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Selected AbstractsThe electronic and electrochemical properties of the TiFe1,xNix alloysPHYSICA STATUS SOLIDI (A) APPLICATIONS AND MATERIALS SCIENCE, Issue 1 2003A. Szajek Abstract Mechanical alloying (MA) process was introduced to produce nanocrystalline TiFe1,xNix alloys (0 , x , 1). XRD analysis showed that, firstly, after 25 h of milling, the starting mixture of the elements had decomposed into an amorphous phase and, secondly, the annealing in high purity argon at 750 °C for 0.5 h led to formation of the CsCl-type (B2) structures with a crystallite sizes of about 30 nm. These materials, used as negative electrodes for Ni,MH batteries, showed an increase in discharge capacity with a maximum for x = 3/4. The band structure has been studied by the Tight Binding version of the Linear Muffin-Tin method in the Atomic Sphere Approximation (TB LMTO ASA). Increasing content of Ni atoms intensified charge transfer from Ti atoms, extended valence bands and increased the values of the densities of electronic states at the Fermi level. [source] Electrochemically Induced Formation of Surface-Attached Temperature-Responsive Hydrogels.ELECTROANALYSIS, Issue 9 2010Amperometric Glucose Sensors with Tunable Sensor Characteristics Abstract Employing thermally responsive hydrogels, the design of an amperometric glucose sensor is proposed. The properties of the biosensor can be modulated upon changing the temperature. Homo- and copolymers of N -isopropylacrylamide (NIPAm) and oligo(ethylene glycol) methacrylate (OEGMA) were prepared by electrochemically induced polymerization thus yielding surface-attached hydrogels. The growth of the films as well as the change in the film thickness in dependence from the temperature were investigated by means of an electrochemical quartz crystal microbalance (EQCM). The layer thickness in the dry state ranged from 20 to 120,nm. The lower critical solution temperature (LCST) of the hydrogel increases with increasing content of the more hydrophilic OEGMA. Hence, the swelling in aqueous electrolyte is composition dependent and can be adjusted by selecting a specific NIPAm to OEGMA ratio. All homo- and copolymer films showed good biocompatibility and no fouling could be observed during exposing the surfaces to human serum albumin. For amperometric glucose detection, glucose oxidase was entrapped in the films during electrochemically-induced polymerization. Both the apparent Michaelis constant (K and the apparent maximum current (i as determined by amperometry could be adjusted both by the film composition as well as the operation temperature. [source] Unconventional Spin Crossover in Dinuclear and Trinuclear Iron(III) Complexes with Cyanido and Metallacyanido BridgesEUROPEAN JOURNAL OF INORGANIC CHEMISTRY, Issue 21 2009alitro Abstract A nonsymmetrical triamine, 1,6-diamino-4-azahexane, was Schiff-condensed with (X-substituted) o -salicylaldehyde to yield pentadentate ligands X-L5: salpet and MeBu-salpet. These ligands form mononuclear, dinuclear, and trinuclear FeIII complexes, whose structures were determined by single-crystal X-ray analysis. Of the mononuclear complexes, [FeIII(salpet)Cl] and [FeIII(MeBu-salpet)Cl] are high spin (S = 5/2), whereas [FeIII(salpet)CN]·MeOH is low spin (S = 1/2). The dinuclear and trinuclear complexes show a kind ofthermally induced spin crossover. The dinuclear complex [L5FeIII(CN)FeIIIL5](ClO4)·2H2O (L5 = salpet) is a mixed-spin assembly: the C -coordinated FeIII center is low spin (L) and the N -coordinated FeIII center is high spin (H) at low temperature; an antiferromagnetic interaction occurs between them. This LH reference state is mixed with the LL one. Upon heating, the system shows an increasing content of the HH state. Also, the dinuclear complex [L5FeIII(CN)FeIIIL5](BPh4)·2MeCN (L5 = MeBu-salpet) exhibits a spin transition between LH and HH spin pairs. The mixed-valence trinuclear complex [L5FeIII{FeII(CN)5(NO)}FeIIIL5]·0.5MeOH·3.75H2O (L5 = salpet) shows spin crossover with a residual high-spin fraction at liquid He temperature owing to the LL + LH ground state. The metallacyanido-bridged complex [L5FeIII{Ni(CN)4}FeIIIL5]·2MeOH (L5 = MeBu-salpet) contains a high-spin pair, HH, over the whole temperature interval with a ferromagnetic exchange interaction. A theoretical model was outlined that allows simultaneous fitting of all available experimental data (magnetic