Coupled oscillation and spinning of photothermal particles in Marangoni optical traps

Abstract

Significance Oscillators, widely found in nature, form the basis of a wide variety of actuating and signal processing mechanisms. While the ability to mimic arrays of oscillators and control their coupling is a central goal in the field of bioinspired soft materials, this has been difficult to achieve. Using Marangoni forces generated during spatially inhomogeneous illumination of photothermally responsive particles, we demonstrate a scheme for optically trapping arrays of particles at air–water interfaces that can incite a range of oscillatory and spinning behaviors. When multiple objects are arranged in proximity, they exhibit complex, collective behavior emerging from geometry-dependent interparticle coupling. This route to achieving collective motion is expected to open opportunities in the study of active materials. Cyclic actuation is critical for driving motion and transport in living systems, ranging from oscillatory motion of bacterial flagella to the rhythmic gait of terrestrial animals. These processes often rely on dynamic and responsive networks of oscillators—a regulatory control system that is challenging to replicate in synthetic active matter. Here, we describe a versatile platform of light-driven active particles with interaction geometries that can be reconfigured on demand, enabling the construction of oscillator and spinner networks. We employ optically induced Marangoni trapping of particles confined to an air–water interface and subjected to patterned illumination. Thermal interactions among multiple particles give rise to complex coupled oscillatory and rotational motions, thus opening frontiers in the design of reconfigurable, multiparticle networks exhibiting collective behavior.