Gas Permeability and Free Volume Hole Properties of Interpenetrating Polymer Network Studied by Positrons

A series of polyurethane/epoxy resin interpenetrating polymer networks （PU/ER IPN） were studied by positron annihilation lifetime spectroscopy （PALS）. The effects of epoxy resin type and content on the free volume properties in IPN were investigated. We found that in PU/ER IPN, the free volume hole size and fractional free volume showed a negative deviation due to closer segmental chain packing through some chemical bonding between PU and epoxy resin. Direct relationship between the gas permeability and the free volume has been established based on the free volume theory. Experimental results revealed that the free volume plays an important role in determining the gas diffusion and permeability.     

正电子谱学技术在功能材料微结构表征中的应用

特殊功能材料是一些具有优良电学、磁学、学、热学、学、力学、化学、物医学功能,在各类高科技领域到泛应用.正电子湮没技术是一种对材料微结构特别有效探测技术,特别是对各种缺陷、空位和微孔尤为灵敏,通过正电子湮没寿命谱、多普勒展宽谱和慢正电子束技术,通过分析正电子湮没参数可以获材料从表面到内部缺陷分布信息和随外部物理和化学条件变化、引起微结构变化.本文选取几种特殊材料正电子湮没实验结果来分析材料内部微结构,表明正电子湮没谱学是一种独特研究微观结构方法.     

Defect properties of GaAs by positron annihilation

Positron lifetime and Doppler Broadening spectra have been measured for three types of GaAs semiconductors. Direct evidence of native vacancy-type defects is found in the semi-insulating (SI-type) and n-type sample as its average lifetime {ie45-1} andS-parameter are larger than the bulk value. No positron trapping occurred in p-type GaAs. The lifetime spectrum of n-GaAs has also been measured as a function of temperature. The increase in average lifetime {ie45-2} from 226 ps to 234 ps at the temperature range 95–330 K was observed and was explained by the ionization of the vacancy. The slight increase in bulk lifetime {ie45-3} with the temperature was caused by the lattice expansion and expansion coefficient α=14×10⁻⁶K⁻¹ was evaluated. Chen Zhiquan: born in May 1969, Ph.D. graduate student. Current research interest is in positron annihilation. Supported by the National Natural Science Foundation of China     

用正电子湮没寿命谱研究锰锌铁氧体纳米晶的缺陷结构

采用溶胶一凝胶法,在不同退火温度下得到了3种不同粒径的锰锌铁氧体纳米晶．利用X射线衍射研究了纳米晶的晶体结构和粒径,借助正电子湮没寿命谱仪讨论了纳米晶的缺陷随粒径的变化．结果显示,所得锰锌铁氧体纳米晶为立方尖晶石结构,且随着温度的升高纳米晶不断长大;随着粒径的增大,纳米晶的表面缺陷减小,晶界间的自由体积发生复合．     

Synthesis, growing processes and physical properties of CdS nanoclusters in Y-zeolite studied by positron annihilation

Direct synthesis of CdS nanoclusters within the pore structure of Y zeolite was made. The location of CdS nanoclusters inside Y zeolite hosts was confirmed by the blue-shifted reflection absorption spectra with respected to that of bulk CdS materials. In this paper, we conducted Positron Annihilation Lifetime Spectrum (PALS) measurements on a series of CdS/Y zeolite samples and concluded that CdS clusters were not located in supercages but in smaller sodalite cages; as the CdS loading concentration increases to 5 wt%, the discrete CdS cubes begin to form bigger superclusters through interaction. The stability of CdS clusters inside the sodalite units is due to the coordination of Cd atoms with the framework oxygen atoms of the double six-ring windows. Moreover, PALS reveals some important information of surface states existing on the interfacial layers between CdS clusters and Y zeolite. Foundation item: Supported by the National Natural Science Foundation of China (19871074) Biography: Peng Hao (1978-), male, Ph. D candidate, research interest: semiconductor nanoclusters.     

正电子湮没寿命谱仪性能的研究

对美国Ortec公司的正电子湮没寿命谱仪的工作条件进行了调整,从而提高了谱仪的计数效率,此外,还研究了谱仪时间刻度的线性性质和在不同能窗下的时间分辨率。     

用符合正电子湮没技术研究Zr、Nb对NiAl合金的d电子影响

采用双探头符合技术测量Ni、Al、Zr、Nb、NiAl及Ni50Al48Zr2、Ni50Al48Nb2样品的正电子湮没辐射的多普勒展宽谱.从谱线提取正电子与样品中d电子湮没的信息,发现正电子与NiAl样品的d电子湮没信号因Ni3d-Al 3p电子杂化而相对降低,Zr、Nb的添加导致合金样品中d-d电子作用增强、谱线d电子信号增大,添加Nb的样品谱线峰高于添加Zr样品,说明Nb的加入比Zr抑制d-p电子作用效果更佳.     

