Development of positron annihilation spectroscopy to test accelerated weathering of protective polymer coatings

A variable mono-energetic positron beam with a computer-controlled system h as recently been constructed at the University of Missouri-Kansas City for weathering studies of polymeric coatings. The beam is designed to measure t he S-parameter from Doppler-broadening energy spectra and the sub-nanometer defect properties from positron annihilation lifetimes (PAL). Significant variations of S-parameter and ortho-positronium intensity in coatings, as o btained from the newly built beam and from the Electrotechnical Laboratory' s beam, respectively, are observed as a function of depth and exposure time due to the Xe-light irradiation. A high sensitivity of positron annihilati on signal response to the early stage of degradation is observed. Developme nt of positron annihilation spectroscopy to test accelerated weathering of polymeric coatings is discussed. (C) 2000 Elsevier Science Ltd. All rights reserved.