Oil-on-water droplets faceted and stabilized by vortex halos in the subphase.

Proc Natl Acad Sci U S A

Center for Soft and Living Matter, Institute for Basic Science, Ulsan 44919, South Korea.

Published: January 2023

For almost 200 y, the dominant approach to understand oil-on-water droplet shape and stability has been the thermodynamic expectation of minimized energy, yet parallel literature shows the prominence of Marangoni flow, an adaptive gradient of interfacial tension that produces convection rolls in the water. Our experiments, scaling arguments, and linear stability analysis show that the resulting Marangoni-driven high-Reynolds-number flow in shallow water overcomes radial symmetry of droplet shape otherwise enforced by the Laplace pressure. As a consequence, oil-on-water droplets are sheared to become polygons with distinct edges and corners. Moreover, subphase flows beneath individual droplets can inhibit the coalescence of adjacent droplets, leading to rich many-body dynamics that makes them look alive. The phenomenon of a "vortex halo" in the liquid subphase emerges as a hidden variable.

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http://www.ncbi.nlm.nih.gov/pmc/articles/PMC9942921PMC
http://dx.doi.org/10.1073/pnas.2214657120DOI Listing

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