Investigations on the Low-Temperature Transitions and Time Effects of Branched Polyethylene by the Positron Lifetime Technique

Abstract

Positron lifetime measurements are performed in branched polyethylene in the temperature range between −195 and +40 °C. The lifetime spectra are resolved into four components, and corresponding annihilation mechanisms are discussed. Within the temperature range mentioned above four different transitions at −145, −95, −58, and −13 °C can be observed. From the behaviour of the lifetime parameters of the longest‐lived component it is possible to deduce a criterion for the glass transition, which is situated at −13 °C. Additionally, time effects of the lifetime parameters are detected.

Influence of Positron Irradiation on Positronium Formation in n-Alkanes

“…Details of this process are described by the spur model [1,2] assuming that positron combines with one of electrons from the last ionization product cluster ("blob"). However, it has been noticed recently [3,4] that with a prolonged duration of experiment, at low temperatures, the probability of the Ps formation (observed via triplet ortho-Ps intensity) rises. The electrons which have been knocked by positron along its ionization track diffuse and locate in intermolecular cavities which are electron traps about 0.5-2 eV deep.…”

The Effect of Visible Light Irradiation on Positronium Formation in Polyethylene at Low Temperature

“…The longest lifetime component (τ 3 ) is assigned to the pick-off annihilation of ortho-positronium (o-Ps) localized in intermolecular spaces (holes) and there is a simple relation between τ 3 and the size of the holes [1,2]. Although it has been recognized that o-Ps intensity (I 3 ) is related to the amount of the intermolecular spaces, the temperature dependence of 13 is not always explained by a simple relation.…”

Free Volume in Plastified Poly(Vinyl Chlorate)

“…The shortest lived component (in these cases flxed at τ1 = 125 ps) is attributed to p-Ps annihilation [16][17][18] Table. In the cases when the measurements were repeated for the sample, weighted means of the results are listed.…”