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 cali bration with the free-volume hole-fraction h(PVT) from pressure-volume-temp erature and equation-of-state (PVT-EOS) analysis using the Simha-Someynsky theory, PALS data (ortho-positronium (o-Ps) lifetime tau(3) and o-Ps intens ity 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-vol ume. The widespread use of this equation, in particular the correlation con stant C, is given some attention, clarification and further improvement. Fr om 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)) a nd h(PVT) = k(1) + k(2) X V(tau(3)), where B, k(1), and k(2) are correlatio n constants. We propose and show that the freezing fraction of polymer glas ses can be calculated from the temperature coefficients of V(tau(3)), which further supports its close relation to h(PVT). (C) 2000 Elsevier Science L td. All rights reserved.