Papers by Author: Shao Jie Wang

Abstract: The microstructure of the polypropylenes (PP) irradiated by gamma ray was studied by positron lifetime technique and differential scanning calorimetry (DSC). Lifetime measurement shows o-Ps intensity decreases with increasing γ irradiation dose. The crystallinity of irradiated samples was detected by DSC method. The correlation between o-Ps intensity and crystallinity indicates γ-ray can induce higher crystallinity in the polypropylene at low irradiation dose.

Abstract: A simple pulsed slow positron beam based on a Penning-trap has been designed and is being constructed in Wuhan University. The cooled positrons from the trap with very low energy dispersion are dumped and chopped to pulses of a few tens of ns in width. Positron pulses are bunched by adjusting the potential of drift tube using an arbitrary wave generator, then accelerated to the target. Influences of the pulse width, the energy dispersion of positrons etc. on the time resolution of bunched positron pulse are simulated. The result shows that lower energy dispersion of positrons leads to much narrower positron pulses, indicating that a trap-based slow positron beam has a great advantage in developing a pulsed slow positron beam.

Abstract: Recently polymer nanocomposites[1,2] have been receiving special attention because of its advantages and unique properties in comparison to the traditional polymer composites.The structural transformation of Epoxy (cured by polyamide) and epoxy/Rectorite nanocomposite(with 0.5% rectorite content) is studied by PALS as a function of temperature from 30K to 490K. For Epoxy and Epoxy/Rectorite nanocomposite, the glass transition temperature (Tg) is observed to be 270K and 260K, the second transition temperature (Tγ) is 160K and 120K, the viscous flow temperature (Tf) is the same as 380K. The result shows that properties of the free-volume in nanocomposite have been changed by the rectorite platelets fully separated in material at low temperature. At the same time, we find that the intensity of o-Ps decreases with increase of the temperature at the softening temperature above the Te.

Abstract: Hydrogen- and corrosion -related defects of pure iron and AISI 304 and 316 stainless steels were investigated by measuring Doppler broadening energy spectra of positron annihilation. The significant increase in S-parameter after corrosion in iron was interpreted as due to the formation of defects and voids during corrosion processes. However, a decrease of the S-parameter in AISI 304 and 316 stainless steels after corrosion was interpreted as dissolution of passivity oxide film. Furthermore, similar results in iron and stainless steels after hydrogen-charging were observed. Hydrogen damage between the surface and the bulk has a significant variation with depth. The larger increase in S-parameter near the surface after hydrogen-charging mainly comes from the formation of large-size defects (e.g. voids); however the increase in S-parameter in the bulk after hydrogen-charging mainly comes from the production of small-size defects.

Abstract: Two types of composites－high density polyethylene/polystyrene (HDPE/PS) with clay, and high density polyethylene grafted with acrylic acid/PS (PEAA/PS) with clay－were prepared via melt compounding. X-ray diffraction (XRD) results revealed that the dispersion of clay in compatibilized blends was better than immiscible blends. Positron annihilation lifetime spectroscopy (PALS) has been utilized to investigate the microstructure of two types of composites. The ortho-positronium (o-Ps) intensity for PEAA/PS was lower than that for HDPE/PS. The results provided evidence that the chain segments with carboxyl group would be easier to intercalate the gallery of silicates.

Abstract: The anneal effect of PP/PA/MMT blends had been studied by positron annihilation lifetime spectra (PALS). The o-Ps lifetime and intensity of unannealed blends were linearly additive basis on the PA weight fraction, which was coincident to the simple compound rule. However, the o-Ps intensity of the samples decreased after samples annealed.

Abstract: MA-g-HDPE and PA6-MMT were selected to improve the compatibility of HDPE and PA6. Positron annihilation lifetime spectroscopy (PALS) and optical microscopy were utilized to characterize the interface of the blends.

Abstract: The free volume property and intermolecular interaction (especially hydrogen bonding) of poly (ether-urethane) (PEU) irradiated by neutron under different atmosphere has been studied by positron annihilation lifetime spectroscopy (PALS) and Fourier transform infrared (FTIR). The results suggested that the hydrogen-bonding interactions and free volume property in PEU depended strongly on the neutron irradiation dose.