Abstract
A part of positrons injected into polymers form positronium (Ps) after loosing their energy through interactions with atoms and molecules. Positron annihilation lifetime spectroscopy (PALS) is capable of determining size, distribution, fraction and anisotropic structure of inter-molecular holes in polymers. The Ps lifetime and intensity in polymers were measured using a short-pulsed slow positron beam system, in which system the Ps lifetime in a polymer near the surface can be measured by changing the injection energies of positron. This measurement has been widely used in the metallographical field; while in the polymer field it has been used only for studies focussed on the simple structures of thermoplastic and thermosetting resins. In this report, the investigation was performed on a phenol-cured epoxy system used as a standard product in the polymer engineering. The result suggested that this polymer had a graded structure near the surface, and the properties of the structure differed from those of the bulk.