susceptibility, magnetization, high-spin mole fraction obtained from the Mössbauer spectra) on a common set of parameters. (© Wiley-VCH Verlag GmbH & Co. KGaA, 69451 Weinheim, Germany, 2009) [source] Acrylic Nanocomposite Resins for Use in Stereolithography and Structural Light Modulation Based Rapid Prototyping and Rapid Manufacturing Technologies,ADVANCED FUNCTIONAL MATERIALS, Issue 16 2008Matthias Gurr Abstract A novel family of optically transparent acrylic nanocomposites containing up to 30,wt,% silica nanoparticles with an average diameter of 20,nm was developed for application in structural light modulation (SLM) and stereolithography (SL) technologies. The uniform dispersion of nanoparticles affords a significantly improved toughness/stiffness-balance of the photopolymerized and postcured nanocomposites. It is possible to increase stiffness, as expressed by Young's modulus, from 1290 to 1700,MPa without encountering the embrittlement typical for many other conventional filled polymers. Fracture behaviour is examined by means of fracture mechanics investigation and SEM analyses of fracture surfaces. According to TEM analyses and measurement of optical transmittance remarkable uniform dispersion of silica nanoparticles was achieved. The silica nanoparticle concentrations up to 17,wt,% give only marginally higher viscosities and do not affect transmittance, while slightly increasing the exposure times needed in photopolymerization. Moreover, the silica nanoparticles afford materials with reduced shrinkage and improved properties. The green effective ankle splay out (EASO) measured on H-shaped diagnostic specimens, is significantly reduced for the nanocomposite materials from 1.38,mm for the unfilled material to 0.82,mm for nanocomposites containing 30,wt,% nanosilica. The building accuracy is increased significantly with increasing content of silica nanofillers. [source] Metallic oxides as fire retardants and smoke suppressants in flexible poly(vinyl chloride)JOURNAL OF APPLIED POLYMER SCIENCE, Issue 5 2010Antonio Rodolfo Jr. Abstract Combustion and smoke emission properties of PVC compounds, modified with copper (II), molybdenum, and zinc oxides, were studied using cone calorimeter, limiting oxygen index (LOI) and thermogravimetry coupled with mass spectrometry (TG/MS). Results showed that the metal oxides have a very significant effect on the combustion and smoke suppression properties of the PVC compounds. The results also confirmed the anticipation mechanisms of the dehydrochlorination reactions, reductive coupling, and elimination of benzene resulting from the presence of copper (II), molybdenum, and zinc, indicated by the increasing content of postcombustion char residue and the significant reduction in benzene production, indicated by the MS measurements performed. The results also provide indications that the combination of the copper (II) and molybdenum oxides is the one with the best balance of combustion properties, as it reduced the heat released and promoted the suppression of smoke more efficiently. The formulations containing ZnO, because of their strong Lewis acid character, indicated a less pronounced reduction of smoke released during the combustion process, when compared with copper (II) and molybdenum oxides. © 2010 Wiley Periodicals, Inc. J Appl Polym Sci, 2010 [source] Effective preparation and characterization of montmorillonite/poly(,-caprolactone)-based polyurethane nanocompositesJOURNAL OF APPLIED POLYMER SCIENCE, Issue 2 2008Eun Hwan Jeong Abstract In this study, montmorillonite (MMT)/poly(,-caprolactone)-based polyurethane cationomer (MMT/PCL-PUC) nanocomposites were prepared and their mechanical properties, thermal stability, and biodegradability were investigated. PCL-PUC has 3 mol % of quaternary ammonium groups in the main chain. The MMT was successfully exfoliated and well dispersed in the PCL-PUC matrix for up to 7 wt % of MMT. The 3 mol % of quaternary ammonium groups facilitated exfoliation of MMT. The 1 wt % MMT/PCL-PUC nanocomposites showed enhanced tensile properties relative to the pure PCL-PU. As the MMT content increased in the MMT/PCL-PUC nanocomposites, the degree of microphase separation of PCL-PUC decreased because of the strong interactions between the PCL-PUC chains and the exfoliated MMT layers. This resulted in an increase in the Young's modulus and a decrease in the elongation at break and maximum stress of the MMT/PCL-PUC nanocomposites. Biodegradability