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The biopolymer matrix synthesized from acrylated epoxidized soybean oil (AESO) and vanillin dimethacrylate (VDM) was examined using the positron annihilation lifetime spectroscopy (PALS) and the amperometry. The matrix version with DMPA (2,2-dimethoxy-2-phenylacetophenone) admixture was also tested in order to check the influence of the admixture on the matrix properties. Samples are intended for the detection of trace pollution with xenobiotics in water. They are carcinogenic substances and have a very negative effect on the human body. The first part of the study examined the nanostructure, and the second tested the matrix for its detection capabilities. The research is aimed at finding the correlation between the nanostructure and the detection properties of the biosensor's biopolymer film. [ABSTRACT FROM AUTHOR]

Samples of healthy and neoplastic myometrial tissues were investigated using Positron Annihilation Lifetime Spectroscopy (PALS). Meaningful differences between normal and diseased tissues were observed for each patient. The differences were also clearly visible for various kinds of lesions in each patient. The set of lifetimes and intensities obtained from PALS was correlated with the histopathological examinations of the same fragments of tissues. Strong coincidence between PALS parameters and histopathological findings was observed only in the case of a very precise correlation of the investigated area in both techniques. Measurements and discussion presented here were carried out to develop a method for measuring the sub-nanometric structure of human tissues. This kind of investigation, using positron probe, creates an opportunity of a new application in Positron Emission Tomography (PET). [ABSTRACT FROM AUTHOR]

Positron annihilation lifetime spectroscopy has shown to be a powerful tool to study the nanostructures of porous materials. Positron emission tomograph is a device allowing imaging of metabolic processes e.g. in human bodies. A newly developed device, the Jagiellonian PET will allow positron annihilation lifetime spectroscopy in addition to imaging, thus combining both analyses providing new methods for physics and medicine. In this contribution we present a computer program that is compatible with the Jagiellonian PET software. We compare its performance with the standard program LT 9.0 by using positron annihilation lifetime spectroscopy data from hexane measurements at different temperatures. Our program is based on an iterative procedure, and our fits prove that it performs as good as LT 9.0. [ABSTRACT FROM AUTHOR]

A new parameter δ based on 3γ annihilation is proposed. It describes the porosity of the materials containing small intermolecular voids below 1 nm. It can be applied to material investigation to compare changes in the material porosity depending on temperature or pressure as well as to study of ageing or manufacturing processes. Particularly it is dedicated to prepare the new imaging method and can be used during positron emission tomography diagnosis allowing determination the kind or stage of pathogenic alteration. [ABSTRACT FROM AUTHOR]

The standard form of the positron annihilation lifetime spectroscopy results presentation are two plots of o-Ps lifetime and intensity as a function of external factor, e.g. temperature, pressure. Both o-Ps parameters change (stepwise) when in the medium phase transitions occur. For a more complete picture of the structural changes occurring in the matter we suggest to use an additional plot, in the coordinates, (T3, I3). The hydrocarbons are selected to show the advantages following from the presentation of the results in the intensity-lifetime (INTI) plot. [ABSTRACT FROM AUTHOR]

Samples of uterine leiomyomatis and normal tissues taken from patients after surgery were investigated using the Positron Annihilation Lifetime Spectroscopy (PALS). Significant differences in all PALS parameters between normal and diseased tissues were observed. For all studied patients, it was found that the values of the free annihilation and orthopositronium lifetime are larger for the tumorous tissues than for the healthy ones. For most of the patients, the intensity of the free annihilation and ortho-positronium annihilation was smaller for the tumorous than for the healthy tissues. For the first time, in this kind of studies, the 3γfraction of positron annihilation was determined to describe changes in the tissue porosity during morphologic alteration. [ABSTRACT FROM AUTHOR]

The Positron Annihilation Lifetime Spectroscopy (PALS) was used to investigate properties of selected Phase Change Materials (PCMs) as a function of temperature from 123 K to 333 K. Three different PCM microcapsules investigated in this work were built of n -eicosane filling and a siloxane polymer as a shell material. It has been found that the properties of ortho -positronium ( o -Ps) annihilating in n -eicosane filler depend on the microcapsule morphology. In the samples where the whole interior is composed of n -eicosane and the polymer forms the outer shell only, the n -eicosane behaves like a neat macroscopic sample. In the microcapsules containing the network of polymer threads inside the globule, n -eicosane shows no rise of o -Ps intensity with time which is typical for all pure alkanes. For this morphology, the melting point of n -eicosane is preceded by the 4 K wide temperature range, where the structure resembling the rotator phase is observed (rotator phase appears in neat even-numbered alkanes with carbon chain over 20 atoms). Supplementary data were obtained by the DSC method. SEM images confirmed the morphological differentiation of microcapsules. Low temperature (close to liquid nitrogen) destroys the structure of microcapsules, particularly their outer shell. [ABSTRACT FROM AUTHOR]

Binary mixtures of even-numbered normal alkanes C n H 2 n +2 and C n +2 H 2 n +6 with n ⩽ 18 were investigated by positron annihilation spectroscopy. Formation of the rotator phase was observed in mixed structures, while no such a phase in neat alkanes in this range of n was found. Phase diagrams for n = 18 and n = 16 are very similar to the diagrams for binary mixtures of odd-numbered alkanes. The effect of positronium formation with trapped excess electrons weakens with decreasing n , at low n values the time constant of Ps rise contains the component much shorter than 1 h. [ABSTRACT FROM AUTHOR]

