A coincidence between the temperature-dependent hole (free volume) fraction h above the glass transition temperature, derived from lattice-hole theory, and the corresponding function hPs obtained from positronium lifetime spectroscopy has been previously observed for four polystyrene fractions ranging from 4000 to 400,000 in molar mass. This result was based on the assumed proportionality of hPs and the product of the orthopositronium intensity I3 and the mean cavity volume, the proportionality constant C being molar mass dependent. However, a recent analysis of the data based on volume arguments by Olson and Jamieson revealed systematic departures between the two sets of free volume functions. We reexamine the situation by departing from the customary assumption of spherical cavities, and allowing for nonspherical geometries represented by prismatic or cylindrical disks. Agreement between spectroscopic and thermodynamic functions ensues with fixed, temperature-independent asymmetry factors decreasing with increasing molar mass. These tentative findings suggest that systematic studies of melts with varying chain flexibility and molar mass should be attempted.

On the Relation between Positron Annihilation Lifetime Spectroscopy and Lattice-Hole Theory Free Volume

CONSOLATI, GIOVANNI;QUASSO, FIORENZA;
2005-01-01

Abstract

A coincidence between the temperature-dependent hole (free volume) fraction h above the glass transition temperature, derived from lattice-hole theory, and the corresponding function hPs obtained from positronium lifetime spectroscopy has been previously observed for four polystyrene fractions ranging from 4000 to 400,000 in molar mass. This result was based on the assumed proportionality of hPs and the product of the orthopositronium intensity I3 and the mean cavity volume, the proportionality constant C being molar mass dependent. However, a recent analysis of the data based on volume arguments by Olson and Jamieson revealed systematic departures between the two sets of free volume functions. We reexamine the situation by departing from the customary assumption of spherical cavities, and allowing for nonspherical geometries represented by prismatic or cylindrical disks. Agreement between spectroscopic and thermodynamic functions ensues with fixed, temperature-independent asymmetry factors decreasing with increasing molar mass. These tentative findings suggest that systematic studies of melts with varying chain flexibility and molar mass should be attempted.
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Utilizza questo identificativo per citare o creare un link a questo documento: https://hdl.handle.net/11311/554606
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