Impedance spectroscopy of thin films of emeraldine base polyaniline and its implications for chemical sensing

The conductivity of an emeraldine base polyaniline thin film on an interdigitated electrode in hydrochloric acid solutions of various pHs between 2.25 and 6 was investigated by impedance spectroscopy. In general, protonation induces an emeraldine base (EB) to emeraldine salt (ES) transformation and an associated increase in conductivity only when the pH of the protonating bath is less than 4. However, impedance spectroscopy detects changes in the conductivity behavior that occur prior to the onset of this increase in total conductivity change. These changes can also be measured with AC impedance measurements at a single frequency, which expands the pH range over which emeraldine base polyaniline can be used as a sensor.