Free-Volume Hole Distribution of Polymers Probed by Positron Annihilation Spectroscopy

摘要

Positron annihilation spectroscopy (PAS) has been developed to characterize the free-volume properties of polymers and polymer blends. Positron annihilation lifetime (PAL) measurements give direct information about the dimension, content, and hole-size distributions of free volume in amorphous polymeric materials. The free-volume hole distribution in epoxy, polypropylene, polycarbonates, and polystyrene is presented as a function of pressure, molecular relaxation, and miscibility. The unique capability of PAS to probe free-volume properties derives from the fact that the positronium atom (Ps) is preferentially trapped in atomic-scale holes ranging in size from 1 to 10 A.