Coating sensation
10 May 2005
A technique for coating conductive polymers onto miniaturised devices could lead to a new generation of toxic gas detectors, according to researchers from NIST.
The team has found a way to deposit polyaniline, a highly promising conductive polymer, onto the surface of a microheater. This was previously impossible because the polymer is insoluble in most solvents.
The researchers got around the problem by not dissolving it. Instead, they made it into a colloid, dispersing nanoscale particles of polyaniline in a mild solvent, then applying this to the heater surface.
‘The beauty of this method is that the polyaniline chain carries a natural positive charge,’ explains Guofeng Li, one of the authors of the team’s paper in the Journal of the American Chemical Society.
Once the particles are formed, the positive charge prevents them from clumping together, allowing the formation of an even coating. Moreover, the researchers found that electrical fields can direct the polymer into complex patterns on the surface of devices.
The polyaniline coating has a spongy texture that can capture gas molecules. These adsorb onto the polymer surface, changing its conductive properties. It’s this that gives the heater-polymer assemblies their potential as gas detectors. The team has already shown that the devices can differentiate between methanol and water vapour, and plans further tests with different gases.
