Positron annihilation lifetime spectroscopy polymers

Wmberg, R, Eldrup, M., and Maurer, R H. J., Nanoscopic properties of silica-filled poly-dimethylsiloxane by means of positron annihilation lifetime spectroscopy. Polymer, 45, 8253-8264 (2004). 

Winberg, P. Eldrup, M. Maurer, F. H. J., Nanoscopic Measurements of Silica Filled Poly(dimethylsiloxane) by Means of Positron Annihilation Lifetime Spectroscopy. Polymer 2004,45,8253-8264. 

Okamoto S, Yano K, Fujiwara M, Aitsu K (2004) Method for producing liquid crystalline polyester. JP Patent 2004083778A, 28 Aug 2002 Okamoto S, Yu R, Djourelov N, Suzuki T (2005) Study on the thermal behavior of a solution-cast liquid-crystalline polymer film by positron-annihilation lifetime spectroscopy. Polymer... 

Positron annihilation lifetime spectroscopy (PALS) provides a method for studying changes in free volume and defect concentration in polymers and other materials [1,2]. A positron can either annihilate as a free positron with an electron in the material or capture an electron from the material and form a bound state, called a positronium atom. Pnra-positroniums (p-Ps), in which the spins of the positron and the electron are anti-parallel, have a mean lifetime of 0.125 ns. Ortho-positroniums (o-Ps), in which the spins of the two particles are parallel, have a mean lifteime of 142 ns in vacuum. In polymers find other condensed matter, the lifetime of o-Ps is shortened to 1-5 ns because of pick-off of the positron by electrons of antiparallel spin in the surrounding medium. 

The aim of this chapter is to introduce the reader to the application of positron annihilation techniques to polymers. An extensive review of the large volume of publications related to positron studies in polymers will not be presented. Rather it is intented to introduce the reader to the theory and techniques used in polymer studies and indicate the types of information that can be obtained about different polymer systems. The main focus of this chapter will be on the use of positron annihilation lifetime spectroscopy (PAL) in polymer studies. Chapter 11 discusses the use of monoenergetic slow positron beams used to study polymers surfaces. One of the interesting new developments in the application of positron annihilation techniques in polymers is the positron age-momentum correlation technique (AMOC). This technique promises to shed new light on the mechanisms of positronium formation and annihilation in polymer systems. A more detailed discussion of this technique can be found elswhere in this text. 

Forsyth, M., Meakin, P., MacFarlane, D.R., Hill, A.J. (1993) Positron annihilation lifetime spectroscopy as a probe of free volume in plasticized solid polymer electrolytes . Electrochimica Acta, 40(13), 2349. 

Bartos, J., Kristiakova, K., Sausa, O., Kristiak, J. (1996) Free volume microstructure of tetramethylpolycarbonate at low temperatures studied by positron annihilation lifetime spectroscopy a comparison with polycarbonate . Polymer, 37(15), 3397. 

As for the volumes of the atoms, the thermal expansion and compressibility is composed of two main terms, the cavity and the hydration. An estimate of the contribution of each factor relies on assumptions that are not easy to check. An estimate of the expansion or compression of the cavities should be possible with positron annihilation lifetime spectroscopy. This approach has proven to be a useful tool for determining the size of cavities and pores in polymers and materials. The lifetime is sensitive to the size of the cavity in which it is localized. A number of empirical relations correlate the distribution of the lifetime and the free volume [33]. Data on the pressure effect on the lifetime are only available for polymers. The results suggest that there may be a considerable contribution of the reduction in cavity size to the compressibility of a protein. 

Positron annihilation lifetime spectroscopy (PALS) allows the quantitative investigation of the polymer free volume [1, 2]. Additionally, the PALS beam technique makes a direct depth resolution possible, by implanting the probe - the positron - within a definite sample depth interval depending on the positron kinetic energy [3]. It is one of the very few nondestructive techniques for investi-... 

MORPHOLOGY OF FREE-VOLUME HOLES IN AMORPHOUS POLYMERS BY MEANS OF POSITRON ANNIHILATION LIFETIME SPECTROSCOPY... 

Consolati, G., Quasso, R, Simha, R., and Olson, G. B., On the relation betwen positron annihilation lifetime spectroscopy and lattice-hole-theory free volume, J. Polym. Sci. B, 43, 2225-2229 (2005). 

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). 

Jean, Y. C., Comments on the paper Can positron annihilation lifetime spectroscopy measure the free-volume hole size distribution in amorphous polymers Macromolecules, 29,5756-5757 (1996). 

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). 

Positron Annihilation Lifetime Spectroscopy. The details of PALS will not be discussed here since several other chapters in this book are specifically concerned wifii this experimental technique and provide more than adequate description. Suffice it to say here that or//ioPositronium (oPs), which is formed when a positron binds to an electron of parallel spin, tends to locate in free volume sites within a polymer, and the time required for it to annihilate via pickoff with an electron of anti-parallel spin residing in the surrounding material is related to the size of the free volume site. There are two parameters that are sensitive to polymer free volume the oPs pickoff component lifetime, xa, which is related to the mean radius of the free volume cavities, and the oPs pickoff component intensity, I3, which is related to the concentration or number of fr volume cavities. 

Positron Annihilation Lifetime Spectroscopy of HIQ-40 Films Positron annihilation lifetime spectroscopy has emerged as a sensitive technique to probe free volume in polymers (33, 34), PALS uses orthoPositronium [oPs] as a probe of free volume in the polymer matrix. oPs resides in regions of reduced electron density, such as free volume elements between and along chains and at chain ends (33), The lifetime of oPs in a polymer matrix, T3, reflects the mean size of free volume elements accessible to the oPs. The intensity of oPs annihilations in a polymer sample, la, reflects the concentration of free volume elements accessible to oPs. The oPs lifetime in a polymer sample is finite (on the order of several nanoseconds), so PALS probes the accessibility of free volume elements on nanosecond timescales (33),... 

Reaction of a positron with an electron gives a metastable positronium (Ps) particle, which may have antiparallel spins (para-positronium, p-Ps) or parallel spins (ort/jo-positronium, o-Ps). Within a polymer, the longer lifetimes of o-Ps may be related to the size, concentration and distribution of free volume elements. There have been a number of studies of PIM-1 by positron annihilation lifetime spectroscopy (PALS) [33-36]. 

The generally recognized and the most reliable method for investigation of free volume in polymers is positron annihilation lifetime spectroscopy (PALS). It was applied for investigation of PTMSN and related polymers. This method is based on the measurement of lifetime spectra of positrons in polymers - lifetimes (ns) and corresponding intensities li (%). Longer lifetimes (or T3 and T4) (so-called o-orthopositronium lifetimes) can be related to the mean size of free volume R. 

G. Dlubek, Positron annihilation lifetimes spectroscopy. Encyclopedia of Polymer Science and Technology, A. Seidel, Ed., John Wiley Sons, Hoboken, NJ, 2008. 

B. W. Rowe, S. J. Pas, A. J. HiU, R. Suzuki, B. D. Freeman, D. R. Paul, A variable energy positron annihilation lifetime spectroscopy study of physical aging in thin glassy polymer films. Polymer, 50, 6149-6156 (2009). 

---