Researchers create anti-fogging, self-cleaning, glare-free glass
Researchers from the Massachusetts Institute of Technology have created a new wonder glass that addresses the problems affecting ordinary glass such as fogging and glare.
The secret lies in a process involving thin layers of material deposited on a surface and then selectively etched away.
"The MIT team produced a surface covered with tiny cones, each five times taller than their width. This pattern prevents reflections, while at the same time repelling water from the surface," the MIT said.
It added the surface textures on glass developed by the MIT team virtually eliminates reflections, producing glass that is "almost unrecognizable."
Aside from the absence of glare, the new glass has a surface that causes water droplets to bounce right off, "like tiny rubber balls," and is self-cleaning.
The researchers hope to have the glass made using a low-cost manufacturing process that could be applied to optical devices, the screens of smartphones and televisions, solar panels, car windshields and even windows in buildings.
The technology is described in a paper co-authored by mechanical engineering graduate students Kyoo-Chul Park and Hyungryul Choi, former postdoc Chih-Hao Chang SM 2004, PhD 2008 (now at North Carolina State University), chemical engineering professor Robert Cohen, and mechanical engineering professors Gareth McKinley and George Barbastathis.
Park said photovoltaic panels can lose as much as 40 percent of their efficiency within six months as dust and dirt accumulate on their surfaces.
But he said a solar panel protected by the new self-cleaning glass would have much less of a problem.
Also, the panel would be more efficient because more light would be transmitted through its surface, instead of being reflected away — especially when the sun’s rays are inclined at a sharp angle to the panel.
During early mornings and late afternoons, conventional glass might reflect away more than 50 percent of the light, whereas an anti-reflection surface would reduce the reflection to a negligible level, the report said.
The surface pattern, which features an array of nanoscale cones five times as tall as their base width of 200 nanometers, is based on a new fabrication approach developed by the MIT team. The approach uses coating and etching techniques adapted from the semiconductor industry.
"Fabrication begins by coating a glass surface with several thin layers, including a photoresist layer, which is then illuminated with a grid pattern and etched away; successive etchings produce the conical shapes. The team has already applied for a patent on the process," the MIT said.
Park and Choi noted it is the shape of the nanotextured surface rather than any particular method of achieving that shape that provides the unique characteristics.
With this, they said glass or transparent polymer films might be manufactured with such surface features simply by passing them through a pair of textured rollers while still partially molten.
Such a process would add minimally to the cost of manufacture, they added.
The researchers said the new multifunctional surfaces created by the MIT team are even more effective at repelling water, keeping the panels clean longer.
Also, they noted existing hydrophobic coatings do not prevent reflective losses, giving the new system yet another advantage.
The report said the antireflective and anti-fogging capabilities could be useful for optical devices, like microscopes and cameras to be used in humid environments.
It added that in touch screen devices, the glass would not only eliminate reflections, but would also resist contamination by sweat.
Choi also said that if the cost of such glass can be lowered sufficiently, even car windows could benefit.
He said car windows can clean themselves of dirt and grit on the exterior surface of the windows, eliminating glare and reflections that can impair visibility, and preventing fogging on the interior surface.
The researchers say the design is inspired by nature, where various purposes are served by textured surfaces, from lotus leaves to desert-beetle carapaces and moth eyes.
"Although the arrays of pointed nanocones on the surface appear fragile when viewed microscopically, the researchers say their calculations show they should be resistant to a wide range of forces, ranging from impact by raindrops in a strong downpour or wind-driven pollen and grit to direct poking with a finger," the MIT said.
Further testing will be needed to demonstrate how well the nanotextured surfaces hold up over time in practical applications, the report noted.
Andrew Parker, a senior visiting research fellow at Oxford University’s Green Templeton College in the UK who was not involved in this work, said multifunctional surfaces in animals and plants are common.
"For the first time, as far as I am aware, this paper learns a lesson in manufacturing efficiency from nature by making an optimized antireflective and anti-fogging device. … This is the way that nature works, and may well be the future of a greener engineering where two structures, and two manufacturing processes, are replaced by one,” he said.
The research was funded by the Army Research Office through MIT’s Institute for Soldier Nanotechnology; the Air Force Office of Scientific Research; Singapore’s National Research Foundation through the Singapore-MIT Alliance for Research and Technology (SMART) Center, and the Xerox Foundation.
Park and Choi are recipients of fellowships from Samsung and the Kwanjeong Educational Foundation/STX Scholarship Foundation, respectively. –CGL/KG, GMA News
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