Ohio – Ohio State University engineers are designing
super-slick, water-repellent surfaces that mimic the
texture of lotus leaves.
patent-pending technology could lead to self-cleaning
glass, and could also reduce friction between the
tiny moving parts inside microdevices.
have long known that the lotus, or water lily, makes
a good model for a water-repellent surface, explained
Bharat Bhushan, Ohio Eminent Scholar and the Howard
D. Winbigler Professor of mechanical engineering at
Ohio State. The leaf is waxy and covered with tiny
bumps, so water rolls off.
studying the lotus leaf, Bhushan realized that the
same texture could be exploited to reduce friction
between moving parts on machines. Small machines,
such as those under development in the fields of micro-
and nanotechnology, can’t be lubricated by normal
means, and would especially benefit from the technology.
general, what’s good for water-repellency is good
for fighting friction,” Bhushan said.
when it comes to designing high-tech surfaces -- for
instance, a water-repellent car windshield or a low-friction
joint on a micromachine -- just copying a lotus leaf
isn’t enough. Bumpy, waxy surfaces can actually become
sticky under some circumstances.
people don’t know is what kind of surface is optimal,”
he and his colleagues have built the first computer
model that calculates the best bumpy surface for different
materials and applications.
the right kind of texture, manufacturers could make
self-cleaning windows. Because the bumps would measure
only a few nanometers (millionths of a meter) high,
and would be made of a transparent material, the window
would look like any other but still repel water and
dirt. That would mean less window cleaning in homes
far, Bhushan’s team has focused on modeling bumps
of different sizes and shapes. All the bumps included
in the model aid water repellency by keeping water
droplets from directly touching the surface.
the bumps are so much smaller than a droplet and so
close together, they can’t puncture the droplet. In
fact, if the droplet were perfectly balanced, it would
just lie on the bumps the way a person can safely
lie on a bed of nails. Bhushan’s model calculates
how and where to place the bumps so that the droplet
will contact the surface in just the right way to
automobiles, water-repellent glass would improve safety
by helping drivers see better, especially during inclement
now, drivers can spray coatings on car windows to
accomplish much the same thing, but those coatings
wear off. Because the new technology builds water-repellency
into the surface of the window, it would continue
to work for the lifetime of the window.
drivers may rejoice at the idea of less window cleaning,
Bhushan is most excited about what his technology
could do for microelectronics. In 2001, his team developed
the first direct method for measuring the friction
between moving parts inside micromachines, and he
has since been working on methods to reduce that friction.
of Bhushan’s industrial partners are building light-based
electronics in which tiny mirrors move to reflect
light in different directions. Others are working
on very small sensors that detect and process chemical
samples. Both kinds of devices are too small to use
traditional lubricants on the moving parts.
way to eliminate the need for lubricant is to build
slick surfaces onto each individual part. Bhushan
suspects his lotus-leaf surfaces might do the job.
Manufacturers would just have to use his model to
figure out what size and shape bumps are best for
has been supporting this work with his own internal
laboratory funds, and he’ll need an industrial partner
to carry the work further. He wants to fabricate some
very high-quality textured materials for scientific
study, so he’ll have to buy time in a clean room facility
-- the kind computer chip manufacturers use.
Bharat Bhushan, (614) 292-0651; Bhushan.firstname.lastname@example.org
Written by Pam Frost Gorder, (614) 292-9475; Gorder.email@example.com