968 resultados para hybrid composite


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In this paper, silica-based transparent organic-inorganic hybrid materials were prepared via the sol-gel process. Tetraethoxysilane (TEOS) and 3-glycidoxypropyltrimethoxysilane (GPTMS) were used as the inorganic and organic precursors, respectively. The terbium complex, Tb(Tfacac)(3)phen (Tfacac = 1,1,1-trifluoroacetylacetone, phen = 1, 10-phenanthroline) was successfully doped into organically modified silicate (ormosil) matrix derived from TEOS and GPTMS, and the luminescent properties of the resultant ormosil composite phosphors [ormosil/Th(Tfacac)(3)phen] were investigated compared with those of the Tb(Tfacac)(3)phen incorporated into SiO2 derived from TEOS (labeled as silica/Tb(Tfacac)(3)phen). Both kinds of the materials show the characteristic green emission of Tb3+ ion. The luminescence behavior of the resultant composite products was dependent on the matrix composition. The optimized lanthanide complex concentration in the ormosil/Tb(Tfacac)(3)phen was increased compared with in silica/Tb(Tfacac)(3)phen. Furthermore, the lifetime of Tb3+ in Tb(Tfacac)(3)phen, silica/Tb(Tfacac)(3)phen and ormosil/Tb(Tfacac)(3)phen follows the sequence: onmosil/Tb(Tfacac)(3)phen>silica/Tb(Tfacac)(3)phen>pure Tb(Tfacac)(3)phen.

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A novel hybrid photochromic composite film composed of Preyssler's heteropoly acid H-12[EuP5W30O110] (EuP5W30) and polyvinylpyrrolidone (PVP) was prepared by dip-coating method. Atomic force microscopy (AFM) was used to investigate the surface topography. The change of characteristic peak in the infrared spectra (IR) was investigated. The TG curve showed three steps of weight loss and approximately revealed the composition of the hybrid film. Ultraviolet-visible adsorption spectra (UV-VIS) and electron resonance spectrum (ESR) were used to investigate the photochromic behavior and mechanism of hybrid film. The photoluminescent behavior of the film at room temperature was investigated to show the characteristic Eu3+ emission pattern of D-5(o)-F-7(J). The occurrence of photoluminescent activity confirms the potential for creating luminescent thin film with polyoxometalates (POMs).

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In situ synthesis of terbium carboxyl complexes in an organic-inorganic hybrid matrix by a sol-gel process has been proposed. The formation of terbium carboxyl complexes in the hybrid matrix is confirmed by the luminescence spectra and IR spectra. It is observed that the location at the amino group in aminobenzoic acid has a large effect on the luminescence properties and lifetimes. Furthermore, the emission intensity decreases with increasing temperature.

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The organic-inorganic hybrid, PSS-silica composite material was developed for the immobilization of tris(2,2'-bipyridyl)ruthenium(II) (Ru(bpy)(3)(2+)) on glassy carbon electrode via ion-exchange (PSS stands for poly(sodium 4-styrene-sulfonate)). The electrochemiluminescence (ECL) and electrochemistry of Ru(bpy)(3)(2-) immobilized in the composite thin films have been investigated with tripropylamine (TPA) as the coreactant. The immobilized Ru(bpy)(3)(2-) underwent a surface process. The modified electrode was used for the ECL detection of TPA and showed high sensitivity. Detection limit was 0,1 mumol L-1 for TPA (S/N = 3) with a linear range from 0.5 mumol L-1 to 5 mmol L-1 (R = 0.998), Moreover, the resulting modified electrode was stable over six months and the good stability may be due to the strong interaction between Ru(bpy)(3)(2-) and the high ion-exchange able PSS-silica composite films on GCE. Compared with other materials. the PSS-silica composite films containing incorporated Ru(bpy)(3)(2-) showed improved sensitivity and long-term stability, Thus, such composite thin film can be a promising material for the construction of ECL sensor.

