scholarly journals Positron Annihilation Lifetime Study on free Volume Changes in TLD by Gamma - irradiation

2004 ◽  
Vol 1 (1) ◽  
pp. 144-148
Author(s):  
Baghdad Science Journal
Keyword(s):  
Gamma Irradiation ◽  
Positron Annihilation ◽  
Free Volume ◽  
Volume Fraction ◽  
Gamma Dose ◽  
Volume Changes ◽  
Positron Annihilation Lifetime ◽  
Free Volume Fraction ◽  
First Time ◽  
Free Volume Hole

Positron annihilation lifetime has been utilized for the first time to investigate the free - volume hole properties in thermolumenscent dosimeter ( TLD ) as a function of gamma-dosc . The hole volume, free volume fraction determined form orthopsitronium lifetime are found to be ?lamatically increase to large values , and then to minimum values as a function ofgamma-dose . The free - volume holes size is found to be 0.163nm’ and to have maximum of 0.166nm^ at the gamma-dose of 0.1 and 0.8 Gy, respectively-

scholarly journals Effect of Free Volume on Curcumin Release from Various Polymer-Based Composite Films Analyzed Using Positron Annihilation Lifetime Spectroscopy

Materials ◽  
2021 ◽  
Vol 14 (19) ◽  
pp. 5679
Author(s):  
Jong-Whan Rhim ◽  
Saygin Kuzeci ◽  
Swarup Roy ◽  
Necmettin Akti ◽  
Cumali Tav ◽  
...  
Keyword(s):  
Positron Annihilation ◽  
Free Volume ◽  
Bioactive Compounds ◽  
Polymer Matrix ◽  
Volume Fraction ◽  
Composite Films ◽  
Positron Annihilation Lifetime Spectroscopy ◽  
Positron Annihilation Lifetime ◽  
Biocomposite Films ◽  
Free Volume Fraction

This work reports the effects of free volume on curcumin release in various polymer-based composite films. Curcumin-reinforced biocomposite films were fabricated with natural biopolymers (carrageenan and chitosan) and bioplastics (poly(lactide) (PLA) and poly (butylene adipate-co-terephthalate) (PBAT)) via the solvent casting method. The curcumin release test was performed using an aqueous medium, and it was found that it was released the fastest in the carrageenan film, followed by the chitosan, PLA, and PBAT films, presumably owing to the dissimilarity of the polymer matrix. The free volume of the polymer films was determined using positron annihilation lifetime spectroscopy (PALS) to understand the release phenomena of curcumin. The free volume fraction was varied and reliant on the type of polymer, with the highest in the PBAT-based film followed by the PLA-, chitosan-, and carrageenan-based films. The free volume method helps analyze the release of bioactive compounds in a polymer matrix and may help to achieve a better understanding of the release of bioactive compounds.

BEYOND THE SPHERICAL APPROXIMATION: ELONGATED FREE VOLUME HOLES IN RUBBERS: A POSITRON ANNIHILATION STUDY

2019 ◽  
Vol 92 (4) ◽  
pp. 709-721
Author(s):  
Giovanni Consolati ◽  
Dario Nichetti ◽  
Francesco Briatico Vangosa ◽  
Fiorenza Quasso
Keyword(s):  
Positron Annihilation ◽  
Free Volume ◽  
Volume Fraction ◽  
Spherical Approximation ◽  
Linear Polymers ◽  
Positron Annihilation Lifetime ◽  
Free Volume Fraction ◽  
Conformational Statistics ◽  
Hole Model ◽  
Positron Annihilation Study

ABSTRACT The free volume fraction, a key parameter for the understanding of mechanical and transport properties of polymers, has been evaluated in a fluoroelastomer and a cis-polyisoprene rubber by means of positron annihilation lifetime spectroscopy and dilatometry. The evaluation showed that the assumption of elongated holes allows one to get a very good agreement between the free volume fraction experimentally determined and the theoretical expectation based on the lattice-hole model. On the other hand, systematic discrepancies are found using the spherical approximation. Moreover, the average hole size is found to be correlated to the effective bond length leff, a parameter connected to reptation motions and largely independent of the polymer structure. The result sheds some light on conformational statistics for the most flexible linear polymers that approach Gaussian chain behavior.

scholarly journals Relationship between the Microstructure and Performance of Graphene/Polyethylene Composites Investigated by Positron Annihilation Lifetime Spectroscopy

Nanomaterials ◽  
2021 ◽  
Vol 11 (11) ◽  
pp. 2990
Author(s):  
Xiaobing Han ◽  
Tao Chen ◽  
Yuan Zhao ◽  
Jie Gao ◽  
Yanan Sang ◽  
...  
Keyword(s):  
Positron Annihilation ◽  
Free Volume ◽  
Volume Fraction ◽  
Quantitative Description ◽  
Interfacial Interaction ◽  
Positron Annihilation Lifetime Spectroscopy ◽  
Structure Property ◽  
Positron Annihilation Lifetime ◽  
Free Volume Fraction ◽  
Interaction Intensity

The quantitative characterization of microstructure is most desirable for the establishment of structure-property relationships in polymer nanocomposites. In this work, the effects of graphene on the microstructure, mechanical, electrical, and thermal properties of the obtained graphene/polyethylene (PE) composites were investigated. In order to reveal the structure-performance relationship of graphene/PE composites, especially for the effects of the relative free volume fraction (fr) and interfacial interaction intensity (β), positron annihilation lifetime spectroscopy (PALS) was employed for its quantitative description. The relative free volume fraction fr gives a good explanation of the variation for surface resistivity, melting temperature, and thermal stability, and the variation of tensile strength and thermal conductivity agree well with the results of interfacial interaction intensity β. The results showed that fr and β have a significant effect on the properties of the obtained graphene/PE composites, and the effect on the properties was revealed.

