Small-angle Neutron Scattering Intensity Research Articles

Ion-induced changes in DNA gels.

Small angle neutron scattering (SANS) measurements are reported for DNA gels under near physiological conditions in which the concentration of monovalent and divalent counter-ions and the pH are varied. The scattering intensity I(q) is described by a two-term equation, one due to osmotic concentration fluctuations and the other coming from static inhomogeneities frozen in by the cross-links. SANS in the low q range indicates the presence of large clusters and the size of which exceeds the resolution of the experiment. In the intermediate q-range, the intensity increases with the CaCl2 concentration and the slope approaches -1, corresponding to linear (rod-like) scatterers. In the highest q region, the scattering response is governed by the local chain geometry. Screening of electrostatic interactions by sodium chloride causes a moderate increase in the SANS intensity that is accompanied by an increase in the mesh size L of the network. Addition of calcium chloride, or a decrease in pH, produces similar trends, and ultimately leads to phase separation. The scattering intensity at q = 0, estimated from independent measurements of the osmotic pressure Π, is in excellent agreement with I(0) from the SANS measurements. Anomalous small angle X-ray scattering (ASAXS) measurements on the uncross-linked DNA show that the monovalent ion cloud is only weakly influenced by the addition of divalent ions. Conversely, the divalent counter-ion cloud tightly follows the contour of polymer chains.

Pore anisotropy in unconventional hydrocarbon source rocks: A small-angle neutron scattering (SANS) study on the Arthur Creek Formation, Georgina Basin, Australia

Small-angle neutron scattering (SANS) measurements were performed on 32 rock samples from the southern Georgina Basin, central Australia to assess nanopore anisotropy. Anisotropy can only be determined from oriented core material, hence the samples were cut perpendicular to bedding in cores selected from three wells that intersect the base of the hydrocarbon-bearing, organic-rich middle Cambrian Arthur Creek Formation; the latter is the source rock for both unconventional and conventional plays in the basin. The evolution of anisotropy of two-dimensional SANS intensity profiles with depth (for pore diameters ranging from 10 nm to 100 nm) was quantified and correlated with SANS intensity and total organic carbon (TOC) content. Our results confirm hydrocarbon generation at the base of the Arthur Creek Formation in the wells analysed. The nanopore anisotropy in the basal Arthur Creek Formation at the well locations CKAD0001 (oil generation window) and MacIntyre 1 (late oil generation window) varies roughly according to normal compaction. When the Arthur Creek Formation is in the gas window, as sampled at Baldwin 1, there is a strong (negative) correlation between the average vertical-to-horizontal pore shape anisotropy and SANS intensity. The results indicate that unconventional gas production from organic-rich regions of overmature shale may be adversely affected by abnormal pore compaction.

Monitoring of Bainite Transformation Using in Situ Neutron Scattering

Bainite transformation behavior was monitored using simultaneous measurements of dilatometry and small angle neutron scattering (SANS). The volume fraction of bainitic ferrite was estimated from the SANS intensity, showing good agreement with the results of the dilatometry measurements. We propose a more advanced monitoring technique combining dilatometry, SANS and neutron diffraction.

Coercive force mechanism in Nd-Fe-B nanocrystalline magnet investigated by SANS

Permanent magnet material with high maximum energy product is demanded for industrial applications such as high-efficiency motors for hybrid and electric vehicles. Maximum energy product depends on the coercive force and the saturation magnetization. In order to achieve the high maximum energy product, current Nd-Fe-B magnets are doped with heavy rare-earth element Dy to enhance the coercive force at the expense of reducing the saturation magnetization. Viewed from another side, a supply of Dy is highly concerned because of the inequitable distribution of rare-earth resources on the Earth. Therefore, development of a Dy-free Nd-Fe-B magnet is desired. In this context, we have fabricated the Dy-free Nd-Fe-B nanocrystalline magnet and performed the small-angle neutron scattering (SANS) experiment to reveal the mechanism of its coercive force. Hot-deformed Nd-Fe-B nanocrystalline magnets with and without the diffusion process of Pr-Cu eutectic alloy were prepared [1]. Coercive forces were 1.46 T and 2.64 T for as-deformed and Pr-Cu infiltrated sample, respectively. Magnetic field dependent SANS experiment was performed to observe the magnetization reversal process. The reversal magnetic field was swept from 0 T to 5 T. SANS intensities exhibit maxima around the coercive force for both as-deformed and infiltrated sample, which indicates the evolution of the magnetic domain structure. In addition, suppressed intensity variation in infiltrated sample compared to that in as-deformed sample indicates the magnetic isolation of Nd2Fe14B grains, which is responsible for the high coercive force. We will compare the results for Pr-Cu infiltrated sample with Nd-Cu infiltrated one [1]. This work was supported by the Elements Strategy Initiative Center for Magnetic Materials under the outsourcing project of the MEXT, Japan. We thank HZB for the allocation of neutron beamtime (Proposal No. MAT-04-2110). The sample preparation was performed under the MagHEM project.

