Inhibiting Surface Diffusion to Synthesize 3D Bicontinuous Nanoporous N-Doped Carbon for Boosting Oxygen Reduction Reaction in Flexible All-Solid-State Al-Air Batteries

Catalyzing oxygen reduction reaction (ORR) and accelerating oxygen diffusion are two key challenges for the requirements of the cathode catalysts in the metal-air batteries. A promising strategy for improving both ORR performance and mass diffusion simultaneously is to build carbon-based catalysts with ORR-active chemical dopants and 3D interconnected porosity. Herein, a 3D nanoporous N-doped carbon with bicontinuous porosity and interconnected open-pore channels is reported, which is prepared by a polyaniline-assisted template method. The polyaniline can efficiently inhibit the surface diffusion-caused template coarsening, achieving a small pore size of 35 nm. The small porous morphology gives rise to a high N-dopant concentration up to 7.20 at.%, which in turn exhibits a commercial Pt/C-comparable ORR performance together with satisfied durability in alkaline media. Using these nanoporous carbon catalysts as air electrodes, an all-solid-state flexible Al-air battery is assembled with the measured maximum power density reaching 130.5 mW cm⁻², as compared to 106.2 mW cm⁻² when the commercial Pt/C standard is used. This study provides an efficient method to synthesize 3D N-doped carbon with bicontinuous nano-sized pore channels for wide-ranging applications in portable and flexible devices.     

Grafting of branched polymers onto nano-sized silica surface: Postgrafting of polymers with pendant isocyanate groups of polymer chain grafted onto nano-sized silica surface

To control the surface wettability of nano-sized silica surface, the postgrafting of hydrophilic and hydrophobic polymers to grafted polymer chains on the surface was investigated. Polymers having blocked isocyanate groups were successfully grafted onto nano-sized silica surface by the graft copolymerization of methyl methacrylate (MMA) with 2-(O-[1′-methylpropylideneamino]caboxyamino)ethyl methacrylate (MOIB) initiated by azo groups previously introduced onto the surface. The blocked isocyanate groups of poly(MMA-co-MOIB)-grafted silica were stable in a desiccator, but isocyanate groups were readily regenerated by heating at 150 °C. The hydrophilic polymers, such as poly(ethylene glycol) (PEG) and poly(ethyleneimine) (PEI), were postgrafted onto the poly(MMA-co-MOIB)-grafted silica by the reaction of functional groups of PEG and PEI with pendant isocyanate groups of poly(MMA-co-MOI)-grafted silica to give branched polymer-grafted silica. The percentage of grafting increased with increasing molecular weight of PEG, but the number of postgrafted chain decreased, because of steric hindrance. The hydrophobic polymers, such as poly(dimethylsiloxane) were also postgrafted onto poly(MMA-co-MOI)-grafted silica. It was found that the grafting of hydrophobic polymer and the postgrafting of hydrophilic polymer branches readily controls the wettability of silica surface to water.     

Pd-catalyzed hydrosilylation polymerization of a dihydrosilane with diyne/triyne mixed systems affording crosslinked silylene-divinylene polymers and their properties

Treatment of a dihydrosilane (methylphenylsilane, 1) with mixtures of a diyne (p- or m-diethynylbenzene, 2a or 2b) and a triyne (1,3,5-triethynylbenzene, 3a or B,B′,B″-triethynyl-N,N′,N″-trimethylborazine, 3b; 1:2:3=100:95:5, 100:90:10, 100:80:20) in the presence of Pd-PCy₃ (Cy=cyclohexyl) catalyst gave new crosslinked silylenedivinylene polycarbosilanes. In TGA the resulting crosslinked polymers tended to show higher Td₅ values and higher char yields than the corresponding linear polymers. On the other hand, UV/vis absorption spectra of the crosslinked polymers obtained in the reactions of 2a or 2b with 3a exhibited increased broad peaks around 390 nm for 2a or 360 nm for 2b. Coincidently, their fluorescence spectra showed significant increase of the emission peaks in 400-550 nm. The crosslinked polymer derived from 2a and 3b, however, showed decrease of the absorption peak around 390 nm and profound depression of fluorescence peaks in 400-550 nm.     

