Studying the Solubility of Carbon Dioxide in Polymide Films Using the IGA

The following article studies CO₂ solubility in polymide films using the IGA system.

The Method

A small piece of film was loaded into the IGA-001 system and outgassed to high vacuum of less than 10^-6 mbar at 60°C. Next, the sample was analyzed isothermally at 20°C, 35°C and 60°C by increasing the pressure to determine the adsorption branch, then decreasing the pressure to determine the desorption branch using CO₂ as the sorbate.

Figure 1 shows the kinetic detail used for plotting isotherms.

Figure 1. Kinetic detail used to plot isotherms

The IGA method was then used to fit the weight relaxation obtained from each pressure step. The F1 model was chosen for this experiment. The IGA technique can predict the point of equilibrium uptake from the fit, and identifies the rate constant of the adsorption k (k=1 / time constant). The method also guarantees that each point on the isotherm is measured to the same accuracy, and enhances the use of instrument time. Permeability is based on both the diffusion constants and the concentration, which can be derived from rate or time constants.

Figure 2. Displays the CO₂ adsorption isotherms measured at 20°C, 35°C and 60°C on the film sample

Figure 3. Displays the time constants measured for each isotherm point shown in figure 1.

Conclusion

The IGA is the ideal tool to study permeability, diffusion constants and concentration independently.

This information has been sourced, reviewed and adapted from materials provided by Hiden Isochema.

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