Combined description of polymer PVT and relaxation data using a dynamic “SL-TS2” mean-field lattice model

Abstract

We develop a combined model to describe the pressure–volume–temperature (PVT) thermodynamics and the α- and β-relaxation time dynamics in glass-forming amorphous materials. The PVT results are described using a two-state modification of the Sanchez–Lacombe equation of state (SL-EoS). The minimization of the Sanchez–Lacombe free energy expression allows one to calculate the density (or specific volume) and the “solid fraction” as a function of temperature and pressure. The solid fraction, ψ(T,P), is then substituted into the TS2 mean-field model (V. V. Ginzburg, Soft Matter, 2020, 16, 810), and the equilibrium relaxation times and the glass transition temperature are calculated. Finally, we use a dynamic model of a Tool–Narayanaswami–Moynihan (TNM)-type to describe the density relaxation as a function of the cooling rate. We applied the new framework to describe experimental data for polystyrene and poly(methylmethacrylate) and found a good qualitative and quantitative agreement.