Determination of hydroxyl radical rate constants in a continuous flow system using competition kinetics

It is important to determine reaction kinetics of the hydroxyl radical (OH) with various water pollutants for understanding advanced oxidation processes (AOPs). Hence, a simple competition kinetics in a continuous flow system was employed to determine the second-order rate constants of OH with 14 organic and inorganic solutes selected in this study. In this method, p-nitrosodimethylaniline (PNDA) was specifically employed as a well-known reference probe for OH, which gave a competitive relationship between the PNDA and each solute over OH radicals. PNDA decay with OH radicals obeyed reaction kinetics in a first-order as long as the initial concentrations of H₂O₂ and PNDA were less than 30 μM and 2 μM, respectively. The second-order rate constants of OH radical with 14 solutes obtained in this study were found to be consistent with literature values using pulse radiolysis method.     

<Emphasis Type="Italic">Abies koreana</Emphasis> Essential Oil Inhibits Drug-Resistant Skin Pathogen Growth and LPS-Induced Inflammatory Effects of Murine Macrophage

Since acne vulgaris is the combined result of a bacterial infection and the inflammatory response to that infection, we examined whether Abies koreana essential oil (AKE) possessed anti-inflammatory and antibacterial activities against skin pathogens. In this study, AKE showed excellent antibacterial activities against drug-susceptible and -resistant Propionibacterium acnes and Staphylococcus epidermidis, which are acne-causing bacteria. In addition, AKE reduced the LPS-induced secretion of tumor necrosis factor-α (TNF-α), interleukin-1β (IL-1β), IL-6, NO and PGE₂ in RAW 264.7 cells, indicating that it has anti-inflammatory effects. Therefore, we suggest that AKE may be an attractive candidate for promoting skin health.     

Examination of acid-base properties of alumina treated with silane coupling agents, by using inverse gas chromatography

This study examined the specific component of the free energy of adsorption, − ΔG_A^SP, of the untreated and four types of silane coupling agent-treated alumina powders using inverse gas chromatography (IGC) by employing the adsorption of several polar and non-polar probes onto their surfaces at various temperatures. The acid-base properties of the untreated and surface-treated alumina powders were quantified using their K_A and K_D parameters, which reflect the ability of a surface to act as an electron acceptor and donor, respectively. The surface of the untreated alumina was found to be amphoteric and was able to function as both an electron acceptor and donor. The acid-base properties of the alumina surfaces treated with γ-glycidoxy propyl trimethoxy silane (GMS) and γ-amino propyl triethoxy silane (AES) were slightly basic, and those of the alumina surfaces treated with γ-methacryloxy propyl trimethoxy silane (MTMS) and γ-mercapto propyl trimethoxy silane (MCMS) were amphoteric.     

Properties of isocyanate‐reactive waterborne polyurethane adhesives: Effect of cure reaction with various polyol and chain extender content

Three series of isocyanate‐reactive waterborne polyurethane adhesives were prepared with various contents of chain extender (4.25/8.25/12.50 mol %) and polyol (20.75/16.75/12.50 mol %). Each series had a fixed amount of excess (residual) NCO group (0.50–2.00 mol %). FTIR and ¹H‐NMR spectroscopy identified the formation of urea crosslink structure mainly above 80°C of various cure temperatures (20–120°C) with excess diisocyanate. The molecular weight, tensile strength, Young's modulus, and adhesive strength depend on excess NCO content and cure temperature and also varied with polyol and chain extender content. The optimum cure temperature was 100°C for all the samples. The tensile strength, Young's modulus, and adhesive strength increased with increasing cure temperature above 60°C up to the optimum temperature) (100°C) and then almost leveled off. Among all the samples, the maximum values of tensile strength, Young's modulus, and adhesive strength were found with 63.22 wt % polyol, 0.93 wt % chain extender, and 1.50 mol % excess (residual) NCO content at 100°C optimum cure temperature. © 2009 Wiley Periodicals, Inc. J Appl Polym Sci, 2009     

Reliability of Au bump flip chip packages with adhesive materials using four-point bending test

In this study, the bending fatigue reliability of Au bump flip chip packages with anisotropic conductive film (ACF) and non-conductive film (NCF) as adhesive materials was evaluated using a four-point bending test. Differential bending between the substrate and the Si chip was the dominant failure driver for the Au bump flip chip packages subjected to the bending test. The bending fatigue life of the NCF joint was longer than that of the ACF joint, regardless of the bending frequency. The main reason for the increased electrical resistance of the packages with ACF and NCF was the delamination between the adhesive material and the electroless Ni-immersion Au (ENIG) pad and between the Au bump and ENIG pad, respectively. For the ACF package, the bending stress was concentrated at the conductive particles between the Au bump and the ENIG pad during the bending fatigue test, resulting in a low bending fatigue strength. The delamination in the packages propagated with increasing bending fatigue cycles and frequency. The Au bump flip chip package with NCF was mechanically robust due to the higher initial strength and the larger bonding area between the Au bump and the ENIG pad.     

Synthesis and characterization of poly(ether sulfone) grafted poly(styrene sulfonic acid) for proton conducting membranes

Two-step synthesis of proton-conducting poly(ether sulfone) (PES) graft copolymer electrolyte membrane is proposed. Fridel Craft alkylation reaction was used to introduce chloromethyl pendant group onto the PES polymer backbone. Later on, atom transfer radical polymerization (ATRP) was applied to synthesize a series of poly(ether sulfone) grafted poly(styrene sulfonic acid) (PES-g-PSSA). Successful chloromethyl substitution and grafting of the pendant group was characterized by the ¹H-NMR and elemental analysis. Electrochemical properties such as ion exchange capacity (IEC), water uptake and proton conductivity increased with increasing PSSA contents. Thermal gravimetric analysis (TGA) showed the thermal stability of membranes up to 270 °C. Proton conductivity for maximum amount of grafting was 0.00297 S/cm.     

