正电子湮没技术（PAT）在高分子材料中的应用（上）

本文引用７０多篇文献，综述了正电子湮没技术（主要是正电子湮没寿命技术）近１０年来在高分子材料各个领域中的应用。     

石墨炔纳米材料的制备及在电化学能源中的应用

石墨炔纳米材料的制备与应用是石墨炔材料研究的重要方向, 通过对其纳米结构进行设计与优化, 可以提高石墨炔材料及其杂化结构的性能, 拓展其在能源储存与转换领域的应用. 本综述介绍了不同形貌和结构的石墨炔基纳米材料, 如纳米墙、 纳米片、 纳米薄膜等结构. 阐述了不同结构特征的石墨炔基纳米材料在电化学储能器件以及电化学能源催化中的应用, 同时也探讨了石墨炔不同纳米形貌和结构在能源应用领域快速发展的机遇及所面临的挑战.     

超细粉氧化铝陶瓷烧结反应正电子湮没谱分析

利用正电子湮没谱（ＰＡＳ）分析技术对超细粉α＿Ａｌ２Ｏ３陶瓷基片（板）的烧结反应过程进行了检测研究。对在４种不同的温度下得到的烧结体作ＰＡＳ分析研究，发现正电子寿命敏感于烧结温度以及不同温度下的微结构效应。根据ＰＡＳ数据分析，对超细粉陶瓷烧结体的微结构缺陷及温度－相变关系作了初步探索。     

纳米修复剂钝化重金属机理研究进展

重金属污染问题是当前环境治理过程中的重点和难点,纳米材料因其比表面积大、表面易功能化、环境友好等性能,被广泛应用于重金属污染的土壤和水体的修复。本文综述了纳米零价金属、纳米非金属单质、纳米金属氧化物、纳米非金属氧化物、纳米金属硫化物、纳米金属氧酸盐,纳米高分子材料等纳米材料对重金属的修复效果和机理,展望了纳米材料在重金属修复方面的应用前景及改进方向,对开发新型重金属修复材料具有重要指导意义。     

双金属纳米材料与催化

双金属纳米材料作为工业上少见的一类催化剂材料,在合成过程中可通过对其组成、结构晶粒大小尺寸的调控,实现其催化性能的合理调控,因此,近年来备受催化材料化学领域科技工作者的广泛关注.随着纳米材料调控合成方面的技术进步,具有均一小尺寸可控结构的纳米材料对于制备高效催化剂材料和研究催化反应机理具有重要的意义.结合纳米技术探索开发设计新型的双金属纳米催化剂材料颇具挑战性.本文围绕双金属纳米催化剂的合成、结构及其相关催化性能,从不同的双金属纳米催化剂出发,对催化剂的性能提高、催化机理研究的若干问题和分析手段及方法在催化研究中的进展发表一点初浅认识.     

纳米材料在组织工程中的应用*

采用纳米技术对传统的组织工程材料进行改造产生的纳米组织工程材料具有独特的生物学性能,引起了人们的足够重视,其在组织工程领域中的应用研究成为人们关注的热点。纳米相陶瓷、碳纳米管、碳纳米线和纳米金属材料在骨和软骨组织工程,钛纳米材料、聚乳酸-丙交酯纳米材料和纳米纤维材料在动脉组织工程,多肽纳米骨架、纳米纤维支架和碳纳米管/纤维在神经组织工程以及纳米结构的多聚物在膀胱组织工程中的应用已有大量报道,研究结果表明纳米材料在组织工程领域有着潜在的应用前景。本文对纳米材料在骨和软骨组织工程、动脉组织工程、神经组织工程以及膀胱组织工程中的应用研究现状及发展前景进行了综述。     

功能纳米材料的化学控制合成、组装、结构与性能

维度限制使得纳米材料具有独特的物理和化学性质,如何对纳米构造单元的结构进行调控,并最终将纳米效应在宏观尺度上体现是当今纳米科技面临的挑战性问题,纳米材料的化学控制合成方法学、组装、结构与性能的研究是解决上述问题的基础．这篇综述文章从四个方面,分别介绍了单分散纳米晶以及纳米管、纳米线、空心纳米微球等系列低维纳米结构在合成方法与技术、“自下而上”的组装、基于微结构的性能表征与应用探索等领域取得的研究进展,试图总结出其中的规律性,同时也展现了纳米科学与技术的魅力和广阔的发展前景．     

新型纳米荧光及其复合材料的可控制备和表征

由于纳米材料具有的独特物理效应,使纳米材料的荧光性能与纳米颗粒的结构、尺寸和形貌等微观特征密切相关,成为当前研究的热点领域.本论文以纳米荧光材料的可控制备技术作为研究重点,结合当前的应用发展趋势,从几个不同的角度制备了几种具有不同微观结构特征的新型纳米荧光及其复合材料,探索了一些新的方法和新的材料,并对其性能进行了表征,主要工作成果如下:     

用正电子湮没方法研究有机导体

本文测量一些新的复合物型有机导体中正电子湮没的寿命谱,线形参数和3γ湮没的相对产额.结果表明,在电荷完全转移的绝缘体和电荷部分转移的导体中,正电子湮没特征有明显的差别.湮没寿命和S参数与该类材料的电导率之间有很强的依赖关系.根据正电子湮没特征讨论了这类材料可能的导电机理.     

