Collective Oscillations of Photothermal Micromotors under Static Illumination

Nonlinear phenomenon widely exists in living organisms in nature. Over the past decades, self-propelled micromotors with oscillatory behaviors have aroused focus of attentions. However, oscillatory behaviors driven by nonchemical mechanisms have rarely been explored. In this paper, we report a collective oscillation of photothermal micromotors driven by the periodic variation of a photothermally induced temperature difference, which leads to an alternating two-mode motion, a slow mode driven by the synergistic effects of self-thermophoresis and thermocapillary forces (∼70 μm/s) and a fast mode driven by thermal convection (∼2422 μm/s). The oscillatory behavior is tunable by adjusting the light intensity and the concentration of microspheres. The present findings not only provide fresh insight into emergent collective behaviors of active matter but also pave the way toward the study of more complex and coupled oscillatory active systems.