Polypropylene Films Studied with Variable Positron Beams |
| M. Dębowskaa, P.G. Colemanb and D.W. Gidleyc a Institute of Experimental Physics, University of Wrocław, Pl. Maksa Borna 9, 50-204 Wrocław, Poland b School of Physics, University of East Anglia, Norwich NR4 7TJ, United Kingdom c Department of Physics, University of Michigan, Ann Arbor, MI 48109, USA |
| Full Text PDF |
| Doppler broadening and positron lifetime spectra have been measured for polypropylene films of constant thickness (≈ 50 μm) and different morphology that crystallized from melt at temperature 0, 100, and 120°C. The S -parameter vs. energy curves do not change in a systematic way with crystallinity of samples. It is supposed that decrease in the fractional free volume for samples of greater crystallinity is not seen in S-values because of their increase resulting from annihilation in defects present both in the crystalline regions and on the lamellae surfaces. Intensities of the components in the positron lifetime spectra: I2 (τ2=1.3 ns) and I3 (τ3≈ 2.3÷2.8 ns) show changes with crystallinity of samples. The evident trend is observed for the longer-lived τ3-component intensity to decrease with crystallinity while the reverse is true for the shorter, fixed τ2-component. The decrease in the intensity of the longer-lived component can result from reduction of the fractional free volume. |
| DOI: 10.12693/APhysPolA.95.496 PACS numbers: 36.10.Dr, 61.41.+e, 71.60.+z, 78.70.Bj |