Permeation with a double mode of sorption.
It may be the case of oxygen and carbone dioxide in oxygenated polymers.The existence of polar interactions between these molecules and polymer macromolecular chains may induce strong interactions. The kinetic permeation curve likes a Fickian kinetic curve and the stationary total concentration profile is linear but higher than in the Henry sorption process because the fraction of trapped molecules on the Langmu´r sites is not negligeable. The time-lag gives a rather good estimation of the diffusion coefficient by Fick law.
Example 2, case of a high concentration of Langmu´r sites and weak interactions :