Hydrodynamic synchronization of externally driven colloids

TL;DR

This study uses three-dimensional simulations to explore how externally driven colloids synchronize their motion in confined fluids, revealing new dynamical mode transitions at specific Reynolds numbers.

Contribution

It uncovers novel dynamical mode transitions in small colloidal systems driven in viscous fluids, expanding understanding of hydrodynamic synchronization phenomena.

Findings

Identification of a critical Reynolds number for mode transition in three-particle systems.

Discovery of a new triplet dynamical mode not previously observed experimentally.

Observation of multiple mode transitions in four-particle systems.

Abstract

The collective dynamics of externally driven $N_{\rm p}$-colloidal systems ($1\le N_{\rm p}\le 4$) in a confined viscous fluid have been investigated using three-dimensional direct numerical simulations with fully resolved hydrodynamics. The dynamical modes of collective particle motion are studied by changing the particle Reynolds number {as determined by the strength of the external driving force} and the confining wall distance. For a system with $N_{\rm p}= 3$, we found that at a critical Reynolds number, a dynamical mode transition occurs from the doublet-singlet mode to the triplet mode, which has not been reported experimentally. The dynamical mode transition was analyzed in detail from the following two viewpoints: (1) spectrum analysis of the time evolution of a tagged particle velocity and (2) the relative acceleration of the doublet cluster with respect to the singlet particle. For a system with $N_{\rm p}=4$, we found similar dynamical mode transitions from the doublet-singlet-singlet mode to the triplet-singlet mode and further to the quartet mode.