α-Fe/Nd2Fe14B复合纳米晶的界面研究

采用正电子寿命谱和双探头Doppler展宽测量在原子尺度上研究了α-Fe/Nd2Fe14B复合纳米晶的界面结构.正电子寿命研究表明, α-Fe/Nd2Fe14B复合纳米晶存在两类界面.一类为非晶界面层, 正电子湮没寿命为155 ps; 另一类为具有原子空位的松懈界面, 含有空位尺寸大于1～2个铁原子空位的结构自由体积, 正电子湮没寿命为246 ps.电子-正电子湮没光子的共谐Doppler展宽测量表明这类松懈界面富集非磁性原子Nd和B, 这将削弱α-Fe/Nd2Fe14B复合纳米晶晶粒间的磁交换耦合.     

正电子湮没技术（PAT）在高分子材料中的应用（下）

正电子湮没技术（ＰＡＴ）在高分子材料中的应用（下）李桂芝，施良和，叶美玲（中国科学院化学研究所高分子物理开放实验室，北京，１０００８０）３．４高分子导体高分子导体有两种：（１）靠共轭分子链导电的高分子；（２）因掺入小分子而具有导电作用的高分子。现在已...     

Electron irradiation induced microstructural modifications in BaCl2 doped PVA: A positron annihilation study

Thin films of pure and 10 wt% BaCl₂ doped poly(vinyl alcohol) (PVA) were prepared by solution casting method. These films were subjected to electron irradiation for different doses ranging from 0 to 400 kGy in air at room temperature. The effect of electron irradiation on the optical and free volume related microstructures of these polymer films was studied using positron annihilation lifetime spectroscopy, FTIR and UV-vis techniques. The FTIR spectral studies indicate that the electron irradiation induces chemical modifications within the doped PVA, which results in chain scission as well as cross-linking of the polymer. The positron lifetime study on these irradiated polymers shows that the chain scissions and cross-linking within the polymer matrix affect the free volume content and hence the microstructure. The UV-vis optical absorption studies show that the induced microstructural change by electron irradiation also modifies the optical properties. Using UV-vis spectra, the optical energy band gap was estimated and it decreases with increase in electron dose. A correlation between positron results and optical results is obtained and electron irradiation induced microstructure modifications within the doped polymer are understood. The results highlight the usefulness of positron annihilation technique in the study of the microstructure of irradiated polymers.     

The current state of sol-gel technology

The current state of sol-gel technology has been reviewed mainly from the standpoint of microstructures of materials which can be achieved by the sol-gel method. It has been shown that the sol-gel method makes it possible to produce a great variety of high technology materials by providing the existing substances with a significant microstructure and producing the material with a novel microstructure. There are microstructures characterized by micropores, preferential crystal orientation, inorganic-organic and inorganic-inorganic composites of hybrid nature and gradient composition. These characteristic microstructures are related to the properties and applications of the materials.     

金刚石膜微结构的慢正电子束测量研究

The microstructure of diamond films was studied by slow positron beam and Raman spectroscopy. For the Raman spectroscopy experiment on diamond films, a high fraction of the sp3 hybridized bond was detected in samples. Positron annihilation spectra analysis further illuminated that the concentration and types of defects were different in each sample. S-E curves of all samples showed that diamond crystal structures had obvious variation in each sample. These results indicated that positron annihilation spectroscopy was an effective means to measure microstructure of diamond films.     

Investigation on the electron-beam curing of vinylester resin

A typical vinylester resin, Derakane 411-350, was electron-beam (EB) cured without initiators. The curing process was investigated by gel-fraction testing, FTIR and Raman spectroscopies. Both dynamic numerical analysis and positron annihilation life spectroscopy were utilized to analyze the microstructure of resin samples irradiated with different doses and dose rates. Resin irradiated with the same dose at a low dose rate achieved a higher degree of cure than those samples irradiated with a high dose rate. Resin irradiated with low dose rates had a lower free-volume fraction with smaller interstices and a more uniform microstructure. The glass-transition temperature of the resin increased with increasing irradiation dose. The mechanical properties of the EB-cured resin confirmed the analysis of changes in microstructure arising from irradiation.     

