Relaxed positronium in polymers

Bertolaccini, M.; Bisi, A.; Gambarini, G.; Zappa, L.

doi:10.1088/0022-3719/7/21/006

Cited by 33 publications

(14 citation statements)

References 6 publications

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“…Experiments confirmed a correlation between Z and t po (in ns) in the form of Z ¼ exp(À0.7/t po ). [72] The dispersion, s 3 , in t 3 ¼ t po analyzed to be 0.8 ns at 235 K (t 3 ¼ 3.10 ns) would lead to a dispersion in t 1 of s 1 ¼ 15 ps which corresponds well with our experiment (Figure 7). Although not too much attention should be paid to the accuracy of the estimation of s 1 , the agreement may show that the analyzed dispersion in the pPs lifetime is a true physical effect.…”

Section: Positron Lifetime Spectra and Their Analysessupporting

confidence: 87%

“…The systematic increase in s 1 with temperature and its relative value at 300 K, s 1 / t 1 ¼ 0.17, may, however, indicate that the analyzed behavior of s 1 is of physical relevance. Due to the size distribution of the empty sites in which Ps annihilate, the relaxation parameter Z [72][73][74][75] and the pick-off annihilation rate, l po ($1/t 3 ), show a distribution. Experiments confirmed a correlation between Z and t po (in ns) in the form of Z ¼ exp(À0.7/t po ).…”

Section: Positron Lifetime Spectra and Their Analysesmentioning

confidence: 99%

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Temperature Dependence of Free Volume in Pure and Silica‐Filled Poly(dimethyl siloxane) from Positron Lifetime and PVT Experiments

Dlubek

Pionteck

et al. 2005

Macro Chemistry & Physics

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Summary:The microstructure of the free volume and its temperature dependence in two poly(dimethyl siloxane)s (PDMS), one in the pure state and the other filled with 35 wt.‐% of an in situ hydrophobized fumed silica with a specific surface area of 200–300 m2 · g−1, were studied by pressure‐volume‐temperature experiments (PVT, T = 22–156 °C, P = 10–200 MPa) and positron annihilation lifetime spectroscopy (PALS, T = −173–100 °C, P = 10−5 MPa). The Simha‐Somcynsky equation of state was used to estimate the hole free volume fraction, h, and free and occupied volumes, Vf = hV and Vocc = (1 − h)V, from the specific total volume, V. The PALS spectra were analyzed with the routine LT9.0, which allowed for a dispersion, σi, in all three of the lifetimes: the para‐positronium (p‐Ps, τ1), positron (e+, τ2), and ortho‐positronium (o‐Ps) lifetime (τ3). This kind of analysis delivered correct p‐Ps lifetime parameters, τ1, σ1, and I1. It was speculated that e+, like o‐Ps, undergoes Anderson localization at empty sites of the, static or dynamic, disordered structure. The hole size distribution, its mean value, 〈vh〉, and dispersion, σh, were calculated from the o‐Ps lifetimes. A comparison of 〈vh〉 with Vf was used to estimate the specific hole number, $N'_{\rm h}$. During melting of the semicrystalline samples at−38 °C (Tm), 〈vh〉 increased abruptly, and σh suddenly decreased. Both effects are explained by the disappearance of the rigid‐amorphous fraction (RAF) and, thus, a reduction in the dynamic heterogeneity. The following leveling‐off in 〈vh〉 and the low value of σh are attributed to the fast segmental relaxation in the PDMS melts which leads to a smearing of the molecule density distribution around a hole during the o‐Ps lifetime. magnified image

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Section: Positron Lifetime Spectra and Their Analysessupporting

confidence: 87%

Section: Positron Lifetime Spectra and Their Analysesmentioning

confidence: 99%

Temperature Dependence of Free Volume in Pure and Silica‐Filled Poly(dimethyl siloxane) from Positron Lifetime and PVT Experiments

Dlubek

Pionteck

et al. 2005

Macro Chemistry & Physics

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“…The existence of four components in teflon was proposed by Kerr [5] and Bertolaccini et al [6]. Initially, Kerr assigned three terms to his spectra.…”

Section: Experimental Procedures and Data Analysismentioning

confidence: 96%

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

Kindl

Puff

Sormann

1980

Phys. Stat. Sol. (a)

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Positron lifetime spectra in γ‐irradiated teflon are measured in the dose range up to 20 Mrad and clearly resolved into four lifetime components without any constraints. With increasing dose, the longest and the second‐longest lifetime decrease slightly, whereas the two shortest lifetimes remain constant. The intensity of the second‐shortest component increases very much on the expense of the other intensities, especially of that of the longest‐lived component. The identification of the four lifetime components with corresponding annihilation mechanisms is discussed.

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“…Positronium (Ps) formation has been confirmed in this polymer by the existence of the long-lived component in positron lifetime spectra (τ r.-.1 2 ns) and its magnetic quenching [9] as well as by the appearance of the narrow component in angular correlation of annihilation radiation (AGAR) curves [6] and the abundance of the three-quantum annihilation events [10]. In the paper [11] a value A.…”

Section: Introductionmentioning

confidence: 99%

“…The relaxation parameter (i.e. the electron density at the position of the positron forming Ps in polystyrene related to that of free Ps) was estimated in [9] as equal to 0.80 ± 0.06 indicating the relaxation of the Ps.…”

Section: Introductionmentioning

confidence: 99%

Positron Annihilation in Chloropolystyrenes

et al. 1993

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Results of angular correlation of annihilation radiation and positron annihilation lifetime measurements are presented for atactic polystyrene and chloropolystyrenes. The inhibition of positronium formation follows the chlorine introduction as the decrease in intensities of the narrow component in angular correlation of annihilation radiation curves and of the longest-lived component in positron annihilation lifetime spectra prove. In general, the chlorine "activity" towards positrons seems to depend on its position in the polymer structure. The annihilation rate distribution as well as the radius and volume distributions of free-volume sites where positronium is assumed to be formed obtained with the use of CONTIN program for the raw sample in the 2nd series are given additionally.

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Relaxed positronium in polymers

Cited by 33 publications

References 6 publications

Temperature Dependence of Free Volume in Pure and Silica‐Filled Poly(dimethyl siloxane) from Positron Lifetime and PVT Experiments

Temperature Dependence of Free Volume in Pure and Silica‐Filled Poly(dimethyl siloxane) from Positron Lifetime and PVT Experiments

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

Positron Annihilation in Chloropolystyrenes

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