Effect of relative humidity and temperature on the gas transport properties of 6FDA-6FpDA polyimide: Experimental study and modelling

Pure water vapour sorption experiments were also conducted on the polymeric films in the same RH and temperature range, showing that water solubility in 6FDA-6FpDA is almost temperature-independent. A strong correlation therefore seems to exist between gas permeability decrease and water content in the membrane, due to the fact that absorbed water molecules occupy a portion of the polymer free volume, that is no longer available for gas permeation. Based on these considerations, the humid permeation results were analysed quantitatively and modelled with a simple approach based on free volume theory.