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  • 1
    ISSN: 0021-8995
    Keywords: Chemistry ; Polymer and Materials Science
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Chemistry and Pharmacology , Mechanical Engineering, Materials Science, Production Engineering, Mining and Metallurgy, Traffic Engineering, Precision Mechanics , Physics
    Notes: The self-diffusion coefficient of water in a perfluorinated ionic membrane has been measured for different water contents corresponding to water vapor pressures less than the saturated one. The isotope method usually employed in the liquid state was extended to vapors, which led us to an observation of three different isotopic species by quantitative far IR spectroscopy. Two measurement methods are presented permitting a determination of the time lag and hence of the diffusion coefficient. The slow variation of the diffusion coefficient with the water concentration, as well as the good agreement of the numerical results given by different methods (permeation-sorption) are explained by the fact that no plasticization occurs. This result has been independently verified by other experiments.
    Additional Material: 5 Ill.
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  • 2
    ISSN: 0021-8995
    Keywords: Chemistry ; Polymer and Materials Science
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Chemistry and Pharmacology , Mechanical Engineering, Materials Science, Production Engineering, Mining and Metallurgy, Traffic Engineering, Precision Mechanics , Physics
    Notes: This study deals with the ion beam irradiation effect on gas permeation properties of polyimide films. 2 MeV α, 500 keV, and 170 keV N+ ions were used for modifying the membranes. It was found that there are two different effects according to the implantation dose. In the case of small-dose irradiation, ion implantation causes a raise of permeability both for CH4 and H2. When the implantation dose reaches a more important level, the implanted membranes have at the same time high permselectivity for H2/CH4 and high permeability for H2. The relationships between the permeation properties and microstructure of the films are also discussed. © 1995 John Wiley & Sons, Inc.
    Additional Material: 4 Ill.
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  • 3
    ISSN: 0098-1273
    Keywords: Physics ; Polymer and Materials Science
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Chemistry and Pharmacology , Physics
    Notes: Perfluorinated ionomer membranes can absorb large amounts of water. DSC experiments show the existence of exothermic or endothermic peaks for water contents larger than 8 wt % at room temperature in Nafion 1200 EW in the acid form. Changes in the number of mobile protons versus temperature have been measured by NMR spectroscopy. A desorption process with an activation energy of 6 kcal/mol is proposed during the sample cooling. Such an explanation quantitatively explains both the DSC and NMR results and is also consistent with the other results obtained from mechanical experiments, low-temperature sorption isotherms, and ESR spectroscopy.
    Additional Material: 10 Ill.
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  • 4
    ISSN: 1572-8943
    Source: Springer Online Journal Archives 1860-2000
    Topics: Chemistry and Pharmacology
    Description / Table of Contents: Résumé L'adsorption de vapeur d'eau sur montmorillonite lithique en provenance de Marnia et Camp Berteaux a été analysée après altération thermique sous vide entre 120 et 500°C. Les données de microgravimétrie et microcalorimétrie d'adsorption ont permis de suivre et d'analyser en fonction de la température et du temps de chauffage, d'une part les effets dus à la migration d'une partie des ions lithium dans le réseau silicate: diminution de capacité d'adsorption, diminution du nombre de sites actifs énergétiques, mais aussi modification du comportement des feuillets vis-à-vis de l'eau (instabilité des stades d'ouverture); d'autre part, les effets dus à l'intervention de la déshydroxylation interne: disparition totale de l'adsorption lamellaire.
    Abstract: Zusammenfassung Die Wasserdampf-Adsorption von aus Marnia und Camp Berteaux stammendem Lithium-montmorillonit wurde nach thermischer Veränderung im Vakuum zwischen 120 und 500°C ermittelt. Die mikrogravimetrischen und mikrokalorimetrischen Versuchsdaten ermöglichten einerseits die Wirkung der Wanderung der Lithium-Ionen im Silikatnetz als Funktion der Temperatur und der Aufheizdauer zu studieren, d.h. die Abnahme der Adsorptionskapazität sowie der Zahl der energetisch aktiven Zentren und die Änderung des Verhalters der Lamellen gegenüber Wasser (die Instabilität der Anfangsstadien zu ermitteln. Andererseits konnten auch die durch die innere Dehydroxylierung bedingten Effekte, d.h. das vollkommene Verschwinden der lamellaren Adsorption beobachtet werden.
