Positron irradiation effects on polypropylene and polyethylene studied by positron annihilation

Suzuki, Takenori; Miura, Taichi; Oki, Yuichi; Numajiri, M.; Kondo, Kenjiro; Ito, Yasuo

doi:10.1016/0969-806x(94)e0030-m

Cited by 65 publications

(30 citation statements)

References 23 publications

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“…This assumption becomes increasingly invalid, however, as trapped electron states accumulate outside the blob during irradiation of the sample with positrons. Thus it is well established that for certain polymers [e.g., polystyrene (Figure 12.1), polyethylene, and polypropylene], the temperature dependence of I 3 exhibits a minimum [Kindl and Reiter, 1987;Reiter and Kindl, 1990;Uedono et al, 1997;Peng et al, 1999], and that at temperatures in the vicinity of the minimum, I 3 decreases with increasing time of exposure to the positron source [Welander and Maurer, 1992;Suzuki et al, 1995a;Wang et al, 1998;Uedono et al, 1997;Peng et al, 1999]. For polystyrene, the minimum temperature occurs in the glassy state [Uedono et al, 1997;Peng et al, 1999], and originally, the time dependence was misinterpreted as being due to physical aging (i.e., a decrease in the free-volume fraction as the glass relaxes toward its equilibrium state) [Kobayashi et al, 1989].…”

Section: Pals As a Probe For Free Volume In Polymersmentioning

confidence: 99%

Positron Annihilation Lifetime Studies of Free Volume in Heterogeneous Polymer Systems

2010

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474 POSITRON ANNIHILATION LIFETIME STUDIES INTRODUCTIONThe theoretical and experimental background related to the positron annihilation lifetime spectroscopy (PALS) technique and its application as a quantitative probe for free volume in polymeric materials have been discussed extensively in Chapters 10 and 11, so we limit ourselves to a brief overview of these issues by way of introduction and commentary. Our principal focus here is to review what evidence has been generated using the PALS technique to provide insight into three topics of current interest, each of which involves probing specific heterogeneities in the amorphous polymeric phase. The first relates to the existence of concentration fluctuations in miscible polymer blends and their effect on materials properties, such as broadening of the glass transition region. The second concerns the fact that to interpret accurately the properties of certain semicrystalline polymers, such as gas transport, it is necessary to invoke a rigid amorphous phase, believed to involve the disordered chain segments that link crystalline lamellae, whose behavior differs from the usual (mobile) amorphous phase that exists far from the crystalline surface. The third topic involves evidence that a similarly rigid amorphous phase exists in polymeric nanocomposites, associated with polymer chains that lie near the surface of the inorganic particles. PALS AS A PROBE FOR FREE VOLUME IN POLYMERSA PALS experiment involves bringing a polymer sample into contact with a source of positrons, typically 22 Na. Energetic positrons emitted into the polymer by the source are slowed through collisions with atoms, creating an ionized radiation track (positron spur). In the last portion of the spur, referred to as the blob, the positron thermalizes, and either annihilates or finds a secondary electron created by the ionization to form a localized positronium atom Byakov, 2003, 2007;Stepanov et al., 2005a Stepanov et al., ,b, 2007. The spin 1 atom, called ortho-positronium (o-Ps), is three times more likely to form than is the spin 0 atom [para-positronium (p-Ps)] and is more stable than the latter, which annihilates within 125 ps. o-Ps has a long lifetime (140 ns in vacuum), which lifetime is determined by interactions with the medium. Typically, o-Ps annihilates via a pickoff mechanism, with the positron "picked off" by an electron of the medium that has opposite spin. Since o-Ps is easily polarizable, and therefore strongly repelled by the medium, it tends to localize in regions of low electron density (holes or free volume). The lifetime of o-Ps is then determined by the electron density and physical size of the hole in which it finds itself, and normally falls in the range of a few nanoseconds.Typically, therefore, a PALS spectrum consists of a minimum of three components: the short-lived p-Ps component with intensity I 1 and lifetime τ 1 = 125 ps; a free positron annihilation component, with intensity I 2 and lifetime τ 2 ; and the o-Ps component, with intensity I 3 and lifetime τ 3 . ...

