Sumio Yamasaki

Poly(p‐phenylene terephthalamide) Film Immobilizing Oligomer Species as a Colored Matrix for Three‐Color Electrochromic Displays

Poly(p-phenylene terephthalamide) (PPTA) was prepared on a transparent indium-tin electrode as a mechanically stable film by electrolysis of a dimethylsulfoxide solution containing PPTA polyanions. The PPTA film was electroactive because of its ionic conductivity. When an aniline derivative, o-phenylenediamine, was electro-oxidized using the PPTA film-covered electrode, the film captured the red oligomer species and the polymerizing solution was barely colored by the species. The oligomer concentrating effect of the film enhanced the polymerization efficiency of o-phenylenediamine. Further, polyaniline was electrodeposited on the orange PPTA film. The composite film showed three-color electrochromism : orange (-0.4 V), green (+0.4 V), and violet (+1.2 V).

Cation Capturing Ability and the Potential Response of a Poly(o-aminophenol) Film Electrode to Dissolved Ferric Ions

Poly(o-aminophenol) (PoAP) film was electrodeposited on an indium-tin oxide electrode. The PoAP film electrode captured dissolved cations such as Fe 3+ because of the coordination ability of the film. The cation capturing ability was confirmed by the X-ray photoelectron spectroscopy and the cyclic voltammograms of the PoAP film. The redox potential of PoAP was lower than that of the Fe 3+ /Fe 2+ redox couple and the Fe 3+ ions captured in the film were partially reduced to form Fe 2+ ions The PoAP film electrode had the Fe 2+ ions, and the electrode showed a Nernstian potential response to dissolved Fe 3+ ions. The response time was less than 10 s, and the response was observed in the concentration range above 10 -5 M. Although the PoAP film electrode captured Zn 2+ , Ni 2+ , and Cu 2+ , it showed no potential response to the corresponding cations because the corresponding reduced forms (Zn, Ni, Cu) were absent in the film.

Simultaneous potentiometric determination of ClO3−–ClO2− and ClO3−–HClO by flow injection analysis using Fe(III)–Fe(II) potential buffer

A rapid potentiometric flow injection technique for the simultaneous determination of oxychlorine species such as ClO(3)(-)-ClO(2)(-) and ClO(3)(-)-HClO has been developed, using both a redox electrode detector and a Fe(III)-Fe(II) potential buffer solution containing chloride. The analytical method is based on the detection of a large transient potential change of the redox electrode due to chlorine generated via the reaction of the oxychlorine species with chloride in the potential buffer solution. The sensitivities to HClO and ClO(2)(-) obtained by the transient potential change were enhanced 700-800-fold over that using an equilibrium potential. The detection limit of the present method for HClO and ClO(2)(-) is as low as 5x10(-8) M with use of a 5x10(-4) M Fe(III)-1x10(-3) M Fe(II) buffer containing 0.3 M KCl and 0.5 M H(2)SO(4). On the other hand, sensitivity to ClO(3)(-) was low when a potential buffer solution containing 0.5 M H(2)SO(4) was used, but could be increased largely by increasing the acidity of the potential buffer. The detection limit for ClO(3)(-) was 2x10(-6) M with the use of a 5x10(-4) M Fe(III)-1x10(-3) M Fe(II) buffer containing 0.3 M KCl and 9 M H(2)SO(4). By utilizing the difference in reactivity of oxychlorine species with chloride in the potential buffer, a simultaneous determination method for a mixed solution of ClO(3)(-)-ClO(2)(-) or ClO(3)(-)-HClO was designed to detect, in a timely manner, a transient potential change with the use of two streams of potential buffers which contain different concentrations of sulfuric acid. Analytical concentration ranges of oxychlorine species were 2x10(-5)-2x10(-4) M for ClO(3)(-), and 1x10(-6)-1x10(-5) M for HClO and ClO(2)(-). The reproducibility of the present method was in the range 1.5-2.3%. The reaction mechanism for the transient potential change used in the present method is also discussed, based on the results of batchwise experiments. The simultaneous determination method was applied to the determination of oxychlorine species in a tap water sample, and was found to provide an analytical result for HClO, which was in good agreement with that obtained by the o-tolidine method and to provide a good recovery for ClO(3)(-) added to the sample.

Mean redox potentials of polyaniline determined by chronocoulometry

Polyaniline film has various domains with different π-conjugated lengths Each domain has an individual redox potential (E i ) and the potential is distributed around a mean redox potential (E). The doping levels (Y) at various oxidation potentials (E) can be expressed theoretically using E i * , E and E. Four polyaniline films were electrodeposited on a Pt electrode from four acid solutions: sulfuric, hydrochloric, perchloric and benzenesulfonic acid. The redox charge at various oxidation potentials (E) is determined chronocoulometrically, and the charge gives the doping level (Y) By simulating the obtained Y-E plots with a newly developed theoretical equation, E is determined for the four polyanilines. The lowest E is obtained for the polyaniline film doped by perchlorate ion. This implies that the film has the longest mean π-conjugated length.

Electrochemically prepared poly(o-phenylenediamine) — Prussian blue composite film for a three-colour expressible ECD material

Both Prussian blue (PB) and poly(o-phenylenediamine) (PoPD) were easily electrodeposited as stable films onto a transparent indium tin oxide (ITO) electrode. The voltammogram of the PB film showed a reversible sharp redox peak current at about 0.25 V. Although the colour change was caused by altering the applied potentials, no colour change was seen after about 104 repetitions. The PoPD film also showed a reversible redox peak current at about −0.05 V. The redox reaction was accompanied by a readily observable colour change between nearly red (vermilion) and colourless. The PoPD film was electrodeposited onto the PB coated electrode to obtain a PB/PoPD composite film. The voltammogram of the film was comprised of the two redox waves of the individual components. The film retained the electrochromic properties of each component and there was no undesirable interference. By changing the potentials, the film exhibited a continuous variety of colours: colourless (-0.2 V), vermilion (0.1 V) and emerald green (0.6 V). The switching time of the colour change was found to be <600 ms. Compared with the PB film, the composite film lasted longer. About 60% of the colouration remained after 105 repetitions since the PoPD worked as a binder which enhanced the adhesion of PB to the electrode surface.

