WASHINTGON: What if scientists create self-cleaning
walls and fabrics or even micro-scale robots that can walk on water?
Well, researchers at the University of Nebraska-Lincoln and Japan's
RIKEN institute claim to have moved a step closer to realising such
The researchers have revealed that their work is
based on a study of a property called super hydrophobia, which is behind
how water beads up and rolls off flowers, caterpillars and some
insects, and how insects like water striders are able to walk
effortlessly on water.
"A lot of people study this and
engineers especially like the water strider because it can walk on
water. Their legs are super hydrophobic and each leg can hold about 15
times their weight. 'Hydrophobic' means water really doesn't like their
legs and that's what keeps them on top. A lot of scientists and
engineers want to develop surfaces that mimic this from nature," said
Xiao Cheng Zeng, Ameritas university professor of Chemistry at UNL.
Zeng and his Japanese colleagues -- Takahiro Koishi of the University
of Fukui and RIKEN, Kenji Yasuoka of Keio University, and Shigenori
Fujikawa and Toshikazu Ebisuzaki of RIKEN -- have now come up with clues
to developing the long-sought super hydrophobic materials.
researchers highlight the fact that caterpillars, water striders, and
the lotus achieve super hydrophobia through a two-level structure -- a
hydrophobic waxy surface made super hydrophobic by the addition of
microscopic hair-like structures that may be covered by even smaller
hairs, greatly increasing the surface area of the organism and making it
impossible for water droplets to stick.
They used the
super-fast supercomputer at RIKEN, the fastest in the world when the
research started in 2005, to design a computer simulation to perform
tens of thousands of experiments that studied how surfaces behaved under
many different conditions.
The team used the supercomputer to
"rain" virtual water droplets of different sizes and speeds on surfaces,
which had pillars of various heights and widths and different amounts
of space between the pillars.
The researchers observed that
there was a critical pillar height, depending on the particular
structure of the pillars and their chemical properties, beyond which
water droplets cannot penetrate.
According to them, if the
droplet can penetrate the pillar structure and reach the waxy surface,
it is in the merely hydrophobic Wenzel state, named for Robert Wenzel,
who found the phenomenon in nature in 1936.
further said if it the droplet cannot penetrate the pillars to touch the
surface, the structure is in the super hydrophobic Cassie state, named
for A.B.D. Cassie, who discovered it in 1942, and the droplet rolls
"This kind of simulation -- we call it 'computer-aided
surface design' -- can really help engineers in designing a better
nanostructured surface. In the Cassie state, the water droplet stays on
top and it can carry dirt away. In the Wenzel state, it's sort of stuck
on the surface and lacks self-cleaning functionality. When you build a
nanomachine -- a nanorobot -- in the future, you will want to build it
so it can self-clean," Zeng said.
Using the supercomputer
enabled the researchers to conduct thousands more repetitions than would
have been possible in a lab, and they didn't have to worry about
variables such as dirt, temperature and airflow. The team could even
control the size of droplets down to the exact number of molecules.
A research paper describing the study has been published in the online
edition of the Proceedings of the National Academy of Sciences