纳米云纹法条纹倍增技术研究

提出了一种纳米云纹法的条纹倍增技术，可用于单晶材料纳米级变形测量.在测量中，单晶材料的晶格结构由透射电镜（TEM）采集并记录在感光胶片上作为试件栅，几何光栅作为参考栅.对纳米云纹条纹的形成原理，透射电镜放大倍数与试件栅的频率关系，条纹倍增技术，位移、应变测量方法等进行了详细讨论.该方法不仅能够测量连续力学参量，如应变和位移，而且能够表征纳观非连续参量，如位错、夹杂.     

Characterization of Brazilian Peat Samples by Applying a Multimethod Approach

Peat is a mixture of compounds formed by the decomposition of plant residues and mineral materials that have accumulated at the bottom of ponds and flooded depressions in riverine areas. Due to their extreme heterogeneity and natural variety, the physical and chemical properties of peat can vary widely within or between deposits, and the characterization of isolated samples is still a challenging task that requires the combination of several chemical and spectroscopic methodologies. In this study, the structural characteristics of two Brazilian peat samples were evaluated using scanning electron microscopy (SEM), elemental (CHNS-O) and thermal (TGA) analysis, X-ray diffraction (XRD), and infrared (FT-IR) and solid-state ¹³C-nuclear magnetic resonance (¹³C-NMR) spectroscopies. Although the samples originated from the same peatland, the data showed that the studied samples have distinct chemical properties and that the stage of decomposition played an important role in the differences observed.     

微纳尺度俄歇电子能谱新技术开发及其应用进展

随着纳米结构材料的广泛应用,新型微纳尺度表征技术成为纳米科学技术发展的重要途径。本文基于局域电子信息全面性的思想,从俄歇电子能谱的原理出发,理论推导出俄歇价电子能谱的简明表述方式,确定俄歇价电子能谱与微观电子结构信息的内在联系和物理意义,建立了俄歇电子能谱探测微区一系列宏观参量的新技术。其中应力测量技术的空间分辨率可优于20nm,为微纳尺度力学测量的发展提供了重要的方法;非接触性的局域电学性质测量技术,超越了传统电学测量方法的思想框架,实现了无外场驱动的电荷密度分布、电场分布等本征电学性质表征、以及半导体异质结构整个空间区域的能带构造;结构相的测定技术,使纳米微区材料的晶体结构相识别成为可能;半导体微区导电类型测定技术,延续了非接触性电学测量的优点,并且能够灵活地探测分析复杂光电器件结构中不同区域的导电类型分布。通过实际应用于侧向外延GaN不同区域、AlxGa1-xN/GaN超晶格量子阱结构、ZnO纳米颗粒等纳米尺度复杂体系的微区宏观性质探测,获得应力/应变、电荷密度/电场、结构相以及导电类型及其分布等结果,验证了所建立的测量技术的有效性和可靠性。     

微纳尺度俄歇电子能谱新技术开发及其应用进展

随着纳米结构材料的广泛应用,新型微纳尺度表征技术成为纳米科学技术发展的重要途径.本文基于局域电子信息全面性的思想,从俄歇电子能谱的原理出发,理论推导出俄歇价电子能谱的简明表述方式,确定俄歇价电子能谱与微观电子结构信息的内在联系和物理意义,建立了俄歇电子能谱探测微区一系列宏观参量的新技术.其中应力测最技术的空间分辨率可优于20 nm,为微纳尺度力学测量的发展提供了重要的方法;非接触性的局域电学性质测量技术,超越了传统电学测量方法的思想框架,实现了无外场驱动的电荷密度分布、电场分布等本征电学性质表征、以及半导体异质结构整个空间区域的能带构造;结构相的测定技术,使纳米微区材料的晶体结构相识别成为可能;半导体微区导电类型测定技术,建续了非接触性电学测量的优点,并且能够灵活地探测分析复杂光电器件结构中不同区域的导电类型分布.通过实际应用于侧向外延GaN不同区域、AlxGa1-xN/GaN超晶格量子阱结构、ZnO纳米颗粒等纳米尺度复杂体系的微区宏观性质探测,获得应力/应变、电荷密度/电场、结构相以及导电类型及其分布等结果,验证了所建立的测量技术的有效性和可靠性.     

