3D Periodic Orbiting of a Photothermal Bubble

The spontaneous periodic oscillations of underwater bubbles are typically confined to a 1D direction or within a 2D plane, whereas realizing 3D autonomous motion of bubbles remains challenging. In this Letter, we present experimental observations of a 3D-periodic orbiting bubble, produced by directing a stationary near-infrared laser at hexane, thereby extending the spectrum of multimode motions beyond the 1D and 2D paradigms. Through numerical simulation by carefully investigating both the thermodynamic and hydrodynamic parameters of several liquids, this 3D-orbiting mode is attributed to the subtle interplay between the interfacial flow due to the thermal Marangoni effect and the bulk flow from the thermal buoyancy effect. Moreover, by developing a unified physical model to elucidate the effect of liquid properties on the motion modes, a phase diagram is constructed through a single dimensionless number (Σ=ReSc/Ma), providing a theoretical guidance to tailor the periodic oscillation modes. These findings not only reveal the underlying intriguing physicochemical hydrodynamics, but also possibly shed light on the bubble-mediated technologies.