    Notes: Abstract Water vapor adsorption on lithium montmorillonite from Marnia and Camp Berteaux was studied after heat treatment in vacuum between 120 and 500°C. From gravimetric and calorimetric data it was possible to follow the effects due to migration of some of the lithium cations into silicate skeleton: decrease of adsorption capacity, decrease of the number of active energetic sites, alteration of the mode of hydration (instability of expanding stages); then the effects due to internal dehydration: total loss of lamellar adsorption.
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  • 5
    ISSN: 0021-8995
    Keywords: Chemistry ; Polymer and Materials Science
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Chemistry and Pharmacology , Mechanical Engineering, Materials Science, Production Engineering, Mining and Metallurgy, Traffic Engineering, Precision Mechanics , Physics
    Notes: The water sorption behavior of styrene-methacrylic acid copolymers and of their sodium salts has been studied as a function of concentration of ionic groups and nature of the sample. The influence of thermal history has also been examined. The salt forms of the copolymers were found to have a greater hydration capacity than the acids, the hydration capacity increasing with ion content for the salts. The hydration energy of the acid forms was found to be in the vicinity of the liquefaction energy of water whereas the energy for the salt forms became much lower than that value, with increasing water content. This decrease in energy has been attributed to a rearrangement of the cluster structure to accommodate more water molecules.
    Additional Material: 16 Ill.
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  • 6
    ISSN: 0021-8995
    Keywords: Chemistry ; Polymer and Materials Science
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Chemistry and Pharmacology , Mechanical Engineering, Materials Science, Production Engineering, Mining and Metallurgy, Traffic Engineering, Precision Mechanics , Physics
    Notes: Sorption of different gases (N2, O2, CH4, and CO2) were performed on as-synthesized polyemeraldine base, on HCl 4M doped, on NH4OH 1M undoped, and on HCl 10-2M redoped powders. In the pressure range examined (100-700 torr), linear sorption isotherms were observed for N2 and correspond to an ordinary dissolution in Henry's law state. Concerning O2, CH4, and CO2, nonlinear isotherms were evidenced and could be described by the dualmode sorption mechanism proposed for glassy polymers, which consists of the combination of a Henry's type dissolution with a Langmuir sorption in unrelaxed gaps between macromolecular chains. Specific interactions between polyaniline (PANi) and O2, CH4, and CO2, were studied. Gas permeation experiments were performed by using different upstream pressures, P1, and have confirmed the dissolution of Henry's type for N2 and the dualmode mechanism for O2 and CO2. From the fits of the sorption isotherms, gas solubilities of N2, O2, CH4, and CO2 were calculated for three different gas pressures and analyzed in terms of gas separation for permeation experiments. © 1995 John Wiley & Sons, Inc.
    Additional Material: 6 Ill.
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  • 7
    ISSN: 0021-8995
    Keywords: Chemistry ; Polymer and Materials Science
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Chemistry and Pharmacology , Mechanical Engineering, Materials Science, Production Engineering, Mining and Metallurgy, Traffic Engineering, Precision Mechanics , Physics
    Notes: Gas permeation experiments of H2, O2, CO2, N2, and CH2 were carried out with freestanding films of the conjugated polymer polyaniline (PANi). At first annealed to remove residual solvent, PANi membranes were doped (i.e., protonated) in a strongly acidic medium (HCl 4M), undoped in a basic medium (NH4OH 1M), and redoped in a slightly acidic medium (HCl 10-2M). Protonation and deprotonation kinetics were studied by elementary analysis Gas permeation experiments were performed with the annealed, doped, undoped, and redoped PANi films. The gas transport mechanism was clearly influenced by the diffusivity factor and it obeyed a Fickian diffusion model. From the variations in permeability coefficients with the doping treatment, gases could be divided in two subgroups comprising H2, O2, and CO2 on one hand and N2 and CH4 on the other. After the doping-undoping-redoping process, gas fluxes were increased by 15% for the smaller gases and were decreased by 45% for the larger gases. As a consequence gas separation factors were approximately doubled for a gas pair involving the two subgroups and these were unchanged for a gas pair involving only one subgroup. The highest O2/N2 and CO2/CH4 selectivity coefficients were, respectively, equal to 14 and 78. © 1995 John Wiley & Sons, Inc.
