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.

No abstract

Spider silks, mainly constructed of spidroin, have received extensive attention for their excellent mechanical properties, slow biodegradability, and high biocompatibility. However, due to uncontrollable protein-folding processes, the structural transition of spidroin, especially when composited with other functional materials under confinement, is insufficiently understood. Herein, we report a pressure-induced conformational transition process of the spidroin which is confined within carbon nanotube (CNT) sponge matrixes. The structural transition of spidroin from α-helix to β-sheet can be induced by a very small hydrostatic pressure (several megapascals) and recover easily through a subsequent solvent vapor annealing process in an ambient atmosphere. Therefore, the spidroin/CNT sponge exhibits reversible vapor-/pressure-sensitive "shape-memory" behavior with the recovery efficiency close to 100%. Our observation reveals a crucial mechanism for the conformational transition of spidroin under confinement, which paves the way toward the fabrication of spider silk-based products with superior performances.

Natural spider silks with striking performances achieve extensive investigations. Nonetheless, a lack of consensus over the mechanism of the natural spinning hinders the development of artificial spinning methods where the regenerated spider silks generally show poor performances compared with the natural fibers. As is known, the Plateau–Rayleigh instability tends to break solution column into droplets and is considered a main challenge during fiber‐spinning. Here in this study, by harnessing the viscoelastic properties of the regenerated spidroin dope solution via organic salt–zinc acetate (ZA), this outcome can be avoided, and dry‐spinning of long and mechanically robust regenerated spider silk ribbons can be successfully realized. The as‐obtained dry‐spun spider silk ribbons show an enhanced modulus up to 14 ± 4 GPa and a toughness of ≈51 ± 9 MJ m−3 after the post‐stretching treatment, which is even better than that of the pristine spider silk fibers. This facile and flexible strategy enriches the spinning methodologies which bypass the bottleneck of precisely mimicking the complex natural environment of the glands in spiders, shining a light to the spider‐silk‐based textile industrial applications.