Small-angle X-ray Scattering Intensity Distribution Research Articles

Simultaneous fast XAS/SAXS measurements in an energy-dispersive mode.

X-ray absorption spectroscopy (XAS) and small-angle X-ray scattering (SAXS) are common materials characterization tools at synchrotron radiation facilities used in many research fields. Since XAS can provide element-specific chemical states and local atomic structures and SAXS can provide nano-scale structural information, their complementary use is advantageous for a comprehensive understanding of multiscale phenomena. This paper presents a new method for simultaneous XAS/SAXS measurements with synchrotron radiation. The method employs a polychromatic X-ray beam as in the energy-dispersive XAS technique and captures both the transmission XAS spectrum and the SAXS intensity distribution with an area X-ray detector, which eliminates the energy scan in the conventional methods and realizes the simultaneous data acquisition in a shorter time. We succeeded in obtaining the atomic and nano-scale structures of Pt and Pt/Pd nanoparticles with a data acquisition time of 0.1 s, suggesting the potential for real-time observation of multiscale phenomena.

Studies on Morphological Parameters, Radius of Gyration, Correlation Length and Invariant of HPMC Polymer Doped with Ferrous (II) Oxide Using SAXS Method

It shed light on morphological parameters which influence radius of gyration, correlation length and invariant of Hydroxy Propyl Methyl Cellulose (HPMC) polymer doped with ferrous (II) oxide (FeO) using small angle X-ray scattering (SAXS) method. SAXS patterns have been recorded for different composition and gives an information about the structure of the polymer on a scale of about 800Ǻ, in which the variation of scattered intensity with angles from 0o to 2.5o has been measured for different composition of FeO with host polymer of HPMC. Employing para-crystalline model and exponential distribution function of phase lengths (amorphous and crystalline), we find a good agreement between the measured and predicted scattering except for a very small range of angles on the low angle side of the peak intensity. The method enabled quantitative parameters describing morphology of the two phases, amorphous and crystalline, consistent with the SAXS intensity distribution. A stepping procedure has been employed to compute the final parameters which gave the best fit between the calculated and experimental data. This was done by minimizing the statistical goodness-of-fit parameter chi-square. It is observed that there are significant changes in distribution of phase lengths due to different percentage weight of FeO in HPMC contents. Additionally, SAXS data has been used to estimate (i) radius of gyration (Rg), ii) correlation length (Lcor) and (iii) invariant (Q) parameters. A functional representation of the long period and also radius of gyration at different dopant concentrations is adopted by viewing them as realizations of a continuous-time stochastic process observed with measurement error. This allows one to estimate the mean functional relationship between long period and the dopant concentration.

Studies on microwave-irradiated kopak cotton fibers (Bombax ceiba): using SAXS technique

Microwave energy at a frequency of 2450 MHz was used to irradiate Bombax ceiba cotton (kopak fibers) samples for different intervals of time. These samples were studied using small angle X-ray scattering (SAXS) method which gives information about the structure of the fiber on a scale of about 700 Ǻ. Using this method, variation in scattered intensity with angles from 0.3° to 2.5° has been measured for the fibers of cotton with and without microwave irradiation and compared with that predicted by the linear paracrystalline model. In these samples, exponential distribution of phase lengths of the measured and predicted scattering is in good agreement with each other except for a very small range of angles on the low-angle side of the peak intensity. The method enabled quantitative parameters describing morphology of the two phases, amorphous and crystalline, consistent with the SAXS intensity distribution. For a given type of distribution function, five parameters describing the model were chosen on a stepping procedure so that the final parameters give the best fit between the calculated distribution from the model and that observed experimentally. This was done by minimizing the statistical goodness-of-fit parameter chi-square. It is observed that there are significant changes in the distribution of phase lengths due to microwave irradiation of fibers.

