Efficient green electroluminescent cells using a poly(p-phenylene vinylene) multiblock copolymer sandwiched between carrier-transporting layers

With a newly synthesized poly(p-phenylene vinylene) (PPV) multiblock copolymer used in a triple-layer structure, efficient green light-emitting diodes with low driving voltage have been fabricated. The devices are turned on at 2.5 V, the brightness at 5 V is above 100 cd/m(2) and at 7 V is about 1650 cd/m(2), with an external quantum efficiency of about 1%. (C) 1998 Elsevier Science S.A. All rights reserved.

Physical aging and crystallization of amorphous poly(aryl ether ether ketone ketone)

Physical aging of poly(aryl ether ether ketone ketone) (PEEKK) was investigated. Heat flow responses were measured after annealing the amorphous samples that were obtained by quenching the melt into an ice-water bath at just below the glass transition temperature. Isothermal cold crystallization of the aged samples was carried out. The Avrami equation was used to determine the kinetic parameters, and the Avrami constant it is about 2. An Arrhenius form was used to evaluate the relaxation activation energy of physical aging and the transport activation energy of isothermal crystallization. The activation energy of physical aging was similar in magnitude to that observed for the temperature dependence of crystallization under conditions of transportation control. Results obtained were interpreted as purely kinetic effects associated with the glass formation process. (C) 1998 John Wiley & Sons, Inc.

Intramolecular energy transfer mechanism between ligands in ternary rare earth complexes with aromatic carboxylic acids and 1,10-phenanthroline

A series of binary and ternary rare earth (Gd, Eu, Tb) complexes with aromatic acids and 1,10-phenanthroline have been synthesized. The lowest triplet state energies of ligands have been obtained by measuring the phosphorescence spectra of binary gadolinium complexes. By comparing the phosphorescence spectra of binary complexes with those of ternary ones, it is found that there exists another intramolecular energy transfer process from the aromatic acids to 1,10-phenanthroline besides the intramolecular energy transfer process between the aromatic acids and the central rare earth ions. The intramolecular energy transfer efficiencies have been calculated by determining phosphorescence lifetimes of binary and ternary gadolinium complexes. The luminescence properties of corresponding europium and terbium complexes are in agreement with the prediction based on energy transfer mechanism. (C) 1998 Elsevier Science S.A. All rights reserved.

Investigation of oxygen- and hydrogen peroxide-reduction on platinum particles dispersed on poly(o-phenylenediamine) film modified glassy carbon electrodes

Composite membrane modified electrodes were prepared by electrochemical deposition of platinum particles in a poly(o-phenylenediamine) (PPD) him coated on glassy carbon (GC) electrodes. The modified electrodes showed high catalytic activity towards the reduction of oxygen and hydrogen peroxide. A four-electron transfer process predominated the reduction process. The pH dependence and the stability of the electrodes were also studied.

The rheological and extrusion behaviour of blends based on phenolphthalein poly(ether-ether-sulfone) and thermotropic liquid crystalline polymer

A novel engineering thermoplastic, phenolphthalein poly (ether-ether-sulfone) (PES-C) was blended with a commercial thermotropic liquid crystalline polymer(TLCP), Vectra A950, up to 30 weight percent of TLCP. A rheometrics dynamic spectrometer (RDS-I) and a CEAST capillary rheometer, a rheoscope 1000 were employed to investigate the melt rheology and extrusion behaviour at both the low and high shearing rates. The morphologies of the blends under different shearing were observed with a scanning electron microscope(SEM) and correlated to the observed rheology. The principal normal stress differences measured with cone-and-plate geometry give a temperature-independent correlation for both blend and PES-C when they are plotted against shear stress. But the extrudate swell of the blends showed a strong temperature dependence at each shear stress. The concentration dependence of extrudate swell shows a contrary behaviour to that of the inorganic filled system. A reasonable hypothesis based on the relaxation and disorientation of TLCP during flowing in the capillary and exiting was given to explain it. The melt fracture was checked after extrusion from capillary and was discussed.

A study of the effect of shell content on the mechanical properties of polycarbonate/poly(butyl acrylate)-cs-poly(methyl methacrylate) blends

The toughening effect of the shell content of a core-shell latex polymer poly(butyl acrylate) (PBA)-cs-poly(methyl methacrylate) (PMMA) on its blends with polycarbonate (PC) was studied. The changes of mechanical properties, morphology, and compatibility of the blends of PC/PBA-cs-PMMA with the change of the shell thickness of PBA-cs-PMMA were investigated. It is interesting to notice that mechanical properties of the blends are very sensitive to the shell thickness (i.e., shell content), and that there is a possibility to adjust the impact and tensile properties of the blend by selecting a PBA-cs-PMMA with a proper core/shell ratio. Hence, a modified PC material with balanced mechanical properties may be prepared.

Crystallization and melting behavior of nylon 66 poly(ether imide) blends

Isothermal crystallization and melting behavior of nylon 66 and its blends with poly(ether imide) (PEI) were investigated by differential scanning calorimetry. Crystallization kinetics such as overall rate constant Z and index n were calculated according to Avrami approach. Crystallization in the blend was retarded with respect to that of pure nylon 66 by incorporation of PEI with high glass transition temperature (T-g). The lowest growth rate of the spherulites was observed in the blends containing 10 and 15 wt% fraction of PEI. A transition temperature where positively birefringent spherulites disappear and negative birefringent spherulites develop was measured by thermal analysis. The transition temperature increased with content of PEI in the blends. A suitable range of isothermally crystallization temperatures, 238.5-246 degrees C, is suggested For determining the equilibrium melting points by means of Hoffman-Weeks approach.