Scientists Develop Transparent, Sun-Activated Coating That Prevents Glass Fogging

(Image: ETH Zurich)If you wear glasses, you probably know how annoying it is for your lenses to fog up as you sip on a hot beverage or step into a warm and humid environment. Just as frustrating (yet perhaps more dangerous) is your windshield’s tendency to cloud when it’s cold outside and you’re cranking up the heater. Thankfully, there appears to be a new way to stop inconvenient fogging from happening in the first place—no electricity required.

A group of scientists at Switzerland’s ETH Zurich has created a thin and transparent coating that, when applied to glass and other clear surfaces, operates as an anti-fog barrier. Using nucleation thermodynamics and a handful of common manufacturing methods, the team of thermodynamics experts and surface nanoengineers created their own metamaterial, or a substance that’s been built to possess a property that doesn’t occur naturally. Metamaterials are frequently used in solar power management, optical filters, medical equipment, and other applications, and they often contain the not-so-secret ingredient used in ETH Zurich’s coating: gold.

The team’s anti-fog coating includes a nanoscopic gold layer, which is sandwiched between two layers of the insulator titanium oxide. The clusters of gold in the middle barely touch each other, which allows them to absorb infrared solar radiation. This increases the coated material’s temperature by 8 degrees Celsius (46 degrees Fahrenheit). The heat is what prevents humidity-induced condensation from forming on the coated material.

In a paper published Monday in the journal Nature Nanotechnology, the scientists say their coating produces a four-fold improvement in fog prevention and a three-fold improvement in fog removal. Because the coating is transparent, it could be used on vehicular and residential windows, eyeglasses, and glass displays. It’s only 10 nanometers thick, too (or 0.01 percent as thick as a sheet of standard printer paper), meaning the coating won’t add bulk to applicable materials. In fact, most people wouldn’t find it noticeable at all, especially on tinted surfaces. The scientists note that the coating won’t heat up vehicles or glasses, either, since the gold layer only absorbs a small portion of the sun’s radiation.

The gold-based coating is categorized as a “passively heated surface coating”—a category that the ETH Zurich team has worked on for a few years. Since the iteration they first published in 2019, the coating has become thinner and more pliable, making it more practical in real-world applications. It also contains less gold than it originally did. Nonetheless, the scientists are moving toward testing different metals within the coating’s conductive layer in an effort to make their patent-pending product more affordable.

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