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

Abstract

Two‐dimensional angular correlation of annihilation radiation (2D‐ACAR) experiments have been performed on an uniaxially oriented polymer, bisphenol‐A polycarbonate. The two‐dimensional hole structures of unoriented and oriented polymers, determined from the momentum distributions, are found to be spherical and ellipsoidal, respectively. The average hole radii are determined to be 2.9 Å in the unoriented sample and between 2.3 and 3.8 Å in the oriented sample. Applications of the 2D‐ACAR method to image the three‐dimensional hole structures of polymeric materials are discussed. © 1996 John Wiley & Sons, Inc.

Mobility and stability of glasses

“…Others have also reported similar observations of enhanced glassy mobility despite decreases in sample volume 4, 35–37. Particularly comprehensive are a series of articles by Shelby and coworkers37–40 in which hot drawn polystyrene and PC samples were quenched in a stretched state and then their physical aging rates were subsequently investigated as a function of molecular alignment. Volume dilatometry studies indicated an increase in the volume relaxation rate β of ∼50% with increased molecular alignment 38.…”

“…This is in agreement with positron annihilation lifetime spectroscopy measurements,35, 41 which found that mechanical deformation initially increased the size of the free volume elements (more mobile regions) to some saturation value and then primarily increased their number. Positron annihilation measurements by Jean et al40 also observed changes in the distribution of the free volume elements corresponding with the increased physical aging rates observed by Shelby and Wilkes 37, 38. Similarly, Bartos et al42 found that cold drawn PC samples exhibited faster dilatometric aging rates that correlated with increased density fluctuations as measured by SAXS.…”

Free-volume hole model for positronium formation in polymers: surface studies

“…Excellent anti-correlation between I 3 and degree of crystallinity has been observed in semi-crystalline polymers [33,34]. Thirdly, many existing temperature and pressure studies all show that I 3 correlates nicely with the expected variations of fraction of free volumes and holes in similar series of polymers [1][2][3][4][5][6][7][8][9][10].…”

Perspective of Positron Annihilation Spectroscopy in Polymers

“…In polymeric materials, two-dimensional angular correlation of annihilation radiation spectroscopy (2D-ACAR) is particularly useful to determine the free-volume anisotropic structure. 2D-ACAR has been demonstrated to measure the two-dimensional shape of free volumes in oriented polymeric materials. , 2D-ACAR is a powerful method in determining the anisotropy of free volumes; however, the radiation damage to polymer samples under a strong positron source (>20 mCi or 7.4 × 10 8 Bq) is a concern since a good 2D-ACAR experiment takes several days. For crystalline or oriented polymeric systems, the 2D-ACAR method is still useful in determining free-volume and void structures.…”