bluuebunny/crossref_metadata_2025_split huggingface dataset:
The Effect of Masked Isocyanates on the Mechanical Properties of My720/dds Epoxy Resin
Authors: Rungsimuntakul N. , Lonikar S.V. , Fornes R. E. , Gilbert R.D. 
Published: March 2011

ABSTRACTThe mechanical properties of epoxy resins and epoxy resin/graphite fiber composites are adversely affected by moisture absorption. Incorporation of masked isocyanates that unmask to release isocyanates in situ at the cure temperatures (150-177ºC) reduce the equilibrium absorption up to ∼70%. Dynamic mechanical analyses and stress-strain properties of epoxy resins containing masked isocyanates were examined to determine their effect on mechanical properties. The ultimate Tg of the epoxy is reduced by incorporation of masked isocyanate, but the actual Tg is comparable to the “as cured” Tg of the epoxy. The dynamic moduli up to the Tg are relatively unaffected. Ina number of cases, the initial modulus, elongation at break and peak stress are equal or better than the unmodified resins.
A Study of Short Metal Fiber Reinforced Composite Materials
Authors: Chung W. C. 
Published: March 2011

ABSTRACTOver the years, the conventional involvement of short fiber reinforced composites in electrical applications has been as electrical insulation. Contrary to this approach, with the increasing need of better electromagnetic interference (EMI), radio—frequencyinterference (RFI) shielding and control of electrostatic charge distribution (ESD) for computer, defense, space exploration and some high—tech structural components, itis expected that the development of conductive polymeric composite materials will grow strongly and significantly.An experimental investigation is designed to systematically evaluate the mechanical properties and electrical properties of metal fiber reinforced composites subjected to various loading conditions. In this study, chopped Inconel 601 (nickel base) metal fiber witha fixed fiber aspect ratio (length/diameter ratio) is used to reinforce commercially available thermoset polyester resin. Mechanical testing of custom made samples, failure analyses using visual inspection, light microscopy and SEM are conducted to understand the fracture behaviors and possible failure causes in such composites. The feasibility of using metal fiber polymeric composites in structural/electrical applicationsis discussed in this paper.
Structural Studies of Semiflexible Fluorocarbon Chains Containing an Aromatic Core
Authors: Schulte A. , Hallmark V. M. , Twieg R. , Song K. , Rabolt J. F. 
Published: March 2011

ABSTRACTThe molecular structure of a series of perfluoroalkane oligomers having two F(CF2)n chains attached to a phenyl group in the para position has beenstudied by Fourier Transform and conventional Raman spectroscopy at ambient and low temperatures. From comparison with model compounds bands attributable to both the substituted phenyl ring and the perfluoroalkane chains could be assigned. In particular, the low frequency region was investigated as a function of temperature and pressure in order to assess the impact of the rigid aromatic core on the bandshapes and frequencies.
The Effect of Low Power Ammonia and Nitrogen Plasmas on Carbon Fibre Surfaces
Authors: Jones C. , Sammann E. 
Published: March 2011

ABSTRACTThe effect of low power nitrogen and ammonia plasmas on carbon fibre surfaces has been studied using X-ray photoelectron spectroscopy(XPS) and scanning electron microscopy (SEM). A comparison is made between two polyacrylonitrile based fibres and a pitch based fibre. Grazing angle techniques have been exploited to probe only the first 12-15A of the fibre surface. Plasma treatments were carried out in an insitu plasma treatment cell which was attached to a PHI 5400 X-ray photoelectron spectrometer enabling the immediate effects of the plasma to be studied before the treated surface was exposed to air.
Synthesis and Characterization of a Thermotropic Polyalkanoate of 4,4'- Dihydroxy-α,α'-Dimethylbenzalazine
Authors: Friutwala H. , Cimecioglu A. L. , Weiss R. A. 
Published: March 2011

Several research projects in our laboratory have used an LCP based on 4,4'-dihydroxy,a-a' dimethylbenzalazine, that was first synthesized by Roviello and Sirigu 1.2 Copolymers with the following qeneral structure,have been used in self-reinforcing polymer blends3 and are currently being used in small angle neutron scattering studies of the molecular conformation of an LCP in a nematic field. In this latter study, it is imperative that the polymer be well characterized, especially with respect to molar mass and thermal stability. This paper describes the effect of molar mass and thermal history on the thermal stability and transitions of this particular LCP.
Origin and Elimination of Scattering Losses in Fluoride Glasses and Fiber
Authors: Sanghera J. S. , Aggarwal I. , Harbisp B. , Busse L. , Pureza P. , Hart P. , Sachon M. G. , Sills L. , Miklos R. 
Published: March 2011

