Schroeder's paradox refers to the phenomenon of certain polymers exhibiting more solvent uptake (observed as swelling) when exposed to a pure liquid versus a saturated vapor.
[1] It is named after the German chemist Paul von Schroeder, who first reported the phenomenon working on a sample of gelatin in contact with water in 1903.
[2] An equivalent observation has also been independently discovered and discussed within the biophysical community as the vapor pressure paradox.
[1] However, even exact measurements support an existence of a systematic difference between sorption from saturated vapor and from pure liquid for certain systems.
[7][3] Mechanistic interpretations based on wetting of micropores in the polymer matrix have also been proposed.