I compare the diffusion coefficients of different substances in polymers. While D in glassy polymers tend to correlate better with the kinetic diameter (size dominates), rubberlike polymers tend to correlate better with the boiling point (solubility dominates). I noticed that in both cases H2O and CO2 are unusual outliers ... When I plot the kinetic diameter of many different molecules against the boiling point, I see (as you would expect) an approximately linear correlation. Carbon dioxide (if you take the sublimation point) and water seem to be clear outliers. Why?
obviously sublimation point is different than boiling point, therefore, I would be surprised if it would fit well.
Concept of correlation with boiling point seems to be similar with Hildebrand parameter, which only regards the cohesivity of the molecules without paying special attention to polar interaction and hydrogen bonding. The latter effect is especially pronounced for water.
The intermolecular force of attraction and of course the difference in energy of activation (EV value) seems different for both
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