Positron annihilation spectroscopy blends

Liu, J., Jean, Y.C., Yang, H. (1995) Free volume properties of polymer blends by positron annihilation spectroscopy Miscibility . Macromolecules. 28, 5774. 

Gomaa, E., Microstructure and miscibility of acrylonilrile-butadiene rubber/ethylene-propylene-diene monomer blends studied by positron annihilation spectroscopy, J. Appl. Polym. ScL, 105, 2564-2570 (2007). 

Positron annihilation lifetime spectroscopy (PALS) can be used to measure the free volume in various materials. Jean et al. discussed the application of positron annihilation spectroscopy (PAS) in the detailed study of polymers and polymers with fillers. The primary experimental PAS technique used in this research is PALS, one of the three techniques in the PAS family and a powerful tool for measuring the free volume in various materials. The free volume has a great role in polymer research and is widely used to explain the behaviour of physical properties such as glass transition temperature, viscosity and physical ageing. Free volume is affected by the blending of polymers, ageing and addition... 

Positron Annihilation Spectroscopy Polymer Blends and Miscibility... 

Positron Annihilation Spectroscopy (PALS) can investigate the free volume existing between polymer chains. The lifetime of particles (positrons) injected into a sample can thus provide information on the void structure existing in polymers and polymer blends. For immiscible polymers, free volume existing at the interface due to poor adhesion can be detected by PALS. In miscible polymers, densification due to favorable interactions may be capable of determination. This technique involves the injection of positrons into a polymeric system from a radioisotope capable of emitting positrons, such as Na. The positrons (positively charged electrons) combine with electrons to annihilate or to form a bound state called a positronium (Ps). If the spins of the positron and electron are antiparaUel, para-positroniums (pPS) with a lifetime of 0.125 ns are formed. If the spins of the positron and electrons are parallel, an orthopositronium (oPs) is formed with a lifetime of 1-5 ns. The oPs hfetime, Ts, is related to the free volume cavity in which the oPs is formed [388,389]. 

Positron annihilation spectroscopy (PALS) is a technique of free volume determination in polymers that involves the injection of subatomic particles and the measurement of their decay times. This technique can be very sensitive to the degree of miscibihty and free volume behavior of polymer blends. The concept of free volume is important to understand polymer characteristics in the glassy state. For instance, PALS was used to evaluate the free volume sites of thermotropic hquid crystalline polymer blends. These blends presented smaller and fewer free volume sites than expected from a weighted average due to their intrinsic affinity. This is interesting because in contrast to thermoplastic blend results, the degree of blend miscibility alters free volume behavior as a function of blend composition [106]. In addition, the order and the dynamics in the mesophase can be accessed by nuclear magnetic resonance [107]. 

Three blends have been studied by Chang et al. [1997] using stress relaxation measurements and positron annihilation lifetime spectroscopy (PALS). It was observed that for blends of PS with PPE and PS with PVME the stress relaxation rates were faster for the blends in comparison with PS alone, whereas the opposite was true for a PMMA/PEG blend when compared with neat PMMA. 

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). 

Giinther-Schade, K., Schubert, D. W., and Faupel, F., Determination of the binodal and spinodal phase separation temperature in the blend system PaMS0.5-co-(Luran)/ OMMA0.95MA0,05(Lucryl) with positron annihilation lifetime spectroscopy. Macromolecules, 35, 9074—9078 (2002). 

Peng, Z. L., Olson, B. G., Srithawatpong, R., McGervey, J. D., Jamieson, A. M., Ishida, H., Maier, T. M., and Halasa, A. R, Study of free volume in high vinyl-polybutadiene/cis-polyisoprene blends by positron annihilation lifetime spectroscopy, J. Polym. Sci. Polym. Phys., 36, 861-871 (1998). 

Wastlund, C., Berndtsson, H., and Maurer, F. H. J., Miscibility of styrene—maleic anhydride and styrene—acrylonitrile blends studied by positron annihilation lifetime spectroscopy, Macmmolecules, 31, 3322-3327 (1998). 

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. 

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). 

Chapter 6 deals with theoretical and experimental developments in the physical aging of polymer blends. In particular, aging data for polymer blends are reviewed and compared to the relevant homopolymer data. The past and present phenomenological, empirical and molecular models of aging are discussed. Enthalpic, volume, and mechanical relaxation, positron annihilation lifetime spectroscopy and other spectroscopic and scattering techniques are also considered. Then, specific examples on aging of blends are presented in systems where the effects of intermolecular interactions are important Finally, complex behaviors of aging of phase separated blends are considered. 

---