Electrochemically instantaneous reduction of conducting polyaniline-coated latex particles dispersed in acidic solution

A cathodic voltammetric wave was observed in an aqueous suspension of mono-dispersed, spherical polyaniline-coated polystyrene particles, whereas no anodic wave was detected. This irreversibility was common to particles with eight different diameters ranging from 0.2 to 7.5 μm. Such irreversibility cannot be found at polyaniline-coated electrodes, and thus is a property of the dispersion of polyaniline latex. The reduction current was controlled by diffusion of dispersed particles. The reduction, being the conversion from the electrical conducting state to the resistive one, should begin at a point of contact between the conducting particle and the electrode in order to be propagated to the whole particle rapidly. In contrast, the oxidation proceeds slowly with the propagation of conducting zone, during which Brownian motion lets the particle detach from the electrode. The number of loaded aniline units per particle, determined by weight analysis, ranged from 6 × 10⁶ (Ø 0.2 μm) to 3 × 10¹¹ (Ø 7.5 μm) and was proportional to 2.9 powers of the particle diameter. The diffusion-controlled current of the cathodic wave was proportional to 2.4 powers of the diameter. The difference in these powers, 0.5, agreed with a theoretical estimation of the diffusion-controlled current, the diffusion coefficient for which was given by the Stokes-Einstein equation.     

Recovery of neutron-induced damage of SiC by thermal annealing up to 1400 °C

Recovery of the specimen length of neutron-irradiated SiC was observed using a precision dilatometer. The specimens were heated isothermally and isochronally. The accuracy of length measurement at high temperature using the dilatometer was compared with that of length measurement at room temperature using a micrometer. It was clarified that the dilatometer method showed high accuracy and stability. The dilatometer method was applied to observe length recovery by isothermal annealing at 1200 °C of the neutron-irradiated SiC, and at least two recovery rates were clarified.     

Effect of Neutron Irradiation on Knoop Microhardness Anisotropy in MgO·3Al2O3 Single Crystals

MgO·3Al₂O₃ single crystals were irradiated with neutron fluences of 8.3 × 10²² n/m² at 100°C and 2.4 × 10²⁴ n/m² at 470°C ( E > 1.0 MeV) in the Japan Materials Testing Reactor. The Knoop microhardness of several orientations on the (100) plane of both the irradiated and unirradiated crystals were measured with different indentation loads. The change in hardness profile of the crystals was almost the same after the two irradiation conditions. The hardness increased by 4–15% because of the irradiations depending on the crystallographic orientation, the larger change being observed at orientations between the (001) and (011) directions. While both the {111}     and {110}     slip systems are simultaneously active in the unirradiated MgO·3Al₂O₃, the {111}     system may be the dominant slip system in the neutron-irradiated crystals. It is concluded that the restriction of the {110}     slip system is caused by irradiation-induced interstitial ions.     

Construction and development of a time-resolved x-ray magnetic circular dichroism-photoelectron emission microscopy system using femtosecond laser pulses at BL25SU SPring-8

A femtosecond pulsed laser system has been installed at the BL25SU soft x-ray beamline at SPring-8 for time-resolved pump-probe experiments with synchronization of the laser pulses to the circularly polarized x-ray pulses. There are four different apparatuses situated at the beamline; for photoemission spectroscopy, two-dimensional display photoelectron diffraction, x-ray magnetic circular dichroism (XMCD) with electromagnetic coils, and photoelectron emission microscopy (PEEM). All four can be used for time-resolved experiments, and preliminary investigations have been carried out using the PEEM apparatus to observe magnetization dynamics in combination with XMCD. In this article, we describe the details of the stroboscopic pump-probe XMCD-PEEM experiment, and present preliminary data. The repetition rate of the laser pulses is set using a pulse selector to match the single bunches of SPring-8's hybrid filling pattern, which consists of several single bunches and a continuous bunch train. Electrons ejected during the bunch train, which do not provide time-resolved signal, are eliminated by periodically reducing the channel plate voltage using a custom-built power supply. The pulsed laser is used to create 300 ps long magnetic field pulses, which cause magnetic excitations in micron-sized magnetic elements which contain magnetic vortex structures. The observed frequency of the motion is consistent with previously reported observations and simulations.     

