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Positron and positronium annihilation lifetime, and free volume in polymers

Yu, Zhibin
http://rave.ohiolink.edu/etdc/view?acc_num=case1058206184

Abstract Details

1995, Doctor of Philosophy, Case Western Reserve University, Physics.
Positron annihilation lifetime measurements were carried out for six polycarbonates of different structures and four polystyrenes of different molecular weight over a wide temperature range covering the glass transition region. The o-Ps mean lifetime is very sensitive to the changes of free volume in those polymers which occur due to change of molecular structure, chain length, and temperature. The influence of the unavoidable e+ irradiation and physical aging on the mean lifetime and the intensity of o-Ps annihilation were studied by conducting time dependent measurements on both very aged and rejuvenated samples. Both irradiation and physical aging reduce the formation of positronium, but have no effect on the mean lifetime of Ps atoms. The free volume fraction h obtained from the positron lifetime measurements was compared with the prediction of the statistical mechanical theory of Simha and Somcynsky; good agreement was found in the melt state though clear deviations were observed in the glassy state. A free volume quantity, computed from the bulk volume, which is in a good numerical agreement with the Simha-Somcynsky h-function in the melt, gives improved agreement with the h value calculated from the positron lifetime measurements. To investigate certain anomalies observed in the computer a nalysis of the positron annihilation lifetime spectra on polymers, we developed a computer simulation of the experimental data, which then was used to test the accuracy of the fitting results in the different circumstances. The influence caused by a possible distribution of the o-Ps mean lifetimes and the width of the spectrometer time resolution function were studied. The theoretical connection between the o-Ps mean lifetime and the free volume hole size was reviewed based on a finite spherical potential well model, and the status of the localized Ps atom in polymers was evaluated by calculation of the barrier transmission probability and the escaping probability of the trapped Ps atom. We conclude that there is no justification for a one-to-one correlation of lifetime components with specific hole sizes.
John McGervey (Advisor)
132 p.
Positron positronium annihilation lifetime free volume polymers

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Citations

  • Yu, Z. (1995). Positron and positronium annihilation lifetime, and free volume in polymers [Doctoral dissertation, Case Western Reserve University]. OhioLINK Electronic Theses and Dissertations Center. http://rave.ohiolink.edu/etdc/view?acc_num=case1058206184

    APA Style (7th edition)

  • Yu, Zhibin. Positron and positronium annihilation lifetime, and free volume in polymers. 1995. Case Western Reserve University, Doctoral dissertation. OhioLINK Electronic Theses and Dissertations Center, http://rave.ohiolink.edu/etdc/view?acc_num=case1058206184.

    MLA Style (8th edition)

  • Yu, Zhibin. "Positron and positronium annihilation lifetime, and free volume in polymers." Doctoral dissertation, Case Western Reserve University, 1995. http://rave.ohiolink.edu/etdc/view?acc_num=case1058206184

    Chicago Manual of Style (17th edition)

case1058206184
711
© 1995, all rights reserved.
This open access ETD is published by Case Western Reserve University School of Graduate Studies and OhioLINK.