Kinetically Stable Bicelles with Dilution Tolerance,Size Tunability,and Thermoresponsiveness for Drug Delivery Applications

Mixtures of a phospholipid (1,2‐dipalmitoyl‐sn‐glycero‐3‐phosphatidylcholine, DPPC) and a sodium‐cholate‐derived surfactant (SC‐C₅) at room temperature formed phospholipid bilayer fragments that were edge‐stabilized by SC‐C₅: so‐called “bicelles”. Because the bilayer melting point of DPPC (41 °C) is above room temperature and because SC‐C₅ has an exceptionally low critical micelle concentration (<0.5 mm ), the bicelles are kinetically frozen at room temperature. Consequently, they exist even when the mixture is diluted to a concentration of 0.04 wt %. In addition, the lateral size of the bicelles can be fine‐tuned by altering the molar ratio of DPPC to SC‐C₅. On heating to ≈37 °C, the bicelles transformed into micelles composed of DPPC and SC‐C₅. By taking advantage of the dilution tolerance, size tunability, and thermoresponsiveness, we demonstrated in vitro drug delivery based on use of the bicelles as carriers, which suggests their potential utility in transdermal drug delivery.     

Adaptive optics instrumentation in submillimeter/terahertz spectroscopy with a flexible polyvinylidene fluoride cladding hollow waveguide

A simple instrument has been developed to carry out temperature dependent submillimeter/terahertz-wave spectroscopy using a polyvinylidene fluoride flexible hollow waveguide and an eggplant-shape launching lens.     

Chemical (Sr,Co)-doping effect on critical current density for Dy123 melt-solidified bulks

The dilute impurity doping for CuO-chain site was found to largely improve the critical current properties of both Y123 single crystals and Y123 melt-solidified bulks in our previous study. In addition, dilute Sr-doping to Ba site is also effective for enhancement of J_c without serious decrease in T_c as in the case of dilute Zn doping for CuO₂-plane site. In the present study, we have attempted further enhancement of flux pinning force of the Dy123 melt-solidified bulk, which is essentially more promising materials than Y123, by impurity doping for Cu site in the CuO-chain and for Ba site. Although the (Sr,Co)-co-doped Dy123 melt-solidified bulks showed systematically suppressed T_c with their doping levels, high T_c's well exceeding 90 K were maintained. All the Sr-doped or Co-doped Dy123 bulks exhibited higher J_c than the undoped one. More improved J_c properties were achieved by (Sr,Co)-co-doping, suggesting that pinning potential at local regions around doped impurities become deeper by Co-doping, resulting in stronger point-defect-like pinning sites. In addition, more detailed studies on the dilute Sr-doping and the dilute (Sr,Co)-Co-doping were carried out for Y123 single crystals in order to clarify the difference between their doping effects on the J_c properties. The vortex transition field, H^*, to the disordered state in the M–H loops for the Co-doped Y123 single crystal was located at the lower field than that of the Sr-doped one, meaning that the Co ions strongly affect the vortex system compared with the Sr ions.     

The YXXL sequences of a transmembrane protein of bovine leukemia virus are required for viral entry and incorporation of viral envelope protein into virions

The cytoplasmic domain of an envelope transmembrane glycoprotein (gp30) of bovine leukemia virus (BLV) has two overlapping copies of the (YXXL)2 motif. The N-terminal motif has been implicated in in vitro signal transduction pathways from the external to the intracellular compartment and is also involved in infection and maintenance of high viral loads in sheep that have been experimentally infected with BLV. To determine the role of YXXL sequences in the replication of BLV in vitro, we changed the tyrosine or leucine residues of the N-terminal motif in an infectious molecular clone of BLV, pBLV-IF, to alanine to produce mutated proviruses designated Y487A, L490A, Y498A, L501A, and Y487/498A. Transient transfection of African green monkey kidney COS-1 cells with proviral DNAs that encoded wild-type and mutant sequences revealed that all of the mutated proviral DNAs synthesized mature envelope proteins and released virus particles into the growth medium. However, serial passages of fetal lamb kidney (FLK) cells, which are sensitive to infection with BLV, after transient transfection revealed that mutation of a second tyrosine residue in the N-terminal motif completely prevented the propagation of the virus. Similarly, Y498A and Y487/498A mutant BLV that was produced by the stably transfected COS-1 cells exhibited significantly reduced levels of cell-free virion-mediated transmission. Analysis of the protein compositions of mutant viruses demonstrated that lower levels of envelope protein were incorporated by two of the mutant virions than by wild-type and other mutant virions. Furthermore, a mutation of a second tyrosine residue decreased the specific binding of BLV particles to FLK cells and the capacity for viral penetration. Our data indicate that the YXXL sequences play critical roles in both viral entry and the incorporation of viral envelope protein into the virion during the life cycle of BLV.     

