Structural changes during photodegradation of poly(ethylene terephthalate)

An investigation has been conducted into the effects of photodegradation on the structure of poly(ethylene terephthalate) (PET). Films, with and without ultraviolet absorbers and prepared by biaxial orientation after extrusion, have been exposed in the laboratory for periods of up to 1020 hours. The samples were investigated by differential scanning calorimetry (DSC), X-ray diffraction and size exclusion chromatography. The appearance of a cold crystallization peak during DSC heating scans was noted for exposed samples and this was considered to be a result of released molecules in the amorphous region that could rearrange into a crystalline phase. From X-ray analysis, a loss of crystalline orientation was observed after degradation and an interpretation was given based on relaxation in the mesophase region. In samples containing the photostabilizer additive the magnitude of changes in structure was lower, possibly due to segregation effects during film production making the non-crystalline region relatively immune to degradation effects.     

Influence of 60Co γ-Ray irradiation on the morphology of crystalline polyethylene studied by high-resolution solid-state 13C NMR

The relationship and influence of varying ⁶⁰Co -ray irradiation doses, in the range 0.77–5.2 MGy, on the morphology of polyethylene have been investigated using high-resolution solid-state ¹³C nuclear magnetic resonance analyses through variation of different phase components, T _1c, T _2c relaxation parameters, and line width. The cross-linking in the irradiated polyethylene takes place mainly in the non-crystalline regions. However, distortion and damage to the folded chain of the crystal lattice are observed in the crystalline regions. For the interfacial phase, both cross-linking and distortion could occur. As a result, part of the crystalline component transformed into a non-crystalline one. It was also found that the orthorhombic crystalline lattice transformed into a monoclinic one within the crystalline phase in polyethylene under higher doses of irradiation.     

Impurities in phthalocyanines and structural modifications induced during thih-film deposition

The impurity contents of H₂Pc, CuPc and FePc powders have been determined by neutron activation analysis. It is shown that H₂Pc contains a much higher amount of impurities than expected, especially highly conducting iodine. Their contents are only slightly decreased by annealing in air at 300°C for 2 h. The X-ray diffraction spectrum of H₂Pc indicates that the iodine and calcium containing impurities are partially crystalline. Vacuum evaporation and plasma discharge deposition of H₂Pc yield almost non-crystalline phthalocyanine which is not modified by subsequent annealing at 300°C. These two thin-film deposition techniques also significantly reduce the degree of crystallinity of the impurities. The influence of the impurities and the specific crystalline structures on the electrical properties of phthalocyanines is also briefly discussed.     

STM研究光盘材料结构转变前后表面形貌的分形维数

采用ＳＴＭ在纳米尺度上对光盘材料结构转变前后表面微观形貌进行了研究，ＳＴＭ结合图象处理和傅利叶分析法可以较好地用于研究薄膜表面形貌的分形特征，用电子束蒸发制备的无定形态记录介质薄膜表面形貌在纳米尺度上呈现出分形特征，经加热晶化后介质薄膜发生结构转变，表面形貌的分形维数增加。     

影响聚丁二酸丁二醇酯降解性能的因素

以氢氧化钠溶液为媒介,研究了分子量、结晶度等因素对聚丁二酸丁二醇酯（PBS）降解性能的影响,并对其降解机理进行了初步探讨。结果表明,PBS的降解性能不仅与结晶度有关,还受到内部球晶形态的影响;分子量仅对降解初期有较大影响,并且随着分子量的增加,降解速率下降不明显。试样降解前后的凝胶渗透色谱（GPC）和差示扫描量热分析（...     

加工工艺对n-HA/PA66复合材料结晶行为和力学性能的影响

采用X射线衍射、差示量热分析和常规力学性能等测试方法研究了纳米羟基磷灰石增强聚酰胺66(n- HA/ PA66) 复合材料在不同加工条件和后处理工艺下的结晶行为和力学性能。结果表明, 提高样品的退火温度会降低纯PA66 及其复合材料中PA66 的结晶峰强度。在n- HA/ PA66 复合材料中, 基体树脂PA66 的α晶体中只有α2 的结晶峰存在,α1 的结晶峰基本消失。提高复合材料的注射压力, PA66 结晶峰的强度降低, 结晶度增加; 退火温度对材料的结晶度没有明显的影响。复合材料的结晶行为与其力学性能之间有着紧密的联系。      

