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To be specific, I am wondering about the dynamics of molecular oxygen diffusion into gas-permeable polymer materials, which is the sensing process of the optical oxygen probe (polymer-encapsulated oxygen-sensitive phosphor).

Although the absolute concentration of dissolved oxygen in water can be 40 times lower than the oxygen concentration in air, the optical response of the probe seemed to be consistent when placed in air and under water (completely equilibrated with air). My guess is that, under equilibrium, the chemical potentials of the gaseous oxygen and the dissolved oxygen are the same. So that the rates of diffusion into the polymer are similar (air-polymer interface vs. water-polymer interface).

I've tried my best to search for textbooks and literature, but cannot find any material that explicitly explains this well. I appreciate it very much if someone can verify my assertion and offer me some references. Sorry for any misconception!

Sincerely,

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If the air and water are in equilibrium, then che chemical potential of the oxygen in the air is equal to the chemical potential of the oxygen in the water. If either is placed in contact with your polymer, oxygen present in the polymer at the interface between the polymer and water or polymer and air will come to equilibrium with the air or water extremely rapidly, and its chemical potential in the polymer at the interface will match that in the air or water. It then will more gradually diffuse into the rest of the polymer.

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