Growth Kinetics of Nanocrystals and Nanorods by Employing Small-angle X-ray Scattering (SAXS) and Other Techniques

In this article, we report the results of our detailed investigations of the growth kinetics of zero-dimensional nanocrystals as well as one-dimensional nanorods by the combined use of small angel X-ray scattering （SAXS）, transmission electron microscopy （TEM） along with other physical techniques. The study includes growth kinetics of gold nanocrystals formed by the reduction of HAuCl4 by tetrakis（hydroxymethyl） phosphonium chloride in aqueous solution, of CdSe nanocrystals formed by the reaction of cadmium stearate and selenium under solvothermal conditions, and of ZnO nanorods formed by the reaction of zinc acetate with sodium hydroxide under solvothermal conditions in the absence and presence of capping agents. The growth of gold nanocrystals does not follow the diffusion-limited Ostwald ripening, and instead follows a Sigmoidal rate curve. The heat change associated with the growth determined by isothermal titration calorimetry is about 10 kcal·mol^-1 per I nm increase in the diameter of the nanocrystals. In the case of CdSe nanocrystals also, the growth mechanism deviates from diffusion-limited growth and follows a combined model containing both diffusion and surface reaction terms. Our study of the growth kinetics of uncapped and poly（vinyl pyrollidone） （PVP）-capped ZnO nanorods has yielded interesting insights. We observe small nanocrystals next to the ZnO nanorods after a lapse of time in addition to periodic focusing and defocusing of the width of the length distribution. These observations lend support to the diffusion-limited growth model for the growth of uncapped ZnO nanorods. Accordingly, the time dependence on the length of uncapped nanorods follows the L3 law as required for diffusion-limited Ostwald ripening. The PVP-capped nanorods, however, show a time dependence, which is best described by a combination of diffusion （L^3） and surface reaction （L^2） terms.

Small Angle X-ray Scattering Study of Precipitation Kinetics in Al-Zn-Mg-Cu Alloys

The evolution of microstructure parameters （precipitate size and volume fraction） for two types of Al-Zn-Mg-Cu alloys （7075 and 7055） during aging has been studied by synchrotron-radiation small angle X-ray scattering （SAXS）.The results show that the precipitates are only a few nanorneters for both alloys ageing even at higher temperature of 160℃ for 72 h （4.44 and 5.82 nm, respectively）. The maximum of the precipitate volume fraction increases with in creasing Zn content and is about 0.023-0.028 and 0.052-0.054, respectively. The coarsening of precipitate is consistent with LSW （Lifshitz-Slyozov-Wagner） model even at the initial stage where volume fraction is still varying.The activation energy of coarsening regime has been determined to be about 1.22±0.02 eV and 1.25±0.02 eV for alloys 7075 and 7055, respectively.

Small angle X-ray scattering beamline at SSRF

Beamline BL16B1 at Shanghai Synchrotron Radiation Facility(SSRF) is dedicated to studying the microstructure and dynamic processes of polymers, nanomaterials, mesoporous materials, colloids, liquid crystals,metal materials, etc. At present, SAXS, wide angle X-ray scattering(WAXS), simultaneous SAXS/WAXS,grazing incident SAXS, and anomalous SAXS techniques are available for end user to conduct diverse experiments at this beamline. The sample-to-detector distance is adjustable from 0.2 m to 5 m. The practicable q-range is 0.03–3.6 nm-1at incident X-ray of 10 ke V for conventional SAXS whilst a continuous q-region of0.06–33 nm-1can be achieved in simultaneous SAXS/WAXS mode. Time-resolved SAXS measurements in sub-second level was achieved by the beamline upgrating in 2013. This paper gives detailed descriptions about the status, performance and applications of the SAXS beamline.

Small-angle X-ray scattering investigation of aging behavior of Al-Cu-Mg-Ag alloys using synchrotron radiation

The aging behavior of Al-Cu-Mg-Ag alloys with high Cu/Mg was studied by transmission electron microscopy (TEM) and small-angle X-ray scattering (SAXS) using synchrotron radiation. TEM study reveals that the major strengthening phases of the alloy after aging at 160?C for 10 h are Ω and less θ′. SAXS study shows that the scattering patterns are composed of several concentric circles at the beginning of aging process, which is replaced by the butterfly-wings scattering patterns with the increase of aging time. The butterfly-wings scattering patterns are composed of several branches. The angles between the branches are roughly equal to that between the habit planes of precipitates. The evolution of Guinier radius with aging time indicates the good coarsening resistance of the precipitates. The evolution of integrated intensity is consistent with the classical two-step precipitation process.

