Evaporative self-assembly of motile droplets

TL;DR

This paper introduces an experimental platform using motile droplets on a lattice to study many-body dynamics, metastable states, and annealing processes, providing insights into controlling self-assembly through external fields.

Contribution

It presents a novel system for visualizing and manipulating many-body droplet interactions and annealing, advancing understanding of self-assembly and metastable state control.

Findings

Droplets exhibit long-range interactions leading to metastable states.

Global gravitational fields can induce phase transitions in droplet behavior.

Field-driven annealing reduces system frustration and guides to stable states.

Abstract

Self-assembly is the underlying building principle of biological systems and represents a promising approach for the future of manufacturing, but the yields are often limited by undesirable metastable states. Meanwhile, annealing methods have long been an important means to guide complex systems towards optimal states. Despite their importance, there have been few attempts to experimentally visualize the microscopic dynamics that occur during annealing. Here, we present an experimental system that enables the study of interacting many-body dynamics by exploiting the physics of multi-droplet evaporation on a prescribed lattice network. Ensembles of motile binary droplets are seeded into a hexagonal lattice template where interactions are mediated through the vapor phase and can be manipulated through the application of a global gravitational field. We show that for finite systems (61 droplets) the interacting droplets have an effective long-ranged interaction that results in the formation of frustrated, metastable states. Application of a periodic, global gravitational field can drive the system through a non-equilibrium phase transition separating phase-locked synchronization from interaction-dominated behavior. Finally, we directly visualize field-driven annealing that leads to terminal states that are less frustrated. Overall, our results represent a new platform for studying many-body physics with long-ranged interactions, enabling the design of field-based control strategies for programming the self-assembly of complex many-body systems.