Small-angle Neutron Scattering Curves Research Articles

Transition from a Sponge-Like to an Onion-Like Nanostructure in the L3 Phase – Part I

HypothesisIn the phase diagram of the system H2O/NaCl – AOT (sodium bis(2-ethylhexyl) sulfosuccinate) a homogeneous L3 channel can be detected at T = 25 °C as a function of the surfactant and the NaCl mass fraction. Our hypothesis is that a structural transition from a sponge-like to an onion-like structure occurs in this channel. ExperimentsWe (a) determined the relevant part of the phase diagram, (b) carried out electrical conductivity and viscosity measurements, (c) visualized the nanostructure with freeze-fracture electron microscopy (FFEM) and freeze fracture direct imaging (FFDI), (d) determined the characteristic length scales from Small Angle Neutron Scattering (SANS) curves. FindingsWe detected a narrow one-phase L3 channel in which the conductivities decrease, while the viscosities increase with increasing surfactant and salt mass fractions. Together with the FFEM/FFDI images and the SANS curves we provide experimental evidence for a structural transition from a sponge-like to an onion-like structure: all structures as well as their coexistences are thermodynamically stable.

Heterogeneous Aggregation of Humic Acids Studied by Small-Angle Neutron and X-ray Scattering.

Aggregation of humic acids (HAs) was studied by small-angle neutron and X-ray scattering techniques. The combination of these techniques enables us to examine the aggregation structures of HA particles. Two HAs with distinctive compositions were examined: a commercial HA (PAHA) and a HA extracted from deep sedimentary groundwater (HHA). While macroscopic coagulation tests showed that these HAs were stable in solutions except for HHA at pH < 6, small-angle neutron scattering (SANS) and small-angle X-ray scattering (SAXS) revealed that they formed aggregates with sizes exceeding the sub-micrometer length scale. The SAXS curves of PAHA remarkably varied with pD = log aD+, where aD+ stands for the activity of deuterium ions, whereas the SANS curves did not. With the help of theoretical fittings, it was revealed that PAHA aggregates consisted of two domains: poorly hydrated cores and well-hydrated proton-rich shells. The cores were (dis)aggregated with pD inside the aggregates of the shells. The SANS and SAXS curves of HHA resembled each other, and their intensities at low q, where q stands for the scattering vector, increased with a decrease of pD, indicating the formation of homogeneous aggregates within the spatial resolutions of SANS and SAXS. This study revealed that distinctive aggregation behaviors exist in humic substances with nm-scale heterogeneous structures like PAHA, which is important for their roles in the fate of contaminants or nutrients in aqueous environments.

Multidimensional Operando Analysis of Li/S Batteries with Neutrons and Photons

Lithium/sulfur (Li/S) batteries have a fivefold higher theoretical gravimetric energy density (2680 Wh/kg) than state-of-the-art lithium-ion batteries [1]. Furthermore, the abundance and environmental friendliness of sulfur qualify this system as a promising candidate for the post-lithium-ion era. However, the strong capacity fading with increasing cycle number is still a major obstacle to a broad technical utilization despite decades of research. Operando techniques [2] are very suitable tools to gain a mechanistic understanding of degradation processes. Especially the simultaneous combination of several independent measurements (multidimensional) while the Li/S cell is in operation allows deep insights into the degradation mechanisms and provides a further mechanistic understanding of the complex Li/S chemistry.Here we present results where up to five independent measurements are simultaneously performed with one setup (see image). Electrochemical impedance spectroscopy (EIS), UV-vis spectroscopy, temperature measurement, and X-ray imaging [3,4] or neutron small-angle scattering [5] were performed over several cycles while the cell was galvanostatically or potentiostatically charged and discharged. Structural changes on the macroscopic and microscopic scale can be correlated to characteristic signals in the EIS, charge-discharge curve, and UV-vis spectroscopy.The first part of the presentation focuses on X-ray imaging studies [3,4] that allow for valuable insights into operating Li/S cells. This method is a suitable tool for the investigation of the formation/dissolution processes of the charge product sulfur. The correlation of image analysis and impedance spectra enables a better mechanistic understanding of this system. Major observations are the formation of macroscopic alpha and beta-sulfur crystals, the formation of non-wetted cathode areas, and voltage-dependent electrolyte movement within the Li/S cell.The second part of the presentation deals with the formation and dissolution process of the discharge product, lithium sulfide. Here operando small-angle neutron scattering (SANS) is the weapon of choice to monitor nanoscopic lithium sulfide particles [5]. The SANS curves are correlated to the distribution of relaxation times calculated from impedance spectra. Furthermore, SANS gives information about the position of sulfur aggregation. In an ether-based electrolyte, neither lithium sulfide nor sulfur precipitate in the micropores.The last part of this presentation will give an outlook over the next experiments and discusses open questions in this field.

