Controlling dispersed state and exfoliation process of clay in polymer matrix

In the present review, the authors do not try to provide a comprehensive review of researches on polymer/clay nanocomposites (PCNs), but some examples to demonstrate different exfoliation processes of the clay in various polymer matrixes and the dispersed state of clay. Interaction between polymers and layered silicates plays an important role in adjusting the exfoliation process of layered silicates and the microstructure of polymer nanocomposites. Properties of polymer/layered silicate nanocomposites mainly depend on the dispersed state of layered silicates. The authors will also address the outline of the present research in the direction of PCNs including the discussion of technical problems and their possible solutions.

Synthesis, characterization, photoluminescent and electroluminescent properties of new conjugated 2,2 '-(arylenedivinylene)bis-8-substituted quinolines

A series of new PPV oligomers containing 8-substituted quinoline, 2,2'-(arylenedivinylene) bis-8-quinoline derivatives, were designed and synthesized via a Knoevenagel condensation reaction of quinaldine, 8-hydroxy-or 8-methoxy-quinaldine with aromatic dialdehydes. These PPV oligomers were characterized by H-1 and C-13-NMR, X-ray diffraction, elemental analysis, UV-visible and fluorescence spectroscopies. The X-ray diffraction investigation showed that there are intermolecular pi...pi interactions in the solid state in 1 and 3. The optical and photoluminescent properties study demonstrated that the emission color of the resulting materials varies from blue to yellow and is dependent on the substituents (pi-donor and pi-acceptor groups) on both sides of the conjugated molecules and the aromatic core in the middle of the conjugated backbones. The electroluminescent devices using compounds 1-4 as the emitters and electron-transporting layers were fabricated with the structure ITO/NPB/emitter/LiF/Al. The best device performance with the maximum brightness of 5530 cd m(-2) and the luminous efficiency of 2.4 cd A(-1) is achieved by using compound 4, with intramolecular charge transfer character, as the emitter; these values represent a more than 5-fold improvement in brightness and efficiency compared to compound 3 without methoxy groups on the phenyl rings.

Formation of regular hole pattern in polymer films

Ordered macroporous materials recently have attracted much attention. A method that utilizes the condensation of monodisperse water droplets on a polymer solution is proposed for the preparation of honeycomb microporous films. Our results show that it is a general method that can be used for patterning a wide range of polymers. The presence of water vapor and polymer is necessary for the formation of regular holes in films. The formation of hexagonal packing instead of other kinds of packing takes place because the hexagonal packing has the lowest free energy. The formation mechanisms of regular hole pattern and imperfections in the hexagonal packing are proposed.

Liquid-liquid phase behavior of toluene/polyethylene oxide/poly(ethyleneoxide-b-dimethylsiloxane) polymer-containing ternary mixtures

The experimental data of phase diagrams for both polyethylene oxide/poly(ethylene oxide-b-dimethylsiloxane) binary and toluene/polyethylene oxide/poly(ethylene oxide-b-dimethylsiloxane) ternary polymer-containing systems was obtained at atmosphere pressure by light scattering method. The critical points for some pre-selected compositions and the pressure effect on the phase transition behavior of ternary system were investigated by turbidity measurements. The chosen system is a mixture of ternary which is one of the very few abnormal polymer-containing systems exhibiting pressure-induced both miscibility and immiscibility. This unusual behavior is related to the toluene concentration in the mixtures. The effect of toluene on the phase transition behavior of the ternary polymer-containing mixture was traced. Such behavior can make it possible to process composite materials from incompatible polymers.

Lanthanide complex/polymer composite optical resin with intense narrow band emission, high transparency and good mechanical performance

Novel composite resins possessing good luminescent properties have been synthesized through a free radical copolymerization of styrene, alpha-methylacrylic acid and the binary or ternary complexes of lanthanide ions (Eu3+ and Tb3+). These polymer-based composite resins not only possess good transparency and mechanical performance but also exhibit an intense narrow band emission of lanthanide complexes under UV excitation. We characterized the molecular structure, physical and mechanical performance, and luminescent properties of the composite resins. Spectra investigations indicate that alpha-methyl-acrylic acid act as both solubilizer and ligand. Photoluminescence measurements indicate that the lanthanide complexes show superior emission lines and higher intensities in the resin matrix than in the corresponding pure complex powders, which can be attributed to the restriction of molecular motion of complexes by the polymer chain networks and the exclusion of water molecules from the complex. We also found that the luminescence intensity decreased with increasing content of alpha-methylacrylic acid in the copolymer system. The lifetime of the lanthanide complexes also lengthened when they were incorporated in the polymer matrix. In addition, we found that the relationships between emission intensity and Tb (Eu) content exhibit some extent of concentration quenching.

