Positron annihilation spectroscopy for chemical analysis: A novel probe for microstructural analysis of polymers☆
TL;DR: Positron annihilation spectroscopy for chemical analysis (PASCA) has been developed to analyze the microstructure of polymers as discussed by the authors, where the positronium atom is trapped in the atomic-scale holes which have a size ranging from 1 to 10 A. Theoretical aspects, experimental developments, and examples in analyzing the microstructures of epoxy, PEEK, and PMMA polymers are presented.
About: This article is published in Microchemical Journal.The article was published on 1990-08-01. It has received 694 citations till now. The article focuses on the topics: Positron annihilation spectroscopy & Positronium.
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21 May 1996-Nuclear Instruments & Methods in Physics Research Section A-accelerators Spectrometers Detectors and Associated Equipment
TL;DR: In this paper, a user friendly program (LT) for analysis of the lifetime spectra has been designed for personal computers, which enables one to analyse both discrete and continuous spectra as well as mixed- partially linear and partially continuous spectras.
Abstract: A user friendly program (LT) for analysis of the lifetime spectra has been designed for personal computers. The program is compared with other existing programs such as POSITRONFIT, CONTIN and MELT. LT enables one to analyse both discrete and continuous spectra as well as mixed- partially linear and partially continuous spectra. The searched parameters are found by using a fully automatic procedure and/or by a nonlinear optimising procedure, starting from a set of chosen parameters. The program is tested for series of simulated data as well as some chosen experimental ones, especially for the two polymers PTFE and hard polyethylene. The analysis of these polymer spectra is carried out on the basis of the log-normal distribution model and a new model of the lifetime spectrum developed by Dauwe et al., recently adapted to LT.
1,099 citations
TL;DR: Positron annihilation spectroscopy is particularly suitable for studying vacancy-type defects in semiconductors and combining state-of-the-art experimental and theoretical methods allows for detailed identification of the defects and their chemical surroundings as mentioned in this paper.
Abstract: Positron annihilation spectroscopy is particularly suitable for studying vacancy-type defects in semiconductors. Combining state-of-the-art experimental and theoretical methods allows for detailed identification of the defects and their chemical surroundings. Also charge states and defect levels in the band gap are accessible. In this review the main experimental and theoretical analysis techniques are described. The usage of these methods is illustrated through examples in technologically important elemental and compound semiconductors. Future challenges include the analysis of noncrystalline materials and of transient defect-related phenomena.
534 citations
TL;DR: In this paper, a double dense-layer structure is formed when glass plate is used as the casting substrate and water as the coagulant, and the structural parameter (St) of the membrane is analyzed by modeling water flux using the theory that considers both external concentration polarization (ECP) and ICP.
350 citations
TL;DR: In this article, the authors modeled the nonlinear viscoelastic behavior as an elastic-inelastic transition, where the energetically distributed nature of inelastic events and their evolution with straining was taken into account.
Abstract: Two features of the glassy state of an amorphous polymer, which play a key role in determining its mechanical properties, are the distributed nature of the microstructural state and the thermally activated (temporal) evolution of this state. In this work, we have sought to capture these features in a mechanistically motivated constitutive model by considering a distribution in the activation energy barrier to deformation in a thermally activated model of the deformation process. We thus model what is traditionally termed the nonlinear viscoelastic behavior as an elastic-inelastic transition, where the energetically distributed nature of inelastic events and their evolution with straining is taken into account. The thermoreversible nature of inelastic deformation is modeled by involving the notion of strain energy stored by localized inelastic shear transformations. The model results are compared to experimental data for constant true strain rate uniaxial compression tests (nonmonotonic) at different rates and temperatures; its predictive capability ties are further tested by comparison with compressive creep tests at different stress levels and temperatures
350 citations
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6,510 citations
TL;DR: The behavior of the Ps atom in molecular substances, particularly liquids, is investigated in this article, where the pickoff rates of oPs in various liquid compounds are found to have a simple empirical relationship to the values of the surface tension of the liquids.
Abstract: The behavior of the Ps atom in molecular substances, particularly liquids, is investigated. The pickoff rates of o‐Ps in various liquid compounds are found to have a simple empirical relationship to the values of the surface tension of the liquids. The relationship is found to have a theoretical foundation. The Ps atom is highly localized in a cavity created by the balance of various molecular forces inside the liquid. From the above relationship, other simple relationships between the pickoff rates of o‐Ps and the various properties of the medium, e.g., polarizability, cohesive energy density, etc., and the temperature or pressure changes can be derived and explained. The diffusion of o‐Ps is discussed. A similar approach can also be used for molecular solids.
1,731 citations
TL;DR: In this article, the temperature dependence of positron lifetimes in both the brittle and plastic phases of trimethylacetic (pivalic) acid was examined using the positron lifetime technique.
1,640 citations
TL;DR: In this article, the viscosity of the liquid normal paraffins can be accurately defined as a simple function of relative free space except for values in the neighborhood of the freezing points of each compound.
Abstract: In this paper it is shown that the viscosity of the liquid normal paraffins can be accurately defined as a simple function of relative free‐space except for values in the neighborhood of the freezing points of each compound A novel method of extrapolating the specific volumes of this family of compounds to absolute zero is described which permits the calculation of reliable values of the relative free‐space from density dataAn expression of the same form as the author's function, but in which temperature rather than free‐space is the primary variable (the so‐called Andrade equation), fails to reproduce the viscosity of n‐heptadecane over the same range of temperatures within the limits of the known accuracy of the measurements
1,495 citations
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