Trapping Skinning in Polymers: Theoretical Predictions

During the desorption of certain saturated polymer films, a thin skin of glassy polymer can form at the exposed surface. Not only does this inhibit desorption, but also trapping skinning, in which an increase in the desorption driving force decreases the accumulated flux, can occur. These behaviors cannot be described by a simple Fickian flux. A theoretical framework is presented for modeling such a system. It is shown that though increasing the driving force will increase the instantaneous flux, the time of accumulation will decrease, thus reducing the accumulated flux. In addition, the model is shown to exhibit sharp fronts moving initially with constant speed, another distinctive feature of non-Fickian polymer-penetrant systems.