A dynamic density functional theory for particles in a flowing solvent

TL;DR

This paper introduces a dynamic density functional theory that accounts for particle advection in flowing solvents, demonstrating its qualitative agreement with Brownian dynamics simulations and revealing significant effects on particle distribution and friction forces.

Contribution

The paper develops a new advected dDFT framework that incorporates solvent flow effects, extending previous models to non-potential flows and applying it to particle-obstacle interactions.

Findings

Qualitative agreement with Brownian dynamics simulations.

Flow reduces the bow-wave and wake effects around obstacles.

Particle-induced friction on colloids can be significantly decreased.

Abstract

We present a dynamic density functional theory (dDFT) which takes into accou nt the advection of the particles by a flowing solvent. For potential flows we can use the same closure as in the absence of solvent flow. The structure of the resulting advected dDFT suggests that it could be used for non-potential flows as well. We apply this dDFT to Brownian particles (e.g., polymer coils) in a solvent flowing around a spherical obstacle (e.g., a colloid) and compare the results with direct simulations of the underlying Brownian dynamics. Although numerical limitations do not allow for an accurate quantitative check of the advected dDFT both show the same qualitative features. In contrast to previous works which neglected the deformation of the flow by the obstacle, we find that the bow-wave in the density distribution of particles in front of the obstacle as well as the wake behind it are reduced dramatically. As a consequence the friction force exerted by the (polymer) particles on the colloid can be reduced drastically.