[Image above] A gentoo penguin. Credit: ravas51; Flickr CC BY-SA 2.0
“What could be a jollier sight than a parade of penguins marching past in Christmas jumpers?”
If you’re asking me, the answer is nothing.
Penguins are iconic when it comes to winter. And while not all species live in cold climates, many penguins do—they glide through frigid waters, slip around on ice, and waddle around on snow as if they’re impervious to temperatures that would make us humans bundle up beyond belief.
While we know that penguins huddle together in complex masses to stay warm, just how do they prevent ice accumulation on their feathers?
New research shows that when it comes to anti-icing surfaces, the animal world’s most dapper creatures have a few tricks on their flippers.
The research, presented at the recent 2015 meeting of the American Physical Society’s Division of Fluid Dynamics, shows that penguin feathers are uniquely suited to prevent ice formation when in contact with water.
Using scanning electron microscopy, researchers showed that the feathers of Antarctic gentoo penguins contain tiny pores, or “nano-sized pits,” and are coated in a special oil that together prevent water from sitting on the surface of the penguins’ coats.
A penguin feather. Credit: Featherfolio; Wikimedia CC BY-SA 3.0 (https://commons.wikimedia.org/wiki/File%3APenguin_Rockhopper%2B.jpg)
Most birds, and particularly aquatic species like penguins, produce preen oil in a gland at the base of their tails. The birds apply this hydrophobic oil to their feathers during preening, in which they collect the oil on their beaks and apply it across their entire black-and-white bodies.
Combining the porous structure of the feathers with the penguins’ hydrophobic coating of preen oil lets them glide in and out of frigid waters without a thought about ice formation, because the combination makes penguin coats superhydrophobic.
“The combination of the feather’s hydrophobicity and surface texture is known to increase the contact angle of water drops on penguin feathers to over 140° and classify them as superhydrophobic,” according to the meeting abstract.
That superhydrophobicity makes water droplets ball up on the surface of the penguins’ coat. According to an APS press release, the researchers hypothesize that the spherical shape of the balled-up droplets on a superhydrophobic surface are precisely what prevents ice formation, because “heat has a hard time flowing out of the water droplet if the droplet does not make much contact with the surface.”
Pirouz Kavehpour, lead researcher of the study and mechanical and aerospace engineering professor at UCLA, likens that explanation to traffic in the release. “Heat flow could be compared to traffic. If you have a freeway that turns into a tiny, two-lane road, the traffic will back up. Similarly, heat does not flow well from the large cross-section of the middle of the drop to the small cross-section where the drop makes contact with the feather.”
Comparing gentoo penguin feathers with those of warmer-climate Magellanic penguins that live in South America gave the researchers confidence that it is the combination of feather porosity and preen oil that make the difference in cold weather. The scientists found that those warmer-climate birds do not have the same small feather pores and that their preen oil is not as hydrophobic as that of the cold-climate gentoos.
Gentoos penguins on Cuverville Island, Antarctica. Credit: David Stanley; Flickr CC BY 2.0
Penguins aren’t the only ones to combine nanostructure and surface coatings to achieve superhydrophobic surfaces—materials scientists have taken the bioinspired cues to study and fabricate such surfaces, too.
Because surfaces influence how a material reacts with the rest of the world, engineered surfaces can tailor how a material performs in particular environments.
For example, the researchers above hope that their insight into penguin coats can help discover anti-icing solutions for our society, too, especially in the big business of de-icing airplane wings.
Ice accumulation on airplane parts—think wings, rudders, flaps, etc.—changes with the craft’s precise aerodynamic design, disrupting airflow and critical principles of physics, like oh-so-important lift.
Engineered superhydrophobic airplane surfaces that are designed to prevent ice formation could help reduce the problems that airplanes encounter in winter weather, while also reducing the vast amounts of chemical de-icers that are currently used in the airline industry.
“It’s a little ironic that a bird that doesn’t fly could one day help airplane fly more safely,” Kavehpour says in the release.