基于正电子湮没寿命谱研究Fe-6.5wt.%Si合金中热空位的生成

正电子湮没技术（PAT）是一种无损伤的材料探测技术,它可以反映正电子所在处电子密度或电子动量分布的信息.由于正电子对原子尺度的缺陷非常敏感,所以正电子湮没技术（PAT）是研究纯金属及金属间化合物中热空位生成的有效工具.基于正电子寿命谱技术对金属间化合物Fe-6.5wt.%Si合金热轧板在不同温度退火后缺陷变化进行研究,发现了正电子平均寿命在673K左右迅速增加,673至1073K温度范围内平均正电子寿命的温度曲线为明显的S形状,1073K以上平均正电子寿命趋于常数,通过分析正电子平均寿命的温度变化曲线,得到了Fe-6.5wt.%Si合金中热空位生成的临界温度值,并计算得到了该合金的空位生成激活焓为HVF=0.54eV.     

Defects in NTD InP probed by positron annihilation spectroscopy

Two samples of high purity InP extracted from the same wafer were examined by positron annihilation spectrum analysis after having been, processed by means of thermal Neutron Transmutation Doping (NTD). Compared with the as grown sample with an average positron lifetime of 246 ps at 300 K, the high dose doped one has an average lifetime of 251 ps and the lower dose doped one 248 ps measured under the same condition, indicating that some defects have been introduced in the NTD process. Annealing experimental results show a steady decrease in the average lifetime with increasing annealing temperature up to 550°C. And a peak in lifetime curve around 500°C was observed which may be attributed to defects related structure conversion. Temperature experiments conducted on the low dose doped sample from 150K to 290 K suggest the existence of vacancy-impurity complex which have given rise to an abnormal reduction of average lifetime with increasing temperature. Also a n-type InP sample (A61) was irradiated with thermal neutrons in another reactor and the lifetime results display an increase of 15 ps. Furthermore, to study epithermal neutron irradiation effects on InP, measurements were performed on an n-type InP sample (N119) along with one p-type sample (P118) after having been irradiated with high fluence of epithermal neutrons. The former has an average lifetime of 262 ps and the latter 247 ps after irradiation. The results prove that on some occassion epithermal neutrons can produce sizable defects in InP. Foundation item: Supported by the Science Foundation of Hubei Province (203980532) Biography: WEN Xiang-e (1976-), male, Master candidate, Research direction; majar research interest is defects in semiconductor materials using positron annihilation spectroscopy.     

Microstructure of polymeric electrolyte PEU-LiClO4 studied by positron spectroscopy

The positron lifetime spectra and ionic conductivity have been measured for polymeric electrolyte PEU-LiClO₄ as a function of temperature in the range of 120≈360 K and as a function of Li-salt concentration at room temperature. From the temperature dependence of positron annihilation parameters, the glass transition and subtransition are observed, and the glass transition temperatureT _g of pure PEU is determined to be 240 K. AboveT _g, the free volume hole size dramatically increases with temperature. The variations of positron annihilation parameters and ionic conductivities with respect to Li-salt concentration at room temperature indicate that the Li salt mainly diffuses into the amorphous region in PEU-LiClO₄. The increase of Li salt concentration brings about an increase in the number of carried ions, and a reduction of the fractional free volume. Supported by the National Natural Science Foundation of China Wang Shaojie: born in Mar. 1942, Professor     

聚合物共混体系的正电子湮没研究

用正电子湮没寿命谱仪对聚丙烯PP和三元乙丙橡胶EPDM的共混体系进行了测量.实验研究表明,正电子湮没寿命灵敏地反映了在95—370K温度范围内PP/EPDM共混物的微观结构变化.经分析得到PP/EPDM是两相共混体系的结论.     

阳极腐蚀法制备发光多孔硅的正电子湮没研究

使用正电子湮没寿命谱仪和真空紫外荧光光谱仪,对不同电流密度腐蚀条件下制备的多孔硅进行微结构及发光性能的表征,通过正电子湮没方法研究多孔硅微结构对多孔硅光致发光性能的影响.实验结果表明,随着腐蚀电流密度的增大,电子偶素在样品中的pick-off湮没寿命先增大后减小,同时样品的发光强度显示出相同趋势.可以推断,在腐蚀电流密...     

决定正电子寿命谱仪分辨函数的一种方法

介绍一种决定分辨函数的方法.通过理论分析和实验证明,利用PROMPTAN 程序从已知正电子寿命的参考样品谱中抽取出的分辨函数可作为一级近似,在此基础上,仅改变分辨函数第三高斯曲线的参数,即可较快地获得更精确的分辨函数.     

