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

Abstract

We report the dependence of the ortho-positronium ( o-Ps) lifetime τ 3 and intensity I 3 on the thermodynamic history of a number of amorphous homopolymer and copolymer glasses that were pressure-densified at pressures up to 200 MPa. Small macroscopic volume changes up to 1.85% yield large microscopic volume changes in the pressure-densified glasses, i.e., τ 3 decreases 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 τ 3 .