Screened hydrodynamic interaction in a narrow channel

TL;DR

This paper investigates how hydrodynamic interactions between colloidal particles in a narrow, linear channel are sharply screened due to confinement, affecting their collective motion and interaction strength.

Contribution

It provides experimental and theoretical insights into hydrodynamic coupling in quasi-one-dimensional channels, revealing unique screening effects and potential sign reversal of interactions.

Findings

Hydrodynamic interactions are sharply screened in narrow channels.

Particles move collectively only within the channel width.

Two-body interactions dominate even at high densities.

Abstract

We study experimentally and theoretically the hydrodynamic coupling between Brownian colloidal particles diffusing along a linear channel. The quasi-one-dimensional confinement, unlike other constrained geometries, leads to a sharply screened interaction. Consequently, particles move in concert only when their mutual distance is smaller than the channel width, and two-body interactions remain dominant up to high particle densities. The coupling in a cylindrical channel is predicted to reverse sign at a certain distance, yet this unusual effect is too small to be currently detectable.