Structure determination of Pt‐coated Au dumbbells via fluctuation X‐ray scattering

A fluctuation X‐ray scattering experiment has been carried out on platinum‐coated gold nanoparticles randomly oriented on a substrate. A complete algorithm for determining the electron density of an individual particle from diffraction patterns of many particles randomly oriented about a single axis is demonstrated. This algorithm operates on angular correlations among the measured intensity distributions and recovers the angular correlation functions of a single particle from measured diffraction patterns. Taking advantage of the cylindrical symmetry of the nanoparticles, a cylindrical slice model is proposed to reconstruct the structure of the nanoparticles by fitting the experimental ring angular auto‐correlation and small‐angle scattering data obtained from many scattering patterns. The physical meaning of the refined structure is discussed in terms of their statistical distributions of the shape and electron density profile.     

Properties,Morphology and Structure of BPDA/PPD/TFMB Polyimide Fibers

The mechanical properties of fibers were notably improved by incorporating 2,2′-bis(trifluoromethyl)- benzidine(TFMB) into 3,3′,4,4′-biphenyltetracarboxylic dianhydride(s-BPDA) and p-phenylenediamine(PPD) backbone. The best strength and modulus of BPDA/PPD/TFMB polyimide(PI) fiber(diamine molar ratio of PPD/TFMB= 90/10) were 1.60 and 90 GPa, respectively, which was over two times that of BPDA/PPD PI fiber. SEM image showed that the cross-section of fibers at each stage was round and voids free. Besides, the “skin-core” and microfibrillar structure were not observed. The thermal properties of PI fibers were also investigated. The results showed that the fibers owned excellent thermal stability, moreover, the structural homogeneity of fibers were significantly improved by heat-drawn stage. The T_g values were found to be around 300℃ by dynamic mechanical analysis(DMA). Wide angle X-ray diffraction(WAXD) and small angle X-ray scattering(SAXS) experiments indicated that the order degree of longitudinal and lateral stacks, the molecular orientation and the structural homogeneity of fibers were improved in the preparation process of fibers.     

Effect of DC bias on microstructural rearrangement of a-SiN:H films on PET substrate

Hydrogenated amorphous silicon nitride (a-SiN:H) films were deposited on flexible polyethylene terephthalate substrates at temperature as low as 100 °C by hot-wire chemical vapor deposition using SiH₄, H₂ and NH₃ precursors. Field emission scanning emission microscopy, Raman spectroscopy, Fourier transform infrared spectroscopy and small angle X-ray scattering were employed to study structural and microstructural properties of a-SiN:H films. The rms surface roughness increased with increase of positive bias to substrate. Intermediate range order, porosity and interface inhomogeneity in amorphous of a-SiN:H films evaluated by acoustic and optical phonon of silicon network, Guinier plot and correlated length from Raman and SAXS characterizations. The fractal behavior of a-SiN:H domains approached the perfect symmetry and the intermediate range order of a-SiN:H films deteriorate with increase of the positive substrate bias. Both correlation length and void size of the a-SiN:H amorphous domain increased with increase of the substrate bias from 0 to +200 V.     

用SAXS/WAXS研究聚氧乙烯/聚氧丁烯嵌段共聚物在n-己烷中的结晶性球形胶束结构

嵌段共聚物在选择性溶剂中能够自组装形成胶束,胶束的不同形状与嵌段共聚物的结构、溶剂和浓度有关．无定形嵌段共聚物通常形成球形胶束,在某些情况下也可以形成其它形状的胶束,关于结晶性嵌段共聚物在无定形链段选择性溶剂中的胶束结构和形状的报道非常少．由于结晶和相似相溶两种作用力的竞争,使得这类胶束的形状丰富多变．通常结晶作用较强时,结晶性嵌段共聚物形成片状的胶束,当结晶组分比较少时,可形成棒状胶束,尽管理论上已经指出存在球形胶束,但尚无关于这方面的报道。     

Morphological and crystalline studies of isotactic polypropylene plastically deformed and evaluated by small-angle X-ray scattering, scanning electron microscopy and X-ray diffraction

