Effect of oxygen on polypyrrole as studied by conductivity and ESR measurements

The effect of oxygen on polypyrrole (PPy) doped with benzenesulfonate has been investigated by electric conductivity and electron spin resonance (ESR) measurements. There are two regions in the changes of the conductivity, the Linewidth and the spin concentration with respect to the pressure of oxygen. When the pressure decreased in the range from ambient pressure to 0.2 Torr (region I), the conductivity increased consistently with the relationship of the Langmuir adsorption, in which we assumed that the amount of adsorption was in proportion to the inverse of conductivity. This effect was reversible with respect to the pressure, indicating physical adsorption in this region I. The oxygen desorption by reducing the pressure caused a rapid decrease of the linewidth as well as the spin concentration. It was concluded that the linewidth variation is due to the reduction of dipole-dipole interactions between the unpaired electrons of the oxygen molecules and radicals of PPy (polarons), while the spin concentration variation is due to the disappearance of the oxygen molecules. Below 0.2 Ton: (region II), the conductivity increased, deviating from the Langmuir relationship, while the ESR spectra almost remained constant. These findings were discussed, considering that the interaction positions of the adsorption were radical sites (polarons) in connection with the conductive process and that only a small number of the oxygen molecules adsorbed in this region II.