Small Angle X-ray Scattering Study of PS Conformation in Tetrahydrofuran Solvent with Gas Anti-solvent

Small angle X-ray scattering (SAXS) was used to study the effect of dissolved CO2 on the conformation of polystyrene (PS) in PS/tetrahydrofuran(THF) solution at 308.15 K and at pressures up to 3 MPa. The cloud pressure and the expansion curve of the solution were also determined. The dependence of the conformation on pressure was discussed.

Scanning Microfocus Small Angle X-ray Scattering Study of the Avian Eggshell

Synchrotron microfocus small angle X-ray scattering was used to investigate the nanostructure and microscopic variation of eggshells. It uses a microbeam allowing the ability to probe interactions between the organic and inorganic components at nanometer level and is ideal for mapping over small areas to obtain a detailed analysis of structural variations. Thin sections of eggshells were scanned from the shell membrane （inner） to the cuticle （outer） surface. The data collected was used to produce two-dimensional maps showing microscopic changes within the different layers of the eggshell. The structural alterations ap- parently could have implications at the macroscopic level of the resulting eggshell. As the organic matrix is embedded within the eggshell this may contribute to the variations observed in calcite crystal form and texture, Structural information obtained about a biomaterial at different length scales is important in relating the structure to its functional properties. This knowledge and the principles behind the formation of biomaterials could be used in the attempt of bioengineering new systems.

Characteristics of AOT Microemulsion Structure: a Small Angle X-ray Scattering Study

The method of synchrotron radiation small-angle X-ray scattering (SR-SAXS) has been used to obtain structural information on the system of bis (2-ethylhexyl) sulfosuccinate (AOT)/H2O/isooctane. By using the Guinier plot (Ln I (q) versus q(2)) on the data sets in a defined small q range (0.03-0.06 Angstrom (-1)), the gyration radius at different water/surfactant molar ratio, W-0, was obtained. With the increase of W-0, the gyration radius (R-g) increased at the range of 23.2 similar to 52.7 Angstrom.

Probing Nanoscale Morphology of PS/PMMA/CdS &PS/PVC/CdS Polymeric Nanocomposites through Small Angle X-Ray Scattering Analysis

Polymeric nanocomposites of PS/PMMA/CdS and PS/PVC/CdS samples have been synthesized through dispersion solution casting technique. The nanoparrticles of CdS were prepared by simple chemical method using CdCl2 and H2S gas produced from thiourea. The nanoscale morphology of the prepared polymeric nanocomposite samples is probed through small angle X-ray scattering (SAXS). The SAXS study reveals that CdS nanoparticles take place at voids position in the respective plymer blend matrix and exhibit their nano nature with very little tendency to agglomerates.

A new package:MySAS for small angle scattering data analysis

In this paper,A MySAS package,which is verified on Windows XP,can easily convert two-dimensional data in small angle neutron and X-ray scattering analysis,operate individually and execute one particular operation as numerical data reduction or analysis,and graphical visualization.This MySAS package can implement the input and output routines via scanning certain properties,thus recalling completely sets of repetition input and selecting the input files.On starting from the two-dimensional files,the MySAS package can correct the anisotropic or isotropic data for physical interpretation and select the relevant pixels.Over 50 model functions are fitted by the POWELL code using x^2 as the figure of merit function.

Stability of the Dividing Distribution Function Method for ParticleSize Distribution Analysis in Small Angle X－Ray Scattering

The Dividing Distribution Function (DDF) method is one of the methods by which the particle size distribution of ultrafine powder can be evaluated from its small angle X-ray scattering data. In this paper, the stability of the solution obtained from DDF method has been investigated through optimizing the coefficient matrix, introducing a damping factor and a least square treatment. All calculations were accomplished with a microcomputer. It was shown that the average deviations of the size distribution obtained are not larger than the assigned random errors to the scattering intensities as long as the corresponding requirements are satisfied.

