Coarse-graining dynamics for convection-diffusion of colloids: Taylor dispersion

TL;DR

This study uses hybrid simulation techniques to analyze how colloidal discs disperse in confined flow, revealing corrections to classical Taylor dispersion theory when colloid size is significant.

Contribution

It introduces a careful coarse-graining approach for colloidal dynamics in flow, highlighting important corrections to classical Taylor dispersion theory.

Findings

Colloids can flow faster than the fluid when their size is significant.

The dispersion coefficient decreases with larger colloids.

Long-time velocity autocorrelation tails are affected by flow.

Abstract

By applying a hybrid Molecular dynamics and mesoscopic simulation technique, we study the classic convection-diffusion problem of Taylor dispersion for colloidal discs in confined flow. We carefully consider the time and length-scales of the underlying colloidal system. These are, by computational necessity, altered in the coarse-grained simulation method, but as long as this is carefully managed, the underlying physics can be correctly interpreted. We find that when the disc diameter becomes non-negligible compared to the diameter of the pipe, there are important corrections to the original Taylor picture. For example, the colloids can flow more rapidly than the underlying fluid, and their Taylor dispersion coefficient is decreased. The long-time tails in the velocity autocorrelation functions are altered by the Poiseuille flow. Some of the conclusions about coarse-graining the dynamics of colloidal suspensions are relevant for a wider range of complex fluids.