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UCLA Chemists Report New Nano Phenomenon: Welding in Response to an Ordinary Camera Flash - nanofibers made of polyaniline
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UCLA Chemists Report New Nano Phenomenon: Welding in Response to an Ordinary
Date: October 28, 2004
Contact: Stuart Wolpert ( [Only registered users see links. ] )
UCLA chemists report the discovery of a remarkable new nanoscale phenomenon:
An ordinary camera flash causes the instantaneous welding together of
nanofibers made of polyaniline, a unique synthetic polymer that can be made
in either a conducting or an insulating form. The discovery, which the
chemists call "flash welding," is published in the November issue of the
journal Nature Materials.
Numerous applications potentially could result from this research in such
areas as chemical sensors, separation membranes and nano devices.
"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."
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.
Jiaxing Huang has started a UC Berkeley postdoctoral fellowship.
The research is funded by the Microelectronics Advanced Research Corp.
"Buddhism elucidates why we are sentient."
|camera , chemists , flash , made , nano , nanofibers , ordinary , phenomenon , polyaniline , report , response , ucla , welding|
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