Two new sealed sample cells for small angle x-ray scattering from macromolecules in solution and complex fluids using synchrotron radiation

Two different vacuum tight sample cells for in situ temperature dependent small angle scattering from liquids are presented in this article. In the first one, the sample fills a 1 mm thickness gap sealed on both sides by two thin parallel mica windows (volume 300 mul). In the second one, the liquid is injected into a 1 mm cylindrical capillary tube (volume 130 mul). The cells are lodged into temperature controlled chambers directly connected to the beamline vacuum path. Several important improvements with respect to similar instrumentation previously reported are: (1) versatile application of the mica cell, that can be used for all types of samples (gels, liquid crystals, and dispersions in organic solvents) and (2) the design of the chamber for the capillary cell allows registration of wider angle data and a convenient replacement of the capillary tube after each experiment. Signal to background ratio and data reproducibility were tested using protein solutions. We give a brief report of scattering experiments performed with different protein samples and two-dimensional data collection. (C) 2004 American Institute of Physics.75114541454

Polystyrene latex by dispersion polymerization: real time SAXS measurements

The purpose of this work was the characterization of polystyrene and poly(styrene-co-Boc-aminostyrene) latex particles obtained by dispersion polymerization as a function of reaction time. Small angle scattering of X-rays (SAXS) using synchrotron radiation was the main technique used to describe the system, by means of real time experiments (in situ) and in samples prepared from extracts of the polymerization reaction taken at several times during the polymerization process (ex situ). Complementary measurements of light scattering were performed on these extracted samples in order to estimate the average particle size at different times during the polymerization reaction. Analysis of the SAXS data gave information on the characteristics of the surface of the latex particles by means of the fractal dimension. The time evolution of the integrated intensity was related to changes in electron density contrast and the volume fraction of the solid polymer phase for both the styrene (ST) homopolymerization and styrene/Boc-aininostyrene (ST/Boc-AMST) copolymerization experiments performed in this work. The results indicated that there is a slight difference in these polymerization reactions taking into account the growth of the macromolecular chains that seems to be faster for the homopolymerization reaction. In the case of copolymerization, the Boc-AMST monomer competes with styrene in the insertion in the growing polymer chains, thus leading to a slow-down of the conversion rate. In both cases, the end product of the reaction is a polydisperse system of micron sized spherical particles with fractally rough surface. (C) 2002 Elsevier Science B.V. All rights reserved.2044169921122

Probing the structure of nanograined CuO powders

The microstructural properties of polycrystalline CuO powders and their evolution during controlled high energetic ball milling (HEBM) were studied using conventional X-ray diffraction (XRD) techniques and in situ temperature-dependent small and wide angle scattering (SAXS-WAXS) synchrotron radiation experiments. Volume weighted average grain size, unit cell expansion, oxygen deficiency, and microstrain values as a function of milling time were obtained from XRD. SAXS data revealed different nanostructures for samples synthesized by one-step solid-state reaction (SSR) or HEBM-treated powders. The latter presented the characteristics of a multilayered nanoscale solid system with surface fractal behavior. Correlation of the XRD microstructural parameters and the power law exponent of the SAXS curves as a function of temperature and milling time provided a coherent picture of the structure of HEBM-treated powders. The overall structural information presented in this article may shed some light on the macroscopic physical properties of CuO nanostructures.43103704371

Structure and morphology of poly(epsilon-caprolactone)/chlorinated polyethylene (PCL/PECl) blends investigated by DSC, simultaneous SAXS/WAXD, and elemental mapping by ESI-TEM

In this work, the structure and morphology of miscible blends of poly(epsilon-caprolactone) and chlorinated polyethylene with 48% chlorine weight content (PCL/PECl) were studied by differential scanning calorimetry (DSC), simultaneous small and wide-angle X-ray scattering (SAXS/WAXD), and electron spectroscopy imaging in the transmission electron microscope (ESI-TEM). A unique glass transition temperature was obtained in each blend. In addition to this, the heat capacity and the width of the glass transition did not have a linear behavior with blend compositions. These facts correlate with the presence of microheterogeneities originated from different local compositions and densities of interactions in each blend. A consistent picture of the mode of segregation of PECl in the blend was obtained. For higher concentration of PCL, the volume fraction of lamellar stacks in the samples decreased as a function of the PECl content, indicating preferential interfibrillar localization of the amorphous component. For lower PCL concentration, interespherulitic segregation was the dominant mode. Elemental maps of chlorine confirmed these results and also revealed changes in the concentration of this element depending on its localization in the microstructure of the system. Gradients of chlorine concentration were measured in larger amorphous regions of the 40/60 and 20/80 PCL/PECl blends. Calculations of the one-dimensional correlation function probed the reduction of the lamellar thickness of PCL when the quantity of PECl in the blend was increased. Such a tendency could be rationalized if the reduction of the fold surface free energy was a dominant factor in terms of the reduction of the degree of supercooling in the final crystal thickness.40225326

Domain structure and miscibility studies of blends of styrene-butadiene-styrene block copolymers (SBS) and styrene-glycidyl methacrylate statistical copolymers (PS-GAAA) using SAXS and DMTA

