Positron annihilation spectroscopy analysis

Network properties and microscopic structures of various epoxy resins cross-linked by phenolic novolacs were investigated by Suzuki et al.97 Positron annihilation spectroscopy (PAS) was utilized to characterize intermolecular spacing of networks and the results were compared to bulk polymer properties. The lifetimes (t3) and intensities (/3) of the active species (positronium ions) correspond to volume and number of holes which constitute the free volume in the network. Networks cured with flexible epoxies had more holes throughout the temperature range, and the space increased with temperature increases. Glass transition temperatures and thermal expansion coefficients (a) were calculated from plots of t3 versus temperature. The Tgs and thermal expansion coefficients obtained from PAS were lower titan those obtained from thermomechanical analysis. These differences were attributed to micro-Brownian motions determined by PAS versus macroscopic polymer properties determined by thermomechanical analysis. 

PASCA Positron annihilation spectroscopy for chemical analysis... 

Jean, Y. C., Positron annihilation spectroscopy for chemical analysis a novel probe for microstructural analysis of polymers, Micwchem. J., 42, 72-102 (1990). 

Since electrons with MeV order energies can produce uniform damage to a depth in the order of mm, tensile tests can be conducted as macroscopic mechanical testing. SAXS or SANS can be conducted as well as TEM, atom probe tomography analysis and positron annihilation spectroscopy measurements. In HVEM irradiation, time-dependent evolution of individual defect clusters such as an interstitial loop or a vacancy cluster can be investigated in an irradiated spot area. Microanalysis using an electron beam probe such as energy dispersive X-ray analysis is also applicable in the beam spot area. However, other analyses or measurements on such small areas are difficult to carry out. 

Example of application Fluorescence spectroscopy, synchrotron radiation Rutherford back-scattering on surfaces Positron annihilation spectroscopy Muon spin resonance spectroscopy Radiation detectors, radiochemistiy Mossbauer effect Nuclide production, activation analysis... 

Positron annihilation Thermal analysis coupled with mass spectroscopy... 

Reaction with a polymerizable mixture, giving nanofibers covalently attached to the polymer, has also been studied [155]. Different techniques, including dynamic mechanical analysis and positron annihilation spectroscopy show that interaction at the nanofiber-polymer interface produces radical changes in the glass transition of the material. The effect of the addition of cellulose nanocrystals on the properties of a polyurethane matrix are theoretically described by the free volume theory. 

Hikmet RAM, Boots HMJ, Michielsen M (1995) Ferroelectric liquid crystal gels—network stabilized ferroelectric display. Liq Cryst 19 65-74 Inoue T, Higuchi N, Fume H (2008) The effect of pol5mer doping on the formation of helical stmcture in ferroelectric liquid crystals. Ferroelectrics 364 113-120 Jean YC (1990) Positron annihilation spectroscopy for chemical analysis a novel probe for microstmctural analysis of polymers. Microchem J 42 72-102 Jean YC, Nakanishi H, Hao LY, Sandreczki TC (1990) Anisotropy of free-volume hole dimensions in polymers probed by positron annihilation spectroscopy. Phys Rev B 42 9705-9708 Jean YC, Mallon PE, Schrader DM (2003) Principles and application of positron and positronium chemistry. World Scientific, Singapore... 

In this chapter we discuss briefly most of these applications. Furthermore, the S-S equations of state are used to describe surface tension in Chapters 8, for analysis of positron annihilation lifetime spectroscopy in Chapters 10 to 12, for analysis of glassy and molten polymeric nanocomposites in Chapters 4 and 14, and to describe flow properties in Chapter 16. 

Dlubek, G., Pionteck, J., Bondarenko, V., Pompe, G., Taesler, Ch., Fetters, K., and Krause-Rehberg, R., Positron annihilation lifetime spectroscopy (PALS) for interdiffusion studies in disperse blends of compatible polymers a quantiative analysis, Macromolecules, 35, 6313-6323 (2002c). 

The positron annihilation lifetime spectroscopy (PALS) iq>paratus used to measure free volume in this work consisted of an automated EG G Ortec fast-fast coincidence system. The 1.3 MBq NaCl source was a 2 mm t source sandwiched between two Ti foils (2.54 pm foils). The source gave a two-component best fit to 99.99% pure, aimealed, chemically polished aluminum (x = 169 2 ps, Ii = 99.2 0.4 %, X2 = 850 25 ps, I2 = 0.8 0.4%). No source correction was used in the analysis of the data with the PFPOSFIT program (9). Measurements were made in air at 50% relative humidity with temperature control of 0.7 C. 

