Those who wear glasses, skis, drives a car or uses a camera have faced the most common problem of coming into a humid environment from the cold and their eyewear, camera lenses or windshields quickly fog up. Researchers at ETH Zurich have developed a transparent material coating that reduces the chances of fogging. The coating is a few nanometers thick, and it is durable as it is made of gold nanoparticles attached in non-conductive titanium oxide.
"Our coating absorbs the infrared component of sunlight along with a small part of the visible sunlight and converts the light into heat," explains Christopher Walker, a doctoral student in ETH Professor Dimos Poulikakos's group and lead author of the study. "This heats the surface up by 3 to 4 degrees Celsius. It is this difference in temperature that prevents fogging."
The answer to the problem of fogging on car windows is heat. The warm air from the in-vehicle heating system heats the front windscreen, while the rear window is fitted with a grid of electrical heating elements. The ETH researchers are different from these elements, however. Their new coating works passively, and the only energy source required is the sun, so it is suitable for items that are wearable like goggles and glasses.
Efstratios Mitridis, another doctoral student in Poulikakos's group, explains what makes the new surface coating so special: "Normally, it's dark surfaces that absorb light and convert it into heat," he says, "but we've created a transparent surface that has the same effect."
This invention is better than anti-fog sprays. Anti-fog sprays for glasses work on the principle of condensation wherein it occurs on a surface whenever there is a drop in temperature or a sudden increase in humidity. It then forms small droplets of water that disperses incident light in numerous directions, the same way as atmospheric fog. Susceptible surfaces are coated with hydrophilic agents, and because they attract water, these agents ensure that the condensation forms a thin film of liquid that is even over the surface instead of separate droplets.
Now, researchers have proven that when exposed to sunlight, surfaces coated with gold nanoparticles and titanium oxide that are fogged up can clear four times faster than the surfaces that are treated with a normal anti-fog spray.
"Spray treatments often lose their effect after a while because the anti-fog film dries up or becomes unevenly distributed," Walker says. "A durable coating like ours lasts much longer than a spray treatment, which you have to apply virtually on a daily basis," he adds.