Structures and interactions in collapsed hydrogels of thermoresponsive interpenetrating polymer networks

Temperature-induced collapse of hydrogels of interpenetrating polymer networks (IPNs) poly(N-vinylcaprolactam)/poly(N-isopropylacrylamide) (PVCL/PNIPAm) and poly(N-isopropylmethacrylamide) (PNIPMAm)/PNIPAm, where both components are thermoresponsive, was studied by combination of 1H nuclear magnetic resonance (NMR) spectroscopy, small-angle neutron scattering (SANS), differential scanning calorimetry (DSC), and dynamic mechanical measurements. Behavior of studied hydrogels (one or two transitions) was found to depend on the ratio of both IPN components. For hydrogels of IPNs containing around 50 mol% of PNIPAm monomer units, separate transitions were revealed for both components. From SANS curves, it follows that compact three-dimensional multi-chain globules are formed in PNIPMAm/PNIPAm and PVCL/PNIPAm IPN hydrogels at temperatures above the phase transition, with a gyration radius of 14–28 nm. A certain portion of spatially restricted bound water (HDO) was established for all the studied IPNs at temperature above the volume phase transition from measurements of 1H NMR spectra, spin-spin relaxation times (T2), and diffusion coefficients (D) of HDO. Slow exchange regime between bound and free water was revealed. Spin–spin relaxation times (T2) and diffusion coefficients (D) as obtained for the bound HDO are up to 2 orders of magnitude smaller in comparison with “free” HDO. Higher content of bound water as found for collapsed hydrogels of IPN PVCL/PNIPAm in comparison with PNIPMAm/PNIPAm hydrogels is in accordance with swelling experiments and lower values of the shear mechanical modulus; this shows the decisive role of bound water in this respect.

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.

Atomistic Ensemble Modeling and Small-Angle Neutron Scattering of Intrinsically Disordered Protein Complexes: Applied to Minichromosome Maintenance Protein

The minichromosome maintenance (MCM) proteins are thought to function as the replicative helicases in archaea and eukarya. In this work we determined the solution structure of the N-terminal portion of the MCM complex from the archaeon Methanothermobacter thermautotrophicus (N-mtMCM) in the presence and absence of DNA using small-angle neutron scattering (SANS). N-mtMCM is a multimeric protein complex that consists of 12 monomers, each of which contains three distinct domains and two unstructured regions. Using an all-atom approach incorporating modern force field and Monte Carlo methods to allow the unstructured regions of each monomer to be varied independently, we generated an ensemble of biologically relevant structures for the complex. An examination of the subsets of structures that were most consistent with the SANS data revealed that large movements between the three domains of N-mtMCM can occur in solution. Furthermore, changes in the SANS curves upon DNA binding could be correlated to the motion of a particular N-mtMCM domain. These results provide structural support to the previously reported biochemical observations that large domain motions are required for the activation of the MCM helicase in archaea and eukarya. The methods developed here for N-mtMCM solution structure modeling should be suitable for other large protein complexes with unstructured flexible regions.

Investigation of the tripoli porous structure by small-angle neutron scattering

The characteristics of the tripoli porous structure have been investigated by small-angle neutron scattering (SANS). Tripoli is a finely porous sedimentary rock formed by small spherical opal particles. Its main component is aqueous silica SiO2 · nH2O (80–90%). Tripoli is widely used in practice as a working medium for sorption filters and in some other commercial and construction technologies. The shape of the experimental SANS curves indicates the presence of small and large pores in tripoli. The small-pore size was estimated to be ∼100 A. The size of large pores turned out to be beyond the range of neutron wave vector transfers Q that are available for the instrument used; however, their size was indirectly estimated to be ∼(2000–2500) A. The pores of both groups behave as surfacetype fractal scatterers with the fractal dimension D ∼ 2.2‐2.6. The densities of pores of these two groups differ by approximately three orders of magnitude (∼1016 and ∼1013 cm−3 for small and large pores, respectively); the fraction of large pores amounts to 70–80% of the total pore volume. The found pore characteristics (their densities, sizes, and relative volumes) are in satisfactory agreement (when a comparison is possible) with the absorption data.

