Droplet impact on solid surfaces
The impact and splashing of droplets depend not only on the liquid properties, but also on the surface characteristics such as roughness and wettability as shown in these series of videos.
Water droplet impacting at 1 m/s on a hydrophilic surface. The droplets spreads and goes out of the field of view.
Water droplet impacting at 1 m/s on a superhydrophobic surface. The droplet reaches a maximum spreading diameter, recedes and eventually bounces off the surface.
Water impacting at 3.7 m/s on a smooth glass superhydrophobic surface. The wettability of the superhydrophobic surface produces a big splash of the droplet. Moreover, after breaking up and reaching a maximum spreading diameter the droplet recedes and bounces off the surface.
Droplet impacting a shallow pool
The outcome of the impact dynamics of a droplet on a shallow pool is heavily influenced by the pool properties.
Droplet impacting a shallow pool of a mix of glycerine and water, with a viscosity three times larger than water.
Droplet impacting a shallow pool with the same liquid as the video of the left. The only difference is that surfactants are added to the mix, reducing the surface tension of the pool.
Droplet impacting a shallow pool of a glycerol and ethanol mix, with the same viscosity as the other two videos on the left. And the same surface tension of the pool containing the surfactant.
Needle-Free Injections
Microfluidic jet impacting a droplet
Skin is very complex, so the first step we took to understand needle free injections was to "inject" on a droplet!
Embedding: The impact of a liquid jet on a water droplet; the video is recorded with a high-speed camera at 50k frames per second, the jet diameter is 100μm and its impact velocity is 12.3 m/s.
Traversing: The impact of a liquid jet on a water droplet; the video is recorded with a high-speed camera at 50k frames per second, the jet diameter is 100μm and its impact velocity is 25.8 m/s.
The impact of a liquid jet on a viscoelastic droplet. In this case, the jet wants to penetrate the droplet, but due to the elastic forces of the liquid is brought back to the main droplet volume.
Numerical simulations of a jet impacting a pool.
Because sometimes experiments does not allow to measure everything we want, we recur to numerical simulations to provide some insights. All the simulations are done with Basilisk.
Jet impacting a deep pool at We = 150. The cavity collapses from the bottom to the top and a Worthington jet is generated.
Jet impacting a deep pool at We = 500. The jet impacts and a dome is created, provoking the cavity to collapse above of the original pool surface.
Velocity field inside the liquid pool after it is impacted by a jet.
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