Wednesday, May 4, 2011

What Do Pigeons have in Common with Fire Ants?

They both exhibit the remarkable hydrophobicity demonstrated by the Cassie-Baxter law of wetting.  For us non-scientists, this law describes the way in which bumpy, hairy or otherwise rough surfaces repel water.  Try wetting a pigeon's feathers.  If you don't have a pigeon handy, collect a colony of fire ants and dump them in the water.  They will cling together and form a tight raft: jaw to  leg; leg to leg; clinging to each other tightly in every possible way.  The recent Proceedings of the National Academies includes a report that describes the raft formed by fire ants in water.  The Cassie -Baxter law explains that the very rough surface of the raft repels water.  Duck feathers do, too. 

I read about this in the Washington Post.  I wanted to know more about Cassie and Baxter.  My search led me to the Farady Society, a British society for the study of physical chemistry founded in 1903.  Such societies encouraged research and engaged in lively meetings to discuss and critique their members' work.  The Transactions of the Farady Society were published from 1901 to 1971.  I can almost smell the cigar smoke and see the members in their leather chairs, sipping port and arguing.
A. B. D. Cassie and S. Baxter's work, The Wettability of Porous Surfaces appeared in volume 40, page 546 in 1944.  England, and the world were at war - the outcome still in doubt.  Anything that could possibly aid the war effort was strictly rationed.  Damage from the Blitz was tidied but not repaired.  Throughout those dark days, the human spirit was not diminished.  We have many examples, and with Cassie and Baxter's work, another.  They were inquisitive, disciplined and undaunted by the deprivations of war-time London.  You can join the Royal Society of Chemistry, and  read their paper, or just think of them and whisper God Save the Queen.

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