Small-angle Neutron Scattering Data Research Articles

Investigation of the Possibilities of Analyzing the Vesicular Structure of PTNS-Based Nanodrugs Using Small-Angle Neutron Scattering Data

Investigation of the Possibilities of Analyzing the Vesicular Structure of PTNS-Based Nanodrugs Using Small-Angle Neutron Scattering Data

Investigation of the Possibilities of Analysis of the Vesicular Structure of PTNS-Based Nanodrugs Using the Small-Angle Neutron Scattering Data

Investigation of the Possibilities of Analysis of the Vesicular Structure of PTNS-Based Nanodrugs Using the Small-Angle Neutron Scattering Data

Data analysis and modeling of small-angle neutron scattering data with contrast variation from bio-macromolecular complexes.

Small-angle neutron scattering (SANS) with contrast variation (CV) is a valuable technique in the structural biology toolchest. Accurate structural parameters-e.g., radii of gyration, volumes, dimensions, and distance distribution(s)-can be derived from the SANS-CV data to yield the shape and disposition of the individual components within stable complexes. Contrast variation is achieved through the substitution of hydrogen isotopes (1H for 2H) in molecules and solvents to alter the neutron scattering properties of each component of a complex. While SANS-CV can be used a stand-alone technique for interrogating the overall structure of biomacromolecules in solution, it also complements other methods such as small-angle X-ray scattering, crystallography, nuclear magnetic resonance, and cryo-electron microscopy. Undertaking a SANS-CV experiment is challenging, due in part to the preparation of significant quantities of monodisperse samples that may require deuterium (2H) labeling. Nevertheless, SANS-CV can be used to study a diverse range biomacromolecular complexes including protein-protein and protein-nucleic acid systems, membrane proteins, and flexible systems resistant to crystallization. This chapter describes how to approach the data analysis and modeling of SANS data, including: (1) Analysis of the forward scattering (I(0)) and calculation of theoretical estimates of contrast; (2) Analysis of the contrast dependence of the radius of gyration using the Stuhrmann plot and parallel axis theorem; (3) Calculation of composite scattering functions to evaluate the size, shape, and dispositions of individual components within a complex, and; (4) Development of real-space models to fit the SANS-CV data using volume-element bead modeling or atomistic rigid body modeling.

Continuous chemical redistribution following amorphous-to-crystalline structural ordering in a Zr-Cu-Al bulk metallic glass

• Crystallization kinetics of Zr 45.5 Cu 45.5 Al 9 bulk metallic glass was investigated. • Simultaneous DSC and SANS was applied to study in situ the crystallization process. • A three-stage structural evolution during crystallization was revealed. • Continuous chemical redistribution following structural ordering was observed. • A new feature, i.e., the transition region, was identified and discussed. Bulk metallic glasses (BMGs) are thermodynamically metastable. As such, crystallization occurs when a BMG is thermally annealed at a temperature above the glass transition temperature. While extensive studies have been performed on the crystallization kinetics of BMGs, most of them have focused on the amorphous-to-crystalline structural ordering, and little attention has been paid to chemical distribution and its relationship with the structural ordering during the crystallization process. In this paper, a new approach, with simultaneous differential scanning calorimetry (DSC) and small angle neutron scattering (SANS) measurements, was applied to study in situ the crystallization of a Zr 45.5 Cu 45.5 Al 9 BMG upon isothermal annealing at a temperature in the supercooled liquid region. Quantitative analysis of the DSC and SANS data showed that the structural evolution during isothermal annealing could be classified into three stages: (I) incubation; (II) amorphous-to-crystalline structural ordering; (III) continuous chemical redistribution. This finding was validated by composition analysis with atom probe tomography (APT), which further identified a transition region formed by expelling Al into the matrix. The transition region, with a composition of (Cu,Al) 50 Zr 50 , served as an intermediate step facilitating the formation of a thermodynamically stable crystalline phase with a composition of (Cu,Al) 10 Zr 7 .