Mechanical properties of blends of poly(methyl methacrylate) and poly(vinylidene fluoride)

The mechanical properties of blends of the crystallizable polymer poly(vinylidene fluoride) and the amorphous material poly(methyl methacrylate) have been investigated as a function of composition both for glassy amorphous materials and for partially crystalline materials. The data obtained were interpreted in terms of the molecular and super-molecular structure of the blends and in terms of their dynamic properties.The main conclusions were that the mechanical properties are not strongly dependent on details of the distribution of the two components in the material nor on the crystal modifications present. The mechanical properties were found to depend primarily on the location of the glass transition temperature relative to the elongation temperature and on the presence or absence of crystalline regions. The degree of crystallinity was found to play an important role in determining the properties only at lower values of this quantity. The advantage of these blends is that the important parameters, namely, the degree of crystallinity and the location of the glass transition temperature, can be adjusted at will by varying the composition appropriately. This allows well-defined variations of the mechanical properties to be achieved.     

Low temperature synthesis and visible light driven photocatalytic activity of highly crystalline mesoporous TiO2 particles

Mesoporous TiO2 powder materials with a high crystallinity have been prepared by evaporation induced self assembly (EISA) process using titanium tetraisopropoxide (TTIP) and pluronic P123 surfactant (EO20PO70EO20) as titanium source and structure-directing reagent, respectively. The prepared materials were characterized by low and wide-angle X-ray diffraction (XRD), scanning electron microscopy (SEM), transmission electron microscopy (TEM), optical absorption, and N2 adsorption-desorption experiments. The crystallinity of the materials was controlled by varying the calcination temperature. The resulting TiO2 materials showed highly crystalline structure with uniform particle size which increases from 11.8 to 23.8 nm with increasing the calcination temperature from 400 to 600 degrees C, respectively, whereas the specific surface area decreases from 125 to 40 m2/g. TEM and XRD results revealed that the calcination temperature of 600 degrees C is the best condition to obtain highly crystalline mesoporous TiO2. The photocatalytic activity of the TiO2 mesoporous materials with different crystallinity and textural parameters has been studied in the decomposition of methylene blue (MB) dye molecules under visible light irradiation. Among the mesoporous TiO2 materials studied, the material with the highest crystallinity, prepared at 600 degrees C, showed the best photocatalytic performance in the decomposition of MB under visible light in a short time.     

Estimation of crystallinity in isotropic isotactic polypropylene with Raman spectroscopy

The Raman spectrum of isotactic polypropylene (iPP) has been found to exhibit vibrational peaks in the region of 750 to 880 cm(-1) that are sensitive to the degree of crystallinity. These features are broadly assigned to various modes of methyl group rocking, rho(CH2), and there have been various attempts to assess crystallinity based on the integrated intensities of these bands. Various vibrational analyses performed in the past in combination with experimental studies have concluded that the presence of crystalline order with trans-gauche conformation gives rise to a peak at 809 cm(-1), which is assigned to a rho(CH2) mode coupled with the skeletal stretching mode. However, the presence of additional peaks at 830 cm(-1), 841 cm(-1), and 854 cm(-1), within the same envelope, have been the subject of controversy. In this work isotropic films of iPP derived from the same precursor of identical tacticity have been subjected to various degrees of annealing and the integrated intensities of the Raman bands were measured. The results showed that true 3d crystallinity in isotropic iPP can only be expressed by the 809 cm(-1) band whereas the band at 841 cm(-1) corresponds to an uncoupled rho(CH2) fundamental mode and thus is a measure of the amorphous content. The less intense satellite bands at 830 cm(-1) and 854 cm(-1) of solid iPP cannot be distinguished from the 841 cm(-1) band in the melt and are generally considered as intermediate phases possibly related to non-crystalline components with 3(1)-helical conformations. Independent differential scanning calorimetry (DSC) crystallinity measurements were in broad agreement with the Raman measurements based on the normalized intensity of the 809 cm(-1) Raman band. By comparing the Raman with the DSC data a new value for the theoretical heat of fusion for the 100% crystalline iPP has been proposed.     

