| Unlike
most polymers, conducting polymers have the electrical
and optical properties of metals or semiconductors.
These materials are of increasing interest in microelectronics
because they are inexpensive, flexible and easy to synthesize.
Polyaniline
is a particularly promising conducting polymer for
microelectronics applications, but it is difficult
to process because it doesn't dissolve in most solvents.
NIST researchers have circumvented this problem by
dispersing nanoscale particles of polyaniline into
a mild solvent.
"The
beauty of the method," says NIST guest researcher
Guofeng Li, "is that the polyaniline chain carries
a natural positive charge." Once the particles
are formed, electrostatic repulsion prevents them
from clumping together. Moreover, the positively charged
particles then can be manipulated and patterned on
complex device structures by applying an electrical
field.
The
process produces a sponge-like coating that efficiently
captures gaseous molecules. So far NIST researchers
have demonstrated that such coatings can detect the
difference between methanol and water vapor. Additional
tests will be needed before the polymer devices could
be used for detecting toxic gases.
NIST
holds patents for previous work using microheaters
coated with nanostructured tin oxide films. As the
microheaters cycle through a series of temperatures,
changes in electrical resistance are used to detect
toxic gases at part per billion levels. Ultimately,
NIST researchers hope to develop inexpensive arrays
of microheater sensors coated with both polymer and
inorganic oxide films optimized to identify the components
of gas mixtures.
*G. Li, C. Martinez, S. Semancik. Controlled electrophorectic
patterning of polyaniline from a colloidal suspension.
Journal of the American Chemical Society, April 6,
2005.
Contact:
Gail Porter
gail.porter@nist.gov
301-975-3392
National Institute of Standards and Technology (NIST)
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