Industrial Applications of Positron Annihilation
J. Phys. IV France 05 (1995) C1-199-C1-203
Free Volumes in Polystyrene Probed by Positron AnnihilationA. Uedono1, T. Kawano2, L. Wei1, S. Tanigawa1, M. Ban3 and M. Kyoto3
1 Institute of Materials Science, University of Tsukuba, Ibaraki 305, Japan
2 Radioisotope Center, University of Tsukuba, Tsukuba, Ibaraki 305, Japan
3 Analytical Characterization Center, R&D Group, Sumitomo Electric Industries Ltd., 1 Taya-cho, Sakae-ku, Yokohama 244, Japan
Polystyrene specimens with different molecular weights were characterized by the positron annihilation technique. Lifetime spectra of positrons were measured in the temperature range between room temperature and ~150 °C. The observed lifetime spectra were resolved into three components, where the longest lifetime, τ3, was associated with pick-off annihilation of orthopositronium (o-Ps) trapped by free-volumes. Above the glass transition temperature (Tg), the temperature coefficient of τ3 was found to be about 4 times larger than that below Tg, wile no drastic change in the intensity corresponding to the annihilation of o-Ps was observed at Tg. These facts suggest that the glass transition mainly affects the expansion rate of the free volumes in polystyrene specimens.
© EDP Sciences 1995