Eur. Phys. J. E (2016) 39: 64
https://doi.org/10.1140/epje/i2016-16064-y

Regular Article

Dimensionality matters in the collective behaviour of active emulsions

Max Planck Institute for Dynamics and Self-Organization (MPIDS), Am Faßberg 17, 37077, Göttingen, Germany

^* e-mail: carsten.krueger@ds.mpg.de

Received: 22 March 2016
Accepted: 2 June 2016
Published online: 27 June 2016

Abstract

The behaviour of artificial microswimmers consisting of droplets of a mesogenic oil immersed in an aqueous surfactant solution depends qualitatively on the conditions of dimensional confinement; ranging from only transient aggregates in Hele-Shaw geometries to hexagonally packed, convection-driven clusters when sedimenting in an unconfined reservoir. We study the effects of varying the swimmer velocity, the height of the reservoir, and the buoyancy of the droplet swimmers. Two simple adjustments of the experimental setting lead to a suppression of clustering: either a decrease of the reservoir height below a certain value, or a match of the densities of droplets and surrounding phase, showing that the convection is the key mechanism for the clustering behaviour.