This gold-based transparent coating will end glasses fog forever

What if there was a way to keep our eyeglasses, windows, and car windshields free of fog all the time? Of course, we can use those anti-fog sprays, but the problem with such applications is that we have to apply them again and again.

A team of researchers at the Swiss Federal Institute of Technology (ETH Zurich) has the perfect long-lasting solution to our fog problem. They recently filed a patent application for an ultrathin and 100 percent transparent coating that performs defogging (removing existing fog on a surface) and anti-fogging (preventing the formation of fog on a surface). 

The special coating is developed using titanium oxide and gold particles. It selectively absorbs infrared radiations from the sunlight and creates a heating effect that is powerful enough to keep fog away from the surface of an object.

How does the gold coating work?

The coating basically employs heat to combat fogging. To heat itself, the coating relies on the most popular and easily available renewable source i.e., sunlight. Interestingly, nearly half of all the energy of sunlight is in the near-infrared spectrum, a wavelength range that we can not see with our human eyes. 

The gold coating does not absorb the remaining 50 percent of sunlight, which is UV rays and visible light. Eventually, the selective absorption of the near-infrared part of the sunlight heats up the surface up to 8°C, preventing the occurrence of fog.

“We achieve this heating effect by fabricating a metal layer (gold) at a very specific thickness (called the percolation threshold), where an optical anomaly occurs. This leads to a strong and broadband absorption of the near-infrared spectrum over just a few nm (10 nm in total),” a Ph.D. student at ETH Zurich and one of the study authors, Iwan Haechler, told IE.

The researchers explain that their coating is a 10-nanometer-thick sandwich comprising two layers of titanium oxide and a middle gold layer. The gold part is 12 times thinner than a regular gold leaf sheet. 

Since the coating is ultrathin, it can easily be integrated beneath existing standard coatings, which guards it against any outdoor influences such as scratches, dirt, or chemicals. Plus, it can also be deposited on flexible substrates and does not break when it is bent.

Anti-fog gold coating versus existing anti-fog applications

Products like anti-fogging- sprays create a very thin film of water on the surface to remove fog. They turn a normal surface into a super-hydrophilic surface having a high affinity for water. However, the problem with such surfaces is contamination. 

Along with water, the sprays also attract dirt, dust, oil, and various other impurities, and just a little impurity on the surface renders it useless. This is why you always have to reapply those sprays, and they are not durable. 

On the other hand, we also have those so-called super-hydrophobic coatings, which repel water. The issue there is scalability, especially on the glass. Like the gold coating, super-hydrophobic coatings also employ heating to prevent fogging, but instead of a renewable source such as sunlight, they use electricity to generate the heat. 

This is why the researchers consider hydrophobic coating as an energetically inefficient and unsustainable way to keep a surface fog-free.

“Our underlying motivation was to show the vast potential of solar energy, and how less sustainable technologies (such as using electricity to prevent fogging) can be circumvented by applying physical concepts and rational engineering. Hence, ideally, our coating contributes to the reduction of electricity consumption for heating,” Haechler told IE. 

This could be helpful, especially for electric cars. In normal cars, the hot air from the engine can be used to convectively blow on the windshields and remove fog. Electric engines do not heat up so much. The authors believe that by using their gold-based coating, we might extend the range of the electric cars, as less electricity will be used to prevent fogging in these cars.

Made of gold but still affordable

They further claim that in addition to using a natural source of power (sunlight). Their coating is produced with standardized, readily scalable methods and can easily be upscaled over large areas, all cost-effectively. However, since the coating uses pure gold, would it be commercially viable to make eyewear and car windshield fog covers using the same?

When we asked this question to Haechler, he explained, “As the gold layer is only 5 nm thin, it requires only very little gold. The amount of gold per square meter of material would be 100 mg. Assuming that a pair of glasses is about 2x15 cm2, this means that a pair of glasses would use approximately 0.3 mg of gold. This leads to a price of about 0.017 USD for the gold required for a pair of eyewear.”

So yes, the coating is affordable. The only limitation of this product is that although it can work at very low levels of solar irradiation, it does rely on a certain amount of light. The researchers have already filed a patent, and they are waiting for it to be approved. Hopefully, this groundbreaking product will soon be available on the market.

The study is published in the journal Nature Nanotechnology.