High resolution digital holographic microscopy for the study of aggregated natural cellulose nanowhisker fibers

In this paper, digital holographic (DH) microscopy demonstrates its ability to perform a full characterization of nanofibers. The high resolution and magnification of the presented method to study the nanofibers are tested using standard MIL-STD-150A 1951 USAF resolution test target. In this investigation, aggregated natural cellulose nanowhisker fibers are positioned in the front of the microscopic objective using a 3D translation stage in the object arm of DH setup. The recorded off-axis holograms are refocused using the angular spectrum method. The reconstructed complex field is used to calculate optical phase and intensity distributions of the object at different reconstruction depths. A simple algorithm is used to define the focused image with suitable accuracy. The dimensions and orientation of the fibers can be evaluated from the optical field at different depths. Then, the shape and textures along the aggregated natural cellulose nanowhisker fiber can be presented in a 3D space.     

Polymerization of aniline on bacterial cellulose and characterization of bacterial cellulose/polyaniline nanocomposite films

Bacterial cellulose/polyaniline nanocomposite film was prepared by the chemical oxidative polymerization of aniline with bacterial cellulose. Polyaniline conducting polymer nanocomposite films with bacterial cellulose fibers was prepared and characterized. In nanocomposite film, the bacterial cellulose was fully encapsulated with polyaniline by direct polymerization of the respective monomers using the oxidant and dopant. These bacterial cellulose/polyaniline nanocomposite films materials exhibited the inherent properties of both components. The deposition of a polyaniline on the bacterial cellulose surface was characterized by SEM. XPS revealed a higher doping level of the nanocomposite films doped with p-TSA dopant. From the cyclic voltammetry results, the polyaniline polymer was thermodynamically stable because redox peaks of electrochemical transitions in the voltagrams were maintained in bacterial cellulose/polyaniline nanocomposite films.     

Formation of fibrous filtering membranes by electrospinning

A technique for production of fibrous materials containing layers of variable-thickness fibers is considered. Membranes in the form of alternating layers of thin and thick fibers are obtained from cellulose acetate and fluoroplastic solutions. The layers of thin fibers specify the filtering properties of the membranes, and those of thick fibers impart them mechanical strength.     

NMR investigation of degradation processes of ancient and modern paper at different hydration levels

The degradation process of cellulose-made materials was investigated by means of nuclear magnetic resonance (NMR) spectroscopy, with particular emphasis on the role of water and on the hydration mechanism of cellulose fibrils. To accomplish this, the structure and dynamics of water within ancient and modern samples with different aging histories were investigated. The results mainly indicated that hydrolytic and oxidative reactions provoked the formation of acidic by-products. Furthermore, degradation processes were enhanced by higher amounts of water giving a progressive consumption of the amorphous regions of the cellulose. We propose NMR experiments as a benchmark for characterization of the degradation state of paper, as well as for investigating the effectiveness of restoration treatments.     

Investigation of growth, coverage and effectiveness of plasma assisted nano-films of fluorocarbon

Plasma-assisted functional films have significant potential in various engineering applications. They can be tailored to impart desired properties by bonding specific molecular groups to the substrate surface. The aim of this investigation was to develop a fundamental understanding of the atomic level growth, coverage and functional effectiveness of plasma nano-films on flat surfaces and to explore their application-potential for complex and uneven shaped nano-materials. In this paper, results on plasma-assisted nano-scale fluorocarbon films, which are known for imparting inertness or hydrophobicity to the surface, will be discussed. The film deposition was studied as a function of time on flat single crystal surfaces of silicon, sapphire and graphite, using microwave plasma. X-ray photoelectron spectroscopy (XPS) was used for detailed study of composition and chemistry of the substrate and coating atoms, at all stages of deposition. Atomic force microscopy (AFM) was performed in parallel to study the coverage and growth morphology of these films at each stage. Combined XPS and AFM results indicated complete coverage of all the substrates at the nanometer scale. It was also shown that these films grew in a layer-by-layer fashion. The nano-films were also applied to complex and uneven shaped nano-structured and porous materials, such as microcellular porous foam and nano fibers. It was seen that these nano-films can be a viable approach for effective surface modification of complex or uneven shaped nano-materials.     

