Ortho-positronium lifetime and intensity in pressure-densified amorphous polymers

We report the dependence of the ortho-positronium (o-Ps) lifetime tau(3) an d intensity I-3 On the thermodynamic history of a number of amorphous homop olymer and copolymer glasses that were pressure-densified at pressures up t o 200 MPa. Small macroscopic volume changes up to 1.85% yield large microsc opic volume changes in the pressure-densified glasses, i.e., tau(3) decreas es by a maximum of 9%, while I-3 remains constant, and the Simha-Somcynsky free-volume fraction decreases by a maximum of 31% and correlates with the free-volume size V(tau(3)). (C) 2000 Elsevier Science Ltd. All rights reser ved.