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Synchrotron small angle X-ray scattering study on the conformation of polystyrene in compressed CO_2-toluene mixture

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Science China(Physics,Mechanics & Astronomy) 2003年第6期46卷 570-579页

作者：董宝中荣利霞柳义李丹韩布兴刘志敏 Institute of High Energy Physics Chinese Academy of Sciences Beijing 100039 China Center for Molecular Science Institute of Chemistry Chinese Academy of Sciences Beijing 100080 China

Synchrotron small angle X-ray scattering (SAXS) was performed to investigate the effect of dissolved CO2 in toluene on the conformation of polystyrene (PS) in the solution. It has been found that the second virial coefficient A2 and the radius of gyration Rg decrease with the increasing antisolvent CO2 pressure. The scattering intensity of PS chain followed l(h)∞h-αunder different antisolvent pressures (0, 0.6, 1.5, 2.4, 3.3, and 4.2 MPa), suggesting that the PS chain has self-similar structure behavior or a fractal structure in the presence of antisolvent CO2.All this reveals a large effect of antisolvent pressure or the solubility of CO2 in the solution on PS structure. The fractal dimensions increase with the increasing antisolvent pressure, indicating that the polymer chain changes from a swollen coil into a rather dense globule in the course of adding antisolvent CO2.

关键词： small-angle X-ray scattering, polystyrene, conformation.

DETERMINATION OF THE SPECIFIC INNER SURFACE OF CRYSTALLINE-AMORPHOUS TWO-PHASE SYSTEM BY small-angle X-RAY SCATTERING

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Science China Mathematics 1991年第6期34卷 740-745页

作者：孟昭富王煜明 Materials Science Institute Jilin UniversityChangchun 130023PRC

The specific inner surface, Sp, of the crystalline-amorphous 2-phase system inCu73Sn6Ni6P15 metallic glass, aged at 473 K, was determined by small-angle X-ray scatteringand wide-angle X-ray diffraction. The experimental results show that the specific innersurface decreases from 144 m2/cm3 to 96 m2/cm3 as aging period increases from 5 min to 4 h.The error of Sp values is about 7%.

关键词： small-angle X-ray scattering metallic glass specific inner surface.

small-angle X-Ray Scattering of Amorphous Germanium: Numerical Modeling

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Advances in Materials Physics and Chemistry 2013年第1期3卷 19-30页

作者： R. Ben Brahim A. Chehaidar Research Unit in Mathematical Physics Department of Physics Faculty of Sciences University of Sfax Sfax Tunisia

The present work deals with a detailed analysis of the small-angle X-ray scattering of nanoporous atomistic models for amorphous germanium. Structures with spherical nanovoids, others with arbitrarily oriented ellipsoidal ones, with monodisperse and polydisperse size distributions, were first generated. After relaxing the as-generated structure, we compute its radial distribution function, and then we deduce by the Fourier transform technique its X-ray scattering pattern. Using a smoothing procedure, the computed small-angle X-ray scattering patterns are corrected for the termination errors due to the finite size of the model, allowing so, for the first time at our best knowledge, a rigorous quantitative analysis of this scattering. The Guinier’s law is found to be valid irrespective of size and shape of the nanovoids over a scattering vector-range extending beyond the expected limit. A weighted combination of the Guinier’s forms accounts for well the nanovoid size distribution in the amorphous structure. The invariance of the Q-factor and its relationship to the void volume fraction are also confirmed. Our findings support then the quantitative analyses of available small-angle X-ray scattering data for amorphous germanium.

关键词： Amorphous Germanium Structure small-angle X-Ray Scattering Modeling

The Significance of Solutions Obtained from Ill-Posed Systems of Linear Equations Constituted by Synchrotron Radiation Based Anomalous small-angle X-Ray Scattering

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Advances in Linear Algebra & Matrix Theory 2018年第1期8卷 64-86页

作者： Günter Johannes Goerigk Institute of Soft Matter and Functional Materials Helmholtz-Zentrum Berlin Berlin Germany

Synchrotron radiation based experimental techniques known as Anomalous small-angle X-ray Scattering (ASAXS) provide deep insight into the nanostructure of uncountable material systems in condensed matter research i.e. solid state physics, chemistry, engineering and life sciences thereby rendering the origin of the macroscopic functionalization of the various materials via correlation to its structural architecture on a nanometer length scale. The techniques constitute a system of linear equations, which can be treated by matrix theory. The study aims to analyze the significance of the solutions of the stated matrix equations by use of the so-called condition numbers first introduced by A. Turing, J. von Neumann and H. Goldstine. Special attention was given for the comparison with direct methods i.e. the Gaussian elimination method. The mathematical roots of ill-posed ASAXS equations preventing matrix inversion have been identified. In the framework of the theory of von Neumann and Goldstine the inversion of certain matrices constituted by ASAXS gradually becomes impossible caused by non-definiteness. In Turing’s theory which starts from more general prerequisites, the principal minors of the same matrices approach singularity thereby imposing large errors on inversion. In conclusion both theories recommend for extremely ill-posed ASAXS problems avoiding inversion and the use of direct methods for instance Gaussian elimination.