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An unusual composite hybrid material [Co-4 (phen)(8) (H2O)(2) (HPO3)(2)](H3O)(3) [PMo8VI V-4(IV) O-40 ((VO)-O-IV) 2] 1 (phen = 1,10-phenanthroline) has been hydrothermally synthesized from a mixture of NH4VO3, Na2MoO4.2H(2)O, CoCl2.6H(2)O, phen, H3PO3 and water. It was characterized by elemental analysis, IR, UV-vis, XPS, EPR, TG and single crystal X-ray diffraction. The title compound is constructed from the organic-inorganic hybrid [Co-4(phen)(8)(H2O)(2) (HPO3)(2)](4+) and highly reduced bi-capped pseudo-Keggin [(PMo8V4O40)-V-VI-O-IV ((VO)-O-IV)(2)](7-) polyoxoanions The structure exhibits an extended 2D network through hydrogen bonds among cations, anions and H2O, combining polyoxometalates with metal phosphonates for the first time.

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A novel organic-inorganic hybrid compound {[Cu (2, 2'-bpy)(2)](2)Mo8O26} has been hydrothermally Synthesized and structurally characterized by single-crystal X-ray diffraction. The compound crystallizes in the orthorhombic space group, Pna2(1), with a=2.4164 (5), b=1.8281 (4), c=1.1877 (2) nm, V=5.247(2) nm(3), Z=4, and final R-1=0.0331, wR(2)=0.0727. The structure consists of discrete {[Cu(2,2'-bpy)(2)](2)Mo8O26} clusters, constructed from a beta -octamolybdate subunit[Mo8O26](4-) covalently bonded to two [Cu(2,2'-bpy)(2)](2+) coordination complex cations via bridging oxo groups. In addition, the spectroscopic properties and thermal behavior of this compound have been investigated by spectroscopic techniques (UV-vis, IR, Raman and EPR spectra) and TG analysis.

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An amperometric biosensor for monitoring phenols in the organic phase was constructed by the silica sol-gel immobilization of tyrosinase on a glassy carbon electrode. The organic-inorganic hybrid materials with different sol-gel precursors and polymers were optimized, and the experimental conditions, such as the effect of the solvent, operational potential and enzyme loading were explored for the optimum analytical performance of the enzyme electrode. The biosensor can reach 95% of steady-state current in about 18 s, and the trend in the sensitivity of different phenols is as follows: catechol > phenol >p-cresol. In addition, the apparent Michaelis-Menten constants (K-m(app)) and the stability of the enzyme electrode were discussed. (C) 2000 Elsevier Science S.A. All rights reserved.

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A new type of inorganic-organic hybrid material incorporating carbon powder and alpha -type 2:18-molybdodiphosphate (P2Mo18) in a methyltrimethoxysilane (MTMOS) based gel has been produced by a sol-gel process and used to fabricate a chemically modified electrode. The P2Mo18-doped carbon ceramic composite electrode was characterized using SEM and cyclic voltammetry. Square-wave voltammetry with an excellent sensitivity was exploited to conveniently investigate the dependence of current and half-wave potential (E-1/2) on pH. The chemically modified electrode has some advantages over the modified film electrodes constructed by the conventional methods, such as long-term stability, reproducibility, and especially repeatability of surface-renewal by simple polishing in the event of surface fouling or dopant leaching. In addition, the modified electrode shows a good catalytic activity for the electrochemical reduction of bromate in an acidic aqueous solution. (C) 2000 Elsevier Science B.V. All rights reserved.

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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.

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A novel inorganic-organic hybrid material incorporating graphite powder and Keggin-type alpha -germanomolybdic acid (GeMo12) in methyltrimethoxysilane-based gels has been produced by the sol-gel technique and used to fabricate a chemically bulk-modified electrode. GeMo12 acts as a catalyst, graphite powder ensures conductivity by percolation, the silicate provides a rigid porous backbone, and the methyl groups endow hydrophobicity and thus limit the wetting section of the modified electrode. The GeMo12-modified graphite organosilicate composite electrode was characterized by cyclic and square-wave voltammetry. The modified electrode shows a high electrocatalytic activity toward the reduction of bromate, nitrite and hydrogen peroxide in acidic aqueous solution. In addition, the chemically-modified electrode has some distinct advantages over the traditional polyoxometalate-modified electrodes, such as long-term stability and especially repeatability of surface-renewal by simple mechanical polishing.

