Electrical conductivity response of dodecylbenzene sulfonic acid-doped polypyrrole films to SO2–N2 mixtures

The effects of using dodecylbenzene sulfonic acid as a dopant on electrical conductivity of polypyrrole films were investigated in N2 atmosphere and SO2–N2 mixtures. For a film with a higher doping level, the time for the specific electrical conductivity σdc to reach its equilibrium value when exposed to SO2 was reduced; and consistently, the short time response (dσdc/dt) at zero exposure time increased. The temporal response of conductive polypyrrole films was improved with the films having higher doping levels. On the other hand, the gas sensitivity or change in the specific electrical conductivity from its base value when exposed to SO2 was independent of dopant concentration, if it was below a critical doping level. Above this critical doping level, the change in the specific electrical conductivity climbed to a maximum value and then declined slightly as the doping level was increased. The dependence of the specific electrical conductivity on dopant concentration can be well correlated with changes in morphology observed. The conductive polymer chains changed from assuming three dimensional random-coil structures to rod-like fabrillar structures.