Like water off a…Butterfly’s Wing?

Article written by: Dr Jared ScarlettDr Stephanie Grant    |   Thursday 28th November 2013

Have you ever wondered why water rolls off a duck’s feathers or even butterfly wings, and did you know that this is the concept behind the development of waterproof materials?

Traditionally, development of hydrophobic (water repelling) materials has been based on the “lotus leaf effect”.  This effect refers to the very high ability of lotus leaves to repel water, due to their rough hydrophobic surface.   Arguably the most well-known of non-wetting and hydrophobic materials to date is GORE-TEX®, which is expanded polytetrafluoroethylene (PTFE), (PTFE is also commonly known as Teflon®). [1] GORE-TEX® was developed in 1969 and has remained one of the premium waterproof materials for clothing and medical applications.

However, the Varanasi research group at the Massachusetts Institute of Technology have developed a new coating material which is believed by the inventors, to outperform existing waterproof materials. [2, 3] This new technology was inspired by nasturtium leaves and butterfly wings.  These natural structures repel water exceptionally well due the presence of minute ridges on their surfaces. [4] 

The new hydrophobic materials are made from oxides, carbides, and fluorides of rare earth elements, such as gadolinium, dysprosium, and ytterbium.  The ridges in the materials alter the angle at which the water makes contact with the surface, which also shortens the length of time that the water is in contact with the surface.  So, when the water droplets make contact, they “bounce” off of the surface more rapidly, resulting in higher repellence.  The group have filed two PCT patent applications, which were published earlier this year, and have yet to enter national phase. [5, 6] 

The Varanasi group envision that such coating materials may find extensive application in the field of medical devices, waterproof consumer products, and even in the aviation industry, to stop water droplets from freezing on the wings of aeroplanes. [3] 

The group have even developed a non-stick coating for the inside of bottles that will repel every tasty morsel of ketchup, leaving nothing stuck in the bottle.  You can check out the video link here:  http://video.mit.edu/watch/liquiglide-11535/.
 


 
1. http://www.gore-tex.com/remote/Satellite/home; http://en.wikipedia.org/wiki/Gore-Tex
2. http://meche.mit.edu/people/?id=372; http://varanasi.mit.edu/
3. http://www.nature.com/nature/journal/v503/n7476/full/nature12740.html
4. Scanning Electron Microscopy images of these minute ridges on butterfly wing can be seen at the following sites: http://www.nhm.ac.uk/about-us/news/2008/july/how-butterfly-wings-shimmer-revealed18265.html;
   http://kqedscience.tumblr.com/post/11917017860/this-is-a-sem-scanning-electron-microscope-image;
   http://www.imaging-git.com/products/electron-and-ion-microscopy/enhanced-resolution-low-kv-region;
   http://www.learnaboutbutterflies.com/Anatomy%204%20-%20SEM%20Rob%20Lineton.htm
5. WO 2013/141877 -
   http://patentscope.wipo.int/search/en/detail.jsf?docId=WO2013141877&recNum=1&docAn=US2012030370&queryString=FP:(WO%202013/141877)&maxRec=1
6. WO 2013/019257 –
   http://patentscope.wipo.int/search/en/detail.jsf?docId=WO2013019257&recNum=1&docAn=US2011061498&queryString=FP:(WO%202013/019257)&maxRec=1

 

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