(414j) Transient Finite Element Modeling of Coupled Diffusion and Triple-Mode Sorption in Porous Polymers

A computational model is presented for modeling diffusion and sorption processes in porous polymers. The diffusion equation is formulated via a normalization method to ensure continuity at material interfaces with discontinuous porosities. The sorption process is modeled using a triple-mode framework in which three separate variables are used to capture the effects of Henry’s absorption, Langmuir adsorption, and pooling sorption. These terms represent microdiffusion into the bulk material, adsorption at the pore interface, and condensation within the pores, respectively. Both Henry’s and pooling sorption are assumed to reach local equilibrium immediately, while Langmuir sorption is modeled as a kinetic reaction term. The coupling of these processes leads to a highly non-linear system of equations. Various solution strategies are presented and compared with respect to their convergence, robustness, and accuracy.

This work performed under the auspices of the U.S. Department of Energy by Lawrence Livermore National Laboratory under Contract DE-AC52-07NA27344.