On bimodal sorption of gases and vapours by glass-like polymers

A quasi-chemical model for the sorption of water vapours by polar glass-like polymers allowing for two sorbate states is proposed. The first state is characteristic of water molecules having limited mobility and is determined by the presence of active centres in the sorbent. The second state is characteristic of molecules distributed in the polymer in accordance with Flory-Huggins theory. A programme is developed for calculating the sorption parameters corresponding to each state from experimental isotherms. The validity of the model is confirmed by thermodynamic calculations and NMR spectroscopy data.