Nano-scale pore distribution characterisation of coal using small angle X-ray scattering

In the process of coal seam fracturing with liquid nitrogen(LN_(2)),the change of coal pore structure has an important influence on the efficiency of coalbed methane(CBM)extraction.The nano-scale pore size distribution(PSD)in coal particles before and after freezing with LN_(2) are experimentally studied in this work.Coal samples are collected from four coal mines,where coal and gas outburst accidents have occurred.Small angle X-ray scattering technology(SAXS)and scanning electron microscopy(SEM)are used to study the pore structure changes of coal samples quantitatively and qualitatively.It is found that the scattering intensity of coal samples increases after freezing.The PSD of all samples significantly changes in the range of 0.8–7 nm,showing new pore spaces in 0.8–4 nm and fewer pores in the 4–7 nm range.Both the pore fractal dimension and the radius of gyration of coal samples increase after freezing and are mainly affected by the changes in pores and the anisotropy of the coal matrix.Crack expansion and pore connections are observed in the surface structure of the coal sample using SEM.This study provides a better understanding of the nano-scale mechanism of coal seam fracturing with LN_(2) for the prevention of coal and gas outbursts.

Small angle X-ray scattering of the colloidal crystal

The monodisperse polystyrene spheres are assembled into the colloidal crystal on the glass substrate by vertical deposition method, which is aimed at the so-called photonic crystal applications. The structural information of the bulk colloidal crystal is crucial for understanding the crystal growth mechanism and devel- oping the various applications of colloidal crystal. Small-angle X-ray scattering （SAXS） technique was used to obtain the bulk structure of the colloidal crystal at Beamline lW2A of BSRF. It is found that the SAXS pattern is sensitive to the relative orientation between the colloidal sample and the incident X-ray direction. The crystal lattice was well distinguished and determined by the SAXS data.

DETERMINATION OF SIZE DISTRIBUTION OF THE CRYSTALLINE PARTICLE IN AGED METALLIC GLASS BY SMALL ANGLE X-RAY SCATTERING

Ⅰ. INTRODUCTIONAlthough many authors have investigated the structure of annealed metallic glass by means of small angle X-ray scattering (SAXS), there has been no report in which size distribution of the crystalline particle in aged metallic glass is determined. Determining size distribution of the crystalline particle will be beneficial to understanding the nucleation and growth process of the crystalline particle. In this note, size distribution of the crystalline parti-

DETERMINATION OF THE SHAPE AND DIMENSION OF PRECIPITATE FROM AGED Lc4 ALUMINIUM ALLOY BY SMALL ANGLE X-RAY SCATTERING

Small angle X-ray scattering (SAXS) is extensively used for determining the dimension of a particle, but rarely used for determining its shape. The difficulty is that it needs to do extensive calculations. In addition, it can only be carried out for the mono-dispersion system. In re cent years, Reuther et al. succeeded in determining the shape and dimension of the particle of a polymer gel.

In-situ SAXS study on PET/PMMT composites during tensile tests

The nanostructures during the tensile drawing of poly（ethylene terephthalate） （PET）/hexadecyl triphenyl phospho- nium bromide montmorillonite （PMMT） nanocomposites were studied by in-situ small angle x-ray scattering. For strain higher than the yield point, the scattering intensity increases dramatically due to the nucleation and growth of nanovoids and crystals. The nanovoids and crystals are significantly dependent on the heating temperature. The effective filling of PMMT in the PET matrix provokes a strong restriction to the long period. The peaks of the long period disappear gradually with the deformation strain increasing from 0% to 34%.

Characterization of the nanopore structures of PAN-based carbon fiber precursors by small angle X-ray scattering

The nanopore structures in precursors Four carbon-fiber precursors are prepared. They are crucial to the performance of PAN-based carbon fibers are bath-fed filaments （A）, water-washing filaments （B） hot-stretching filaments （C） and drying-densification filaments （D）. Synchrotron radiation small angle X-ray scattering is used to probe and compare the nanopore structures of the four fibers. The nanopore size, discrete volume distribution, nanopore orientation degree along the fiber axis and the porosity are obtained. The results demonstrate that the nanopores are mainly formed in the water-washing stage. During the processes of the subsequent production technologies, the slenderness ratio of nanopores and their orientation degree along the fiber axis increase further and simultaneously, the porosity decreases. These results are helpful for improving the performance of the final carbon fibers.

