Emergent behavior in active colloids

TL;DR

This paper reviews the movement mechanisms, individual dynamics, and collective behaviors of active colloids, highlighting experimental findings and modeling approaches including hydrodynamic and phoretic interactions.

Contribution

It provides a comprehensive overview of emergent behaviors in active colloids, integrating experimental observations with advanced modeling techniques.

Findings

Active colloids generate flow fields via self-phoresis or Marangoni effects.

Collective behaviors depend on hydrodynamic and phoretic interactions.

Modeling advances help understand large-scale collective dynamics.

Abstract

Active colloids are microscopic particles, which self-propel through viscous fluids by converting energy extracted from their environment into directed motion. We first explain how articial microswimmers move forward by generating near-surface flow fields via self-phoresis or the self-induced Marangoni effect. We then discuss generic features of the dynamics of single active colloids in bulk and in confinement, as well as in the presence of gravity, field gradients, and fluid flow. In the third part, we review the emergent collective behavior of active colloidal suspensions focussing on their structural and dynamic properties. After summarizing experimental observations, we give an overview on the progress in modeling collectively moving active colloids. While active Brownian particles are heavily used to study collective dynamics on large scales, more advanced methods are necessary to explore the importance of hydrodynamic and phoretic particle interactions. Finally, the relevant physical approaches to quantify the emergent collective behavior are presented.