When you're skiing down a mountain or driving a car, it helps to be able to see where you're going – but your goggles, glasses and windshield can fog up if there's a difference in temperature or humidity. Though there are ways to address this using electricity, researchers at ETH Zurich have developed a new anti-fog coating that warms up the surface using light instead.
Fogged-up lenses are far from a new problem, and there are plenty of ways to tackle it. The simplest are water-repelling coatings that are often applied to glasses or visors, with some claiming to be permanent. Other more active methods build heating elements into the lenses to prevent water droplets from gathering, but that obviously requires batteries.
The ETH Zurich team's new design works like a heating element that doesn't need to be plugged in. The new coating contains gold nanoparticles embedded in titanium oxide, which catches the infrared part of sunlight and a portion of visible light and heats up the surface, preventing condensation. Importantly, that coating is still transparent.
The team says the coating cranks up the heat by 3° C or 4° C (5.4° F to 7.2° F), and in tests it was able to clear fog four times faster than regular anti-fog sprays. And because the mechanism is built in, the new coating should also keep working for much longer, with the team planning to tweak the recipe to make it last years.
"Spray treatments often lose their effect after a while because the anti-fog film dries up or becomes unevenly distributed," says Christopher Walker, lead author of the study. "A durable coating like ours lasts much longer than a spray treatment, which you have to apply virtually on a daily basis."
Because it doesn't need batteries or any electronics, the researchers say the new coating would be particularly useful for wearable items like glasses, ski goggles, diving masks or motorbike helmets. And of course, it could also find its way into more permanent surfaces like windows or windshields.
That said, we have to wonder how well it works outside of direct sunlight. In the lab, other light sources were shown to have the same effect, but take the coating diving, for example, where there's limited light and we're not sure how it would perform.
The team is now looking to develop the technology in order to commercialize it. The coating is described in the video below.
The research was published in the journal Nano Letters.
Source: ETH Zurich
