Positron age–momentum correlation studies of free volumes in polymers

Sato, K.; Murakami, H.; Ito, Kenji; Hirata, Koichi; Kobayashi, Yoshinori

doi:10.1016/j.radphyschem.2009.06.029

Cited by 12 publications

(9 citation statements)

References 11 publications

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“…The S (t) parameter versus the positron age for pristine epoxy shows a typical profile, as reported for various polymers in the literature. [55] The S (t) parameter is highest at the beginning (0-0.1 ns), where p-Ps has a maximum contribution, then it falls and reaches a minimum (~1.0 ns), where the contribution from free positron annihilation nearly ends, and it further increases with the contribution from o-Ps pick-off annihilation. In the positron-age range above 2.0 ns, the contribution is solely from o-Ps pick-off annihilation and S (t) remains nearly constant in this region.…”

Section: Resultsmentioning

confidence: 93%

Investigation of Nanoscopic Free Volume and Interfacial Interaction in an Epoxy Resin/Modified Clay Nanocomposite Using Positron Annihilation Spectroscopy

et al. 2012

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Epoxy/clay nanocomposites are synthesized using clay modified with the organic modifier N,N-dimethyl benzyl hydrogenated tallow quaternary ammonium salt (Cloisite 10A). The purpose is to investigate the influence of the clay concentration on the nanostructure, mainly on the free-volume properties and the interfacial interactions, of the epoxy/clay nanocomposite. Nanocomposites having 1, 3, 5 and 7.5 wt. % clay concentrations are prepared using the solvent-casting method. The dispersion of clay silicate layers and the morphologies of the fractured surfaces in the nanocomposites are studied using X-ray diffraction (XRD) and scanning electron microscopy (SEM), respectively. The observed XRD patterns reveal an exfoliated clay structure in the nanocomposite with the lowest clay concentration (≤1 wt. %). The ortho-positronium lifetime (τ(3)), a measure of the free-volume size, as well as the fractional free volume (f(v)) are seen to decrease in the nanocomposites as compared to pristine epoxy. The intensity of free positron annihilation (I(2)), an index of the epoxy-clay interaction, decreases with the addition of clay (1 wt. %) but increases linearly at higher clay concentrations. Positron age-momentum correlation measurements are also carried out to elucidate the positron/positronium states in pristine epoxy and in the nanocomposites. The results suggest that in the case of the nanocomposite with the studied lowest clay concentration (1 wt. %), free positrons are primarily localized in the epoxy-clay interfaces, whereas at higher clay concentrations, annihilation takes place from the intercalated clay layers.

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Section: Resultsmentioning

confidence: 93%

Investigation of Nanoscopic Free Volume and Interfacial Interaction in an Epoxy Resin/Modified Clay Nanocomposite Using Positron Annihilation Spectroscopy

et al. 2012

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“…Positron age-momentum correlation (AMOC) was carried out to elucidate how the positron/Ps annihilation sites were influenced by GE in ENR-GE composites. 44,75 As shown in Fig. 6b, the changes in the S(t) parameter value with the positron age occur in three stages, the self-annihilation of para-positronium ( p-Ps, 0-0.6 ns), the ''free'' positron annihilation (0.6-2 ns) and o-Ps pickoff annihilation (above 2 ns).…”

Section: Influence Of Ge Network On Free-volume Propertiesmentioning

confidence: 94%

“…[75][76][77] The free-volume hole probability density function V f (pdf) is shown in Fig. 44,75 As shown in Fig. The appearance of lower size freevolume holes can be attributed to the formation of GE networks which provide a high density interfacial region that is missing in the neat ENR.…”

Section: Influence Of Ge Network On Free-volume Propertiesmentioning

confidence: 98%

“…The positron source 22 Na (20 mCi) was deposited on a 6 mm thick Kapton foil and then sandwiched between pieces of identical samples (with a diameter of 1 cm and a thickness of 0.15 cm). 44 The positron source 22 Na (40 mCi) was deposited on a 6 mm thick Kapton foil and then sandwiched between samples. 43 Positron age momentum correlation (AMOC) measurements were performed by acquiring the Doppler broadening and positron lifetime data coincidently.…”

