在有限空间内生成的晶格高度取向的ZnO纳米颗粒

应用固态反应的方法,在260和300 oC空气中分别热分解层状锌油酸固体得到氧化锌纳米颗粒/团簇．高分辨透射电子显微镜和选区电子衍射表明,这种团簇是带有各种缺陷的单晶．光致发光激发光谱表明这两个样品在272和366 nm有两个频段．前者可能是由于不到200个氧化锌分子组成的团簇从价带到导带的电子转移引起的．     

Structure of unsupported antimony nanoclusters

In this study we present results of electron diffraction experiments on unsupported antimony nanoclusters with mean sizes in the range of 20-40 nm. An inert-gas aggregation source was used to produce the cluster beam. Electron diffraction patterns reveal phase transitions between crystalline and amorphous phases as well as particles composed of Sb₄ tetramers. The diffraction results are correlated with electron microscope investigations of the morphology of films formed by deposition of the clusters.     

Dual improvement in curcumin encapsulation efficiency and lyophilized complex dispersibility through ultrasound regulation of curcumin–protein assembly

Ultrasound has a recognized ability to modulate the structure and function of proteins. Discovering the influential mechanism of ultrasound on the intramolecular interactions of egg-white protein isolate–curcumin (EPI–Cur) nanoparticles and their intermolecular interaction during freeze drying and redispersion is meaningful. In this study, under the extension of pre-sonication time, the protein solubility, surface hydrophobicity, and curcumin encapsulation rate showed an increasing trend, reaching the highest value at 12 min of treatment. However, the values decreased under the followed extension of ultrasound time. After freeze drying and redispersion were applied, the EPI–Cur sample under 12 min of ultrasound treatment exhibited minimal aggregation degree and loss of curcumin. The retention and loading rates of curcumin in the lyophilized powder reached 96 % and 33.60 mg/g EPI, respectively. However, under excessive ultrasound of >12 min, scanning electron microscopy showed distinct blocky aggregates. Overexposure of the hydrophobic region of the protein triggered protein-mediated hydrophobic aggregation after freeze drying. X-ray diffraction patterns showed the highest crystallinity, indicating that the free curcumin-mediated hydrophobic aggregation during freeze drying was enhanced by the concentration effect and intensified the formation of larger aggregates. This work has practical significance for developing the delivery of hydrophobic active substances. It provides theoretical value for the dynamic dispersity change in protein-hydrophobic active substances during freeze drying and redissolving.     

One‐pot synthesis of silver particle aggregation as highly active SERS substrate

Silver particles with different degrees of aggregation were synthesized through a sodium dodecyl sulfate‐assisted one‐pot reaction in an aqueous medium. The products were characterized by transmission electron microscopy, scanning electron microscopy and UV‐visible spectroscopy. The results showed that the degree of aggregation of the Ag nanoparticles could be tuned by changing the reaction parameters, such as the reaction temperature and time. A possible formation process of the Ag aggregate is proposed on the basis of a series of experimental results. Moreover, the surface‐enhanced Raman scattering (SERS) effect of the Ag aggregates was evaluated by using rhodamine 6G as a Raman probe molecule. It was demonstrated that the SERS enhancement ability is related to the degree of aggregation of Ag particles, and a high SERS signal can be observed by selecting Ag nanoparticles with the proper degree of aggregation as substrates. Moreover, the aggregates showed good reproducibility and stability to SERS from organic molecules. Copyright © 2010 John Wiley & Sons, Ltd.     

A structural study of biocompatible magnetic nanofluid with synchrotron radiation-based X-ray scattering techniques

In this paper, water colloidal solutions of nanoparticles of magnetite (magnetic nanofluids, (MNFs)) are investigated by synchrotron X-ray diffraction (XRD) and small-angle scattering (SAXS). To prevent aggregation, nanoparticles are coated with polyacrylic acid (PAA) in a single solution and citric (CA) in the other solutions. In both cases, the maxima of the particle size distribution from SAXS (9?C10 nm) correspond to the sizes of the magnetite crystallites that were estimated from the broadening of the diffraction lines. In addition, the SAXS data indicate the presence of a significant proportion of aggregates (up to 60 nm in diameter) in both colloidal solutions, although fundamental differences in the structures of aggregates between the MNFs stabilized by PAA and CA were not observed. In this study determination of the structural characteristics of MNFs were carried out in order to obtain stable dispersive non-aggregating nanoparticles of magnetite for use as contrast agents in magnetic resonance tomography, drug carriers, and other biomedical applications.     

