Delay of ice formation on penguin feathers
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part of Springer Nature, 2020 https://doi.org/10.1140/epjst/e2020-900273-x
THE EUROPEAN PHYSICAL JOURNAL SPECIAL TOPICS
Regular Article
Delay of ice formation on penguin feathers? Elaheh Alizadeh-Birjandi1 , Faryar Tavakoli-Dastjerdi1 , Judy St. Leger2 , Kym F. Faull3 , Stephen H. Davis4 , Jonathan P. Rothstein5 , and H. Pirouz Kavehpour1,a 1
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Department of Mechanical and Aerospace Engineering, UCLA, Los Angeles, CA, USA SeaWorld Parks and Entertainment, San Diego, USA Department of Psychiatry and Biobehavioral Sciences, UCLA, Los Angeles, CA, USA Department of Engineering Sciences and Applied Mathematics, Northwestern University, Evanston, IL, USA Department of Mechanical and Industrial Engineering, University of Massachusetts, Amherst, MA, USA Received 1 December 2019 / Accepted 23 July 2020 Published online 14 September 2020 Abstract. Cold-weather penguins continually dive in and out of the water and get splashed by waves during the frigid Antarctic winter. Yet, even under these extreme sub-zero conditions, macroscopic ice crystals are typically not observed on their feathers. In this work, we hypothesize that the origin of the anti-icing properties of a cold-weather penguin’s feathers comes from a unique combination of the feather’s macroscopic structure, the nanoscale topography of its barbules, and the hydrophobicity of its preen oil. We show that, the combination of all three, make cold-weather penguin feathers both highly water repellant and icephobic. In this paper, we present the results from a series of droplet freezing experiments performed on feathers from a number of species of both cold-weather and warm-weather penguins. Compared to a smooth glass substrate, freezing was delayed by a factor of 30-times for drops deposited on warm-weather penguin feathers and 60-times for cold-weather penguins. The difference in freezing time between warm- and cold-weather penguins was statistically significant and can be attributed to the increase in the contact angle measured between the drop and the feather of the cold-weather penguin. This increased contact angle is the result of an increase in the hydrophobicity of the preen oil and the inclusion of nanoscale, air-trapping dimples on the surface of the barbules. The physics of this delay are explained through the development of a simple heat transfer model which demonstrates that increasing contact angle is a primary cause of increased freezing time and icephobicity. The results of this study can be used to motivate the designs of biomimetic surfaces to minimize ice formation in extreme conditions for a number of important engineering applications.
? Supplementary material in the form of one pdf file available from the Journal web page at https://doi.org/10.1140/epjst/e2020-900273-x. a
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The European Physical Journal Special Topics
1 Introduction Penguins are flightless birds living in diverse geographical locations in the southern hemisphere. Humboldt penguins live in temperate zones near the equator whereas circ
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