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  • 1
    ISSN: 0887-6266
    Keywords: substituent group of polyimide ; sorption and diffusion of gas ; free volume ; cohesive energy density ; activation energy for diffusion ; Chemistry ; Polymer and Materials Science
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Chemistry and Pharmacology , Physics
    Notes: Sorption rate curves of CO2, N2, and He gases below 1 atm were measured for polyimide films prepared from benzophenone tetracarboxylic dianhydride (BTDA) with 3,5-diaminotoluene trifluoride (DATF), 2,4-diaminotoluene (DAT), m-phenylenediamine (MPD), and diaminobenzoic acid (DABA). The molecular structures of these four polyimides differ only in the substituent groups of the diamine structure. These polyimides exhibit dualmode type sorption isotherms for carbon dioxide that are concave to the pressure axis, typical of glassy polymer/gas system. The apparent diffusion coefficients below 1 atm pressure of carbon dioxide for this series of compounds decrease in the order: BTDA-DATF 〉 BTDA-DAT 〉 BTDA-MPD 〉 BTDA-DABA. A linear relation between the logarithm of the apparent diffusion coefficient and the reciprocal of free volume, calculated by the method of Bondi using density data, is found for these polyimides. However, this tendency is not observed for the other two gases. The activation energies of the apparent diffusion coefficients at 20 cmHg pressure of carbon dioxide increase with increasing cohesive energy density of the polyimides. The energy per mole of free volume elements in a liquidlike structure in each cohesive energy density may be equated to the activation energy and used to calculate the free volume. The values from the activation energy are almost the same as those from Bondi's method.
    Additional Material: 7 Ill.
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  • 2
    Electronic Resource
    Electronic Resource
    New York, NY [u.a.] : Wiley-Blackwell
    Journal of Applied Polymer Science 20 (1976), S. 703-714 
    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: Diffusion and solubility coefficient data of gases for styrene-grafted high-density polyethylene obtained by γ-irradiation are reported. Diffusion coefficients were determined by the time lag method. Solubility coefficients were determined by a new, more accurate static method. Densities and volume fractions of grafted polystyrene were calculated from the observed values of extent of grafting and density of the graft copolymer films. The solubility coefficients obey simple additivity in terms of volume fraction of side-chain polystyrene and amorphous polyethylene. However, behavior of the diffusion coefficients is more complex. Inasmuch as diffusion is a kinetic process, it is influenced by morphology. The experimental results reported here, together with x-ray diffraction and DSC data, provide a basis for discussing the morphology of the graft copolymers.
    Additional Material: 10 Ill.
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  • 3
    Electronic Resource
    Electronic Resource
    New York, NY [u.a.] : Wiley-Blackwell
    Journal of Applied Polymer Science 21 (1977), S. 535-541 
    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: Melting and glass transition data are reported employing DSC for styrene-grafted high-density polyethylene obtained by γ radiation. Judging from the data of the melting point and the heat of fusion, the grafted polystyrene had no effect on the polyethylene crystallites, but the half-width of the thermogram was observed to increase slightly, showing an effect on the crystallite size distribution. As no effect was observed on the glass transition temperature by grafting, the amorphous region of the polyethylene apparently was not affected. It is suggested, therefore, that the free volume or segmental mobility will not be decreased by radiation-induced grafting. Very few but long grafted chains had negligible effect on the average polyethylene chain length available for segmental motion, and grafted polystyrene should be expected to differ little from the styrene homopolymer in thermal motions.
    Additional Material: 5 Ill.
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  • 4
    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: Hardware and software for collecting and storing the data of gas permeation in polymer membranes from the vacuum detector and various sensors have been developed for the GP-IB microcomputer online system. The system uses BASIC language programs. In comparison to manual inputs and calculations, the programs allow reductions in the time required for data treatment and in the standard deviation for a determination and, moreover, an improvement in the reproducibility of the results.
    Additional Material: 6 Ill.
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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: Numerical solutions were applied to the dual-mode sorption and transport model for gas permeation, sorption, and desorption rate curves allowing for mobility of the Langmuir component. Satisfactory agreement is obtained between integral diffusion coefficient from sorption and desorption rate curves and apparent diffusion coefficient from permeation rate curves (time lag method). These rate curves were also compared to the curves predicted by Fickian-type diffusion equations. © 1992 John Wiley & Sons, Inc.
