Activation energy for permeation

The permeability varies with temperature according to equation 12 where is a constant, E is the activation energy for permeation, E. is the gas constant, and Tis the absolute temperature. 

Ep Activation energy for permeation of small penetrant molecules through polymers. 

The activation energies for permeation in the co-VDC film were all positive. The activation energies for the diffusion coefficient are shown in Figure 9. The heats of solution for the esters are shown in Figure 10. 

The parameter 77 is the activation energy for permeation and Oq is a constant, while T and R are the absolute temperature and universal gas constant. 

This empirical treatment, when compared with the standard Arrhenius expression for temperature dependence of permeation, states that the preexponential term is effectively a constant for water in all polymers (2.5 x 10 ). The "Permachour" correlates the apparent activation energy for permeation as Ep = 60.511. This tacit theoretical relationship is not completeTy satisfactory, it can be circumvented or revised to derive more rigorous expressions (8), but the ease of application and established success of the present form can justify its use in this present case. 

As these materials are potentially interesting for gas separations at elevated temperatures, the influence of temperature on permeation properties has been measured. Evaluation of the crosslinked 25 wt% DIA blend was made because this material possesses an attractive combination of properties. Results are presented in Figure 4 for temperatures up to 300 °C. The slope of the plot represents the activation energy for permeation divided by the gas constant, R (24). The calculated activation energies for permeation are presented in Table II. The activation energies for permeation through these crosslinked polyimides are on the same order as those reported for other polymers, including polyimides (25,26). 

Table II Activation energy for permeation through crosslinked blends containing 25 wt% 1,1-6FDA-DIA (10 atm feed pressure).

Permeability coefficients of CO2 and water vapor and their temperature effect, activation energy for permeation, have been tabulated for most polymers. PS and PMMA (poly(methyl methacrylate)) are usually not used in packaging material, therefore experimental data for these two materials are scarce. However, the barrier properties of polymer nanoconposites have drawn interest recently. To the... 

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