SAXS investigation of the structure of high-pressure crystallized poly(ethylene terephthalate): a new nanostructured material?

The common crystallization conditions of poly(ethylene terephthalate) (PET) were replaced by an anabaric high-pressure crystallization at 320 °C. The PET samples were characterized by differential scanning calorimetry, density and microhardness. The resulting two-phase microstructure was studied by means of absolute small-angle X-ray scattering (SAXS). A complete SAXS analysis utilizing the interface distribution function (IDF) method was carried out. The resulting structure exhibited the presence of stacks of 10 nm thick crystalline lamellae which were separated by amorphous layers of about 1.3 nm thickness. Similar structures have been found after annealing of amorphous metals and have been termed nanocrystalline. Microhardness and structure have been discussed in analogy with the notions from the field of nanostructured materials. Theoretically, a multi-component lamellar two-phase structure has been discussed. The equations derived allow the computation of volume fractions and specific surfaces of the components (different kinds of stacks). This revised version was published online in November 2006 with corrections to the Cover Date.     

小角X射线散射技术在材料研究中的应用

小角X射线散射(SAXS)是一种有效的材料亚微观结构表征手段。简单介绍了小角X射线散射理论,并综述了小角X射线散射技术在材料研究中的应用,内容涉及纳米颗粒尺寸测量,合金中的空位浓度、合金中的析出相尺寸以及非晶合金中的晶化析出相的尺寸测量,高分子材料中胶粒的形状、粒度以及粒度分布测量,以及高分子长周期体系中片晶的取向、厚度、结晶百分数和非晶层厚度的测量等等。     

The structure of granular amorphous carbon films with cobalt nanoparticles

The films of amorphous hydrogenated carbon containing cobalt nanoparticles are studied by small-angle X-ray scattering (SAXS). The SAXS pattern structure reveals the presence of two types of scattering centers, one of which represents cobalt particles. It is suggested that the second type of scattering centers can represent the groups of nanoparticles possessing a localized electron wavefunction and forming a cluster electron state.     

Structure and mechanical properties of a Fe90Zr10 amorphous alloy

The structure of a Fe₉₀Zr₁₀ amorphous alloy was investigated by means of small angle X-ray scattering as well as large-angle diffraction measurements. For as-quenched specimens, SAXS was found to be relatively weak, but spread over a wide scattering angle. After quantitative analysis, it was concluded that a compositional fluctuation occurs on a fine scale of about 0.6 nm. When the specimen was heat treated below the crystallization temperature, the amorphous structure changed to a more stable dual structure consisting of pure iron and a structure similar to Fe₃Zr. By prolonged heat treatment, the iron-rich regions crystallized initially from the amorphous state. An apparent correspondence was found to exist between the changes in the amorphous structure and in the mechanical properties. The microscopic phase separation within the amorphous state resulted in an increase of ultimate tensile strength and fracture toughness. The deterioration of mechanical properties was suggested to be attributed to the gradual crystallization of iron-rich regions.     

The effects of amorphous phase separation on crystal nucleation kinetics in BaO-SiO2 glasses

The nucleation kinetics of barium disilicate spherulites were determined by optical microscopy in BaO-SiO₂ glasses containing 27.0 to 33.3 mol % BaO for isothermal treatments at 718 to 760‡ C. Amorphous phase separation in two glasses was studied by small-angle X-ray scattering (SAXS) and transmission electron microscopy (TEM). The average diameter, number and surface area of amorphous droplets were obtained by SAXS as a function of time at 743 and 760‡ C. In glasses not showing amorphous phase separation the crystal nucleation rate,I, was constant at a given temperature. In glasses undergoing phase separation,I increased with time approaching a constant value, which was identical for different phase-separated glasses. There was a striking correlation between the time to reach a constantI and the time required to attain the equilibrium composition of the amorphous (baria-rich) matrix phase, as revealed by a constant integrated SAXS intensity. The crystal nucleation rate,I, depended primarily on the composition of the baria-rich phase. There was no apparent relationship betweenI and the surface area or number of droplets from SAXS. However, possible evidence of additional crystal nucleation at droplet interfaces was found, although the effect was small. Viscosities and crystal growth rates for the phase-separated glasses are also discussed.     

