Colloid-colloid and colloid-wall interactions in driven suspensions

TL;DR

This paper studies non-equilibrium forces between colloids driven in suspensions, revealing velocity-dependent interactions and force enhancements or reductions, with implications for colloidal dynamics.

Contribution

It provides a detailed analysis of driven colloid interactions using analytical and numerical methods, highlighting velocity-dependent forces and comparing different approximation techniques.

Findings

Enhanced friction for side-by-side colloids and wall-traveling colloids.

Reduced friction for tailgating colloids.

Side-by-side colloids repel; tailgating colloids attract.

Abstract

We investigate the non-equilibrium fluid structure mediated forces between two colloids driven through a suspension of mutually non-interacting Brownian particles as well as between a colloid and a wall in stationary situations. We solve the Smoluchowski equation in bispherical coordinates as well as with a method of reflections, both in linear approximation for small velocities and numerically for intermediate velocities, and we compare the results to a superposition approximation considered previously. In particular we find an enhancement of the friction (compared to the friction on an isolated particle) for two colloids driven side by side as well as for a colloid traveling along a wall. The friction on tailgating colloids is reduced. Colloids traveling side by side experience a solute induced repulsion while tailgating colloids are attracted to each other.