Mobility of Pressure-Densified and Pressure-Expanded Polystyrene Glasses: Dilatometry and a Test of KAHR Model

Abstract

The structural recovery of pressure-densified (PDG) and, for the first time, pressure-expanded (PEG) glasses are experimentally investigated using pressurizable dilatometry. Both glasses show early devitrification on heating, indicating that these glasses have more mobility, compared to the conventional isobarically formed glass. The Kovacs−Aklonis−Hutchinson−Ramos (KAHR) model of structural recovery is able to reasonably predict the behavior of the pressure-expanded glass, but the KAHR model fails with the pressure-densified glass. The results suggest two limitations of the model: (i) the structural recovery is assumed to depend on the instantaneous liquid state and (ii) the same relaxation kinetics are assumed for the temperature and pressure perturbations. Modification of the KAHR model, allowing the departure from equilibrium, δ, to initially depend on the liquid state that the glass came from and to evolve toward the state that the glass is going to, improves the ability of the model to predict the early devitrification for the pressure-densified glass. Another modification of the KAHR model, allowing the temperature and pressure perturbations to relax independently of one another, results in effectively capturing the increased thermal expansion coefficient of glass lines during heating, as well as a "memory"-like aging behavior, for the pressuredensified glass.

Combined description of pressure–volume–temperature and dielectric relaxation of several polymeric and low-molecular-weight organic glass-formers using SL-TS2 approach

“…In this paper we utilized the specific volume data for eight liquids and polymers: glycerol, 75,76 phenylphthalein-dimethylether (PDE), 77 polychlorinated biphenyls (PCB), 78 o-terphenyl (OTP), 59 polycyclohexylmethacrylate (PCHMA), 79 polyvinylacetate (PVAc), 80,81 polystyrene (PS), [82][83][84] polymethylmethacrylate (PMMA). 85 The data reported in this paper have been previously published with a detailed description of the experimental setup.…”

Unifying Physical Framework for Stretched-Exponential, Compressed-Exponential, and Logarithmic Relaxation Phenomena in Glassy Polymers

“…Relaxation (dielectric, − mechanical, − specific volume, − or enthalpy − ) experiments and simulations − are important tools in understanding the behavior of glassy and near-glassy polymers. ,, Unlike conventional liquids, glassy materials exhibit relaxations that substantially deviate from the standard Debye single-exponential decay. In some cases, the material property of interest changes slowly over many decades in time (“stretched relaxation”), while in others, it exhibits no change until a sudden avalanche-like event takes place (“compressed relaxation”).…”