Shu-Min Li

ON THE AGING CHARACTERIZATION OF POLY(ETHYLENE TEREPHTHALATE) BY POSITRON SPECTROSCOPY

Abstract Positron spectroscopy was used to study the free volume properties of glassy poly(ethylene terephthalate) as a function of temperature and aging time. The experimental results indicate that the glass transition temperature increases with increasing aging time. This is confirmed by differential scanning calorimetry measurements. From the aging time dependence of the intensity of the ortho-positronium (o-Ps) component I3 and the fractional free volume, we observe that the concentration of free volume holes and the fractional free volume show a continuous decrease at a fixed aging temperature, which suggests that structural relaxation and segmental rearrangement occur during physical aging.

A theoretical prediction on laser assisted Ps formation including multiphoton processes

Abstract In the first Born approximation, a theoretical prediction on positronium formation in laser assisted positron-atom collisions is made. It is found that the collisions are accompanied by multiphoton processes. The cross sections are notably modified by the laser.