June 16, 2006 12:45 PM PDT
To harvest water from air, MIT copies beetles
Robert Cohen and Michael Rubner, professors at the Massachusetts Institute of Technology, have developed a material inspired by the outer shell of the beetle that is capable of extracting liquids from the atmosphere and channeling it into storage areas.
The material could potentially be used to harvest water from moist air or to create mini-cooling devices. The U.S. military also has expressed interest in using the material, or some variant of it, to collect harmful substances. Such a material would allow machinery or other equipment to disinfect itself.
The material consists of a glass or plastic substrate coated in several layers of charged polymers and silicon nanoparticles. The polymer layers make the substrate porous, while the silicon particles create voids. In the end, both cause the substrate to collect water. The coated substrate is then covered with a patterned layer of a Teflon-like material that repels water. As a result, water collects in the areas where the hydrophobic material isn't present.
In the case of the beetle, water collects on bumps 15 microns to 20 microns in diameter. When enough water droplets gather, they break free of the bump and roll into the beetle's mouth.
Although the experiments are in the early stages, the hydrophilic/hydrophobic material can be patterned in a variety of ways to achieve different results.
Last year, Rubner also showed off a fogless glass, which exploited similar physical principles. The glass contained bumps that collected water. By placing several bumps in an even pattern across the glass, a thin layer of water formed on it, which prevented fog. Goggle manufacturers and carmakers are experimenting with it.
Conversely, Ohio State University professor Bharat Bhushan has come up with a bumpy material that repels water that was inspired by lotus leaves. The material, he said, could be used to reduce friction in tiny machines called microelectricalmechanical systems or to create glass that sheds water.