Showing papers on "Thermal stability published in 1996"
TL;DR: New, hydrophobic ionic liquids with low melting points (<−30 °C to ambient temperature) have been synthesized and investigated, based on 1,3-dialkyl imidazolium cations and hydrophilic anions and thus water-soluble.
Abstract: New, hydrophobic ionic liquids with low melting points (<−30 °C to ambient temperature) have been synthesized and investigated, based on 1,3-dialkyl imidazolium cations and hydrophobic anions. Other imidazolium molten salts with hydrophilic anions and thus water-soluble are also described. The molten salts were characterized by NMR and elemental analysis. Their density, melting point, viscosity, conductivity, refractive index, electrochemical window, thermal stability, and miscibility with water and organic solvents were determined. The influence of the alkyl substituents in 1, 2, 3, and 4(5)-positions on these properties was scrutinized. Viscosities as low as 35 cP (for 1-ethyl-3-methylimidazolium bis((trifluoromethyl)sulfonyl)amide (bis(triflyl)amide) and trifluoroacetate) and conductivities as high as 9.6 mS/cm were obtained. Photophysical probe studies were carried out to establish more precisely the solvent properties of 1-ethyl-3-methylimidazolium bis((trifluoromethyl)sulfonyl)amide). The hydrophobi...
4,089 citations
TL;DR: In this paper, Nanocomposites are prepared by a simple technique of emulsion polymerization using MMA monomer and Na+-montmorillonite, and the products are purified by hot toluene extraction and characterized by FT-IR, X-ray diffraction, TGA, DSC, and tensile testing.
Abstract: Nanocomposites are prepared by a simple technique of emulsion polymerization using MMA monomer and Na+-montmorillonite. The products are purified by hot toluene extraction and characterized by FT-IR, X-ray diffraction, TGA, DSC, and tensile testing. The structural investigation confirms that the products are intercalated with PMMA chain molecules oriented parallel to the direction of lamellar layers whose separation is consequently more enlarged than in the polymer-free clay. DSC traces also corroborate the confinement of the polymer in the inorganic layer by exhibiting no observable transition in the thermogram. Both the thermal stability and tensile properties of the products appear to be substantially enhanced. The ion-dipole bonding is believed to be the driving force for the introduction and fixation of the organic polymer to the interfaces of montmorillonite. © 1996 John Wiley & Sons, Inc.
451 citations
TL;DR: If one assumes that a region of reduced chain mobility exists near the solid substrate-polymer interface, an analysis of the measured thermal expansion behavior below the transition temperature indicates that the length scale of substrate interactions is on the order of the macromolecular size.
Abstract: The thermal behavior of ultrathin films of poly-(2)-vinylpyridine spin-cast on acid-cleaned silicon oxide substrates is considered. The interaction between the polymer and the substrate is polar in nature and very favorable. As a means of examining the thermal properties of the films, x-ray reflectivity is used to measure the temperature dependence of the film thickness. This experimentally measured thickness-temperature data is used to determine transition temperatures and thermal expansivities. Significantly increased transition temperatures (20-50 \ifmmode^\circ\else\textdegree\fi{}C above the measured bulk glass transition temperature) are observed in ultrathin polymer films. The transition temperature increases with decreasing film thickness, while the degree of thermal expansion below the transition temperature decreases with decreasing film thickness. If one assumes that a region of reduced chain mobility exists near the solid substrate-polymer interface, an analysis of the measured thermal expansion behavior below the transition temperature indicates that the length scale of substrate interactions is on the order of the macromolecular size.
398 citations
TL;DR: In this paper, the authors used polybenzimidazole membrane doped with phosphoric acid (PBI) for use as a polymer electrolyte in a high temperature (ca. 150 to 200 C) proton exchange membrane direct methanol fuel cell.
