Temperature and time dependence of orthopositronium formation in polystyrene

Three measurement protocols were performed to investigate the temperature dependence of positron lifetime spectra for polystyrene over the temperature range −70 to 180°C. The polystyrene samples were first subjected to a heating schedule in sequential 10°C increments. This was followed by a cooling...

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Bibliographic Details
Published in:Polymer (Guilford) 1999-05, Vol.40 (11), p.3033-3040
Main Authors: Peng, Z.L, Olson, B.G, McGervey, J.D, Jamieson, A.M
Format: Article
Language:English
Subjects:
Aging effect
Applied sciences
Exact sciences and technology
Organic polymers
Physicochemistry of polymers
Positronium formation probability
Properties and characterization
Radiation effects
Thermal and thermodynamic properties
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Summary:Three measurement protocols were performed to investigate the temperature dependence of positron lifetime spectra for polystyrene over the temperature range −70 to 180°C. The polystyrene samples were first subjected to a heating schedule in sequential 10°C increments. This was followed by a cooling schedule, again in 10°C increments. The third schedule involved rejuvenation of the specimen above T g between each measurement. The measured lifetime spectra were resolved into three components. We observed a minimum in the temperature dependence of the o-Ps intensity I 3 at ∼20°C for polystyrene specimens subjected to the heating and cooling schedules, but not for the rejuvenated samples. The influence of the duration of e +-irradiation on the lifetime and intensity of o-Ps annihilation was investigated under isothermal conditions. A decrease in o-Ps intensity I 3 with duration of exposure to e +-irradiation was found whose rate was maximal at 23°C. The results suggest that the time dependence of the o-Ps intensity in the glass can be interpreted within the framework of the spur-model. Specifically, the variation of I 3 is ascribed to the formation at low temperature of free radicals with small electron affinities. After correcting for the e +-irradiation effect, no significant aging effect in the glassy state was detected in the o-Ps intensity and lifetime.
ISSN:0032-3861
1873-2291
DOI:10.1016/S0032-3861(98)00401-7