N.Y. -- Imagine this: A tiny, fast switch that uses
water droplets to create adhesive bonds almost as
strong as aluminum by borrowing a mechanism found
in palm beetles.
The new beetle-inspired switch, designed by Cornell
University engineers, can work by itself on the scale
of a micron -- a millionth of a meter. The switches
can be combined in arrays for larger applications
like powerful adhesive bonding. Like the transistor,
whose varied uses became apparent only following
its invention, the uses of the new switch are not
yet understood. But the switch's simplicity, smallness
and speed have enormous potential, according to the
all the greatest technological advances have depended
on switches, and this is a switch that is fast
and can be scaled down," said Paul Steen,
a professor of chemical and biomolecular engineering
at Cornell and co-author of a paper published in
the Proceedings of the National Academy of Sciences
(Vol. 102, No. 34).
Steen dreamed up the idea of the switch after listening
to Cornell entomologist Tom Eisner lecture on palm
beetles, which are native to the southeastern United
Like the beetle, which clings to a palm leaf at
adhesive strengths equal to a hundred times its own
body weight -- the human equivalent of carrying seven
cars -- the switch in its most basic form uses surface
tension created by water droplets in contact with
a surface, in much the same way as two pieces of
wet paper cling together.
When attacked, the palm beetle attaches itself to
a leaf until the attacker leaves. It adheres with
120,000 droplets of secreted oil, each making a bridgelike
contact between the beetle's feet and the leaf. Each
droplet is just a few microns wide. Whereas the beetle
controls the oil contacts mechanically, Steen's switch
uses water and electricity.
For the switch to make or release a bond created
by surface tension, a water droplet moves to the
top or bottom of a flat plate surface using electricity
from electrodes. The electricity moves positively
charged atoms, called ions, in the water through
the minute capillaries of a thin disk of porous glass
embedded in the plate. The water moves and wells
up into a micrometer-sized droplet on the plate surface.
The exposed droplet can then stick to another surface.
To break the bond, electricity pulls the exposed
water back through the capillary pores.
With millimeter-sized water droplets and micron-sized
pores, 5 volts can turn the switch on in one second.
At the same time, the researchers predict that smaller
droplets will require less energy to move and have
faster switching times. Steen and his colleagues
believe that a switch as small as hundreds of nanometers,
close to a billionth of a meter and one-tenth the
size of the beetle droplets, is within reach. Researchers
could also create large effects from many tiny switches
by connecting them in various arrangements, Steen
"This new technology bridges the gap between
scales as large as our hands and nanoscales," said
Steen. "We need devices that allow us to communicate
between the two scales."
Co-authors include Michael Vogel, a postdoctoral
researcher in Cornell's Department of Chemical and
Biomolecular Engineering, and researcher Peter Ehrhard
at the Institute for Nuclear and Energy Technologies
in Karlsruhe, Germany. Since much of this work was
conducted while the three scientists were at the
German institute, the patent application was filed
The study was supported by NASA, the National Science
Foundation, the Forschungszentrum Karlsruhe and the
Deustcher Akademischer Austausch Dienst.
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