X射线小角散射研究碳纤维原丝预氧化过程中的微孔结构

本文利用X射线小角散射(SAXS)研究碳纤维原丝预氧化过程中微孔的变化。计算出随着预氧化过程中牵伸比的加大, 预氧化丝中微孔结构的变化。预氧化丝中的微孔大多是一些长条状微孔, 并且取向趋向于纤维轴方向。碳纤维中的微孔对于其模量有着重大影响, 因而对于碳纤维以及其原丝中微孔结构的研究有着重要的意义。     

二维多丝室探测器读出方法的优化

中国散裂中子源将建设一台基于~3He气体的二维多丝室,作为多功能反射谱仪束线的中子探测器.基于已有的研究,为优化选择二维多丝室探测器的丝结构,本文研究了三种不同的丝结构,并采用重心读出方法和数字读出方法进行了探测器的性能测量,得到了满足多功能反射谱仪探测器需求的读出方法.实验结果表明:对同种丝结构的二维多丝室探测器,重心读出方法的位置分辨和成像性能都好于数字读出方法;基于重心法读出的多丝室探测器位置分辨率可以达到约160μm,基于数字读出方法的多丝室探测器位置分辨率可以达到约400μm.优化设计的丝结构为:基于重心读出法的阳极丝间距1.5 mm、读出通道间距4 mm,基于数字读出法的阳极丝间距1.5 mm、读出通道间距2 mm.优化设计的丝结构均能满足谱仪的位置分辨要求.     

介质阻挡放电丝结构转变中的缺陷研究

在介质阻挡放电中,对放电丝结构从四边形向四边形格子态结构转变中的缺陷进行了研究.实验发现,在四边形向四边形格子态结构的转化中,存在两种缺陷:角缺陷及错位缺陷.为了研究缺陷的形成机理,实验测量了四边形格子态结构中不同放电丝的发光信号,结果发现八边形晶胞的中心放电丝发光强度强于边缘放电丝发光强度.通过引入准势场,研究了放电丝之间的相互作用及其对放电丝结构转变的影响,并由此分析了在转变过程中出现的缺陷,结果与实验符合得很好. 关键词： 介质阻挡放电 角缺陷 错位缺陷 超四边格子态     

取向玻璃体系中分子之间取向关联的模型化及其模拟与分析

提出了一个描述取向玻璃系统中分子间取向关联的有效键模型.基于该模型对该系统中分子之间取向关联的拓扑结构进行了计算机模拟.结果表明当成键概率较小时,成键分子大部分以分子串的形式出现,并基于概率分析对此现象进行了解释.深入地,用分子串模型对模拟结果进行了分析,并且基于分析结果讨论了分子串模型的合理性和可行性. 关键词： 玻璃化转变 取向玻璃 拓扑结构 分子串模型     

LC共振型巨磁阻抗效应的研究

采用化学镀方法成功制备了自带电容构成LC共振回路的CoP/Insulator/BeCu复合结构丝.研究了这种新型复合结构丝产生LC共振型巨磁阻抗效应的特征,长度为lm=9.5cm的复合结构丝,当驱动电流频率为LC共振频率fr=29.0MHz时,LC共振型巨磁阻抗效应为487.5%,磁场灵敏度为0.46%/A·m-1,大于常规复合结构丝;远离此频率时的巨磁阻抗效应很小,巨磁阻抗效应表现出很好的频率选择特性.根据LC共振型复合结构丝的特征建立了等效电路模型,采用等效电路模型对这种复合结构丝进行了数值模拟,等效电路的数值计算与实验测量结果符合较好.从等效电路角度分析了LC共振型巨磁阻抗效应产生的机理,以及复合结构丝的长度对LC共振型巨磁阻抗效应的影响.     

介质阻挡放电中的局域态六边形结构

在氩气介质阻挡放电中得到了稳定的局域态六边形结构，并对其进行了时空动力学的测量.发现位于中心的放电丝的放电时刻总是领先，相邻两次放电的时间间隔表现出长短交替的周期性.利用壁电荷放电模型对上述结果进行了分析，表明微放电丝在放电过程中不仅受自身场的作用，还受到周围其他微放电丝的影响. 关键词： 介质阻挡放电 壁电荷 自组织 局域态结构     

BESⅢ漂移室单元结构和丝层安排的设计与优化

介绍了BES Ⅲ漂移室单元结构的设计和丝层安排，讨论了如何设置斜丝倾斜角以及直、斜丝交界处存在的问题，并通过对漂移时间与距离关系的模拟优化了漂移室丝层半径.     

