Interplay between electron affinity and free volume on positronium formation in polyimides

Abstract

Our recent PAL results on a series of polyimides (PI) are summarized. It is shown that PIs are properly grouped according to whether there is long-lived o-Ps or not, and that those that do not produce o-Ps have strong electron affinities. Secondly the pore size was changed by exposing PIs to 50 atm CO 2 gas. I 3 was increased substantially for the PIs that have moderate I 3 values. For the PIs that have large o-Ps yield the increase in I 3 was small, and for those having no o-Ps the o-Ps component did not appear. In a third experiment where the pore structure was changed by introducing vapor molecules, both τ 3 and I 3 were reduced. This contrasts to low density polyethylene (or which τ 3 and I 3 were increased. These results are viewed as an aspect of the spur model in which both electron affinity and pore size are affecting Ps formation