Galloping Bubbles
Spontaneous self-propulsion of bubbles.
This line of research was initiated with our discovery of galloping bubbles, a new mode of self-propulsion that arises when a millimetric bubble resting against the inside wall of a vertically vibrated fluid chamber is driven beyond a critical threshold. Nonlinear coupling between the bubble’s shape oscillations leads to spontaneous symmetry breaking and sustained horizontal motion, perpendicular to the forcing direction.
In contrast to conventional propulsion mechanisms that rely on imposed asymmetries, galloping bubbles move while maintaining zero net linear momentum and without viscous traction, their motion arising purely from nonreciprocal body deformations and inertial forces. Individual bubbles exhibit a rich variety of behaviors — including rectilinear motion, orbiting trajectories, and run-and-tumble dynamics — all stemming from the nonlinear coupling between oscillatory modes and the surrounding fluid. They can navigate mazes, self-sort and even clean surfaces, suggesting potential uses in microfluidic transport, and heat-transfer applications.
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When interacting, galloping bubbles exhibit rich collective behaviors arising from their deformable bodies, leading to lattice arrangements, coordinated motion, clustering, and other emergent dynamics. This minimal system reveals a new route to self-organized locomotion at fluid interfaces and illustrates how parametric instabilities can endow deformable bodies with motility.
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Introducing Galloping Bubbles
(APS GFM Award Winner)
HIGHLIGHTED PROJECTS
Galloping Bubbles
Guan, J. H., Tamim, S. I., Magoon, C. W., Stone, H. A., & Sáenz, P. J.
Nature Communications, 16(1), (2025) - https://doi.org/10.1038/s41467-025-56611-5
Despite centuries of investigation, bubbles continue to unveil intriguing dynamics relevant to a multitude of practical applications, including industrial, biological, geophysical, and medical settings. Here we introduce bubbles that spontaneously start to ‘gallop’ along horizontal surfaces inside a vertically-vibrated fluid chamber, self-propelled by a resonant interaction between their shape oscillation modes. These active bubbles exhibit distinct trajectory regimes, including rectilinear, orbital, and run-and-tumble motions, which can be tuned dynamically via the external forcing. Through periodic body deformations, galloping bubbles swim leveraging inertial forces rather than vortex shedding, enabling them to maneuver even when viscous traction is not viable. The galloping symmetry breaking provides a robust self-propulsion mechanism, arising in bubbles whether separated from the wall by a liquid film or directly attached to it, and is captured by a minimal oscillator model, highlighting its universality. Through proof-of-concept demonstrations, we showcase the technological potential of the galloping locomotion for applications involving bubble generation and removal, transport and sorting, navigating complex fluid networks, and surface cleaning. The rich dynamics of galloping bubbles suggest exciting opportunities in heat transfer, microfluidic transport, probing and cleaning, bubble-based computing, soft robotics, and active matter.