Chemist's technique enables creation of novel carbon nanoparticles...
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Chemist's technique enables creation of novel carbon nanoparticles
Wolley technique 'linchpin' to success
May 4, 2004 - Using a technique pioneered by Washington University in St.
Louis chemist Karen Wooley, Ph.D., scientists have developed a novel way to
make discrete carbon nanoparticles for electrical components used in
industry and research.
A technique developed by Karen Wooley has proved vital in the creation
of novel carbon nanoparticles with colleagues at Carnegie Mellon University.
The method uses polyacrylonitrile (PAN) as a nanoparticle precursor and is
relatively low cost, simple and potentially scalable to commercial
production levels. It provides significant advantages over existing
technologies to make well-defined nanostructured carbons. Using the method,
PAN copolymers serving as carbon precursors can be deposited as thin films
on surfaces (for example, silicon wafers), where they can be patterned and
further processed using techniques currently employed to fabricate
microelectronic devices. Such a seamless manufacturing process is important
to generate integrated devices and would be difficult to achieve with other
methods currently used to synthesize nanostructured carbons, said Tomasz
Kowalewski, Ph.D., assistant professor of chemistry at the Mellon College of
Science and principal investigator on this research.
The research was presented March 28, 2004, at the 227th annual meeting of
the American Chemical Society in Anaheim, Calif. The research findings have
been accepted for publication in Angewandte Chemie, International Edition.
The work was funded by the National Science Foundation.
The new approach is based on a method the Carnegie Mellon group previously
developed to form nanostructured carbons by using block copolymers in which
PAN is linked to other polymers with which it normally does not mix. In the
current method, PAN, a water-hating compound, is copolymerized with
polyacrylic acid, a water-loving polymer. In water-containing solutions,
PAN-polyacrylic acid copolymers self assemble into nanoscale droplets, or
micelles. Each micelle has a water-insoluble PAN core and a water-soluble
polyacrylic acid outer coat that forms an outer shell.
The linchpin to make carbon nanoparticles from micelles is a
shell-crosslinking technique that Wooley developed with Ph.D. student K.
Bruce Thurmond II - now a research scientist at Access Pharmaceuticals,
Dallas, Tex. - in the late 1990s at Washington University. Whereas polymer
micelles are dynamic assemblies that can be reorganized or destroyed, the
shell crosslinking technique allowed the Carnegie Mellon researchers to
contain the PAN within the polyacrylic acid to maintain discrete
nano-objects during manipulation of the materials. The scientists then
deposited thin and ultra-thin films of these nanoparticles on various
substrates. The Carnegie Mellon team heated the nanoparticles to high
temperatures in a process called pyrolysis, decomposing the polyacrylic acid
shell scaffolding and converting the chemically stabilized PAN domains into
arrays of discrete carbon nanostructures.
"The preparation, manipulation and study of these highly interesting,
discrete carbon nanoparticles were facilitated by an interdisciplinary
collaboration that has involved the open sharing of knowledge, ideas,
resources and researchers between several laboratories located at Washington
University and Carnegie Mellon University," said Wooley. "This kind of
cross-institutional teamwork provides for enhanced student experiences and
allows for research accomplishments that would not ordinarily be possible,
activities which have been supported in large part by the National Science
"This work really illustrates a particularly attractive strategy in the
evolution of nanotechnology," said Kowalewski, principal investigator on
this research and a postdoctoral researcher at Washington University in the
late 1990s, and long-time collaborator with Wooley. "Our well-defined carbon
nanoparticles should find a wide range of applications, especially in energy
storage/conversion devices and in display technologies."
The Carnegie Mellon group is currently working on using carbon nanoparticles
as active materials in field emitter arrays for flat panel screen displays.
This technology to produce carbon nanostructures also could be adapted to
produce solar panels that convert sunlight into electrical energy. Other
applications include the development of carbon-based nanosensors or
high-surface area electrodes for use in biotechnology or medicine.
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