Wide Angle Neutron Scattering Research Articles

Quality assessment of the wide-angle detection option planned at the high-intensity/extended Q-range SANS diffractometer KWS-2 combining experiments and McStas simulations.

For a reliable characterization of materials and systems featuring multiple structural levels, a broad length scale from a few ångström to hundreds of nanometres must be analyzed and an extended Q range must be covered in X-ray and neutron scattering experiments. For certain samples or effects, it is advantageous to perform such characterization with a single instrument. Neutrons offer the unique advantage of contrast variation and matching by D-labeling, which is of great value in the characterization of natural or synthetic polymers. Some time-of-flight small-angle neutron scattering (TOF-SANS) instruments at neutron spallation sources can cover an extended Q range by using a broad wavelength band and a multitude of detectors. The detectors are arranged to cover a wide range of scattering angles with a resolution that allows both large-scale morphology and crystalline structure to be resolved simultaneously. However, for such analyses, the SANS instruments at steady-state sources operating in conventional monochromatic pinhole mode rely on additional wide-angle neutron scattering (WANS) detectors. The resolution must be tuned via a system of choppers and a TOF data acquisition option to reliably measure the atomic to mesoscale structures. The KWS-2 SANS diffractometer at Jülich Centre for Neutron Science allows the exploration of a wide Q range using conventional pinhole and lens focusing modes and an adjustable resolution Δλ/λ between 2 and 20%. This is achieved through the use of a versatile mechanical velocity selector combined with a variable slit opening and rotation frequency chopper. The installation of WANS detectors planned on the instrument required a detailed analysis of the quality of the data measured over a wide angular range with variable resolution. This article presents an assessment of the WANS performance by comparison with a McStas [Willendrup, Farhi & Lefmann (2004). Physica B, 350, E735-E737] simulation of ideal experimental conditions at the instrument.

Visualization of Self-Assembly and Hydration of a β-Hairpin through Integrated Small and Wide-Angle Neutron Scattering.

Fundamental understanding of the structure and assembly of nanoscale building blocks is crucial for the development of novel biomaterials with defined architectures and function. However, accessing self-consistent structural information across multiple length scales is challenging. This limits opportunities to exploit atomic scale interactions to achieve emergent macroscale properties. In this work we present an integrative small- and wide-angle neutron scattering approach coupled with computational modeling to reveal the multiscale structure of hierarchically self-assembled β hairpins in aqueous solution across 4 orders of magnitude in length scale from 0.1 Å to 300 nm. Our results demonstrate the power of this self-consistent cross-length scale approach and allows us to model both the large-scale self-assembly and small-scale hairpin hydration of the model β hairpin CLN025. Using this combination of techniques, we map the hydrophobic/hydrophilic character of this model self-assembled biomolecular surface with atomic resolution. These results have important implications for the multiscale investigation of aqueous peptides and proteins, for the prediction of ligand binding and molecular associations for drug design, and for understanding the self-assembly of peptides and proteins for functional biomaterials.

Sodium Diffusion in Hard Carbon Studied by Small- and Wide-Angle Neutron Scattering and Muon Spin Relaxation

Hard carbon is the most common anode material for Na-ion battery. The structure of the hard carbon and the dynamics of Na-ion in hard carbon were studied with small- and wide-angle neutron scattering and muon spin relaxation technique. The neutron scattering revealed the increase of interlayer distance between graphenes and decrease of the size of nanopores with increasing sodium intercalation in hard carbon. The muon spin relaxation revealed that a systematic increase in the field fluctuation rate with increasing temperature evidenced a thermally activated sodium diffusion. Assuming the two-dimensional diffusion of Na-ion in the graphene layers, the self-diffusion coefficient of Na-ion was estimated to be 2.6 × 10−11 cm2/s at 310 K, with a thermal activation energy of 39(7) meV.

On the Highly Ordered Graphene Structure of Non-Graphitic Carbons (NGCs)—A Wide-Angle Neutron Scattering (WANS) Study