Three-color electrochromism of an aramid film containing polyaniline and poly(o -phenylenediamine)

Abstract An aramid, poly( p -phenylene terephthalamide) (PPTA), was prepared as a mechanically stable film. When aniline was electro-oxidi/ed using the PPTA-filmed electrode, the film captured polyaniline (PANI). For the obtained composite film. PPTA strongly suppressed the oxidative deterioration of PANI, and fully oxidized PANI (pernigraniline form) was stable without deterioration. The film showed three-color electrochromism: pale yellow (−0.4 V). green (+0.4 V), and violet (+1.2 V). Different color change was also obtained with a PANI-PoPD-PPTA composite film: vermilion (−0.4 V), green (+0.4 V), and violet (+1.2 V).

Potentiometric flow-injection determination of trace hydrogen peroxide based on its induced reaction in iron(III)-iron(II) potential buffer containing bromide and molybdenum(VI)

A rapid and highly sensitive potentiometric flow-injection method for the determination of trace hydrogen peroxide was developed by use of an Fe(III)-Fe(II) potential buffer solution containing bromide and Mo(VI). The analytical method was based on a linear relationship between a concentration of hydrogen peroxide and a largely transient potential change of an oxidation-reduction potential electrode due to bromine generated by the reaction of hydrogen peroxide with the potential buffer solution. The oxidation of bromide to bromine by hydrogen peroxide occurred very rapidly with the assistance of Mo(VI) when Fe(II) existed in the potential buffer solution. It was estimated by batchwise experiments that hydroxyl radical, OH., was generated by the reaction of hydrogen peroxide with Fe(II) as an intermediate, and subsequently oxidized bromide to bromine. In a flow system, analytical sensitivities to hydrogen peroxide obtained by the detection of the transient change of potential were enhanced about 75 fold compared with those obtained by using the potential change caused by the reaction of hydrogen peroxide with the potential buffer solution without bromide and Mo(VI). Sensitivities increased with decreasing concentration of the Fe(III)-Fe(II) buffer in the reagent solution. The detection limit (S/N = 3) of 4 x 10(-7) M (13.6 ppb) was achieved by using the 1 x 10(-4) M Fe(III)-Fe(II) buffer containing 0.4 M NaBr, 1.0 M H(2)SO(4) and 0.5% (NH(4))(6)Mo(7)O(24). Analytical throughput was approximately 40 h(-1) and the RSD (n = 6) was 0.6% for measurement of 4 x 10(-6) M hydrogen peroxide. The proposed method was applied to the determination of hydrogen peroxide in real rainwater samples, and was found to provide a good recovery for H(2)O(2) added to rainwater samples.

Potentiometric flow-injection determination of trace chlorine based on its redox reaction with an iron(III)/iron(II) buffer

A very sensitive and rapid potentiometric determination of trace chlorine in water is described. The method is based on the transient potential changes which appears during the reduction of dissolved chlorin with an iron(III)/iron(II) potential buffer containing chloride and sulfuric acid. The sample is injected into a water carrier stream and merged with a stream of this potential buffer solution; chlorine is reduced during passage through a short reaction coil. The potential change from the baseline is measured with a flow-through ORP (oxidation-reduction potential) electrode. Potential changes (peak heights) are proportional to chlorine concentrations from 10−7 M to 10−5 M. The detection limit is 5 × 10−8 M (3.5 μgl−1 as Cl2). The sample throughput is 45 h−1. Reproducibility is in the range 2.5–1.1%. Results for potable water agree with those obtained by the o-tolidine method.

Morphology of poly (N-methylaniline) electrodeposited from different acid solutions

The electropolymerization of N-methylanilite was accomplished in five different acid solutions: HCl, HNO 3 , H 2 SO 4 , HBF 4 and HClO 4 . Although the electrical conductivity of each obtained poly(N-methylaniline) (PNMA) was on about the same order, the nucleation process and their morphologies were quite different. For the electropolymerization in the HCl, HNO 3 and H 2 SO 4 solutions, the 1D nucleation growth of PNMA took place resulting in a network structure of fibrils (for HCl) or irregular granular structures (for HNO, and H 2 SO 4 ). It was suggested that the PNMA growth in the HBF 4 and HClO 4 solutions was caused by the precipitation of the oligomer-coupling polymers. It was interesting to find that the surface of the PNMA obtained from the HClO 4 and HBF 4 solutions had spherical microparticles on the compact PNMA layer, whose diameters were in the range of 2-8 μm.

Potential response of poly(o-aminophenol) film electrode to dissolved ferric ion

Abstract Pory(o-aminophenol) (PoAP) film was electrodeposited on an indium-tin oxide electrode. The PoAP film electrode captured dissolved cations such as Fe3+ because of the coordination ability of the film. The redox potential of PoAP was lower than that of the Fe3+/Fe2+ redox couple, and Fe3+ ions captured were partially reduced to form Fe2+ in the film electrode. The electrode showed a Nernstian response to dissolved ferric ions. Although the PoAP film electrode captured Zn2+, Ni2+ and Cu2+, it showed no potential response to the corresponding cations because the corresponding reduced forms (Zn, Ni, Cu) were absent in the film.