Researchers in Switzerland have developed a special coating to prevent moisture condensation on lenses. The scientists say in a new paper that their approach could also be used on car windshields. It’s one of a growing number of technologies that aim to solve the mundane but persistent problem of fogged glass. “Most approaches basically rely on altering the surface wettability,” Iwan Haechler, one of the researchers on the Swiss team, told Lifewire in an email interview. “For instance, there are anti-fogging sprays, which create a very thin film of water on the surface. This is called a super hydrophilic surface. The problem is contamination. As the water loves water, it also loves everything else, including dirt. And just a little impurity on the surface renders it useless. This is why you always have to reapply those sprays; hence they are not durable.”
Golden Coating
The team from Switzerland’s ETH Zurich institute developed a coating made in a special cleanroom in which tiny amounts of gold are deposited onto the surface. The layer absorbs solar radiation selectively. Half of the energy in sunlight resides in the infrared spectrum, and the other half in the visible light and UV radiation spectrum. “Our coating absorbs a large proportion of the infrared radiation, which causes it to heat up—by up to 8 degrees Celsius,” Haechler said. “It absorbs only a fraction of the radiation in the visible range, which is the reason why the coating is transparent.” “The coating is heated by sunlight,” Haechler said. “The challenge with heat-driven antifogging coatings that do not require electricity is the following: How can you stay thin, simple in terms of fabrication, and transparent at the same time,” he added. “You can imagine that the heating effect can also be achieved if you darken the surface. But then you sacrifice transparency. Our technology tries to offer both.” Gold might be expensive, but the researchers said their coating requires so little that the material costs remain low. The coating comprises minuscule, extremely thin clusters of gold sandwiched between two ultrathin layers of titanium oxide, an electrically insulating material. Due to their refractive properties, these two outer layers increase the efficacy of the heating effect. The top layer of titanium oxide acts as a finish that protects the gold layer from wear. This whole “sandwich” is just 10 nanometers thick.
New Approaches to Anti-Fog Coatings
The gold technique isn’t the only new approach to keeping the glass from fogging up. Researchers at Singapore’s Singapore’s Nanyang Technological University (NTU) have developed a new technology that could make polycarbonate lenses permanently fog-free and self-cleaning. The coating consists of a thin double-layered silicon dioxide-titanium dioxide film. The titanium dioxide can ‘self-clean’ by reacting with and removing organic residues under exposure to sunlight and (ultraviolet light). In lab tests of its ‘self-cleaning’ ability, the newly developed coating was able to break down contaminants (i.e., bacteria, dirt) on the plastic surface after a full day of ultraviolet light exposure. The newly developed coating is also anti-reflective with a superior visible light transmittance of up to 89 percent on a regular plastic lens, about 5 percent better than the same lens without a coating. This result means that the product could be useful for eyeglasses, as higher visible light transmittance allows more light to travel through the plastic and reach the eye, allowing greater clarity. “Our innovation is promising for use in industrial applications of various optical components, for example, on surveillance camera protective covers,” Rajdeep Singh Rawat, the head of natural sciences and the science education academic group at NTU, said in a news release. “The ability for the coating to ‘self-clean’ makes it a low-maintenance and trouble-free solution since the cover may be less obscured by surface dirt and grime, providing a clearer view for surveillance.” While the latest research promises new anti-fog coatings that could take years to make it onto eyeglasses for users, optometrist Bhavin Shah pointed out in an email interview with Lifewire that less sophisticated anti-fog coatings are already available. “I’ve had a pair since the start of the pandemic and started having to wear a mask,” Shah added. “I also sell a spray that temporarily makes glasses anti-fog for a day or so. New coatings are constantly being developed, but now that mask-wearing is reducing, the new coating tends to focus on scratch resistance and optical clarity.”
