Highly sensitive humidity sensors made from composites of HEC filled by carbon nanofillers

Abstract

Resistive type humidity sensors made from the composite films of HEC (hydroxyethyl cellulose) and MWCNTs (multiwalled carbon nanotubes) were developed. Three kinds of HEC/MWCNT composite films were fabricated, which contained 7.0, 8.0 and 9.0 wt-% MWCNTs. Rapid response capability and high sensitivities of the composite sensors were confirmed. For the convenience of sensor’s calibration, the non-linear resistance change ratios can be linearised by performing natural logarithm operation on them. A new sensitivity factor was defined based on this linear relationship between the logarithm of the resistance change ratio and relative humidity. For comparison, a reference humidity sensor was also made from the composite film of HEC filled by 50.0 wt-% CBs (carbon blacks). Compared with the HEC/MWCNT sensors, the HEC/CB sensor was of much higher sensitivity, but lower repeatability and stability under cyclic humidity changes. Possible sensing mechanisms were discussed in detail.

Keywords:

• Humidity sensor
• Composite
• Carbon nanotube
• Carbon black
• Tunneling effect

Acknowledgements

This work is financially supported by National Natural Science Foundation of China (grant nos. 11372104, 11332013 and 11372363).