Structural relaxation in poly(ethylene terephthalate) studied by positron annihilation lifetime spectroscopy

Abstract

Positron lifetime technique was used to study the physical ageing process in poly(ethylene terephthalate) (PET). Positron lifetime results show that the structural relaxation processes in PET encompass two different time regimes, one short and the other long. The relaxation function constructed from the measured o‐Ps intensity I3 exhibits non‐exponential character, which can be best fitted with two additive exponentials. The Narayanaswamy model (Kohlraush‐William Watt (KWW) function) is invoked to extract the stretching parameter β indicating the extent of deviation from exponential relaxation. Based on the relaxation times, the activation energies calculated seem to label the different kinetic units of PET structure participating in the relaxation process. © 2002 Society of Chemical Industry

Differential scanning calorimetric and free volume study of reactive compatibilization by EPM‐g‐MA of poly(trimethylene terephthalate)/EPDM blends

“…PALS is one of the sophisticated tools currently available for determining directly the nanometer‐sized free volume cavities and their relative number density (concentration) in polymers10–14 and recently, in polymer blends 10. To enunciate the versatility of this method, we mention only a few of the interesting studies carried out using this technique: water sorption in contact lens polymers,15 polymers containing silver nanoparticles,16 structural relaxation of polyethylene terephthalate and polycarbonate,17–19 ageing studies on polymers,20 etc. When positrons from a radioactive source ( 22 Na) are injected into a molecular medium like polymers or blends, they reach thermal energy in a very short time (∼1 ps), through the interaction with the surrounding atoms and molecules, losing the energy by inelastic collisions.…”

“…However, in molecular media like polymers, o‐Ps annihilates through a fast channel called pick‐off annihilation, where the positron of o‐Ps picks up an electron from the surrounding medium and annihilates, thereby its lifetimes gets shortened to few nanoseconds. It has been clearly established that, o‐Ps preferentially scans the free volume holes of the polymer system 10–17, 21. Therefore, the o‐Ps lifetime parameters, namely lifetime (τ 3 ) and its intensity ( I 3 %), have been widely used in the study of microstructural behavior of polymeric materials.…”

Influence of SHI upon nanohole free volume and micro scale level surface modifications of polyethyleneterephthalate polymer films

“…The calculated values of E g for pristine as well as irradiated samples are given in Table 1. The E g value for pristine sample is 3.90 eV which is in close agreement with the values calculated by other groups in the literature [57,49,25]. The number of carbon atoms per conjugation length (N) was calculated by using following equation given by Fink et al [58,59].…”

Thermally induced microstructural changes and its influence on electrical conductivity of a polymer‐based bakelite RPC detector material: A positron lifetime study

“…When the temperature is increased above T g , the segmental relaxation rate is faster than the volume relaxation rate and hence excess free volume will be trapped within the polymer. As a result, there will be an increase in size of the free volume of a polymer . Upon cooling, the molecular segments begin to relax towards an equilibrium state.…”