Abstract: Recently, polybenzimidazole membrane doped with phosphoric acid (PBI) was found to have promising properties for use as a polymer electrolyte in a high temperature (ca. 150 to 200 C) proton exchange membrane direct methanol fuel cell. However, operation at 200 C in strongly reducing and oxidizing environments introduces concerns of the thermal stability of the polymer electrolyte. To simulate the conditions in a high temperature fuel cell, PBI samples were loaded with fuel cell grade platinum black, doped with ca. 480 mole percent phosphoric acid (i.e., 4.8 H{sub 3}PO{sub 4} molecules per PBI repeat unit) and heated under atmospheres of either nitrogen, 5% hydrogen, or air in a thermal gravimetric analyzer. The products of decomposition were taken directly into a mass spectrometer for identification. In all cases weight loss below 400 C was found to be due to loss of water. Judging from the results of these tests, the thermal stability of PBI is more than adequate for use as a polymer electrolyte in a high temperature fuel cell.
395 citations
TL;DR: In this paper, the thermal stability of thin films of Group III nitrides prepared by low-pressure chemical vapor deposition from organometallic precursors was investigated by elastic recoil detection analysis (ERDA).
Abstract: We present results on the thermal stability as well as the thermally induced hydrogen, hydrocarbon, and nitrogen–hydrogen effusion from thin films of Group III nitrides prepared by low‐pressure chemical vapor deposition from organometallic precursors. We have deposited amorphous, polycrystalline, and epitaxial InN, GaN, and AIN films on (0001) Al2O3 substrates using the chemical reaction of azido[bis(3‐dimethylamino)propyl]indium, triethylgallium, and tritertiarybutylaluminium with ammonia. The substrate temperature was varied between 400 °C and 1100 °C. The elemental composition, in particular its dependence on the growth temperature, was investigated by elastic recoil detection analysis (ERDA). The influence of growth rate and crystallite size on the concentration of surface adsorbed hydrocarbons and carbon oxides is determined by a combination of ERDA and thermal desorption measurements. In addition, the stability of and the nitrogen flux from the InN, GaN, and AIN surfaces was determined by x‐ray diffraction and thermal decomposition experiments.
276 citations
TL;DR: In this paper, Nafion samples were loaded with fuel-cell grade platinum black and heated under atmospheres of nitrogen, 5% hydrogen, or air in a thermal gravimetric analyzer and the products of decomposition were taken directly into a mass spectrometer for identification.
Abstract: Nafion{reg_sign} is an important polymer electrolyte for polymer electrolyte fuel cell applications due to its inertness and high proton conductivity. Operation of these fuel cells for extended periods of time at temperatures approaching 100 C introduces concerns of the thermal stability of the Nafion electrolyte. To simulate the conditions in a fuel cell, Nafion samples were loaded with fuel-cell grade platinum black and heated under atmospheres of nitrogen, 5% hydrogen, or air in a thermal gravimetric analyzer. The products of decomposition were taken directly into a mass spectrometer for identification. In all cases, Nafion was found to be thermally stable up to 280 C, at which temperature the sulfonic acid groups began to decompose. A mechanism for the decomposition is proposed which explains many of the evolved compounds observed during heating.
274 citations
TL;DR: Ta-TMS1 as mentioned in this paper is a new member of a growing family of hexagonally packed transition-metal oxide mesoporous molecular sieves (termed TMS1) and exhibits a hexagonal array of pores which can be varied in size from 20 to 40 A and surface areas of over 500 m2/g.
Abstract: The synthesis and characterization of Ta-TMS1, a new member of a growing family of hexagonally packed transition-metal oxide mesoporous molecular sieves (termed TMS1) is described. Ta-TMS1 exhibits a hexagonal array of pores which can be varied in size from 20 to 40 A and surface areas of over 500 m2/g. The thermal and hydrothermal stabilities of Ta-TMS1 are 500 and 450 °C, respectively, making this system the most stable transition-metal oxide molecular sieve yet isolated. The high hydrocarbon adsorption capacities of this material make it a promising candidate as a catalyst support for hydrocarbon re-forming processes. The synthesis of this material was achieved by a novel approach involving the careful hydrolysis of long-chain primary amine complexes of Ta(OEt)5. This ligand-assisted templating mechanism represents a new approach to the synthesis of porous materials in that the inorganic precursor is covalently bonded to the template throughout synthesis. The high thermal stability, ease of synthesis a...
268 citations
TL;DR: A microporous SiO2 material isomorphous to zeolite-β showing an enhanced crystallinity and thermal stability due to the absence of connectivity defects, spontaneously nucleates and grows in a hydrothermal system containing tetraethylammonium and fluoride ions at near neutral pH as mentioned in this paper.
