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Wing surface self-cleans: Morpho butterfly

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Morpho sulkowskyi from Seitz Macrolepidoptera of the World Fauna Americana / Source / LicensePD - Public Domain

Wing surface of Morpho butterfly sheds water and dirt via hydrophobic microstructure.

BIOMIMICRY TAXONOMY
Summary

Like some plants, the wings of many large-winged insects remain dirt-free (e.g., butterflies, moths, dragonflies, lace wings), an obvious advantage for effective flight, and they do so without using chemical detergents or expending energy. This is accomplished by the interaction between the multi-scale micro- and nano- topography on their wing surfaces and the physical properties of water molecules.

While a variety of specific structures appear in this wing surface topography, all share a similar mathematical set of proportions in the size and distance of protrusions that are associated with superhydrophobicity (extreme non-wettability). For example, butterfly wings show two key periodic structures: the individual epidermal scales or squama (roughly 40x80 microns each) which comprise the wings of butterflies and the micro-relief of raised ridges covering each wing scale, each between 1000-1500 nm wide.

Because water and air adhere less well than water and solids, roughened surfaces can reduce adhesive force on water droplets, as trapped air in the interstitial spaces of the roughened surface result in a reduced liquid-to-solid contact area. This allows the self-attraction of the polar molecule of water to express more fully, causing it to form spheres. Dirt particles on the wing’s surface stick to these droplets, both due to natural adhesion between water and solids and because contact with the wing surface is reduced by the wing’s micro-topography. The slightest angle in the surface of the wing then cause the balls of water to roll off due to gravity, taking the attached dirt particles with them, cleaning the wing without using detergent or expending energy. Micro- and nano- surface finishes inspired by self-cleaning biological surfaces have now been applied to paints, glass, textiles, and more, reducing the need for toxic chemistries and costly labor.

This video shows/exemplifies the structures discussed in this strategy.

Excerpt
"Many biological surfaces are hydrophobic because of their complicated composition and surface microstructure. Butterflies were selected to study their characteristics by Confocal Light Microscopy, Scanning electron Microscopy and Contact Angle measurement. The contact angle of the water droplets on the butterfly wings surface consistently measured to be more than 140 degrees. The dust on the surface can be easily cleaned by moving spherical droplets when the inclining angle is larger than 3 degrees.  It can be concluded that the butterfly wing's surface possess a water-repellent, self-cleaning, or 'Lotus-effect' characteristic." (Collins 2004:245)
About the inspiring organism
Med_seitzfa2 Morpho sulkowskyi
Morpho sulkowskyi Kollar 1850

Habitat(s): Forest
Learn more at EOL.org
Some organism data provided by: LepIndex: The Global Lepidoptera Names Index
Organism/taxonomy data provided by:
Species 2000 & ITIS Catalogue of Life: 2008 Annual Checklist

IUCN Red List Status: Unknown

Bioinspired products and application ideas

Application Ideas: Self-cleaning windows, paints, lenses, and other surfaces.

Industrial Sector(s) interested in this strategy: Manufacturing, building, automotive, architecture, paint



References
Collins, M. 2004. Design and nature II: comparing design in nature with science and engineering. Southampton: WIT.
Learn More at Google Scholar Google Scholar  

Nature's Raincoats. Nottingham Trent University, University of Oxford.
http://www.naturesraincoats.com/index.html.
Learn More at Google Scholar Google Scholar  

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