Sedimentation of active colloidal suspensions

TL;DR

This study experimentally explores the sedimentation behavior of chemically powered active colloids under gravity, revealing their 'hot' particle-like dynamics and establishing a connection between individual activity and macroscopic density profiles.

Contribution

First experimental investigation linking active colloid self-propulsion to sedimentation profiles in a microfluidic setup, advancing understanding of out-of-equilibrium active matter.

Findings

Active colloids behave as 'hot' particles in dilute regimes.

Density profiles correlate with individual self-propulsion dynamics.

Microfluidic measurements reveal out-of-equilibrium steady states.

Abstract

In this paper, we investigate experimentally the non-equilibrium steady state of an active colloidal suspension under gravity field. The active particles are made of chemically powered colloids, showing self propulsion in the presence of an added fuel, here hydrogen peroxide. The active suspension is studied in a dedicated microfluidic device, made of permeable gel microstructures. Both the microdynamics of individual colloids and the global stationary state of the suspension under gravity - density profiles, number fluctuations - are measured with optical microscopy. This allows to connect the sedimentation length to the individual self-propelled dynamics, suggesting that in the present dilute regime the active colloids behave as 'hot' particles. Our work is a first step in the experimental exploration of the out-of-equilibrium properties of artificial active systems.