MICROSTRUCTURE OF POLYCARBONATE SEEN BY POSITRONS AS AN IN-SITU PROBE

Positron Annihilation Lifetime Spectroscopy (PALS) is used to probe th e micro-structural changes in the polymer polycarbonate in terms of th e changes in free volume hole size and their content as a function of temperature. The measured spectra are best fitted to three lifetime co mponent analysis. The average hole size in the amorphous regions is de termined from the measured Ortho Positronium (O-Ps) lifetime tau(3) by following the treatment of Nakanishi et al. On the other hand, inform ation about defects in the crystalline regions is revealed by trapped positrons lifetime tau(2). In this polymer the average hole radius var ies from 2.71 A to 2.77 Angstrom. The present study indicates that thi s polymer has a glass transition temperature of 152 degrees 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 i n the amorphous and crystalline regions separately.