Traversing with quantitative fidelity through the glass transition of amorphous polymers: Modeling the thermodynamic dilatational flow of polycarbonate.

This article presents a thermodynamically consistent model for the pressure-temperature-dilatation response of polycarbonate (PC) polymers as they undergo the glass transition. The model is based on a mechanical analog involving two elastic springs—one instantaneous and one back-stress element—each with associated thermal expansion, combined with a viscous flow component whose viscosity depends on temperature and the elastic back-strain. A key internal state variable, the unloaded equilibrium temperature, correlates with prior processing and links mechanical aging to thermodynamic behavior. Parameters for the model were extracted from experimental data on different PC grades, including pressure-volume-temperature (PVT) data, heat capacity, and shear viscosity above the glass transition, and the model successfully reproduces various experimental observations such as cooling/heating at different rates, aging after quenching, and responses under hydrostatic pressure. The study highlights the model’s computational efficiency and its potential to unify mechanical and thermodynamic descriptions of glass transition phenomena, while noting its current limitation to isotropic volumetric deformation and single relaxation behavior.