金纳米粒子聚集体系的制备及其SERS效应表征

以Na2S作为金纳米粒子的还原制备与聚集剂制备了金纳米粒子聚集体系。在制备过程中通过紫外可见光谱对制备条件进行了优化。TEM表征显示聚集体系中的金纳米粒子均为球形,且聚集状态呈现出较好的均匀性。将这一聚集体系作为SERS基底应用于若干氨基酸分子的SERS光谱表征与分析。初步的研究表明Na2S-金纳米粒子聚集体系可有效地应用于生物分子的SERS光谱表征与分析。     

Monitoring Alzheimer Amyloid Peptide Aggregation by EPR

Plaques containing the aggregated β-Amyloid (Aβ) peptide in the brain are the main indicators of Alzheimer’s disease. Fibrils, the building blocks of plaques, can also be produced in vitro and consist of a regular arrangement of the peptide. The initial steps of fibril formation are not well understood and could involve smaller aggregates (oligomers) of Aβ. Such oligomers have even been implicated as the toxic agents. Here, a method to study oligomers on the time scale of aggregation is suggested. We have labeled the 40 residue Aβ peptide variant containing an N-terminal cysteine (cys-Aβ) with the MTSL [1-oxyl-2,2,5,5-tetramethyl-Δ-pyrroline-3-methyl] methanethiosulfonate spin label (SL-Aβ). Fibril formation in solutions of pure SL-Aβ and of SL-Aβ mixed with Aβ was shown by Congo-red binding and electron microscopy. Continuous-wave 9 GHz electron paramagnetic resonance reveals three fractions of different spin-label mobility: one attributed to monomeric Aβ, one to a multimer (8–15 monomers), and the last one to larger aggregates or fibrils. The approach, in principle, allows detection of oligomers on the time scale of aggregation.     

Synthesis of ZnO nanoparticles using nanosecond pulsed laser ablation in aqueous media and their self-assembly towards spindle-like ZnO aggregates

ZnO nanoparticles were fabricated by pulsed laser ablation (PLA) of a Zn metal in aqueous media, and aging effects on the morphology and photoluminescence properties of ZnO nanoparticles were investigated. The crystalline phase and particle morphology were characterized by X-ray diffraction (XRD), scanning electron microscopy (SEM), and transmission electron microscopy (TEM). It was found that small, well-defined ZnO nanoparticles were obtained by PLA of a Zn plate in aqueous media, and subsequent aging of the obtained ZnO nanoparticle suspension produced in cetyltrimethylammonium bromide (CTAB) solution led to the formation of spindle-like ZnO aggregates. However, in deionized water not the spindle-like ZnO aggregates but fluffy round aggregates were obtained. High-resolution transmission electron microscopic (HRTEM) observation indicated that the spindle-like ZnO aggregates were composed of many well-defined nanoparticles. Spindle-like aggregates exhibited strong exciton emission, while green emission could be suppressed via an aging process in the presence of CTAB. Moreover, thin films prepared by electrophoretic deposition (EPD) of ZnO nanoparticles after PLA in the presence of CTAB also possessed highly elongated aggregate structures that were possibly formed by surrounding the ZnO nanoparticles with double layers of CTAB molecules.     

Three-dimensional growth characteristics of antimony aggregates on graphite

The growth of antimony aggregates on the basal plane of graphite via diffusion and aggregation of Sb₄ clusters has been investigated with scanning electron microscopy, and in 3-dimensions with atomic force microscopy. The aggregate morphologies depend critically on the deposition conditions. It is shown that a transition from compact to branched morphologies with increasing aggregate size, depends on the particle flux. Also, the aggregate heights are strongly influenced by flux, with higher fluxes producing flatter aggregates. The heights of individual island branches are also shown to depend on the local diffusion field.     