265 citations
TL;DR: In this article, the Schottky barrier height of Ni on n−GaN has been measured to be 0.56 and 0.66 eV by capacitance-voltage (C-V) and current density-temperature (J-T) methods, respectively.
Abstract: The Schottky barrier height of Ni on n‐GaN has been measured to be 0.56 and 0.66 eV by capacitance–voltage (C–V) and current–density–temperature (J–T) methods, respectively. Gallium nickel (Ga4Ni3) is formed as Ni is deposited on the GaN film, which affects the barrier height markedly. The thermal stability of Ni on GaN is also investigated by annealing these specimens at various temperatures. Specimen annealing at temperatures above 200 °C leads to the formation of nickel nitrides Ni3N and Ni4N at the interface of Ni and GaN. These interfacial compounds change the measured barrier height to 1.0 and 0.8 eV by C–V and J–T methods, respectively. Comparisons of Schottky characteristics of Ni with those of Pt, Pd, Au, and Ti are also discussed.
172 citations
TL;DR: Heme transfer studies from the peroxidases to apomyoglobin indicate that SBP holds onto its heme much more tightly than does HRP, and this is consistent with a thermodynamically more stable enzyme.
Abstract: Soybean peroxidase (SBP) has an extremely high melting temperature of 90.5 °C at pH 8.0 in the presence of 1 mM CaCl 2 . The enzyme is substantially more thermostable than the peroxidases from horseradish (HRP) and Coprinus cinereus (CIP). SBP denaturation does not precisely fit the two-state denaturation model due to the formation of the apoenzyme upon initial melting. A pseudo-two-state denaturation can be assumed, however, and this gives rise to apparent kinetics for irreversible inactivation. The apparent kinetics indicate that irreversible deactivation is comprised primarily of enthalpic contributions, with ΔH ? deact = 22.4 kcal/mol and TΔS ? deact = 0.2 kcal/mol at 95 °C. Heme transfer studies from the peroxidases to apomyoglobin indicate that SBP holds onto its heme much more tightly than does HRP, and this is consistent with a thermodynamically more stable enzyme.
150 citations
TL;DR: Highly sulfonated poly(phenylene sulfide) prepared from the polysulfonium cation exhibits excellent thermal stability (T d = 265°C) and high conductivity (> 10 -2 S/cm).
Abstract: Highly sulfonated poly(phenylene sulfide) prepared from the polysulfonium cation exhibits excellent thermal stability (T d = 265°C) and high conductivity (> 10 -2 S/cm). These properties arise from the two sulfonic acid groups substituted on one phenyl ring
TL;DR: In this paper, a two-step approach for synthesizing NLO side-chain aromatic polyimides with different polymer backbones and different chromophores was developed. And the chromophore loading level was controlled efficiently from 0 to 50% by weight using a mild post-Mitsunobu reaction.
Abstract: A two-step, generally applicable synthetic approach for NLO side-chain aromatic polyimides was developed. This is a one-pot preparation of a preimidized, hydroxyl polyimide, followed by the covalent bonding of a chromophore onto the backbone of the polyimide via a mild post-Mitsunobu reaction. NLO side-chain aromatic polyimides with different polymer backbones and different chromophores were synthesized, and the chromophore loading level in the polyimides was controlled efficiently from 0 to 50% by weight. This facile method provides the synthesis of NLO polyimides with a broad variation of polymer backbone and side-chain chromophores to fine-tune the electrical and structural properties. All the synthesized NLO side-chain polyimides have high glass transition temperatures (Tg > 220 °C) and thermal stability. A large electro-optic (E-O) coefficient (r33) value (11 pm/V measured at 0.83 μm and 34 pm/V at 0.63 μm) and long-term stability (>500 h at 100 °C) of the dipole alignment were observed.
TL;DR: In this article, the thermal analysis of polyamides modified with magnesium hydroxide fire retardant filler is studied using combined TGA, DSC EGA and on-line FTIR techniques.
TL;DR: In this paper, the effect of pH, temperature, monomer/oxidant molar ratio, catalysts and ionic strength on the reaction yield and electrical conductivity of chemically synthesized poly (o-methoxyaniline) was studied.