Chemical physics of cellulose nitration

The physical mechanisms responsible for the kinetics of nitration of cellulose raw materials of different origin have been studied. It has been shown that the main nitration rate-limiting factor is the speed of untwisting of supercoiled cellulose fibers. This process limits the penetration of nitrating agents into microcrystalline regions and, thus, the total reaction rate. The constructed physical model provides an adequate explanation of all the experimentally observed features of the cellulose nitration process, particularly as a function of cellulose origin (cotton, flax, wood) and preparation/treatment methods (sulfite, sulfate, bleached, refined with sulfurous or boric acids or acetone). The theoretical results have been tested in practice.     

Characterization of mineral paper by air-coupled ultrasonic spectroscopy

A novel technology in the paper industry makes possible to produce paper by using a mineral powder and a polymer instead of cellulose fibers. This new product is called mineral paper, it presents some potential environmental advantages compared with conventional paper, while it exhibit a similar appearance and properties. The purpose of this work is to determine the possibilities of an air-coupled ultrasonic technique using wide band signals and spectral analysis to study this kind of materials. As no direct contact nor coupling fluids between the paper and the transducers is required, this technique is specially well suited to this problem. It also offers good perspectives for the development of a on-line quality control system. A through transmission technique (0.15-2.3 MHz) is employed and Fourier analysis is performed to obtain both magnitude and phase spectra of the transmission coefficient. Properties in the thickness direction as well as in the paper plane has been determined by the excitation and analysis of thickness and plate resonances at several incident angles and different directions within the paper plane. Different paper grades (from 140 to 480 g/m²) have been studied. Very high attenuation coefficients and very low propagation velocities (and hence elastic constant) have been obtained for most cases, this can be explained by considering the large porosity of this material (up to 50%) and the microstructure: a mixture of solid grains with a resin with a relatively large fraction of air-filled pores. Measurements show that unlike conventional cellulose machine made paper this material is transversely isotropic (isotropic in the paper plane) and that the degree of anisotropy (when in-plane directions are compared with the thickness direction) largely depends on the level of resin impregnation.     

Simulation study on the avalanche process of the fiber bundles with strong heterogeneities

The fiber bundle with strong heterogeneities is an extension of a fiber bundle model based on the classical fiber bundle model to describe the failure process of strongly heterogeneous materials. In order to explore the breaking dynamic properties of strongly heterogeneous materials in short-range correlation, the fiber bundle model with strong heterogeneities in local load redistribution is numerically studied in detail. The impacts of the proportion of two kinds of fibers and the distribution of the failure thresholds on the macroscopic constitutive behavior, the avalanche size distribution and increasing step number of the external load are investigated, respectively. The numerical results show that there is a local plastic plateau in the constitutive curve at a critical proportion of two kinds of fibers. Strong intensity fibers in material can nontrivially increase the intensity and stability of the system by altering the microscopic properties of the failure process.     