The effect of nano-sized BNBT on microstructure and dielectric/piezoelectric properties

(Bi_0.5Na_0.5)_0.94Ba_0.06TiO₃ (abbreviated as BNBT6) ceramic of near MPB composition was synthesized by two different processes. The first one is the addition of pre-synthesized BaTiO₃ and pre-milled Bi₂O₃, Na₂CO₃, BaCO₃ powders and calcination powder milled with a high energy milling machine in order to obtain a nano-particle size. The second one is a conventional one to compare with the former process. The pre-milling and the pre-synthesis process of raw materials lowered the calcination temperature to the extent of 59 °C as compared with conventionally fabricated BNBT6. The particle size of the powder exposed to heavy high energy milling reduced to 50–70 nm, whereas that of the conventionally ball-milled powder without the pre-milling and the pre-synthesis process had a larger size of 280 nm. To investigate the effects of the modified process on the characteristic of BNBT6 ceramics, the dielectric and the piezoelectric properties of sintered specimens fabricated by the two different processes were evaluated. It was found that the properties of the nano-sized BNBT6 ceramic near the MPB composition were increased by the modified mixing and milling method, showing superior characteristics in terms of the piezoelectric/dielectric constant and sintering density compared with those of the conventional process. The modified mixing and milling method was considered to be a new and promising process for lead-free piezoelectric ceramics owing to their excellent piezoelectric/dielectric properties.     

Mullite whiskers derived from kaolin

Short mullite whiskers prepared by firing compacts of kaolin and NH₄Al(SO₄)₂·12H₂O powders, with a small addition (0.8, 1.5 wt%) of NaH₂PO₄·2H₂O, in air 1300 and 1400 °C for 15 h have been characterized in terms of whisker morphology, composition and structure. Relatively uniform whisker shaped crystals grew within the silicate glass matrix. After chemically leaching the glass matrix with HF solution using a microwave heating source, the resulting whiskers were exposed as isolated crystals and exhibited an aspect ratio of >17 (～0.5 μm in diameter). The mullite whiskers had a composition of 51.06 mol% Al₂O₃ and 48.94 mol% SiO₂, with an orthorhombic crystallographic structure.     

Low-temperature preparation and microwave dielectric properties of ZBS glass–Al2O3 composites

The preparation and microwave dielectric properties of ZnAl₂O₄-based glass–ceramic composites were investigated. Using zinc borosilicate (ZBS) glass and Al₂O₃, glass–ZnAl₂O₄ composites with high quality factor was successfully prepared at temperatures below 950 °C. The linear shrinkage for 50 vol% ZBS glass–ZnAl₂O₄ composite showed a steep increase up to 650 °C and a plateau between 700 °C and 950 °C, implying that one-stage densification process occurred. The crystallization of ZnAl₂O₄ was observed above 700 °C and an insufficient densification occurred due to the consumption of the glass. As the sintering temperature increased, the quality factor (Q × f₀) showed an increase with an S-type curve whereas the dielectric constant was almost constant. The formation of ZnAl₂O₄ might correspond to the increase of Q × f₀; a high value of 17,757 GHz (1415 at 12.6 GHz) was obtained for the specimen sintered at 900 °C.     

Chemosensors for pyrophosphate

The selective detection of the anion pyrophosphate (PPi) is a major research focus. PPi is a biologically important target because it is the product of ATP hydrolysis under cellular conditions, and because it is involved in DNA replication catalyzed by DNA polymerase, its detection is being investigated as a real-time DNA sequencing method. In addition, within the past decade, the ability to detect PPi has become important in cancer research. In general, the sensing of anions in aqueous solution requires a strong affinity for anions in water as well as the ability to convert anion recognition into a fluorescent or colorimetric signal. Among the variety of methods for detecting PPi, fluorescent chemosensors and colorimetric sensors for PPi have attracted considerable attention during the past 10 years. Compared with the recognition of metal ions, it is much more challenging to selectively recognize anions in an aqueous system due to the strong hydration effects of anions. Consequently, the design of PPi sensors requires the following: an understanding of the molecular recognition between PPi and the binding sites, the desired solubility in aqueous solutions, the communicating and signaling mechanism, and most importantly, selectivity for PPi over other anions such as AMP and ADP, and particularly phosphate and ATP. This Account classifies chemosensors for PPi according to topological and structural characteristics. Types of chemosensors investigated and reported in this study include those that contain metal ion complexes, metal complexes combined with excimers, those that function with a displacement approach, and those based on hydrogen-bonding interaction. Thus far, the utilization of a metal ion complex as a binding site for PPi has been the most successful strategy. The strong binding affinity between metal ions and PPi allows the detection of PPi in a 100% aqueous solution. We have demonstrated that carefully designed receptors can distinguish between PPi and ATP based on their different total anionic charge densities. We have also demonstrated that a PPi metal ion complex sensor has a bioanalytical application. This sensor can be used in a simple and quick, one-step, homogeneous phase detection method in order to confirm DNA amplification after polymerase chain reaction (PCR).