TL;DR: In this article, a deuterated polysiloxane with high transparency and high thermal stability was synthesized for use as optical waveguide material, and single-mode channel waveguides using the polymer were fabricated by conventional photolithography and dry etching.
Abstract: Deuterated polysiloxane with high transparency and high thermal stability was newly synthesized for use as optical waveguide material. Single-mode channel waveguides using the polymer were fabricated by conventional photolithography and dry etching. The propagation loss of the channel waveguides was measured and found to be 0.17 dB/cm at 1.31 /spl mu/m and 0.43 dB/cm at 1.55 /spl mu/m. The thermal and environmental stability of the waveguides was demonstrated by the fact that the propagation loss remained unchanged after tests at 200/spl deg/C for 30 min, at 120/spl deg/C for 1000 h, and at 75/spl deg/C and 90% RH for 1000 h.
TL;DR: In this paper, a network-like structure of polypyrrole embedded in the insulating polymer matrix was investigated by low-voltage scanning electron microscopy (LVSEM) and potential contrast measurements as a function of the acceleration voltage were used to prove the perfection of the PPy network structure.
TL;DR: In this article, the relationship between the chromophore loading level and the physical properties of the copolymers was studied, and it was found that decreasing the loading level increased the glass transition temperature more than 40 °C, and the stability of the electric field induced dipole orientation of nonlinear optical chromophores was enhanced.
Abstract: Nonlinear optical (NLO) copolyimides exhibiting high glass transition temperatures (Tg) and high thermal stabilities were synthesized to achieve long-term stability of optical nonlinearity at elevated temperatures. The relationship between the chromophore loading level and the physical properties of the copolymers was studied. It was found that decreasing the chromophore loading level increased the glass transition temperature more than 40 °C. As a result, the stability of the electric field induced dipole orientation of the nonlinear optical chromophores was enhanced. The second harmonic generation (SHG) signal maintained 85% of its initial value after 700 h at 180 °C. Sizable second-order nonlinear optical coefficients and electro-optic coefficients were obtained.
TL;DR: In this paper, a straightforward electrochemical method for increasing the thermal stability of alkanethiol-based self-assembled monolayers (SAMs) on polycrystalline gold surfaces is described.
Abstract: This letter details a straightforward electrochemical method for increasing the thermal stability of alkanethiol-based self-assembled monolayers (SAMs) on polycrystalline gold surfaces. Ex situ ell...
IBM1
TL;DR: A number of mixed aromatic/cycloaliphatic as well as fully nonaromatic polyimides have been prepared as discussed by the authors, which are obtained from hexafluoroisopropylidene diphthalic anhydride (6FDA) and trans-1,4-diaminocyclohexane (DACH).
Abstract: A number of mixed aromatic/cycloaliphatic as well as fully nonaromatic polyimides have been prepared. Whereas all the poly(amic acids) derived from nonaromatic diamines involved salt-formation during the initial stages of the polymerization, the majority of these eventually formed homogeneous, highly viscous polymer solutions. Only in a few select cases involving all nonaromatic monomers traditional solution polymerization was unsuccessful. The polyimide derived from hexafluoroisopropylidene diphthalic anhydride (6FDA) and trans- 1,4-diaminocyclohexane (DACH) yielded films with tough mechanical properties, a glass transition temperature of ∼360°C, good solvent resistance, and a low dielectric constant of 2.6. Thermal stability of this polyimide as determined by thermal gravimetric analysis in both air and nitrogen was quite good, exhibiting a weight loss of only 0.07 wt%/h at 350°C under isothermal conditions in nitrogen. However, mechanical properties as a function of thermal aging in both air and nitrogen indicated a maximum use temperature of only 350°C under inert conditions and less than 300°C in the presence of oxygen.
TL;DR: In this article, the authors compared the thermal and thermo-oxidative stability of thermoplastic and thermoset epoxy resin model systems based on the diglycidyl ether of bisphenol A (DGEBA) and contrasted as a function of (mostly) aromatic amine curative structure.
TL;DR: In this article, the synthesis and liquid-crystalline and thermal properties of a fullerene functionalized by a framework containing two cholesterol derivatives through a methanofullerene structure are reported.