同心旋转圆柱间隙流场中纤维取向的动态模拟

本文对两同心旋转圆柱间隙形成的流场以及处于流场中的纤维运动和取向进行了数值研究. 在贴体坐标网格下求解了流场控制方程, 得到了流场中的速度、压力等物理量. 研究了两同心圆柱同速反向旋转以及仅内层圆柱旋转这两种情况下的纤维运动和取向状态. 得到了处于这两种情况下的纤维在流场中从静止到开始运动和取向直至最终达到稳定状态的动态详细过程. 结果表明, 当两个圆柱同速反向旋转时, 纤维运动与取向也相应的呈现两层结构; 而仅内圆柱旋转时, 纤维运动与取向呈单层结构. 在两种情况下, 纤维均沿流线方向运动和取向. 讨论了纤维长径比对纤维取向的影响, 结果表明随着纤维长径比的增加, 纤维沿流线取向的取向度逐渐增强.     

介质阻挡放电中放电丝结构相变过程研究

在氩气和空气混合气体介质阻挡放电中,研究了放电丝结构随外加电压及气体压强的变化,并从二维体系相变的角度进行了分析.随着电压的增加,放电丝结构的演变过程为:稀疏的随机放电丝—稠密的随机放电丝—六边形结构—超六边形结构—混沌态,此过程相应于二维体系的气相—液相—简单晶体—超点阵晶体—液相的相变过程.实验还研究了相变过程中超六边形形成中晶格常数及相邻格点间距离的变化、超六边形结构中大点的形成过程以及超六边形结构的Penta-Hepta缺陷.     

动态光散射和透射电镜法研究pH和NaCl对 丝胶蛋白微观结构的影响

应用近红外光谱法、动态光散射法及透射电镜扫描法,研究了pH和NaCl浓度对丝胶蛋白聚集微观结构的影响。近红外光谱显示丝胶蛋白在酰氨Ⅰ带1 700～1 600 cm-1附近有较强吸收峰。通过zeta电势法测定丝胶蛋白的表观等电点为pH 3.7。应用动态光散射法测定了在不同pH和NaCl浓度下丝胶蛋白颗粒的分散粒径,pH 4及高NaCl浓度时,丝胶蛋白聚集颗粒粒径大且分散系数大;pH 3或pH 8及低NaCl浓度时丝胶蛋白聚集颗粒粒径和分散系数相对较小。采用透射扫描电镜观察丝胶蛋白在pH 3或pH 8条件下聚集形成松散的松针状微观结构,在pH 4或者高NaCl浓度下会聚集形成相对紧密的微观结构。pH 4时可以观察到丝胶蛋白的椭圆形单聚体大小约为(60±6)nm(n=10)。并探讨了静电斥力、氢键和范德华吸引力对丝胶蛋白微观结构形成的影响,为丝胶蛋白作为生物材料的应用提供了理论依据。     

IR—ATR法研究聚对苯二甲酸乙二酯三维卷曲中空纤维的取向

应用红外衰减全反射法考察了聚对苯二甲酸乙二酯三维卷曲中空纤维在加工过程中的结构和取向的变化。结果表明，此种ＰＥＴ中空纤维中，其羰基倾向生趣于纤维表面的取向。     

Structure Formation of Blend and Sheath/Core Conjugated Fibers in High-Speed Spinning of PET,Including a Small Amount of PMMA

The blend of poly(ethylene terephthalate) (PET) and a small amount of polymer that has higher T _g than PET, such as polymethylmethacrylate (PMMA)—and is dispersed finely as immiscible particles in PET—exhibits lower molecular orientation than pure PET under high-speed fiber spinning. To obtain insight into the mechanism of the lower molecular orientation of the blend fiber, the sheath/core structure of PET (sheath)/PMMA (core) conjugated fiber (the same PET/PMMA weight ratio as in the blend fiber), was produced as a model. The thinning profile of the fiber diameter along the spinning line and the birefringence distribution of the cross-section were examined and compared among pure PET fiber, the conjugated fiber, and the blend fiber. The conjugated fiber had the lowest molecular orientation of PET in the sheath part, and its thinning process was accelerated similar to the blend fiber. As a result of the distribution of molecular orientation across the diameter of the conjugated fiber, it is considered that PMMA, having the high T _g , tends to solidify at a higher temperature (upstream) than PET in the thinning process, making the flow of PET accelerate as if it was pushed by PMMA. This causes the maximum dv/dx just before the solidification point to be smaller; therefore, the lower spinning stress, resulting in smaller birefringence of PET, can be considerable. This acceleration was generated at the interface of PET and PMMA, and spread toward the fiber surface as both polymers were thinning in elongational flow (in melt). On the other hand, close to the interface, molecules of PET were stretched by PMMA, resulting in an increase of birefringence. Such discussion is also considered to apply to the blend fiber. However, because the blend fiber had a significantly larger interface area compared with the conjugated fiber, it is considered that the increase of birefringence of PET by the interface drag force cannot be neglected. The larger particles of PMMA dispersed in PET results in the lower birefringence of PET that is supported by the elongation effect (i.e., the interface drag force).     

