The Rubber-Band Drop: How an Elastic Liquid Bounces Back Whole ⚡ экспресс
When a viscoelastic, shear-thinning droplet with high elasticity impacts a superhydrophobic surface, a tail-like ligament grows vertically from the contact point. As the contact line recedes, this ligament swells into a balloon-like shape and then fully detaches from the surface (the 'balloon' regime). The ligament forms because the fluid squeezes into the gaps between microscopic surface bumps during impact. This process can be controlled by altering the surface roughness and wettability. The ligament's elongation is dominated by inertia and gravity, while the high elasticity prevents rupture, ensuring complete separation and rebound of the droplet.
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.