Relation between free-volume quantities from PVT-EOS analysis and PALS

Unique information about the properties of free-volume sites in polymers is gained from position annihilation lifetime spectroscopy (PALS). After calibration with the free-volume hole-fraction h(PVT) from pressure-volume-temperature and equation-of-state (PVT-EOS) analysis using the Simha-Someynsky theory, PALS data (ortho-positronium (o-Ps) lifetime tau(3) and o-Ps intensity I-3) may be used to calculate free-volume fractions h(PALS) from h(PALS) = C X V(tau(3))X I-3. where V(tau(3)) is the subnanometer cavity hole-volume. The widespread use of this equation, in particular the correlation constant C, is given some attention, clarification and further improvement. From PVT data and PALS data, measured on chemically and physically identical amorphous poly(methyl methacrylate) samples, both below and above the glass transition temperature, we find improved relations: h(B) = B x V(tau(3)) and h(PVT) = k(1) + k(2) X V(tau(3)), where B, k(1), and k(2) are correlation constants. We propose and show that the freezing fraction of polymer glasses can be calculated from the temperature coefficients of V(tau(3)), which further supports its close relation to h(PVT). (C) 2000 Elsevier Science Ltd. All rights reserved.