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

Abstract
Our recent PAL results on a series of polyimides (Pl) are summarized. It is shown that Pls 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 ex-posing Pls to 50 atm CO₂ gas. I₃ was increased substantially for the Pls that have moderate I₃ values. For the Pls that have large o-Ps yield the increase in I₃ 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 [MATH]3 and I₃ were reduced. This contrasts to low density polyethylene for which , τ₃ and I₃ 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.