Study of α-Crystallin Structure by Small Angle Neutron Scattering with Contrast Variation

The structure of the oligomeric protein α-crystallin from bovine eye lens was investigated by small-angle neutron scattering (SANS) with contrast variation. Based on the SANS curves, the match point for α-crystallin (43% D2O) and its average scattering length density at this point (2.4·10(10) cm(-2)) were evaluated. The radius of gyration and the distance distribution functions for α-crystallin were calculated. On the basis of these calculations, it was concluded that α-crystallin is characterized by homogeneous distribution of scattering density in the domains inaccessible for water penetration, and all polypeptide subunits in α-crystallin oligomers undergo equal deuteration. The latter indicates that all α-crystallin subunits are equally accessible for water and presumably for some other low molecular weight substances. These conclusions on the α-crystallin structure (homogeneous distribution of scattering density and equal accessibility of all subunits for low molecular weight substances) should be taken into account when elaborating α-crystallin quaternary structure models.

High-pressure small-angle neutron scattering studies of glucose isomerase conformation in solution

Small-angle neutron scattering (SANS) of solutions of glucose/xylose isomerase fromStreptomyces rubiginosuswas measured as a function of pressure. It is shown that the structure of the enzyme in solution as seen by SANS is practically the same as that in the crystal and does not change with pressure up to 150 MPa. This reflects the unusually high structural stability of this material, which makes it extremely interesting to use as a secondary standard for pressure-dependent SANS experiments. This lack of pressure dependence of the SANS data also indicates that any possible change in hydration of the protein induced by pressure is not visible in the SANS curves. An appropriate correction procedure must be used for the SANS data in order to account for the distortion of the intensity curve due to hard-sphere and electrostatic interactions. After this correction, the isomerase can be readily used as a secondary standard for SANS measurements.

Morphology of Comb-Shaped Proton Exchange Membrane Copolymers Based on a Neutron Scattering Study

Highly fluorinated comb-shaped membranes made by solution casting have shown high proton conductivity coupled with low dimensional swelling upon hydration, which demonstrates their potential as materials for proton exchange membranes (PEM) for fuel cells (FC). Small-angle neutron scattering (SANS) and neutron diffraction studies on the copolymers have been conducted to resolve the morphological structures. Two peaks were found in the SANS curves: the low-q peak is assigned to the strong interaction among the self-aggregating hydrophilic and hydrophobic domains, whereas the high-q peak is attributed to the ionomer peak. We propose a new structural model to fit the SANS data in the q range covering 0.005-0.4 A -1 . This model combines a form factor of flexible wormlike aggregates with an ellipsoidal cross section and a structure factor of hard-disk interaction accounting for the low-q scattering as well as the Teubner-Strey model for the high-q ionomer peak. Water uptakes can be derived from the best-fitting results of the current model and are consistent with the measured values. The neutron diffraction data indicate that there is little long-range orientation, if any, of the hydrophilic or hydrophobic domains.

Aqueous Laponite Clay Dispersions in the Presence of Poly(ethylene oxide) or Poly(propylene oxide) Oligomers and their Triblock Copolymers

The effect of polyethylene oxide (PEO) or polypropylene oxide (PPO) oligomers of various molecular weight (Mw) as well as of triblock copolymers, based on PEO and PPO blocks, on aqueous laponite RD suspensions was studied with small-angle neutron scattering (SANS). The radius of gyration (RG) increases for low M w whereas the opposite occurs for larger Mw. This behavior is explained on the basis that an effective R G is given by two contributions: (1) the size of the particles coated with the polymer and (2) the interactions between the laponite RD particles which are attractive for small and repulsive for large polymers. The SANS curves in the whole Q-range are well described by a model of noninteracting polydisperse core+shell disks, where the thickness of the polymer layer increases with the Mw. The adsorbed polymer is in a more compact conformation compared to a random coil distribution while the fraction of the polymer in the shell formed around the laponite RD particles is nearly independent of Mw. For increasing laponite RD amounts, at a given polymer composition, the thickness of the polymer slightly changes. In some cases, where also gelation is sped up, a structure factor with attractive interaction was employed which allowed to evaluate the attractive forces between the laponite RD particles. The gelation time was determined for mixtures at fixed copolymer and laponite RD concentrations. Surprisingly, it is observed that gels are formed despite the fact that the binding sites of the laponite RD particles are almost covered but the polymer size is too small to prevent aggregation. The gelation rate is correlated to structure and thermodynamics of these systems. Namely, when the balance between the steric forces and the depletion attractive forces undergoes an abrupt change the gelation time also undergoes a sharp variation. For lower and comparable Mw, PPO speeds up the gelation more efficiently than PEO while for higher Mw the gelation kinetics is slowed down again. Interestingly, copolymers of PEO and PPO blocks do not induce gelation in the time-window where the homopolymers do.