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Section: Pals As a Probe For Free Volume In Polymersmentioning

confidence: 99%

Positron Annihilation Lifetime Studies of Free Volume in Heterogeneous Polymer Systems

2010

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“…It is possible that the sample turned amorphous with increasing hours of ball-milling but tiny nanocrystalline intermetallic islands are formed because of the radiation-induced particle agglomeration. Suzuki et al [29] had confirmed the effect of continued exposure of polymer samples to positron sources. The extremely light nanoparticles could utilise the energy dissipated by the positrons to migrate and grow in size and with an added feature that the same process further leads to the formation of additional phase formation.…”

Section: Positron Radiation Effectsmentioning

confidence: 80%

Amorphisation and intermetallic nanophase formation in ball-milled Al–Ti–Si studied through positron lifetime spectroscopy

Nandi

Nambissan

Manna

2004

Journal of Alloys and Compounds

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“…At higher doses, I 3 decreases presumably due to chemical degradation of the lattice [9]. Similarly, chemical degradation is said to inhibit Ps formation in the amorphous phase of samples: chain scission could induce the formation of methyl groups free to rotate and thus limiting the number of free spaces where Ps can form [10]. However, the observed decrease in I 3 can be attributed to either an increase in the crystallinity of the irradiated PMMA and/or due to the inhibition of the Ps formation process by some of the radiolytic species in the irradiated PMMA matrix.…”

Section: Resultsmentioning

confidence: 96%

Irradiated polymethylmethacrylate studied by positron annihilation spectroscopy

Mohamed

Abdel-Hady

Mohamed

2007

Phys. Status Solidi (c)

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The effect of gamma irradiation dose on microscopic structure of polymethylmethacrylate (PMMA) has been studied using positron annihilation lifetime (PAL) and Doppler broadening of annihilation radiation (DBAR) techniques. The measurements were performed at room temperature as a function of the γ-irradiation doses from 60-1200 kGy. The observed lifetime spectra were resolved into three components. The size and the fraction of the o-Ps hole volume were estimated from the positron annihilation parameters. The effect of γ-irradiation was identified at lower doses to be cross-linking while at higher doses the chemical degradation of the polymer was observed. Moreover, the distribution of the free volume shifts from a large to small size as the irradiation increases and has very similar Gaussian-like distribution. The PAL results were confirmed with X-ray measurement. A correlation between the macroscopic mechanical properties Hv and positron annihilation parameters has been demonstrated.1 Introduction Positron annihilation lifetime spectroscopy has been widely applied to study vacancies in metals and intermolecular spaces in polymers. It is a relatively simple technique which can probe the properties of the free volume holes in a non-destructive way. Radiation methods are successfully used for polymerization, for polymer modification and many other applications [1,2]. The radiation processing is a useful technology to induce suitable modifications of materials. In particular, it is a very important way to generate or to improve new properties in materials as well as new means of production. The radiation damage and the oxidative degradation cause chemical changes in the polymer structure with build up of a variety of new functional groups. These changes cause severe deterioration of the polymers, which shows up very early, with consequent decay of important properties such as electrical insulation power, transparency and hydrorepellency. Polymethylmethacrylate, PMMA is completely amorphous but it has high strength and excellent dimensional stability due to its rigid polymer chains. It has exceptional optical clarity, very good weather-resistance, and impact resistance. The PMMA polymers have many applications; e.g. diffusers, indoor and outdoor lighting, lenses, and contact lenses [3].The aim of the present work is to understand the changes induced by γ-irradiation on the microscopic structure of the PMMA samples using positron annihilation lifetime (PAL) and Doppler broadening of annihilation radiation (DPAR) techniques.

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Positron irradiation effects on polypropylene and polyethylene studied by positron annihilation

Cited by 65 publications

References 23 publications

Positron Annihilation Lifetime Studies of Free Volume in Heterogeneous Polymer Systems

Positron Annihilation Lifetime Studies of Free Volume in Heterogeneous Polymer Systems

Amorphisation and intermetallic nanophase formation in ball-milled Al–Ti–Si studied through positron lifetime spectroscopy

Irradiated polymethylmethacrylate studied by positron annihilation spectroscopy

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