Continuous Chemical Redistribution Following Amorphous-to-Crystalline Structural Ordering in a Zr-Cu-Al Bulk Metallic Glass

Bulk metallic glasses (BMGs) are thermodynamically metastable. As such, crystallization occurs when a BMG is thermally annealed at a temperature above the glass transition temperature. While extensive studies have been performed on the crystallization kinetics of BMGs, most of them have focused on the amorphous-to-crystalline structural ordering, and little attention has been paid to chemical distribution and its relationship with the structural ordering during the crystallization process. In this paper, a new approach, with simultaneous differential scanning calorimetry (DSC) and small angle neutron scattering (SANS) measurements, was applied to study in situ the crystallization of a Zr45.5Cu45.5Al9 BMG upon isothermal annealing at a temperature in the supercooled liquid region. Quantitative analysis of the DSC and SANS data showed that the structural evolution during isothermal annealing could be classified into three stages: (I) incubation; (II) amorphous-to-crystalline structural ordering; (III) continuous chemical redistribution. This finding was validated by composition analysis with atom probe tomography (APT), which further identified a transition region formed by expelling Al into the matrix. The transition region, with a composition of (Cu,Al)50Zr50 , served as an intermediate step facilitating the formation of a thermodynamically stable crystalline phase with a composition of (Cu,Al)10Zr7 .

Model of Fractal Particles of Hydrated Zirconium Dioxide, Based on Small-Angle Neutron Scattering Data

The parameters of the mesostructure of amorphous zirconium dioxide and their evolution at different stages of heat treatment are determined by small-angle neutron scattering. Particles of amorphous zirconium dioxide, which form mass fractals with the dimension Dv = 2.21, are rearranged into surface fractals with a surface dimension of Ds = 2.52 upon annealing at a temperature of 400°C or higher. In the resulting system, a shell with a fractal structure is formed over a dense core (a cluster of nanoparticles of zirconium dioxide with a constant density). Transformation of the fractal system from a mass fractal into a surface one is characterized by the appearance of a core, and its growth is due to the crystallization of hydrated zirconia particles at high temperatures. A model for the formation of a fractal particle, implying the existence of a core–shell surface fractal system, is proposed. The characteristic radius of ZrO2 nanoparticles increases from 14 to 200 A with an increase in the annealing temperature from 400 to 600°C.

VC-Precipitation Kinetics Studied by Small-Angle Neutron Scattering in Nano-Steels

Nanosteels are used in automotive applications to accomplish resource-efficiency while providing high-tech properties. Quantitative data and further understanding on the precipitation kinetics in Nanosteels can contribute to fulfil this goal. Small-Angle Neutron Scattering measurements are performed on a Fe-C-Mn-V steel, previously heat-treated in a dilatometer at 650°C for several holding times from seconds to 10 hours. The evolution of the precipitate volume fraction, size distribution and number density is calculated by fitting the experimental Small-Angle Neutron Scattering curves. The effect of phase transformation on precipitation kinetics is also discussed. Complementary Transmission Electron Microscopy, Scanning Electron Microscopy and Inductively Coupled Plasma Optical Emission Spectroscopy measurements are performed to support the Small-Angle Neutron Scattering data analysis.

Viscoelasticity of colloidal polycrystals doped with impurities.

We investigate how the microstructure of a colloidal polycrystal influences its linear visco-elasticity. We use thermosensitive copolymer micelles that arrange in water in a cubic crystalline lattice, yielding a colloidal polycrystal. The polycrystal is doped with a small amount of nanoparticles, of size comparable to that of the micelles, which behave as impurities and thus partially segregate in the grain boundaries. We show that the shear elastic modulus only depends on the packing of the micelles and varies neither with the presence of nanoparticles nor with the crystal microstructure. By contrast, we find that the loss modulus is strongly affected by the presence of nanoparticles. A comparison between rheology data and small-angle neutron-scattering data suggests that the loss modulus is dictated by the total amount of nanoparticles in the grain boundaries, which in turn depends on the sample microstructure.

Small angle neutron scattering on an absolute intensity scale and the internal surface of diatom frustules from three species of differing morphologies

The internal nanostructure of the diatoms Cyclotella meneghiniana, Seminavis robusta and Achnanthes subsessilis was investigated using small angle neutron scattering (SANS) to examine thin biosilica samples, consisting of isotropic (powder) from their isolated cell walls. The interpretation of SANS data was assisted by several other measurements. The N2 adsorption, interpreted within the Branuer-Emmet-Teller isotherm, yielded the specific surface area of the material. Fourier transform infrared (FTIR) and Raman spectroscopy indicates that the isolated material is amorphous silica with small amounts of organic cell wall materials acting as a filling material between the silica particles. A two-phase (air and amorphous silica) model was used to interpret small angle neutron scattering data. After correction for instrumental resolution, the measurements on two SANS instruments covered an extended range of scattering vectors 0.0011 nm(-1) < q < 5.6 nm(-1), giving an almost continuous SANS curve over a range of scattering vectors, q, on an absolute scale of intensity for each sample. Each of the samples gave a characteristic scattering curve where log (intensity) versus log (q) has a -4 dependence, with other features superimposed. In the high-q regime, departure from this behaviour was observed at a length-scales equivalent to the proposed unitary silica particle. The limiting Porod scattering law was used to determine the specific area per unit of volume of each sample illuminated by the neutron beam. The Porod behaviour, and divergence from this behaviour, is discussed in terms of various structural features and the proposed mechanisms for the bio-assembly of unitary silica particles in frustules.