AbstractThe sources of scattering losses in fluorozirconate glasses and fibers are reviewed. Results are presented which show that the predominant mechanism responsible for the presence of fluoride crystals is heterogeneous nucleation. The nature and origin of the different nuclei are discussed and possible ways to eliminate them from the glasses assessed. It is proposed that extreme care be employed in the processing of the glasses with particular emphasis on the preform fabrication step as this is critical to the design of ultra-low loss fibers.
Fabrication of ALF3-Based Glass Fibers
Authors: Shahriari Mahmoud R. , Iqbal Tariq , Foy Paul R. , Saggese Steve J. , Sigel G. H. 
Published: March 2011

AbstractSeveral glass systems based on AIF3 have been synthesized and fabricated into preforms by controlled melting and rotational casting. High optical quality preforms have been drawn into fibers using a specially modified drawing facility. The drawing tower is enclosed with a vertical glove box in which the levels of both moisture and oxygen are kept below 1 ppm during the drawing. The AIF3 -based fibers have shown dramatically superior chemical durability relative to the ZrF4 -based glass fibers. Selected optical, mechanical and thermal properties of these fibers will be presented. AIF3 -based glass fibers offer interesting opportunities for short range applications in the 2–4 micron region of the infrared such as sensing, remote spectroscopy and laser power delivery.
Property-Composition Relationship of Chalcogenide Glasses Containing Germanium
Authors: Yi Jay J. L. , Strutt Peter R. 
Published: March 2011

AbstractIn-depth studies of property-composition relationship in chalcogenide glasses have revealed some interesting structural features. For example, specific discoveries in the Ge-Se-Sb and similar systems were of (i) meta-stable phase separation for glasses with a high Se or S content ( >70 at.% ), and (ii) abnormal behavior of some structure-sensitive properties ( e.g. optical band-gap energy ) for glasses with Se or S in the range of 60–70 at.%. In carefully studying the Ge-Se system, the liquidus curve ( reported by H. Ipser et al, 1982 ).was reexamined; this was found to have an S-shape at the phase-separation region. Another interesting finding was the dependence of the band-gap energy on composition in (1−x)GeSe2 xSb2Se3 glasses; this was not a linear relation but a curve with a maximum band-gap energy at 9 at.% Sb.
Sol-Gel Processing for Fiber Optic Applications
Authors: Thomas Ian M. 
Published: March 2011

AbstractThe sol-gel process is a versatile process for the preparation of many types of glass and ceramics. This includes optical fibers. In this paper, the general principles of sol-gel processing are described first. This is followed by details of the specific methods that can be used for the fabrication of optical fibers. Finally, some conclusions are drawn as to the commercial potential of the various methods.
Mechanical Strength of Low-Dimension Class Fibers
Authors: Cerqua K. A. , Behrman E. C. , Lacourse W. C. 
Published: March 2011

AbstractChalcogenide glasses present a unique opportunity for the study of the effect of dimensionality of the properties of amorphous systems. Presented here are preliminary results of experiments on fibers of these materials. Strength in these fibers is related both to dimensionality, which is a continuously variable function of composition and to drawing conditions, which produce ordering. A simple theoretical model for the ordering effect is proposed and discussed.
The Growth and Characterization of Tungsten Bronze SrxBa1−xNb2O6 Single Crystal Fibers
Authors: Yamamoto Joyce K. , Bhalla A. S. 
Published: March 2011

AbstractThe growth of SrxBal−xNb2O6 solid solution single crystal fibers has been achieved using a modified float zone technique. The technique is described and the results of several property measurements are presented.
Infrared Spectroscopy of Protons in KTiOPO4
Authors: Crawford M. K. , Morris P. A. , Roelofs M. , Gashurov G. 
Published: March 2011

AbstractWe report infrared (IR) measurements of protons (H+), present as OH−, in KTiOPO4 grown by various techniques. The IR spectra are sensitive to the growth technique used. In high temperature hydrothermally grown crystals we observe IR bands which have strongly temperature dependent linewidths. The Arrhenius-type activation energies for these linewidths are small (6–15 meV). The IR bands are polarized and this information can aid in making OH− site assignments.
Diffusion of Hydrogen Through Hermetic Carbon Films on Silica Fibers
Authors: Lemaire P. J. , Walker K. L. , Kranz K. S. , Huff R. G. , DiMarcello F. V. 
Published: March 2011

