Watch water droplets literally jump off a ‘water-hating’ material

Insects that walk on the surface of ponds and self-cleaning lotus leaves are just two examples of the myriad ways nature has devised surfaces that are ultra–water-repellant. Researchers have devised their own versions of what are known as superhydrophobic surfaces. Typically these are made up of microscale or nanoscale spikes, which repel droplets landing on top, and can even cause tiny droplets to leap off the surface. But the approach doesn’t always work. If water vapor gets in between spikes as it condenses, it can hold droplets down. In a new study, researchers crafted a 3D network of vertically aligned copper nanowires. The sides of the wires were coated with extra–water-repellant material, and the network was tightly packed, preventing water from getting between the wires. The result: Water droplets leap off the surface just after they begin to condense from water vapor, the team reports today in Joule. When they do so, jumping droplets can take heat from the surface with them. And the researchers found that their copper nanowire surface removes twice as much heat as the previous best material. Such surfaces could improve everything from water desalination to cooling electronics.