Article ID | Journal | Published Year | Pages | File Type |
---|---|---|---|---|
10732171 | Radiation Physics and Chemistry | 2005 | 9 Pages |
Abstract
Temperature dependence of the lifetime Ï3 and intensity I3 of the long-lived ortho-positronium (o-Ps) component was measured for two polyimides PI189 and PI304 both below and above glass-transition temperatures Tg of these polymers. First heating runs of the experiments revealed anomalous, irregular behavior of the lifetime Ï3 in both PI in the vicinity (below) of the glass transition temperature. The effect was similar to that discussed recently for a number of PI. However, on the cooling stage of the first cycle and on the heating run of the second cycle, such irregularities disappeared. These results show that anomalous behavior of annihilation characteristics of o-Ps in our PI samples were due not to anomalous behavior of PI structure itself close to Tg point (not to a specific phase transition), but to removal of residual solvent in vicinity of Tg during the first heating cycle. Different approaches to estimations of the specific hole volume and of the holes number density N on the basis of positron annihilation data are discussed. Final estimation for PI189 gives the fractional free volume h=3.35% and N=0.44Ã1027m-3. The effects of positron trapping by polarâCO groups on annihilation characteristics of PI and on the obtained value of N are also considered.
Related Topics
Physical Sciences and Engineering
Physics and Astronomy
Radiation
Authors
V.P. Shantarovich, T. Suzuki, C. He, Y. Ito, Y.P. Yampolskii, A.Yu. Alentiev,