📝 SummarXiv

Abstract

Macroscopic objects supported by surface tension at the fluid interface can self-assemble through the action of capillary forces arising from interfacial deformations. The resulting self-assembled structures are typically ordered but remain trapped in one of potentially many metastable states in the capillary energy landscape in the absence of external forces. In contrast, microscopic colloidal systems leverage both thermal and active fluctuations to overcome energy barriers, enabling transitions between microstates of the system. We herein utilize supercritical Faraday waves to drive structural rearrangements between metastable states of few-particle clusters of millimetric spheres bound by capillary attractions at the fluid interface. By tracking all microstate transitions experimentally, we find that the system is endowed with a non-zero entropy production rate reflecting broken detailed balance and the system's departure from equilibrium. Our experimental results are in quantitative agreement with simulations of a many-body active Ornstein-Uhlenbeck model, pointing to universal features of active and driven self-assembly across scales. These findings invite a corresponding investigation at the microscale using colloids that are themselves active or are placed in a wider class of athermal environments such as bacterial baths.