关键词： Matrix Inversion Condition Numbers LU-Decomposition Gaussian Elimination Synchrotron Radiation Anomalous small-angle X-Ray Scattering

In situ observation of synthesized nanoparticles in ultra-dilute aerosols via X-ray scattering

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Nano Research 2019年第1期12卷 25-31页

作者： Sarah R.McKibbin Sofie Yngman Olivier Balmes Bengt O.Meuller Simon Tagerud Maria E.Messing Giuseppe Portale Michael Sztucki Knut Deppert Lars Samuelson Martin H.Magnusson Edvin Lundgren Anders Mikkelsen Department of Physics and Nanolund Lund UniversityBox 11822100 LundSweden MaxIV Laboratory Lund UniversityBox 11822100 LundSweden University of Groningen Zemike Institute for Advanced MaterialsNijenborgh 4NL-9747 AG GroningenThe Netherlands ESRF-The European Synchrotron CS 4022038043 Grenoble Cedex 9France

In-air epitaxy of nanostructures(Aerotaxy)has recently emerged as a viable route for fast,large-scale production.In this study,we use small-a ngle X-ray scatteri ng to perform direct in-flight characterizati ons of the first step of this process,i.e.,the en gineered formatio n of Au and Pt aerosol nan oparticles by spark gen erati on in a flow of N2 gas.This represe nts a particular challe nge for characterizati on because the particle density can be extremely low in con trolled production.The particles produced are exami ned duri ng producti on at operatio nal pressures close to atmospheric conditions and exhibit a log no rmal size distributi on ranging from 5-100nm.The Au and Pt particle productio n and detection are compared.We observe and characterize the nanoparticles at different stages of synthesis and extract the corresponding domi nant physical properties,in cludi ng the average particle diameter and sphericity,as in flue need by particle sintering and the prese nee of aggregates.We observe highly sorted and sin tered spherical Au nano particles at ultra-dilute concen tratio ns(<5×10^5 particles/cm^3)corresponding to a volume fraction below 3×10^-10,which is orders of magnitude below that of previously measured aerosols.We independently confirm an average particle radius of 25 nm via Guinier and Kratky plot analysis.Our study indicates that with high-intensity synchrotron beams and careful con sideratio n of backgro und removal,size and shape info rmati on can be obtai ned for extremely low particle concentrations with industrially relevant narrow size distributions.

关键词： aerosol nanoparticle synthesis in situ analysis small-angle X-ray scattering Aerotaxy

Determination of Three Activation Energies for Metallic Glass by SAXS

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Science China Mathematics 1994年第7期37卷 870-877页

作者：孟昭富 Materials Science Institute Jilin University Changchun 130023 PRC

Activation energies for nucleation of the crystalline particle, En = 238 kJ.mol-1, for the growth, Eg=140 kJ . mol-1 and for the crystallization, Ec=210 kJ.mol-1, are obtained for Cu73Sn6Ni6P15 metallic glass in the temperature range of 443 K-473 K by SAXS. The incorrectness of using the growth rate of diameter of the crystalline particle to determine Eg has been shown: the correct method should be by using the growth rate of volume of particles. An improved method for correcting background errors of intensities scattered by aged metallic glass is proposed

关键词： small-angle X-ray scattering metallic glass activation energy for crystallization background correction.

Preparation, morphology, size quantization effect and photocatalytic properties of CdS Q-nanocrystals

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Science China Chemistry 2003年第2期46卷 196-206页

作者：章伟光钟昀范军孙姒巧唐宁谭民裕吴隆民 Department of Chemistry South China Normal University College of Chemistry and Chemical Engineering Lanzhou University

CdS nanoclusters were synthesized by using n- octylthiol as a ligand and n- hexadecyl- trimethyl-ammonium bromide (or n-tetrabutylammonium bromide) as an organic cation. Size- selective precipitation techniques have enabled the preparation of different CdS Q-nanoparticles with narrow size distribution and mean diameters ranging from 2 to 5 nm. UV-Vis spectroscopy, transmission electron microscopy (TEM) and small-angle X-ray scattering were used to determine the mean cluster size. Their size quantization effect has been observed in UV-Vis spectra, fluo-rescence spectra and small-angle X-ray diffraction, but it became too weak to be observed for large particles (2r > 10 nm). Moreover, their photo-catalysis has been studied by ESR technique and the results revealed that the photo-catalytic reaction occurred in the solution system and some free radicals such as CH2-OH in methanol, or CH3-CH-OH in ethanol were generated if some CdS Q-particles were added to methanol (or ethanol) and initiated by UV light at the same time, which may be very crucial in organic synthesis.

关键词： Q-nanoparticle, CdS nanocrystal, photocatalysis, small-angle X-ray diffraction, size quantization effect.

How Polymers Behave as Viscosity Index Improvers in Lubricating Oils

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Advances in Chemical Engineering and Science 2015年第2期5卷 134-151页

作者： Michael J. Covitch Kieran J. Trickett Applied Sciences Department The Lubrizol Corporation Wickliffe USA Applied Sciences Department Lubrizol Ltd. Hazelwood Derby UK

One of the requirements of engine lubricating oil is that it must have a low enough viscosity at low temperatures to assist in cold starting and a high enough viscosity at high temperatures to maintain its load-bearing characteristics. Viscosity Index (VI) is one approach used widely in the lubricating field to assess the variation of viscosity with temperature. The VI of both mineral and synthetic base oils can be improved by the addition of polymeric viscosity modifiers (VMs). VI improvement by VMs is widely attributed to the polymer coil size expanding with increasing temperature. However, there is very little physical data supporting this generally accepted mechanism. To address this issue, intrinsic viscosity measurements and small-angle Neutron Scattering (SANS) have been used to study the variation of polymer coil size with changing temperature and concentration in a selection of solvents. The results will show that coil size expansion with temperature is not necessary to achieve significant elevation of viscosity index.

关键词： Viscosity Index Improver Viscosity Modifier Polymer small-angle Neutron Scattering Rheology