Degradation of polymer coating systems studied by positron annihilation spectroscopy. 1. UV irradiation effect

The degradation of polymer coating systems due to UV irradiation is studied using positron annihilation spectroscopy. Doppler broadened spectra of positron annihilation are measured as a function of slow positron implantation energy in a series of polymer coating systems which were exposed to UV irradiation for up to 2000 h. The S parameters from the Doppler broadened energy spectra vs positron energy show an increase at very low positron energy (<575 eV) and then a decrease to about 8 keV, followed by a slight increase up to 50 keV. The UV irradiation systematically decreases the S parameter as a function of exposure duration. The significant S parameter decrease is interpreted as the degradation of polymers and the change of the sub-nanometer defect profiles due to UV irradiation. These interpretations are supported by the data from the atomic force microscope, UV absorption, Fourier transform infrared, and profilometry measurements.