A Highly Crystalline Perylene Imide Polymer with the Robust Built-In Electric Field for Efficient Photocatalytic Water Oxidation

A highly crystalline perylene imide polymer (Urea-PDI) photocatalyst is successfully constructed. The Urea-PDI presents a wide spectrum response owing to its large conjugated system. The Urea-PDI performs so far highest oxygen evolution rate (3223.9 µmol g⁻¹ h⁻¹) without cocatalysts under visible light. The performance is over 107.5 times higher than that of the conventional PDI supramolecular photocatalysts. The strong oxidizing ability comes from the deep valence band (+1.52 eV) which is contributed by the covalent-bonded conjugated molecules. Besides, the high crystallinity and the large molecular dipoles of the Urea-PDI contribute to a robust built-in electric field promoting the separation and transportation of photogenerated carriers. Moreover, the Urea-PDI is very stable and has no performance attenuation after 100 h continuous irradiation. The Urea-PDI polymer photocatalyst provides with a new platform for the use of photocatalytic water oxidation, which is expected to contribute to clean energy production.     

熱處理影響碳黑/聚乙烯復合材料導電性之探討

針對碳黑填充聚乙烯復合材料進行實難的結果發現,通合的時效熱處理可使材料的電阻有效地降低至底值.經過輻射的材料若加熱至高于聚乙烯熔點的温度,并再進行時效熱處理,會使材料的電阻出現跳升的現象,而且電阻跳升的程度與材料中的碳黑種類有關.若于輻射之前實施材料的時效熱處理,這對電阻跳升的程度并無明顯的影響.     

熱處理影響碳黑/聚乙烯復合材料導電性之探討

針對碳黑填充聚乙烯後合材料進行實驗的結果發現,適合的時效熱處理可使材料的電阻有效地降低至底值.經過輻射的材料若加熱至高于聚乙烯熔點的温度,并再進行時效熱處理,會使材料的電阻出現跳升的現象,而且電阻跳升的程度與材料中的碳黑種類有關.若于輻射之前實施材料的時效熱處理,這對電阻跳升的程度并無明顯的影響.     

直立式医用聚丙烯输液瓶的熔融行为和结晶结构

利用DSC和W AXD研究了医用聚丙烯专用料(TPC)及其密封式直立吹塑瓶(TPCC)的熔融行为和结晶结构。结果表明经过吹塑成型过程后,TPCC的熔融温度、结晶度均较TPC有所提高,DSC熔融半峰宽明显下降,微晶尺寸明显增大,同时晶面取向因子发生显著变化,表明成型过程中晶区尺寸增大,且晶体结构更均匀规整,赋予了输液瓶良好的性能。     

碳原料结构对激光法合成纳米金刚石的影响

为了确定在较低激光能量密度下（10^6W／cm^2）激光法合成纳米金刚石最适宜的碳原料，研究了三种结构不同的碳原料（炭黑、片状石墨、土状石墨）对合成纳米金刚石的影响，采用拉曼光谱对碳原料的结构进行了分析，结果显示炭黑、土状石墨和片状石墨这三种碳原料的结晶程度依次增强，用Nd：YAG脉冲激光分别轰击不同碳原料的悬浮液，实验产物的透射电镜分析显示在激光照射炭黑和片状石墨的产物中没有金刚石生成，而在激光照射石墨的产物中发现了立方结构的金刚石，其颗粒尺寸约为5Bin．因此，在10^6W／cm^2的脉冲激光作用下，无序炭黑和结晶较完整的片状石墨均不利于合成金刚石，只有有序化程度适中的土状石墨有利于合成金刚石．     

Hydrogen in semiconductors

Hydrogen in crystalline semiconductors has become a recent curiosity because of its high diffusivity and strong chemical activity in such materials. In contrast to the proton motion in ionic materials which gives rise to an enhanced conductivity, hydrogen in electronic materials interact with structural disorders and chemical impurities to control the electronic flow. Deep gap states in crystalline semiconductors due to various disorders such as surface/interface, grain boundaries, dislocations, irradiation and implantation damage etc. have been removed due to hydrogen bondings. Hydrogen incorporation is done by plasma and direct ion beam hydrogenation methods, implantation technique and by a novel technique of damage free introduction. The most studied materials are silicon and gallium arsenide.I - V,C - V, DLTS and IR studies have been carried out on hydrogenated semiconductors to characterize the electronic flow, gap states and the nature of chemical bonds. Improvement in ideality factors of diodes, reduction in free carrier concentration, removal or reduction of deep states and appearance of new bondings such as Si-H, P-H, B-H etc. have been observed from various techniques. The present paper reviews the various features of hydrogenation studies in crystalline silicon and gallium arsenide and highlights our results of hydrogenation studies on Pd/semiconductor devices.     

