Enhanced performance of organic light-emitting diodes by inserting wide-energy-gap interlayer between hole-transport layer and light-emitting layer

We demonstrated that driving voltages, external quantum efficiencies, and power conversion efficiencies of organic light-emitting diodes (OLEDs) are improved by inserting a wide-energy-gap interlayer of (4,4′-N,N′-dicarbazole)biphenyl (CBP) between a hole-transport layer of N,N-di(naphthalen-1-yl)-N,N′-diphenyl-benzidine (α-NPD) and a light-emitting layer of tris(8-hydroxyquinoline)aluminum. By optimization of CBP thicknesses, the device with a 3-nm-thick CBP layer had the lowest driving voltage and the highest power conversion efficiency among the OLEDs. We attributed these improvements to enhancement of a carrier recombination efficiency and suppression of exciton–polaron annihilation. Moreover, we found that the degradation of the OLEDs is caused by decomposition of CBP molecules and excited-state α-NPD molecules.     

Plastic deformation and creep damage evaluations of type 316 austenitic stainless steels by EBSD

The inspection method of plastic and/or creep deformations has been required as the quantitative damage estimation procedure for structural components especially used in electric power plants. In this study, the method using electron backscatter diffraction (EBSD) was applied to the deformation and damage evaluation of austenitic stainless steels strained by tension or compression at room temperature and also tested in creep at high temperature. It was found that the value of Grain Average Misorientation (GAM) which showed the average misorientation for the whole observed area including over several dozen grains, was a very useful parameter for quantifying the microstructural change as either the plastic or creep strain increased. The unique linear correlation was obtained between GAM and plastic strain in tension and compression. For creep damage evaluation, the difference of grain average misorientation from the value of the unstrained specimen (ΔGAM) showed an excellent correlation with the inelastic strain below strain at which the tertiary creep began.     

Encapsulation of glucose oxidase (GOD) in polyelectrolyte complexes of chitosan–carrageenan

The purpose of this study was to investigate the potential ability of carrageenan (κ-, ι-, λ-) and chitosan to form a controlled-release system for glucose oxidase (GOD). GOD was encapsulated in chitosan/carrageenan complexes at charge ratios (+/?) of 3 and 5 in mildly acidic solution. The encapsulation efficiency and activity of the loaded GOD were investigated. Among the different complexes prepared, chitosan/κ-carrageenan complex showed high encapsulation efficiencies of 79% and 62.5% at charge ratios of 3 and 5, respectively. The order of encapsulation efficiency decreases toward chitosan/λ-carrageenan complex (κ > ι > λ). After treatment with chitosanase and pepsin solutions, the activity of encapsulated glucose oxidase (GOD) was preserved for all complexes. The chitosan/κ-carrageenan complex was able to preserve 80.2% of GOD activity in pH 1.2 solution, 73.3% in chitosanase solution and 66.4% in pepsin solution. Controlled release of GOD was observed when the complexes were treated with different physiological and enzyme solutions; the complex of chitosan/κ-carrageenan had the lowest release rate of GOD. The simple preparation of chitosan/carrageenan complexes and their ability to protect protein integrity under acidic conditions make them a promising drug delivery system for the oral administration of peptides and proteins.     

Enhancement of the actuation performance of dielectric triblock copolymers modified with additives

To enhance actuation performance without prestrain, an elastomeric acrylic triblock copolymer, poly(methyl methacrylate)‐block‐poly(n‐butyl acrylate)‐block‐poly(methyl methacrylate), was modified with two kinds of additives, oligomeric poly(n‐butyl acrylate) and the plasticizer dibutyl sebacate. An actuator modified with those additives showed about 6% strain, whereas the unmodified actuator showed only 1% strain for the same applied electric field without prestrain. In addition, actuation was attained at lower critical electric field strength (625 and 1000 V mm^?1 for modified and unmodified actuators, respectively). Upon increasing the amounts of the additives, the electrically induced actuation velocity and degree of deformation increased. These results are explained by the dielectric and mechanical properties of the elastomers. The dielectric constants for elastomers modified with dibutyl sebacate were larger than those for elastomers modified with oligomeric poly(n‐butyl acrylate). The initial tensile stresses of both of the modified elastomers were much smaller than that of unmodified elastomer. The results provide a route to enhancing actuation performance of dielectric elastomers without prestrain. Copyright © 2011 Society of Chemical Industry     

Consolidation of Al2O3–GdAlo3 eutectic powder prepared from induction-melted solid and strength at high temperatures

A eutectic powder of Al₂0₃–GdA10₃ was melted using a Mo crucible by induction heating. The melt was slowly solidified, resulting in a eutectic solid with coarse Al₂0₃ and GdAl0₃ phases. The eutectic solid was ground and sieved into 3–44 µm and 64–124 µm particles. The powders were consolidated to produce a eutectic composite by spark plasma sintering. Mechanical properties of the consolidated eutectic composite were measured at room temperature. High temperature strength was obtained at temperatures up to 1673 K. Superplastic deformation of the eutectic composite was not observed on stress–strain curves at 1673 K, but did occur in the case of a conventional composite at 1573 K.     