Decoration of Carbon Nanotubes with Metal Nanoparticles by Wet Chemical Method: A Small-Angle Neutron Scattering Study

Multi-wall carbon nanotubes have been synthesized by catalytic chemical vapour deposition method. Attempts have been made to decorate the walls of these nanotubes with various metal nanoparticles (Ni, Cu and Fe) after functionalizing the nanotubes walls by wet chemical method. Small-Angle Neutron Scattering data reveals chain cluster type morphology of the carbon nanotubes. Transmission electron microscopy, Energy dispersive analysis of X-rays and Small-Angle Neutron Scattering measurements show that decoration of nanotube walls by metallic nano-particles could be realized for Ni and Cu nano-particles. Further, wall decoration by nano-particles of Fe could not be achieved by wet chemical method due to strong agglomeration behavior of Fe nano-particles.

Effect of field-dependent core size on reversible magnetization of high-κsuperconductors

The field dependence of the vortex core size $\ensuremath{\xi}(B)$ is incorporated in the London model, in order to describe reversible magnetization $M(B,T)$ for a number of materials with large Ginzburg-Landau parameter $\ensuremath{\kappa}$. The dependence $\ensuremath{\xi}(B)$ is directly related to deviations in $M(\mathrm{ln}\phantom{\rule{0.2em}{0ex}}B)$ from linear behavior prescribed by the standard London model. A simple method to extract $\ensuremath{\xi}(B)$ from the magnetization data is proposed. For most materials examined, $\ensuremath{\xi}(B)$ so obtained decreases with increasing field and is in qualitative agreement both with behavior extracted from $\ensuremath{\mu}\mathrm{SR}$ and small-angle neutron-scattering data and with that predicted theoretically.

The polymerization of actin: Structural changes from small-angle neutron scattering

We present a new analysis of small-angle neutron-scattering data from rabbit muscle actin in the course of the polymerization from G-actin to F-actin as a function of temperature. The data, from Ivkov et al. [J. Chem. Phys. 108, 5599 (1998)], were taken in D2O buffer with Ca2+ as the divalent cation on the G-actin in the presence of ATP and with KCl as the initiating salt. The new analysis of the data using modeling and the method of generalized indirect fourier transform (O. Glatter, GIFT, University of Graz, Austria, http://physchem.kfunigraz.ac.at/sm/) provide shapes and dimensions of the G-actin monomer and of the growing actin oligomer in solution as a function of temperature and salt concentration. This analysis indicates that the G-actin monomer, under the conditions given above, is a sphere 50-54 A in diameter as opposed to the oblate ellipsoid seen by x-ray crystallography. The F-actin dimensions are consistent with x-ray crystal structure determinations.

Determination of the Shape of Dendrimer Macromolecules in Solutions from Small-Angle Neutron Scattering Data

Determination of the Shape of Dendrimer Macromolecules in Solutions from Small-Angle Neutron Scattering Data

A study on structural and diffusion properties of porcine stratum corneum based on very small angle neutron scattering data.

Generation of valuable information about the biphasic geometrical configuration of porcine stratum corneum from Very Small Angle Neutron Scattering (VSANS) data and investigation of its effect on the corresponding effective diffusivity. Spectra of porcine stratum corneum are mathematically transformed in order to obtain the corresponding auto-correlation function (ACF). Model stratum corneum structures, matching this experimentally determined ACF, are then produced based on the "brick-and-mortar" configuration. The effective diffusivity through these model domains is calculated using an appropriate numerical method. The most appropriate geometry of porcine stratum corneum's lipid and protein phases in a "brick-and-mortar" configuration is quantitatively determined and correlated with the barrier properties (diffusivity) of the stratum corneum model structures. The ACF analysis indicates the most appropriate values for the dimensions of the corneocyte thickness and the surrounding lipid gap, while the corneocyte length is estimated from the diffusion study.

A Method for Interpreting Small Angle Neutron Scattering Data from Quasi-Spherical Objects

ABSTRACTSmall angle scattering data are traditionally interpreted in terms of scattering patterns at the Porod and the Guinier limits. It is difficult to fit the entire scattering pattern to account for scattering from spheres because Rayleigh's formula contains oscillatory terms which are smeared out in practice by perturbations in the sizes of the scattering agents.It is proposed that a Lorenztian type function be used instead of Rayleigh's function. By using this equation it is possible to fit the entire small angle scattering pattern and obtain the correct forms of the Guinier and Porod limits.The effects of correlation and multiple scattering are also explored.