Energy transfer as a tool in aggregation studies in NaCl:Pb,Mn

The aggregation kinetics of impurity-vacancy dipoles in NaCl:Pb, Mn has been studied by different techniques: Luminescence, ionic thermocurrents (ITC) and electron paramagnetic resonance (EPR).Energy transfer between Pb²⁺ and Mn²⁺ ions in NaCl has proved its usefulness to follow the small aggregates concentration.The experimental data has been fitted with a model that considers dimers and trimers formation, being dimers, the aggregates preferentially formed at low temperatures.     

Structure of unsupported bismuth nanoparticles

We present new results of electron diffraction experiments on unsupported nanometer-sized bismuth clusters. The high intensity cluster beam, necessary for electron diffraction, is provided by an inert-gas aggregation source. The cluster beam contains particles with average cluster sizes between 4.5 and 10 nm. When using Helium as a carrier gas we are able to observe a transition from crystalline clusters to a new structure, which we identify with that of amorphous or liquid clusters. Received 28 November 2000     

The effect of particle aggregation on the absorption and emission properties of mono- and polydisperse soot aggregates

This study concerns the effect of soot-particle aggregation on the soot temperature derived from the signal ratio in two-color laser-induced incandescence measurements. The emissivity of aggregated fractal soot particles was calculated using both the commonly used Rayleigh–Debye–Gans fractal-aggregate theory and the generalized Mie-solution method in conjunction with numerically generated fractal aggregates of specified fractal parameters typical of flame-generated soot. The effect of aggregation on soot temperature was first evaluated for monodisperse aggregates of different sizes and for a lognormally distributed aggregate ensemble at given signal ratios between the two wavelengths. Numerical calculations were also conducted to account for the effect of aggregation on both laser heating and thermal emission at the two wavelengths for determining the effective soot temperature of polydisperse soot aggregates. The results show that the effect of aggregation on laser energy absorption is important at low fluences. The effect of aggregation on soot emissivity is relatively unimportant in LII applications to typical laminar diffusion flames at atmospheric pressure, but it can become more important in flames at high pressures due to larger primary particles and wider aggregate distributions associated with enhanced soot loading.     

Aggregation,fracture initiation,and strength of PP/CaCO3 composites

Polypropylene/CaCO₃ composites were homogenized in a twin-screw compounder and then injection molded into tensile bars. Six different fillers were used in a wide range of average particle sizes between 0.08 and 12 μm. Tensile and flexural properties were measured by standard techniques, while impact resistance was determined by instrumented impact testing. Structure was characterized by light and electron microscopy, while failure initiation and propagation was studied with in situ high-voltage electron microscopy. The results showed that aggregation of particulate fillers occurs when their particle size is smaller than a critical value. This critical size depends on component properties and processing conditions. Strength and impact resistance usually decrease with increasing number of aggregates. The presence of aggregation can be detected by the use of a simple semiempirical model. Comparison of samples prepared by two different technologies showed that twin-screw extrusion and injection molding leads to relatively homogeneous composites, which was indicated by smaller deviations of the properties from theoretical predictions. In spite of the acceptable dispersion, impact resistance showed a large standard deviation, probably determined by the local variation of structure. In composites containing relatively large particles, the dominating micromechanical deformation process is debonding, while in the presence of extensive aggregation of small particles, cracks are initiated inside and propagate through aggregates. Mixed-mode failure may also occur at certain intermediate panicle sizes.     

Order—Disorder phase transformation in ZrS2 single crystals

Order-disorder phase transformation has been observed in ZrS₂ single crystals on annealing them at a temperature of 400 ± 10°C. Loss of sulphur, resulting in its deficiency, on annealing of crystals is thought to be the cause of the observed phase transformation. Evidence in its support, based on X-ray and electron diffraction results, is advanced.     

Structural Modifications and Clustering of Low-Density Lipoproteins in Solution Induced by Heating

This work presents a systematic study of low-density lipoprotein (LDL) in solutions subjected to subtle temperature changes, monitored by small angle X-ray scattering. From the data analysis, information about the equilibrium aggregation of the particles, as well as changes on the internal structure of the lipoproteins, were observed. The electron density profiles of the LDL particles were retrieved with a recently developed deconvolution method. Our results indicate that LDL particles keep their structure in the temperature range from about 22 °C up to 60 °C. Moreover, the formation of aggregates and their evolution as a function of time were monitored. Interestingly, when the temperature is raised to 80 °C, the results indicate the rupture of the particle and unspecific aggregation.     

