Dynamic sorption and transport of water vapor in dense polyimide membranes

Series of polyimide membranes were synthesized using varied monomers such as pyromellitic dianhydride, 3,3′4,4′‐benzophenonetetracarboxylic dianhydride, 4,4′‐diaminodiphenylether, 4,4′‐diaminodiphenylmethane, and phenylenediamine, and the properties of polyimide membranes were measured by experimental techniques. The dynamic sorption and transport processes of water vapor in those dense polyimide membranes were measured using computer on‐line recorded gravimetric sorption method at 298.15 and 308.15 K. Modeling of these processes involved the total change of excess Gibbs free energy, which was considered as a sum of three parts calculated by the modified Scatchard‐Hildebrand model, Flory‐Huggins theory, and linear viscoelastic theory, respectively. The calculated results were in agreement with the experimental data and the maximal relative deviation was no more than 8.57% and the average relative deviation is 4.62%. The calculated results had also shown that this model describe not only Fickian diffusion but also non‐Fickian very well. Furthermore, the influence of chemical structure, morphological structure, etc. of polyimide membranes on the water sorption concentration and water diffusion coefficient were interpreted by considering the experimental data and calculation results. © 2006 Wiley Periodicals, Inc. J Appl Polym Sci 102: 2189–2198, 2006