Voltammetric potentials of polyaniline varying with electric percolation

The reduction of the emeraldine form of polyaniline film into leucoemeraldine, which corresponds to the conversion of an electric conductor into an insulator, shifted in the positive direction with increasing scan rate and film thickness. Similar dependence was found in the diffusion-controlled voltammograms of dispersed polyaniline latex particles with eight diameters ranging from 0.2 to 7.5 μm. The particles were synthesized by coating dispersed polystyrene latex with polyaniline. These variations were explained in terms of electric percolation of the conducting species to the electrode. The theoretical expression for the Nernst equation was derived on the assumption that the percolated and the un-percolated conducting species took inner potentials of the electrode and the solution phase, respectively. The conducting species does not participate in the determination of the equilibrium potential, though it participates in the Faradaic current. The cathodic peak potential shifted in the negative direction with an increase in particle size, solution viscosity, and film thickness, as predicted from the derived Nernst equation.     

Electron microscope study of the formation of graphitic nanostructures in nickel-loaded wood char

We investigated the graphitization of carbonized larch wood chars impregnated with aqueous solution of nickel acetate, using scanning electron microscopy (SEM), both in secondary and transmission modes, and high-resolution transmission electron microscopy (HRTEM). Heat treatment of the chars at 500 °C brought about homogeneous distribution of metallic Ni particles about 5 nm in size in the amorphous carbon matrix. Graphitization sporadically started at this temperature, and some of the Ni particles are aggregated. SEM observations on chars heat-treated at 900 °C suggested that graphitic nanoshells about 50–200 nm in diameter, formed by catalytic effects of the Ni particles, grow in a “meandering” manner inside the amorphous carbon matrix. Some graphitic protrusions are found to grow outwards. Upon removal of the residual amorphous carbon matrix, long chains of the graphitic nanoshells exhibited a three-dimensionally intertwined structure, while transmission SEM showed that the interior of the shells is empty. HRTEM images exhibited not only stacked graphitic layers, but also cross-sectional contrasts expected from the hexagonal net of the graphite structure. These findings are discussed from the viewpoints of processing parameters, such as the use of aqueous solutions and atmosphere, specific to the catalytic graphitization of lignocellulosic materials.     

Properties of blends of syndiotactic-rich and atactic poly(vinyl alcohols)

The crystallinity, solubility, degree of swelling, and hygroscopicity of the blends of syndiotactic-rich (st-PVA) and atactic poly(vinyl alcohols) (at-PVA) were studied. The crystallinity of the blends increased with increasing annealing temperature and that of the blends annealed at 200°C was larger than that of at-PVA. In the 200°C annealed blends containing st-PVA about 50%, the insoluble fraction in boiling water was larger than the fraction of st-PVA in each blend. The soluble fraction for the blend containing 75% st-PVA was 1.7%. The moisture regain of the blends was less than that of at-PVA.     

Mechanism of color breakup in field-sequential-color projectors

Abstract— To investigate color breakup in field-sequential-color projectors, we measured the threshold of color fusion frequency relative to retinal velocity of the moving edge on the color flicker field. The characteristic changed as the velocity approached saccade. The result suggests that the mechanism of color breakup differs according to the velocity of the image on the retina.     

Saccharomycodes ludwigii has seven chromosomes

Tetrad distributions for 108 different gene pairs in 1346 asci of 113 diploids heterozygous for various combinations of 24 genes in Saccharomycodes ludwigii were investigated. Tetratype tetrads occurred only rarely and the 24 genes tested were classified into seven linkage groups. Electrophoretic karyotypes of three independent strains of S'codes ludwigii showed seven bands of chromosome-sized DNA having molecular sizes of 0·8 to 2·3 Mb with strain-specific polymorphic chromosomal DNAs as determined based on their migration distances.