Positron lifetime investigations on linear polyethylene compared to branched polyethylene

Abstract

Positron lifetime measurements on linear polyethylene are performed in the temperature range between -192 and + 180 "C. The results are compared with works on branched polyethylene. The criterion for the glass transition given earlier is proved. Branched and linear polyethylene show the same transitions at approximately the same temperatures. The only exception is the transition at -58 "C found in branched polyethylene only. Most deviations between the results of the two polyethylene samples can be explained by the different number of branching points or different cristallinity. Time effects of the lifetime parameters below the glass transition are observed. Positronen-Lebensdauermessungen in linearemPolyathylen werden im Temperaturbereich von -192 bis + 180 "C durchgefiihrt. Die Resultate werden mit Untersuchungen an verzweigtem Polyathylen verglichen. Ein friiher fiir den Glasiibergang abgeleitetes Kriterium bestatigt sich. Verzweigtes und lineares Polyathylen zeigen dieselben Ubergange bei etwa denselben Temperaturen. Die einzige Ausnahme bildet der obergang bei -58 "C, der nur beim verzweigten Polyathylen nachweisbar ist. Die meisten Abweichungen zwischen den Resultaten beider Polyathylenproben konnen auf die verschiedene Anzahl der Verzweigungspunkte und unterschiedliche Kristallinitat zuriickgefiihrt werden. Unter dem Glasiibergang werden zeitliche Effekte der Lebensdauerparameter beobachtet.

The temperature dependence of the local free volume in polyethylene and polytetrafluoroethylene: A positron lifetime study

“…The positron lifetimes and their temperature variation correlate with results in the literature. 24,27,35,37 As already mentioned, they correspond to four stationary states of positron and Ps existence. In molecular materials a fraction P of positrons penetrating the specimen may form Ps.…”

“…The separation of neighboring carbon atoms in hydrocarbonates is 0.15 off annihilation in interstitial free volumes of polymer crystals. We mention that some aunm; the CH 2 and the CF 2 groups occupy van der Waals volumes of 0.017 and 0.0246 nm 3 , respecthors 24,25,35,38 have attributed this medium o-Ps component to an attachment (or something simitively. 47,49,50 The increase of the hole size may be attributed to segmental motion which can occur lar) of the Ps atom to molecules.…”

Positron Annihilation Studies of Polyethylene-Carbon Black Composites

“…The influence of different physical parameters such as crystallinity, density, temperature, pressure, electric or magnetic field, irradiation dose, etc., has been examined within this context to study stuctural changes and primarily to identify the origin of the various lifetime components (e.g. [1][2][3][4][5][6][7][8][9]). In general, the positron annihilation lifetime (PAL) spectra in polymers have been resolved into three or four components.…”

Influence of Temperature and Pressure on the Free Volume in Thermo-Shrunken Polyethylene by Positron Annihilation

“…Figure 2 shows these changes. Characteristic minimum of the I 3 curve at about 240 K, in heating cycle, was observed also in polyethylene [12] and in polyethylene-co-vinyl acetate [13]. Reiter and Kindl [12] explained the existence of this minimum taking into account the temperature caused contraction of the sample and freezing of local motions of polymers chains.…”