scholarly journals Shape and Temperature Expansion of Free Volume Holes in Some Cured Polybutadiene-Polyisoprene Rubber Blends

2021 ◽  
Vol 22 (3) ◽  
pp. 1436
Author(s):  
Giovanni Consolati ◽  
Eros Mossini ◽  
Dario Nichetti ◽  
Fiorenza Quasso ◽  
Giuseppe Maria Viola ◽  
...  
Keyword(s):  
Free Volume ◽  
Radial Direction ◽  
Volume Fraction ◽  
Spherical Shape ◽  
Suitable Model ◽  
Positron Annihilation Lifetime ◽  
Rubber Blends ◽  
Free Volume Fraction ◽  
Hole Model ◽  
Best Fit

The free volume fraction of a macromolecular structure can be assessed theoretically by using a suitable model; however, it can also be evaluated from experimental data obtained from dilatometry and positron annihilation lifetime spectra. In this second case, a regular geometry of the sub-nanometric cavities forming the free volume has to be assumed, although in fact they are irregularly shaped. The most popular approach is to guess spherical holes, which implies an isotropic growth of these last with temperature. In this work, we compared the free volume fraction, as obtained from experiments in a set of polybutadiene and polyisoprene cured rubbers and their blends, with the analogous quantity expected by using the lattice-hole model. The results allowed us to obtain insights on the approximate shape of the holes. Indeed, a cylindrical flattened geometry of the cavities produced a better agreement with the theory than the spherical shape. Furthermore, the best fit was obtained for holes that expanded preferentially in the radial direction, with a consequent decrease of the aspect ratio with temperature.

A Positron-Annihilation-Lifetime study of Polymer Blends

1993 ◽  
Vol 321 ◽  
Author(s):  
J. Liu ◽  
Y. C. Jean ◽  
H. Yang
Keyword(s):  
Bisphenol A ◽  
Polymer Blends ◽  
Positron Annihilation ◽  
Free Volume ◽  
Weight Fraction ◽  
Bisphenol A Polycarbonate ◽  
Positron Annihilation Lifetime ◽  
Miscible Blend ◽  
Immiscible Blend ◽  
Free Volume Hole

ABSTRACTPositron-annihilation-lifetime (PAL) spectroscopy has been utilized to investigate the free-volume properties of two types of polymer blends, a miscible blend of bisphenol-A polycarbonate (PC) and tetramethyl bisphenol-A polycarbonate (TMPC), and an immiscible blend of PC and polystyrene (PS). In the miscible blend, the free-volume hole size and its fraction follow a linear relationship with respect to the weight fraction while in the immiscible blend, the relationship is not linearly additive. The free-volume hole distributions in the immiscible blend are found to be significantly broader than those in the pure polymers. The difference is thought to be a result of the free volume formed and associated with the conformation and interchain packing between the dissimilar chains in incompatible polymers.

Positron Annihilation Lifetime Studies on Free Volume Changes in Polymers by CO2 Conditioning

1994 ◽  
Vol 175-178 ◽  
pp. 789-792 ◽  
Author(s):  
K. Tanaka ◽  
M. Ito ◽  
Hideki Kita ◽  
Katsutomo Okamoto ◽  
Yasuo Ito
Keyword(s):  
Positron Annihilation ◽  
Free Volume ◽  
Volume Changes ◽  
Positron Annihilation Lifetime ◽  
Lifetime Studies

Positron annihilation lifetime studies of free volume changes in polycarbonate under static tensile deformation

1992 ◽  
Vol 25 (9) ◽  
pp. 2407-2411 ◽  
Author(s):  
M. Y. Ruan ◽  
H. Moaddel ◽  
A. M. Jamieson ◽  
R. Simha ◽  
J. D. McGervey
Keyword(s):  
Positron Annihilation ◽  
Free Volume ◽  
Tensile Deformation ◽  
Volume Changes ◽  
Positron Annihilation Lifetime ◽  
Static Tensile ◽  
Lifetime Studies

Relaxation Behavior of Zr-Cu-Al Ternary Bulk Glassy Alloy Studied by Using Positron Annihilation Techniques

2010 ◽  
Vol 654-656 ◽  
pp. 1070-1073 ◽  
Author(s):  
Akito Ishii ◽  
Shinya Mineno ◽  
Akihiro Iwase ◽  
Yokoyama Yoshihiko ◽  
Toyohiko J. Konno ◽  
...  
Keyword(s):  
Positron Annihilation ◽  
Free Volume ◽  
Isothermal Annealing ◽  
Glassy Alloy ◽  
Volume Ratio ◽  
Charpy Impact ◽  
Volume Changes ◽  
Appreciable Change ◽  
Positron Annihilation Lifetime ◽  
Bulk Glassy Alloy

Zr-based bulk glassy (BG) alloys show high tensile strength and a high Charpy impact value. In this study, the free volume changes for the hypoeutectic Zr60Cu30Al10 BG alloy during isothermal annealing below glass transition temperature (Tg) have been investigated by positron annihilation lifetime and coincidence Doppler broadening (CDB) measurements. The positron lifetime of hypoeutectic and eutectic BG alloys is almost the same, although the atomic volume ratio, estimated by the density for the eutectic BG alloy is different from that for the hypoeutectic BG alloy. The CDB spectra show a marked difference between eutectic and hypoeutectic BG alloys; that is, the spectrum of the hypoeutectic BG alloy is closes to that of Zr metal than that of the eutectic BG alloy. This result exhibits that the elemental fraction of Zr atoms around free volume in hypoeutectic BG alloy is greater than that in eutectic BG alloy. The CDB ratio profiles for the hypoeutectic BG alloy during annealing shows no appreciable change. The same trend was observed in the eutectic BG alloy.

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