Distribution of Sulfur in Carbon/Sulfur Nanocomposites Analyzed by Small-Angle X-ray Scattering.

The analysis of sulfur distribution in porous carbon/sulfur nanocomposites using small-angle X-ray scattering (SAXS) is presented. Ordered porous CMK-8 carbon was used as the host matrix and gradually filled with sulfur (20-50 wt %) via melt impregnation. Owing to the almost complete match between the electron densities of carbon and sulfur, the porous nanocomposites present in essence a two-phase system and the filling of the host material can be precisely followed by this method. The absolute scattering intensities normalized per unit of mass were corrected accounting for the scattering contribution of the turbostratic microstructure of carbon and amorphous sulfur. The analysis using the Porod parameter and the chord-length distribution (CLD) approach determined the specific surface areas and filling mechanism of the nanocomposite materials, respectively. Thus, SAXS provides comprehensive characterization of the sulfur distribution in porous carbon and valuable information for a deeper understanding of cathode materials of lithium-sulfur batteries.

Morphology of crystalline-amorphous olefin block copolymers in solution characterized by small-angle neutron scattering and microscopy.

The single-chain properties and self-assembly behavior in dilute solution of olefin block copolymers obtained by chain-shuttling technology and consisting of alternating crystallizable and amorphous ethylene/1-octene blocks were investigated by pinhole and focusing small-angle neutron scattering techniques, optical microscopy in bright-field and crossed-polarizer modes, and differential scanning calorimetry. The complex hydrocarbon soluble (precipitant free) macro-aggregates formed with decreasing temperature are characterized by spherulitic textures. The spherulites yield, on one hand, a morphology that depends on the chain structure properties and, on the other hand, multiple structural levels with a hierarchical organization that ranges from 10 Šup to tens of micrometres. This morphology displays peculiarities dictated by the polydisperse character of these materials.

Coaggregation of Two Anionic Azo Dyestuffs: A Combined Static Light Scattering and Small-Angle X-ray Scattering Study.

The formation of azo dyestuff aggregates in dilute aqueous solution induced by the addition of Mg2+, Ca2+, Sr2+, or Ba2+ ions is followed by time-resolved static light scattering (SLS) and time-resolved small-angle X-ray scattering (SAXS). Time-dependent molar mass data of the growing aggregates is interpreted by means of a kinetic model introduced by Lomakin et al. ( Proc. Natl. Acad. Sci. U.S.A. 1996 , 93 , 1125 ) for the description of ß-amyloid aggregation. This interpretation reveals significant trends within the homologous series of alkaline earth cations. The trends refer to the nucleation and the growth rate of the dyestuff fibers. Time-resolved SAXS experiments indicate that these first two stages are followed by a third one during which a network forms by partial lateral alignment of fibers. At high enough dyestuff concentrations, this network formation even leads to a gel-like phase. Anomalous SAXS (ASAXS) on such a gel phase formed upon the addition of Sr2+ revealed the extent of neutralization of the dyestuff molecules within the gel by the specifically interacting alkaline earth cations.

Unbinding transition in lipid multibilayers induced by copper(II) ions.

We describe our observations on an unbinding transition in a multilamellar dispersion of phosphatidylcholine (PC) vesicles induced by copper(II) ions. The small-angle X-ray measurements clearly show that the increasing amount of CuCl2 in the millimolar concentration range continuously increases the amount of the unbound bilayers in the gel phase. Moreover, this phenomenon becomes more pronounced when the samples are heated above the so-called pretransition temperature between the gel and the ripple gel phase. The proposed reason for the latter is the increased repulsive electrostatic interaction due to the appearance of the surface modulation in the ripple gel phase. The observed effects reveal a new aspect of the unbinding phenomena since only the transition induced by the steric repulsion due to the layer fluctuations has been considered so far. Here, we show that the unbinding can also be triggered by the change in the electrostatic interactions. These findings are connected to the physical basis of the crucial role of copper(II) ions in biological processes such as neurodegenerative diseases and cell evolution.

Nanostructure of gel-derived aluminosilicate materials.