Estimation of Phosphorus and Sulphur Contents in Nuclear Constituents by Means of Image-EELS Analysis Using Ribosomes as Internal Standards

A quantitative study by means of electron energy-loss spectroscopic imaging (image-EELS) is performed on a biological specimen, using ribosomes as internal standard. Phosphorus and sulphur are studied; it is shown in the case of phosphorus analysis that results obtained are in agreement with a previous study using a different energy filtering microscope.

In most biological specimens, atoms of sulphur may be present in the vicinity of phosphorus atoms; in such cases the signal obtained from sulphur will overlap with the continuum coming from the phosphorus signal, thus making the element-specific maps of sulphur superimposed on a background signal coming from phosphorus. In this work a method is suggested of separating the phosphorus contribution to the sulphur signal, using a reference spectrum from gallium phosphide.     

Measurement of Aggregate Fractal Dimensions Using Static Light Scattering

Aggregates formed from colloidal particles will vary in shape according to the aggregation regime prevalent. Compact structures are formed when the aggregation is slow, whilst loose tenuous structures are formed when rapid (or diffusion limited) aggregation prevails. These structures can be fractal in nature, that is, there is a relationship between porosity and the number of primary particles making up the aggregate, and is described by the fractal dimension, d_F. Fractal dimensions of hematite aggregates have been measured experimentally using the static light scattering technique. Fractal dimensions varied with aggregation regimes; for the rapid aggregation regime, d_F was found to be 2.8, whilst for conditions in which aggregation was slow (retardation forces prevail), d_F's of 2.3 were measured. For conditions which lead to aggregation in which both diffusion and retardation forces play a part, structures with fractal dimensions such that 2.3 < d_F < 2.8 were found. The effects of adsorbed fulvic acid, a naturally occuring organic acid, on the kinetics of hematite aggregation and on the resulting structure of hematite aggregates were also investigated. The study of aggregate structure shows that the fractal dimensions of hematite aggregates which are partially coated with fulvic acid molecules are higher than those obtained with no adsorbed fulvic acid. The scattering exponents obtained from static light scattering experiments of these aggregates range from 2.83 ± 0.08 to 3.42 ± 0.1. The scattering exponents of greater than 3 indicate that the scattering is the result of objects that contains pores which are bounded by surfaces with a fractal structure, and can be related only to surface fractal dimension. The high fractal dimensions are due to restructuring within the aggregates, which only occured at low coverage by the organic acid.     

Influence of sulphur atom on the qualitative behavior of electron impact total cross sections of some sulphur containing molecules

Absolute elastic differential cross sections (DCS) have been measured experimentally for several sulphur containing molecules such as SF₆, CS₂, DMS and DMSO using a novel high resolution electron spectrometer. The measured DCS’s were extrapolated in the forward and backward angles using a tenth order legendre polynomial based least squares fitting technique. Total cross sections (TCS) were determined by integrating the DCS over all angles for each incident energy. The influence of the sulphur atom on the molecular TCS is studied by comparing the qualitative behavior of electron impact cross sections for the sulphur containing molecules against the TCS of the sulphur atom at each incident energy. Theoretical calculations based on independent atom model are also presented as a guide to understand the nature of the electron-molecule collision processes measured in this study.     

Kinetics of colloidal fractal aggregation by differential dynamic microscopy

We study the kinetics of an aggregation process induced by adding salt to a stable colloidal suspension of 73 nm (diameter) particles. Despite the subdiffraction size of the colloidal particles, the process is monitored via optical microscopy, which is used here to obtain time-resolved scattering information about the colloidal aggregates. The radius of the aggregates is determined as a function of time and their fractal dimension is extracted. Our results are compatible with a diffusion limited aggregation process, as independently confirmed by spectral turbidimetry measurements on the same sample.     

分形凝聚粒子的光散射特性研究

粒子的形状和凝聚对光散射特性有着很大的影响.基于分形生长的受限扩散(DLA)模型,模拟了凝聚粒子的三维空间分形结构,并采用回转半径法计算了凝聚粒子的分形维数.利用离散偶极子近似(DDA)方法研究了纳米石墨凝聚粒子的光散射特性,对于原始粒子数不同的凝聚粒子及分形结构不同的凝聚粒子,数值计算了散射强度和偏振度随散射角的分布...