Transparent coating combines nanoscale structuring with selective solar absorption to delay ice formation at subzero temperatures while preserving visible light transmission for optical and energy device surfaces.
(Nanowerk Spotlight) Keeping transparent surfaces ice-free sounds like a basic design problem. In practice, it’s anything but. Windshields fog and freeze. Solar panels lose efficiency. Camera lenses blur over. The fix often involves energy—heat strips, chemical sprays, mechanical scrapers—or coatings that repel water but fall short when temperatures drop. For anything that needs to stay both clear and functional in freezing conditions, most solutions involve trade-offs that don’t scale well.
One option is to use sunlight. Photothermal coatings can trap solar energy and convert it into heat, warming the surface just enough to hold off ice. But here’s the catch: most materials that absorb sunlight efficiently also absorb visible light. That’s fine for a black roof tile, but not for a window, a lens, or anything that needs to stay optically transparent.
One part of the system uses nanoscale surface structuring to interfere with the earliest stages of ice growth. The other adds photothermal materials that selectively absorb infrared and ultraviolet, heating the surface while letting most visible light through. The result is a clear coating that stays unfrozen for over an hour at minus 30 degrees Celsius, and even longer under sunlight.
Visible light transparent coatings combing active and passive anti-icing strategies. a) Schematic diagram illustrating the design and fabrication process of the coatings. b) Scanning electron microscopy images depicting the surface morphology of the coatings. c) Schematic illustration demonstrating the anti-icing performance of the transparent coating (Nano-PMC) under 1.0 sun illumination. (Image: Reprinted with permission by Wiley-VCH Verlag) (click on image to enlarge)
The researchers developed the coating using a polymer base mixed with two specific additives. Cesium tungsten bronze nanoparticles absorb near-infrared light and convert it into heat. Methylene bis-benzotriazolyl tetramethylbutylphenol absorbs ultraviolet and provides additional photothermal support. Both are transparent in the visible spectrum, which means the coating can absorb heat-generating wavelengths without darkening the surface. The polymer matrix, made from polyacrylic acid, forms a thin membrane that can be applied to glass and other surfaces using straightforward curing methods.
That’s only part of the design. Ice formation starts at the microscopic level, when water molecules begin to arrange into the crystalline structure of ice. This requires a certain cluster size—called a critical nucleus—and a surface that helps organize it. If the interface is structured at the right scale, it becomes harder for ice to start growing. The team used this idea to shape the surface at the nanoscale, introducing features about 5 nanometers across, comparable to the size of the initial ice-forming clusters.
They tested two methods to achieve this. In one, they applied silica nanoparticles to create a thin, grainy top layer. In the other, they used a mold to imprint nanoscale textures into the surface during fabrication. Both versions, called Nano PMC, showed strong resistance to ice formation. Compared to bare glass or smooth coatings, these nanostructured surfaces made it significantly harder for ice to nucleate and grow.
The results were clear. In lab conditions, water droplets on Nano PMC stayed liquid for over an hour at minus 30 degrees Celsius without any added heat. Under simulated sunlight, the coating’s surface warmed by up to 40 degrees, keeping it above freezing and ice-free indefinitely. This performance held up without sacrificing visibility. The coating maintained over 80 percent visible light transmittance with minimal haze. For applications like lenses, sensors, or solar cells, that’s critical.
To evaluate how well the coating handled real-world stresses, the team ran durability tests. After repeated freeze-thaw cycles, UV exposure, and high-pressure water jets, the coating’s performance didn’t degrade. Its anti-icing ability remained consistent, and its surface structure stayed intact.
They also looked at how the coating performed during condensation and frost events. When exposed to humid air on one side and cold air on the other, the coating held off both frost and condensation longer than untreated glass or unstructured coatings. When sunlight was turned off, the surface cooled and droplets formed, but even then, freezing was delayed by over an hour. On untreated glass, frost formed in under 20 minutes.
When ice did form, the coating still provided an advantage. In de-icing tests, a one-gram icicle placed on the Nano PMC surface started to melt within seven minutes of sunlight exposure and slid off completely by the ten-minute mark. On untreated glass, the ice didn’t budge after an hour. The coating also melted frost quickly, evaporating the moisture entirely within 11 minutes, while the frost on glass remained unchanged.
To benchmark their approach, the researchers compared Nano PMC to coatings made with MXenes—another class of photothermal materials that absorb across the full solar spectrum. While MXenes generate heat effectively, they block visible light, which limits their use on clear surfaces. Nano PMC delivered similar thermal performance with far less loss of transparency. At equivalent temperature increases, it preserved five times more visible light.
The study also quantified how nanoscale structure affects freezing using a parameter called the interfacial correlation factor. Higher values mean a surface makes it harder for ice to nucleate. Nano PMC had the highest scores among the surfaces tested, confirming that tuning the surface at the critical nucleus scale provides a real thermodynamic barrier to ice formation. That makes this approach more than just a surface treatment—it’s a method rooted in control of phase-change physics.
The implications go beyond a single coating. The materials used are commercially available, and the fabrication steps are compatible with standard polymer processing. Because the coating combines transparency with both passive and active ice resistance, it could be adapted to a range of applications: camera housings, optical sensors, building glass, drone lenses, or anything else that needs to function in the cold without clouding over.
The coating is not a universal fix. Ice will still form if temperatures stay low long enough and there’s no light. But the dual-mode protection—delaying ice passively and actively heating the surface when sunlight is available—offers a level of control that hasn’t been available in transparent systems before. And because the method targets the earliest stages of freezing, it shifts the problem from managing ice after it forms to making it harder to form in the first place.
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