Predator-Prey Interactions between Droplets Driven by Nonreciprocal Oil Exchange

TL;DR

This study demonstrates how chemically minimal oil droplets can exhibit predator-prey-like chasing behaviors driven by nonreciprocal chemotactic interactions, leading to emergent self-organization in microscale systems.

Contribution

It reveals chemical design principles for tuning nonreciprocal droplet interactions and combines experiments with simulations to understand active droplet behavior.

Findings

Droplets exhibit predator-prey chasing interactions.

Interactions are tunable via oil and surfactant chemistry.

System demonstrates emergent self-organization similar to biological systems.

Abstract

Chemotactic interactions are ubiquitous in nature and can lead to nonreciprocal and complex emergent behavior in multibody systems. Here we show how chemotactic signaling between microscale oil droplets of different chemistries in micellar surfactant solutions can result in predator-prey-like chasing interactions. The interactions and dynamic self-organization result from the net directional, micelle-mediated transport of oil between emulsion droplets of differing composition and are powered by the free energy of mixing. The nonreciprocal behavior occurs in a wide variety of oil and surfactant conditions, and we systematically elucidate chemical design rules for tuning the interactions between droplets by varying oil and surfactant chemical structure and concentration. Through integration of experiment and simulation, we also investigate the active behavior and dynamic reorganization of multi-droplet clusters. Our findings demonstrate how chemically-minimal systems can be designed with controllable, non-reciprocal chemotactic interactions to generate emergent self-organization and collective behaviors reminiscent of biological systems.