AbstractRecent work has made it possible to deposit hermetic carbon coatings on optical fibers during the drawing process. These coatings are used to protect the silica portion of the fiber from undesirable loss increases and strength reductions caused by H2 and H2O, respectively. The hermetic properties of the carbon films have been evaluated using accelerated test conditions where the coated fibers are exposed to H2 at elevated temperatures and hydrogen pressures. In-situ spectral loss monitoring has made it possible to measure changes in the characteristic optical loss features associated with either molecular H2or with species such as OH which form when hydrogen reacts with defects in the silica. By using long lengths of fiber it is thus possible to optically measure the extremely small amounts of hydrogen that penetrate the carbon films during accelerated tests. At temperatures in the range of 100 to 145°C the diffusion of H2 is readily modeled using classical diffusion theories for a composite cylinder, allowing calculation of the diffusion coefficient and the solubility for H2 in the carbon. At higher temperatures the diffusing H2 is partially depleted by reaction with defects in the glass. For these conditions the inward diffusion of the H2 and its reaction at defect sites tend to balance each other, giving rise to a constant, but extremely low, concentration of H2 in the fiber.
EPR Characterization of Carbon Coated Fiber
Authors: Inniss Daryl 
Published: March 2011

AbstractAn amorphous carbon coating has been developed to improve the resistance of silica optical fibers to static fatigue and hydrogen permeation. The carbon coated optical fibers are characterized by electron paramagnetic resonance spectroscopy. A Lorentzian lineshape is observed, centered at the g value of 2.002. Intensity measurements as a function of temperature suggest that localized spin centers contribute to the spin resonance. It is shown that atmospheric control of the carbonaceous environment results in the removal of these EPR active sites.
High Magnetic Field Phases of the (TMTSF)2X (X = CLO4, PF6) Charge Transfer Complexes
Authors: Brooks J. S. , Fortune N. A. , Chaikin P. M. , Chiang L. Y. , Montambaux G. , Perenboom Jos. A. A. J. 
Published: March 2011

ABSTRACTThe purpose of this talk is to discuss the physical properties of the (TMTSF)2X charge transfer salts in high magnetic fields. This class of materials is of great interest since the effective lower dimensionality and the various ground states are magnetic field dependent at low temperatures. At present, the so-called “standard model” provides a good theoretical description of the low field field induced spin density wave transitions (FISDW). However the reentrance from the last FISDW back to a high field metallic state, and the coexistence of “fast oscillations” in all measured properties, is yet to be accurately described theoretically. The emphasis of this paper is on recent specific heat results which have been obtained on (TMTSF)2ClO4 in magnetic fields as high as 30 T. Here we observe both the reentrant phase transition and the fast oscillations in the specific heat. A main conclusion we draw from our measurements is that the density of states in the reentrant phase is less than it is in the low field metallic state at low temperatures.
Magnetic Evidence for Reentrant Field-Induced Spin Density Waves
Authors: Naughton M. J. , Chamberlin R. V. , Yan X. , Chaikin P. M. , Chiang L. Y. 
Published: March 2011

ABSTRACTHigh magnetic field (to 31T) d.c. magnetization measurements on the quasi-one dimensional organic conductor (TMTSF) 2ClO4 yield thermodynamic evidence for the reentrance of a metallic phase from the magnetic field-induced spin density wave state. The H-T phase diagram developed previously from magnetotransport measurements is reproduced from 8 to 26 tesla. The reentrance occurs as a sharp collapse of M(H) to (near) zero magnetization in the high field metal phase. For fields above 27 tesla, deHaas-van Alphen-like oscillations appear, similar to earlier resistance data, as well as other features possibly signifying multiple transitions in the very high field regime.
Sound Velocity Measurements in (Tmttf)2X Salts, X = ReO4, AsF6, SbF6
Authors: Brown S. E. , Javadi H. H. S. , Laversanne R. 
Published: March 2011

ABSTRACTYoung’s modulus E measurements using the vibrating reed technique are reported for salts of the (TMTTF)2X series, where X = ReO4, SbF6, AsF6. All three exhibit softening of the modulus at the structureless transition, with the largest effect in the material with the non–centrosymmetric anion ReO4. The behavior is typical of quadratic coupling to an order parameter plus effects from fluctuations. There is a large stiffening of E below the anion ordering temperature of (TMTTF)2ReO4.
Electron Tunneling in Charge-Density and Spin-Density Waves
Authors: Huang X. Z. , Maki K. 
Published: March 2011

