SAXS Curves Research Articles

Correlation between the Porous Silicon Morphology and the Photoluminescence Efficiency

AbstractSmall‐angle X‐ray scattering is applied to investigate the microstructure and the morphology of three photoluminescent porous silicon samples of the same porosity (80%) but prepared using different electrochemical treatments: (A) as‐prepared, (B) as‐prepared 65% porosity, followed by an oxidation treatment and an oxide dissolution in HF, (C) as‐prepared 65% porosity followed by a HF dissolution. Although the PL spectra are almost similar in energy, there are differences in their intensities: the luminescence intensity of the as‐prepared sample A is a bit greater than the one observed for sample B and much more greater than the one corresponding to sample C. If one assumes the same surface passivation (Si‐H) for the three samples then these differences in luminescence intensity may be due to the different PS morphologies which are evidenced in SAXS curves at low q values.

SAXS investigations of the influence of the length of methylene chain on supermolecular structure of poly(alkylene phosphates)

The influence of the number of CH 2 groups and the evennes of thais number on the lamellar arrangement of macromolecules of poly(alkylene phosphates) PPbn were investigated by SAXS method. The results indicate that deviations from the ideal lamellar model for the polyphosphates with asymmtric mers (n-odd number) are generally larger and qualitatively different as compared with that for the polyphosphates with symmetric mers (n-even number). The heterogeneity of phases were measured by the ratio of the mean square electron density fluctuations calculated from the SAXS curves before and after background subtraction. It was found that the heterogeneity of the PPb8 polyphosphate is smallest. Besides, a Linear relationship between the weight average long period L w and the molecular mass of PPhn polyphosphates was confirmed

Small-angle X-ray scattering study of the phase structure of poly( d-(−)-3-hydroxybutyrate) and atactic poly(epichlorohydrin) blends

Isothermally crystallized and annealed blends of poly( d-(−)-3-hydroxybutyrate) (PHB) and atactic poly(epichlorohydrin) (aPECH) were examined by wide-angle X-ray diffraction and small-angle X-ray scattering (WAXD and SAXS). The lateral crystal dimensions of PHB increased with annealing treatment and with increasing aPECH component in the blends, while the long-period distances of the blends were slightly smaller than for pure PHB. The scattering observed for the blends resulted from the superposition of the scattering arising from the crystalline regions (made up by alternate stacking of lamellae and thin amorphous layers) and from the aPECH inhomogeneity present outside them. The structural information was obtained, from the SAXS curves, on the basis of Glatter and Debye-Bueche approaches. The results suggest that, during melt-crystallization of PHB, segregation of aPECH occurs within the growing spherulite with its dispersion in the interfibrillar zones that are larger than the interlamellar regions but smaller than the overall spherulite. The aPECH molecules are dispersed at the molecular level in the interfibrillar zones where they can assume a random-coil conformation. The detection of a glass transition temperature ( T g) close to the aPECH T g value indicates low interactions at the segmental level between the two polymers. The annealing treatment produced a general perfectioning and rearrangement of the sample morphology, enhancing the crystallinity and the crystal dimensions of PHB in the pure state and in the blends, and probably favouring the trend of the aPECH molecules to assume a globular conformation.

Saxs study of silica gel formation from aqueous silicate solutions

In situ SAXS measurements of silica gel formation in the presence of different cations are presented as a function of reaction time. Conditions used are similar to those applied to prepare catalyst supports. The data can be interpreted in terms of aggregation of elementary silica particles with sizes of approximately 1 nm, thus finally forming a continuous silica gel network. The aggregates are fractal with respect to their masses, in the range 2–10 nm. The dimensionality of the fractals can be determined from the SAXS curves; it increases from 1.8 to 2.5 during gelformation, corresponding with a diffusion limited aggregation process (DLA) of gel formation followed by densification of the silica gel network. The finding that the rate of change in fractal dimensionality does not change as a function of cation, indicates strongly that gelformation is a diffusion limited aggregation process.

Structure of Soluble Silicates

ABSTRACTSmall angle x-ray scattering (SAXS) is the technique of choice for the determination of structure on the 10–1000Å scale. We have used this technique to study the growth and topology of the macromolecules which precede gelation in several chemical systems used in sol-gel glass technology. The results show that branched polymers, as opposed to colloids, are formed. The alcoholic silica system is akin to organic systems where gelation occurs through growth and crosslinking of chain molecules. Data are reported from both the Porod and Guinier regions of the SAXS curve and these data are interpreted in terms of geometrical structures predicted by various disorderly growth processes. The results indicate that the degree of crosslinking can be controlled by catalytic conditions. The degree of crosslinking may, in turn, control phase separation and processability to a dense glass.

Determination of the miscibility gap in the Al-Be system by resistivity measurements and X-ray small-angle scattering

Abstract The high-solute concentration branch of the coherent miscibility gap for the AI-Be system has been determined by combining resistometric and SAXS results. The analysis of SAXS curves indicates that G.P. zones are platelets. a :shape that is in agreement with anisotropic elasticity considerations.

Formation of layer-like voids in irradiated polytrioxane

The formation of voids and defects is investigated by X-ray diffraction methods, by weight loss measurement and by electron microscopy, for an irradiated polytrioxane (PTOX) obtained by theγ-ray-induced polymerization of trioxane in the solid state. The main reasons for the formation of the layer-like voids are transverse decomposition at a selective point accessible to the radiation in the micro-fibrils, and the subsequent extensible depolymerization which may occur from the unstable chain end with increase of the radiation dose. The analysis of the SAXS curve for the irradiated PTOX, according to Tsvankin's method gives reasonable results for the void structure, where the reduction of the sub-crystal fraction and also the weight loss of the sample by irradiation are taken into account.