Effect of Gallia Addition on the Sintering Behavior of Samaria-Doped Ceria

Samaria-doped ceria (SDC) was prepared by using the solid-state reaction method. Sintering of SDC was significantly promoted by adding a small amount of gallium. SDC that had 1% of gallium added, sintered at 1450°C, showed almost the same properties as SDC sintered at 1600°C. Measurements showed that the addition of gallia could reduce the sintering temperature by 150°C without deteriorating the properties of SDC as an electrolyte for solid oxide fuel cells.     

Controlling Ion‐Transport Selectivity in Gold Nanotubule Membranes

We have developed a new class of synthetic membranes that consist of a porous polymeric support. This support contains an ensemble of gold nanotubules that span the complete thickness of the support membrane. The support is a commercially available microporous polycarbonate filter with cylindrical nanoscopic pores. The gold nanotubules are prepared via electroless deposition of Au onto the pore walls, and tubules that have inside diameters of molecular dimensions (<1 nm) can be prepared. Hence, these membranes are a new class of molecular sieves. We review in this paper the ion‐transport properties of these Au nanotubule membranes. We will show that these membranes can be cation‐permselective or anion‐permselective, and that the permselectivity can be reversibly switched between these two states. Ion permselectivity can be introduced by two different routes. The first entails chemisorption of an ionizable thiol, e.g., a carboxylated or ammonium‐containing thiol to the Au tubule walls. If the thiol contains both of these functionalities (e.g., the amino acid cysteine), the permselectivity can be reversibly switched by varying the pH of the contacting solution phase. Ion permselectivity can also be introduced by potentiostatically charging the membrane in an electrolyte solution. By applying excess negative charge, cation permselective membranes are obtained, and excess positive charge yields anion permselective membranes. In this case the permselectivity can be reversibly switched by changing the potential applied to the membrane.     

Monomolecular layer epitaxy of GaAs for ideal static induction transistor

An ideal static induction transistor (ISIT) structure was fabricated using molecular layer epitaxy (MLE). The doping method of MLE enabled us to achieve a sufficiently high level of doping for ISIT fabrication. In the fabrication process a low growth temperature was very important for the device structure, which requires very sharp dopant profiles. For the ISIT, two MLE processes, namely source–drain growth and gate regrowth, were required. The electrical characteristics of the source–drain were changed after heat treatment at a temperature higher than 480°C. The effect of the redistribution of dopants of the source–drain structure (n⁺⁺–i–p⁺⁺–i–n⁺) during gate regrowth was clearly shown by SIMS (secondary ion mass spectroscopy) measurements for various temperatures of heat treatment. As a result the doped Se diffused from the n⁺⁺ source region to the other layers and the doped Zn diffused from the p⁺⁺ layer to the i-layers. The source was a heavily Se-doped layer at the doping level of (2–3)×10¹⁹ cm⁻³ containing a larger amount of interstitial Se atoms in the lattice. The redistribution of Se from the heavily doped region was detectable even after heat treatment at 480°C for 30 min. For the p⁺⁺ layer the profile of the C-doped layer was stable even after heat treatment at 620°C for 30 min, but the profile of Zn changed markedly after heat treatment at 480°C for 30 min. In addition, the carbon-doped p⁺⁺ layer acted as a gettering layer for diffused interstitial Se from the source region. The driving force of the redistribution of dopants results in the electric field in the device structures. © 1997 John Wiley & Sons, Ltd.