Differential solvent vapor sorption

Differential solvent vapor sorption procedures to measure % and the activities of solvent in uncross-linked and cross-linked polymers are described in this Section A schematic diagram of the apparatus designed by Yen and Eichinger is reproduced... 

Fig. 3. Schematic diagram of differential solvent vapor sorption measurement apparatus. (Reprinted from Yen, L. Y., Eichinger, B. E. J. Polym. Sci., Polym. Phys. Ed. 16, 121, 1978)...

The volume fraction of polymer at equilibrium (maximum) swelling is designated i 2m- Then, equations (144) and (146) may be used to test the phenomenological or molecular theories of elasticity, and to characterize elastomeric networks by differential solvent vapor sorption and swelling equilibrium measurements, respectively. 

The experimental values reported for the differential vapor pressure, gravimetric sorption, and piezoelectric methods are the weight fraction of solvent in the polymer solution and the pressure of the solvent vapors in equilibrium with the polymer solution. Differential vapor pressure measurements are performed by adding a known amount of solvent to a weighed polymer sample and measuring the vapor pressure of the solvent over the polymer solution (Bawn et al., 1950). 

Valve F is opened to allow solvent vapor into the system. The amount of solvent introduced is controlled by controlling the temperature of the solvent reservoir. Valve F is closed after each addition of vapor. Solvent vapor and polymer samples are then allowed to equilibrate. The integral and differential sorptions are observed on the respective balances and the pressure of solvent vapor is recorded. It is then possible to calculate the volume fraction of polymer in the cross-linked and uncross-linked swollen samples, v and vj respectively, at a solvent pressure p = pj and thus to know pj and pj at equal volume fractions v = vj and to calculate the ratio of activities af/aj = pj/p . From knowledge of p , p , vj and x, x(v ) is deduced through equations 3, 4 and 5. 

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