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[Image above] Humboldt penguins. Credit: Pionites melanocephalus; Flickr CC BY-NC-ND 2.0

Back in December, I reported on how penguins were inspiring anti-icing strategies for planes.

That research indicated that the reason that penguins in frigid environments don’t become encased in ice is because their feathers contain nano-sized pores and are coated with preen oil, the combination of which makes penguins’ coats superhydrophobic.

But is that the whole story?

Researchers at the Key Laboratory of Bio-Inspired Smart Interfacial Science and Technology at Beihang University (Beijing, China) instead say that in conditions of high humidity or ultra-low temperatures—which may well be encountered by penguins—even superhydrophobic surfaces aren’t impervious to ice accumulation.

So what gives?

The Beihang researchers’ work shows that in addition to being superhydrophobic, the feathers also owe their ice-shedding abilities to anti-adhesive qualities, according to a new press release from the American Chemical Society.

Using SEM, the team found that Humboldt penguins’ feathers (quick note: the previous study examined gentoo penguin feathers, which live at more southern latitudes) are microstructured with “barbs, wrinkled barbules, and interlocking hooks.” These features, which trap little pockets of air, give the feathers anti-adhesive properties that the researchers think helps to explain why ice can’t stick to penguins’ coats.

The researchers went beyond microscopic feather observations, however. To prove that the feathers’ aversion to water and adhesion is what keeps them free of ice, the team fabricated membranes mimicking the microstructure of the penguin feathers.

By recreating the microstructure in an electrospun polyimide fiber membrane, the team showed that hydrophobic and anti-adhesive abilities can keep ice at bay.

The scientists’ experiments show that the membrane’s microstructure forms a gradient density, creating a subsequent gradient in contact angle and adhesive force, the authors write in the paper.

Translation? The microstructure makes the membrane, like the penguins’ feathers, icephobic.

The paper, published in The Journal of Physical Chemistry C, is “Icephobicity of penguins Spheniscus humboldti and an artificial replica of penguin feather with air-infused hierarchical rough structures” (DOI: 10.1021/acs.jpcc.5b12298).