Rapid microwave-assisted preparation of amino-functionalized polymers

Two different methods for the rapid microwave-assisted amination of halide-functionalized polymers were investigated. Nucleophilic substitution by phthalimide, followed by ring opening with methylamine to liberate the free amine, afforded amino-substituted polymers with up to 76% conversion. The second method involves nucleophilic substitution with azide ions and subsequent treatment with triphenylphosphine. The latter method was found to be more efficient, with up to 99% conversion in favourable cases and with a reaction time of 2 × 30 min.     

Surface modification of thermoplastic polyurethane in order to enhance reactivity and avoid cell adhesion

Recently, the definition of coating procedures which leads to strong cell repellent surfaces has been an extremely important issue. In the present study, the cell repellency of thermoplastic polyurethane material (Elastollan®1180A50) surfaces was achieved by chemical treatment. Samples of Elastollan®1180A50 processed by injection molding, were oxidized with hydrogen peroxide (H₂O₂) and then impregnated with poly(ethylene glycol). The oxidation time was evaluated as were the effects of the PEG impregnation. Of all the evaluated modifications, a surface oxidation for 2 h, followed by impregnation with poly(ethylene glycol) resulted in the best cell repellent surface.     

High anisotropy of the field-effect transistor mobility in magnetically aligned discotic liquid-crystalline semiconductors

A magnetic field has been utilized for producing highly oriented films of a substituted hexabenzocoronene (HBC). Optical microscopy studies revealed large area HBC monodomains that covered the entire film, while wide-angle X-ray measurements showed that the HBC molecules are aligned with their planes along the applied field. On the basis of this method, solution-processed field-effect transistors (FET) have been constructed with charge carrier mobilities of up to 10(-3) cm2/V.s, which are significantly enhanced with respect to the unaligned material. Exceptionally high mobility anisotropies of 25-75 for current flow parallel and perpendicular to the alignment direction have been measured as a function of the channel length. Atomic force microscopy performed on the FET structures reveals fibril superstructures that are oriented perpendicularly to the magnetic field direction, consisting of molecular columns with a slippage angle of 40 degrees between the molecules. For channel lengths larger than 2.5 mum, the fibrils are smaller than the electrode spacing, which adversely affects the device performance.     

A high-throughput optical screening method for the optimization of colloidal water oxidation catalysts

A high-throughput method has been developed for screening and optimization of colloidal water oxidation catalysts. The catalysts are irradiated in parallel by visible light from an overhead projector in solutions containing tris(2,2'-bipyridyl)ruthenium(II) (Ru(bpy)(3)(2+)) and persulfate. The array of reaction solutions is held in a 96-well plate, and absorbance readings are taken intermittently using a bioassay plate reader. The absorbance at 430 nm is indicative of the amount of Ru(bpy)(3)(2+) remaining in solution. The best catalysts give the most persistent absorbance, because the oxygen evolution reaction is kinetically competitive with decomposition of Ru(bpy)(3)(3+). Reagent concentrations were varied using a factorial design-of-experiment approach in order to optimize reaction conditions for a IrO(2).xH(2)O colloidal catalyst. A higher colloid concentration, a lower Ru(bpy)(3)(2+) concentration, and a higher pH buffer doubled the number of turnovers relative to the original conditions. Metal oxide colloids consisting of IrO(2).xH(2)O doped with varying amounts of Pt, Ru, and Os were made using a parallel microwave synthesis technique and were tested both by the parallel screening method and by direct measurement of oxygen evolution. The correlation between the two methods was good, with Ir-Pt-Os oxide compositions showing the highest activity. The effect of adding small amounts of Pt and Os to IrO(2).xH(2)O appears to be predominantly to reduce the particle size of the colloids.     

Photosensitized production of doubly reduced methylviologen followed by highly efficient methylviologen radical formation using self-assembling ruthenium(II) complexes

Supramolecular fibers of Ru(II) complexes act as efficient photosensitizers, photochemically generating methylviologen radical (MV.+) and then converting it quantitatively to doubly reduced methylviologen, (MV0), in the presence of triethanolamine.     

Synthesis of unsymmetrical dibenzoquinoxaline discotic mesogens

Unsymmetrical dibenzophenazine discotic mesogens were prepared via the corresponding tetraalkoxybenzil derivatives. These dibenzophenazines exhibit Colho phases over extremely broad temperature ranges.     

Centralized and Decentralized Purchasing with Quality Inspections

The economic trade-off analysis between centralized and decentralized purchasing within the Canadian Forces is examined. A break-even analysis model for slow moving items has been developed. A simple isocost equation has been established relating the difference in item purchase cost, the freight tariff and the quality related costs. The case of the two purchasing modes with and without quality inspections will also be highlighted.     

Comparison of InGaN/GaN light emitting diodes grown on m ‐plane and a ‐plane bulk GaN substrates

InGaN/GaN‐based light emitting diodes (LEDs) grown on m ‐plane, a ‐plane and off‐axis between m ‐ and a ‐plane GaN bulk substrates were investigated. A smooth surface was obtained when a ‐plane substrate was applied; however, large amounts of defects were observed. Photoluminescence measurements of the LEDs with a well thickness of 2.5 nm revealed that all the LEDs showed the peak emission wavelength at 389 nm. The PL intensity of the a ‐plane LED is one order of magnitude lower than that of the m ‐plane LED. The a ‐plane LEDs showed significant lower electroluminescence output powers than m ‐plane LEDs, suggesting that excitons are trapped by the defects, which act as non‐radiative recombination centers. (© 2008 WILEY‐VCH Verlag GmbH & Co. KGaA, Weinheim)     

Improved electroluminescence on nonpolar m ‐plane InGaN/GaN quantum wells LEDs

Improved nonpolar m ‐plane light emitting diodes (LEDs) with a thick InGaN multi‐quantum‐well (MQW) structure have been fabricated on low extended defect bulk m ‐plane GaN substrates using metal organic chemical vapor deposition (MOCVD). The peak wavelength of the electroluminescence emission from the packaged LEDs was 402 nm, which is in the blue‐violet region. The output power and EQE were 28 mW and 45.4%, respectively, at a pulsed driving current of 20 mA. With increasing current, the output power increased linearly, and fairly flat EQE was observed with increasing drive current. At 200 mA, the power and EQE were 250 mW and 41%, respectively. (© 2007 WILEY‐VCH Verlag GmbH & Co. KGaA, Weinheim)