According to Technology Review, scientists from the MIT have found a new material which can at the same time attract and repel water. These opposing characteristics have been obtained by "assembling a nano-structured film made of alternating layers of positively and negatively charged polymers and silica nanoparticles." This super plastic could be used in dry areas or to collect water. But it also could be used elsewhere to decontaminate water or in biomedical applications to make microfluidic chips. Read more...
Here is a short description of the manufacturing process of this new material.
Robert Cohen, Michael Rubner, and colleagues 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.
Below are two images coming from Rubner's research group, Nanoscale Processing and Properties of Polymeric Multilayer Thin Films. The first one shows "a glass slide partially coated with a superhydrophilic multilayer" (Credit: Michael Rubner, MIT).
And below you can see "drops of water on a superhydrophilic multilayer surface patterned with hydrophilic regions" (Credit: Michael Rubner, MIT).
But what could be this material useful for?
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.
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.
But it also can be used to clean water.
"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," Rubner says. This decontaminates the water as it accumulates so that the collected water is safe for use. Applying this technique, the researchers have been able to kill common harmful bacteria in four minutes, he says.
Finally, this super plastic could also be used in biomedical applications to make microfluidic chips which wouldn't need pumps or valves.
Right now, the researchers are not sure of what could be the future uses of this odd new material. In the mean time, you can read about another Cohen's research projects, Structure-Property Relations for Polymeric Materials.
Sources: Prachi Patel-Predd, Technology Review, May 30, 2006; and various web sites
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