ABSTRACTFirst we calculate the tunneling density of states of quasi-two dimensional charge density waves (CDW) or spin density waves (SDW) in the presence of impurity scattering. Second, we consider the tunneling current between two CDWs or two SDWs. We point out the existence of new contribution, which gives rise to the a.c. current when one CDW is sliding relative to the other one.
Fibers of Conducting Polymers: High Electrical Conductivity Combined with Attractive Mechanical Properties
Authors: Andreatta Alejandro , Tokito S. , Smith P. , Heeger A. J. 
Published: March 2011

ABSTRACTWe present a summary of our recent results on the electrical and mechanical properties of fibers made from poly(2,5-dimethoxy-p-phenylene vinylene), PDMPV and poly(2,5-thienylene vinylene), PTV, using the precursor polymer methodology, and from polyaniline, PANI, using the method of processing as polyblends with poly-(p-phenylene terephthalamide), PPTA, from sulfuric acid. The solubility of both PANI and PPTA in H2SO4 presents a unique opportunity for co-dissolving and blending PANI and PPTA to exploit the excellent mechanical properties of PPTA and the electrical conductivity of PANI; we summarize the electrical and mechanical properties of such composite fibers. For PDMPV and PTV fibers, we find a strong correlation between the conductivity and the tensile strength (and/or modulus), and we show from basic theoretical concepts that this relationship is an intrinsic feature of conducting polymers.
Spectroscopic and Molecular Weight Studies of Polytoluidines
Authors: Wei Y. , Hsueh K. F. , Nagy S. , Ray A. , MacDiarmid A. G. , Dykins J. , Epstein A. J. , Wnek G. E. 
Published: March 2011

ABSTRACTPoly(o-toluidine) and poly(m-toluidine) in base form have been characterized by infrared and lH NMR spectroscopy. Assignments of the proton NMR signals have been facilitated by the use of model compounds. The distinction between benzenoid and quinoid methyl resonances in the NMR permits a semi-quantitative estimation of the oxidation states of the polytoluidines. Infrared studies are consistent with a polyaniline-type backbone having pendant methyl groups. Field desorption mass spectrometry (FD-MS) was employed for estimation of the molecular weight of poly(o-toluidine). Gel-permeation chromatography of the same sample showed a bimodal elution pattern, suggesting that the FD-MS technique detects only the lower molecular weight fraction of the polymer. Despite this inherent limitation, FD-MS yields the interesting information that the polymer contains chains of both odd and even numbers of repeat units, necessitating the coexistence of different oxidation states in the base form of the polymer.
Electrically Conductive Composite of Polyaniline and Poly(p-Phenylene-Terephthalamide)
Authors: Bi Xian-Tong , Wang C. , Bao J. S. 
Published: March 2011

ABSTRACTThe improvement of the processibility and mechanical properties of poly-aniline (PAn) by processing a concentrated sulfuric acid solution of the mixture of chemically prepared conductive PAn powders and poly(p-phenylene-terephthalamide) (PPTA) in different weight ratios are presented.The concentrated sulfuric acid solution of PAn and PPTA were processed to films and threads, they are liquid crystalline conductive polymer composites, the electrical conductivities of the composites are between 10−4 -10−1 s/cm.PAn enhanced the tensile strength of PPTA, but does not effect the elongation. The morphology of the PPTA/PAn composite surfaces are fiberlike texture.
Magnetic Properties of Microcrystalline Poly(Phenyl- Diacetylenes) Carrying Radical or Carbene Centers on the Side Chains
Authors: Koga Noboru , Inoue Katsuya , Sasagawa Noriko , Iwamura Hiizu 
Published: March 2011

ABSTRACT1-Phenyl-l,3-butadiyne derivatives (3 and 4) carrying stable t-butylnitroxide and diazomethyl groups, respectively, have been prepared. Mixed crystals of 3 and the corresponding hydroxylamine 2 (x003c:1:1) polymerized in the solid state at 100°C to give black-violet microcrystals with a metallic luster. A microcrystalline sample of 4 underwent spontaneous polymerization at room temperature when crystallized to give an insoluble polymer which was then photolyzed at cryogenic temperature to generate triplet carbene centers attached to the phenyl rings of the poly(phenyldiacetylene). Some of these microcrystalline polymeric samples were responsive to a magnet at room temperature. Magnetic susceptibility measurements on the two samples revealed only weakly coupled independent spins Hydrogen bonding between the polydiacetylene chains as estimated by X-ray crystal structure of 2 is expected to be effective for increasing the dimension of the spin alignment.
New Second-Order Nonlinear Optical Organic Crystals
Authors: Donald D.S. , Cheng L.-T. , Desiraju G. , Meredith G. R. , Zumsteg F. C. 
Published: March 2011