Influence of energy bandwidth of pink beam on small angle X-ray scattering

Background Compared with the traditional monochromatic synchrotron radiation beam,a pink beam is a quasimonochromatic beam which can be obtained by screening a harmonic of the undulator.The energy bandwidth(E/E)of a pink beam is about 10−2.Despite the intensity gain from the quasi-monochromatic beam,the decrease in the energy resolution will lead the collected data to be smeared.Purpose To study the influence of the energy bandwidth on the small angle X-ray scattering(SAXS)by experiments and verify the feasibility of SAXS with a pink beam.Method Firstly,the influence of different energy bandwidths on SAXS has been studied by simulation and experiment.Then,TEM tests have been performed and compared with the experimental results.Result It has been shown that the scattering curves deviate slightly from the traditional monochromatic ones.This deviation does not influence the data processing for the maximum deviation of the results is just less than 2%.In return,the gain in the intensity(one to two orders of magnitude)makes the pink beam very important for the time-resolved SAXS.Further,the results of TEM and SAXS have shown an excellent agreement.Conclusion Thiswork proves that the pink beam could be used for SAXS directly without a desmearing procedure.Benefiting from the increase in the beam intensity,the exposure time can be greatly shortened,thus enhancing the utilization efficiency of the synchrotron radiation.

限制性核酸内切酶Asc I蛋白质的表达纯化、酶活测定及小角散射结构解析

限制-修饰系统(RMS)是细菌为了防御外来DNA入侵而进化产生的一种保护机制。RMS系统可分为Ⅰ型、Ⅱ型、Ⅲ型和Ⅳ型。Asc I是一种Ⅱ型限制性核酸内切酶,能识别8-bp DNA基序。尽管Asc I已经被广泛应用于分子克隆研究中,然而目前尚无关于Asc I蛋白质的表达、纯化以及结构机制等方面的研究报道。本研究基于大肠杆菌重组表达体系建立了Asc I重组蛋白质的高效表达和纯化方法,从每升细菌培养物中可获得约2.5 mg纯度大于95%的Asc I蛋白质。进一步的酶学性质研究表明,Asc I酶切反应的最适温度是37℃,最适pH为7.5~8.5,反应依赖于Mg^(2+)和Mn^(2+)等二价金属离子。基于小角X射线散射(SAXS)分析技术,我们还建立了Asc I蛋白质及其与底物DNA复合物在溶液状态下的三维空间模型,并结合点突变对该模型进行了验证。总之,本研究对Asc I蛋白质的重组表达、纯化、酶活性质以及结构机制进行了比较系统地研究,为了解RMS系统的工作机制提供了结构基础,同时也为Asc I作为分子克隆工具酶的进一步开发和改造提供了理论依据。

聚合物对硫化铅钠米微粒的稳定作用

以含铅聚合物微凝胶与Ｈ＿２Ｓ气体反应制得ＰｂＳ纳米微粒／聚合物复合体系，利用小角Ｘ光散射方法对复合在聚合物中的ＰｂＳ纳米微粒的粒度及分布进行了表征，研究了不同反应条件对其粒度及复合体系稳定性的影响．实验结果证明Ｈ＿２Ｓ的用量及小分子含铅反应物的引入对复合的ＰｂＳ纳米微粒的粒度有一定的控制作用．由于聚合物对ＰｂＳ纳米微粒具有非常好的稳定作用，ＰｂＳ纳米微粒的粒度随Ｈ２Ｓ量的增加变化很小，且分布均一，体系具有长期稳定性；而不同量的小分子铅盐的引入对ＰｂＳ纳米微粒粒度变化影响很大，随着小分子铅盐比例的增加粒度分布变宽，体系稳定性下降．

聚丙烯腈基碳纤维及其原丝中的微孔尺寸分布

利用二维小角X射线散射技术（SAXS）研究了聚丙烯腈基碳纤维及其原丝的微孔结构。结合逐级切线法、对数正态分布及麦克斯韦分布函数对2类实验样品内部微孔的尺寸分布进行了分析。结果表明，2类样品中的孔结构具有显著差别，原丝微孔在4～8nm范围内分布比较集中，碳纤维中微孔的分布区域则移向1．3～1．8nm。散射数据显示出明显的分形特征，碳纤维与其原丝的孔分形维数分别为1．33和1．55，表明原丝中具有较大的孔隙缺陷。相对于原丝，碳纤维微孔尺寸分布走向均匀和集中，前者则表现出比后者更宽的尺寸分布。就拟合方法而言，逐级切线法的解析手段容易引入误差，低角区的纤维表面散射和高角区的噪音容易对其结果造成影响。正态分布得到了比较窄的尺寸分布，但对于低尺寸区域孔隙的拟合不理想。麦氏分布在一定程度上弥补了以上不足，能够较好地拟合两类纤维样品中微孔的分布状况。