Investigation of Structure and Electrical Conductivity in Doped Polyaniline

Polyaniline (PAn) was synthesized chemically and doped with various dopants, such as HCl, HCOOH, I₂ and methylene blue (C₁₆ H₁₈ ClN₃ S), by an immersion method. The structure of these samples was investigated by infrared (IR) spectroscopy and wide-angle X-ray diffraction (WAXD) analysis. Remarkable changes have been observed in the IR spectra of doped PAn, indicating that doping is affecting the chemical structure. The percentage crystallinity was also found to increase after doping. The electrical conductivity (σ) of these samples was measured at various temperatures (T=308K to 423K). Plots of log σ versus T^y, where y=-1/2, -1/3, -1/4, were obtained and used to identity the conduction mechanism. Undoped PAn shows semiconducting behaviour, while doped samples show a variable range hopping mechanism. A primary cell was constructed with HCl-doped PAn as one of the electrodes and a copper plate as the other electrode. It gave an open circuit voltage of 0·38V and a short circuit current of about 5·4mA. © of SCI.