of the MMT/PCL-PUC nanocomposites was dramatically increased with increasing content of MMT, likely because of the less phase-separated morphology of MMT/PCL-PUC. © 2007 Wiley Periodicals, Inc. J Appl Polym Sci, 2008 [source] Nonisothermal cure kinetics of DGEBA with novel aromatic diamineJOURNAL OF APPLIED POLYMER SCIENCE, Issue 5 2007M. Ghaemy Abstract The effect of the molar ratio of diglycidyl ether of a bisphenol-A based epoxy (DGEBA) and synthesized 4-phenyl-2,6-bis(4-aminophenyl)pyridine (PAP) as curing agent during nonisothermal cure reaction by the Kissinger, Ozawa, and isoconversional equations was studied. The cure mechanism was studied by FTIR analysis. Kinetic analysis of the curing reaction of DGEBA at two different concentrations (42 and 32 phr) of the curing agent was studied by using DSC analysis. With an increasing PAP content, the pre-exponential factor increased by increasing collision probability between epoxide and primary or secondary amine groups in noncataltyic or catalytic modes. The activation energy also increased because of the increasing content of crosslink density. The activation energies obtained from three equations were in good agreement. © 2006 Wiley Periodicals, Inc. J Appl Polym Sci 103: 3076,3083, 2007. [source] Influence of stereochemistry on the thermal properties of partially cycloaliphatic polyamidesJOURNAL OF POLYMER SCIENCE (IN TWO SECTIONS), Issue 12 2002Bert Vanhaecht Abstract The effects of the partial substitution of 1,4-disubstituted cyclohexane monomers for linear aliphatic monomers in polyamides are discussed. More specifically, the relation between the stereochemistry of the cycloaliphatic residues and the thermal properties [melting temperature (Tm) and crystallization temperature (Tcr)] was investigated. For this purpose, two different types of copolyamides were synthesized: in polyamides 12.6, the adipic acid residues were partially replaced by cis/trans -1,4-cyclohexanedicarboxylic acid (1,4-CHDA), whereas in polyamides 4.14, the 1,4-diaminobutane residues were partially substituted with cis/trans -1,4-diaminocyclohexane (1,4-DACH). For both systems, increasing the degree of substitution of cycloaliphatic residues for linear aliphatic residues resulted in a rise of both Tm and Tcr. This points to the isomorphous crystallization of the linear and cycloaliphatic residues. In contrast to the use of 1,4-DACH as a comonomer, 1,4-CHDA residues showed isomerization upon thermal treatment of the polyamides. This isomerization of the cyclohexane residues influenced the thermal properties of the copolyamides. The use of a nonisomerizing cis,trans mixture of 1,4-DACH exhibited the large influence of the stereochemistry of the cycloaliphatic residues on the Tm of the copolyamides. For both the 1,4-CHDA- and 1,4-DACH-based copolyamides, differential scanning calorimetry analysis revealed that recrystallization occurs during melting. This exothermal effect becomes less pronounced with an increasing content of rigid cycloaliphatic residues. © 2002 Wiley Periodicals, Inc. J Polym Sci Part A: Polym Chem 40: 1962,1971, 2002 [source] Processing of Lightweight, High-Strength Porcelains Using an Alumina Cement to Replace Feldspars and ClaysJOURNAL OF THE AMERICAN CERAMIC SOCIETY, Issue 7 2000Weon-Pil Tai New lightweight, high-strength porcelain bodies, using only nonplastic raw materials such as glass microspheres, quartz, and alumina cement, were fabricated and the effect of quartz particle size was investigated. Decreases in the green strength, relative to an increasing content of glass microspheres, were attributed to the decrease in the density and the relative decrease in the volume of alumina cement. The phases in the fired body were glass, ,-quartz, cristobalite, anorthite, and a small amount of ,-alumina. The large quartz particles (10,32 ,m in size) could not be densified to closed porosity, because of underfiring, whereas smaller quartz particles (4,10 ,m in size) permitted densification to closed porosity at 1300°C. The high flexural strength when using medium-sized quartz particles (6,20 ,m, content of 30 wt%) was attributed to a stronger prestress and higher density that was due to better vitrification. [source] Nitroxide spin probe study of probe size, hydrogen bonding and polymer matrix rigidity effects on poly(acrylic acid)/poly(ethylene oxide) complexesMAGNETIC RESONANCE IN CHEMISTRY, Issue 7 2003Li Tan Abstract An electron