Gas Sensing Properties of SWCNT and Teflon AF Composites

The electrical properties of Telfon AF thin films loaded with single walled carbon nanotubes (SWCNT) have been studied in the presence of water vapor, CO, CH₄, and NO₂. In pure Teflon AF and at low concentration of SWCNT the impedance of the films decreased approximately exponentially with increasing the relative humidity, whereas the addition of nanotubes amplified the change by two orders. At higher concentration of nanotubes (above the percolation threshold), the effect of H₂O on the conductance was negligible. However, a significant effect was observed in these films for NO₂ -the sensitivity (expressed as a relative change of the resistance DeltaR/R per ppm of the target gas) was in the order of 1%. For the other gases studied the effects were at least 103 times smaller. It was also found that the sensitivity to NO₂ could be enhanced by irradiation with UV light, which induced both photo-desorption and -adsorption phenomena. The title compound provides hence a chemically inert and non-swelling material with a rigid SWCNT network suitable for detecting high humidity levels or low NO₂ levels. The material can be used for sensing at room temperature as well as in high temperature environments (up to 280degC in case of NO₂).