NanoPlastic Both Attracts and Repels Water-a boon in dry regions with limited access to clean water
This month Technology Review has an interesting story about a newly created super material, a plastic that both attracts and repels water at the same time.
This new nano-material could be a boon in dry regions with limited access to clean water.
Scientists have reported numerous applications of water-attracting (superhydrophilic) and water-repelling (superhydrophobic) surfaces, including harvesting water in the desert, micro-channels for devices for medical tests, microfluidic chips, micro chemical synthesis, fog-free eyeglasses and windshields, and self-cleaning cloth and glass.
Now a group of researchers in MIT's materials science and engineering department has combined those opposing characteristics on a single surface, by using a simple and versatile fabrication process.
Technology Review reports that:
Robert Cohen, Michael Rubner, and colleagues from MIT started by assembling a nano-structured film made of alternating layers of positively and negatively charged polymers and silica nanoparticles. The film's structure and a coating of waxy fluorinated silane cause water to bead on it, forming near-perfect spheres that easily roll off. To add the superhydrophilic regions (to which water droplets cling), the researchers applied a naturally hydrophilic polymer to selected areas.
In dry regions of the world, without easy access to clean water, such a material could be used for collecting water. In this application, the hydrophilic areas of the material would attract moisture in the air, collecting water drops that accumulate, until they spill over into the hydrophobic regions and roll into a collecting channel. Currently, in countries with limited access to clean water, the inhabitants typically use large polypropylene fiber meshes to harvest water from fog.
The new technology "would provide a more than tenfold increase in water capture compared to the inefficient nets that are used currently," says Andrew Parker, a biologist at Oxford University and the Natural History Museum in London, who has studied the desert beetle that inspired the MIT work. If the new material "could be added simply to the roofs of houses in areas subjected to desert fogs," says Parker, "then a water supply could be gained with little effort."
Rubner's lab is also taking the technique further. "When we harvest water, we have chemistry built into the hydrophilic area so that it has an antibacterial agent to kill off bacteria and other things that cause harm,"
The above plastic could be coated on the opposite face with an electrical conductor that would then allow electrostatic cooling to drop the surface temperature to the ambient DEW point resulting in the faster condensation and harvesting of water from air. This electrostatic cooling can be powered by a solar panel.
While the exact uses of this new material are still uncertain, it opens up many possibilities, says Kenneth Wynne, a chemical engineering professor at Virginia Commonwealth University. "Patterning ultra-hydrophilic patches on a ultra-hydrophobic surface in this way is new and useful," he says.
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