spin resonance (ESR) spin probe study was performed on 1 : 1 by weight poly(acrylic acid) (PAA)/poly(ethylene oxide) (PEO) complex over the 100,450 K temperature range with a series of tetramethylpiperidyloxy-based spin probes. Measurements of the parameters T5mT, Ta and Td demonstrated the effects of probe size and the strength of hydrogen bonding. The probes in the series Tempone, Tempo, Tempol and Tamine (respectively 4-oxo-, unsubstituted, 4-hydroxy- and 4-amino-2,2,6,6,-tetramethylpiperidine -1-oxyl) displayed noticeable increases in the hydrogen-bonding effect, as indicated by Ta and Td. These increases correlated with increasing hydrogen bond acceptor strength. On the other hand, as the probe size became larger, T5mT gradually increased due to the free volume decrease. These effects were analyzed using the established theoretical relationship of T5mT to probe volume expressed by f. Meanwhile, in order to investigate the effect of polymer matrix rigidity, a similar study was performed with a nitroxide spin probe, 2,2,6,6-tetramethyl-1-piperidine-1-oxyl (Tempo), on PAA/PEO complexes of different weight compositions. The quantitative fast motion fraction in the composite ESR spectrum was calculated. The influence of changes in the composition of PAA on the molecular mobility was characterized by changes of the spectral parameters and ,c. The molecular mobility was shown to diminish with increasing content of PAA in PAA/PEO blends duo to the restriction of the polymer matrix rigidity increase. Copyright © 2003 John Wiley & Sons, Ltd. [source] Polymer,nanofiller prepared by high-energy ball milling and high velocity cold compactionPOLYMER COMPOSITES, Issue 3 2008Bruska Azhdar High-energy ball milling using comilling in a solid state by low-temperature mechanical alloying to prepare nickel-ferrite (NiFe2O4) nanopowders and ultrafine poly(methyl methacrylate) (PMMA), dispersing nanoparticles in a polymer matrix, and a uniaxial high-velocity cold compaction process using a cylindrical, hardened steel die and a new technique with relaxation assists have been studied. The focus has been on the particle size distributions of the nanocomposite powder during the milling and on the surface morphology of the nanocomposite-compacted materials after compaction with and without relaxation assists. Experimental results for different milling systems are presented showing the effects of milling time and material ratio. It was found that a longer mixing time give a higher degree of dispersion of the nanopowder on the PMMA particle surfaces. Furthermore, with increasing content of NiFe2O4 nanopowder, the reduction of the particle size was more effective. Different postcompacting profiles, i.e. different energy distributions between the upper and lower parts of the compacted powder bed, lead to different movements of the various particles and particle layers. Uniformity, homogeneity, and densification on the surfaces in the compacted powder are influenced by the postcompacting magnitude and direction. It was found that the relaxation assist device leads to an improvement in the polymer powder compaction process by reducing the expansion of the compacted volume and by reducing the different opposite velocities, giving the compacted composite bed a more homogeneous opposite velocity during the decompacting stage and reducing the delay time between the successive pressure waves. POLYM. COMPOS., 2008. © 2007 Society of Plastics Engineers [source] An Investigation on Thermal Decomposition of DNTF-CMDB PropellantsPROPELLANTS, EXPLOSIVES, PYROTECHNICS, Issue 6 2007Wei Zheng Abstract The thermal decomposition of DNTF-CMDB propellants was investigated by pressure differential scanning calorimetry (PDSC) and thermogravimetry (TG). The results show that there is only one decomposition peak on DSC curves, because the decomposition peak of DNTF cannot be separated from that of the NC/NG binder. The decomposition of DNTF can be obviously accelerated by the decomposition products of the NC/NG binder. The kinetic parameters of thermal decompositions for four DNTF-CMDB propellants at 6,MPa were obtained by the Kissinger method. It is found that the reaction rate decreases with increasing content of DNTF. [source] An impedance spectroscopy study in poly(butylene adipate) ionomersANNALEN DER PHYSIK, Issue 10 2004F. Yakuphanoglu Abstract Poly(butylenes adipate) ionomers (PBAi) were synthesized using dimethyl 5-sulfoisophthalate