Anisotropy of hole structures in polymers probed by two-dimensional angular correlation of annihilation radiation

Two-dimensional angular correlation of annihilation radiation (2D-ACAR) experiments have been performed in a semicrystalline polymer, polyaryl-ether-ether-ketone. The two-dimensional hole structures of unstretched 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 \AA{} in the unstretched sample and between 1.9 and 3.6 \AA{} in the stretched sample. Applications of the 2D-ACAR method to image the three-dimensional hole, free-volume, and cavity structures of molecular systems are discussed. \textcopyright{} 1996 The American Physical Society.