Re:The Water-Repelling Surface That Lives Outside My Window
by peterwwillis on Friday June 20, 2014 @04:23PM
(#7922686)
I was going to say before I read the rest of the article that there's probably an uneven surface on the leaf that's allowing the droplet to retain its superior surface tension.
Conversely, the waterproofing nature of bird feathers is, apparently, not well understood. It was originally posited that the hydrophilic oils from the Uropygial gland spread during preening added to the waterproofing nature of the feather, but (according to a Wikipedia edit which has no citation that I can find no further evidence of on the Internet) there's some theory about an electrostatic state due to the mechanical process of preening keeping the feathers free from water sticking to them. It's also claimed that powder-down birds use their feather residue as waterproofing, but that seemingly hasn't been proved either.
Ah, I found the paper, I think [1]: Here's a paper from the 1950s which did an intense study of ducks and various states which might affect their water-repellent nature. It turns out that removing the Uropygial gland from newly hatched ducklings resulted in their feathers being just as water-repellent as ducks that still had the gland. Interestingly, the diet of the birds seemed to effect the water-repellent nature more than anything else, but also completely dependent on where they were fed.
The end of page 6 and the rest of 7 point out the theory of the barbules in the feathers being responsible for the waterproof nature. The idea is that when they are properly aligned, air between the barbs (when at a constant distance from each other) keeps a narrow enough distance that the surface tension of the water is maintained, similar to this leaf. So this is probably where the idea of an "electrostatic" force came from (or the paper by Madsen that's cited: "Madsen, H., 1941: Hvad gor Fuglenes Fjer-Dragt vandskyende ?. Dansk Ornithologisk Forenings Tidsskrift, 35: 49-59")
Can somebody stick all that into the Wikipedia article? I'm lazy.
Conversely, the waterproofing nature of bird feathers is, apparently, not well understood. It was originally posited that the hydrophilic oils from the Uropygial gland spread during preening added to the waterproofing nature of the feather, but (according to a Wikipedia edit which has no citation that I can find no further evidence of on the Internet) there's some theory about an electrostatic state due to the mechanical process of preening keeping the feathers free from water sticking to them. It's also claimed that powder-down birds use their feather residue as waterproofing, but that seemingly hasn't been proved either.
Ah, I found the paper, I think [1]: Here's a paper from the 1950s which did an intense study of ducks and various states which might affect their water-repellent nature. It turns out that removing the Uropygial gland from newly hatched ducklings resulted in their feathers being just as water-repellent as ducks that still had the gland. Interestingly, the diet of the birds seemed to effect the water-repellent nature more than anything else, but also completely dependent on where they were fed.
The end of page 6 and the rest of 7 point out the theory of the barbules in the feathers being responsible for the waterproof nature. The idea is that when they are properly aligned, air between the barbs (when at a constant distance from each other) keeps a narrow enough distance that the surface tension of the water is maintained, similar to this leaf. So this is probably where the idea of an "electrostatic" force came from (or the paper by Madsen that's cited: "Madsen, H., 1941: Hvad gor Fuglenes Fjer-Dragt vandskyende ?. Dansk Ornithologisk Forenings Tidsskrift, 35: 49-59")
Can somebody stick all that into the Wikipedia article? I'm lazy.
[1] http://wildfowl.wwt.org.uk/index.php/wildfowl/article/downlo... [2] http://www.ncbi.nlm.nih.gov/pubmed/20437221 (a modern paper confirming the results)