A free four-term analysis of positron lifetime spectra of γ-irradiated Teflon

Kindl, Peter; Puff, Werner; Sormann, H.

doi:10.1002/pssa.2210580219

Cited by 36 publications

(23 citation statements)

References 21 publications

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“…Above T g , concentration of reactive centers will decrease due to the recombination of mobile ions and radicals. This may lead to the new increase of the o-Ps intensity above 293 K. Such behavior was already observed for polyetheylene by Kindl et al [10]. Taking τ 3 as a measure of the free hole radius, R, the average volume hole size was calculated as V h = 4πR 3 /3 and its variation with temperature is shown in Fig.…”

mentioning

confidence: 75%

Temperature dependence of the free volume holes in polyhydroxybutyrate biopolymer: A positron lifetime study

Abdel-Hady

Hamed

Fareed

2007

Phys. Status Solidi (c)

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The size of the free volume holes and their distributuion in polyhydroxybutyrate (PHB) biopolymer have been studied using positron annihilation lifetime spectroscopy (PALS). The measurements were performed as a function of the temperature from 243 to 363 K. The temperature dependence of the free volume hole shows a glass transition temperature, T g at 278 K. The free volume behaviour of PHB shows a small linear increase with temperature below T g and a steeper increase above T g . The thermal expansion coefficients of the free volume hole were determined to be 4.78 x 10 -3 and 12.5 x 10 -3 / K below and above T g , respectively. The free volume hole distribution shows a narrow distribution below T g . With increasing temperature, the maximum of the distributions of the free volume holes shifts to higher values. Meanwhile, widening of the distribution is smaller in lower temperature ranges and more pronounced at higher temperatures, especially above T g .1 Introduction Polymers contain local free volumes, these are cavities or holes of atomic and molecular dimensions that arise because of (1) irregular molecular packing in the amorphous phase (static and pre-existing holes) and (2) molecular relaxation of the polymer chains and terminal ends (dynamic and transient holes). Positron annihilation lifetime spectroscopy (PALS) has recently emerged as a unique nano-probe capable of measuring the free volume hole sizes in polymers [1][2][3][4]. When positrons are injected into materials, they lose their kinetic energy within a few picoseconds. After thermalization, a positron diffuses in the media, and annihilates with an electron from the surrounding emmiting two γ-rays. In polymers, a positron might annihilate from a positronium (Ps) state, a bound state of a positron and electron. A positronium has two spin states: a singlet state (para-Ps, p-Ps) and a triplet state (orthoPs, o-Ps).The most important component is the o-Ps lifetime, τ oPs which gives us information about the free volume holes in which annihilation of positrons takes place.Nowadays plastics and synthetic polymers are mainly produced using petrochemical materials that cannot be decomposed. Therefore they contribute to environmental pollution and are a danger to many animals. During the last decade, much attention has been focused on the production of bacterial polyesters. Different bacterial types [5] of microorganisms produce polyhydroxybutyrate (PHB) from renewable sources such as sugar and molasses as intracellular storage materials. The possible applications of PHB are in medicine, in pharmacology and in packaging for deep drawing articles in the food industry.Only one measurement was reported in the study of the properties of the free volume in PHB biopolymer [6]. The aim of this work is to invesigate the potential of PALS for studying the free volume properties of semicrystalline PHB bioolymer. This can be achieved via a systematic study of the temperature dependence of the mean size of local free volumes and their distributions.

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mentioning

confidence: 75%

Temperature dependence of the free volume holes in polyhydroxybutyrate biopolymer: A positron lifetime study

Abdel-Hady

Hamed

Fareed

2007

Phys. Status Solidi (c)

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“…This constraint is very often used in the literature (see, for example, Refs. [19,20]). The lifetimes and intensities behave almost as those used in the simulation, with only t 1 appearing clearly smaller (124 ps) than simulated.…”

Section: Lifetime Parameters From the Discrete-term Routine Lifspecfitmentioning

confidence: 96%

Does the MELT Program Accurately Reveal the Lifetime Distribution in Polymers?

Dlubek

Eichler

Hübner

et al. 1999

phys. stat. sol. (a)

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In previous studies we have investigated artefacts which appear in analysed parameters of positron lifetime spectra containing distributed o‐Ps lifetimes. Recently, we discovered also that the disagreements between the experimental positronium lifetime parameters and theoretical expectations, I1/I3 > Ip‐Ps/Io‐Ps = 1/3 and τ1 > τp‐Ps, may be well understood by assuming a distribution of e+ lifetimes in addition to an o‐Ps lifetime distribution. In this paper we give further experimental evidence for these deviations by taking positron lifetime spectra of high statistical accuracy for various amorphous polymers. Furthermore, a systematic study of the influence of the widths of the e+ and o‐Ps lifetime distributions on the analysed lifetime parameters will be presented. The analysis of computer‐generated spectra showed that all of the analysed lifetimes τ1, τ2 and τ3 increase artificially with increasing width of the e+ and o‐Ps lifetime distributions. The intensity I1 increases also, while I2 and I3 decrease. The deviations of I1/I3 and τ1 from the theoretical expectations are mainly controlled by the width of the e+ lifetime distribution. Suggestions for suitable constraints in the discrete‐term analysis in order to get reliable lifetime parameters are also made.

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“…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.…”

Section: Introductionmentioning

confidence: 99%

“…In general, the positron annihilation lifetime (PAL) spectra in polymers have been resolved into three or four components. For example, according to the four components analysis for te flon performed by Kindl et al [2,3], the longest component includes all the positrons forming orthopositronium (oPs) and annihilation via electron pick-off; the intermediate long-lived component arises from positrons bound in the amorphous domains; the intermediate short-lived component is exclusively due to free positrons; the shortest component is partly due to para-positronium (p-Ps) self-annihilation and partly to a bound positron state of short lifetime. The former authors come to the conclusion that the intermediate long-lived component may be also due to a positronium (Ps) state.…”

Section: Introductionmentioning

confidence: 99%

Positron Annihilation Studies of Polyethylene-Carbon Black Composites

Kostrzewa¹,

Michno²,

Majcherczyk³

1995

Acta Phys. Pol. A

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Results of investigations of the angular correlation of annihilation radiation and positron annihilation lifetime measurements are presented for polyethylene-carbon black composites. The inhibition of positronium formation due to the carbon black introduction is evidenced by a decrease in intensities of the narrow component in angular correlation of annihilation radiation curves and of the longest-lived components in positron annihilation lifetime spectra. A qualitative interpretation of the data in terms of the free-volumes model is proposed.

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A free four-term analysis of positron lifetime spectra of γ-irradiated Teflon

Cited by 36 publications

References 21 publications

Temperature dependence of the free volume holes in polyhydroxybutyrate biopolymer: A positron lifetime study

Temperature dependence of the free volume holes in polyhydroxybutyrate biopolymer: A positron lifetime study

Does the MELT Program Accurately Reveal the Lifetime Distribution in Polymers?

Positron Annihilation Studies of Polyethylene-Carbon Black Composites

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