Small angle x—ray scattering study on the conformation of polystyrene in toluene during adding anti—solvent CO2

The conformatiopn of polystyrene in the anti-solvent process of supercritical fluids(compressed CO2 polystyrene toluene)has been studied by small angle x-ray scattering with synchrotron radiation as an x-ray source.Coilto-globule transformation of the polystyrene chain was observed with the increase of the anti-solvent CO2 pressure;i.e.polystrene coiled at a prssure lower than the cloud point pressure(Pc)and turned into a globle with a uniform density at pressures higher than Pc.Fractal behaviour was also found in the chain contraction.and the mass fractal dimension increased with increasing CO2 pressure.     

STUDY OF MESOPOROUS SILICA MATERIALS BY SMALL ANGLE X—RAY SCATTERING

Small angle X-ray scattering experiments have been performed to study the microstructure of messoporous silica meterials prepared by condensation of tetraethylorthosilicate using nonionic alkylpolyethyleneoxide(AEO9) and ionic cetyltrimethylammonium bromide (CTAB) surfactant as templates.It is the pores within the nanometre range that produce the main cattering.The scattering of the pure silica systems obey Porod’s law.This may be because the templates produce some additional scattering background and then make the scattering of pores distorted.The results show that the full removal of templates from the pores of the materials by Soxhlet extraction is very easy for AEO9,but it is difficult for CTAB.The positive deviation correction is also perfromed.     

SAXS andalysis of interface in organo—modified mesoporous silica

A small-angle x-ray scattering(SAXS)technique using synchrotron radiation as the x-ray source has been employed to characterize the microstructure of mesoporous silica prepared by one-pot template-directed synthesis methodology.The scattering of pure silica agreed with Porod’s law.the scattering of organomodified mesoporous silica showed a negative deviation from Porod’s law,suggesting that an interfacial layer exists between the pores and silica matrix.It was the organic groups comprising the interface,as shown by ^29Si cross-polarization magic-angle spinning nuclear magnetic resonance imaging (^29Si cp MAS/NMR) and Fourier transform infrared spectroscopy(FTIR),that caused this negative deviation of SAXS intensity from Porod’s law,and the average thichness of the interfacial layer could be deduced from this negative deviation.Copyright 2001 john Wiley and Sons,Ltd.     

Self—assembly behaviour of amphiphilic diblock copolymer in selective solvents studied by synchrotron small—angle x—ray scattering

The aggregation behaviour of styrene-vinyl benzoic acid (PS_m-b-PVBA_n) amphiphilic diblock copolymers in selective solvents with different m and n was investigated by synchrotron small-angle x-ray scattering (SAXS). We have carried out a detailed analysis of scattering intensity, dimension, shape and microstructure of the diblock copolymers of narrow distribution in water, methanol, ethanol and isopropanol selective solvents, respectively. We have found that the aggregation behaviour of the copolymer depends on the nature of the solvent and the micelle forms flat disc objects with the ratio of radius ω=0.4. The average radius gyration R_g of the copolymer decreases as solvents change from isopropanol to ethanol and to methanol, and increases with increasing pH in aqueous solution, but decreases with the addition of CoCl_2 in ethanol solvent. The scattering intensity of diblock copolymer micelle follows I(h)∝h^{-α} in different selective solutions, suggesting that the PS_m-b-PVBA_n coils have self-similar structure behaviour or a fractal structure in the selective solvents. All of these revealed that the aggregation behaviour of the diblock copolymer changes dramatically with experimental condition in the selective solvent. The increase of mass fractal dimension (D_m) from 2.12 to 2.47 indicates that the copolymer chain changes from a swollen coil to a rather compact disc in the course of changing solvents, decreasing surface fractal dimension (D_s) from 2.98 to 2.58 indicates that the copolymer micelle change from a rather rough surface to a smooth form in the course of increasing pH in aqueous solutions, and increasing D_m and D_s from 2.29 to 2.35 and 2.70 to 2.90, respectively, indicates the shrinkage of copolymer micelle to a rather compact and rough disc form by adding CoCl_2 in ethanol solvents.     

A negative deviation from Porod’s law in SAXS of organo—MSU—X

Small-angle X-ray scattering(SAXS)using synchrotron radiation as X-ray source has been employed to charactcizc the microscopic structrure of organo-modified mesoporous molecular sieves(organo-MSU-X)prepared by a one-pot template-directed synthesis.It is shown that the SAXS profile is hardly constant with Porod’s law showing a negative slope,i.e.,negative deviation.This suggests that there is diffuse interfacial layer located between the pores and the matrix.This suggests that the organic groups remain covalently linked to the matrix,as indicated by ^29SiCP MAS NMR and FT-IR.The average thickness of the interfacial layer was found to be about 1nm for each of the three samples with different kinds and the same amounts(20? of organic groups.This kind of material has also been proved to possess both surface and mass fractal structure of the amophous porous silica materials.2001 Elsevier Science B.V.All rights reserved.     

