Book Review

Ice-Proof Penguin Feathers Inspire New Material

Paper: Wang, S., Yang, Z., Gong, G., Wang, J., Wu, J., Yang, S., Jiang, L., (2016).  Icephobocity of Penguins Spheniscus Humboldti and an Artificial Replica of Penguin Feather with Air-Infused Hierarchical Rough Structures.  The Journal of Physical Chemistry. doi: 10.1021/acs.jpcc.5b12298

Humboldt Penguin (Image Credit: Aurelien Guichard from London, United Kingdom)
Humboldt Penguin (Image Credit: Aurelien Guichard from London, United Kingdom)

A cool adaptation:

Humboldt penguins (Spheniscus humboldti) are able to thrive in extreme conditions. They range from Peru to Chile, and frequently swim in the cold Antarctic ocean current. Despite living in subzero environments, frost and ice are rarely found on their feathers.

While there has been a lot of research interest in the thermal insulating qualities of penguin feathers, the ability of body feathers to resist water adhesion and their anti-icing properties have so far been a mystery. While penguin feathers are hydrophobic, causing water to slide off their bodies before freezing, ice can still adhere to hydrophobic substances in high humidity or very low temperature conditions.  See Figure 1 to see the different parts of a feather.

Anatomy of a Feather (Left Image Credit: Featherfolio, Wikipedia Commons, terrible drawings by the author)
Figure 1: Anatomy of a Feather (Left Image Credit: Rockhopper penguin feather by Featherfolio, Wikipedia Commons, Right: terrible drawings by the author)


Taking a (really) close and slow look:

To discover exactly how feathers prevent ice buildup, a team of scientists obtained feathers from captive Humboldt penguins at the Beijing Pacific Underwater World. The feathers were cut into small squares and ‘sputtered’ or coated in a thin layer of gold. This allows them to be scanned with an environmental scanning electron microscope. This particular kind of microscope can scan wet specimens using a beam of electrons at very small scales. Then, feather samples were also placed in temperature-controlled chambers to mimic natural conditions and sprayed with supercooled deionized water droplets. The behaviour of the droplets was analyzed using a high-speed camera system and measurements of adhesive forces were measured with a special (DCATT11) machine.

It is only when we observe the micro and nano structures of penguin feathers that we can appreciate their anti-icing and antiadhesion characteristics. The feather structures are intricately branched, and a closer look reveals the surface of the barbules and hamuli are wrinkled. The result is that air becomes trapped between these micro and nano structures which decreases the surface area of water droplets that contact the feather. This not only gives penguin feathers hydrophobic qualities, but anti-adhesive qualities as well (Figure 2).

Schematic diagram of water contact with feather surface. (Image Credit: terrible drawings by the author)
Figure 2: Schematic diagram of water contact with feather surface. The left shows a water droplet resting on three hamuli with wrinkled surfaces. The right shows a close-up image of the air pocket created by the wrinkled hamuli surface. (Image Credit: terrible drawings by the author due to copyright on original photo).


A new ice-proof material is made!

Inspired by the anti-icing properties of penguin feathers, a manmade material was made by electrospinning polyimide nanofibers.  Polyimide was chosen because similarly to penguin feathers, it maintains mechanical strength in low temperatures. While some frost and ice were found on the some parts of the material, it successfully prevented ice formation for the most part. This new material can potentially have a wide range of applications including electrical insulation, as well as ship and airplane protection from extreme cold.

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