MIT scientists have created a new kind of hydrophobic material that is incredibly slippery, beating existing hydrophobic surfaces by a factor of 10,000.
(Enhanced Condensation on Lubricant-Impregnated Nanotextured Surfaces video)
The key to the improved hydrophobic (water-shedding) surface is a combination of microscopic patterning—a surface covered with tiny bumps or posts just 10 um across, about the size of a red blood cell—and a coating of a lubricant, such as oil. The tiny spaces between the posts hold the oil in place through capillary action, the researchers found.
The team discovered that droplets of water condensing on this surface moved 10,000 times faster than on surfaces with just the hydrophobic patterning. The speed of this droplet motion is key to allowing the droplets to fall from the surface so that new ones can form, increasing the efficiency of heat transfer in a power plant condenser, or the rate of water production in a desalination plant.
With this new treatment, "drops can glide on the surface," Varanasi says, floating like pucks on an air-hockey table and looking like hovering UFOs—a behavior Varanasi says he has never seen in more than a decade of work on hydrophobic surfaces. "These are just crazy velocities."
The amount of lubricant required is minimal: It forms a thin coating, and is securely pinned in place by the posts. Any lubricant that is lost is easily replaced from a small reservoir at the edge of the surface. The lubricant can be designed to have such low vapor pressure that, Varanasi says, "You can even put it in a vacuum, and it won't evaporate."
In Frank Herbert's 1965 novel Dune, Dune has no surface water; all water is precious and is carefully measured and stored, so the native Fremen perfected a water repellent surface:
A splashing sounded on her left. She looked down the shadowy line of Fremen, saw Stilgar with Paul standing beside him and the watermasters emptying their load into the pool through a flowmeter. The meter was a round gray eye above the pool's rim. She saw its glowing pointer move as the water flowed through it, saw the pointer stop at thirty-three liters, seven and three-thirty-seconds drachms.
Superb accuracy in water measurement, Jessica thought. And she noted that the walls of the meter trough held no trace of moisture after the water's passage. The water flowed off those walls without binding tension. She saw a profound clue to Fremen technology in the simple fact: they were perfectionists.