Preparation of polymer/silica nanoscale hybrids through sol-gel method involving emulsion polymers. II. Poly(ethyl acrylate)/SiO2

Poly(ethyl acrylate) (PEA)/SiO2 hybrids with different compositions were prepared under different casting temperatures and pH values. Their morphology as investigated by transmission electron microscopy (TEM) shows that samples with different compositions have different morphologies. When the SiO2 content is lower, PEA is the continuous phase and SiO2 is the dispersed phase. At higher SiO2 content, the change in phase morphology takes place, nd PEA gradually dispersing in the form of latex particles in SiO2 matrix. Change in phase morphology depends mainly on the time the sol-gel transition occurs. At suitable casting temperature and pH value, PEA/SiO2 in 95/5 and 50/50 hybrids with even dispersion was obtained.

Study of the ionic conductivity of polymer electrolyte using imaginary impedance spectroscopy

Polymeric electrolytes of (PEO1)(10) LiClO4-Al2O3 (PEO: poly (ethyleneoxide)) and (PEO2)(16)LiClO4-EC (EC: ethylene carbonate) were prepared. We proposed an equivalent circuit and gave the meaning of the concerned circuit elements. When the impedance spectrum deformed severely, the ionic conductivity of polymer electrolyte was determined by using the maximum of imaginary impedance, which is a convenient method.

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.

Preparation and characterization of poly(ethyl acrylate)/bentonite nanocomposites by in situ emulsion polymerization

Transparent poly(ethyl acrylate) (PEA)/bentonite nanocomposites containing intercalated-exfoliated combinatory structures of clay were synthesized by in situ emulsion polymerizations in aqueous dispersions containing bentonite. The samples for characterization were prepared through direct-forming films of the resulting emulsions without coagulation and separation. An examination with X-ray diffraction and transmission electron microscopy showed that intercalated and exfoliated structures of clay coexisted in the PEA/bentonite nanocomposites. The measurements of mechanical properties showed that PEA properties were greatly improved, with the tensile strength and modulus increasing from 0.65 and 0.24 to 11.16 and 88.41 MPa, respectively. Dynamic mechanical analysis revealed a very marked improvement of the storage modulus above the glass-transition temperature. In addition, because of the uniform dispersion of silicate layers in the PEA matrix, the barrier properties of the materials were dramatically improved. The permeability coefficient of water vapor decreased from 30.8 x 10(-6) to 8.3 x 10(-6) g cm/cm(2)s cmHg. (C) 2002 Wiley Periodicals, Inc.

Sol-gel-derived alpha(2)-K7P2W17VO62/graphite/organoceramic composite as the electrode material for a renewable amperometric hydrogen peroxide sensor

The conductive alpha (2)-K7P2W17VO62/graphite/organoceramic composite was prepared by dispersing alpha (2)-K7P2W17VO62 and graphite powder in a propyltrimethoxysilane-based sol-gel solution; it was used as the electrode material for an amperometric hydrogen peroxide sensor. The modified electrode had a homogeneous mirror-like surface and showed well defined cyclic voltammograms. Square-wave voltammetry was employed to study the pH-dependent electrochemical behavior of c alpha (2)-K7P2W17VO62 doped in the graphite organoceramic matrix, and the experiment showed that both protons and sodium cations participated in the odor process. A hydrodynamic voltammetric experiment was performed to characterize the electrode as an amperometric sensor for the determination of hydrogen peroxide. The sensor can be renewed easily in a repeatable manner by a mechanical polishing step and has a long operational lifetime. (C) 2000 Elsevier Science B.V. All rights reserved.

Sol-gel-derived ceramic carbon composite electrode containing isopolymolybdic anions

A new class of polyoxomelalate (POM)-modified electrodes is fabricated by the sol-gel technique and demonstrated for nitrite sensing. The electrode material comprises an interconnected dispersion of graphite powder and a uniform dispersion of isopolymolybdic anions (Mo8O26) in a porous methylsilicate matrix. The chemically modified electrodes showed well-defined cyclic voltammograms with three reversible redox couples in acidic aqueous solutions because of the good physicochemical compatibility of Mo8O26 and the carbon ceramic matrix. The Mo8O26-modified electrodes show good stability and reproducibility, especially the renewal repeatability by simple polishing in the event of surface fouling. (C) 2000 Elsevier Science Ltd. All rights reserved.

