Interface-Driven Spontaneous Differentiation-Repulsion Behavior in Isochemical Droplet Populations

Summary

An important exercise for understanding the emergent behavior in biology is to study it using minimal synthetic systems. Current biomimetic systems involving directed motion and collective migration require at least three components: two immiscible solvents to form an emulsion, and external agent(s), usually surfactants, to give rise to asymmetric interactions and induce transient non-equilibrium conditions. Here, the most minimal system thinkable, consisting of only two components, is presented, in the form of micron-sized oil (1-decanol) droplets dispersed in a finite water reservoir. Spontaneous emergent dynamics within chemically identical droplet populations is reported, in the form of physical differentiation of droplets in a stochastic manner leading to an immediate repulsive behavior amongst their neighbors. Using a microfluidic production platform, fluorescence microscopy experiments, and modelling, it is showed that this cyclic phenomenon of differentiation-repulsion results from oil droplets entering the air-water interface leading to Marangoni flows and their coupling with evaporative flux of decanol. The potential of this platform is illustrated by demonstrating control over the event frequency, its use as Marangoni tweezers to trap droplet clusters, and proof-of-principle reorganization of multi-component assemblies. The presented collective behavior with exceptional chemical simplicity makes it amenable for potentially developing self-assembled biomimetic and bioengineered structures.