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MIT researchers have succeeded in improving the hydropobic nature of surfaces, taking inspiration from leaves and butterfly wings. Image credit: photos.com.
Researchers have succeeded in breaking the theoretical limit on how long a drop of water takes to bounce from a surface, which could lead to the creation more efficient hydrophobic surfaces.
Hydrophobic materials, as the name suggests, repel bodies of water owing to the non-polar nature of their constituent molecules. Natural hydrophobes include fats and oils, whilst butterfly wings and leaves possess similar properties as survival mechanisms.
Essentially, if the contact time between a given surface and an encroaching drop of liquid can be limited, said surface will stay drier for longer.
Kripa Varanasi, the Doherty Associate Professor of Mechanical Engineering at MIT explains why this should be:
“The time that the drop stays in contact with a surface is important because it controls the exchange of mass, momentum, and energy between the drop and the surface. If you can get the drops to bounce faster, that can have many advantages.”
Researchers from MIT have now shown that the hydrophobic properties of a surface can be greatly enhanced beyond what was thought possible, and have succeeded in reducing this contact time by at least 40%.
It is common practise when creating hydrophobic materials to try and minimise surface interaction between the water and the surface, by creating low-adhesion superhydrophobic surfaces.
Conversely, the researchers at MIT decided to increase the interaction between the surface and liquid by adding in macroscopic features such as ridges. These surface imperfections were noted to cause the water to lose its symmetry and bounce off in a variety of forms and shapes. The following video demonstrates how surfaces with and without ridges interact with a drop of water.
Droplets break a theoretical time barrier on bouncing
What’s more, creating these textured surfaces is a relatively simple task, and can be performed by common milling tools. This means that apart from being extremely interesting scientific research, the new technique could be scalable to industrial levels.
This is not the first time this year that MIT have been involved in groundbreaking research regarding hydrophobic materials - in January, researchers came up with a new class of hydrophobic ceramics.
This discovery of course opens the door for all sorts of waterproofing techniques for electronic devices and clothing, but a more important use may be in air travel safety. Whilst a plane is in flight ice can build up on the wings, as water droplets hit the surface and freeze in place. This can lead to aerodynamic stall, as the ice changes how air flows over the wings, which can lead to loss of control of the aircraft. With the new hydrophobic material this could potentially be prevented, by bouncing away droplets before they get the chance to freeze.
The research team is even hoping for better results in the future, by perfecting the texture of the surface.
“We can reduce it further. I hope we can manage to get a 70 to 80 percent reduction.” - Kripa Varanasi
Original source: Massachusetts Institute of Technology
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