Effect of Surface Decoration of CNTs on the Interfacial Interaction and Microstructure of Epoxy/MWNT Nanocomposites

Epoxy resin nanocomposites with different contents of multiwalled carbon nanotubes (MWNTs) are prepared. The interaction between MWNTs and the epoxy resin matrix and the microstructure and mechanical properties of the composites are systematically investigated by Fourier‐transform infrared (FTIR) spectroscopy, transmission electron microscopy, scanning electron microscopy, and positron annihilation technology. FTIR spectra reveal that two kinds of hydrogen bonds exist at the interface for the nanocomposites modified by amine, one between the epoxy group on the side chain and the NH group, and the other between the epoxy group on the alicycle and the NH group. Compared to unmodified MWNT composites, the modified MWNT composites possess better mechanical properties, which are attributed to stronger interfacial interaction resulting from an efficient load transfer from matrix to MWNTs. Positron annihilation lifetime spectroscopy is used to characterize the microstructure of the epoxy/MWNT composites. The subtransition and glass transition temperatures are determined by finite‐term positron lifetime analysis and the variation of the free‐volume size as a function of temperature. Shifts of structure transition temperatures of the composites are observed with increasing MWNT weight content. Interestingly, the continuous lifetime analysis reveals the existence of two long‐lived lifetime components above the glass transition temperature, which may be attributed to the formation of local ordered regions related to the packing density of chains.     

Copolyimides containing alicyclic and fluorinated groups: Characterization of the film microstructure

The microstructures of a series of copolyimide films were characterized with different experimental methods such as density measurements, X‐ray diffraction, ultraviolet‐visible spectrophotometry, positron annihilation spectroscopy, and dynamic mechanical analysis. The experimental data were linked to the chemical structures of the polymers and especially the alicyclic and fluorinated monomers. Some analysis responses were directly dependent on the fluorine atoms and, therefore, did not provide clear information about the microstructures. The chain organization in the amorphous films appeared to be significantly dependent on the effect of the casting solvent. The influence of the alicyclic group content was quite significant for a nonsubstituted diamine but was strongly attenuated with a fluorinated diamine. © 2003 Wiley Periodicals, Inc. J Polym Sci Part B: Polym Phys 41: 2998–3010, 2003     

Investigation of structural transformation in ripening cotton fiber by the methods of positron annihilation

The microstructure of cotton fiber (sort 175-F, 4 type) at various ripeness stages has been investigated by measuring the spectra of positron life-time and the angular correlation of annihilation radiation. It has been established that the macro strength (breaking load) depends on the concentration and sizes of microdefects (radius less than 10 Å) in amorphous interfibrillar areas. These defects can be studied by registering the characteristics of positron and positronium atom decay and which are hard to reach by traditional physical methods for the analysis of the cotton fiber structure.     

Study of electrical,mechanical, and nanoscale free‐volume properties of NBR and EPDM rubber reinforced by bentonite or kaolin

The effect of Na bentonite, Ca bentonite, and kaolin fillers on the macrostructure and microstructure of acrylonitrile butadiene rubber, ethylene propylene diene rubber, and their blend (50/50) was studied through electrical and mechanical measurements, as well as with positron annihilation lifetime spectroscopy. The real part of permittivity (ε′), dielectric loss (ε″), and the crosslinking density were found to increase with increasing filler content. The increase of crosslinking density of the blend with increasing amount of fillers reflects a decrease in the equilibrium swelling up to 21.50 wt % compared with that of the unfilled blends. The mechanical investigation showed pronounced increase in the tensile strength, and in elongation at break with the addition of up to 21.50 wt % of filler. In addition, comparing between different fillers showed that the reinforcing effect of Na bentonite is more effective than Ca bentonite and kaolin but the physico‐mechanical of Ca bentonite is less than that for kaolin. The positron annihilation lifetime measurements revealed that the free‐volume properties were strongly affected by the amount and type of filler, in particular, the free‐volume fraction was dramatically decreased with increasing filler content. Furthermore, correlations were made between the free‐volume parameters and both electrical and mechanical properties. © 2009 Wiley Periodicals, Inc. J Polym Sci Part B: Polym Phys 47: 1825–1838, 2009     

Study of annihilation processes of positrons in polystyrene-related polymers

The positrons injected into a polymer annihilate with electrons through several kinds of processes influenced by environmental conditions. The AMOC is an appropriate method to investigate the influences of functional groups in polymer on positron and positronium annihilation process. The experiments were performed for polystyrene-related materials. The results showed that the S-parameters relating to ortho-positronium were higher than those relating to free annihilation in all samples and the annihilation process was affected by functional group.