FREE-VOLUME HOLE DISTRIBUTIONS OF POLYMERS BY POSITRON-ANNIHILATION LIFETIME SPECTROSCOPY

Positron lifetime spectra of polymers have been resolved into continuous lifetime distributions with the aid of the Laplace inversion algorithm implemented in the CONTIN program. The free-volume hole size distributions are calculated from the o-Ps lifetime distributions based on the semi-empirical quantum mechanical model of a spherical hole. Due to various factors such as the statistics, instrument drift, and choice of the reference spectrum, the obtained lifetime distributions are only close to the real ones. Experiences in using the CONTIN program and experimental techniques in approaching the true free-volume distributions are discussed. A variety of free-volume distributions as a function of temperature, pressure, and aging time in several polymers is reported, which are in good agreement with the current free-volume theories on polymers. This paper summarizes the results obtained at the University of Missouri-Kansas City (UMKC) during the past three years (1991-93).