    Additional Material: 6 Ill.
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  • 8
    ISSN: 0021-8995
    Keywords: Chemistry ; Polymer and Materials Science
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Chemistry and Pharmacology , Mechanical Engineering, Materials Science, Production Engineering, Mining and Metallurgy, Traffic Engineering, Precision Mechanics , Physics
    Notes: The characterization of KEVLAR-29 fibers has been performed by studying their interactions with three model compounds in gaseous form. Water, aniline, and epoxystyrene were used for this purpose. The effects on the nature of these interactions of two types of surface engineering, namely the coating with an epoxy resin and a reactive plasma treatment, were also studied. The results obtained from the three analytical techniques used in this work provide a more fundamental understanding of the fiber bulk properties vs. their surface characteristics. The diffusion, condensation, plasticization, and adsorption mechanisms involved during the interactions between the probes and the KEVLAR fibers are evidenced and discussed. © 1995 John Wiley & Sons, Inc.
    Additional Material: 6 Ill.
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  • 9
    ISSN: 1042-7147
    Keywords: Polyaniline ; Oxygen ; Gas permeation ; Polarons ; ESR ; Chemistry ; Polymer and Materials Science
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Chemistry and Pharmacology , Mechanical Engineering, Materials Science, Production Engineering, Mining and Metallurgy, Traffic Engineering, Precision Mechanics
    Notes: High selectivity between oxygen and nitrogen has been found by gas permeation with doped polyaniline. Because of the small difference in kinetic diameters, solubility rather than diffusion may explain the preferential oxygen permeation. Electron spin resonance (ESR) measurements have been performed to check whether interactions of oxygen with polarons in polyaniline exist. A tenfold decrease in the spin number was observed when the polymer was in the presence of oxygen rather than nitrogen. This result was interpreted as being due to interactions between oxygen triplet states and polarons of polyaniline.
    Additional Material: 5 Ill.
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  • 10
    ISSN: 0003-3146
    Keywords: Chemistry ; Polymer and Materials Science
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Chemistry and Pharmacology , Physics
    Description / Table of Contents: Gravimetric and microcalorimetric results connected with regard to 1,4-dioxane vapour sorption at 20°C into polyethylene terephthalate enable to specify the mechanism of solvent action in terms of relative pressure. Near vapour saturation we can discern: non-reversing fixation of dioxane on special sites, partition in the amorphous region, adsorption at the surface of crystallites gradually formed by solvent action and organized into a swollen texture.According to the conditions of pretreatment with dioxane, of rinsing and drying, a further ethanol sorption displays: a non-reversing exchange mole to mole of fixed dioxane, an adsorption at the surface of crystallites, a diffusion into the free volume of the swollen texture.
    Notes: Les résultats de gravimétrie et microcalorimétrie couplées concernant la sorption en phase vapeur à 20°C du dioxanne-1,4 par le polytéréphtalate d'éthylène glycol permettent de préciser le mécanisme d'action du solvant en fonction de la pression partielle. Au voisinage de la pression saturante il est possible de distinguer: la fixation irréversible sur certains sites, la disolution dans les zones amorphes, l'adsorption à la surface des cristallites progressivement formées sous l'action du solvant et organisées selon une texture gonflée. Selon les conditions de prétraitement par le dioxanne, de lavage et de séchage, une sorption ultérieure d'éhanol met an évidence: un échange irréversible mole à mole du dioxane fixé, une adsorption à la surface des cristallites, une diffusion dans les volumes libres de la texture gonflée.
    Additional Material: 6 Ill.
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