Nonequilibrium thermodynamics in driven macroscopic self-assembly

Equilibrium statistical mechanics provides a robust framework for characterizing phase transitions in systems whose microsopic dynamics are time-reversible. Efforts to develop and validate theoretical frameworks for time-irreversible, nonequilibrium systems are constrained by experimental data that capture only partial measurements of the system dynamics. We herein address this limitation using a tunable macroscopic platform for nonequilibrium physics: millimetric spheres bound by capillary attractions at the fluid interface and driven out of equilibrium by a field of supercritical Faraday waves. The external driving induces correlated motion in the particle trajectories and excites structural rearrangements between distinct metastable cluster topologies. By tracking all microstate transitions experimentally, we directly measure a nonzero entropy production rate reflecting broken detailed balance and quantifying the system’s departure from equilibrium. The measured stochastic dynamics are in quantitative agreement with a many-body active Ornstein-Uhlenbeck model, thus establishing a bridge to a wider class of athermal, self-propelled systems at the microscale. These results invite corresponding studies with active colloids or passive particles immersed in bacterial baths and shed light on the dynamics and control of nonequilibrium self-assembly kinetics.