ANISOTROPY OF HOLE STRUCTURES IN POLYMERS PROBED BY 2-DIMENSIONAL ANGULAR-CORRELATION OF ANNIHILATION RADIATION

Two-dimensional angular correlation of annihilation radiation (2D-ACAR ) experiments have been performed in a semicrystalline polymer, polyar yl-ether-ether-ketone. The two-dimensional hole structures of unstretc hed and stretched polymers, determined from the momentum distributions , are found to be spherical and ellipsoidal, respectively. The average hole radii are determined to be 2.6 Angstrom in the unstretched sampl e and between 1.9 and 3.6 Angstrom in the stretched sample. Applicatio ns of the 2D-ACAR method to image the three-dimensional hole, free-vol ume, and cavity structures of molecular systems are discussed.