A mechanistic model of case-II diffusion of a diluent into a glassy polymer

We present a new mechanistic model for the self-similar propagation of Case-II sorption fronts of diluents into glassy polymers, The model makes clear differentiation between chemical-potential-induced driving forces and material misfit-induced pressures that develop in the Fickian pre-cursor field that counteract the driving forces but also set up conditions for visco-plastic extrusion of diluent-enriched polymer out of the surface or into a zone of a rubbery gel behind the Case-II process front. The quantitative predictions of the model are capable of giving accurate comparisons with experimental measurements, particularly with those of Kramer and co-workers on the penetration of iodoalkanes into polystyrene. (C) 1999 Elsevier Science Ltd. All rights reserved.