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Poly(epsilon -caprolactone) (PCL) and silica (SiO2) organic-inorganic hybrid materials have been synthesized by the sol-gel method. The crystallization behavior of PCL in silica networks has been investigated using differential scanning calorimetry (DSC) and scanning electron microscopy (SEM). The degree of PCL crystallinity in PCL/SiO2 hybrid networks reduces with increase of SiO2. PCL is in an amorphous state when the concentration of PCL is lower than 40wt% in the hybrid system. The melting point of PCL in the networks is lower than, but close to that of pure PCL. WAXD and SEM results show that the crystalline behavior of PCL in PCL/SiO2 hybrid system is strictly confined. (C) 2001 Elsevier Science Ltd. All rights reserved.

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Ternary europium complex with dibenzoylmethane (DBM) and 1,10-phenanthroline (phen) was in-situ synthesized in thin SiO2/polyvinyl butyral (PVB) hybrid films by a two-step sol-gel process and characterized by;means of fluorescence spectroscopy. The luminescence spectra, fluorescence lifetimes and photostability were all investigated. The results showed that the hybrid films exhibited the characteristic emission bands of the Central rare earth Eu3+. In addition, Eu3+ presented longer fluorescence lifetime than in an ethanol solution and the complex had a higher photostability in the hybrid film than in the PVB film containing the corresponding pure complex.

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A novel functionalized inorganic-organic hybrid material with cation exchange property was prepared by sol-gel method. The H2O2 biosensor was fabricated by simply dipping the horseradish peroxidase-containing functionalized membrane modified electrode into Meldola's blue (MDB) solution. MDB was adsorbed and firmly immobilized within the membrane. The electrochemical behavior of MDB incorporated in the membrane was more reversible compared with that of the solution species and suitable as mediator for the horseradish peroxidase. The response time was less than 25 s. Linear range is up to 0.6 mM (COH. coeff. 0.9998) with detection Limit of 9 x 10(-7) M. High sensitivity of 75 nA mu M cm(-2) was obtained due to high MDB-loading. The biosensor exhibited a good stability. (C) 1999 Elsevier Science B.V. All rights reserved.

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Among the key challenges present in the modelling and optimisation of composite structures against impact is the computational expense involved in setting up accurate simulations of the impact event and then performing the iterations required to optimise the designs. It is of more interest to find good designs given the limitations of the resources and time available rather than the best possible design. In this paper, low cost but sufficiently accurate finite element (FE) models were generated in LS Dyna for several experimentally characterised materials by semi-automating the modelling process and using existing material models. These models were then used by an optimisation algorithm to generate new hybrid offspring, leading to minimum weight and/or cost designs from a selection of isotropic metals, polymers and orthotropic fibre-reinforced laminates that countered a specified impact threat. Experimental validation of the optimal designs thus identified was then successfully carried out using a single stage gas gun. With sufficient computational hardware, the techniques developed in this pilot study can further utilise fine meshes, equations of state and sophisticated material models, so that optimal hybrid systems can be identified from a wide range of materials, designs and threats.

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A number of experimental studies have shown that postbuckling stiffened composite panels, loaded in uniaxial compression, may undergo secondary instabilities, characterised by an abrupt change in the buckled mode-shape of the skin between the supporting stiffeners. In this study high-speed digital speckle photogrammetry is used to gain further insight into an I-stiffened panel's response during this transient phase. This energy-dissipating phenomenon will be shown to be able to cause catastrophic structural failure in vulnerable structures. It is therefore imperative that an accurate and reliable methodology is available to predict this phenomenon. The shortcomings of current non-linear implicit solution schemes, found in most commercially-available finite element codes, are discussed. A robust and efficient strategy, which utilises an automated quasi-, static/pseudo-transient hybrid scheme, is presented in this paper and validated using a number of experimental tests. This approach is shown to be able to predict mode-jumping with good accuracy.