Long-Term Stability of Humidity Sensor Using Polyaniline Blend Films Upon DC Operation

Resistive-type humidity sensors using polyaniline blend films were fabricated, and their long-term stability upon application of dc voltage was investigated. The use of blended films of electron-conducting polyaniline (PANI) and polystyrene was effective in depressing the sensor drift caused by polarization and/or electrolysis, which is a serious problem for polyelectrolyte sensors. However, another kind of drift caused by morphological change in the blend film was observed. To prevent this morphological change, cross-linked polystyrene with divinylbenzene (c-PSt) was used as a matrix polymer. The sensor using blended films of PANI and c-PSt exhibited excellent initial sensing characteristics and improved long-term stability.