Study of strain and compostion of the self—organized GE dots by grazing incident X—ray diffraction

Grazing incident X-ray diffraction at different grazing angles for self-organized Ge dots grown on Si(001) are carried out and lattice constant expansions of 1.2?parallel to the surface as compared with the Si lattice are found within the Ge dots.A 3.1?lattice expansion of the Ge dots along the growth direction is also fund by ordinary X-ray(004) diffraction.According to the Poisson equation and the Vegard law,our results infer that the Ge dot should be a partially strain relaxed SiGe alloy with Ge content of abuot 55?2001 Elsevier Science B.V.All rights reserved.     

Beijing synchrotron radiation total—reflection X—ray fluorescence analysis facility and its applications on trace element study of cells

The feasibility of total-reflection X-ray fluorescence(TXRF) analysis excited by synchrotron radiation applied to trace element analysis of biological cells is investigated.The Beijing synchrotron radiation TXRF facility and the related xperimental method are also described.The elemental mininum detection limits of some standard reference materials are determined.The elemental compositions of a cluster of small intestine cells of a small white mouse are given,and hence the average trace element contents of the single small intestine cell are also obtained.With this technique,the changes of some trace elements in the cells of lung and cervix cancer before and after apoptosis are also preliminarily studied.2001 Elsevier Science B.V.All rights Reserved.     

Synchrotron X—Ray Study on Structures of Ni80Fe20／Cu Superlattices

We have shown that,in contrast to the results in the literature,the Bragg peak intensity of Ni80Fe20/Cu superlattices is enhanced at the incident x-ray energy slightly higher than the absorption edge of the heavier element(Cu).The atomic density at Ni80Fe20/Cu interface was analysed by the diffraction anomalous fine structure technology with the incident angle of x-ray fixed at the first Bragg peak.Our results demonstrate the epitaxy growth of Ni80Fe20/Cu superlattices.Upon annealing,the epitaxity of Ni80Fe20/Cu multilayers becomes poor but the local crystallinity in each layer is improved.     

Crystal growth of β’—Gd2（Mo4）3 and in situ observation of its domain structure by the microscope and the synchrotron X—ray topography

We report that β’-Gd2(MoO4)3 crystals have been grown by the Czochralski(CZ) method.We studied the growth conditions fo β’-Gd2(MoO4)3 crystal.A compatison between the resistance-heated method and radio frequency induction-heated method is described.Also,the in situ observation of the domain structure by the microscope and by synchrotron radiation X-ray topography under the conditions of DC polarization voltage and tempertature change were carried out.Experiments showed that multidomain structure including ferroelectric and ferroelastic domains occurred in β’-Gd2(MoO4)3 cystal.Usually ferroeletiric domains appeared in the as-grown crystal and ferroelastic domains appeared in the polished thinner piece.Both ferroelectric and ferroelastic domains disappeared when the temperature of the crystal piece was higher than the Curie tempperature Tc and they could be reproduced when the temperature of the crystal piece was lowered below TC.When a DC polarization voltage ranging from 150 to 500V was applied on a c-axis β’-Gd2(MoO4)3 piece having a thickness of 0.5mm ,the multidomain would gradually transform to a single domain.This resual means that it is possible to make a periodically poled β’-Gd2(MoO4)3 crystal.2001 Elsevier Science B.V.All rights reserved.     

Study of Ni80Fe20／Fe50Mn50 superlattice microstructures by transmission electron microscopy and x—ray diffraction

The detailed microstructures of Ni80Fe20/Fe50Mn50 superlattices have been characterized using both x-ray diffraction techniques and transmission electron microscopy.The obrivous layered structure,typical column structure and twins which exist in Ni80Fe20/Fe50Mn50 superlattices were observed through performing transmission microscopy.By combining the technique of lowangle x-ray reflectivity(specular and off-specular scans)with the anomalous scattering effect and high-angle x-ray diffraction(using conventional x-ray),wequantitatively analysed the microstructural variation as a function of annealing temperature.It is found that the lateral correlation length,the(111)peak intensity of the superlattices and the average multilayer coherence length all increase with a rise in annealing temperature annealing can decrease the rootmean-square roughness at the interfaces of Ni80Fe20/Fe50Mn50 superlattices.the obtained microstructural knowledge will be helpful in understanding the magnetic properties of the ni80Fe20/Fe50Mn50 exchange bias system.     

Micro—structural analysis of YBa2Cu3O7—x thin films grown on different substrates by X—ray techniques

YBa2Cu3Ox(YBCO) thin films grown on different substrates with and/or without Eu2CuO4(ECO) buffer layer were investigated by X-ray wide angle diffraction,reflection,diffuse scattering and topography.Theresults show that for the yttria stabilized ZrO2(YSZ) substrate,the presence of an ECO buffer layer improves the crystalline quality of the YBCO film,while a negative effect is observed for the SrTiO3(STO) substrate.The lateral correlation length for a sample grown on a YSZ substrate with ECO buffer Layer is much greater than grown on an STO subetrate.The STO substrate used has mosaic structure.2001 Elsevier Science B.V.All rights reserved.