Abstract: The synthesis and liquid-crystalline and thermal properties of a fullerene[60] functionalized by a framework containing two cholesterol derivatives through a methanofullerene structure are reported. The targeted fullerene derivative showed high thermal stability.
TL;DR: In this paper, the authors show some differences in the properties and the behaviour at high temperature of two concretes (ordinary and high strength) made with the same calcareous aggregates.
TL;DR: Porous poly(3-aminopropyl)siloxane matrices have been produced by hydrolytical polycondensation of poly(poly)-triethoxysilane with tetraethoxylsilane and methyltriethoxisilane in alcohol/aqueous solutions, the mechanism of poly-condensation being discussed as discussed by the authors.
Abstract: Porous poly(3-aminopropyl)siloxane and poly(3-aminopropyl, methyl)siloxane matrices have been produced by hydrolytical polycondensation of (3-aminopropyl)triethoxysilane with tetraethoxysilane and methyltriethoxysilane in alcohol/aqueous solutions, the mechanism of polycondensation being discussed. The porous structure, composition, thermal stability, solubility and acid-base properties of the matrices produced have been investigated. It has been seen that the surface of aminopolysiloxanes in contact with aqueous media exists in a zwitter-ion-like form over a wide pH range. The speciation of surface coatings at various pH has been calculated. Some kinetic and thermodynamic peculiarities of acid-base reactions of surface groups have been pointed out.
TL;DR: The grain size of the powder compacts, determined using transmission electron microscopy, was found to be 11 ± 5 nm as mentioned in this paper. But the grain size was not maintained when the heat treatment temperature was increased to 1373 K, or over 75% of the melting point of Fe.
Patent•
12 Jul 1996TL;DR: A laminate has at least two layers, at least one of which comprises a polymer having more than one perfluorocyclobutane group as discussed by the authors, which impart qualities of environmental or protection, chemical and solvent resistance, hydrolytic stability, lubricity, low dielectric, hydrostatic stability, weatherability, flame resistance, chemical resistance, hydrophoresis, and lubricity.
Abstract: A laminate has at least two layers, at least one of which comprises a polymer having more than one perfluorocyclobutane group. Such polymers impart qualities of environmental or protection, chemical and solvent resistance, hydrolytic stability, lubricity, low dielectric, hydrostatic stability, weatherability, flame resistance, chemical resistance, hydrolytic stability, lubricity, environmental protection, scratch resistance, solvent resistance, surface passivation, water repellancy, lower surface refractive index, lower surface coefficient of friction, fluid barrier properties, oil repellancy, thermal stability, and/or reduced moisture pick-up. Additionally, the coatings are optically clear, easy to apply either neat, in a solvent or otherwise, have relatively low cure temperatures for their temperature resistance, and exhibit insulating and planarizing capabilities.
TL;DR: The incorporation of sol-gel-processed SiO(2) prevented the thermal decomposition of PVP and provided remarkably low optical propagation losses, and this technique provides lower absorption loss and scattering loss compared with the direct laser-densification technique, which uses UV lasers, and produces narrow waveguides that are difficult to fabricate with a CO( 2) laser.
Abstract: Sol-gel-processed composite materials of polyvinylpyrrolidone (PVP) and SiO2 were studied for optical waveguide applications. PVP is a polymer that can be crosslinked, so it is expected to have high thermal stability after crosslinking. However, thermal crosslinking and thermal decomposition of pure PVP take place around the same temperature, 200 °C, therefore pure PVP had a high optical propagation loss as a result of the absorption of the decomposed molecules after crosslinking. The incorporation of sol-gel-processed SiO2 prevented the thermal decomposition of PVP and provided remarkably low optical propagation losses. The PVP/SiO2 composite material also produced thick (>2-μm) crack-free films when the PVP concentration was 50% or higher. An optical propagation loss of 0.2 dB/cm was achieved at 633 nm in the 50% PVP/SiO2 composite planar waveguide. Several aspects of the thermal stability of the waveguides were evaluated. The slab waveguide was then used for fabrication of channel waveguides with a selective laser-densification technique. This technique used metal lines fabricated with photolithography on the slab waveguide as a light absorbent, and these metal lines were heated by an Ar laser. The resultant channel waveguide had an optical propagation loss of 0.9 dB/cm at 633 nm. This technique provides lower absorption loss and scattering loss compared with the direct laser-densification technique, which uses UV lasers, and produces narrow waveguides that are difficult to fabricate with a CO2 laser.
