When a viscous liquid thread breaks, classical fluid mechanics tells us to expect a cylindrical column that pinches into drops, a process described since Rayleigh. In this project, we uncovered a very different pathway: when a horizontal thin film drains, it does not form a column but rather an annular sheet surrounding a column of air. This fragile geometry evolves through a remarkable sequence, through thinning, rupture, and healing that reveals new principles of interfacial dynamics.

Using high-speed imaging and a long-wavelength model, we showed that the thinning of the film and the collapse of the inner air column follow a universal curve once rescaled by viscous, capillary, and gravitational forces. After rupture, the film does not simply break apart. Instead, surface tension pulls the edges back together, “healing” the annulus. The inner surface forms a retracting conical tip that moves at nearly constant speed, set by the balance of viscous and capillary stresses. This dynamic healing process can trap an air bubble inside the resulting droplet or even generate chains of satellite bubbles—phenomena rarely seen in spontaneous dripping.

By documenting this new mode of breakup, we expanded the century-old paradigm of jets and filaments to include the dripping of annular films, a geometry with its own singularities and scaling laws.

Publication

  • 📄 F. Yang and H. A. Stone. Formation and healing of an annular viscous film. Physical Review Letters (2020). HTML

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