Tag Archives: Doris Vollmer

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.