Evidence of Positron Trapping into Defects in Zn-Doped GaAs

0　IntroductionPositronlifetimespectroscopy ,whichisdirectlysensitivetovacancy typedefects,isanestablishedmethodforstudyingthedefectinsemiconductor[1 ] .Uptonow ,manyworkshavebeenreportedonn typeGaAsandsemi insulating (SI) typeGaAsusingthistechnique.Ithasbeenprovedthatpositronanni hilationspectroscopyisaefficientmethodtodetectdefectsinsemiconductor[2 ,3] .However,muchlessstudiesconcernedwithp typematerialshasbeendone .Thereisadiscrepancyonpositrontrappingintodefectsin p \|typeGaAs.Somestu…     

PVA/淀粉接枝P(AA-AM)互穿网络水凝胶的合成与性能研究

以马铃薯淀粉、丙烯酸(AA)、丙烯酰胺(AM)和聚乙烯醇(PVA)为原料,过硫酸钾为引发剂,三氯化铝为交联剂,利用水溶液法制备PVA/淀粉接枝AA、AM互穿网络水凝胶(PVA/St-g-P(AA-AM)IPN)。红外光谱(FT-IR)分析表明,PVA与St-g-P(AA-AM)间形成较强的氢键或部分共聚反应。X射线衍射(XRD)分析表明,当PVA用量较少时,PVA能均匀的穿插于凝胶网络中,形成完善的互穿网络结构;当PVA用量过多时,有部分的PVA结晶出现。水凝胶性能测试结果表明,随PVA用量增加水凝胶的吸水率先增大后减小,抗压缩强度不断升高,压缩应变持续降低,对蒸馏水的最大吸水率为650 g.g-1,在60min内达到溶胀平衡,保水性良好;水凝胶在pH<4时几乎不发生溶胀,在pH=12附近出现体积突变,表现出敏感的pH响应性。     

SPEK-C膜的正电子湮灭寿命谱学研究

利用正电子湮灭寿命谱(PALS)法及原子力显微镜(AFM)，研究了磺化及溶剂蒸发对(磺化)酚酞侧基聚芳醚硐(SPEK-C)膜制备的影响．结果表明：磺化基团的引入，降低了分子间的作用力，使得分子间排列不紧密，导致聚合物的自由体积大小与强度同时增加；铸膜液溶剂挥发，聚合物浓度增加，胶束聚集体的相互聚集产生较大的胶束聚集体孔，使自由体积减小而强度增大，聚合物的自由体积较好地反映了胶束聚集体的聚集特征．     

丙烯酸酯系互穿网络聚合物乳液的微观形貌

采用乳液聚合法,合成了聚甲基丙烯酸甲酯(MMA)-苯乙烯(St)/聚丙烯酸乙酯(EA)-丙烯酸丁酯(BA)的丙烯酸酯系互穿网络聚合物(IPNs)系列乳液,使用磷钨酸(PTA)负染技术将乳液粒子染色,使用透射电子显微镜(TEM)观察乳液粒子的微观形貌,对乳液微粒微观互穿网络壳-核结构的形成过程进行了研究.结果表明,网络质量配比、溶胀时间以及溶胀方式等因素均对乳液粒子微观形貌的形成产生显著影响;网络质量配比是决定乳液粒子大小的重要因素之一,溶胀时间影响互穿网络壳结构的厚度,溶胀方式影响乳液的成膜性能.     

pH敏感型聚乙烯醇/壳聚糖互穿网络水凝胶的溶胀及载药释药性能研究

以聚乙烯醇(PVA)和壳聚糖(CS)为原料,采用物理交联与化学交联相结合的工艺,即通过循环冷冻—解冻法结合京尼平交联法,制备了具有互穿网络结构(IPN)的PVA/CS复合水凝胶,研究了pH值对其溶胀率的影响;选用氯霉素为模型药物,探讨了PVA/CS水凝胶在模拟胃液(SGF)和模拟肠液(SIF)中的载药、释药性能.结果表明,PVA/CS IPN水凝胶在酸性条件下具有较高的溶胀率,而在碱性条件下,溶胀率较小;其载药量、释药量都随着复合水凝胶中PVA含量的增大而增大;且在SGF中的药物释放率高于SIF的释放率;在SGF中的药物释放速率随着组分中PVA含量的增加而增大.     

Optimum sintering conditions for optical properties of translucent aluminum nitride ceramics

High translucency is one of the excellent properties of AlN ceramics because of its wide optical band gap energy of 6.2 eV. We have achieved success in producing AlN ceramic tube of 98% total visible light transmittance at 0.6 mm thick tube wall by applying an improved sintering technique. This AlN ceramic was produced by sintering at 1880℃ using Ca3Al2O6 as a sintering additive and in reduction atmosphere to remove the sintering additive from the final sintered material. After the sintering, the annealing ...