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Water, Water Everywhere
25 May 2006 (All day)
A desert beetle that wrings water from fog has inspired scientists to create a nanomaterial that literally plucks moisture from the air. The invention could boost water supplies in the driest regions, say experts, and a similar setup could be used to precisely control the flow of tiny amounts of fluids for sensitive diagnostic tests.
Stenocara beetles live in the Namib Desert, one of the driest places on Earth. Located on the southwest coast of Africa, the region has scarce, unpredictable rainfall and no streams. On mornings when thick fog drifts in from the Atlantic Ocean, the insect climbs to the top of a dune and does a headstand, tilting its back into the breeze. Water droplets collect on the tops of smooth bumps until they spill into waxy, water-repellent grooves studded with smaller bumps that shunt the water down the insect's shell into its mouth (ScienceNOW, 1 November 2001).
To copy the beetle's water-collecting design, materials scientist Michael Rubner, chemical engineer Robert Cohen, and colleagues at the Massachusetts Institute of Technology in Cambridge created a rough coating so water repelling--or hydrophobic--that water sprayed onto it stood up in nearly spherical droplets. First, they wrinkled polymer films onto glass to create micrometer-sized hills and valleys. Then, to prevent droplets from getting trapped in the valleys, the team decorated the surface with glass nanoparticles coated with water-repellent Teflon-like molecules.
To make the material capture rather than shed water, the researchers took another cue from the Stenocara beetle. They created water-grabbing bumps with charged polymers that are full of pores and function "like a nanocapillary or a nanosponge that just sucks the water up," Rubner says. The polymers could be printed onto other surfaces such as fabrics to harvest water from fog, they report 14 June in Nano Letters.
The new material is much more efficient than current mist-catching nets, in which most of the water passes through uncollected, says Andrew Parker, the Oxford University zoologist who originally described the beetle's unique surface. "There is potential to help people's lives," he says, "although in most cases there isn't really any potential to make any money out of it."