    Additional Material: 7 Ill.
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  • 6
    Electronic Resource
    Electronic Resource
    Bognor Regis [u.a.] : Wiley-Blackwell
    ISSN: 0887-6266
    Keywords: polyimide ; sorption equilibrium ; sorption rate curve ; non-Fickian transport ; time dependent diffusion ; Chemistry ; Polymer and Materials Science
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Chemistry and Pharmacology , Physics
    Notes: Sorption and diffusion of gases (CO2, N2, and He) in a polyimide (PI2080) film were measured by using an apparatus which gives the sorption rate curves from the initial state to the equilibrium state. Nonlinear isotherms observed for CO2 sorption were interpreted successfully in terms of the dual-mode model for sorption in glassy polymers. Linear isotherms observed for N2 and He seemed to obey Henry's law. Two diffusion coefficients (DI and DE) were obtained using the short-time method and the long-time method for a Fickian diffusion model, together with the equilibrium solubility (Ce) from each experiment. The initial sorption rate curves agreed with the calculated curves using DI, however near sorption equilibrium the curves are in accord with the calculated curves using DE. These observations suggest that some relaxation process is superimposed on the diffusion process. The non-Fickian transport data were correlated successfully with a model that combines time-dependent diffusion and the Fickian model.
    Additional Material: 11 Ill.
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  • 7
    ISSN: 0887-6266
    Keywords: permeation rate curve ; sorption rate curve ; polyimides ; chemical structure ; cohesive energy density ; gas separation ; Chemistry ; Polymer and Materials Science
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Chemistry and Pharmacology , Physics
    Notes: The permeation rate curves and sorption rate curves of oxygen and nitrogen below 1.3 atm were measured for seven polyimides of which chemical structures were systematically changed. These rate curves were applied Fickian model curves. The Fick's law was found to hold from the pressure independencies of diffusion coefficients for both the experiments. The solubility was better described according to dual-mode sorption model rather than Henry-s law from the sorption experiments. The diffusivities of both the gases were correlated with packing density (reciprocal of specific free volume) of the polymer, except two polyimides. The packing density of these two polymers could not be successfully calculated from Bondi's method. However, all the diffusion coefficients decreased linearly with an increase in the cohesive energy density (CED), which was calculated by the group contribution method of van Krevelen. These results suggest that the gas diffusions in polyimides better correlate with CED than with the packing density. Therefore, the cohesive energy density may be considered as a more reliable indication of the efficient gas separation. © 1995 John Wiley & Sons, Inc.
    Additional Material: 18 Ill.
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  • 8
    Electronic Resource
    Electronic Resource
    New York, NY [u.a.] : Wiley-Blackwell
    Journal of Applied Polymer Science 28 (1983), S. 3589-3592 
    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
    Additional Material: 2 Ill.
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  • 9
    Electronic Resource
    Electronic Resource
    Stamford, Conn. [u.a.] : Wiley-Blackwell
    Polymer Engineering and Science 20 (1980), S. 30-35 
    ISSN: 0032-3888
    Keywords: Chemistry ; Chemical Engineering
    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 pressure dependence of the apparent diffusion and permeation coefficients were observed by using the permeation time-lag method for CO2 in glassy poly(ethylene terephthalate) (PET), polystyrene (PS) and poly(vinyl chloride) (PVC) below 1 atm. The results show that the permeation coefficient is constant whereas the diffusion coefficient increases with pressure. According to the theoretical prediction of Paul, it can be concluded that the adsorbed CO2 in these glassy polymers is completely immobilized and does not participate directly in the diffusion. A computer was used in the numerical calculation to determine the true diffusion coefficient from the model of Paul, et al. A comparison of the curves calculated with these constants and experimental values gave excellent agreement for the three glassy polymers. But there is a large difference between the values of one of the parameters obtained by this time-lag method and the sorption method. Relations between this difference and the magnitude of the parameters are discussed.
    Additional Material: 10 Ill.
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