Dynamic oscillatory cluster ordering of self-propelled droplets

TL;DR

This paper describes a novel dynamic clustering behavior of self-propelled droplets driven by Marangoni effects, exhibiting periodic ring formations and collapses, serving as a model for complex collective dynamics.

Contribution

It introduces a new self-organized oscillatory clustering state in droplet systems and proposes an inhomogeneous force model to explain this behavior.

Findings

Droplets form periodic ring clusters with 5-20 minute cycles.

The clustering process involves immediate collapse after formation.

The system models complex dynamical states of self-propelled particles.

Abstract

We report here a peculiar dynamically ordered state of clustering droplets of a mixture of organic solvent. There droplets are driven by the solutal Marangoni effect on the surface of aqueous surfactant solution. They form temporal ring clusters which start collapsing immediately after its formation. This process is repeated for more than several hours with the period of 5--20 minutes. We propose an inhomogeneous force model to phenomenologically understand the basic mechanism of this dynamics, where the forces acting on each particle are controlled differently. This droplet system offers a simple, non-biological experimental model for the study of complex dynamical states realized by a group of self-propelled particles.