Whether the goal is keeping ice from building up on an airplane wing or a wind turbine blade, or preventing heat loss from a surface during rainfall, or preventing salt buildup on surfaces exposed to ocean spray, making droplets bounce away as fast as possible and minimizing the amount of contact with the surface can be key to keeping systems functioning properly.
While previous attempts, including by members of the same team, have focused on minimizing the amount of time the droplet spends in contact with the surface, the new method instead focuses on the spatial extent of the contact, trying to minimize how far a droplet spreads out before bouncing away.
The work is a follow up on an earlier project by Varanasi and his team, in which they were able to reduce the contact time of droplets on a surface by creating raised ridges on the surface, which disrupted the spreading pattern of impacting droplets.
But the new work takes this farther, achieving a much greater reduction in the combination of contact time and contact area of a droplet.
In order to prevent icing on an airplane wing, for example, it is essential to get the droplets of impacting water to bounce away in less time than it takes for the water to freeze.
"Reducing the contact area of the impacting droplet should also have a dramatic impact on transfer properties of the interaction," Varanasi says.