涤纶短纤维在纺程中的XRS、DMA研究

应用ＦＲＳ－ＸＲＳＡ、ＳＡＸＳ、ＤＭＡ等研究了涤纶短纤维在纺丝及后处理过程中的结晶,取向与超结构的形成与变化,并讨论了涤纶纤在后加工过程中玻璃化温度与纤维聚集态结构的关系。     

The silicon neighborhood across the a-Si:H to μc-Si transition by X-ray absorption spectroscopy (XAS)

We report a synchrotron X-ray absorption spectroscopy study of the average neighborhood of Si near the transition from a-Si:H to μc-Si on wedge-shaped samples prepared by hot-wire CVD in a chamber using a movable shutter. The thickness of the wedge varies from 30 to 160 nm. Nucleation of μc-Si occurs at a critical thickness of approximately 100 nm. X-Ray absorption was measured at the Si K-edge (1.84 keV) by total electron photoemission yield. The absorption oscillations in the EXAFS region are very similar to all along the wedge. Analysis indicates an average tetrahedral first neighbor shell with radial disorder decreasing with crystallization. In the near-edge (XANES) region multiple scattering effects appear at the onset of crystallinity. Unlike single crystal silicon, these effects involve only double scattering within the first neighbor shell, indicating an ill-formed second shell in μc-Si.     

Study of the structure and crystallization of an Fe-17 at % B amorphous alloy

The structure of an Fe₈₃B₁₇ amorphous alloy was examined in detail, mainly by means of small-angle X-ray scattering (SAXS) measurements. The electron density-density correlation derived from the observed intensity had the following characteristic features: a strong correlation concentrated in the short radial distances within about 1.2 nm and a rather weak correlation towards larger distances. After quantitative analysis, it was concluded that a compositional fluctuation occurs on a fine scale of about 1 nm in the amorphous Fe-B alloys, even though phase separation is not present as completely as in the structure model proposed by Boudreaux. Electrical resistivity measurements as well as transmission electron microscope (TEM) observations were performed to investigate the crystallization process. By using the theoretical equation of electrical resistivity reported by Landauer, the temperature dependence for the partially aged amorphous alloys was analysed. The volume fraction of crystalline phase estimated from the present analysis was in good agreement with the results obtained from TEM observation.     

Melting and crystallization of UHMWPE skived film

Commercial skived film from ultra-high molecular-weight polyethylene (UHMWPE) with considerable uniaxial orientation of lamellae is studied by ultra-small-angle X-ray scattering (USAXS) and wide-angle X-ray scattering (WAXS) during melting and crystallization in order to identify its mechanisms of crystallization. For the analysis of the nanostructure two-dimensional USAXS patterns are analyzed by means of the multidimensional chord distribution function (CDF) method. WAXS shows that crystallization is always isotropic and fast. WAXS reflections are observed before—under certain processing conditions—the SAXS pattern becomes anisotropic. Thus crystallization is decoupled from a slower process of oriented nanostructure formation (nanoforming). If nanoforming is performed isothermally at 105 °C, the evolving nanodomain layers obtain some preferential orientation, as long as the orientation of the melt has not previously been erased by melt-annealing at temperatures of 140 °C or above. Crystallization at temperatures ≥110 °C followed by quenching leads to isotropic nanostructure. Although crystallization is always observed early in the WAXS patterns, the USAXS patterns exhibit only weak discrete scattering during isothermal treatment at temperatures of 110 °C and higher. At 105 °C anisotropic isothermal nanoforming starts after 1.5 min. The melting of the original material resembles an inverted random car-parking mechanism. Only next-neighbor correlations are observed among the crystalline layers. The average nanodomain layer thickness is only slightly increasing (26–30 nm), whereas the long period increase is strong (from 60 nm to 140 nm).     

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 AI-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 nanometers 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.     

