Flow of colloidal solids and fluids through constrictions: dynamical density functional theory versus simulation

TL;DR

This study compares dynamical density functional theory and Brownian dynamics simulations to analyze flow behaviors of colloidal solids and fluids through constrictions, revealing diverse flow regimes and predicting flow oscillations.

Contribution

It demonstrates that dynamical density functional theory can accurately describe complex flow scenarios of colloids, including oscillations and stop-and-go behavior, with some limitations.

Findings

Four flow regimes identified: blockade, steady flow, oscillations, stop-and-go.

DDFT predicts undamped oscillations, but simulations show damping.

Flow behaviors linked to symmetry conditions of colloidal solids.

Abstract

Using both dynamical density functional theory and particle-resolved Brownian dynamics simulations, we explore the flow of two-dimensional colloidal solids and fluids driven through a linear channel with a geometric constriction. The flow is generated by a constant external force acting on all colloids. The initial configuration is equilibrated in the absence of flow and then the external force is switched on instantaneously. Upon starting the flow, we observe four different scenarios: a complete blockade, a monotonic decay to a constant particle flux (typical for a fluid), a damped oscillatory behaviour in the particle flux, and a long-lived stop-and-go behaviour in the flow (typical for a solid). The dynamical density functional theory describes all four situations but predicts infinitely long undamped oscillations in the flow which are always damped in the simulations. We attribute the mechanisms of the underlying stop-and-go flow to symmetry conditions on the flowing solid. Our predictions are verifiable in real-space experiments on magnetic colloidal monolayers which are driven through structured microchannels and can be exploited to steer the flow throughput in microfluidics.