Yoshihiko Tezuka

Concentration distribution of conducting species with time resolution in electrochemical undoping process at the polypyrrole-film-coated electrode in the light of electric percolation

Concentration distribution of conducting species of polypyrrole films in the electrochemical undoping process was determined by a spectroscopic method using a photodiode array in the simulated film experiment. A polypyrrole film in the doped state was set on an insulating glass plate and connected to an electrode at the end of the film. The length of the film corresponds to the film thickness in the ordinary experiment of film-coated electrodes. The film was reduced or undoped by the potential step. Absorbance responding to the potential step was monitored at 14 segments of the film by the photodiode array with effective spatial resolution of 0.36 mm. Then the concentration distribution of the oxidized conducting species was determined every 50 ms. The conversion occurred not only near the electrode but also at the top of the film. It stopped at the conversion ratio 0.87. 13% of the conducting species was left behind from the reduction in the uniform distribution. The incomplete conversion was attributed to electrical disconnection of conducting clusters from the electrode on the basis of the percolation theory.

Concentration profiles of conducting species in polypyrrole films in cyclic voltammetry by means of a diode array detector

The first scan effect, which makes the voltammetric anodic peak of conducting polymers sharp and shifted in the positive direction only on the first scan, was investigated by determining the time-dependent concentration distribution of conducting species of polypyrrole films by means of the UV-visible diode array system with spatial resolution of 0.36 mm. The film in the insulating state was set on a glass plate and connected to an electrode at the end of the film. This experimental set-up corresponds to magnifying the film thickness by three or four orders of magnitude. On the first positive scan, a steep part of the concentration profiles was propagated from the electrode towards the top of the film, exhibiting a clear phase boundary. The anodic peak of the voltammogram appeared at the time when the conducting front reached the top of the film. In contrast, the conversion during the negative scan proceeded uniformly over the film and stopped at a conversion ratio of 0.9, which was regarded as a threshold value of the electric percolation. The second positive scan made the profile smooth. The dependence of the profile on the scanning direction agreed with the voltammetric features. The faradaic component of the voltammogram was constructed from the profile, and compared with the ordinary voltammogram.

Alternation of conducting zone from propagation-control to diffusion-control at polythiophene films by solvent substitution

The conducting zone of polythiophene films grew under the propagation-control in acetonitrile solution at application of the positive potential to the reduced film whereas it grew under the diAusion-control when it was transferred into the propylene carbonate solution. The electrochemically polymerized film was peeled oA from the electrode, and a current feeder was connected to an end of the film. The distribution of the conducting species was detected with a diode array detector through the 850 nm beam irradiated to the film. When the fully reduced film was oxidized potentiostatically in the 0.1 M LiClO4+acetonitrile solution, the conducting zone developed linearly with the electrolysis time at almost a constant speed. This is in accord with the theory of the propagation of the conducting zone. When the reduced film was transferred into the 0.1 M LiClO4+propylene carbonate solution, the conducting zone grew exhibiting a vague boundary. Quantitative analysis said that the growth obeyed at first the propagation theory and then obeyed the square root of the time, represented by diAusion of dopant ions. The diAusion coeAcient was 310 ˇ10 cm 2 s ˇ1 . A new growth model was proposed, in which the filmvsolution interface was oxidized at first by the propagation mechanism and then the conducting zone was dispersed into the film center by diAusion. # 1999 Elsevier Science Ltd. All rights reserved.

Photo-crosslinking polymers by fullerene

Abstract Photochemical addition of furan derivatives to fullerene C60 was applied to the photo-crosslinking of polymers with C60. A polymer having furan units in the side chains was synthesized by the reaction of poly(2-hydroxyethylmethacrylate) with 2-furoic chloride. A 1,1,2,2-tetrachloroethane solution of the polymer was exposed to visible light in the presence of C60. The solution turned to a gel after 10 h and then solidified completely. The photo-crosslinking process was monitored in situ by dynamic viscoelasticity measurement.

Dispersion of the interface of a conducting insulating zone temporarily generated in a polypyrrole film

A partially oxidized polypyrrole film with a well-defined interface between the conducting and insulating zones is expected to become uniform when the current is interrupted. In practice, this homogenizing process is observed in conducting polymer batteries when they are charged or discharged instantaneously. This process was analyzed by spectroscopic determination of the concentration distribution of the conducting species in the film which was mounted on a glass plate and was connected to an electrode at the end of the film. The film was partially oxidized by applying an oxidation potential for a short time, and then the current was interrupted by disconnecting the electrode. During the anodic electrolysis, the conducting zone became larger, exhibiting a clear front. The localized conducting zone generated in this way was dispersed into the insulating zone under open-circuit conditions, leading to formation of a homogeneous film. The homogenization rate estimated from the speed of dispersion of the conducting zone was closely related to the concentration of the conducting species near the electrode. The proposed mechanism is that oxidation at the conducting front causes reduction near the electrode via a current flowing in the conducting zone. When the concentration of the conducting species near the electrode decreased to 20%, the homogenization stopped, resulting in a localized non-uniform distribution. This was defined as the limit of electric percolation.

Carbohydrate analysis of porcine thyroglobulin isoforms with different iodine contents.

