Tag: droplet rebound

Droplet Bounce
A droplet falling on a liquid bath may, if slow enough, rebound off the surface. Its impact sends out a string of ripples — capillary waves — on the bath’s surface and sends the droplet itself into jiggling paroxysms. A new pre-print study delves into this process through a combination of experiment, simulation, and modeling. Impressively, they find that the most of the droplet’s initial energy is not dissipated during impact. Instead it’s fed into the capillary waves and droplet deformation that follow. (Image and research credit: L. Alventosa et al.; via Dan H.)
A droplet falls on a bath, partially coalesces and rebounds. The process repeats until the droplet is small enough to coalesce completely.
November 8, 2022
“Viscoelasticity Gives You Wings!”
What happens when you drop a hydrogel bead on a water droplet? Because of the hydrogel’s viscoelasticity and its hydrophilic nature, the rebounding bead carries the droplet with it. As seen in the video above, when the impact energy is small enough, the droplet forms a reverse crown during lift-off, kind of like giving the hydrogel bead a skirt. The key feature for lift-off is the bead’s deformation on impact. Because the hydrogel widens at its base, it is sometimes able to push the entire droplet off its initial footprint and detach it from the surface. (Image, research, and video credit: R. Rabbi et al.)
January 7, 2020
Rebounding
A water droplet can rebound completely without spreading from a superhydrophobic surface. The photo above is a long exposure image showing the trajectory of such a droplet as it bounces. In the initial bounces, the droplet leaves the surface fully, following a parabolic path with each rebound. The droplet’s kinetic energy is sapped with each rebound by surface deformation and vibration, making each bounce smaller than the last. Viscosity damps the drop’s vibrations, and the droplet eventually comes to rest after twenty or so rebounds. (Image credit: D. Richard and D. Quere)
April 17, 2014
Hydrophobia
On a recent trip to G.E., the Slow Mo Guys used their high-speed camera to capture some great footage of dyed water on a superhydrophobic surface. Upon impact, the water streams spread outward, flat except for a crownlike rim around the edges. Then, because air trapped between the liquid and the superhydrophobic solid prevents the liquid from wetting the surface, surface tension pulls the water back together. If this were a droplet rather than a stream, it would rebound off the surface at this point. Instead, the jet breaks up into droplets that scatter and skitter across the surface. There’s footage of smaller droplets bouncing and rebounding, too. Superhydrophobic surfaces aren’t the only way to generate this behavior, though; the same rebounding is found for very hot substrates due to the Leidenfrost effect and very cold substrates due to sublimation. As a bonus, the video includes ferrofluids at high-speed, too. (Video credit: The Slow Mo Guys/G.E.)
January 9, 2014
Rebounding Off Dry Ice
Droplet rebound is frequently associated with superhydrophobic surfaces but can also be generated by very large temperature differences. For very hot substrates, a thin layer of the drop vaporizes on contact via the Leidenfrost effect and helps a drop rebound by preventing it from wetting the surface. This video shows almost the opposite: a water droplet hitting solid carbon dioxide (-79 degrees C). Upon contact, the solid carbon dioxide sublimates, creating a thin layer of gas that separates the droplet from the surface. You can also see the vortex ring that accompanies the drop’s impact. Water vapor near the carbon dioxide surface has condensed into tiny airborne droplets that act as tracer particles that reveal the vortex’s formation and the rebounding droplet’s wake. (Video credit: C. Antonini et al.; Research paper)
August 13, 2013