sodium salt (DMSI) up to 5 mol% of diacid monomer. We have investigated electrical and dielectric properties of the ionomers to evaluate alternating current (AC) parameters such as impedance, conductance, dielectric constant, admittance, susceptance, dielectric loss, and resistance by an impedance spectroscopy. It is seen that the ionic conductances of the ionomers increase with increasing content of DMSI. The AC conductance for the ionomers was found to vary as ,s with the index s , 1. A decrease in the relative dielectric constant of the ionomers is observed with the increase in the ionic content. The electrical relaxation in the dielectric spectra of the ionomers was not observed due to the orientation polarization of the dipoles. It is also observed that the tangent loss increases with the increase in the ionic content. [source] Effect of the protein/energy ratio on the growth of Mediterranean yellowtail (Seriola dumerili)AQUACULTURE RESEARCH, Issue 11 2008Ana Tomás Vidal Abstract Yellowtails weighing 490 g were fed five experimental diets with different protein/energy ratios, 24.6, 26.9, 28.9, 31.8 and 35.8 g MJ,1, for 152 days. The energy content was similar in all the diets and the protein and lipid levels were 40/26, 45/26, 50/18, 50/26 and 55/18 %CP/%CL respectively. The final weight and SGR were lower in fish fed diets with a lower PD/ED ratio (24.6 and 26.9 g MJ,1), and the mortality of fish fed diet 24.6 g MJ,1 was higher. In fact, only fish that consumed diet 35.8 g MJ,1 had a haematocrit and a normal erythrocyte number similar to that in healthy yellowtail. No differences appeared in feed intake and feed conversion ratio. Digestible energy ingestion was similar for all the diets and digestible protein intake was also low for 24.6 compared with 35.8 g MJ,1. The meat composition was similar for fish fed all the diets, but the profiles of muscle fatty acids indicated an increasing content of saturates and n-3 HUFA, while the levels of monounsaturates decreased, corresponding to an increase in the PD/ED relation. The economic conversion ratio and economic profit index were not different for fish fed the experimental diets. [source] Cationic, water-soluble, fluorene-containing poly(arylene ethynylene)s: Effects of water solubility on aggregation, photoluminescence efficiency, and amplified fluorescence quenching in aqueous solutionsJOURNAL OF POLYMER SCIENCE (IN TWO SECTIONS), Issue 19 2006Yan-Qin Huang Abstract Three novel fluorene-containing poly(arylene ethynylene)s with amino-functionalized side groups were synthesized through the Sonogashira reaction. They were poly{9,9-bis[6,-(N,N -diethylamino)hexyl]-2,7-fluorenylene ethynylene}- alt - co -{2,5-bis[3,-(N,N -diethylamino)-1,-oxapropyl]-1,4-phenylene} (P1), poly{9,9-bis[6,-(N,N -diethylamino)hexyl]-2,7-fluorenylene ethynylene} (P2), and poly({9,9-bis[6,-(N,N -diethylamino)hexyl]-2,7-fluorenylene ethynylene}- alt - co -(1,4-phenylene)) (P3). Through the postquaternization treatment of P1,P3 with methyl iodide, we obtained their cationic water-soluble conjugated polyelectrolytes (WSCPs): P1,,P3,. The water solubility was gradually improved from P3, to P1, with increasing contents of hydrophilic side chains. After examining the ultraviolet,visible absorption and photoluminescence (PL) spectra, fluorescence lifetimes, and dynamic light scattering data, we propose that with the reduction of the water solubility from P1, to P3,, they exhibited a gradually increased degree of aggregation in H2O. The PL quantum yields of P1,,P3, in H2O displayed a decreasing tendency consistent with the increased degree of aggregation, suggesting that the pronounced degree of aggregation was an important reason for the low PL quantum yields of WSCPs in H2O. Two structurally analogous water-soluble trimers of P2, and P3,, model compounds 2,7-bis(9,,9,-bis{6,-[(N,N -diethyl)- N -methylammonium] hexyl}-2,-fluorenylethynyl)-9,9-bis{6,-[(N,N -diethyl)- N -methylammonium]hexyl}fluorene hexaiodide and 1,4-bis(9,,9,-bis{6,-[(N,N -diethyl)- N -methylammonium]hexyl}-2,-fluorenylethynyl)benzene tetraiodide, were synthesized. The amplified fluorescence quenching of these WSCPs by Fe(CN)64, in H2O was studied by comparison with a corresponding analogous trimer. The effects of aggregation on the fluorescence quenching may be two-edged in these cases. © 2006 Wiley Periodicals, Inc. J Polym Sci Part A: Polym Chem 44: 5778,5794, 2006 [source] | ||||||||||||||||