One thing nanotechnology can do, besides create new materials, is use some ‘old’ things in new ways. Take, for example, bubbles. Some bubbles are trapped air. Air repels water, or more specifically air and water don’t mix (immediately) so bubbles are formed. Thinking like a nanotechnologist: What if there were nano-sized bubbles trapped in a substrate, could this make a surface that is super water repellant? To find out, a team from Brookhaven National Laboratories (U.S.A.) created a surface in silicon with nano-cavities (that’s tiny pockets less than one thousandth the diameter of a human hair) – a trillion cavities on an otherwise flat surface. Then they used a surfactant (in this case, a waxy coating) to seal the cavities and forming nanobubbles.
Now one of the problems with creating nanotech is, of course, it’s invisibility to the human eye, or in fact, anything but extremely high powered equipment. So to verify that they had created a surface with nano-size bubbles, the samples were taken to the National Synchrotron Light Source for x-ray measurements. The x-rays diffracted (bounced) off the surface, which was captured in images that showed the cavities to be filled mostly with air. The bubbles were only about 10 nanometers in size and rather surprisingly had flat tops (most bubbles have convex – upward curving – tops). This would significantly increase the slippage along the tops of the bubbles. They also discovered that water barely penetrated the cavities, perhaps only 15-30 molecules deep, which meant the bubbles would be very stable.
The end result was an extremely water-repellant surface, for which the team coined a word – superhydrophobicity (try that in Scrabble sometime). This has a wide variety of potential (and important) applications. As a member of the team put it…
“Our results explain how these nanocavities trap tiny bubbles which render the surface extremely water repellent,” said Brookhaven physicist and lead author Antonio Checco. The research could lead to a new class of non-stick materials for a range of applications, including improved-efficiency power plants, speedier boats, and surfaces that are resistant to contamination by germs.
Non-stick surfaces are important to many areas of technology, from drag reduction to anti-icing agents. These surfaces are usually created by applying coatings, such as Teflon, to smooth surfaces. But recently — taking the lead from observations in nature, notably the lotus leaf and some varieties of insects — scientists have realized that a bit of texture can help. By incorporating topographical features on surfaces, they’ve created extremely water repellant materials.
[Source: Brookhaven National Laboratories]
As is often the case with nanotechnology, this work is a long way from commercial application. In some respects, this was a proof of concept more than a technical demonstration. There is still much work to be done with other materials (like the surfactant) as well as addressing many questions about manufacturing in quantity.