Study of polymer/metal coating under stress using positron annihilation spectroscopy

Positron annihilation spectroscopy (PAS) has proven to be a very useful technique for, e.g., the study of defects in materials and the characterization of polymer free-volume. Positron lifetime, Doppler broadening of the annihilation radiation (characterized by the so-called S parameter) and angular correlation of annihilation radiation (ACAR) are the techniques used mostly. In the last few years these techniques have been extended to the study of physical defects at the atomic level of coating systems. These studies show that positron lifetime and the S parameter can monitor the degradation of the coating due to environmental changes (water or UV exposure). The present work is focused on the behavior of coatings under external stresses as studied by PAS. Results of positron annihilation measurements (before and after stretching) on interstitial free (IF) steel coated with epoxy using the Delft variable energy positron (VEP) beam facility are discussed.