Miscibility and Hydrogen Bonding Interactions in Blends of Poly(hydroxyether ketone) and Poly(4-vinyl pyridine)

The influence of silica nanoparticles on the tensile properties of poly(ethylene terephthalate)(PET) fibers was investigated. The results showed that mechanical properties of PET fibers were improved through nano‐silica incorporation. Two maxima of the modulus‐strain curves of PET/silica nanocomposites (PETS) fibers are always higher than those of pure PET (PET0) fibers. The results of microstructure investigations suggested that the amorphous orientation factor of PETS fibers is higher than that of PET0 fibers. It is suggested that the increase of amorphous orientation factor contributed to the improvement of tensile properties of PET fibers. Considering the difference in modulus‐strain curves of PET0 and PETS fibers, it is believed that the addition of nanoparticles not only improved the amorphous orientation factor but also changed the load units of PET fibers when strained, which also resulted in the improvement of tensile properties.     

Influence of laser irradiation on the optical and structural properties of poly(ethylene terephthalate) fibres

Laser irradiation has been previously investigated for achieving uniform heating of polyethylene terephthalate (PET) fibres in the hot-drawing stage of the production process, so as to obtain better fibre mechanical properties. The optical properties and dye uptake of PET fibres also depend on the polymer chain orientation and crystallinity within the fibre structure. This paper reports an investigation of a concept whereby laser irradiation and interferometry could be used to modify and trace a small change in the optical properties of a PET monofilament fibre, but the corresponding change in the dye uptake would not be detected visually. A copper vapour laser (550-580 nm wavelengths) was used to expose consecutive 4 mm lengths along a running length of monofilament to 39.8 W cm⁻², at a pulse rate of 9.89 kHz in order to modify, in a controlled way, the polymer crystallinity and orientation. A 3D finite element simulation, based on uncoupled heat-transfer analysis, indicated that rapid heating and cooling could be obtained with the laser to give the small changes required. Irradiated and untreated samples were analysed by interferometry and a 0.16% change was detected in the birefringence profiles, corresponding to a small reduction in the degree of orientation and crystallinity of the irradiated samples. Density measurements and wide-angle X-ray scattering (WAXS) analysis confirmed the change in crystallinity. Tests conducted for dye adsorption and tensile strength showed a small increase in the former and only a very small decrease in the latter. It was concluded that these changes in property provide the opportunity for a laser-irradiated PET monofilament fibre to be used as a subtle tracer element in brand labels for textile garments as an anti-counterfeit measure.     

Uniformity analysis of dielectric barrier discharge (DBD) processed polyethylene terephthalate (PET) surface

A dielectric barrier discharge (DBD) plasma, operating in air at atmospheric pressure, has been used to induce changes in the surface properties of polyethylene terephthalate (PET) films. The effects that the key DBD operating parameters: discharge power, processing speed, processing duration, and electrode configurations, have on producing wettability changes in the PET surface region have been investigated. The approach taken involves the application of an Taguchi experimental design and robust analysis methodology. The various data sets obtained from these analyses have been used to studies the effect of the operating parameters on the surface uniformity and efficiency of the said treatment.In general, the results obtained indicate that DBD plasma processing is an effective method for the controlled surface modification of PET. Relatively short exposures to the atmospheric pressure discharge produces significant wettability changes at the polymer film surface, as indicted by pronounced reductions in the water contact angle measured. It was observed that the wettability of the resultant surface shows no significant differences in respect to orientation parallel (L-direction) or perpendicular (T-direction) to the electrode long axis. However, there was significant differences between the data obtained from these two orientations. Analysis of the role of each of the operating parameters concerned shows that they have a selective effectiveness with respect to resultant surface modification in terms of uniformity of modification and wettability. The number of treatment cycles and the electrode configuration used were found to have the most significant effects on the homogeneity of the resultant PET surface changes in L- and T-orientation, respectively. On the other hand, the applied power showed no significant role in this regard. The number of treatment cycles was found to be the dominant factor (at significance level of 0.05) in respect of water contact angle changes at the processed PET surface in both orientations. The driven metal electrodes (stainless steel or aluminium) were apparently superior to the driven dielectric electrode (ceramic or quartz) configurations. The grounded electrode in each case was a silicon rubber-covered aluminium plate (see later). The nature and scale of the surface changes that originate from the various processing conditions employed have been considered so as to determine the optimum treatment conditions in respect of processing outcomes, properties and any orientation dependence. Thus, it was revealed that higher processing speeds and longer processing durations are key for uniformity along the electrode axial orientation, while lower processing speeds and short exposure durations are key considerations, in the corresponding perpendicular orientation. In general, longer processing durations (low processing speeds and a high number of treatment cycles) and higher plasma powers induced greater changes in the surface wettability of the PET, as demonstrated by the observed water contact angles. This behaviour is taken to indicate that different combinations of DBD operating parameters and electrodes produce discharge conditions that can result in different plasma chemical processes in respect of uniformity, treatment efficiency and orientation dependence.     

