Originally Posted by
facial
Hi I'm new here... but I have some curiosity in this scientific assertion.
Can you refer me to any publications or online literature for the diffusion characteristics of CO2?
Because right now I tend to believe that the molecular size determines the diffusive characteristics of a gas rather than its solubility in solids -
this abstract's last sentence seems to imply that concentration has a relatively small influence on diffusion - the classic pressure gradient, temperature, etc. factors appear to be more important for carbon dioxide diffusion rather than chemical solubility (influenced by concentration). Although CO2 is well known to dissolve in water, however. I'm not sure how it would do in polymers.
I've always thought CO2 was used for those quick-fill canisters b/c it had good diffusion characteristics.
Here we also see that the diffusion coefficient for CO2 is lower than O2, which itself is lower than H2O - almost completely hierarchical on size.
To be more clear on this I should have said that it is well known from BikeForum anecdotal evidence that CO2 diffuses out of tubes faster than air. This comes up a lot. The polymers that are discussed in the paper you cite are much different animals than the elastomers that are used to make tubes.
After numerous, and I mean numerous, discussions on this topic many of us have come to the conclusion that the CO2 isn't just diffusing through the rubber but it is dissolving in the rubber and passing out. The N2 and O2 in air follow a diffusion pathway and thus take longer to get through the rubber.
I know of no one who has done a controlled experiment, however it wouldn't be hard to do as a homebrew measurement.