Processing and characterization of new thermoset nanocomposites based on cellulose whiskers

In the present study, the processing and the mechanical properties of new thermoset nanocomposites prepared from aqueous suspensions of microcrystalline cellulose fillers and epoxy are described. The nature of cellulose fibers, which display a large aspect ratio and the ability to associate by means of H-bonds implies that the processing method chosen in this study avoids the problem of a high level of viscosity of the epoxy reactive system-whiskers mixture. The reinforcing effect of this type of natural fiber in an epoxy matrix is mainly shown from the dynamic mechanical properties in the rubbery state. This unusual reinforcement is due to (i) the strong interactions existing between the cellulose whiskers and the epoxy network and, (ii) the creation of a percolating network linked by H-bonds between cellulose fibers. The existence of such a percolation effect is evidenced from the analysis of the rubbery shear modulus of nanocomposites based on various volume fractions of whiskers with mechanical modeling such as Halpin-Kardos and percolation approaches.     

Characterization Method of Polycrystalline Materials Using Conductive Atomic Force Microscopy

An apparatus for characterization of polycrystalline materials based on conductive atomic torce microscopy （cAFM） is developed and a quantitative measurement of electrical characteristics of individual grains in polycrystalline ZnO ceramic is demonstrated. Improvement of the experimental method is presented. Experimental results illuminate unambiguously the different electrical characteristics between individual grains, suggesting the suitability and maneuverability of this method in the study of local structure or properties and their relationship in polycrystalline materials such as semi-conducting ceramics.     

Optimum Plasma Surface Treatment of Luffa Fibers

Luffa fiber is a renewable resource material with low cost and that contributes to a healthier ecosystem by its biodegradability. Its natural structure can be considered as a naturally occurring composite consisting mainly of cellulose fibrils imbedded in a lignin matrix. Surface pretreatment is necessary to maximize their potential use. In this work, plasma treatment at atmospheric pressure was carried out on the raw luffa fibers. The orthogonal method was used to optimize the plasma treatment condition. The optimal conditions were obtained at a discharge time of 10 s, power of 110 W, and electrode distance of 6 mm for the system used. The surface characterization of untreated and pretreated luffa fibers was investigated by Fourier transform infrared spectroscopy (FTIR), scanning electron microscopy (SEM), and thermogravimetric (TGA) analysis. The results showed that plasma treatment did not cause significant harm to the fiber integrity and the inner cellulose fibrils were exposed from the lignin matrix. Plasma-treated luffa fibers also showed a slightly better thermal stability than the untreated fibers. Compared with chemical pretreatment, plasma treatment had a significantly shorter duration, no consumption of solvent, and improved the cellulose contents.     

红外光谱在纤维质文物材料鉴别中的应用研究

纺织纤维和纸张纤维是常见纤维质文物材料,是构成博物馆精美文物如服饰手稿书画的基本材料,近年来寻求通过无损或微损方法对这一类材料的鉴别以及劣化状况评价备受文物鉴赏家和文物保护工作者的关注。借助傅里叶变换红外光谱,研究博物馆常见纺织纤维材料棉、麻、桑蚕丝、柞蚕丝、羊毛的红外光谱特征和它们的分子结构组成异同,研究传统纸纤维稻草、麦草、龙须草、龙旗松、桑皮红外光谱特征。结果表明：衰减全反射傅里叶变换红外光谱无损分析技术可通过比较3 300～2 800 cm-1 CH,NH,OH振动区间光谱形状以及指纹区峰位以区别不同种类纺织品纤维;碳氧振动纸张纤维最明显光谱差异位置出现在与纤维素OH伸缩振动相关波数3 300 cm-1和与C—O—C相关波数1 332,1 203,1 050 cm-1。文章探索研究红外光谱技术结合主成分分析法在快速鉴别纤维材料中的应用。通过对全光谱数据多元散射校正(MSC)预处理后进行主成分分析,可以把红外光谱十分相似的纺织纤维棉和亚麻、桑蚕丝和柞蚕丝明显分类;对光谱相似的纸纤维,可采用选择不同光谱波数段进行主成分分析,比较发现能够把五种纸纤维明显区分的光谱区间为3 800～2 800 cm-1。本研究为分子光谱无损分析技术应用于文物材料鉴别、科学评估纤维材料保存状况提供基础研究。     

