Kosuke Amano

Thermal stability of chemically synthesized polyaniline

Abstract Two polyanilines (PAns) were prepared by utilizing two different oxidizing agents, ammonium persulfate (APS) and ammonium dichromate (ADC) in aqueous toluene sulfonic acid (TSA). The thermal stability of the resulting as-prepared PAns was evaluated in both air and nitrogen, and the results were compared. With ADC, TSA-doped PAn was obtained, while with APS, PAn doped with sulfuric acid was obtained. For the letter, the dopant (sulfuric acid) originated from the APS during the oxidation of aniline. At a temperature between 100 and 180 °C in both air and nitrogen atmosphere, the conductivity of PAn prepared from APS decreases monotonically with time. The decreasing conductivity is governed approximately by first-order kinetics, and its dominant cause is the addition of sulfate to the PAn aromatic ring. However, the conductivity of PAn prepared using ADC increases with aging time at 130 °C regardless of the atmosphere and, at 160 °C, it shows a peak with aging time. This behavior is explained in terms of a change in the arrangement of the polyaniline chain.

Electrical conductivity of annealed polyaniline

The electrical conductivity of chemically synthesized and annealed polyaniline has been investigated. The room‐temperature conductivity varies with the time and the temperature of annealing, and exhibits a maximum peak on its time‐dependence curves for the polymer annealed above 120 °C. The time showing the maximum peak of the conductivity shifts to the shorter side with higher annealing temperature. The linear dependence of the conductivity on temperature with T−1/2 is observed in all samples as explained for this polymer with the quasi‐one‐dimensional variable‐range‐hopping processes. In the initial stage of annealing, the conductivity increases in the whole temperature range without varying the exponential factor of the variable range hopping. This indicates that the density of states remains unchanged in this stage. The results concerning the pre‐exponential factor of the quasi‐one‐dimensional variable‐range‐hopping mechanism demonstrate the increase of the mean free time, the transverse localization ...

Highly conducting polypyrrole prepared from homogeneous mixtures of pyrrole/oxidizing agent and its applications to solid tantalum capacitors

Abstract Reaction parameters for the cationic oxidative polymerization of pyrrole are investigated for the preparation of a highly conductive material for electronic devices. The homogeneous reaction mixture is prepared by dissolving pyrrole and iron(III) dodecylbenzenesulfonate at a very low temperature of −70 °C, which gives polypyrrole with high conductivity. The conductivity increases with increasing concentrations of monomer and oxidizing agent. The maximum conductivity reaches 80 S/cm, which is comparable to that of electrochemically prepared film. The method is successfully used for the formation of the counter electrode of a tantalum solid capacitor. The capacitor demonstrates the proportional decrease of impedance up to the resonance frequency with capacitance above 90% of the design value.

Characterization of a tantalum capacitor fabricated with a conducting polypyrrole as a counter electrode

Summary form only given. A tantalum solid electrolytic capacitor using a conducting polypyrrole com posite as a counter electrode has been investigated on the current-voltage characteristics at various temperatures. The capacitor demonstrates the features of an ideal capacitor, meaning a constant capacitance and proportion al decrease of impedance with frequency up to the resonance point. The leak age current at the working voltage is nearly two orders of magnitude smaller than of a conventional tantalum capacitor using a MnO/sub 2/ electrode. The resistance changes along the curve expected from the variable range hopping model similarly to the case of polypyrrole alone. The current-voltage curve follows the Schottky or Pool-Frenkel emission process and shows that the area and depth of the defects on dielectric (Ta/sub 2/O/sub 5/) layers are smaller than those of the conventional tantalum capacitor. Furthermore, the healing effect is observed for broken samples. In this case, the current decreases dramatically by applying the working voltage.

Structure and properties of polypyrrole synthesized under air and oxygen-free conditions

We have succeeded in manufacturing a chip-type tantalum capacitor using conducting polypyrrole (PPy) as a solid electrolyte. PPy was fabricated by the direct polymerization of pyrrole on the dielectric layer of the capacitor. Diffuse reflection-absorption FT-IR spectroscopy indicates that the PPy has an oxidized structure with covalently bonded oxygen, which differs from native PPy synthesized under oxygen-free conditions. We investigated the thermostability of oxidized and native PPys in an inert atmosphere. The room temperature conductivity of both PPys remained unchanged despite annealing at up to 260°C. Gas chromatography-mass spectrometry indicated that the elimination of dopants begins at 330°C and the main chain decomposes at 480°C. We observed no difference in the thermostability of oxidized and native PPy. These results prove that PPy in a sealed container can be adapted for use as a material for electronic devices that need to remain stable at high temperatures. A sealed tantalum capacitor made using PPy was able to operate continuously at 125°C.

Elongation of high-molecular-weight poly(3-octylthiophene) and its electrical properties

Abstract The electrical conductivity of molecular-weight-controlled poly(3-octylthiophene) is investigated. The molecular weight affects the electrical conductivity and elongation ratio to break. The elongated films show the anisotropy in conductivity. The linear dependence of log σ against T − 1 4 is observed on the plots in all directions of measurement. The conductivity increases with the square of elongation ratio for high-molecular-weight poly(3-octylthiophene). The multiplier constant reduces with decreasing molecular weight, which is explained by considering the internal slip of the conducting elements.