Active droploids

TL;DR

This paper introduces active droploids, self-organizing superstructures formed by colloidal particles and their environment through mutual feedback, advancing active matter by enabling environmental coupling and dynamic structure formation.

Contribution

It demonstrates a novel two-way coupling mechanism in active matter, leading to the creation of active superstructures called active droploids, which was not previously achieved.

Findings

Active droploids form under light illumination in experiments and simulations.

They exhibit self-propulsion driven by colloidal engines.

Environmental feedback enables the formation of complex active superstructures.

Abstract

Active matter comprises self-driven units, such as bacteria and synthetic microswimmers, that can spontaneously form complex patterns and assemble into functional microdevices. These processes are possible thanks to the out-of-equilibrium nature of active-matter systems, fueled by a one-way free-energy flow from the environment into the system. Here, we take the next step in the evolution of active matter by realizing a two-way coupling between active particles and their environment, where active particles act back on the environment giving rise to the formation of superstructures. In experiments and simulations we observe that, under light-illumination, colloidal particles and their near-critical environment create mutually-coupled co-evolving structures. These structures unify in the form of active superstructures featuring a droplet shape and a colloidal engine inducing self-propulsion. We call them active droploids -- a portmanteau of droplet and colloids. Our results provide a pathway to create active superstructures through environmental feedback.