(46f) Synchronization Behaviors of Active Oscillating Particles

Relaxation oscillators are nonlinear oscillators characterized by two separate timescales that define an impulse event and recovery event. They arise in nature commonly at a number of length scales and are crucial for many biological processes, such as the animalian cardiovascular system (heartbeats) or brain function (neuron firing). They are a critical component in computer circuits, defining the “clock frequency” of microprocessors. In these examples, oscillator synchrony is crucial to maintain the functionality of the machine. Recently, several relaxation oscillators have been implemented in out-of-equilibrium colloidal systems. Here, we demonstrate low-frequency colloidal clocks in the form of chemically-driven coupled relaxation oscillators at a liquid-gas interface. These particles actuate due to a competition between oxygen bubble generation and surface tension gradients to produce expanding and collapsing assemblies. Their rhythmic beating only emerges as a result of their interactions with one another, which we can deterministically simulate with a mechanistic model. This complex system-level oscillation emerging from particles sharing a deceptively simple physical design exhibits highly tunable frequency. We also demonstrate, through both experiment and simulation, that this emergent oscillator system can be reliably tuned to move in and out of an aperiodic oscillation phase, providing further opportunities to introduce system-level control. At low particle counts and oxygen evolution rates, the particles synchronize into a regular frequency mode. At higher particle counts and reaction rates, oscillator ensembles enter regimes of complex aperiodic dynamics. These oscillators could be used to design beating colloidal machines that share a common clock and for creating microfluidic pumps and mixers.