Using a combination of thermal analysis, viscosity measurements and positron annihilation lifetime spectroscopy, Buttafava and co-workers [77] noted that PET decreases in molecular weight and increases in crystallinity when y-irradiated. 

It has been observed [24] that for PEG (200g/mol) modified Pebax membrane for CO2 separation the CO2 permeability increased by a factor of about 2 (from 73 to 151 Barrer) and the separation factor CO2/H2 also increased by PEG addition (50 wt.%). This enhancement was attributed to the appearance of additional ethylene oxide (EO) units and free volume increase. Higher content of EO units results in an increase in the solubility of CO2. Later, the total free volume increase and hence the increase of the permeability was demonstrated by measurements of density and by positron annihilation lifetime spectroscopy (PALS) analysis [75]. 

In this chapter, first, the individual thermal and mechanical properties of chitosan and PVA as-cast films were investigated for as-cast films containing water and perfectly dried films in relation to molecular mobility of PVA chains by using x-ray, DSC, positron annihilation, and viscoelastic measurements. Based on the results, the detailed characteristics of the blends were analyzed as a function of chitosan content in terms of the individual properties of chitosan and PVA. Further analysis of the blend films was carried out for chitosan content on the film surface of drawn films by electron spectroscopy for chemical analysis (ESCA) and water-contact angle experiments. 

Figure 5.49 Cavity size analysis of (a) precursor polyimides and (b) PBOs by positron annihilation lifetime spectroscopy. Reproduced with permission from Ref. [67].

Recent developments have been in the area of microthermal analysis using thermal conductivity with thermal diffiisivity signals or AFM to visualize specific areas or domains in the material and perform localized thermal analysis studies (183,184). Relaxational behavior over time and temperature is related to changes in free volume of the material. Positron annihilation lifetime spectroscopy (PALS) measurements of positron lifetimes and intensities are used to estimate both hole sizes and free volume within primarily amorphous phases of polymers. These data are used in measurement of thermal transitions (185,186) structural relaxation including molecular motions (187-189), and effects of additives (190), molecular weight variation (191), and degree of crystallinity (192). It has been used in combination with DSC to analyze the range of miscibility of polymethyl methacrylate poly(ethylene oxide) blends (193). 

Instrumentation used in the measurement of polymer crystallinity includes light scattering, positron annihilation lifetime spectroscopy, differential scanning calorimetry, differential thermal analysis, infrared spectroscopy, NMR spectroscopy and wide and small angle x-ray diffraction (Chapter 14). 

The techniques most commonly used in thermo-oxidative studies on polymers are mainly based on thermal analysis methods such as thermogravimetric analysis (TGA) and differential scanning calorimetry (DSC) and on pyrolysis-gas chromatographic studies (particularly if they are linked to complimentary techniques such as mass spectrometry or infrared spectroscopy). Other techniques that have been used to a much lesser extent include chemiluminescence analysis, nuclear magnetic resonance (NMR) spectroscopy, electron spin resonance, and positron annihilation lifetime mass spectrometry. 

The principle techniques used in thermooxidalive studies are based on thermal analysis methods such as thermogravimetric analysis and differential scanning calorimetry and on methcxds based on polymer pyrolysis followed by gas chromatography and mass spearometry and/or infrared spectroscopy of the volatiles produced. Other techniques which have have been include nuclear magnetic spectroscopy, electron spin resonance spectroscopy and meilxids based on chemiluminescence and positron annihilation lifetime mass spectrometry. 

Free volume present in nanocomposite systems plays a major role in determining the overall performance of the membranes. Positron annihilation lifetime spectroscopy (PALS) is an efficient technique used for the analysis of free volume. The diffusion of permeant through polymeric membranes can be described by two theories, namely, molecular and free-volume theories. According to the free-volume theory, the diffusion is not a thermally activated process as in the molecular model, but it is assumed to be the result of random redistributions of free-volume voids within a polymer matrix. Cohen and Turnbull developed the free-volume models that describe the diffusion process when a molecule moves into a void larger than a critical size, Vc- Voids are formed during the statistical redistribution of free volume within the polymer. It is found that the relative fractional free volume of unfilled polymer decreases on the addition of layered silicates. The decrease is attributed to the interaction between layered silicate and polymer because of the platelet structure and high aspect ratio of layered silicates. The decrease is explained to the restricted mobility of the chain segments in the presence of layered silicates. This results in reduced free-volume concentration or relative fractional free volume [49]. 

As a whole, McKeown and Budd present criteria for polymers with intrinsic microporosity by using more than 100 monomers."" With the analysis by BET sorption measurement, positron annihilation lifetime spectroscopy and atomistic computer simulation, they emphasized the importance of microporous materials in several applications. 

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