Pressure-induced reentrant micellization of amphiphilic block copolymers in dilute aqueous solutions

The pressure-induced structural changes of a block copolymer, poly(2-ethoxyethoxyethyl vinyl ether)-block-poly(2-hydroxyethyl vinyl ether) (pEOEOVE-b-pHOVE) in aqueous solutions, were studied by means of small-angle neutron scattering (SANS) and dynamic light scattering (DLS) from atmospheric pressure up to 400 MPa. pEOEOVE-b-pHOVE formed a spherical micellar structure above 40 degrees C due to poor solubility of pEOEOVE. Micellization phase diagram was determined by DLS, and a covex-upward pressure-temperature (P-T) phase diagram was obtained having a peak around (P,T)=(150 MPa,48 degrees C). The SANS curves at 50 degrees C were analyzed as a function of P. The micellar core size decreased by pressurizing at low P's (P<or=150 MPa) and then increased by further pressurizing (150 MPa<P<400 MPa). It was confirmed that the water volume fraction in the micellar core was larger at high P's than that at low P's even when the core sizes are the same at both pressure regions. This means that the temperature dependence of hydration is more selective at low pressures than at high pressures, in good accordance with our previous results on concentrated aqueous solutions of block copolymers [Phys. Rev. Lett. 96, 048303 (2006)].

SANS Study of Coated Block Copolymer Micelles

AbstractSummary: Multishell particles were prepared by γ‐radiation‐induced polymerization of methyl methacrylate (MMA) in polystyrene‐block‐poly(methacrylic acid) (PS‐b‐PMA) aqueous micellar solution and their structure was studied by small‐angle neutron scattering (SANS). Before polymerization, almost all MMA molecules are distributed in aqueous phase and only 1% of MMA is accumulated inside the micelles. The newly formed polymer (PMMA) is deposited on the surface of PS cores of the original micelles. The effect of the MMA concentration, micelle concentration, absorbed radiation dose, and absorbed dose rate on the characteristics of the resulting particles was examined. The thickness of the PMMA shell (20–218 Å for the presented series of samples) can be easily controlled by variation of monomer and/or micelle concentration. Universal plots of the core volume (PS+PMMA) and SANS curve were presented. These plots facilitate choosing proper monomer and micelle concentrations and detecting possible irregularities in the parameters of the resulting particles. magnified image

SANS study of the precipitates microstructural evolution in Al 4032 car engine pistons

Small angle neutron scattering (SANS) technique has been used to study the microstructural evolution of precipitates in real pistons made from commonly used AlSi12CuNiMg alloy. The experiment was performed on new and worn out piston crowns. SANS curves were measured at five different points (possible critical locations) of both pistons. At the central points of the new sample an isotropic scattering was observed, while in the lateral parts of the piston the scattering became anisotropic, indicating the presence of a manufacturing induced texture. The Al–Mg–Si alloys exhibit mechanical properties, which are highly sensitive to thermal treatments. The operating temperature is usually very close or, in certain parts of the crown, can exceed the ageing temperature. A comparison of the ageing treatment-caused alteration of mechanical properties with the changes of the precipitates structure is reported.

Microstructure of Alkyl Glucoside Microemulsions: Control of Curvature by Interfacial Composition

The phase behavior of water/n-octane/n-octyl-β-d-glucopyranoside (C8G1)/1-octanol (C8E0) permits formulating temperature-insensitive microemulsions spanning the whole water−oil composition range. The types of microstructures formed along the trajectory of the middle-phase microemulsion are examined by NMR diffusometry, yielding the respective diffusion coefficients of all the components. The diffusion experiments provide clear evidence of the transition from oil-in-water to water-in-oil microemulsions via bicontinuous structures in a remarkably large range around phase inversion. Small-angle neutron scattering (SANS) along the same path confirm the picture. Furthermore, SANS curves on the absolute scale permit extracting the specific internal interface in the microemulsion as it passes through phase inversion. When the composition of the internal interface is known, the mean area per surfactant molecule is determined. It is found that as the interfacial film becomes increasingly rich in C8E0, that is, the...