Non-graphitic carbons (NGCs), such as glass-like carbons, pitch cokes, and activated carbon consist of small graphene layer building stacks arranged in a turbostratic order. Both structure features, including the single graphene sheets as well as the stacks, possess structural disorder, which can be determined using wide-angle X-ray or neutron scattering (WAXS/WANS). Even if WANS data of NGCs have already been extensively reported and evaluated in different studies, there are still open questions with regard to their validation with WAXS, which is usually used for routine characterization. In particular, using WAXS for the damping of the atomic form factor and the limited measured range prevent the analysis of higher-ordered reflections, which are crucial for determining the stack/layer size (La, Lc) and disorder (σ1, σ3) based on the reflection widths. Therefore, in this study, powder WANS was performed on three types of carbon materials (glass-like carbon made out of a phenol-formaldehyde resin (PF-R), a mesophase pitch (MP), and a low softening-point pitch (LSPP)) using a beamline at ILL in Grenoble, providing a small wavelength and thus generating WANS data covering a large range of scattering vectors (0.052 Å−1 < s < 3.76 Å−1). Merging these WANS data with WANS data from previous studies, possessing high resolution in the small s range, on the same materials allowed us to determine both the interlayer and the interlayer structure as accurately as possible. As a main conclusion, we found that the structural disorder of the graphene layers themselves was significantly smaller than previously assumed.

CENTAUR-The small- and wide-angle neutron scattering diffractometer/spectrometer for the Second Target Station of the Spallation Neutron Source.

CENTAUR has been selected as one of the eight initial instruments to be built at the Second Target Station (STS) of the Spallation Neutron Source at Oak Ridge National Laboratory. It is a small-angle neutron scattering (SANS) and wide-angle neutron scattering (WANS) instrument with diffraction and spectroscopic capabilities. This instrument will maximally leverage the high brightness of the STS source, the state-of-the-art neutron optics, and a suite of detectors to deliver unprecedented capabilities that enable measurements over a wide range of length scales with excellent resolution, measurements on smaller samples, and time-resolved investigations of evolving structures. Notably, the simultaneous WANS and diffraction capability will be unique among neutron scattering instruments in the United States. This instrument will provide much needed capabilities for soft matter and polymer sciences, geology, biology, quantum condensed matter, and other materials sciences that need in situ and operando experiments for kinetic and/or out-of-equilibrium studies. Beam polarization and a high-resolution chopper will enable detailed structural and dynamical investigations of magnetic and quantum materials. CENTAUR's excellent resolution makes it ideal for low-angle diffraction studies of highly ordered large-scale structures, such as skyrmions, shear-induced ordering in colloids, and biomembranes. Additionally, the spectroscopic mode of this instrument extends to lower momentum transfers than are currently possible with existing spectrometers, thereby providing a unique capability for inelastic SANS studies.

Ionomer Dispersions in Water/Alcohol Solutions by Coarse-Grained Molecular Dynamics

The polymer electrolyte membrane (PEM) is one of the principal components for polymer electrolyte fuel cells. As the phase separation is considered one of the primary factors affecting its performance, the morphological properties of PEM have been studied experimentally and theoretically. Under good solvent conditions for the polymer backbone, where solvents dissolve the backbone chains, ionomers exhibit polyelectrolyte-type behavior, forming loose ionic aggregates. In sufficiently polar solvents, ionomer backbones undergo aggregation and phase separation. This process results in the formation of a solid PEM at high ionomer concentration. Perfluorosulfonic acid (PFSA) ionomers such as Nafion (developed by DuPont) are currently the principal electrolyte and separator materials adopted for use as PEMs. Chemically, Nafion is a random copolymer that consists of hydrophilic sulfonate groups and a hydrophobic polytetrafluoroethylene backbone, which together form microphase-separated higher-order structures. Under sufficiently hydrated conditions, PEMs exhibit high mechanical robustness, warranted by hydrophobic backbone segments, as well as good water retention and high proton conductivity, conferred by the high volumetric ion density. The characterization of the ionomer structures has been extensively studied using experimental measurements such as small-angle neutron scattering (SANS), wide-angle neutron scattering (WANS), small-angle X-ray scattering (SAXS), and nuclear magnetic resonance (NMR). They observed that hydrophobic backbones of Nafion form the cylindrical-like core of self-assembled ionomer structures while ionic groups are located at the periphery of this aggregates. Based on a combination of scattering and microscopy, the rod-like aggregates in well-hydrated PEMs were observed. The proton conductivity and mechanical strength of solution-cast membranes are correlated with the properties of ionomer dispersions in solutions. Theoretically, while most of studies have primarily focused on the solid membrane state with water volume fraction significantly below 50%, ionomer aggregations in solutions can also be an important phenomenon to understand the self-assembly behaviors of ionomers as key structure-forming elements in ionomer films. In this study, ionomer aggregations in water/alcohol solutions have been investigated using coarse-grained (CG) molecular dynamics simulations to understand the dependence of aggregation behaviors on the water and alcohol fractions. The use of CG models is a valuable tool to prove the time and length scales of systems beyond what is feasible with traditional all atom models. Our model has been developed based on the MARTINI force fields, which is in close connection with more detailed atomistic models in terms of thermodynamic data, in particular hydration/partitioning free energies. The whole CG model of Nafion copolymer, as shown in Fig. 1, includes a part of the atomistic level configuration of a Nafion chain. A three-monomer unit of polytetrafluoroethylene (PTFE) (-(CF2)3-) are coarse-grained as a spherical bead of diameter 0.47 nm, and one side chain is coarse-grained as two spherical beads. This model is comparable to the inter-distance of ~2 nm between side chains and a side chain length of ~1 nm in the Nafion ionomer with EW = 1100. To include the effect of polarization in water model, which is significant at the interfaces between water and other phases and in the vicinity of charged particles. The initial configurations were generated by randomly placing 15 ionomer chains in a box with periodic boundary condition in all directions. Water and 1-propanol CG beads were then added based on the water/1-propanol molar fractions. All the solutions were fixed at an ionomer concentration of 5 wt%. The equilibration of the systems was first carried out with NPT MD simulations at T = 300 K and P = 1 atm for 100 ns. The additional NPT ensemble for 50 ns was then performed for the production. The dependence of NPA content on the ionomer structures was studied by systematically changing the NPA content in the system. It was found that ionomers form the bundle-like structures with cylindrical shape as shown in Fig. 2, which are in general agreement with cylindrical-like structures found in experimental scattering measurements of Nafion solutions. The ionomer aggregation size was found to tend to be larger and more dispersive at higher NPA contents, although the ionomers aggregated into one cluster at all NPA contents. Figure 1

