Synthesis and characterization of proton‐conducting copolyimides bearing pendant sulfonic acid groups

A series of sulfonated copolyimides (co‐SPIs) bearing pendant sulfonic acid groups were synthesized from 1,4,5,8‐naphthalenetetracarboxylic dianhydride (NTDA), bis(3‐sulfopropoxy) benzidines (BSPBs), and common nonsulfonated diamines via statistical or sequenced polycondensation reactions. Membranes were prepared by casting their m‐cresol solutions. The co‐SPI membrane had a microphase‐separated structure composed of hydrophilic and hydrophobic domains, but the connecting behavior of hydrophilic domains was different from that of the homo‐SPIs. The co‐SPI membranes displayed clear anisotropic membrane swelling in water with negligibly small dimensional changes in the plane direction of the membrane. With water uptake values of 39–94 wt %, they showed dimensional changes in membrane thickness of about 0.11–0.58, which were much lower than those of homo‐SPIs. The proton conductivity σ values of co‐SPI membranes with ion exchange capacity values ranging from 1.95–2.32 meq/g increased sigmoidally with increasing relative humidity. They displayed σ values of 0.05–0.16 S/cm at 50 °C in liquid water. Increasing temperature up to 120 °C resulted in further increase in proton conductivity. The co‐SPI membranes showed relatively good conductivity stability during the aging treatment in water at 100 °C for 300 h. © 2005 Wiley Periodicals, Inc. J Polym Sci Part A: Polym Chem 43: 1545–1553, 2005     

Note on Norm and Pointwise Convergence of Exponential Products and their Integral Kernels for the Harmonic Oscillator

The aim of this paper is to study the exponential symmetric product formula for the semigroup of the one-dimensional harmonic oscillator to discuss its convergence pointwise of the integral kernels as well as in norm with sharp optimal error bound.      

Transparent conductive films based on polymer composites containing the mixed‐valence tetrathiafulvalene nanofibers

We report the facile preparation of the conductive polymer composites containing the mixed‐valence tetrathiafulvalene (TTF) nanofibers and their applications as all‐organic transparent conductive materials. TTF can be used as a nanofiller for transforming conventional polymers to conductive materials. Self‐assemble nanofibers of the neutral and radical cation of TTF can be formed in the polymer solutions during the film deposition, and the resulting composite films with several micron thickness can serve as the conductive material with high transparency. Several kinds of conventional polymers, such as polystyrene, poly(methyl methacrylate) (PMMA), and poly(vinylpyrrolidone), can be used as a polymer matrix of the composites. The conductivities of the PMMA film containing 35 mol % of the mixed‐valence TTF and the PEDOT–PSS film showed similar values (2.8 × 10^–2 and 5.4 × 10^–1 S/cm, respectively). In contrast, the normalized transmittance of the PMMA film by 1‐μm thickness greatly increased (96%/μm) when compared with that of the PEDOT–PSS film (10%/μm). In addition, the degradation of the conductivity of the nanofibers by heating and aging was effectively suppressed in the composite samples. © 2009 Wiley Periodicals, Inc. J Polym Sci Part A: Polym Chem 47: 6441–6450, 2009     

Distribution of uranium in human lungs

Several human lung samples were dissected into lobes and uranium and silicon contents in each lobe were determined by the fission track method and the inductively coupled plasma-atomic emission spectrometry (ICP-AES), respectively. It was found that both uranium and silicon concentrations were high in the upper lobe compared with those in the lower one. Though the tendency may be mainly interpreted by the deposition way of airborne dust in the lung, the higher U/Si concentration ratio in the upper part than that in the lower part of lungs may suggest the partial removal of uranium deposited in the lower part of the tissue.     

Discovery of Hexagonal Structured Pd–B Nanocrystals

We report on hexagonal close-packed (hcp) palladium (Pd)–boron (B) nanocrystals (NCs) by heavy B doping into face-centered cubic (fcc) Pd NCs. Scanning transmission electron microscopy–electron energy loss spectroscopy and synchrotron powder X-ray diffraction measurements demonstrated that the B atoms are homogeneously distributed inside the hcp Pd lattice. The large paramagnetic susceptibility of Pd is significantly suppressed in Pd–B NCs in good agreement with the reduction of density of states at Fermi energy suggested by X-ray absorption near-edge structure and theoretical calculations.     

Effect of cation doping on ionic and electronic properties for lanthanum silicate-based solid electrolytes

Electronic as well as ionic conducting properties for oxyapatite-type solid electrolytes based on lanthanum silicate, La_9.333 + xSi₆O_26 + 1.5x (LSO) were investigated in the oxygen-excess region (x > ca. 0.3). We have found that the oxygen excess-type LSO (OE-LSO), namely La₁₀Si₆O₂₇ on weighted basis, exhibited high conductivity, and substitution of the Si-site of LSO with some dopants (Mⁿ⁺) had a positive effect toward the conducting property. Furthermore, it was also found that addition of a very small amount of iron ions into the M-doped OE-LSO, La₁₀(Si_6-yMⁿ⁺_y)O_27-(2-0.5n)y, improved its conductivity. On the other hand, replacement of the La-site with various ions for La₁₀(Si_6-yMⁿ⁺_y)O_27-(2-0.5n)y did little to improve conductivity. The electronic transport numbers for Al-doped OE-LSO with Fe-addition, (1-α){La₁₀(Si_5.8Al_0.2)O_26.9}-α(FeO_γ), evaluated with the Hebb-Wagner polarization method were very low: i.e., 1.1 × 10^− 3 and 2.9 × 10^− 3 under P(O₂) = 1.1 × 10⁴ Pa at 1073 K for α = 0.00 and 0.005, respectively. Conductivity for each sample was unchanged under humidified atmosphere at 1073 K sustained for over 50 h, revealing that both compositions were chemically stable. It was concluded that 0.995{La₁₀(Si_5.8Al_0.2)O_26.9}-0.005(FeO_γ) is suitable for the fuel cell electrolytes because of its high and almost pure ionic conductivity, and its good chemical stability under humidified as well as reducing conditions.     

Mesoscopic nanomaterials generated by interfering femtosecond laser processing

Mesoscopic nanomaterials with a size ranging from a few nanometers to hundreds of nanometers were generated on a metallic thin film by interfering femtosecond (fs) laser processing. Because the nanomaterials seemed to demonstrate liquid behavior, we named their structure nano water drop. The structure is considerably similar to that of a real water drop observed with a high-speed camera. Using the phase shift between interfering beams, a duplicate structure was generated. This is a new surface modification technique, using a top-down approach.     

Enhancement of the electrocatalytic O2 reduction on Pt–Fe alloys

The design of high performance cathode electrocatalysts is essential for polymer–electrolyte fuel cells, which are now attracting enormous interest as a primary power source for zero-emission electric vehicles. We have discovered a significant enhancement of electrocatalytic activity of Pt by alloying with Fe, and found a maximum activity at ca. 50% Fe content, which results in 25 times higher activity than pure Pt activity. It was confirmed experimentally at Pt–Fe bulk alloys that the alloy catalyst surface consists of a pure Pt skin-layer (<1 nm in thickness) that is modified in the electronic structure by that of the bulk alloy. The enhancement could be well explained by the 5d-vacancy of the surface, but not by Pt interatomic distance or roughening of the surfaces.