Fracture toughness of silica particulate‐filled epoxy composite

The relationship between the postcuring conditions and fracture toughness on three silica particulate‐filled epoxy composites was investigated. The glass transition temperature, T_g, and the fragility parameter, m, derived from the thermo‐viscoelasticity, were used to characterize the composites, which were postcured under various conditions. The glass transition temperature and fragility both depended on both of the curing conditions and the volume fraction of silica particles. The glass transition temperature increased with the postcuring time and temperature, while the fragility generally decreased as the volume fraction increased. There was no direct correlation between the glass transition temperature and fragility. The fracture toughness depended on both the glass transition temperature and fragility. The composites with a high glass transition temperature and low fragility had high fracture toughness. These results indicate that the glass transition temperature and fragility are useful parameters for estimating the fracture toughness of the silica particulate‐filled epoxy composites. © 2002 Wiley Periodicals, Inc. J Appl Polym Sci 86: 2261–2265, 2002     

Electrochemical formation of AlN in molten LiCl-KCl-Li3N systems

Electrochemical formation of aluminum nitride was investigated in molten LiCl-KCl-Li₃N systems at 723 K. When Al was anodically polarized at 1.0 V (versus Li⁺/Li), oxidation of nitride ions proceeded to form adsorbed nitrogen atoms, which reacted with the surface to form AlN film. The obtained nitrided film had a thickness of sub-micron order. The obtained nitrided layer consisted of two regions; the outer layer involving AlN and aluminum oxynitride and the inner layer involving metallic Al and AlN. When Al electrode was anodically polarized at 2.0 V, anodic dissolution of Al electrode occurred to give aluminum ions, which reacted with nitride ions in the melt to produce AlN particles (1-5 μm of diameter) of wurtzite structure.     

Hemicellulose Composition in Different Cell Wall Fractions Obtained using a DMSO/LiCl Wood Solvent System and Enzyme Hydrolysis

In our previous studies on the relationships between lignin structure and hemicellulose composition in a wide range of hardwood species, we showed that the higher the syringyl ratio, the higher the xylan/mannan ratio. In this study, the relationship of the syringyl ratio and xylan/mannan ratio was further studied using fractions obtained by stepwise extraction of finely milled beech wood by use of aqueous dioxane and subsequent dimethyl sulfoxide (DMSO)/LiCl solvents with increasing LiCl concentration. Each soluble fraction obtained with a different LiCl concentration was compared with the corresponding insoluble residue, and it was shown that both the syringyl ratio and xylan/mannan ratio were always higher in the insoluble fraction. To analyze polysaccharides closely located with lignin, milled wood lignin (MWL), and cellulolytic enzyme lignin (CEL) obtained by enzyme treatment after DMSO/LiCl swelling were investigated. Although the xylan/mannan ratio of MWL was higher, that of CEL with more than 80% lignin yield was lower.     

Demulsification of oil-in-water emulsion under freezing conditions: Effect of crystal structure modifier

The demulsification of oil-in-water (O/W) emulsions under freezing conditions is connected to fat crystallization in the oil droplet. Therefore, demulsification can be prevented by the use of oil with a low melting point, and also by lowering the O/W ratio. However, an oil with a low melting point, such as sunflower, is rather expensive, and the O/W ratio has a significant effect on the texture of emulsions. We searched for an oil that is suitable for the production of a freeze-stable emulsion and found that soybean oil has unique characteristics. Normally, emulsions are more unstable at lower temperatures; soybean oil emulsion is unstable at −10°C and stable at −20°C. This unique characteristic results from the following two reasons. First, the solid fat content of soybean oil is almost the same at −10 and −20°C. Second, small crystals form a larger network over a period of time, and the higher temperature promotes faster restructuring. This structure formation was microscopically observed with the use of a thermostated stage. Structure formation was suppressed with the addition of a crystal structure modifier, polyglycerol fatty acid full ester, which also suppressed coalescence.     

Reducing the Photocatalytic Activity of Zinc Oxide Quantum Dots by Surface Modification

The use of zinc oxide (ZnO) nanoparticles as ultraviolet (UV) absorbers for many organic substrates is limited because of the high photocatalytic activity of ZnO. In this study, a facile and efficient technique for the preparation of a hybrid material of silica-coated ZnO nanoparticles was used to reduce the photocatalytic activity of ZnO. Monodispersed ZnO nanopartcles were prepared by wet chemistry and the particle surface was modified by tetraethylorthosilicate to form a silica coating via the Stöber method. ZnO samples, both before and after the coating process, were investigated by transmission electron microscopy, X-ray diffraction, dynamic light scanning, infrared, and UV-Vis absorption spectroscopy. The effect of the surface modification on the photocatalytic activity of ZnO was studied by monitoring the degradation of Rhodamine B caused by photo-generated free radicals. The results implied that the photo-generation of free-radicals was strongly quenched by the presence of silica on the particle surface.     