Catechol derivatives inhibit the fibril formation of amyloid-β peptides

The inhibition of fibril formation of amyloid β proteins (Aβ) would be attractive therapeutic targets for the treatment of Alzheimer's disease (AD). Dopamine (DA) and other catechol derivatives were used as inhibitory factors for Aβ fibril formation. The fibril formation of Aβ was monitored by Thioflavin T fluorescence, a transmission electron microscopy (TEM) and a total internal reflection fluorescence microscopy (TIRFM). Catechol and its derivatives showed the dose-dependent inhibitory effects on the spontaneous Aβ fibril formation. The inhibitory activity depended on the chemical structure of catechol derivatives both in the presence and absence of the liposome a model of biomembrane. Formation of catechol quinone-conjugated-Aβ adduct by a Schiff-base is a key step for the inhibition effect of Aβ fibril formation.     

Permeation properties of hydrogen and water vapor through porous silica membranes at high temperatures

Silica and cobalt‐doped silica membranes that showed a high permeance of 1.8 × 10^?7 mol m^?2 s^?1 Pa^?1 and a H₂/N₂ permeance ratio of ～730, with excellent hydrothermal stability under steam pressure of 300 kPa, were successfully prepared. The permeation mechanism of gas molecules, focusing particularly on hydrogen and water vapor, was investigated in the 300–500°C range and is discussed based on the activation energy of permeation and the selectivity of gaseous molecules. The activation energy of H₂ permeation correlated well with the permeance ratio of He/H₂ for porous silica membranes prepared by sol–gel processing, chemical vapor deposition (CVD), and vitreous glasses, indicating that similar amorphous silica network structures were formed. The permeance ratios of H₂/H₂O were found to range from 5 to 40, that is, hydrogen (kinetic diameter: 0.289 nm) was always more permeable than water (0.265 nm). © 2010 American Institute of Chemical Engineers AIChE J, 2011     

The embrittlement mechanism and improvement of impact strength for lead-free solder joints in BGA packaging using electrolytic Ni/Au plating

Impact strength evaluation and fracture mechanism analysis in board level of Sn–3mass%Ag–0.5mass%Cu solder joints of ball grid arrays (BGA) using electrolytic Ni/Au plating were performed. The cause of impact strength degradation of BGA solder ball joints is the existence of low density defects, which contain organic materials, in the (Cu,Ni)₆Sn₅ intermetallic compound grain boundary formed in the solder joints. These organic materials are taken in by the nickel plating film at the time of nickel plating. To improve the impact strength of the Sn–3mass%Ag–0.5mass%Cu solder joint of the BGA, it is necessary to lower the concentration of these organic materials. The contamination prevention and nickel plating bath sanitization, solder mask material selection (to minimize nickel plating bath contamination) and higher current density of nickel plating are effective to keep a lower concentration of organic materials in nickel plating film.     

Organic nonvolatile memory transistors based on fullerene and an electron-trapping polymer

We report for the first time organic n-type nonvolatile memory transistors based on a fullerene (C₆₀) semiconductor and an electron-trapping polymer, poly(perfluoroalkenyl vinyl ether) (CYTOP). The transistors with a Si++/SiO₂/CYTOP/C₆₀/Al structure show good n-type transistor performance with a threshold voltage (V_th) of 2.8 V and an electron mobility of 0.4 cm² V⁻¹ s⁻¹. Applying gate voltages of 50 or −45 V for about 0.1 s to the devices induces the reversible shifts in their transfer characteristics, which results in a large memory window (ΔV_th) of 10 V. A memory on/off ratio of 10⁵ at a small reading voltage below 5 V and a retention time greater than 10⁵ s are achieved. The memory effect in the transistor is ascribed to electrons trapped at the CYTOP/SiO₂ interface. Because of the use of high-electron-mobility C₆₀, the switching voltages of our memory transistors become significantly lower than those of conventional memory transistors based on pentacene.     

Secondary nucleation of Aβ fibrils on liposome membrane

The amyloid fibrils of amyloid β protein (Aβ) from Alzheimer's disease are likely to show the cytotoxicity, depending on their morphology. The relationship between the nucleation kinetics of the Aβ fibrils and their morphology has been investigated. From the perspective of a crystallization technique assuming primary/secondary nucleation steps and an elongation step, the secondary nucleation rate B [# m^?3 s^?1], was experimentally and coarsely determined by using total internal reflection fluorescence microscopy combined with thioflavin T. In an aqueous solution, linear and rigid fibrils were formed with a relatively smaller B value ((2.83 ± 0.55) × 10⁵ # m^?3 s^?1), whereas spherulitic amyloid assemblies were formed in the presence of negatively charged liposome including oxidized lipids, with a larger B value ((7.65 ± 0.47) × 10⁵ # m^?3 s^?1). Those findings should lead to a better understanding of the mechanism for the formation of fibrils and senile plaques in Alzheimer's disease. © 2012 American Institute of Chemical Engineers AIChE J, 2012