Microstructure of polycarbonate seen by positrons as an in-situ probe

Positron Annihilation Lifetime Spectroscopy (PALS) is used to probe the micro-structural changes in the polymer polycarbonate in terms of the changes in free volume hole size and their content as a function of temperature. The measured spectra are best fitted to three lifetime component analysis. The average hole size in the amorphous regions is determined from the measured Ortho Positronium (O-Ps) lifetime ₃ by following the treatment of Nakanishi et al. On the other hand, information about defects in the crystalline regions is revealed by trapped positrons lifetime ₂. In this polymer the average hole radius varies from 2.71 Å to 2.77 Å. The present study indicates that this polymer has a glass transition temperature of 152°C. Further, we have calculated the trapping rates in the ordered and disordered regions of the polymer based on Goldanskii's kinetic equations and an attempt is made for the first time to estimate the activation energy in the amorphous and crystalline regions separately.