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Variable-Energy Positron Annihilation as Highly Sensitive Nanoporosimetry for Porous Thin Films

100%
Ito K., Kobayashi Y.
Acta Physica Polonica A
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2005
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vol. 107
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issue 5
717-723
EN
Positron annihilation was applied to measuring critical pore sizes in various materials. In recent years, positron annihilation with a variable-energy positron beam has emerged as a powerful tool for the investigation of porous thin films synthesized as low-k dielectrics, high performance gas sensor materials, and so on. This paper is a brief overview of recent progress in nanopore characterization of thin films by means of positron annihilation with a description of several important issues relevant to positron annihilation.
2
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Change of Free Volume in Polymer Gels As Studied by Positron Annihilation Lifetimes

81%
Ito K., Ujihira Y., Yamashita T., Horie K.
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vol. 95
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issue 4
551-556
EN
Variations of a free volume size of a poly(N-isopropylacrylamide) gel and a polyacrylamide gel during a volume phase transition induced by a change of external environment - temperature, solvent composition, pH, and ion strength, are described. The free volume size is probed by positron annihilation lifetime technique. Variations of the free volume size suggest that a nanoscopic environment of the gels is affected by the free volume of the solvent phase and an interaction between the polymer chain and the solvent molecule in the swollen state, and by the aggregation of the polymer chain and a balance of the interaction among the polymer chain and the solvent molecules in the collapsed state. It is revealed that the free volume size reflects the essential change of the nanoscopic environment in the gels which could induce the macroscopic volume phase transition.
3
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Free Volume Study on Three Types of Shape Memory Polymers by Positron Annihilation

81%
Ujihira Y., Li H., Ito K.
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vol. 95
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issue 4
677-682
EN
Temperature dependence of nanoscopic environment of shape memory polymers such as polynorbornene (T_{g}≈313 K), polyurethane (T_{g}≈321 K=dynamic viscoelasticity, destruction of hydrogen bond ≈353 K) and styrene-butadiene copolymer (T_{m}=333 K) is observed in terms of free volume parameters - average size, numerical concentration and size distribution - estimated from positronium lifetime measurement, and mechanisms of their shape recoveries are discussed at a molecular level.
4
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Positron and Positronium Annihilation in Polymers Studied by Age-Momentum Correlation Spectroscopy

71%
Sato K., Murakami H., Ito K., Hirata K., Kobayashi Y.
Acta Physica Polonica A
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2008
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vol. 113
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issue 5
1511-1516
EN
Positron (e⁺) and positronium (Ps) annihilation processes in polymers are studied by positron age-momentum correlation spectroscopy, which can sensitively probe momentum distributions of e⁺, p-Ps, and o-Ps. For polyether sulfone and ethylene tetrafluoroethylene copolymer belonging to oxygen-containing polymers (O group) and fluorine-containing polymers (F group), respectively, significant effects of positron trapping by polar element are observed. The Doppler profile of o-Ps pick-off annihilation is strongly influenced by F atoms, giving rise to anomalous broadening. The results are discussed together with our previous data of the S-I₃ correlation in order to explore the feasibility of chemical analysis around the free volumes by age-momentum correlation spectroscopy.
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