Incorporation of surface-derivatized gold nanoparticles into electrochemically generated polymer films

Stable colloidal solutions of gold nanoparticles surface-derivatized with a thiol monolayer have been prepared using two-phase (water-nitrobenzene) reduction of AuCl4- by sodium borohydride in the presence of 2-mercapto-3-n-octylthiophene (MOT). This kind of surface-functionalized gold nanoparticles can be easily incorporated into the poly(3-octylthiophene) (POT) films on electrode in the process of electrochemical polymerization leading to POT-gold nanoparticle (POT-Au) composite films. Scanning probe microscopy (SPM) and X-ray photoelectric spectroscopy (XPS) have been employed to characterize the surface-derivatized particles and the resulting films. The method of incorporation of nanoparticles into polymer by surface-derivatization and in situ polymerization can also be employed to prepare many other polymer-nanoparticle compostie materials.

Improvement of luminescence efficiency by electrical annealing in single-layer organic light-emitting diodes based on a conjugated dendrimer

In this paper, we study the effects of electrical annealing at different voltages on the performance of organic light-emitting diodes. The light-emitting diodes studied here are single-layer devices based on a conjugated dendrimer doped with 2-(4-biphenylyl)-5-(4-tert-butylphenyl)-1,3,4-oxadiazole as the emissive layer. We find that these devices can be annealed electrically by applying a voltage. This process reduces the turn-on voltage and enhances the brightness and efficiency. We obtained an external electroluminescence quantum efficiency of 0.07% photon/electron and a brightness of 2900 cd m(-2) after 12.4 V electrical annealing, which are about 6 times and 9 times higher than un-annealing devices, respectively. The improved luminance and efficiency are attributed to the presence of a space charge field near the electrodes caused by charging of traps.

Plasticizer effect on the ionic conductivity of PEO-based polymer electrolyte

The effects of plasticizer ethylene carbonate (EC) on the AC impedance spectra and the ionic conductivity are reported. With increasing of EC concentration the semicircle in high frequency disappears, and the slope of the straight line in low frequency decreases. The data obtained from impedance experiments can be explained using an equivalent circuit proposed. On the other hand, the room temperature conductivity increases with EC concentration because of the increase of the segmental flexibility of PEO. For lower EC concentration samples, the temperature dependence of conductivity in low temperature range follows Arrhenius type, but when EC concentration is larger than 20%, the temperature dependence of conductivity obeys the Vogel-Tamman-Fulcher (VTF) equation in all temperature ranges.

Design, synthesis and characterization of novel nitrogen-and sulfur-containing polymers with well-defined conjugated length

A series of novel nitrogen- and sulfur-containing conjugated polymers with well-defined conjugation length have been synthesized via an acid-induced self-polycondensation of functional monomers with methylsulfinyl groups. Synthesized polymers exhibit good solubility in common solvents, such as CHCl3, THF, DMF, DMSO, and NMP. With increased numbers of aminophenyl groups, these polymers have shown similar electrical properties to polyaniline (PAn), and these are demonstrated by UV-vis spectroscopy and cyclic voltammetry (CV) measurements on the polymers. The conductivity of preliminarily protonic-doped poly[phenylene sulfide-alt-tetrakis(aniline)] (PPSTEA) is up to 10(-1) S cm(-1).

Sol-gel preparation and luminescence properties of nano-structured hybrid materials incorporated with europium complexes

Microporous silica gel has been prepared by the sol-gel method utilizing the hydrolysis and polycondensation of tetraethylorthosilicate (TEOS). The gel has been doped with the luminescent ternary europium complex Eu(TTA)(3)(.)phen: where HTTA=1-(2-thenoyl)-3,3,3-trifluoracetone and phen=1,10-phenanthroline. By contrast to the weak f-f electron absorption bands of Eu3+, the complex organic ligand exhibits intense near ultraviolet absorption. Energy transfer from the ligand to Eu3+ enables the production of efficient, sharp visible luminescence from this material. Utilizing the polymerization of methyl methacrylate, the inorganic/polymer hybrid material containing Eu(TTA)(3)(.)phen has also been obtained. SEM micrographs show uniformly dispersed particles in the nanometre range. The characteristic luminescence spectral features of europium ions are present in the emission spectra of the hybrid material doped with Eu(TTA)(3)(.)phen.

