Polypyrrole films investigated by electrochemical quartz crystal oscillator and four-probe techniques

Electrochemical quartz crystal oscillator and four-probe techniques were employed to investigate the changes in microrheological properties of polypyrrole (PPy) during electrochemical growth in aqueous electrolyte solutions and the four-probe resistivity with the electrochemically grown PPy films, respectively. PPy films grew elastic at the initial stage and viscoelastic at the later stage in hydrochloric acid solution, while the films remained nearly elastic in the whole range of the thickness examined (8000 Hz) in sulfuric acid solution. Usual negative temperature coefficient of resistivity (TCR) was observed from 77 to 300 K with most PPy samples, but the crossover of TCR with a broad minimum peak near 200 K was found with PPy samples prepared at 0.8 V versus SCE in both hydrochloric acid and sulfuric acid solution.