The volume changes caused by the sorption of
H2O, Ar, N2, CO2, CH4
and Acetone in
Bisphenol-A polycarbonate and of CO2 in different
substituted polycarbonates and in Kapton were
measured in a dilatometer at room temperature. The partial molar
volumes of the small molecules are
much smaller than the ones obtained in the liquid or rubbery state of
polymers. It is a special feature
of the glassy state that the partial molar volume increases as
concentration increases. Both findings are
explained by a model developed recently, where the volume of the site
occupied by small molecules is
related via elastic distortions to the solution energy into this site.
Assuming a spherical shape of site
volumes and a Gaussian distribution of the volumes yields an average
value of 33 to 38 Å3/site and a
width of about 10 Å3. These quantities vary in a
systematic manner with the glass transition temperature
and the nature of side groups of the polymer. The results are
compared with values calculated from life
times of o-positronium and values of the d-spacings from
X-ray.
We report measurements on diffusion of CO2 and Ar in aged and conditioned (exposed to high CO2 pressure) samples of BPA-PC. In contrast to intuitive expectations and some previous experimental results on diffusion of larger molecules in polymer glasses, diffusion in a "more open" conditioned matrix is slower than in a denser aged one. We offer an explanation of this effect based on the recently developed site distribution model for sorption and transport of small molecules in polymer glasses. The observed modification of diffusion rates could be described in terms of increasing activation energy for gas diffusion in conditioned in comparison with aged samples. This difference of activation energies could be understood through changes in free volume distribution, which were evaluated from the measured sorption isotherms.
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