Investigation of Insulator-to-Semiconductor Fast Transition in Sheet-Like Polyaniline Films

Ethylenediamine-doped (EDA-doped) polyaniline (PANI) films were deposited via spin coating technique on a glass substrate. The samples were annealed at different times and temperatures. The characterizations of the prepared PANI films were described by X-ray diffraction (XRD), transmission electron microscopy (TEM), and Fourier transform infrared spectroscopy (FT-IR). It is found that the conductivity changes under deep mouth exhaling for 150/1 h sample is 1.65 times faster than the films annealed at 100°C/4 h. The response and recovery time of the 150/1 h EDA-doped PANI film is decreased by order of 0.63 and 1.29 s than those films dried at 100°C for 4 h, respectively. The 150/1 h EDA doped PANI film during deep exhaling its conductivity increased abruptly from 2.2 × 10^–7 to 0.026 S/cm^–1. In a few seconds, following an inhalation, there occurs a complete transition to the dry state conductivity. Furthermore, the increment in conductivity of the EDA-doped PANI films was determined at various RH levels (20, 40, 60, 80, and 90%) with exposure and evacuation of the humid air. The doped PANI sample annealed at 150°C for 1 h exhibit the highest conductivity at 90% RH. The conductivity was increased from 2.16 × 10^–7 S/cm for the insulating state at the dry state to 0.23 S/cm for the semiconducting state at 90% RH. Consequently, the 150/1 h sample showed an increase in conductivity by order of 10⁶ at 90% RH. For all samples, the conductivity progressively rises as the RH value increases till 90% of RH value samples exhibit an abrupt increase in conductivity except the 100°C/4 h sample. The highest conductivity is 0.041 S/cm at 90% RH obtained for the case of 150/30 min sample, whereas the 150/1 min and 100/4 h films show maximum conductivity of 0.027 and 0.007, respectively.