Water in a Soft Confinement: Structure of Water in Amorphous Sorbitol.

The structure of water in 70 wt % sorbitol-30 wt % water mixture is investigated by wide-angle neutron scattering (WANS) as a function of temperature. WANS data are analyzed using empirical potential structure refinement to obtain the site-site radial distribution functions (RDFs). Orientational structure of water is represented using OW-OW-OW triangles distributions and a tetrahedrality parameter, q, while water-water correlation function is used to estimate size of water clusters. Water structure in the sorbitol matrix is compared with that of water confined in nanopores of MCM41. The results indicate the existence of voids in the sorbitol matrix with the length scale of approximately 5 Å, which are filled by water. At 298 K, positional water structure in these voids is similar to that of water in MCM41, whereas there is a difference in the tetrahedral (orientational) arrangement. Cooling to 213 K strengthens tetrahedrality, with the orientational order of water in sorbitol becoming similar to that of confined water in MCM41 at 210 K, whereas further cooling to 100 K does not introduce any additional changes in the tetrahedrality. The results obtained allow us to propose, for the first time, that such confinement of water in a sorbitol matrix is the main reason for the lack of ice formation in this system.

Colloid Research on the Small and Wide Angle Neutron Scattering Instrument TAIKAN at MLF/J-PARC

Colloid Research on the Small and Wide Angle Neutron Scattering Instrument TAIKAN at MLF/J-PARC

The atomic scale structure of graphene powder studied by neutron and X-ray diffraction

The structure of graphene obtained by chemical exfoliation of graphiteviathe oxidation/reduction procedure has been determined using wide-angle scattering of neutrons and X-rays combined with computer simulations based on classical molecular dynamics (MD). A comparison of results obtained from wide-angle neutron scattering (WANS) with the D4 neutron diffractometer dedicated for liquids and amorphous materials (Institute Laue–Langevin in Grenoble) and from wide-angle X-ray scattering (WAXS) with the laboratory Rigaku-Denki D/MAX RAPID II diffractometer has shown that both techniques provide data of a good quality that can be used to derive precise and valuable structural information about graphene. To obtain detailed structural information, the paracrystal formalism has been used along with MD simulations. The MD simulations were performed at 300 K with second-generation reactive empirical bond order potential for atoms lying in the same layer and the Lennard–Jones potential for interlayer interactions. The proposed models consist of three-layered systems, 36 Å in diameter, in which mono-vacancy, di-vacancy and Stone–Thrower–Wales types of defects are introduced. The reported results show that the WANS and WAXS methods together with the MD simulations contribute to a detailed description of the graphene materials, including the presence of topological defects, which is important as their structure at the atomic scale dramatically affects their electrical and mechanical properties.

