Comparison of surface and bulk doping levels in chemical polypyrroles of low, medium and high conductivity

Chemical polypyrroles (PPys) of low (sigma < 75 S/cm), medium (75 < sigma < 200 S/cm) and high electrical conductivity (sigma > 200 S/cm) having chloride dopants have been investigated by XPS, chloride ion-selective electrode (ISE) measurements and high-resolution termogravimetric analysis (TGA). The average surface doping level in these PPys was 0.28 +/- 0.03 as determined from deconvoluted XPS N 1s, Cl 2p and C 1s spectra by using the well-established N+/N and Cl-/N atomic ratios as well as a new ratio denoted as C alpha*/C alpha(Total). This new ratio provides an estimation of the relative amount of alpha-C atoms in charged pyrrole units per total a-C atoms. The average bulk doping level in these materials was 0.31 +/- 0.02 from direct chloride ISE measurements. High-resolution TGA was employed for the first time in the determination of the amount of hydrogen chloride evolved from the PPy samples during degradation at high temperatures. The resulting average bulk doping level by TGA was 0.30 +/- 0.04 for these PPys, in very good agreement with the ISE results. Since surface and bulk doping levels are almost identical for the PPys of low, medium and high conductivity, the differences in conductivity between samples have been attributed to differences in conjugation length among them. For PPy of high conductivity (sigma = 288 S/cm), a conjugation length 2.6 times higher than that of PPy of low conductivity (sigma = 29 S/cm) has been calculated. Copyright (C) 2006 John Wiley & Sons, Ltd.