Pulse Heating as a Tool to Study the High-Temperature Properties of Unstable Liquids

The method of controlled pulse heating of a wire probe in good contact with a liquid has been developed for estimation of the thermophysical properties in the region of instability of this liquid with respect to the temperature and the heat flux. It ensures rapid penetration into the region of short-lived states and maintenance of a given temperature in this region. This paper presents and discusses the character of variations of the values of the thermal activity and the lifetime of a system, before its disintegration, for thermally unstable liquids, such as polymeric and microheterogeneous systems, for different heating paths.     

Temperature-dependent properties of FePO4 cathode materials

The temperature of formation and crystallinity of iron phosphate, FePO₄, is critical in determining its electrochemical behavior in lithium cells. Amorphous FePO₄ formed by heating amorphous iron phosphate dihydrate was found to have good capacity both in chemical and electrochemical lithiation. Initial capacities of up to 140 mAh/g were obtained at a current density of 0.2 mA/cm². Material formed from crystalline iron phosphate dihydrate was found to be much less active, due to both the crystallinity of the product and to the iron being in tetrahedral coordination. The trigonal quartz phase of FePO₄ loses almost all capacity after heating to 700°C, which might be due to glass formation on the surface.     

Nanostructural metallic materials: Structures and mechanical properties

The trade-off of strength and ductility of metals has long plagued materials scientists. To resolve this issue, great efforts have been devoted over the past decades to developing a variety of technological pathways for effectively tailoring the microstructure of metallic materials. Here, we review the recent advanced nanostructure design strategies for purposely fabricating heterogeneous nanostructures in crystalline and non-crystalline metallic materials. Several representative structural approaches are introduced, including (1) hierarchical nanotwinned (HNT) structures, extreme grain refinement and dislocation architectures etc. for crystalline metals; (2) nanoglass structure for non-crystalline alloys, i.e. metallic glasses (MGs); and (3) a series of supra-nano-dual-phase (SNDP) nanostructures for composite alloys. The mechanical properties are further optimized by manipulating these nanostructures, especially coupling multiple advanced nanostructures into one material. Particularly, the newly developed SNDP nanostructures greatly enrich the nanostructure design strategies by utilizing supra-nano sized crystals and MGs, which exhibit unique size and synergistic effects. The origins of these gratifying properties are discussed in this review. Furthermore, based on a comprehensive understanding of microscopic mechanisms, a broad vision of strategies towards high strength and high ductility are proposed to promote future innovations.     

Diverse effects of microwave heating on anatase crystallization in ionothermal synthesis of nanostructured TiO<Subscript>2</Subscript>

This article examines anatase crystallization in the ionothermal synthesis [sol gel method in the presence of ionic liquid (IL)] of nanostructured TiO₂ under microwave (MW) irradiation. MW heating can lead to rapid temperature increase of chemical reactions. In this study, we found that rapid temperature increasing effects on anatase crystallization were diverse and dependent on initial water concentration, MW irradiation time, and IL concentration. The results indicated that higher anatase crystallinity was obtained at high water amount irrespective of IL concentration. However, at lower water amounts, higher anatase crystallinity occurred only when MW heating was applied after the mixtures reacted for certain duration, especially at lower initial temperature and at a specific IL concentration. Different MW heating effects on the hydrolysis–condensation reaction and the post-treatment stage under MW/IL conditions can explain this diversity. Heating characteristics of IL/water mixtures under MW irradiation were also discussed.     

The tensile deformation of flax fibres as studied by X-ray scattering

Small and wide-angle X-ray scattering experiments with in-situ deformation of dry flax fibres have been carried out. An increase in the (200) peak intensity during deformation has been attributed to strain-induced crystallisation of the cellulose microfibrils, and provides evidence that the non-crystalline cellulose chains are initially oriented. However, no change in the equatorial small-angle streak (from cellulose microfibrils), the meridional reflection (from a crystalline/non-crystalline repeat along the fibre), or the microfibril orientation was seen.