Development Of Positron Annihilation Lifetime Spectroscopy And Its Application In Polymer Materials

As we all know,the macroscopic properties of materials is largely determined by the micro defects. therefore, in order to study the material characteristics, a variety of methods have been usually used to observe and analyse the micro defects about the material from different angles. Only mastering the information about these defects, can we understand the nature of the materials. As so far, a lot of means have been adopted to study the microscopic world, such as XRD?PS, SIMSTEM, 3DAP, SEM and PAT.In this paper, the basic principles and applications of positron annih ilation spectroscopy techniques, and the process about how to develop a high temporal resolution of positron annihilation lifetime spectrometer have been introduced in detail. we use the Ba F2 as the crystals of the detector, and incise it into cylinder with ?30mm×20mm size. And the photomultiplier tube's model number is R2059, which is produced by HAMAMATSU. Crystals were encapsulated by umbrella-shaped mode, and the material adopted is polytetrafluoroethylene. The voltage ratio of the photomultiplier tube has been used the recommended value. The final testing results show that detector rise time is about 2.5 ns, and the highest time resolution of positron annihilation lifetime spectrometer can achieve up to190 ps.Positron annihilation spectroscopy technique is a nondestructive testing technology. It can give microcosmic sizes about the material for studying the microstructure of the material. In this paper the PDMS-MIL-101(Cr)(poly(methyl siloxane- MIL101(Cr)), which is a polymer- metal organic framework materials hybrid membrane, has been studied. The PALS results showed that the size of both the space at crosslinking site and the free volume of polymer matrix decreased as the MIL101(Cr) keep increasing, which indicate that MOFs penetrated into the free volume of polymer. Moreover, according to the CDB ratio spectra of Hybrid membranes to single silicon crystal, it can be found that the effect of positron preferential annihilation with oxygen atoms was weakened with much more MIL101(Cr) in hybrid membranes, and a fraction of positro ns annihilated with the electrons of metal atoms locating at the center of subnanometer particles of MIL101(Cr). It is inferred that after entering the free volume of polymer, MIL101(Cr) particles may interact with oxygen atoms, thus partly block the way for positron,s access to oxygen atoms. It has been proved that positron annihilation technique is effective to characterize the microstructure of organic-inorganic hybrid membranes.