Morphological and structural properties of isotactic polypropylene (i-PP) submitted to uniaxial plane strain deformation at ambient temperature with compression pressures of 3, 10 and 20 MPa, were investigated using wide angle X-ray diffraction (WAXD), small-angle X-ray scattering (SAXS), transmission electron microscopy (TEM) and scanning electron microscopy (SEM). Two kinds of samples were studied, namely: sample A: Mw = 117,400 g/mol Mn = 17,300, Mw/Mn = 6.8 and sample B: Mw = 271,000 g/mol Mn = 43,700 Mw/Mn = 6.2, both with isotactic content = 95%. Crystalline α- and β-phases are clearly identified by WAXD. The lamellar long period, as well as, the crystalline and amorphous lamellar thickness for the non-deformed samples measured by SAXS indicates the presence of a more symmetric spherulitic structure for sample A, while the sample B displays anisotropic scattering. The WAXD study of the apparent relative crystallinity and the orientation of crystallites, revealed that plastic deformation of i-PP by plane-strain compression, leads to preferred orientation of main axis of crystallites at relatively early stage of the deformation process induced a monocrystal texture and an excellent molecular alignment along the FD, in both samples. The SEM evaluation shows that a gradual change occurs in the spherulitic structure and seems to transform gradually and disappear almost for the 37% deformations. The sample with highest deformation shows thin shear bands oriented along the FD-view which originate an appearance of a layered structure. Concomitantly the crystalline lamellae were detected by TEM technique.     

pH- and Ionic-Strength-Induced Structural Changes in Poly(acrylic acid)-Lipid-Based Self-Assembled Materials

Summary: The effect of a polyanion introduced as a lipid conjugate (poly(acrylic acid)- dimyristoyl-sn-glycero-3-phosphoethanolamine, PAA-DMPE) on the structure of a self-assembled, biomembrane mimetic has been evaluated using synchrotron small-angle X-ray scattering (SAXS). At high grafting density (8–11 mol.%), the PAA chains were found to produce significant changes in structure in response to changes in pH and electrolyte composition. At low pH and in the absence of salt (NaCl), the neutral PAA chains adopt a coil conformational state that leads to the formation of a swollen lamellar structure. Upon the addition of salt at low to intermediate pH values, two lamellar phases, a collapsed and an expanded structure, coexist. Finally, when the polymer is fully ionized (at high pH), the extended conformation of the polymer generates a cubic phase. The results of this study contribute to an understanding of how polyelectrolytes may ultimately be harnessed for the preparation of self-assembling materials responsive to external stimuli.     

一款小角X射线散射原位测量专用简易样品加热装置

原位加热实验是同步辐射小角X射线散射领域的新热点。本文针对同步辐射小角X射线散射中需要加热并原位实时检测的实验而设计的一款样品简易原位加热专用装置,该装置主要由温控器、样品池、固定架组成,它具有结构简单、操作容易的特点。本文介绍该装置的基本结构、特点并采用该装置进行原位加热干燥褐煤实验,通过分析实验结果验证装置的可行性。     

Supercritically-Dried Alginate Aerogels Retain the Fibrillar Structure of the Hydrogels

Summary: SAXS patterns of a Ca-alginate hydrogel and of the derived alcogel and aerogel have been recorded. All patterns correspond to disordered arrays of rod-like fibrils. The calculated size of the fibrils of the aerogel, 8 nm, is in good agreement with the results of scanning electron microscopy and N₂ adsorption. The results suggest that ethanol exchange and CO₂ supercritical drying do not affect the spatial organisation of the secondary structures of the gel and that characterisations of the aerogel can provide information on the organisation of the parent hydrogel.     

同步辐射在分子自组装研究中的应用

同步辐射是一种高亮度、高准直性、宽频谱的优质光源,其在物质原子或分子尺度的结构表征方面具有独特的优势。本文介绍了同步辐射在分子自组装研究中的一些应用,主要包括同步辐射X射线散射、时间分辨的小角X射线散射、时间分辨的X射线衍射、X射线精细结构谱,以及红外光谱,详细阐述了同步辐射X射线散射在层状结构、管状结构以及溶液中的组装体结构表征方面的应用。     

Simultaneous birefringence,small‐ and wide‐angle X‐ray scattering to detect precursors and characterize morphology development during flow‐induced crystallization of polymers

An experimental configuration that combines the powerful capabilities of a short‐term shearing apparatus with simultaneous optical and X‐ray scattering techniques is demonstrated, connecting the earliest events that occur during shear‐induced crystallization of a polymer melt with the subsequent kinetics and morphology development. Oriented precursors are at the heart of the great effects that flow can produce on polymer crystallization (strongly enhanced kinetics and formation of highly oriented crystallites), and their creation is highly dependent on material properties and the level of stress applied. The sensitivity of rheo‐optics enables the detection of these dilute shear‐induced precursors as they form during flow, before X‐ray techniques are able to reveal them. Then, as crystallization occurs from these precursors, X‐ray scattering allows detailed quantification of the characteristics and kinetics of growth of the crystallites nucleated by the flow‐induced precursors. This simultaneous combination of techniques allows unambiguous correlation between the early events that occur during shear and the evolution of crystallization after flow has stopped, eliminating uncertainties that result from the extreme sensitivity of flow‐induced crystallization to small changes in the imposed stress and the material. Experimental data on a bimodal blend of isotactic polypropylenes are presented.