FINITE-DIFFERENCE MODELING OF THE GAS-TRANSPORT PROCESS IN GLASSY-POLYMERS

Finite difference modeling has been used to predict the results of gas transport experiments for a concentration-dependent diffusion coeffic ient. Experiments on the transport of CO2 in poly(ethylene terephthala te) and poly(ethylene naphthalate) had previously shown a difference b etween the effective diffusion coefficients for absorption and desorpt ion runs of a double-sided experiment, but this effect had not been se en for single-sided experiments. The finite difference calculations sh ow that such results are to be expected, and the parameters included i n the models that attempt to describe the diffusion process in glassy polymers, such as the dual-mode model, and which lead to concentration -dependent diffusion coefficients, can be found by fitting the experim ental data for the double-sided experiment using finite difference mod eling. The dependence of the effective diffusion coefficient on pressu re for the single-sided experiment can be correctly predicted using re sults from the double-sided experiment for an identical sample. (C) 19 96 John Wiley & Sons, Inc.