Splash proof surfaces may be on their way thanks to research from Wadham Engineer Alfonso Castrejon-Pita. It’s well known that when a drop hits a surface at sufficiently high speeds, it can break up into multiple smaller droplets - it splashes. His research has found a simple solution; coating a surface in a thin layer of a soft material like a gel, or soft rubber.
An impacting droplet can require more than twice as much energy to splash on a soft surface as it does on a rigid one. This is not merely due to soft surfaces absorbing all the extra impact energy: in fact soft surfaces absorb only a fraction more of a droplet’s impact energy than rigid ones.
The research, published in Physical Review Letters, shows the importance of the maximum fluid pressure that builds up under a droplet in the first few moments (microseconds) of impact. When this exceeds a critical amount, tiny deformations of the substrate occur which, surprisingly, can be just enough to completely suppress splashing.
This key mechanism was uncovered through a mixture of careful experiments, numerical simulations and mathematical modelling by Alfonso and fellow researchers Christopher J. Howland, Arnaud Antkowiak, J. Rafael Castrejón-Pita, Sam D. Howison, James M. Oliver and Robert W. Style.
Applications range from safer biomedical enclosures and (maybe) splash-free urinals!
Click on the video below to see a 2.8mm drop of ethanol at 3m/s hitting a solid substrate without soft coating.