Isopiestic sorption

Isopiestic sorption/desorption methods, i.e., gravimetric sorption, piezoelectric sorption, or isothermal distillation... 

Equation-of-state approaches are preferred concepts for a quantitative representation of polymer solution properties. They are able to correlate experimental VLE data over wide ranges of pressure and temperature and allow for physically meaningful extrapolation of experimental data into unmeasured regions of interest for application. Based on the experience of the author about the application of the COR equation-of-state model to many polymer-solvent systems, it is possible, for example, to measure some vapor pressures at temperatures between 50 and 100 C and concentrations between 50 and 80 wt% polymer by isopiestic sorption together with some infinite dilution data (limiting activity coefficients, Henry s constants) at temperatures between 100 and 200 C by IGC and then to calculate the complete vapor-liquid equilibrium region between room temperature and about 350 C, pressures between 0.1 mbar and 10 bar, and solvent concentration between the common polymer solution of about 75-95 wt% solvent and the ppm-region where the final solvent and/or monomer devolatilization process takes place. Equivalent results can be obtained with any other comparable equation of state model like PHC, SAFT, PHSC, etc. 

The concentrated polymer solution between 30 and 85 wt% is controlled by vapor pressure measurements which were usually performed by various isopiestic sorption methods. The ultracentrifuge can also be applied for solutions up to 80 wt% polymer, but this was only scarcely done in the literature. 

Broka and Ekdunge investigated water uptake from the vapor phase by Nafion 117 membrane and recast film. The results show water vapor uptake by both Nafion 117 membrane and recast film decreased with increasing temperature. The lower water uptake at higher temperatures has also been reported by other researchers. Broka and Ekdunge also found PFSA membrane water uptake from the liquid water is higher than those for water vapor. This phenomenon is known as Schroeder s paradox. Zawodzinski et al. explored the isopiestic sorption curve for Nafion 117-H". ... 

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