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  • Chemical Engineering  (1)
  • polyimide  (1)
  • polyimides  (1)
  • time dependent diffusion  (1)
  • Wiley-Blackwell  (3)
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  • Wiley-Blackwell  (3)
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  • 1
    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.
    Type of Medium: Electronic Resource
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  • 2
    Electronic Resource
    Electronic Resource
    Bognor Regis [u.a.] : Wiley-Blackwell
    Journal of Polymer Science Part B: Polymer Physics 33 (1995), S. 777-784 
    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.
    Type of Medium: Electronic Resource
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  • 3
    Electronic Resource
    Electronic Resource
    Bognor Regis [u.a.] : Wiley-Blackwell
    Journal of Polymer Science Part B: Polymer Physics 30 (1992), S. 549-556 
    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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