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Polypropylene Films Studied with Variable Positron Beams

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Dębowska M., Coleman P., Gidley D.

Acta Physica Polonica A

1999

vol. 95

issue 4

496-504

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: I_{2} (τ_{2}=1.3 ns) and I_{3} (τ_{3}≈ 2.3÷2.8 ns) show changes with crystallinity of samples. The evident trend is observed for the longer-lived τ_{3}-component intensity to decrease with crystallinity while the reverse is true for the shorter, fixed τ_{2}-component. The decrease in the intensity of the longer-lived component can result from reduction of the fractional free volume.

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1 Acta Physica Polonica A

1 1999

1 Coleman P.

1 Dębowska M.

1 Gidley D.

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Polypropylene Films Studied with Variable Positron Beams