Wednesday, October 16

Scientists at UCLA create stronger nano-sized fiber


Professors use electrospinning technique inspired by spider webs

Researchers at UCLA have taken an old method from a common
spider and spun it into a new idea for creating stronger
materials.

The idea was to copy the approach spiders use in spinning a web
and to apply this to a method for creating stronger nano-sized
fiber materials, according to Thomas Hahn, mechanical and aerospace
engineering professor at UCLA’s Henry Samueli School of
Engineering and Applied Science, and Frank Ko, a materials
engineering professor from Drexel University.

For the last seven months, the two professors worked at the
Multi-Functional Composite Laboratory at UCLA, developing the
“electrospinning” technique, which spins a web of
fibers using an electrostatic force.

The process starts with a polymer solution mixed with nano-sized
particles to form a composite solution. The particles are so small
that they can only be seen through high-powered microscopes.

“In general, nanotechnology and nano-sized particles allow
us to get down to the quantum level,” Ko said. “This
effect describes how performance can be enhanced exponentially,
where chemical reactions can occur much more quickly, electrons
move faster, and heat is conducted much better.”

“And because of the fineness of the material, and the
cohesion between the atoms, the material is much stronger,”
he added.

The fibers Hahn and Ko are spinning measure approximately 100
nanometers in diameter. A typical strand of human DNA measures just
1.5 nanometers in diameter.

With the solution mixed with nano-sized particles in place, Hahn
and Ko connect it to a positive voltage supply to create an
electric field, which induces an electrostatic force that pulls the
solution out of its container.

Once the solution is drawn out of its container, it passes
through an open space and is drawn toward a “collector
plate,” where it solidifies into fiber form.

“You can’t see (the fiber), because it’s on a
nano scale,” Ko said. “But if you put your hand (in the
electric field), you can feel a nanofiber in your hand, so you know
it’s there.”

Once the fibers solidify onto the collection plate, researchers
then analyze them for their strength, conductivity and overall
functionality using a scanning electron microscope.

Analyzing the samples and their content is a job left up to
Russell Luoh, one of Hahn’s graduate students working with
the device.

“We are discovering that depending on the composite
material used, they react differently with the polymer, and
that’s something we are trying to understand more,”
Hahn said.

While Hahn focuses on mixing nano-particles into the polymer
solution to add different functions, Ko’s expertise lies with
the nanocomposites in fiber form.

Ko believes these nanofibers will have many applications for
electronic, biological and structural components. Their experiments
using nanofibers as a conductive layer have already yielded better
results than some of the most state-of-the-art materials for
electronic components, according to Ko.

He believes nanofibers will also play a role in biomedical
engineering.

“You can use this material as a sensor or use it for
regeneration of tissues, and it’s compatible to
nature’s (nano-sized) scale, so you can grow cells and
implant it in your skin, muscles or even nerves,” Ko said.
“The biological implication is really an area of great
interest for both of us.”

These nanofibers can also be applied to structural engineering
and building techniques, from tennis rackets to military
aircraft.

Hahn, who has worked with the U.S. Navy and Air Force for many
years, believes that the aerospace industry has many applications
for strong and lightweight materials, including military aircraft
and satellites.

The whole project has been a learning process for both Hahn and
Ko, who are experts in working with composite materials and have
known each other for over twenty years.

Part of this learning process was the interdisciplinary nature
of their work.

“Suddenly, we find that we have to know a lot of chemistry
and electrical engineering,” Ko said. “One thing about
nano is you have to work with many groups with good
cooperation.”

One such group is led by chemistry professor Richard Kaner, who
was responsible for supplying the researchers with the
nano-particles used in testing the device.

“A lot of tests still have to be done, but this is
extremely exciting,” Ko said. “In industry, they look
at this data and they are very interested, and we need to start
working with industry to scale this up. But it’s still a long
way between where we are now and covering the wing of an
airplane.”

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