IPP／Zn—SEPDM共混物的DMA和SAXS研究

本文通过SAXS、DMA和TEM研究了乙丙三元橡胶(EPDM)和乙丙橡胶磺酸锌盐(Zn-SEPDM)对等规聚丙烯(IPP)晶体结构的影响以及IPP/Zn-SEPDM和IPP/EPDM共混物的相容性。用一维电子密度函数分别求得IPP晶区、非晶区和聚丙烯晶相和非晶过渡层厚度,用虚拟两相模型描述了IPP的晶体结构。EPDM和Zn-SEPDM与IPP的非晶相和过渡相均有一定相互作用,随磺化度提高,相互作用增强。由于在乙丙橡胶分子链中引入了磺酸锌盐基团,离子基团聚集成离子微区,形成物理交联点,抑制了共混物的相分离,提高了制品的韧性和强度。     

Synchrotron radiation small-angle X-ray scattering study on fracture process of carbon nanotube/poly(ethylene terephthalate) composite films

Time-resolved small-angle X-ray scattering (SAXS) measurements have been conducted during tensile deformation of carbon nanotube (CNT)/amorphous poly(ethylene terephthalate) (PET) composite films using synchrotron radiation in order to investigate the fracture process. The observed SAXS patterns consisted of the streaks parallel to the loading direction caused by the total reflection at craze/polymer interfaces, the streaks perpendicular to the loading direction caused by the fibril/void structure of crazes and the scattering from CNTs. The formation, widening and fracture processes of the crazes were investigated based on the changes of SAXS patterns during deformation and the fracture toughness of the composite films determined with essential work of fracture method. The influences of CNT addition on the mechanical properties of PET varied depending on the specimen geometries used for the mechanical tests and marked influences were obtained with surface-notched specimens. The CNT addition increased the energy needed to widen the crazes and retarded the growth and fracture of the crazes during deformation. This lead to the increases in the plastic work of fracture and the fracture toughness of PET. The CNT aggregates formed at the CNT fraction beyond 3 wt%, however, caused reduction of the fracture toughness.     

Low temperature precipitation kinetics of niobium nitride platelets in Fe

Single plane platelets of niobium nitride have been observed to form in a Fe-Nb-N alloy during ageing at 600 °C, using High Resolution Electron Microscopy, Field Ion Microscopy and Atom Probe Tomography. Small-angle neutron scattering has been used to investigate the kinetics of formation of these platelets. They are shown to nucleate in less than 5 min at this ageing temperature, and subsequently to grow in-plane to a size of about 10 nm without experiencing any change in thickness.     

Long periods in oriented semicrystalline polymers at low temperatures

The reflection peak intensity in the small-angle X-ray scattering (SAXS) curves of oriented semicrystalline isotactic poly(propylene) and low-density poly(ethylene) films exhibits a reversible severalfold decrease upon cooling the samples to −90°C. At the same time, the other supermolecular structure parameters (long periods and the longitudinal dimensions of crystallites and amorphous regions, etc.) remain unchanged. The observed reversible SAXS peak intensity variations are explained by the fact that a part of the polymer chains penetrate from inter-to intrafibril (amorphous) regions or return back into the interfibril (crystalline) regions.     

Superparamagnetic maghemite nanorods: analysis by coupling field-flow fractionation and small-angle X-ray scattering

We report on the online coupling of asymmetrical flow field-flow fractionation (A4F) with small-angle X-ray scattering (SAXS) for the detection of nanoparticles. The A4F was used to fractionate superparamagnetic maghemite nanoparticles, which were prepared continuously with a micromixer. The outlet of the A4F was directly coupled to a flow capillary of a SAXSess instrument (Kratky type of camera). SAXS curves were recorded in a 1 s time interval. This was possible by using intense synchrotron radiation. The radii of gyration of the nanoparticles, as determined from Guinier plots, increased from 2 to 6 nm with increasing fractionation time of the A4F. A more detailed analysis of the scattering curves revealed that the particles were cylindrical in shape (nanorods), which we attributed to the micromixing preparation technique. The radii of the nanorods increased only slightly from 1.2 to 1.7 nm with increasing fractionation time, while the lengths increased strongly from 7.0 to 30.0 nm. The volume distribution of the nanorods was determined and described by Schultz-Zimm and log-normal distributions. Nanorod volumes increased from 45 to 263 nm(3), corresponding to molar masses of 140 x 10(3) to 820 x 10(3) g mol(-1). We propose A4F-SAXS coupling as a new method for analysis of nanoparticles of complex composition in solution. It allows precise online determination of the particle's shape and size distributions. This method can be applied to mixtures of nanoparticles of arbitrary shapes and sizes (1-100 nm). Moreover, the total time needed for fractionation and online SAXS data recording is usually only 20 min.     

