Study of the effect of electric field on positron annihilation parameters in polymers

Positron annihilation lifetime measurements have been performed to study the effect of an external electric field in several polymers. The application of the electric field on polytetrafluoroethylene (PTFE) and ultrahigh-molecular weight polyethylene (UHMWPE) noticeably decreased the ortho-positronium ( o-Ps) intensity. The o-Ps intensity increased with increasing electric field strength in the poly(ethylene terephthalate), PET, poly(ethylene naphthalate), PEN, and poly(aryl-ether-ether-ketone), PEEK samples. The data are consistent with a hypothesis that nonpolar polymers (PTFE and UHMWPE) show a decrease in the o-Ps intensity with increasing electric field, while the effect seems to be opposite in polar polymers (PEN, PET and PEEK).