FREE-VOLUME DISTRIBUTIONS OF AN EPOXY POLYMER PROBED BY POSITRON-ANNIHILATION - TEMPERATURE-DEPENDENCE

We have performed a series of positron annihilation lifetime (PAL) experiments to measure the free-volume hole distributions in an epoxy (DGEBA/DDH/DAB) polymer (T(g) = 62-degrees-C) at temperatures between 25 and 150-degrees-C. A Laplace inversion technique has been employed to analyze the PAL spectra to continuous lifetime distributions, and the hole volume distributions are determined from the results of ortho-positronium lifetime distributions. At each temperature, we have obtained three distinct PAL distributions with the peaks positioned at 0.07-0.12, 0.39-0.41, and 1.6-2.2 ns, respectively. The free-volume hole radii are distributed between 1.7 and 3.1 angstrom with a peak at 2.45 angstrom at room temperature, and the distributions are shifted to a larger radius as the temperature increases.