Nanostructured CeO2 thin films: A SAXS study of the interface between grains and pores

The analysis of the interface between grains and pores in thin films of CeO₂, prepared by two different sol-gel procedures, was performed using grazing incidence small-angle X-ray scattering. The existence and the average thickness of an interfacial layer, formed during one of the preparation procedures, were examined by analyzing the depletion of scattering intensity in the Porod's scattering region.     

A correlation analysis of isothermal crystallization of long paraffins

The small-angle X-ray scattering (SAXS) curves for ultralongn-alkanes obtained by Ungar and Keller at different times after reaching the crystallization temperature have been Fourier analysed. The correlation curves so obtained at different temperatures and different annealing times reflect sensitively all those morphological features which are broadly characteristic of the scattering curves. In addition the correlation curves clearly show a transition from a non-integer-fraction length to extended chain structure. Crystalline and amorphous lengths, degree of order and half-widths which characterize kinetics of morphological changes are also reported.     

同步辐射小角X射线散射及其在材料研究中的应用

小角X射线散射(small angle X-ray scattering,SAXS)是研究物质内部一纳米到数百纳米甚至到微米尺度级别微观结构的有力工具.近年来随着我国同步辐射技术的不断发展,同步辐射SAXS技术被越来越多地应用到各种材料的研究领域.然而,由于SAXS图谱是倒空间的信号,并不像显微镜那么直观,也不如X射线...     

Structure and optical function of amorphous photonic nanostructures from avian feather barbs: a comparative small angle X-ray scattering (SAXS) analysis of 230 bird species

Non-iridescent structural colours of feathers are a diverse and an important part of the phenotype of many birds. These colours are generally produced by three-dimensional, amorphous (or quasi-ordered) spongy β-keratin and air nanostructures found in the medullary cells of feather barbs. Two main classes of three-dimensional barb nanostructures are known, characterized by a tortuous network of air channels or a close packing of spheroidal air cavities. Using synchrotron small angle X-ray scattering (SAXS) and optical spectrophotometry, we characterized the nanostructure and optical function of 297 distinctly coloured feathers from 230 species belonging to 163 genera in 51 avian families. The SAXS data provided quantitative diagnoses of the channel- and sphere-type nanostructures, and confirmed the presence of a predominant, isotropic length scale of variation in refractive index that produces strong reinforcement of a narrow band of scattered wavelengths. The SAXS structural data identified a new class of rudimentary or weakly nanostructured feathers responsible for slate-grey, and blue-grey structural colours. SAXS structural data provided good predictions of the single-scattering peak of the optical reflectance of the feathers. The SAXS structural measurements of channel- and sphere-type nanostructures are also similar to experimental scattering data from synthetic soft matter systems that self-assemble by phase separation. These results further support the hypothesis that colour-producing protein and air nanostructures in feather barbs are probably self-assembled by arrested phase separation of polymerizing β-keratin from the cytoplasm of medullary cells. Such avian amorphous photonic nanostructures with isotropic optical properties may provide biomimetic inspiration for photonic technology.     

WAXD/SAXS study and 2D fitting (SAXS) of the microstructural evolution of PAN-based carbon fibers during the pre-oxidation and carbonization process北大核心CSCD

Microstructutal evolution in polyacrylonitrile (PAN) fibers at different temperatures during pre-oxidation and carbonization under stretching was studied by. synchrotron wide-angle X-ray diffraction (WAXD) and small-angle X-ray scattering (SAXS). Microvoids were characterized by the classical SAXS method, and were compared with simulation results obtained by fitting 2D SAXS patterns to a model based on a dilute system of cylindrical microvoids randomly distributed and preferentially orientated along the fiber axis and having a log-normal size distribution. The WAXD results showed that the crystal size, d-spacing and preferred orientation decreased during pre-oxidation, and increased during carbonization. A diffraction peak for PAN fibers at 2 theta = 13. 6 degrees disappeared during the final stage of pre-oxidation, meanwhile a new peak at 2 theta = 23.6 degrees appeared, whose intensity increased during carbonization, indicating the formation of the graphite structure. The average length of the microvoids increased, and new microvoids were formed, which became oriented along the fiber axis as the fiber manufacturing process proceeded. The length of microvoids from simulation results is consistent with that from the classical method, indicating that the model is valid to describe the microvoid structure of fibers.