PMo12-doped carbon ceramic composite electrode based on sol-gel chemistry and its electrocatalytic reduction of bromate

A conductive carbon ceramic composite electrode (CCE) comprised of cc-type 1:12 phosphomolybdic acid (PMo12) and carbon powder in an organically modified silicate matrix was fabricated using a sol-gel method and characterized by scanning electron microscopy, cyclic voltammetry, and Osteryoung square-wave voltammetry. Osteryoung square-wave voltammograms of the modified electrode immersed in different acidic aqueous solutions present the dependence of current and redox potential on pH. The PMo12-doped CCE shows more reversible reaction kinetics, good stability and reproducibility, especially the renewal repeatability by simple polishing in the event of surface fouling or dopant leaching. Moreover, the modified electrode shows good catalytic activity for the electrochemical reduction of bromate.

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.

Layer-by-layer assembly of multilayer films consisting of silicotungstate and a cationic redox polymer on 4-aminobenzoic acid modified glassy carbon electrode and their electrocatalytic effects

A novel 4-aminobenzoic acid (4-ABA) monolayer film is formed on glassy carbon electrode (GCE) by amino cation radical method. Silicotungstic heteropolyanion (SiW12O404-, denoted as SiW12)-containing multilayer films have been fabricated on the 4-ABA modified GCE surface by alternate deposition with a quaternized poly(4-vinylpyridine) partially complexed with [Os(bpy)(2)Cl](2+/+) (denoted as QPVP-Os). Cyclic voltammetry (CV), X-ray photoelectron spectroscopy (XPS) and X-ray reflectivity (XR) have been used to characterise the as-prepared multilayer films. It is proved that the multilayer films are uniform and stable. The average thickness for a bilayer of QPVP-Os/SiW12 in the multilayer film is 30.2 Angstrom. The electrocatalytic activities of the multilayer films have been investigated on the reduction of three substrates of important analytical interests, HNO2, BrO3- and H2O2. Especially, the influence of layer number of the multilayer films on the electrocatalytic reduction of HNO2 has been investigated in detail. (C) 2000 Elsevier Science B.V. All rights reserved.

Stimulated emission in the film of polymer/dye blend

Optically pumped stimulated emission behavior in an organic film was demonstrated in this study. The gain material consists of a laser dye perylene doped into polystyrene (PS) matrix in an appropriate weight ratio. The sample was transversely pumped by the three harmonic output of a mode-locked Nd:YAG laser. The change of the emission spectra showed a clear threshold action and gain narrowing phenomenon when increasing the excitation intensity. Three emission peaks were observed below the excitation threshold, which are locate at 446, 475 and 506 nm, respectively. However, only the gain narrowing peak centered at 475 nm could be detected above the threshold. The spectra narrowing observed results from the amplified spontaneous emission (ASE) in the gain material. (C) 2000 Elsevier Science S.A. All rights reserved.

Amperometric biosensor for hydrogen peroxide based on sol-gel/hydrogel composite thin film

A reagentless amperometric hydrogen peroxide biosensor was developed. Horseradish peroxidase (HRP) was immobilized in a novel sol-gel organic-inorganic hybrid matrix that is composed of silica sol and a grafting copolymer of poly(vinyl alcohol) with 4-vinylpyridine (PVA-g-PVP). Tetrathiafulvalene (TTF) was employed as a mediator and could lower the operating potential to -50 mV (versus Ag/AgCl). The sensor achieved 95% of the steady-state current in 15 s. Linear calibration for hydrogen peroxide was up to 1.3 mM with the detection limit of 2.5 x 10(-7)M. The enzyme electrode retained about 94% of its initial activity after 30 days of storage in a dry state at 4 degreesC.

