Hydrodynamic Pair Attractions Between Driven Colloidal Particles

TL;DR

This paper investigates how the curvature of a circular path causes hydrodynamic interactions to induce pairing of driven colloidal particles, revealing new nonequilibrium attractions influenced by temperature and confinement.

Contribution

It introduces a combined simulation and analytical approach to show that path curvature breaks symmetry, leading to stable particle pairs via hydrodynamic coupling.

Findings

Curvature induces hydrodynamic pairing of colloids.

Pairing stability depends on temperature and confinement stiffness.

Hydrodynamic interactions are asymmetric due to the curved trajectory.

Abstract

Colloidal spheres driven through water along a circular path by an optical ring trap display unexpected dynamical correlations. We use Stokesian Dynamics simulations and a simple analytical model to demonstrate that the path's curvature breaks the symmetry of the two-body hydrodynamic interaction, resulting in particle pairing. The influence of this effective nonequilibrium attraction diminishes as either the temperature or the stiffness of the radial confinement increases. We find a well defined set of dynamically paired states whose stability relies on hydrodynamic coupling in curving trajectories.