Preliminary Positron Lifetime Results on Free Volumes in Cyclodextrins

2010 ◽  
Vol 666 ◽  
pp. 99-102 ◽  
Author(s):  
Maria Fatima Ferreira Marques ◽  
A.M.G. Moreira Da Silva ◽  
P.M. Gordo ◽  
Z. Kajcsos
Keyword(s):  
Positron Annihilation ◽  
Free Volume ◽  
Positron Lifetime ◽  
Positron Annihilation Lifetime Spectroscopy ◽  
Positron Source ◽  
Lifetime Component ◽  
Positron Annihilation Lifetime ◽  
Long Lifetime

Positron annihilation lifetime spectroscopy was used to study the free-volume parameters in various pure -, - and -cyclodextrins samples and, in the case of β-cyclodextrin, with inclusion of S-carvone and thymoquinone. The results clearly indicate the presence of long lifetime components related to Ps-formation. The data show that the addition of S-carvone to β-cyclodextrin results in a decrease of o-Ps lifetime that we ascribe to a reduction of free volume holes from 81.8 to 63.7 Å3. The long lifetime component disappears when thymoquinone is added to -cyclodextrin, indicating this substance acts as an o-Ps quencher. For all samples studied, a decrease in the long lifetime component values was observed with increasing source in situ time, a result that might be attributed to the irradiation of the sample by the 22Na positron source.

Encapsulation of Natural Flavors in Cyclodextrins: Free Volume Studies by PALS

2012 ◽  
Vol 733 ◽  
pp. 88-91
Author(s):  
Maria Fatima Ferreira Marques ◽  
P.M. Gordo ◽  
S.D. Santos ◽  
R.F. Marques ◽  
A. Moreira da Silva ◽  
...  
Keyword(s):  
Essential Oils ◽  
Positron Annihilation ◽  
Free Volume ◽  
Allium Sativum ◽  
Positron Annihilation Lifetime Spectroscopy ◽  
Lifetime Component ◽  
Positron Annihilation Lifetime ◽  
Long Lifetime ◽  
Natural Flavors ◽  
Origanum Majorana

Positron annihilation lifetime spectroscopy (PALS) is used to study the free-volume in β-cyclodextrin (CD) with the encapsulation of two different essential oils: garlic (Allium sativum) and marjoram (Origanum majorana). The data reveal the presence of a long lifetime component related to the o-Ps. It is observed that the addition of garlic (or marjoram) oil to β-CD results in a decrease of the o-Ps lifetime which was ascribed to a reduction of the free volume holes from 83.6 to 67.7 Å3 (79.1 to 72.6 Å3). Different mechanisms for the encapsulation of garlic and marjoram oils in β-CD are suggested by the PALS parameters.

Sealed 22Na Sources for Positron Annihilation Lifetime Spectroscopy

2012 ◽  
Vol 733 ◽  
pp. 310-313 ◽  
Author(s):  
Masato Yamawaki ◽  
Yoshinori Kobayashi ◽  
K. Ito ◽  
Mikio Matsumoto ◽  
Hidetake Ishizu ◽  
...  
Keyword(s):  
Positron Annihilation ◽  
Positron Lifetime ◽  
Positron Annihilation Lifetime Spectroscopy ◽  
Legal Regulations ◽  
High Quality ◽  
Positron Annihilation Lifetime ◽  
Lifetime Spectrum ◽  
Long Lifetime ◽  
Sealed Source ◽  
Sealing Materials

Sealed radioactive sources of 22Na for positron annihilation lifetime spectroscopy (PALS), free from the legal regulations, are commercially available from an American company. However, thick foils are used to seal 22Na in these sources and large fractions of the positrons annihilate in the sealing materials. Further, it is pointed out that a long lifetime component over 1 ns appears in the positron lifetime spectrum acquired with the Kapton sealed source (POSK-22, IPL Inc.). In this research, attempts were made to develop high quality sealed positron sources, potentially free from regulations, for ubiquitous application of PALS. The sources prepared in the present work are of high quality and applicable to our new PALS, which does not require sample cutting and is potentially applicable to truly nondestructive, onsite inspection of various materials

Ceramide increases free volume voids in DPPC membranes

RSC Advances ◽  
2015 ◽  
Vol 5 (55) ◽  
pp. 44282-44290 ◽  
Author(s):  
E. Axpe ◽  
A. B. García-Arribas ◽  
J. I. Mujika ◽  
D. Mérida ◽  
A. Alonso ◽  
...  
Keyword(s):  
Positron Annihilation ◽  
Free Volume ◽  
Lipid Membranes ◽  
Positron Annihilation Lifetime Spectroscopy ◽  
Positron Annihilation Lifetime

We have measured by positron annihilation lifetime spectroscopy (PALS) that ceramide increases the size of the free volume holes in DPPC lipid membranes.

On the Limits of Sensitivity of PALS to Incorporated Free Volume Holes in Polymeric Membranes and Sorbents: Effect of sc-CO2 in Polyhexafluoropropylene

2017 ◽  
Vol 373 ◽  
pp. 261-264 ◽  
Author(s):  
Victor Shantarovich ◽  
Valentin Bekeshev ◽  
Nikolai Belov ◽  
Irina Kevdina ◽  
Mikhail Filimonov ◽  
...  
Keyword(s):  
Low Temperature ◽  
Size Distribution ◽  
Positron Annihilation ◽  
Free Volume ◽  
Polymeric Membranes ◽  
Positron Annihilation Lifetime Spectroscopy ◽  
Membrane Materials ◽  
Positron Annihilation Lifetime

Positron annihilation lifetime spectroscopy (PALS) is a recognized instrument for the studies of size-distribution of nanopores (intrinsic free volume holes FVH) in polymers, particularly membrane materials. The limits of this application in the case of “alien” pores, produced by swelling of poly (hexafluoro propylene) PHFP in the gas (CO2) in super-critical (sc-) state are discussed. The obtained conclusions are controlled by measurements of low temperature gas (N2) sorption (LTGS) and by comparison of the data with the results on permeation of various gases through the PHFP membrane. Attention is payed to relaxation with time of the newly created FVH in the PHFP membrane.

Positron Annihilation in IR Transmitting GeS2-Ga2S3 Glasses

2015 ◽  
Vol 230 ◽  
pp. 221-227 ◽  
Author(s):  
Halyna Klym ◽  
A. Ingram ◽  
O. Shpotyuk ◽  
R. Szatanik ◽  
E. Petracovschi ◽  
...  
Keyword(s):  
Positron Annihilation ◽  
Free Volume ◽  
Decisive Role ◽  
Density Variation ◽  
Positron Annihilation Lifetime Spectroscopy ◽  
Annihilation Radiation ◽  
Doppler Broadening ◽  
Positron Annihilation Lifetime ◽  
Positron Trapping ◽  
Trapping Process

Positron annihilation lifetime spectroscopy combined with Doppler broadening of annihilation radiation was applied to study free-volume entities in GeS2-Ga2S3glasses affected by Ga additions. It is shown that Ga-related void sub-system plays a decisive role in positron trapping process, while the overall density variation is defined mainly by Ge-related sub-system. These results serve as basis for new characterization route for inner free-volume structure of these glasses.

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