Mechanical Behavior of Bulk Poly(Ethylene Terephthalate) Subjected to Simple Shear

Abstract

Mechanical behavior of bulk semicrystalline poly(ethylene terephthalate) (PET) processed through simple shear is investigated. The equal channel angular extrusion (ECAE) process was used to achieve the simple shear condition. The PET samples were processed in one and two ECAE passes in the same direction, with the sample rotated 180° about the extrusion axis for the second pass. Microstructural features at the nanometer and micrometer scales were studied by small‐angle x‐ray scattering (SAXS) and scanning electron microscopy (SEM). SAXS results showed that at the nanometer scale, two types of lamellar orientations are induced in both samples, but with different extents of orientation. In the ECAE‐oriented PET structures on the micrometer scale, as revealed by SEM, are well‐defined macrofibrils. However, the fibrillar structures in the sample extruded once are more oriented than those in the sample extruded twice. Fractography investigations suggest that the ECAE‐induced fibrillar structure and stretched amorphous chains are responsible for the change in mechanical properties.     

Fabrication of high-performance supercapacitors based on transversely oriented carbon nanotubes

High-performance supercapacitors with organic electrolyte 1 M TEABF₄ (tetraethyl ammonium tetrafluoroborate) in PC (propylene carbonate) were fabricated and tested, based on multiwall carbon nanotubes (MWNTs) deposited by electrophoresis on three types of alternative substrates: aluminium foil, ITO (indium tin oxide) coated PET (polyethylene terephthalate) film and PET film. In all cases, SEM (scanning electron microscopy) and STEM (scanning transmission electron microscopy) micrographs demonstrated that protruding, transversely oriented MWNT structures were formed, which should increase the transverse conductivity of these MWNT electrodes. The best supercapacitor cell of MWNT electrodes deposited on aluminium foil displayed good transverse orientation of the MWNT structures as well as an in-plane MWNT network at the feet of the protruding structures, which ensured good in-plane conductivity. Capacitor cells with MWNT electrodes deposited either on ITO-coated PET film or on PET film demonstrated lower but still very good performance due to the high density of transversely oriented MWNT structures (good transverse conductivity) but some in-plane inhomogeneities. Capacitor cells with drop-printed MWNTs on aluminium foil, without any transverse orientation, had 16–30 times lower specific capacitance and 5–40 times lower power density than the capacitor cells with the electrophoretically deposited MWNT electrodes.     

高阻隔碳氢膜的制备及性能研究

利用射频等离子体化学气象沉积法（r.f.PECVD），在12μm厚的聚对苯二甲酸乙二醇酯 (PET)上制备了碳氢膜. 用原子力显微镜（AFM），x射线光电子能谱（XPS），激光拉曼光谱，傅里叶红外光谱等仪器，对碳氢膜的表面形貌和内部结构特性进行了较详细研究. 镀碳氢膜PET的阻隔性能在标准透水蒸气测试仪上进行检测. 实验结果证明：沉积工艺参数对碳氢膜的生长速率及结构性能有重要影响；在PET上沉积的是纳米碳氢膜，该膜主要由sp2和sp3杂化的碳氢化合物组成；当PET上碳氢膜厚度为900nm时，阻水蒸气性能可提高7倍. 关键词： 碳氢膜 射频等离子体化学气象沉积法 聚对苯二甲酸乙二醇酯 阻隔性能     

Deformation and annealing behavior. I. Polyethylene terephthalate films

The morphology and deformation behavior of uniaxially and biaxially oriented thin polyethylene terephthalate (PET) films was examined by bright field, diffraction and dark field electron microscopy. A large, 250-500 Å, nodule structure was observed under a variety of conditions, in addition to the smaller 75–100 Å nodules that have been reported previously. Dark field micrographs indicate that oriented PET, heat set at 180° to 240° C, is composed of small (140 Å) isometric crystallites, with a tendency to orient the 100 plane in the plane of the film. It is suggested that the nodular structure and small isometric crystallites may contribute to PET ductility at low temperatures.     

Effect of crystallographic orientation on the dislocation structure development in ion implanted Si

Transmission electron microscopy (TEM) has been employed to study the damage structure of P⁺-implanted (001) and (111) Si annealed in inert and oxidizing atmospheres. Both the dislocation structure composition and the density of misfit dislocations have been found to be strongly dependent upon the crystal orientation. Role of the crystal orientation in the dislocation structure development has been discussed.