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  lotus effect with Colocasia fallax
From: Theodore Held <oppenhauser2001 at gmail.com> on 2011.01.12 at 18:04:17(21731)

The lotus effect is quite common in my experience. It has been getting
a lot of attention in the popular press lately and there are a number
of academic studies of the phenomenon using nano materials. A Google
search will turn up many hits.

One of the best displays can be seen on the humble aroid Pistia.
Leaves of Pistia will support quite a large water droplet with no
wetting of the leaf surface that supports the hairs.

Ted Held.

From: =?iso-8859-1?B?ZGF2aWQgYnL2ZGVyYmF1ZXI=?= <david_dav44 at hotmail.com> on 2011.01.13 at 12:53:25(21740)
Hi Ted,

Pistia is in fact a very beautiful example for a water-repellent surface. It has to be kept in mind - as you mention - that it generates this superhydrophobic effect with hairs (not with papillate cells like in Nelumbo or Colocasia) that are covered with wax. So, the term 'lotus-effect' describes the syndrom of superhydrophobicity (which means that the contact angle of a water droplet is at least 150°), but there are different structures within the Araceae and other plant families, that produce this effect.

David Broederbauer



From: Theodore Held <oppenhauser2001 at gmail.com> on 2011.01.16 at 21:09:12(21758)

I have no idea whether or not individual Pistia hairs are coated with
some form of wax or whether the wetting by water of an individual hair
is simply poor enough to provide a bridge for the droplet surface over
to the next surface hair, which bridging prevents wicking of the water
down into the hairy structure.

This would be a good research topic: Dry some Pistia leaves and see
what is extracted (meaning dissolved by some liquid, ordinarily
followed by gentle drying to investigate the residual - Steve Lucas
was right to insist on technical terms being defined) by solvent
(hexane or toluene would be good solvent candidates for wax) and if it
is indeed a waxy substance. If no one has done this I'll do it myself
and report back to this forum.

Another thing that might be of interest to aroiders is that the net
result of Pistia hydrophobicity (which merely means its reluctance to
be wetted by water, typically observed as a tendency for water on a
hydrophobic surface to "bead up" into discrete droplets) is the
extreme buoyancy of the species. Try to submerge one of these plants
and it's almost like you are trying to submerge an air bubble. It is
curious to me how insubstantial a Pistia leaf is. It looks big, but
when compacted and dried there is almost nothing left. Much of the
apparent volume is simply air.

Ted Held

From: =?iso-8859-1?Q?Genevi=E8ve_Ferry?= <jpcferry2 at wanadoo.fr> on 2011.01.17 at 18:20:00(21759)
Dear Theodore,

Many thanks for your help .
The students have find many things with google .
Best regards


From: =?iso-8859-1?Q?Genevi=E8ve_Ferry?= <jpcferry2 at wanadoo.fr> on 2011.01.18 at 05:35:59(21760)
Dear David ,

Many thanks for your help .




From: =?iso-8859-1?B?ZGF2aWQgYnL2ZGVyYmF1ZXI=?= <david_dav44 at hotmail.com> on 2011.01.18 at 08:17:38(21763)
Hi Ted,

As far as I know it was the Barthlott-group in Germany who studied the Pistia-leave under SEM. They showed that the hairs are coated with wax...




From: Theodore Held <oppenhauser2001 at gmail.com> on 2011.01.21 at 18:16:29(21787)

Yes, I find what you say is correct. In fact, if anyone would like to
read about the phenomenon in depth, including the Pistia references,
just Google >Barthlott Pistia< and you'll get a Google book page that
describes what the Barthlott people found as well as quite a bit more
information about superhydrophobicity.

Thanks for the reference.

Ted Held

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