Marangoni swimmer pushing particle raft under 1D confinement

TL;DR

This study investigates how a Marangoni swimmer's self-propulsion is affected by interactions with passive particles in a confined environment, revealing distinct motion regimes and proposing a model for swimmer speed.

Contribution

It provides the first experimental analysis of how passive particles influence active Marangoni swimmer propulsion under 1D confinement, identifying different motion regimes and developing a predictive force-balance model.

Findings

Two motion regimes identified: steady uni-directional and oscillatory.

Swimmer speed decreases with increasing particle packing fraction.

A force-balance model captures the trend in swimmer speed.

Abstract

Active matter systems, due to their spontaneous self-propulsion ability, hold potential for future applications in healthcare and environmental sustainability. Marangoni swimmers, a type of synthetic active matter, are a common model system for understanding the underlying physics. Existing studies of the interactions of active matter with passive particles have mostly focused on the modification of the behavior of the passive particles. In contrast, we analyse here experimentally the impact on the self-propulsion of camphor-infused agarose disks (active) of their interactions with floating hollow glass microspheres (passive) within an annular channel. Two distinct regimes are observed: a steady regime with uni-directional motion of the swimmer at low packing fractions (\phi_{\textrm{ini}} \lesssim 0.45) and an oscillatory regime with to-and-fro motion at higher packing fractions (\phi_{\textrm{ini}} \gtrsim 0.45). In the former, the swimmer pushes nearly the entire particle raft together with it, like a towing cargo, causing a decrease in swimmer speed with increasing packing fraction due to the additional drag from the particle raft. A simplified force-balance model is finally proposed that captures the experimental trend in swimmer speed reasonably well.