Preparation and luminescence properties of sol-gel hybrid materials incorporated with europium complexes

Microporous silica gel has been prepared by the sol-gel method utilizing the hydrolysis and polycondensation of tetraethylorthosilicate (TEOS). The gel has been doped with the luminescent ternary europium complex Eu(TTA)(3). phen: where HTTA = 1-(2-thenoyl)-3,3,3-trifluoracetone and phen = 1,10-phenanthroline. By contrast to the weak f-f electron absorption bands of Eu3+, the complex organic ligand exhibits intense near ultraviolet absorption. Energy transfer from the ligand to Eu3+ enables the production of efficient, sharp visible luminescence from this material. Utilizing the polymerization of methyl methacrylate or ethyl methacrylate, the inorganic/polymer hybrid materials containing Eu(TTA)(3). phen have also been obtained. SEM micrographs show uniformly dispersed particles in the nanometre range. The characteristic luminescence spectral features of europium ions are present in the emission spectra of the hybrid material doped with Eu(TTA)3 phen. (C) 2000 Kluwer Academic Publishers.

Nanocluster-containing mesoporous magnetoceramics from hyperbranched organometallic polymer precursors

Pyrolysis of hyperbranched poly[1,1'-ferrocenylene(methyl)silyne] (5) yields mesoporous, conductive, and magnetic ceramics (6). Sintering at high temperatures (1000-1200 degrees C) under nitrogen and argon converts 5 to 6N and 6A, respectively, in similar to 48-62% yields. The ceramization yields of 5 are higher than that (similar to 36%) of its linear counterpart poly[1,1'-ferrocenylene(dimethyl)silylene] (1), revealing that the hyperbranched polymer is superior to the linear one as a ceramic precursor. The ceramic products 6 are characterized by SEM, XPS, EDX, XRD, and SQUID. It is found that the ceramics are electrically conductive and possess a mesoporous architecture constructed of tortuously interconnected nanoclusters. The iron contents of 6 estimated by EDX are 36-43%, much higher than that (11%) of the ceramic 2 prepared from the linear precursor 1. The nanocrystals in 6N are mainly alpha-Fe2O3 whereas those in 6A are mainly Fe3Si. When magnetized by an external field at room temperature, 6A exhibits a high-saturation magnetization (M-s similar to 49 emu/g) and near-zero remanence and coercivity; that is, 6A is an excellent soft ferromagnetic material with an extremely low hysteresis loss.

Effects of rubber content and temperature on dynamic fracture toughness of ABS materials

The effects of rubber content and temperature on dynamic fracture toughness of ABS materials have been investigated based on the J-integral and crack opening displacement (COD, delta) concepts by an instrumented Charpy impact test. A multiple specimens R-curve method and stop block technique are used. It is shown that the materials exhibit a different toughness behavior, depending on rubber content and temperature. The resistance against stable crack initiation (J(0.2) or delta(0.2)) increases with increasing rubber content. However, J(0.2) first increased with increasing temperature until reaching the maximum value; after that, it decreases with further increasing the temperature. (C) 2000 John Wiley & Sons, Inc.

Charge transport in a blue-emitting alternating block copolymer with a small spacer to conjugated segment length ratio

We analyze current versus voltage data obtained using single carrier injection in several metal/polymer/metal sandwich structures. The polymer used in each case is a soluble blue-emitting alternating block copolymer. Our experimental results demonstrate that the electron transport is space-charge limited by the high density of traps having an exponential energy distribution (temperature dependent characteristic energy) in the copolymer. The electron mobility of 8x10(-10) cm(2)/V s is directly determined using space-charge-limited current analytical expressions. Hole transport is also space-charge limited, with a mobility of 2x10(-6) cm(2)/V s. A hole trap with energy 0.17 eV is observed. We compare these results with those obtained for related block copolymers with different spacer and conjugated segment lengths and discuss the influence of spacer length and conjugated segment length on the charge transport properties. (C) 2000 American Institute of Physics. [S0021-8979(00)04501-1].

Ceramic carbon/polypyrrole materials for the construction of bienzymatic amperometric biosensor for glucose

A novel amperometric glucose biosensor was constructed by electrochemical formation of a polypyrrole (PPy) membrane in the presence of glucose oxidase (GOD) on the surface of a horseradish peroxidase (HRP) modified ferrocenecarboxylic acid (FCA) mediated sol-gel derived ceramic carbon electrode. The amperometric detection of glucose was carried out at +0.16 V (vs. SCE) in 0.1 mol/L phosphate buffer solution (pH 6.9) with a linear response range between 8.0x10(-5) and 1.3x10(-3) mol/L of glucose. The biosensor showed a good suppression of interference and a negligible deviation in the amperometric detection.