The Rubber-Band Drop: How an Elastic Liquid Bounces Back Whole ⚡ экспресс
When a drop of highly elastic viscoelastic fluid hits a superhydrophobic surface, it doesn't just bounce back — a thread-like tail stretches up from the point of impact, then balloons into a sphere and finally detaches completely. Scientists showed that this effect is driven by the fluid pushing into microscopic surface roughness during impact. By tuning roughness and wettability, you can control the formation of these 'threads'. The tail's stretch is mainly governed by inertia and gravity, while its high elasticity keeps it from snapping, letting the droplet make a clean getaway.
A drop of water with added elastic polymers falls onto a surface that repels water as well as a lotus leaf. On impact, the liquid pushes into microscopic pits, stretching out a thin tail—like a stretched rubber band. Then elasticity causes the tail to snap back, but inertia and gravity, described by Newton, stretch it even more. Eventually, the tail tip balloons into a sphere, and the entire drop bounces off, like a released rubber band. This process was captured using photometry—a highly sensitive technique that detects the tiniest light changes.
By changing the surface texture—the size of its bumps and pits—you can control the tail shape and the bounce. The paradox is that these very irregularities, which should hold the liquid, make it bounce. This discovery will be useful for self-cleaning glass, water-repellent clothing, and precise inkjet printing—ink drops will hit their target exactly.
🎯 A lotus leaf stays dry thanks to microscopic bumps with a waxy coating—this is the lotus effect. Scientists mimic these structures to create superhydrophobic coatings.
🎬 The elastic drop resembles the T-1000 liquid metal from Terminator 2: it can also change shape and reconstitute without tearing.