Slippery Coating Keeps Metals Frost-Free

Researchers have found an easy way to encrust metals with a material that is super slippery and repels water (ACS Nano, DOI: 10.1021/nn302310q). By preventing water droplets from sticking to surfaces and then freezing, the coating could keep airplane wings, wind turbines, and refrigerator coils frost-free.

Today’s defrosting techniques involve either environmentally harmful chemicals or periodic heating, which consumes power. Meanwhile, most water-repellent coatings fail in high humidity. These coatings often have nanoscale features that cause water to bead up and bounce off. But in high-humidity, low temperature conditions, such as those on a snowy day, condensation builds up inside the nanostructures and can freeze.

Joanna Aizenberg and her colleagues at Harvard University previously had developed flat, ultrasmooth water-repellent coatings called slippery liquid-infused porous surfaces, or SLIPS (Nature, DOI: 10.1038/nature10447). These coatings consist of a porous network of polymer nanofibers infused with a lubricant.

The team thought a SLIPS could prevent frost buildup on metal surfaces, in addition to plastic, which they had coated in their previous work. To test the coatings on aluminum refrigerator coils, the researchers first deposited a bumpy polypyrrole layer on the metal. They then added DuPont’s lubricating Krytox oil to the layer and allowed it to infuse into the polymer matrix.

Unlike untreated aluminum, the treated metal surface stayed completely ice-free down to -4 ºC. Ice formed at lower temperatures, but it didn’t adhere well: The researchers could shake or melt it off in seconds.