Electrical, magnetic, and structural properties of chemically and electrochemically synthesized polypyrroles

We report the results of temperature-dependent dc conductivity (σdc(T)), EPR (electron paramagnetic resonance) magnetic susceptibility, and XPS (X-ray photoelectron spectroscopy) experiments for chemically and electrochemically synthesized polypyrrole (PPy) samples. For chemically synthesized dodecylbenzenesulfonic acid (DBSA) or naphthalenesulfonic acid (NSA) doped PPy samples (PPy-DBSA or PPy-NSA, respectively) soluble in m-cresol solvent, dc conductivity and its temperature dependence show the strong localization behavior, while those of electrochemically synthesized PPy doped with hexafluorophosphate (PPy-PF6) are in the critical regime. Pauli susceptibility (χp) and the density of states are obtained from the temperature dependence of EPR magnetic susceptibility. The density of states of chemically synthesized PPy is one-third of that of electrochemically synthesized PPy. From the analysis of the area ratio of carbon 1s XPS peak, the disorder effect due to interchain links or side chains of PPy-DBSA (m-cresol) samples is ∼22%, while that of PPy-PF6 samples is ∼33%. This result indicates that the percent of interchain links or side chains of chemically synthesized PPy-DBSA (m-cresol) samples is reduced by ∼10% compared to that of electrochemically synthesized PPy-PF6 samples. We analyze that the side chains or interchain links of chemically synthesized PPy samples are relatively reduced due to the synthesis method using large size dopants, and subsequently the interchain interaction weakens. The results of EPR experiments of PPy-DBSA (m-cresol) samples with different doping levels are discussed.