Tag Archives: self-clearning glass

A superhydrophobic coating for glass from the University of Pennsylvania (US) with promises that it’s better than others

Anyone who’s read this blog with any frequency has likely encountered my obsession with self-cleaning glass (specifically, windows). Frankly, I’ve almost given up hope of ever seeing the product in my lifetime several times and then I see another announcement such as this in a Nov. 26, 2013 news item on Nanowerk,

Hanging hundreds of feet off the ground to wash a skyscraper’s windows or pumping water out to a desert solar array to keep its panels and mirrors clean is more than just a hassle—it’s an expensive problem with serious ecological implications.

A spin-off company from Penn has found a way to solve the problem of keeping surfaces clean, while also keeping them transparent.

The undated University of Pennsylvania article by Evan Lerner, which originated the news item, describes both the university’s spin-off company and the research which it is exploiting (Note: Links have been removed),

Nelum Sciences, created under an UPstart program in Penn’s Center for Technology Transfer, has developed a superhydrophobic coating that can be sprayed onto any surface. The water-based solution contains nanoscopic particles that add a nearly invisible layer of roughness to a surface. This increases the contact angle of the material to which these particles are applied.

A contact angle is the angle the edges of a resting drop of liquid make with a surface. When the angle is low, a drop resembles a flattened hemisphere, with edges that are stuck to the surface. But as the angle increases, a drop begins to look more like a ball, until it literally rolls away instead of sticking.

When these balls of liquid roll off a superhydrophobic surface, they pick up any debris they encounter in their paths, keeping a surface clean.

Co-founded in 2011 by Shu Yang, professor of materials science and engineering in Penn’s School of Engineering and Applied Science, Nelum Science’s coating is based on her nanotechnology research. Fabricating the coating’s nanoparticles at sizes smaller than the wavelength of light—the quality that makes them transparent—is the product of cutting-edge laboratory techniques. The company’s inspiration, however, came from structures created by nature.

“Some plants, like lotuses, and other biological structures, like butterfly wings, have this kind of nano-roughness to keep them clean and dry,” Yang says. “That’s why we named the company after the lotus’ Latin name, nelumbo.”

Other superhydrophobic sprays have recently come on the market, but they give surfaces a hazy, frosted appearance, making them inappropriate for applications where cleanliness is critical, such as windows, lenses, safety goggles, and solar panels.

Here’s a University of Pennsylvanis video illustrating the technology,

I wasn’t able to find much information about Nelum Sciences but there is this page on the University of Pennsylvania’s Center for Technology Transfer website, which leads me to suspect I may not be seeing the product in the market place any time soon.

Halleluiah! one step closer to self-cleaning glass

I cannot tell you the joy this news gives me. From the Dec. 6, 2011 news item on Nanowerk,

Eyeglasses need never again to be cleaned, and dirty windscreens are a thing of the past! Researchers at the Max Planck Institute for Polymer Research in Mainz and the Technical University Darmstadt are now much closer to achieving this goal. They have used candle soot to produce a transparent superamphiphobic coating made of glass (“Candle Soot as a Template for a Transparent Robust Superamphiphobic Coating”). Oil and water both roll off this coating, leaving absolutely nothing behind. Something that even held true when the researchers damaged the layer with sandblasting. The material owes this property to its nanostructure. Surfaces sealed in this way could find use anywhere where contamination or even a film of water is either harmful or just simply a nuisance.

Actually, I’m hoping for a little more than eye glasses—I never want to wash another window or mirror. More from the news item,

The coating essentially consists of an extremely simple material: silica, the main constituent of all glass. The researchers coated this with a fluorinated silicon compound, which already makes the surface water and oil repellent, like a non-stick frying pan. The really clever part is the structure of the coating, however. This is what makes the glass super water repellent and super oil repellent. In a frying pan with this type of coating, water and oil would simply roll around in the form of drops. The structure of the layer resembles a sponge-like labyrinth of completely unordered pores, which is made up of tiny spheres.

Such a coating would be ideal for numerous applications, not least because it is so easy to produce. “We can even produce it in jam jars,” says Doris Vollmer [head of a research group at the Max Planck Institute for Polymer Research]. And the soot from a candle flame, from which the researchers made something akin to a glass imprint, served as the model for the porous structure of the spheres. The researchers began by holding a glass slide in a flame so that the soot particles, which measure around 40 nanometres in diameter, formed a sponge-like structure on the glass. The next step was to coat it with silica in a glass vessel – even a jam jar would do – by vapour depositing a volatile organic silicon compound and ammonia onto the soot deposit. When they subsequently heated the material, the soot decomposed. The next step was to vapour deposit a fluorinated silicon compound as well onto the hollow silica structure.

They then attempted to wet this coating with different liquids. However, they didn’t succeed, even when they let hexadecane drip from a great height onto it; in a non-stick frying pan, hexadecane spreads out like water in a washbasin. “Initially, a drop of the oil penetrated into the sponge-like structure, but then bounced back like a rubber ball,” explains Doris Vollmer. Although a portion of the liquid remained in the pores and wet the material, when most of the drop returned to the surface at a slower speed after bouncing up, it drew the small amount of the hexane that had remained out of the glass pores again. Finally, the reunited drop remained lying on the surface like a ball. The researchers in Mainz tested the superamphiphobic layer with a total of seven liquids and found that none was sucked up by the glass sponge.

Sadly, it seems I will have to wait a bit longer as there is no mention of a product being commercialized now or in the near future.