Skinning During Desorption of Polymers: An Asymptotic Analysis

Desorption of saturated polymers can be inhibited if a nearly dry (glassy) skin with a low diffusion coefficient forms at the exposed surface. In addition, trapping skinning can occur, where an increase in the force driving the desorption decreases the accumulated flux desorbed. The dynamics of such systems cannot be described by the simple Fickian diffusion equation. The mathematical model presented is a moving boundary-value problem with a set of two coupled partial differential equations. Most previous studies of this model focused on sorption studies; this is the first that considers desorption into an environment of arbitrary concentration. Since the derived equations cannot be solved by similarity variables, integral equation techniques are used to obtain asymptotic estimates for the solution. The skinning solution obtained also exhibits fronts moving with constant speed, another distinctive feature of non-Fickian polymer-penetrant systems.