Cellulose-based biocomposites: comparison of different multiphasic systems

Biocomposites (biodegradable composites) are obtained by blending biodegradable polymers and fillers. Since the main components are biodegradable, the composite as a whole is also expected to be biodegradable. This paper presents various biocomposites that have been elaborated with cellulose or lignocellulose fibers from diverse sources, with different lignin contents. This paper is targeted on the analysis of 'fiber–matrix' interactions of two types of biocomposites based on agropolymer (plasticized wheat starch) and biopolyester (polybutylene adipate-co-terephthalate), named APB and BPB, respectively. Processing and main properties of both biocomposites are shown and compared. Polyolefin-based composite (PPC), which is known to present very poor 'fiber–matrix' interactions, is used as a reference. Through the Young's modulus, mechanical properties have shown that the reinforcement, by increasing fiber content, is much more significant for APB compared to BPB. The evolution of chains mobility, evidenced through shift of T _g values, according to the increase in fiber content and thence in interfacial area, have shown that the fiber–matrix interactions are higher for APB. BPB presents intermediate values, higher than PPC ones. These results are in agreement with the analysis of the composite morphologies performed by SEM on cryogenic fractures. Finally, by determining the theoretical works of adhesion and the interfacial tensions from contact angle measurements, it is shown that these parameters are partially able to predict the level of interaction between the fibers and the matrix. We could show that the perspectives of such work seem to be of importance to tailor new materials with a controlled end-use.     

Predicting the sound absorption of natural materials: Best-fit inverse laws for the acoustic impedance and the propagation constant

Natural materials are becoming a valid option for sound absorption treatments. In particular, among them, natural fibers have received increasing attention given their good thermal insulation properties, lack of harmful effects on health, and availability in large quantities. This paper discusses an inverse method to predict the acoustical properties of nine natural fibers. Six vegetative fibers: kenaf, wood, hemp, coconut, straw, and cane; one animal fiber, sheep wool; recycled cardboard; and granular cork are investigated. The absorption coefficient and the flow resistance for samples of different thickness have been measured. Moving from the Delany-Bazley model, this study compares the impedance tube results with the theoretically predicted ones. Then, using a least-square fit procedure based on the Nelder-Mead method, the coefficients that best predict both the acoustic impedance and the propagation constant laws are calculated. The inverse approach used in this paper allows to determine different physical parameters and to obtain formulas to include the investigated natural fibers in software modelling for room acoustics applications.     

A comprehensive review on surface modification,structure interface and bonding mechanism of plant cellulose fiber reinforced polymer based composites

Abstract

Plant cellulose fiber polymer composites are readily applied in wide range of applications due to ecological and economical alternative to traditional materials. The considerable amount of residues and organic wastes from agricultural process are still employed as lower energy resource. Organic materials are generally disposed in composting, landfilling or anaerobic digestion. The utilization of these wastes in plant fiber composites shows significant alternative and environmental friendly in nature. The production of plant cellulose fiber composite with higher structural properties is optimized by interfacial bonding between polymer and reinforced fiber. The interface plays a vital role in regulating mechanical properties by distributing bonds and stress transferring, which is one of least understood element of composites. This paper presents the comprehensive review of fiber structures, different modification techniques to reduce the incompatibility between matrix and fiber, assessment of structure interface and bonding, clarifies the interfacial adhesion of cellulose fiber composites.     

Probing mechanical properties of thin film and ceramic materials in micro- and nano-scale using indentation techniques

In this study, we report on the mechanical properties, failure and fracture modes in two cases of engineering materials; that is transparent silicon oxide thin films onto poly(ethylene terephthalate) (PET) membranes and glass-ceramic materials. The first system was studied by the quazi-static indentation technique at the nano-scale and the second by the static indentation technique at the micro-scale. Nanocomposite laminates of silicon oxide thin films onto PET were found to sustain higher scratch induced stresses and were effective as protective coating material for PET membranes. Glass-ceramic materials with separated crystallites of different morphologies sustained a mixed crack propagation pattern in brittle fracture mode.