Generalized Diffusion–Relaxation Model for Solvent Sorption in Polymers
Dominik Borrmann, Andreas Danzer, Gabriele Sadowski
Abstract
Solvent sorption in polymers is of general interest for a wide variety of applications. It is well known that solvent sorption in polymers depends on both solvent diffusion and the slow rearrangement of the polymer, also known as polymer relaxation. This study provides a physically meaningful model approach for describing solvent diffusion in polymers, while considering relaxation in its most generalized form. A diffusion–relaxation model was created by combining the Stefan–Maxwell equations with multiple Maxwell elements. Parameter studies reveal the capability of the developed approach to describe anomalous solvent sorption behavior in polymers like sigmoidal, two-stage, pseudo-Fickian, case II, and super case II behavior. These parameter studies also provide detailed insights into the physical reasonings behind these phenomena. Moreover, to the best of our knowledge, this is the first time that first-principles modeling of multistage sorption curves is reported.