The domain structure and miscibility in the solid state of a series of blends of styrene-butadiene-styrene (SBS) block copolymers and styrene-glycidyl methacrylate (PS-GMA) statistical copolymers with varying molecular weights and compositions were studied using small angle X-ray scattering and dynamic mechanical thermal analysis. Depending on the molecular characteristics of each component, different types and degrees of solubilization of PS-GMA in SBS were found which, in addition to the initially SBS phase morphology, lead to materials with multiphase domain morphologies with differences in size and structure. The degree of solubilization of PS-GMA into the PS domains of SBS was found to be higher for blends containing PS-GMA with lower molecular weight (M-w = IS 100 g mol(-1)) and lower GMA content (I wt%) and/or for SBS with higher PS content (39 wt%) and longer PS blocks (Mw = 19 600 g mol(-1)). Localized solubilization of PS-GMA in the middle of PS domains of SBS was found to be the most probable to occur for the systems under study, causing swelling of PS domains. However, uniform solubilization was also observed for SBS/PS-GMA blends containing SBS with composition in the range of a morphological transition (PS block M-w = 19 600 g mol(-1) and 39 wt% of PS) causing a morphological transition in the SBS copolymer (cylinder to lamella). Copyright (c) 2006 Crown in the right of Canada. Published by John Wiley & Sons, Ltd.56330831

The effects of radiation on the density of an aluminoborosilicate glass

Glasses used for nuclear waste immobilization are subjected to high levels of radiation, and this may affect their physicochemical properties. Alpha radiation is responsible for an important fraction of the radiation energy dissipated in these glasses. It has been reported previously that some borosilicate glasses increase their density during irradiation while the density of other glasses decreases. Although the density increase of silica after irradiation has been understood, thanks mainly to molecular dynamics calculations and diffraction experiments, the processes involved in more complex glasses could be more varied. In this work we irradiated an aluminum-borosilicate glass which is a candidate for the aforementioned purposes and which increases density during alpha irradiation from the B-10 (n,alpha) Li-7 reaction. We studied the effects of alpha irradiation on its microstructure, using several experimental techniques, and subsequently correlated the results. Small angle X-ray scattering (SAXS) measurements revealed the presence of inhomogeneities of about 10 Angstrom in the untreated samples. After annealing these samples, TEM images displayed a contrast structure and helium pycnometry revealed density changes, both typical of glass phase separation. After irradiation, the glass density increased and the SAXS intensity decreased, indicating a compositional homogenization process in the samples subject to a higher dose of irradiation. Atomic displacements were calculated by means of the TRIM [1] computer code. The number of displacements produced by each 10B(n,alpha) Li-7 reaction was estimated at 580 and involved distances of up to 15 Angstrom An increase in the density of the irradiated samples can be explained in terms of the atomic displacements produced by the nuclear reaction cascades of the reaction B-10 (n,alpha) Li-7, in the scenario of pre-existing phase separation in the samples. In the case of the aluminum-borosilicate glasses studied here, which exhibit a fine phase separation, the density of the Si-rich phase increases with the incorporation of Na and B atoms. The B-rich phase also increases its density with the flow of Si atoms from the matrix. Vacancies created by irradiation in the glass structure, are responsible for a density decrease. The final effect is due to the sum of all contributions described, which in this case results in a net density increase of the irradiated samples. An understanding of this phenomenon can lead to the design of new glasses which overcome radiation with a minimum of density change. (C) 2001 Elsevier Science BY. All rights reserved.2894169917518

Polymorphic Phases of Natural Fat from Cupuassu (Theobroma grandiflorum) Beans: A WAXS/SAXS/DSC Study

Conselho Nacional de Desenvolvimento Científico e Tecnológico (CNPq)Fundação de Amparo à Pesquisa do Estado de São Paulo (FAPESP)The polymorphic phases of natural fat extracted from cupuassu beans were studied by performing in situ temperature-dependent X-ray scattering experiments and differential scanning calorimetry (DSC) using synchrotron radiation. Cupuassu (Theobroma grandiflorum) is a native plant of the Theobroma Species originally found in Brazil's Amazon region, with a great potential for utilization in the chocolate industry. The experiments and data analysis were performed using as a reference the known polymorphic phase behavior of cocoa butter. The results led to the identification of cupuassu fat polymorphic crystalline phases. Using the nomenclature generally found in the literature for triaceylclycerols (TAGS) systems, these phases were labeled gamma, alpha, beta', and beta in increasing order of melting temperature and stability. Differential scanning calorimetry measurements of fusion temperatures indicated the existence of two beta states in cupuassu fat. These phases were labeled beta(2) and beta(1), following the aforementioned nomenclature. In spite of the different melting points, the existence of a beta(2) -> beta(1) transition could not be proven, due to the great deal of structural similarity of the corresponding X-ray patterns obtained in our experiments. A comparison of our results with those reported for several pure compounds and ternary mixtures of TAGS indicated that these components are mainly responsible for the cupuassu fat phase behavior. This study provided the first experimental results of an in-situ follow-up of the polymorphic phase transitions and crystallization of fat from Brazilian cupuassu beans, an industrially important natural product.91251555163Laboratorio Nacional de Luz Sincrotron (LNLS)Conselho Nacional de Desenvolvimento Científico e Tecnológico (CNPq)Fundação de Amparo à Pesquisa do Estado de São Paulo (FAPESP)Conselho Nacional de Desenvolvimento Científico e Tecnológico (CNPq)Fundação de Amparo à Pesquisa do Estado de São Paulo (FAPESP