Section: Characterizationmentioning

confidence: 99%

“…43 Positron age momentum correlation (AMOC) measurements were performed by acquiring the Doppler broadening and positron lifetime data coincidently. 44 The positron source 22 Na (40 mCi) was deposited on a 6 mm thick Kapton foil and then sandwiched between samples. The birth signal and the annihilation signal were acquired using a coincidence set-up having two BaF 2 scintillation detectors placed at 901.…”

Section: Characterizationmentioning

confidence: 99%

See 2 more Smart Citations

Graphene networks and their influence on free-volume properties of graphene–epoxidized natural rubber composites with a segregated structure: rheological and positron annihilation studies

She

Peng

et al. 2015

Phys. Chem. Chem. Phys.

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Epoxidized natural rubber-graphene (ENR-GE) composites with segregated GE networks were successfully fabricated using the latex mixing combined in situ reduced technology. The rheological behavior and electrical conductivity of ENR-GE composites were investigated. At low frequencies, the storage modulus (G') became frequency-independent suggesting a solid-like rheological behavior and the formation of GE networks. According to the percolation theory, the rheological threshold of ENR-GE composites was calculated to be 0.17 vol%, which was lower than the electrical threshold of 0.23 vol%. Both percolation thresholds depended on the evolution of the GE networks in the composites. At low GE concentrations (<0.17 vol%), GE existed as individual units, while a "polymer-bridged GE network" was constructed in the composites when GE concentrations exceeded 0.17 vol%. Finally, a "three-dimensional GE network" with percolation conductive paths was formed with a GE concentration of 0.23 vol%, where a remarkable increase in the conductivity of ENR-GE composites was observed. The effect of GE on the atom scale free-volume properties of composites was further studied by positron annihilation lifetime spectroscopy and positron age momentum correlation measurements. The motion of ENR chains was retarded by the geometric confinement of "GE networks", producing a high-density interfacial region in the vicinity of GE nanoplatelets, which led to a lower ortho-positronium lifetime intensity and smaller free-volume hole size.

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Revealing the Nano‐Level Molecular Packing in Chitosan–NiO Nanocomposite by Using Positron Annihilation Spectroscopy and Small‐Angle X‐ray Scattering

et al. 2013

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Chitosan-NiO nanocomposite (CNC) is shown to be a potential dielectric material with promising properties. CNCs containing NiO nanoparticles (0.2, 0.6, 1, 2, 5 wt %) are prepared through chemical methods. The inclusion of NiO nanoparticles in the chitosan matrix is confirmed by scanning electron microscopy (SEM) and X-ray diffraction. The morphology of the NiO nanoparticles and the nanocomposites is investigated by transmission electron microscopy and SEM, respectively. Positron annihilation lifetime spectroscopy (PALS) and the coincidence Doppler broadening (CDB) technique are used to quantify the free volume and molecular packing in the nanocomposites. The triplet-state positronium lifetime and the corresponding intensity show the changes in nanohole size, density, and size distribution as a function of NiO loading. Small-angle X-ray scattering indicates that the NiO aggregates are identical in all the CNCs. The momentum density distribution obtained from CDB measurements excludes the possibility of a contribution of vacant spaces (pores) available in NiO aggregates to the free volume of nanocomposites upon determination by using PALS. The results show systematic variation in free-volume properties and nano-level molecular packing as a function of NiO loading, which is presumed to play a vital role in determining the various properties of the nanocomposites.

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Positron age–momentum correlation studies of free volumes in polymers

Cited by 12 publications

References 11 publications

Investigation of Nanoscopic Free Volume and Interfacial Interaction in an Epoxy Resin/Modified Clay Nanocomposite Using Positron Annihilation Spectroscopy

Investigation of Nanoscopic Free Volume and Interfacial Interaction in an Epoxy Resin/Modified Clay Nanocomposite Using Positron Annihilation Spectroscopy

Graphene networks and their influence on free-volume properties of graphene–epoxidized natural rubber composites with a segregated structure: rheological and positron annihilation studies

Revealing the Nano‐Level Molecular Packing in Chitosan–NiO Nanocomposite by Using Positron Annihilation Spectroscopy and Small‐Angle X‐ray Scattering

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