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"We used an ordinary 35-millimeter camera, but you
could also use a laser, or any other high-intensity light source,"
said Richard B. Kaner, UCLA professor of inorganic chemistry and
materials science and engineering, and a member of the California
NanoSystems Institute at UCLA.
"I was very surprised," Kaner said. "My graduate
student, Jiaxing Huang, decided to take some pictures of his
polyaniline nanofibers one evening when he heard a distinct popping
sound and smelled burning plastic. Jiaxing recalled a paper that we
had discussed during a group meeting reporting that carbon nanotubes
burned up in response to a camera flash. By adjusting the distance of
the camera flash to his material, he was able to produce smooth films
with no burning, making this new discovery potentially useful."
Release URL, if available: The URL must point to
the specific release, not a general page of The camera flash induces a
chemical reaction; it starts a chain reaction in which the tiny
nanofibers interact and cross-link, producing heat, which leads to
more spontaneous cross?linking across the entire surface of the
nanofibers, welding them together, Kaner said. Unlike carbon nanotubes,
which burn up, this material is thermally absorbent and can dissipate
the heat well enough so that it does not burn.
"We can envision welding other materials together
as well," Kaner added. "One way to do this is to take two blocks of a
conventional polymer and insert polyaniline nanofibers between them,
then induce the cross-linking reaction to produce enough heat to weld
the polymer blocks together. We can weld polyaniline to itself or to
another polymer or potentially use it to join conventional polymers
together." (A polymer is a long chain of molecules, commonly known as
plastics.)
Because only the part exposed to light welds
together, chemists can create patterns by covering sections that they
do not want welded; they can control what parts weld together.
Kaner's research team searched for whether any
conventional techniques have this same welding property. They found a
recent commercial process called laser welding, now used in the
electronics industry, in which a laser beam is used to weld together
conventional polymers. "The trouble with laser welding," Kaner said, "is
that lasers generally have a small cross-section and consume a lot of
power. Our research has the potential of revolutionizing this process."
Nanofibers have high surface areas and important
properties, from sensing to flash welding. "This shows why nano is
important," Kaner said. "Here's a good example of where nano materials
possess a property that conventional materials do not have."
Kaner and Huang were the first chemists to produce
large quantities of pure polyaniline nanofibers, which can also be
used for sensors -- findings they published last year in collaboration
with Dr. Bruce Weiller and Shabnam Virji at Aerospace Corp. The
nanofibers have a much greater response in a shorter time than sensors
made with conventional polyaniline. |