The Small and Wide Angle Neutron Scattering Instrument TAIKAN at J-PARC

The Small and Wide Angle Neutron Scattering Instrument TAIKAN at J-PARC

Micro- and mesoscopic structure of poly(vinyl alcohol) gels determined by neutron and light scattering

We studied the structure of poly(vinyl alcohol) (PVA) gels formed in mixtures of dimethyl sulfoxide (DMSO) and water using several scattering techniques such as wide-angle neutron scattering (WANS), small-angle neutron scattering (SANS), ultra-small-angle neutron scattering (U-SANS) and light scattering (LS) to cover a very wide Q range from 10 -4 to 10 Å -1. The WANS measurements have revealed that the cross-linking points of the gels are crystallites, and the size and its distribution have been evaluated by the SANS measurements. The SANS results have also shown that the structure observed in the low Q range below 10 -2 Å -1 is dominated by a liquid–liquid-phase separation. The early stage of the phase separation has been studied in detail using the time-resolved LS technique, while the late stage has been investigated by the U-SANS technique because the LS measurements cannot access the opaque samples. On the basis of the results, we present a quantitative sketch of the structure of the PVA gel.

Nanostructured amorphous SiAu alloys — Structure and atomic correlations

Nanostructured amorphous Si 1− x Au x alloys ( 0.1 ⪕ x Au ⪕ 0.35 ) were produced by an inert gas condensation and in situ consolidation technique. Small-angle neutron scattering (SANS), density measurements and wide-angle neutron scattering (WANS) were employed to characterize the microstructure and local atomic order. The SANS results are interpreted in terms of a microstructure which consists of nanometre-sized amorphous grains embedded in a matrix of lower density, formed by grain boundaries and free volumes. The relative densities depend on the average particle size, but not on the alloy composition. In all samples, the SANS intensity decreases at low Q according to a power law − Q −3.37, which is attributed to a surface fractal structure of dimension D s = 2.63. WANS reveals two contributions: (a) a continuously decreasing part resulting from the presence of about 10 at.% hydrogen, and (b) a modulation of the intensity as a function of the scattering angle, characteristic of amorphous material. The total pair correlation function g( R) presents maxima corresponding to the first and second atomic neighbours. Nanostructured amorphous SiAu alloys exhibit a reduced short-range order compared with systems with dense random packing of hard spheres, e.g. metallic glasses, or continuous random network structures, e.g. covalent systems.

The structure of pumice by neutron diffraction

Small-angle neutron scattering (SANS) and wide-angle neutron scattering (WANS) measurements on pumice, an amorphous natural aluminosilicate used as support for metals in the preparation of catalysts, are reported. The SANS spectrum indicates the presence of a broad size distribution of pores and the absence of volume fractality. Surface fractality, however, cannot be ruled out. The structure of pumice, suggested by the pair-correlation function derived from the WANS spectrum and simulated by a random-network structure model, is very similar to that of vitreous silica, consisting mainly of SiO4−4 tetrahedra interconnected by bridging O atoms with additional local disorder generated by the replacement, on average, of one in ten Si atoms by aluminium.

Vanadium pentoxide gels: III. X-ray and neutron diffraction study of highly concentrated systems: One-dimensional swelling

The swelling by water of V 2O 5 lamellar hydrogels in the highly concentrated range, i.e., from nearly zero to about 20 H 2O per V 2O 5 has been investigated by means of X-ray diffraction and wide angle neutron scattering (WANS). The study of the basal d-spacing variation with water content clearly asserts an almost one-dimensional swelling behavior, stepwise in first stages of hydration up to 3 interlamellar water layers at least, and probably more continuous beyond. Slight deviations from the ideal model are discussed both in terms of experimental uncertainties and intrinsic gel properties.

Chain conformation in the crystalline state by means of neutron scattering methods

Neutron scattering experiments have been performed with n-alkane and polyethylene (PE) samples crystallized from melt and solution. Differences between different conformation models are most pronounced in the short-range order region covered by intermediate angle neutron scattering (IANS) experiments. The angular range has been extended up to k≲ 1.2 A–1 and highly concentrated mixtures of PE(H)+ PE(D) have been used. The problem of phase segregation of PE(H) and PE(D) was investigated by wide angle neutron scattering (WANS). In connection with extensive analytical and Monte Carlo calculations conformation models are proposed which explain the marked differences of the scattering curves in the IANS range between melt and solution crystallized samples. During rapid crystallization from the melt sequences of the randomly oriented molecules are apparently incorporated into the growing crystal with a minimum of chain reorganization (solidification model), whereas during crystallization from dilute solution sheets along (110) planes are formed (stacked-sheets model). IANS experiments with n-hexatriacontane reveal no short-range order tendencies between tagged alkane molecules.