Positron miscibility

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

Srithawatpong, R., Peng, Z. L., Olson, B. G., Jamieson, A. M., Simha, R., McGervey, J. D., Maier, T. R., Halasa, A. F., and Ishida, H., Positron annihilation lifetime studies of changes in free volume on cross-linking cw-polyisoprene, high-vinyl polyhutadiene, and their miscible blends, J. Polym. Sci. B, 37, 2754-2770 (1999). 

Dlubek, G., Taesler, C., Pompe, G., Pionteck, J., Petters, K., Redmann, F., and Krause-Rehberg, R., Interdiffusion in a particle matrix system of two miscible polymers an investigation by positron annihilation lifetime spectroscopy and differential scanning calorimetry, J. Appl. Polym. Sci., 84, 654-664 (2002). 

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). 

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). 

Raj et al. °" have compared the efficiency of microwave and e-beam irradiations to stabilize the interface of various partially miscible or nonmiscible blends polystyrene (PS)/polymethyl methacrylate (PMMA), polyvinyl chloride (PVC)/ethylene vinyl acetate (EVA), PP/acrylonitrile butadiene rubber (NBR), and polyvinyl chloride (PVC)/poly(styrene acrylonitrile) (SAN). For this purpose, they used positron annihilation lifetime measurements, and they considered particularly a hydrodynamic interaction parameter a. This... 

The second study (Meghala and Ranganathaiah 2012) was dedicated to the evaluation of interfaces in poly(styrene-co-acrylonitrile) (SAN)-based ternary polymer blends using also positron lifetime spectroscopy. The method successfully applied for binary blends (single interface), mentioned above, was theoretically modified for ternary blends and experimentally verified by measuring free volume content in blends and their constituents. They tested the efficacy of this method in two ternary blends S AN/PVC/PMMA and SAN/EVA/PVC at different compositions. The effective hydrodynamic parameter evaluated using individual values turned out to be handy in predicting the overall miscibility level of a ternary blend. 

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). 

Positron Annihilation Spectroscopy Polymer Blends and Miscibility... 

The first positron annihilation lifetime (PAL) measurements on polymer blends were conducted by Jean et al. [9], who investigated the free volume properties of (i) a miscible blend, namely tetramethyl-bisphenol A polycarbonate (TMPC) and polystyrene (PS) and (ii) an immiscible blend, namely bisphenol A polycarbonate (PC) and PS. It was observed that TMPC formed a miscible blend with PS as it had larger fractional free volume cavities than PC. For the miscible blend, the free volume showed negative deviation from the linear additivity rule (Eq. (27.19)), whereas for immiscible blend it was observed that the free volume, as detected by o-Ps lifetime as a function of composition, was complicated due to the presence of... 

It is evident from the above discussion that the free volume data derived from positron lifetime measurements is incapable of providing information on the composition-dependent miscibility level of the blend. At this point, a new method based on the same free volume data measured from positron lifetime measurements was introduced to determine the miscibility of binary blends. The new method was based on hydrodynamic interactions (the mathematics required have been explained in detail earlier), and calculations of the y parameter derived from the hydrodynamic interaction approach were made for three selected polymer blends, namely poly(styrene-co-acrylonitrile) (SAN)/poly(methyl methacrylate) (PMMA) (completely miscible), poly(vinyl chloride) (PVC)/poly(methyl methacrylate) (PMMA) (partially miscible) and poly(vinylchloride) (PVC)/polystyrene (PS) (immiscible) (see Figure 27.13). As can be seen, this parameter behaves similar to the interchain interaction parameter /3, in the sense that it exhibits a complex behavior making it difficult to determine the composition-dependent miscibility of the blends. 

The hydrodynamic interaction approach appears adequate in most cases for describing the composition-dependent miscibility level. Currently, a considerable amount of data is available on binary polymer blends, particularly from positron annihilation studies. Hence, the interpretation offered with regard to misabiUty may not be effective, especially in the case of partially miscible blends when some inferences are vague. 

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