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  • Articles  (4)
  • Physics  (3)
  • polyimide  (1)
  • time dependent diffusion  (1)
  • 1
    Electronic Resource
    Electronic Resource
    New York : Wiley-Blackwell
    ISSN: 0098-1273
    Keywords: Physics ; Polymer and Materials Science
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Chemistry and Pharmacology , Physics
    Notes: The sorption and diffusion of gases in poly(ethylene terephthalate) (PET) films have been measured by using a newly devised apparatus which gives the sorption rate curves from the initial to the equilibrium state. By analysis of sorption data for carbon dioxide in PET film, it was shown that the diffusion rate, as well as the equilibrium solubilities, could be explained by the dual-mode sorption mechanism proposed by Vieth et al. Constants of their equation were used in the analysis of our experimental results, in which the apparent diffusion coefficients were dependent on pressure. The result showed that the dual-mode sorption mechanism indeed applies to diffusion. The value of the real diffusivity obtained in amorphous PET was 5.7 × 10-9 (± 8%) cm2/sec in the range of pressure from 0 to 1 atm. It is believed that this apparatus has wide applicability, not only to diffusion of gases in polymers, but also to the measurement of surface properties, and can be used to study the morphology of a variety of polymers.
    Additional Material: 10 Ill.
    Type of Medium: Electronic Resource
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  • 2
    ISSN: 0098-1273
    Keywords: Physics ; Polymer and Materials Science
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Chemistry and Pharmacology , Physics
    Notes: Temperature dependences of diffusion and permeation coefficients of hydrogen and deuterium in glassy and rubbery polymer films have been measured. The size of the free volume element in rubbery polymers has been calculated according to the theory of Frisch and Rogers for the quantum isotope effect, but the free volume is too large for precise calculation below the glass-transition temperature. The cooperative movement of segments is also discussed using the ratio of preexponential factors for diffusion mechanisms above and below the glass-transition temperature.
    Additional Material: 7 Ill.
    Type of Medium: Electronic Resource
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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: The permeability and time lag at pressures below 1 atm were measured for carbon dioxide in five polystyrene samples with different molecular weights at 25 to 40°C. The apparent permeability coefficient decreases with increasing carbon dioxide pressure and also decreases with increasing molecular weight of polystyrene, whereas the apparent diffusion coefficient calculated from time lag increases with pressure and is independent of molecular weight. Parameters for the partial-immobilization model were determined from the apparent diffusion and permeation coefficients by using a nonlinear least-squares optimization program without using sorption data. The results suggest that the void-saturation constant C′H decreases as the molecular weight of the polymer increases or as the chain-end free volume decreases. The significance of these observation and their interpretation is discussed in terms of free-volume theory for glassy polymers.
    Additional Material: 7 Ill.
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  • 4
    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.
    Type of Medium: Electronic Resource
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