SANS study of concentration effect in magnetite/oleic acid/benzene ferrofluid

The effect of the colloidal particle concentration on the structure of the magnetite/C6D6 ferrofluid stabilized by oleic acid is investigated by small-angle neutron scattering (SANS). A significant decrease in the thickness of the surfactant layer with increase in the magnetite concentration is observed. This points to the fact that the interparticle interaction increasing with the concentration presses the surfactant tails in the layer closer against the magnetite surface. The influence of magnetic scattering on the SANS curves is considered.

Small-angle neutron scattering and the Mössbauer effect in nitrogen austenite

Small-angle neutron scattering (SANS) in Fe-19%Cr-19%Mn-0.9%N and Fe-18%Cr-10%Mn-16%Ni-0.5%N (wt %) high-nitrogen austenites is investigated. The neutron diffraction patterns and Mossbauer spectra are measured and analyzed. The SANS curves are approximated in the framework of the Guinier and Porod models. The nature of small-angle neutron scattering in nitrogen austenite is explained in terms of microinhomogeneities whose structure depends on the alloying with nickel. The mean size and shape of inhomogeneities are evaluated. The effect of low-temperature annealing of the Fe-19%Cr-19%Mn-0.9%N austenite on small-angle neutron scattering and the parameters of the Mossbauer spectra is analyzed.

SANS Investigation of Nitrogen Sorption in Porous Silica

The mechanism of nitrogen sorption in porous silica was investigated by small-angle neutron scattering (SANS). Two samples of porous silica were studied containing mesopores (pore sizes 5.5 and 9.5 nm, respectively) and additional micropores of irregular shape and statistical distribution. SANS curves were recorded at a temperature of 78 K at various relative pressures p/p0 during adsorption. The experiment is based on contrast matching between silica and condensed nitrogen with regard to neutron scattering. The sorption process was characterized by the evaluation of the chord-length distributions extracted from SANS data for each p/p0. In addition, a general approach was developed to relate the SANS pattern during capillary condensation to the size distribution and the morphology of ordered mesopores. On the basis of these evaluation methods, various uptake mechanisms could be described, which are micropore filling, the formation of nitrogen layers, and capillary condensation. The analysis of the SANS data shows that the mean size of the remaining empty mesopores formally increases, and their size distribution becomes narrower during capillary condensation, which is in agreement with the predictions of the Kelvin equation. Furthermore, our study indicates a significant degree of additional microporosity, the origin of which is discussed. For comparison, the experiment and the data evaluation were also applied to a disordered porous silica with a broad pore size distribution. The combination of SANS and nitrogen sorption turned out to be a powerful technique to investigate both the mechanisms of sorption and the structure of porous silicas in one experiment.

Characterization of thin Polymeric Nanofoam films by Transmission Electron Microscopy and Small Angle Neutron Scattering

ABSTRACTThin film polymer nanofoams are produced from triblock copolymers of a fluorinated polyimide, 3F/PMDA (derived from pyromelletic dianhydride (PMDA) and 1,1-bis(4-aminophenyl)-1-phenyl-2,2,2-trifluoroethane (3F)) as the center block and polypropylene oxide (PO) as the end blocks. The nanofoam is produced using a three step process: 1.) spin casting the triblock copolymer onto a silicon substrate, 2.) thermal treatment in an Argon atmosphere to imidize the center block and 3.) thermal treatment in air to degrade the PO domains and form nanoscale voids. This process was characterized using both transmission electron microscopy (TEM) and small angle neutron scattering (SANS). For the TEM studies, Ruthenium tetroxide staining was used to enhance the contrast between the polyimide (PI) matrix and the PO microdomains or voids, which permitted a more detailed view of the microstructure of both the foamed and unfoamed materials. From the two dimensional Fourier transform of the micrographs the spatial correlation between the PO microdomains in the unfoamed material and between the voids in the foam were found. An interdomain separation distance of -37 nm was observed. SANS was performed to follow the imidization and foaming processes both in-situ and on a Si substrate. The SANS results indicated that the films are homogeneous when spun from solution and that the microphase separation of the PO domains occurs during the imidization step. The subsequent foaming step leaves the morphology generally intact with the PO domains converting to voids. A peak was found in the SANS curve with a spacing of about 26 nm, which is qualitative agreement with the TEM data.

Small angle neutron scattering (SANS) investigation of irradiated manet steel

SANS was used to investigate the growth of He-bubbles in a martensitic steel developed for fusion reactors («MANET»). The investigated sample were simultaneously irradiated at high temperature with high-energy protons and alpha particles and then submitted to fatigue. Differences in the SANS curves were observed between the irradiated and non irradiated samples; they were attributed to radiation induced inhomogeneities and in particular to helium bubbles