I’m planning a new personal safeboat design. I quess the molecular sizes of both oxygen and carbon dioxide are much smaller than the one of water. Is it possible to manufacture plastic with small enough holes to let O2 and CO2 flow freely and leave H2O outside the design?
According to wikipedia liquefied hydrogen should be stored in cryogenic conditions to avoid boiling off. How can H2 boil in a pressurized bottle? Can the bottle explode at room temperature?
Hydrogen has no liquid phase at room temperature, for any pressure. I guess that means it either breaks or leaks out of any container that tries to constrain it as it warms, or in an unobtanium cylinder, maybe it undergoes fusion as it warms and the pressure rises.
Hydrogen atoms are very small compared to Oxygen or Carbon atoms. I’m not sure why a molecule of oxygen (O2) or carbon dioxide (CO2) would be smaller than water (OH2).
Water is much more polar than molecular oxygen or carbon dioxide, but I’m not sure you can exploit that to block water vapor. Now thanks to that polarity liquid water forms droplets, even on a very small scale, so it is possible to make a membrane that blocks liquid water while passing gases (water vapor can also pass). Guy named Gore (not Al) invented that, and started making raincoats out of it.
Gore-Tex and it’s many similar fabrics do just that. They let water vapor (your evaporating sweat) through but keep water molecules (rain) out, all based on molecule size.
The problem with positively discriminating against water is that plastics like water better than air molecules. Water molecules have a large dipole, and this is has a positive energy of attraction for any other molecule, including plastic, whereas there is little attraction for the nonpolar oxygen or nitrogen . Given that a water molecule is also lighter than say nitrogen or oxygen molecule, it moves faster. So water vapour goes 5-10 x faster through most plastics than oxygen due to the combination of the two effects.
Water molecules are of similar size to oxygen and carbon dioxide is even a little bigger so no luck there