In the present work, aluminosilicate aerogels prepared under various conditions were compared with respect to their nanostructures and porosity. The purpose of this investigation was to find a suitable way to predict the final product structure and to tailor a required texture. Several Al and Si precursors (Al nitrate, Al isopropoxide, Al acetate, tetraethoxysilane (TEOS), and sodium silicate) were used in our examinations; the solvent content (water and alcohols), surfactants, as well as the catalysts were varied. In addition, the aerogels were subjected to various heat treatments. Hybrid aerogels were synthesized by the addition of different polymers (poly(acrylic acid), polyvinyl acetate, and polydimethylsiloxane). Aluminosilicate and hybrid aerogel structures were investigated by 27Al MAS NMR, SAXS, SEM, and porosity measurements. Loose fractal structures with a good porosity and high Al incorporation can be achieved from TEOS and Al nitrate or isopropoxide via a sol-gel preparation route. The use of Al acetate led to compact aerogel structures independently of the Si precursor, the pH, and the catalyst.

Gold nanoparticles decorated with oligo(ethylene glycol) thiols: protein resistance and colloidal stability.

The interactions between proteins and gold colloids functionalized with protein-resistant oligo(ethylene glycol) (OEG) thiol, HS(CH2)11(OCH2CH2)6OMe (EG6OMe), in aqueous solution have been studied by small-angle X-ray scattering (SAXS) and UV-vis spectroscopy. The mean size, 2R, and the size distribution of the decorated gold colloids have been characterized by SAXS. The monolayer-protected gold colloids have no correlations due to the low volume fraction in solution and are stable in a wide range of temperatures (5-70 degrees C), pH (1.3-12.4), and ionic strength (0-1.0 M). In contrast, protein (bovine serum albumin) solutions with concentrations in the range of 60-200 mg/mL (4.6-14.5 vol %) show a pronounced correlation peak in SAXS, which results from the repulsive electrostatic interaction between charged proteins. These protein interactions show significant dependence on ionic strength, as would be expected for an electrostatic interaction (Zhang et al. J. Phys. Chem. B 2007, 111, 251). For a mixture of proteins and gold colloids, the protein-protein interaction changes little upon mixing with OEG-decorated gold colloids. In contrast, the colloid-colloid interaction is found to be strongly dependent on the protein concentration and the size of the colloid itself. Adding protein to a colloidal solution results in an attractive depletion interaction between functionalized gold colloids, and above a critical protein concentration, c*, the colloids form aggregates and flocculate. Adding salt to such mixtures enhances the depletion effect and decreases the critical protein concentration. The aggregation is a reversible process (i.e., diluting the solution leads to dissolution of aggregates). The results also indicate that the charge of the OEG self-assembled monolayer at a curved interface has a rather limited effect on the colloidal stabilization and the repulsive interaction with proteins.

Biological systems as nanoreactors: anomalous small-angle scattering study of the CdS nanoparticle formation in multilamellar vesicles.

The formation of cadmium sulfide (CdS) particles in the gaps between the layers of the multilamellar vesicles is described, introducing a new pathway in the preparation of nanometer-scale particles. The in situ structural characterization of both the CdS particles and the vesicles as a reaction medium was performed in the early and final states of the process by using anomalous small-angle X-ray scattering (ASAXS) and freeze-fracture methods. The ASAXS method provides the separation of the scattering of nanoparticles present in a small amount, whereby the monitoring of their formation and growth in the whole time range of manufacturing has become possible.

Localization of dibromophenol in DPPC/water liposomes studied by anomalous small-angle X-ray scattering.

The localization of 2,4-dibromophenol molecules along the bilayer normal was investigated by anomalous small-angle X-ray scattering (ASAXS) with synchrotron radiation. The ASAXS measurements, executed at three different energies, provide the separation of the scattering of the bromine atoms of dibromophenol molecules from that of the whole system. Using a full q-range model, the localization of the dibromophenol molecules was characterized at a lower (0.1) and a higher (1) dibromophenol/lipid molar ratio corresponding to the gel and to the interdigitated phases of the vesicle matrix, respectively.

Quantitative investigations of supported metal catalysts by ASAXS.

Limits and potentiality of anomalous small-angle X-ray scattering for the investigation of supported metal catalysts are discussed. The different sources of statistical errors are illustrated using two catalysts containing metals with absorption edges at very different energies (Au and Pd). Optimized experimental conditions and measuring strategy are proposed, and data-evaluation methods for obtaining quantitative reliable results are suggested. By this method, Au content as low as 0.2 wt% and Pd content of 3 wt% could be investigated with success. The detection limits for palladium are higher, mainly due to its smaller electronic contrast.