additive (PA) scheme, uses exact two-body hydrodynamic mobility tensors. It is in good agreement with the ASD simulations of H(q) and the high-frequency viscosity, for smaller volume fractions up to about 10% and 20%, respectively. The second scheme is a hybrid method combining the virtues of the \delta\gamma-scheme by Beenakker and Mazur with those of the PA scheme. It leads to predictions in good agreement with the simulation data, for all considered concentrations, combining thus precision with computational efficiency. The hybrid method is used to test the accuracy of a generalized Stokes-Einstein (GSE) relation proposed by Kholodenko and Douglas, showing its severe violation in low salinity systems. For hard spheres, however, this GSE relation applies decently well.