Deicing coatings go transparent

A new transparent deicing coating that can also clean itself could be a boon for solar panels, windows, and windshields (Adv. Mater. 2021, DOI: 10.1002/adma.202108232).

Preventing ice buildup on car windshields and aircraft today requires spraying the surfaces with glycol-based antifreeze or deicing fluids. For a simpler, more eco-friendly alternative, researchers are developing anti-ice coatings. These include superhydrophic or super-slippery surfaces that make water roll or slip off to delay freezing. Some groups have also made surfaces that heat up electrically or by absorbing sunlight to melt ice.

Solar-heating materials are the most economical and environmentally friendly method to combat ice, says Xiaokong Liu, a chemist at Jilin University. But light-absorbing materials generally tend to be dark.

Liu and his colleagues made see-through coatings with MXenes, a recently discovered class of 2D transition-metal carbides and nitrides. They deposited alternating nanosheets of the negatively charged titanium carbide MXene and of the positively charged polymer poly(diallyldimethylammonium) (PDDA) onto various substrates. The charged layers stick strongly to each other and to the substrate via electrostatic forces. The MXene is excellent at absorbing sunlight and generating heat.

After depositing four layers each of the MXene and PDDA, the researchers coated the top with a novel transparent copolymer they made by combining 2-(perfluorooctyl) ethyl methacrylate and n-butyl methacrylate monomer units. The composite coating lets 77% of light through, appearing transparent, and the surface cleanly sheds drops of water, oil, and alcohol easily when kept slightly tilted. The team made meters-wide coatings on commercial plastic window films and glass. The coatings could easily be made on large scale for a material cost of about $ 4/m², Liu says.

The slippery polymer helps delay freezing when the coated surfaces are wet. Ice eventually forms, but heat created by the MXene under sunlight melts the ice at the coating surface so it can slip off. When the researchers placed an ice-covered, coated glass piece outdoors on a sunny, –12 °C day, the ice slid off after 15 min.

“The coating’s durability remains to be explored in real applications,” says Zuankai Wang, a mechanical engineer at the City University of Hong Kong. But the fusion of transparent, photothermal and slippery properties is impressive and this work brings new insights in material design, he says.