TL;DR: In this article, the thermal stability of self-assembled monolayers of symmetrical and mixed alkyl fluoroalkyl disulfides on gold was investigated and annealed in air at temperature at room temperature.
Abstract: The investigation of the thermal stability of self-assembled monolayers of symmetrical and mixed alkyl fluoroalkyl disulfides on gold is reported. The monolayers were annealed in air at temperature...
TL;DR: In this article, the effect of chemical structures of diisocyate compounds on the degree of crystallinity and the thermal stability of polyurethane hard-segment crystallinity decreases in the following order: 4,4´-diphenylmethane diisocyanate (MDI), XDI, and 2,4-toluene diiscynate (TDI).
Abstract: Polyurethanes were synthesized from polyester and butanediol with three different diisocyanates, ie, 4,4´-diphenylmethane diisocyanate (MDI), m-xylene diisocyanate (XDI), and 2,4-toluene diiscynate (TDI) The effect of chemical structures of diisocyate compounds on the degree of crystallinity and the thermal stability were observed Differential scanning calorimetry (DSC) and small-angle X-ray scattering (SAXS) were used to determine the degree of crystallinity of the hard segment The thermal degradation of polyurethanes was studied by the thermogravimetric method It has been shown that the polyurethane hard-segment crystallinity decreases in the following order: MDI> XDI> TDI> The experimental results also indicated that polyurethanes with aralkyl diisocyanates, ie, XDI, had the best thermal stability The polyurethanes synthesized from aromatic diisocyanates, ie, MDI and TDI, had worse thermal stability than from XDI However, owing to the higher degree of hard-segment crystallinity for polyurethanes from MDI, these polyurethanes had a better thermal stability than those based on TDI © 1996 John Wiley & Sons, Inc
TL;DR: In this paper, a new type of epoxy resin which contained cyclic phosphine oxide group in the main chain was synthesized, and the structure of the new epoxy resins was confirmed by elemental analyses (EA), infrared spectroscopy (IR), and 1H-NMR and 13C NMR spectroscopies.
Abstract: A new type of epoxy resin which contained cyclic phosphine oxide group in the main chain was synthesized. The structure of the new type of epoxy resin was confirmed by elemental analyses (EA), infrared spectroscopy (IR), and 1H-NMR and 13C-NMR spectroscopies. In addition, compositions of the new synthesized cyclic phosphine oxide epoxy resin (EPCAO) with three curing agents, e.g., bis(3-aminophenyl)methylphosphine oxide (BAMP), 4,4′-diamino-diphenylmethane (DDM), and 4,4′-diaminodiphenylsulfone (DDS), were used for making a comparison of its curing reactivity, heat, and flame retardancy with that of Epon828 and DEN438. The reactivities were measured by differential scanning calorimetry (DSC). Through the evaluation of thermal gravimetric analysis (TGA), those polymers which were obtained through the curing reactions between the new epoxy resin and three curing agents (BAMP, DDM, DDS) also demonstrated excellent thermal properties as well as a high char yield. © 1996 John Wiley & Sons, Inc.
TL;DR: The polyetheretherketone (PEK-C) prepared from phenolphthalein in this paper is an amorphous, rigid, and tough material with good mechanical properties over a wide temperature range.
Abstract: The novel polyetheretherketone (PEK-C) prepared from phenolphthalein in our institute is an amorphous, rigid, tough material with good mechanical properties over a wide temperature range. To improve its water vapor permeability for the application of gas drying, PEK-C was sulfonated with concentrated sulfuric acid and transferred in sodium, cupric, and ferric salt forms. Sulfonation degree can be regulated by controlling the temperature and reaction time. Characterization of sulfonated PEK-C in sodium form was made by infrared spectroscopy. Some properties of the sulfonated PEK-C, such as solubility, glass transition temperature, thermal stability, mechanical properties, and transport properties to nitrogen and water vapor, are also discussed. (C) 1996 John Wiley & Sons, Inc.