Effects of dopants on percolation behaviors and gas sensing characteristics of polyaniline film

Effects of dopants on the correlation between the polyaniline (PAn) film resistance (R) and the reduction charge (Q) injected to the PAn film was investigated in dry acetonitrile solutions during electrochemical reduction by using the double potential step method. The R–Q correlation behaves as S-type curves, leading to the determination of the critical reduction charge (Qc). The latter represents the reduction charge required for the formation of a continuous partially reduced phase in the PAn film. It was observed that the PAn film doped with sodium dodecylbenzene sulphate (SDBS) yielded a smaller Qc than that doped with perchlorate, when the PAn films were electrochemically reduced under given conditions. The resistance of the pre-doped PAn film will increase significantly when the film is injected with reduction charge more than Qc. Hence, a smaller Qc means that the film can respond to very light reduction (or dedoping), being indicative of better sensing ability toward alkaline and reducing gases. This was confirmed by the increased sensitivity of the PAn/SDBS sensor toward 100 ppm NH3 vapor, compared with the PAn/ClO4− sensor.