Positron annihilation lifetime spectroscopy was applied to investigate the microcapsules composed of n-eicosane (filling material) and polysiloxane polymer (shell) in the range of temperatures 123-333 K. Pure components of microcapsules were also investigated as a base for interpretation of the measurement results. The temperature of phase transitions in microcapsules was determined. It showed the appearance of a rotary phase, which is not present in pure n-eicosane. In the considered material, two types of free volume have been identified. The sizes of free volumes able to accommodate Ps were estimated using standard models. On the basis of the o-Ps intensities, the content of polysiloxane in microcapsules was estimated as about 40%. Internal structure of the microcapsules (morphology) was observed by scanning electron microscopy. [ABSTRACT FROM AUTHOR]

Abstract: Positron annihilation lifetime spectra (PALS) in binary mixture of alkanes were measured as a function of pressure. It was found that after rapid transition from rotator to rigid phase the intensity of positronium formation is not stable in time; its relaxation contains two components differing by an order of magnitude. The appearance of transient rotator phase, analogous to that observed in temperature dependences for the same mixture was not observed. Two-stage increase of spectrum parameters at crossing the rigid–rotator transition by pressure reduction can be an indication of the appearance of an additional phase preceding the rotator. [Copyright &y& Elsevier]

Abstract: Isothermal transformations of supercooled 1-butanol were observed by positron lifetime spectroscopy. Transformation rate is the highest near 150K, whereas below 140K it slows down becoming undetectable below 120K. At the temperature range of 123–135K the ortho-positronium lifetime achieves the final value which is higher than the one observed for crystalline phase. This is an indication of transition to a new (meta)stable structure, in which the ortho-positronium lifetime and intensity reach values that are intermediate between liquid and crystal phases. Consistency of positron annihilation data with the concept of two coexisting phases is discussed. [Copyright &y& Elsevier]

Abstract: Positron annihilation method was applied to study phase transitions in argon intercalated n-nonadecane. Particular phases are easily recognizable due to large differences in ortho-positronium lifetimes. It was found that melting temperature is a non-monotonous function of pressure. In the range of temperatures 301.5–303K with the rise of pressure the phase sequence rotator – liquid–rigid crystal was observed. After the pressure induced transition to the rigid phase the sample structure became porous due to escape of dissolved argon. The triple point in intercalated samples is located at much lower pressure and temperature than in pure ones. An admixture of alkane with other length of carbon chain increases the ortho-positronium lifetime in rigid phase, indicating Ps location in the interlamellar gaps. [Copyright &y& Elsevier]

Abstract: Positron annihilation lifetime spectroscopy was used to observe the effects of argon intercalation in some solid long-chain alkanes at high pressure. The ortho-Ps lifetime rises with argon pressure, which means increase of free volumes in the alkane structure. The range of pressures in which the rotator phase exists increases, comparing to pure alkane. In n-heptadecane, n-nonadecane, and possibly n-heneicosane, a stepwise change of ortho-Ps lifetime and intensity at ≈12MPa is observed, suggesting the transition to a new kind of the rotator phase. The transition rate is low, final lifetime value is ≈3.3ns. Despite a large size of free volumes corresponding to such a lifetime, their compressibility is found negligible up to the pressure of 90MPa. At low pressures the compressibility of free volumes in the rotator phase is negative. [Copyright &y& Elsevier]

Abstract: Positron annihilation lifetime spectra in solid n-pentacosane were measured as a function of the temperature and positron irradiation time. Phase IV was found to be well visible in the cooling runs due to its easy supercooling; a small increase of ortho-Ps lifetime in phase IV compared to low-temperature phase indicates that predominant intramolecular defects are end-gauche ones. The effect of excess electron accumulation, typical mainly of polymers, was also observed; two kinds of electron traps were found. The main trap component had activation enthalpy 0.6 eV and disappeared at about 250 K; an additional fast accumulating component existed up to the temperatures near the transition to the rotator phase. [Copyright &y& Elsevier]

The Tao-Eldrup model, commonly applied in estimation of free volume sizes in solids, uses the concept of infinitely deep potential well, which can lead to inaccuracies when the ortho -positronium ( o -Ps) lifetime is very short (less than 1.5 ns). A simple correction allowing to estimate properly the free volume radii at the o -Ps lifetime down to 0.8 ns is proposed. [ABSTRACT FROM AUTHOR]

The pore formation in CYTOP polymer under high pressure of argon or nitrogen gases was investigated by positron annihilation spectroscopy. In the range 0-70 MPa, formation of large open pores was observed. After reduction of pressure to normal one, the free volumes inside the polymer structure remained enlarged. The structure of CYTOP can be restored by applying the temperature over 470 K at normal pressure. [ABSTRACT FROM AUTHOR]

Abstract: Positronium formation and annihilation in solid methanol have been investigated. A metastable phase appears in the range (135–140)K; the observed effects can be explained as transformation of the supercooled β phase into α one. The effect of local melting at the positron site is discussed. [ABSTRACT FROM AUTHOR]

Abstract: Positron annihilation lifetime spectra for n-nonadecane in nitrogen atmosphere were measured as a function of pressure and temperature and compared with similar results for argon atmosphere. The phase diagram constructed from the nitrogen data is essentially different from that for argon. Nonmonotonous dependence of the melting point on pressure, typical of argon, does not appear. Sample damage at solidification is much smaller. The triple point rigid–liquid–rotator phase is estimated as (311K, 70MPa). [Copyright &y& Elsevier]