Synthesis and thermal cure of high molecular weight polybenzoxazine precursors and the properties of the thermosets

High molecular weight polybenzoxazine precursors have been synthesized from aromatic or aliphatic diamine and bisphenol-A with paraformaldehyde. The precursors were obtained as soluble white powder. Molecular weight was estimated from the size exclusion chromatography to be several thousands. The structure of the precursors was confirmed by IR, ¹H NMR and elemental analysis, indicating the presence of cyclic benzoxazine structure. The ratio of the ring-closed benzoxazine structure and the ring-opened structure in the high molecular weight precursor was estimated from ¹H NMR spectrum and also from the exotherm of DSC, showing that the ratio of the ring-closed benzoxazine structure was 77–98%. The precursor solution was cast on glass plate, giving transparent and self-standing precursor films, which was thermally cured up to 240 °C to give brown transparent polybenzoxazine films. The toughness of the crosslinked polybenzoxazine films from the high molecular weight precursors was greatly enhanced compared with the cured film from the typical low molecular weight monomer. Tensile measurement of the polybenzoxazine films revealed that polybenzoxazine from aromatic diamine exhibited the highest strength and modulus. While, polybenzoxazine from longer aliphatic diamine had higher elongation at break. The viscoelastic analyses showed that the glass transition temperature of the polybenzoxazines derived from the high molecular weight precursors were as high as 238–260 °C. Additionally, these novel polybenzoxazine thermosets showed excellent thermal stability.     

Micro machining for control of wettability with surface topography

A micro fabrication is presented to manufacture hydrophobic surfaces with micro-scale structures. Hydrophobicity is controlled with the shape and the alignment of micro pillars in the structure. The structures are manufactured in large areas at high production rates in the following processes: (1) the structure is fabricated on a tool by focused ion beam sputtering; (2) the reverse structure is formed on a metal plate by incremental stamping using the structured tool; and (3) the structure is transferred onto plastic plates by molding. A consecutive stamping is also proposed to fabricate several structures on a surface accurately with a structured tool, in which the moving pitch of the structured tool is numerically controlled. The effect of the surface topography on hydrophobicity is discussed with measuring contact angles on the structured surfaces in the water droplet tests. Hydrophobicity on the plastic plate is associated with the solid fraction on the structured surface based on the Cassie–Baxter model. A larger contact angle is observed for a smaller solid fraction of the surface.     

Exchange rate constants of invisible protons in proteins determined by NMR spectroscopy

Although labile protons that are exchanging rapidly with those of the solvent cannot be observed directly, their exchange rate constants can be determined by indirect detection of scalar-coupled neighboring nuclei. We have used heteronuclear NMR spectroscopy to measure the exchange rate constants of labile protons in the side chains of lysine and arginine residues in ubiquitin enriched in carbon-13 and nitrogen-15 at neutral pH. Exchange rate constants as fast as 40x10(3) s(-1) were thus measured. These results demonstrate that NMR spectroscopy is a powerful tool for the characterization of lysine NH3(+) and arginine NH groups in proteins at physiologically relevant pH values.     

Re-evaluation of Radiation-Energy Transfer to an Extraction Solvent in a Minor-Actinide-Separation Process Based on Consideration of Radiation Permeability

ABSTRACT

Absorbed-dose estimation is essential for evaluation of the radiation tolerance of minor-actinide-separation processes. We propose a dose-evaluation method based on radiation permeability, with comparisons of heterogeneous structures seen in the solvent-extraction process, such as emulsions forming in the mixture of the organic and aqueous phases. A demonstration of radiation-energy-transfer simulation is performed with a focus on the minor-actinide-recovery process from high-level liquid waste with the aid of the Monte Carlo radiation-transport code PHITS. The simulation results indicate that the dose absorbed by the extraction solvent from alpha radiation depends upon the emulsion structure, and that from beta and gamma radiation depends upon the mixer-settler-apparatus size. Non-negligible contributions of well-permeable gamma rays were indicated in terms of the plant operation of the minor-actinide-separation process.