Water sorption polymer volume fraction

Further anomalies are seen in the diffusional behavior of cesium ion for the perfluorosulfonate membrane. Figure 10 represents the plot of the logarithm of the diffusion coefficient vs. the function Vp/(l-Vp), where Vp is the volume fraction of polymer in the water-swollen material and 1 - Vp is the volume fraction of water, as calculated from sorption measurements. This plot corresponds to a test of the equation... 

The function Vp/(1-Vp), where Vp is the volume fraction of polymer in a water swollen material, is plotted as the abscissa in Figure 2. The denominator of this term is therefore the volume fraction of water in the membrane, calculated from sorption results. This function was developed by Yasuda and co-workers to treat diffusion in various hydrophilic polymers (12). Their equation ... 

For a large number of polymers, a plot of the reciprocal of water sorption against the reciprocal of the partial pressure of water exhibits near-linear behavior. With the expectation that the volume fraction of water will be the expression of water concentration relevant to basic pol3rmer solution thermodynamics, this measure has been used. However, a variety of other expressions of concentration can be used (weight or volume per unit weight or volume of polymer, weight percent, etc.) and substitution of these will alter the slope and Intercept, but not the linearity of the plot. 

Data on poly(ethyl methacrylate) from Williams et al (5 ) were specified as volume fraction of water sorbed as a function of partial pressure. In an earlier publication of Stannett and Williams (7) the glass temperature of the polymer was given as 65 C. Sorption and desorption measurements showed a very close concordance. Data on poly(methyl methacrylate) by Brauer and Sweeney ( ) were transformed from gravimetric to volume fraction using a density of 1.19. The glass temperature of this polymer Is 105°C. The authors report that "thin specimens reach a steady state value within a short time." Data for poly(methyl acrylate)... 

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