Stress transfer and damage evolution simulations of fiber-reinforced polymer-matrix composites

The stress transfer from broken fibers to unbroken fibers in fiber-reinforced thermosetting polymer-matrix composites and thermoplastic polymer-matrix composites was studied using a detailed finite element model. In order to check the validity of this approach, an epoxy-matrix monolayer composite was used as thermosetting polymer-matrix composite and a polypropylene (PP)-matrix monolayer composite was used as thermoplastic polymer-matrix composite, respectively. It is found that the stress concentrations near the broken fiber element cause damage to the neighboring epoxy matrix prior to the breakage of other fibers, whereas in the case of PP-matrix composites the fibers nearest to the broken fiber break prior to the PP matrix damage, because the PP matrix around the broken fiber element yields. In order to simulate composite damage evolution, a Monte Carlo technique based on a finite element method has been developed in the paper. The finite element code coupled with statistical model of fiber strength specifically written for this problem was used to determine the stress redistribution. Five hundred samples of numerical simulation were carried out to obtain statistical deformation and failure process of composites with fixed fiber volume fraction.

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.

Multi-color long-lasting phosphorescence of rare earth ions in CdSiO3 matrix

A series of rare earth ions doped CdSiO3:RE3+(RE=Y, La, Ce, Pr, Nd, Sm, Eu, Gd, Tb, Dy, Ho, Er, Tm, Yb, Lu) multi-color long-lasting phosphorescence phosphors are prepared by the conventional high-temperature solid-state method. The results of XRD measurement indicate that the products fired under 1050degreesC for 3 h have a good crystallization without any detectable amount of impurity phase. Rare earth ions doped CdSiO3 phosphors possess excellent luminescence properties. When rare earth ions such as Y3+, La3+, Gd3+, Lu3+, Ce3+, Nd3+, Ho3+, Er3+, Tm3+ and Yb3+ are introduced into the CdSiO3 host, one broadband centered at about 420 nm resulting from traps can be observed. In the case of other earth ions such as Pr3+, Sm3+, Eu3+, Tb3+ and Dy3+, their characteristic line emitting as well as the similar to420 nm broadband luminescence can be obtained. The mixture of their characteristic line emitting with the similar to420 nm broadband luminescence results in various afterglow color.

Luminescence properties of lanthanide complexes doped in hybrid material from tetraethoxysilane and 3-glycidyioxyropyl-trimethoxysilane

Hybrid materials, containing in-situ synthesized lanthanide complexes with intense green light, have been prepared via sol-gel process. The luminescence properties and the decay times of as-synthesized samples were investigated. The excitation spectrum of the samples indicates the formation of complexes between terbium (III) and P-Sulfosalicylic acid. The hybrid materials that contain in-situ synthesized terbium complexes exhibit the characteristic emission bands of the rare earth ions. In addition, the effect of concentration of terbium on the luminescence properties as well as the thermal stability were also studied.

Luminescence properties of rare earth-polyoxometalate thin film deposited by sol-gel process

The rare earth (Eu3+, Dy3+)-polyoxometalate thin films were fabricated on quartz plate by the sol-gel method. The thin films were demonstrated by the luminescence spectra. The thin films exhibit the characteristic emission bands of the rare-earth ions. It is noticed that the yellow to blue intensity ratio (Y:B) of Dy3+ and the red to orange ratio (R:O) of Eu3+ in the films are different from that of the corresponding solids. Furthermore, the thin films present shorter fluorescence lifetime than the pure complexes. The reasons that were responsible for these results were also discussed.

Preparation and luminescence properties of hybrid materials containing europium(III) complexes covalently bonded to a silica matrix

A new kind of luminescent organic-inorganic hybrid material (denoted Hybrid I) consisting of europium 1,10-phenanthroline complexes covalently attached to a silica-based network was prepared by a sol-gel process. 1,10-Phenanthroline grafted to 3-(triethoxysilyl)propyl isocyanate was used as one of the precursors for the preparation of an organic-inorganic hybrid materials. For comparison purposes, the hybrid material (denoted Hybrid II) in which phenanthroline was not grafted onto the silica backbone of the frameworks was also prepared. Elemental analysis; NMR, FT-IR, UV/vis absorption, and luminescence spectroscopies, and luminescence decay analysis were used to characterize the obtained hybrid materials. It is shown that the homogeneity of Hybrid I is superior to that of Hybrid II, and a higher concentration europium can be incorporated into Hybrid I than Hybrid II. Excitation at the ligand absorption wavelength (283 nm) resulted in the strong emission of the Eu3+ D-5(0)-F-7(J) (J = 0-4) transition lines as a result of the efficient energy transfer from the ligands to the EU3+ in Hybrid I. The number of water molecules coordinated to the europium ion was estimated, and the structure of the as-synthesized Hybrid I was predicted on the basis of the experimental results.

Rapid molecular weight determination of recombinant hirudin by matrix-assisted laser desorption/ionization time-of-flight mass spectrometry

The molecular weight of recombinant hirudin ( rHV-2) was determined rapidly by matrix-assisted laser desorption/ionization time of fight mass spectrometry (MALDI-TOF-MS). The effects of the three types of matrixes were compared and discussed, alpha-cynao-4-hydroxycinnamic acid was proved to be the best matrix. It showed that MALDI-TOF-MS was superior to the traditional method of molecular weight determination of the biological macromolecules. The mass spectrum data proved that the primary structure of rHV-2 was correct and there was no amino acid deletion, mutation and modification in its expression, refolding and purification.

