Analysis of DC and AC properties of a humidity sensor based on polyaniline–chromium oxide composites

Polyaniline–Chromia (PANI–Cr₂O₃) composites were synthesized by in situ polymerization. The prepared composites were characterized by scanning electron microscopy, X-ray diffraction and Fourier transforms infrared spectroscopy. The structural studies confirm the polymerization of aniline over Cr₂O₃ particles which results into strong interaction between PANI and Cr₂O₃ particles. Direct current conductivity of composites increases with increase in temperature. Among all composites, 30 wt% shows high conductivity. The humidity sensing mechanism of the PANI–Cr₂O₃ composites is studied and change in its resistance with respect to percentage relative humidity ranging from 20 to 95 % is recorded. The humidity sensing studies shows that the change in the resistance is due to the uncurling of polymer chains by the absorption of water vapor which leads to increase in conduction paths. The results indicate better humidity sensing response by the addition of Cr₂O₃ particles to PANI, among all the composites, 30 wt% composite shows higher sensitivity.