Dynamical scaling property of colloidal aggregation in a zirconia-based precursor sol during gelation

Zirconia precursor gels, prepared in the zirconium n-propoxide, n-propanol, acetylacetone and water system, are studied by small angle X-ray scattering (SAXS). The SAXS intensity pattern exhibits a pronounced maximum for a scattering vector q different from zero. The intensity maximum of the finite q-vector peak increases during gelation while its position q m moves towards smaller and smaller q—vectors. The SAXS intensity distribution is well accounted for by recent direct numerical calculations of diffusion-limited cluster aggregation (DLCA). The structural aspects of cluster growth can be described by scaling assumptions. The position q m of the intensity maximum and the structure function S(q/q m,t) are shown to scale according to S(q/q m ,t) = q m(t)−d F(q/q m) where F(q/q m) is a time-independent scaling function. This scaling requires d=D f, the fractal dimension of the clusters, instead of d=3 for spinodal decomposition. The gel structure is made up of connected fractal clusters, around 50 nm in size, with an apparent fractal dimension of 1.7, resulting from the aggregation of very small primary particles about 2.5 nm in diameter.

Interpretation of small-angle x-ray scattering intensity distribution from fluctuating lamellae in a ternary system: sodium octyl sulfate-water-decanol

We have observed a clear small-angle X-ray scattering (SAXS) signal from a ternary surfactant-water-alcohol liquid mixture in a lamellar neat phase and have attributed the origin of the small-angle scattering to the fluctuation of the surfactant-alcohol bilayers.

Small-angle x-ray scattering by crystalline polymer fibers 2. Investigation of the linear paracrystalline model using various materials

The linear position-sensitive detector is well-suited to measure quantitatively the distribution parallel to the fibre axis of the intensity of small-angle x-ray scattering (SAXS) by polymer fibres, except that in the case of four-point patterns their width is greater than that of the detector window. A method is described which overcomes this problem, and which has high angular resolution. Using this method, the variation of scattered intensity with angles from 0.3° to 2.5° has been measured for fibres of poly(ethylene terephthalate), nylon, and low density poly(ethylene) (LDPE), and compared with that predicted by the linear paracrystalline model. In all cases except LDPE, when the distribution of phase lengths was given by the Reinhold function, there was no significant disagreement between the measured and predicted scattering except for a very small range of angles on the low angle side of the peak intensity. With LDPE small but significant discrepancies were found at other angles as well, and these were worse if the symmetrical Gaussian distribution function was used. The method enabled quantitative parameters describing the morphology to be obtained. It is concluded that the morphology of the linear paracrystalline stack is consistent with the SAXS intensity distribution, and that the Reinhold function is a reasonable approximation to the distribution of phase lengths. A small modification so that this decays more rapidly at long lengths might be necessary to explain the scattering for all materials over the entire angular range and other small changes might be needed with LDPE, although the asymmetrical nature of the distribution must be retained.

Characterization of the Structure of Carbon Fibers by Wide-Angle and Small-Angle X-ray Scatterings

A characteristic feature of carbon fiber structure is that the fibers comprise the preferentially oriented carbon-layer stacks and the needle-like microvoids oriented nearly parallel to the fiber axis. In order to study the anisotropic nature of the carbon fiber structure by the X-ray measurement, it is necessary to carry out the measurement on a unidirectionally aligned fiber bundle. For this purpose, it is inappropriate to apply the Bragg, Scherrer, and Warren equations for wide-angle X-ray diffraction and the currently used theories for the small-angle X-ray scattering of isotropic bodies. The present authors have developed previously the methods enabling one to analyse the wide- and small-angle X-ray scatterings from a carbon fiber bundle. In this paper, these methods, together with a convenient method determining the primary beam power by using air scattering, are concisely summerized to facilitate their practical application, and are discussed in relation to the Bragg, Scherrer, and Warren equations. By the proposed methods, the structural parameters characterizing the stacks of carbon layers, such as lattice constants, stacking regularity, sizes, orientation and volume fraction are evaluated from the wide-angle X-ray diffraction intensity distribution, and the characteristic parameters of microvoids, such as cross-sectional sizes, volume fraction, number per unit cross-sectional area of the fiber, inter-void spacing, variation in electron density, crosssectional size distribution and cross-sectional shape are evaluated from the small-angle X-ray scattering intensity distribution.