POSITRON LIFETIME STUDIES OF FREE-VOLUME HOLE SIZE DISTRIBUTION IN GLASSY POLYCARBONATE AND POLYSTYRENE

Positron lifetime spectroscopy has been applied to estimate the free v olume hole size distribution in polycarbonate (PC) and in polystyrene (PS) at room temperature. The hole radius density distributions are de termined from the ortho-positronium lifetime distributions obtained vi a a Laplace inversion of the measured positron lifetime spectra. The h ole volume density distributions and the number density distributions of holes are estimated from the hole radius density distributions. All of the distributions may be well approximated by single Gaussians. Th e hole radius and the hole number density distributions have centres [ r(f)] and [v(fn)] at 0.29 nm and 0.1 nm(3) in PC, and 0.28 nm and 0.09 nm(3) in PS. The FWHM of the corresponding distributions are 0.042 nm and 0.040 nm(3) (PC), and 0.039 nm and 0.34 nm(3) (PS), respectively. Both, the shape and the width of the distributions correlate well wit h the free volume theory of Bueche. The possible influence of differen t effects, such as a nonspherical shape of holes and a scanning of sev eral holes by positronium before annihilation, on the mean hole size a nd the hole size distribution as detected by the positron lifetime met hod is finally discussed.