Aggregation of a semifluorinated n-alkane in perfluorooctane

The phase behavior of solutions of two semifluorinated n-alkanes, heptadecafluorotetracosane (F(CF[sub 2])[sub 8](CH[sub 2])[sub 16]H) and pentacosafluorooctacosane (F(CF[sub 2])[sub 12](CH[sub 2])[sub 16]H), in perfluorooctane and isooctane is studied. Viscosity, dynamic light-scattering, and small-angle neutron-scattering data show the presence of small, nearly spherical aggregates in heptadecafluorotetracosane/perfluorooctane solutions in the liquid phase above the critical micelle concentration. The authors determined the size and average aggregation number of these aggregates as a function of the fluorohydrocarbon concentration. Small-angle neutron-scattering results show that the perfluorooctane solvent penetrates appreciably into the micellar core. 21 refs., 6 figs., 2 tabs.

Conditions for the existence of a reentrant solid phase in a sheared atomic fluid.

A nonequilibrium molecular-dynamics method is proposed to simulate the behavior of simple fluids under high shear rates. A thermostat that makes no assumptions regarding the form of the streaming velocity of the fluid is introduced. Simulations are carried out for a Weeks-Chandler-Andersen dense liquid. With the form of the streaming velocity partially or wholly constrained, we find evidence for a reentrant solid or string phase, but the phase disappears if constraints are removed. Small-angle neutron-scattering data from a sheared colloidal suspension are presented. There is no evidence of a steady-state shear-induced structure in the suspension.

Theory of the pressure effect on the curvature and phase behavior of AOT/propane/brine water-in-oil microemulsions

Pressure effects on both the curvature and phase behavior of water-in-oil microemulsions (swollen reverse micelles) are predicted with a unified classical and molecular thermodynamic theory developed by Peck et al. (this issue). The theory is used to identify quantitatively the roles of the intramicellar interfacial interactions and micelle-micelle interactions. A supplementary molecular model is used to calculate the strength of attractive intermicellar interactions over a wide range of conditions, based on previous small-angle neutron-scattering data. An important distinction is made between systems with a small water-to-oil ratio and those where the water-to-oil ratio is much larger, on the order of unity. In the latter the micelle radius is controlled primarily by intramicellar interfacial interactions, specifically the enthalpic propane-surfactant tail interactions. For a small water-to-oil ratio, the micelle radius is limited by attractive micelle-micelle interactions. As pressure increases, the radius increases but eventually reaches a maximum governed by the intramicellar interfacial interactions. There is good agreement between the predictions and experiments over a wide range of water-to-oil ratios.

Fluctuation-induced first-order transition of an isotropic system to a periodic state.

Small-angle neutron-scattering data, obtained from a near-symmetric isotropic diblock copolymer, demonstrate non-mean-field behavior over a wide temperature range (\ensuremath{\ge} 57\ifmmode^\circ\else\textdegree\fi{}C) above the weakly first-order microphase-separation transition. These results are quantitatively explained by a fluctuation theory based on the Hartree approximation employed by Brazovskii to describe such phase transitions.

Thermodynamic analysis of polydispersity in ionic micellar systems and its effect on small-angle neutron scattering data treatment

The authors analyze small-angle neutron scattering (SANS) data of sodium dodecyl sulfate (SDS) and sodium bis(2-ethylhexyl) sulfosuccinate (AOT) ionic micellar solutions taking into account the effect of size polydispersity on the particle form factor. The intermicellar structure factor is computed by a generalized one-component macroion theory (GOCM) assuming a constant fractional charge. The model fittings to SANS data for different concentrations allow us to extract the free energy parameters of micelle formation and growth, the size distribution function of micelles, and the minimum micelle size which is consistent with the fully stretched hydrocarbon tail lengths of the surfactant molecules. The critical micellar concentration (cmc) is predicted from the free energy parameters correctly. Combining the free energy of micelle formation with the double-layer free energy around the averaged micellar surface calculated by the nonlinear Poisson-Boltzmann equation, they obtain the hydrophobic free energy of micellization which is in quantitative agreement with the literature value. These analyses confirm the applicability of the ladder model of micellar growth in salt free ionic micellar solutions at moderate concentrations. The degree of polydispersity in size is about 11% for 2% SDS solution at 40/degrees/C and 17% for 1% AOT at 22.6/degrees/C.