To further validate the relationship between thyroid hormone formation and the carbohydrate structure of thyroglobulin (Tg), we reinvestigated the relationship between the iodine content and the asparagine-linked oligosaccharide structures of porcine Tg. Purified porcine Tg was further separated into isoforms (Tg-F1, -F2 and -F3) with a DEAE-cellulose ion-exchange chromatography column. The iodine residues, neutral sugar and sialic acid were analyzed for the separated Tg isoforms and their asparagine-linked oligosaccharide structures were analyzed. The asparagine-linked oligosaccharides were released from Tg-F1, -F2 and -F3 by hydrazinolysis and each oligosaccharide was labeled with p-aminobenzoic acid octyl ester (ABOE). The ABOE-labeled oligosaccharides from Tg-F1, -F2 and -F3 were analyzed for their relative content in oligosaccharides of each structure type by chemical methods and DEAE- and ConA high-performance liquid chromatography (HPLC) columns. As a result, it was revealed that the Tg fraction eluted at higher ionic strength from a DEAE-cellulose column is apt to contain more of each iodoamino acid, as well as total content of iodine, larger negative zeta-potential, conforming to sialic acid content in the Tg molecule and to a higher content of di-sialo-bi-antennary complex and to high mannose type oligosaccharides. These results support the conclusion that iodine organification of the Tg molecule is correlated with asparagine-linked oligosaccharide completion.

Photodecomposition of copolymers between 9-anthrylmethylmethacrylate and methymethacrylate by XeF excimer laser irradiation

Abstract Laser photodecomposition of copolymer films (9-anthrylmethylmethacrylate and methylmethacrylate polymerized at various ratios) and polymethylmethacrylate (PMMA) film doped with 9-anthrylmethylisobutylate (AMIB) (model compound of the copolymer) was studied using an XeF excimer laser (351 nm) with variation of the irradition fluence and pulse number. As the laser fluence (F) is increased, the etch rate for films with high dopant concentrations increases linearly with log F. For films with lower dopant concentrations, a steep increase in the etch rate is obtained at higher fluence. The molecular weight distribution of the fragments of the irradiated films was studied using high performance liquid chromatography (HPLC). For copolymer films, the higher molecular weight fraction is produced via photocrosslinking of anthryl groups in the polymer and the lower molecular weight fraction is generated via the simultaneous degradation of the polymer. However, for the dopant-dispersed films, the higher molecular weight fraction is not produced and only decomposition of the polymer occurs. Photodecomposition and photoablation of PMMA are caused by highly excited anthracene molecules attained via two or three multiphoton excitations. It is revealed that photothermal mechanism via multiphoton excitation has an important role in the photocrosslinking of the copolymer.

Photochemical reaction of furans in the presence of [60] fullerene

Abstract The first evidence was presented which supports a photochemical pathway during the reaction of furan derivatives in the presence of C60, which was formerly believed to proceed via a thermal [2+4]-concerted cycloaddition reaction of furans with C60. LD-TOF-MS, UV-vis, FT-IR and 1H-, 13C-NMR spectra showed that

Laser Flash Photolysis Studies on the Model System for Photo-Oxidation-Induced Polycondensation Polyimides with Fullerene C60

Laser flash photolysis studies were carried out to elucidate the quenching mechanism of the triplet state of fullerene C60 (3C60*) by furan-substituted diimides, which are the model compounds for photosensitive polyimides based on the photo-oxidation-induced polycondensation (POP) reaction. The decay kinetics of transient 3C60* triplet-triplet absorption at 740 nm revealed that the model diimides quenched 3C60* in γ-butyrolactone, with the quenching rate constants, kq(obsd), being determined to be on the order of 105 to 106 M-1s-1. The free-energy changes for electron transfer from the model diimides to 3C60*, ΔGet, and the calculated electron transfer rate constants, kq(calcd), were also evaluated from the Rehm-Weller equation using the oxidation potentials for the model diimides. The kq(obsd) values were found to be, on the whole, correlated with ΔGet and to be in fair agreement with the kq(calcd) values. These results indicate that the quenching reaction occurs primarily by electron transfer from the diimide to 3C60*. Furthermore, the kq(obsd) value for benzyl 2-furoate, which constitutes a part of the model diimide molecule was found to be small compared with those for the model diimides. We therefore drew the conclusions that the electron transfer occurs predominantly from the benzimido moiety to 3C60*, not from the furoate moiety and, consequently, the furoate moiety may not take part in electron transfer.

Evaluation of Tap Water Quality by Spectrofluorometry.

Spectrofluorometry was applied to the detection of micropollutants in tap water. Tap water contains a small quantity of humic substances, such as chlorinated fulvic acids. Survey of tap water in various parts of Japan revealed that raw water from the river in big cities contains relatively large quantities of those substances. A part of fluorescent substances is eliminated in the purification process and its fluorescence intensity is reduced by chlorination. Fluorescence intensity is also reduced by ozonation process, but changes little by subsequent chlorination. Thus, Ozone/AC (activated carbon) treatment enables us to reduce both fluorescence intensity and a trihalomethane formation potential. Tap waters in Japan show a lower fluorescence intensity, about 1/10 of those of various cities of the world. Although all the fluorescent substances are not always the chlorinated fulvic acid because of different disinfection processes in foreign countries, more attention should be paid to fluorescent substances in tap water.