Study of electron transfer across the liquid/ice-like matrix interface by scanning electrochemical microscopy

In this work, we report the findings of a study on scanning electrochemical microscopy (SECM) to investigate the interfacial electron-transfer (ET) reaction between the 7,7,8,8-tetracyanoquinodimethane radical anion (TCNQ(.-)) in 1,2-dichloroethane and ferricyanide in an ice-like matrix (a mixture of insulting ice and conductive liquid) under low temperatures. Experimental results indicate that the formed liquid/ice-like matrix interface is superficially similar in electrochemical characteristics to a liquid/liquid interface at temperatures above -20 degreesC. Furthermore, imaging data show that the surface of the ice-like matrix is microscopically flat and physically stable and can be applied as either a conductive or an insulting substrate for SECM studies. Perchlorate ion was selected as the common ion in both phases, the concentrations of which controlled the interfacial potential difference. The effect of perchlorate concentration in the DCE phase on interfacial reactions has been studied in detail. The apparent heterogeneous rate constants for TCNQ(.-) oxidation by Fe(CN)(6)(3-) in another phase under different temperatures have been calculated by a best-fit analysis, where the experimental approach curves are compared with the theoretically derived relationships. Reaction rate data obey Butler-Volmer formulation before and after the freezing point, which is similar to most other known cases of ET reactions at liquid/liquid interfaces. However, there is a sharp change observed for heterogeneous rate constants around the freezing point of the aqueous phase, which reflects the phase transition. At temperatures below -20 degreesC, surface-confined voltammograms for the reduction of ferricyanide were obtained, and the ice-like matrix became an insulating one, which indicates that the aqueous phase is really a frozen phase.

XAFS at Eu-L-3 edge and UV-VUV excited luminescence of europium doped strontium borophosphate prepared in air

The local structure and the valences of europium in SrBPO5:Eu prepared in air were checked by means of XAFS at Eu-L-3 edge. From the EXAFS results, it was discovered that the doped europium atoms were nine-coordinated by oxygen atoms and the distances of bond Eu-O were 2.42 Angstrom in the host. From the XANES data, it was found that the divalent and trivalent europium coexisted in the matrix. The emission spectra excited by VUV or UV exhibited a prominent broad band due to the 4f(6)5d-4f(7) transition of Eu2+ ions, which indicated that the trivalent europium ions were reduced in air in the matrix at high temperature by the defects [V-Sr]" formed by aliovalent substitution between Sr2+ and Eu3+ ions. The VUV excitation spectra in 100-200 nm range showed that the matrix had absorption bands with the maxima at about 130 and 150 nm, respectively.

VUV excited luminescence of europium activated calcium borophosphate prepared in air

XAFS (EXAFS and XANES) at Eu-L-3 edge were used to determine the local structure and the valences of europium in CaBPO5:Eu prepared in air. The results of EXAFS showed that the doped europium atoms were nine-coordinated by oxygen atoms and the distances of bond Eu-O were 2.39 Angstrom in the host lattice. XANES at Eu-L-3 edge exhibited that Eu2+ and Eu3+ coexisted in the matrix. The luminescent spectrum of the material excited by VUV at 147 nm presented a similar spectrum with that excited by f-f transition of Eu2+ at 396 nm and f-d transition of Eu2+ at 312 nm. The broad emission band due to both 4f(6)5d - 4f(7) transition of EU2+ and f - f transition of Eu3+ could be observed in emission spectra, which indicated that the trivalent europium ions were reduced in air in the matrix at high temperature by the defects [V-Cn]" formed by aliovalent substitution between Ca2+ and Eu3+ ions. The UV excitation spectrum showed the typical f-f transition of Eu3+ and f-d transition of Eu2+. The bands with the maxima at about 113 and 158 nm in VUV excitation spectrum were assigned to originate from the absorption of the host lattice.

Novel trichromatic phosphor codoped with two rare earth ions in a single matrix

The luminescence properties of CaBPO5: Eu, Tb phosphor and the sensitization of Ce3+ were investigated. The CaBPO5: Eu, Tb phosphors were synthesized in the ambient air and the emission spectra of Eu3+, Tb3+ and Eu2+ were Observed in the phosphor. The result shows that there is electron transfer between conjugate rare earth ions. Sensitization of Ce3+ can improve the intensity of emission of Tb3+ and Eu2+. A novel trichromatic lamp phosphor codoped with Eu3+-Tb3+ in matrix CaBPO5 is then predicted.

Matrix effects in flow injection-inductively coupled plasma mass spectrometry

Matrix effects in now injection (FI) inductively coupled plasma mass spectrometry has been studied,and the results have been compared with those of continuous nebulization. The matrix element As and nu with higher ionization potential ( > 9eV) have enhancement effect on the analyte signal,and the heavier the analyte mass, the smaller the enhancement effects by Fl. The matrix elements Cu, In, Li, Na and Pb with lower ionization potential have suppression effect on the analyte signal. The heavier the matrix element mass, the more severe the suppression effects. The heavier the analyte mass, the smaller the suppression effects. The higher ionization potential of analyte, the more severe the suppression effects. Compared with continuous nebulization, the degree of suppression effect is smaller and the degree of the enhancement effect is larger by Fl.

Luminescence properties of Eu(phen)(2)Cl-3 doped in sol-gel-derived SiO2-PEG matrix

Rare earth complex Eu(phen)(2)Cl-3 was introduced into a SiO2-PEG-400 hybrid material by a sol-ger method. The result indicated that Poly(ethylene glycol) (PEG) could associate with Eu3+ and change the surroundings of Eu3+ in the hybrid material, greatly improving the decay time. Transparent SiO2-PEG400 hybrid doped with a very small amount of Eu(phen)(2)Cl-3 has better mechanical properties and can retain excellent luminescence properties of the rare earth complex. (C) 2000 Elsevier Science B.V. All rights reserved.