ABSTRACTThe design of molecular crystals with specific optical properties, which are thought to arise from constituent molecules’ polarizability properties, is a desirable but currently unachievable goal. One can partially achieve this goal by choosing compounds with specific molecular attributes and empirically determining the manner in which these are translated into crystal properties. Besides the fact that there are no certain rules for prediction of crystal packing arrangements, there is also a problem in specifying molecular properties from what are today incomplete polarizability structure-property relationships. We have, realizing these limitations, identified new molecular crystals by a nonlinear optical (powder-SHG) scouting-screening program from lists of compounds chosen because of desirable molecular properties. Examination of successful materials has revealed interesting, new alignment motifs. Some of these materials, a set of halogen and cyano derivatives of aromatic compounds, are described relating properties and structures of molecules and crystals. In particular, the orientation directing influence of intermolecular halogen-cyano interactions and the use of heterocyclic compounds to improve transparency in the near infrared and in the blue and near ultraviolet spectral regions are demonstrated.
Role of Topology in Spin Alignment of Organic Materials
Authors: Itoh Koichi , Takui Takeji , Teki Yoshio , Kinoshita Takamasa 
Published: March 2011

ABSTRACTIt is shown that the spin alignment in organic molecules as determined by single crystal ESR is highly dependent on the topological nature of their molecular pi electron networks. The three topological isomers of a high-spin molecule, biphenyl-n,n′-bis(phenylmethylene), abbreviated as BP-3,3′-BPM, BP-3,4′-BPM and BP-4,4′-BPM are taken as model compounds. BP-3,3′-BPM has a unique spin alignment for which the simple molecular orbital and valence bond methods predict different ground-state spin multiplicities. The above remarkable feature of spin alignment in organic high-spin molecule is interpreted in terms of their spin density distributions which have been determined by a single crystal ENDOR technique and compared with theoretical values calculated on the basis of a generalized Hubbard model as well as the Heisenberg model. This approach is extended to magnetic polymers in order to characterize their structure of the spin sites.
Fused, Three-Ring Donor-Acceptor Molecules as Potential Materials for Efficient Second Harmonic Generation
Authors: McLean Malcolm R. , Badr Mamoun , Dalton Larry R. , Devine Robert L. S. , Steier William H. 
Published: March 2011

ABSTRACTA series of fused three-ring compounds have been synthesized and characterized for their possible use as organic crystals for second-harmonic generation. Polymer films doped with these compounds were aligned via corona poling and their second order non-linear optical properties compared with layers doped with stilbene like molecules. Values of ¼β0 have been obtained and the effects of different heteroatoms and substituents on λ max and on ¼β0 were examined. An X-ray diffraction crystal structure on one member of the series, 1,2,4-Trichloro-8-nitro-phenoxazin-3-one (Compound 1), revealed a centrosymmetric crystal habit in a P21/n space group, with a = 9.829(3), b = 8.300(2) and c = 15.542(4) Å. Final R(F) = 0.0939 for 754 reflections where I σ; 3σ(I).
Role of High-Spin Molecules as Models for Organic Ferro- and Ferri-Magnets, and Pi-Toporegulated Magnetic Polymers
Authors: Takui Takeji , Endoh Makoto , Okamoto Masayuki , Satoh Kazunobu , Shichiri Toyohiro , Teki Yoshio , Kinoshita Takamasa , Itoh Koichi 
Published: March 2011

ABSTRACTA chemical modification exploiting functional groups such as ether and methylene as bridges between high-spin assemblies has been carried out as a usable method to increase dimensionality of spin structure. Exchange interaction via an ether or a methylene bridge between two high-spin assemblies has been studied by single-crystal ESR spectroscopy. Whether it is ferromagnetic or antiferromagnetic depends upon the substituted position of the bridge, demonstrating the important role of the topological nature in spin alignment. It turns out that superexchange interaction or hyperconjugation mechanism can dominate spin alignment between high-spin assemblies. Using the criteria obtained, model compounds for units of organic ferrimagnets have been synthesized. They possess antiferromagnetically-exchange coupled heterospins and the salient features of their spin structures are characterized in terms of the spin density distribution as determined by single-crystal 1H-ENDOR (Electron-Nuclear-DOuble Resonance) spectroscopy.