Radiation effects on the immiscible polymer blend of nylon1010 and high-impact strength polystyrene (II): mechanical properties and morphology

The paper studies the morphology and mechanical properties of immiscible binary blends of the nylon 1010 and HIPS through the radiation crosslinking method. In this blend, the HIPS particles were the dispersed phases in the nylon 1010 matrix. With increasing of dose, the elastic modulus increased, However, the tensile strength. elongation at bleak and the energy of fracture increased to a maximum at a dose of 0.34 MGy, then reduced with the increasing of dose. SEM photographs show that the hole sizes are not changed obviously at low dose and at high dose, remnants that cannot be dissolved in formic acid and THF can be observed in the holes and on the surface. TEM photographs showed that radiation destroys the rubber phases in the polymer blend. (C) 2001 Elsevier Science Ltd. All rights reserved.

Matrix-assisted laser desorption/ionization time-of-flight mass spectrometric analysis of phospholipase A(2) and fibrinolytic enzyme, two enzymes obtained from Chinese Agkistrodon blomhoffii Ussurensis venom

Matrix-assisted laser desorption/ionization time-of-flight mass spectrometry (MALDI-TOFMS) was used to analyze two enzymes, phospholipase AZ and fibrinolytic enzyme isolated from Chinese Agkistrodon blomhoffii Ussurensis venom. Using sinapinic acid as the matrix, positive ion mass spectra of the enzymes were obtained, In addition to the dominant protein [M+H](+) ions, multimeric and multiply charged ions were also observed in the mass spectra, The higher the concentration of the enzymes, the more multiply charged polymer and multimeric ions were detected, Our results indicate that MALDI-TOFMS can provide a rapid and accurate method for molecular weight determination of snake venom enzymes, Mass accuracies of 0.1 and 0.3 % were achieved by analysis of highly dialyzed phospholipase A2 and fibrinolytic enzyme, and these results are much better than those obtained using sodium dodecyl sulfate-palyacrylamide gel electrophoresis. MALDI-TOFMS thus provides a reliable method to determine the purity and molecular weight of these enzymes, which are of potential use as therapeutants, Copyright (C) 1999 John Wiley & Sons, Ltd.

Crystallization of micelles and matrix in dilute diblock copolymer/homopolymer solutions

The crystallization, morphology, and crystalline structure of dilute solid solutions of tetrahydrofuran-methyl methacrylate diblock copolymer (PTHF-b-PMMA) in poly(ethylene oxide) (PEO) and PTHF have been studied with differential scanning calorimetry (DSC), X-ray, and optical microscopy. This study provides a new insight into the crystallization behavior of block copolymers. For the dilute PTHF-b-PMMA/PEO system containing only 2 to 7 wt % of PTHF content, crystallization of the PTHF micellar core was detected both on cooling and on heating. Compared the crystallization of the PTHF in the dilute solutions with that in the pure copolymer, it was found that the crystallizability of the PTHF micellar core in the solution is much greater than that of the dispersed PTHF microdomain in the pure copolymer. The stronger crystallizability in the solution was presumably due to a softened PMMA corona formed in the solution of the copolymer with PEG. However, the "soft" micelles formed in the solution (meaning that the glass transition temperatures (T-g) of the micelle is lower than the T-m of the matrix phase) showed almost no effects on the spherulitic morphology of the PEO component, compared with that of the pure PEO sample. In contrast, significant effects of the micelles with a "hard" PMMA core (meaning that the T-g of the core is higher than the T-m of the PTHF homopolymer) on the nucleation, crystalline structure, and spherulitic morphology were observed for the dilute PTHF-b-PMMA/PTHF system. (C) 1998 John Wiley & Sons, Inc.

Study on the self-packing of SnO2 nanoparticles at the air-hydrosol interface and its composite LB films with arachidic acid

SnO2 nanoparticles were found to self-pack at the air-hydrosol interface and form a nanoparticulate film. The self-packed films were observed under a Brewster angle microscope, and investigated by recording the time evolution of surface pressure and pi-A isotherms. The results show that SnO2 nanoparticles take 3 h to form a complete film at the air-hydrosol interface. Composite monolayers of SnO2 and arachidic acid were obtained by spreading arachidic acid onto a fresh hydrosol surface. Composite Y-type LB films were transferred from the air-hydrosol interface onto substrates, and characterized by FTIR, UV-vis, X-ray diffraction spectroscopy and TEM techniques. The results show that the composite films have good structure, with SnO2 nanoparticles uniformly and compactly distributed in the arachidate matrix. (C) 1998 Elsevier Science S.A. All rights reserved.