Sedimentation and Levitation of Catalytic Active Colloids

TL;DR

This study investigates how gravity influences the behavior of catalytic active colloids, revealing that buoyant weight adjustments affect their sedimentation and levitation, which is crucial for understanding active matter systems.

Contribution

It demonstrates that gravitational effects cannot be ignored in active colloids, showing how buoyant weight impacts their accumulation and motion near surfaces.

Findings

Decreased buoyant weight causes accumulation at the top wall.

Gravity influences active motion even near flat surfaces.

Active colloids exhibit gravity-dependent orientation and behavior.

Abstract

Gravitational effects in colloidal suspensions can be easily turned off by matching the density of the solid microparticles with the one of the surrounding fluid. By studying the motion of catalytic microswimmers with tunable buoyant weight, we show that this strategy cannot be adopted for active colloidal suspensions. If the average buoyant weight decreases, pronounced accumulation at the top wall of a sample cell is observed due to a counter-alignment of the swimming velocity with the gravitational field. Even when the particles reach a flat wall, gravitational torques still determine the properties of the quasi two-dimensional active motion. Our results highlight the subtle role of gravity in active systems.