The electrical responses to humidity of a composite of polyaniline and polyelectrolyte

Poly(dimethylaminoethyl methacrylate) and poly(glycidyl methacrylate) were simultaneously cross-linked to form a polyelectrolyte humidity sensitive film on an interdigitated gold electrode, which was further coated with a layer of soluble polyaniline (PANI). The composite so prepared was characterized by UV–vis spectroscopy and scanning electron microscopy. Its electrical response towards humidity was investigated at room temperature and compared with that of PANI and the polyelectrolyte separately. It was revealed that the composite showed an impedance as low as 1.8 × 105 Ω even at 0%RH. In contrast, the impedance of the polyelectrolyte at less than 20%RH was too high to be measured, and PANI showed very low humidity sensitivity. The low impedance, good sensitivity as characterized by a linear change in impedance from 1.8 × 105 to 9 × 103 Ω over 0–95%RH, fast response and small hysteresis, makes the composite a promising candidate for humidity sensors capable of detecting very low humidity.