Distribution of functional groups in periodic mesoporous organosilica materials studied by small-angle neutron scattering with in situ adsorption of nitrogen

Periodic mesoporous materials of the type (R′O)3Si-R-Si(OR′)3 with benzene as an organic bridge and a crystal-like periodicity within the pore walls were functionalized with SO3H or SO3− groups and investigated by small-angle neutron scattering (SANS) with in situ nitrogen adsorption at 77 K. If N2 is adsorbed in the pores the SANS measurements show a complete matching of all of the diffraction signals that are caused by the long-range ordering of the mesopores in the benzene-PMO, due to the fact that the benzene-PMO walls possess a neutron scattering length density (SLD) similar to that of nitrogen in the condensed state. However, signals at higher q-values (>1 1/Å) are not affected with respect to their SANS intensity, even after complete pore filling, confirming the assumption of a crystal-like periodicity within the PMO material walls due to π–π interactions between the organic bridges. The SLD of pristine benzene-PMO was altered by functionalizing the surface with different amounts of SO3H-groups, using the grafting method. For a low degree of functionalization (0.81 mmol SO3H·g−1) and/or an inhomogeneous distribution of the SO3H-groups, the SLD changes only negligibly, and thus, complete contrast matching is still found. However, for higher amounts of SO3H-groups (1.65 mmol SO3H·g−1) being present in the mesopores, complete matching of the neutron diffraction signals is no longer observed proving that homogeneously distributed SO3H-groups on the inner pore walls of the benzene-PMO alter the SLD in a way that it no longer fits to the SLD of the condensed N2.

中性子小角散乱法で見るネオジム系焼結磁石の平均内部構造

Small-angle neutron scattering (SANS) method is applied for the investigation of average internal structures of Neodymium-Iron-Boron (Nd-Fe-B) sintered magnets. The information obtained using SANS is average structure of the magnet and sometimes complementary to the microstructural information using the scanning electron microscopy. The SANS patterns were sensitive to internal structural changes introduced by the sintering process and the formation of magnetic domains, and we found a correlation between the SANS intensity and the coercivity. These observations indicate that SANS is a promising tool to investigate the origin of the coercivity of Nd-Fe-B sintered magnets. This article is a brief introduction to SANS and gives several examples of its application to investigation of Nd-Fe-B sintered magnets in the viewpoint of the correlation between the average structure and the coercivity.

Structure and Properties of High Performance Gels Made by Module Assembling Method

ABSTRACTHigh performance polymer network gels consisting of tetra-arm poly(ethyleneglycol) (Tetra-PEG) gels were fabricated via a module assembling method and their mechanical properties and structure were investigated by stretching and compression measurements, dynamic mechanical measurements, and small-angle neutron scattering (SANS). It was found that Tetra-PEG gels are nearly-ideal polymer network with negligible fractions of defects and entanglements. SANS intensity functions indicated that the network structure was uniform free from spatial inhomogeneities. It is deduced that this uniform structure is ascribed to its unique preparation method, i.e., module assembling method (cross-end-coupling of tetra-functional macromers with complementary functional groups). Characteristic properties originated from the near-ideality as polymer networks are demonstrated, including its application to ion gels, i.e., polymer network in ionic liquid.

Inhomogeneous dynamic nuclear polarization of protons in a lamella-forming diblock copolymer investigated by a small-angle neutron scattering method

By combining two methods of selective doping of paramagnetic species into a microdomain and small-angle neutron scattering (SANS), thespatially inhomogeneous proton polarizationcreated by dynamic nuclear polarization (DNP) has been precisely evaluated. A lamella-forming diblock copolymer composed of polystyrene (PS) and polyisoprene (PI) block chains (PS-b-PI) was employed, the SANS profile of which clearly shows scattering peaks up to the third order due to interlamellar interference. As a source of electron spin for DNP, 2,2,6,6-tetramethylpiperidine 1-oxyl (TEMPO) was doped into one or other of the microdomains; samples with PS or PI microdomains selectively doped with TEMPO are designated PS.-b-PI and PS-b-PI., respectively. The SANS intensity at the first- and third-order peaks is well reproduced by assuming that the proton polarization is homogeneous throughout the sample, but that at the second-order peak cannot be explained by this assumption. This anomaly regarding the second-order peak was successfully explained by a model postulating that proton polarization in a doped microdomain decreases with increasing distance from the interface with a neighbouring doped microdomain. The decrease in proton polarization at the centre of a doped microdomain was estimated to be 0.07 (2) for PS-b-PI.and 0.05 (1) for PS.-b-PI, relative to constant proton polarization in a doped microdomain. The inhomogeneous proton polarization results from two competing dynamic processes,i.e.spin diffusion from doped to undoped microdomains, and spin lattice relaxation occurring on the pathway of proton spin diffusion.

Shear-Induced Changes in Rheological Reponses and Neutron Scattering Properties of Hydrophobic Silica Suspensions at Low Silica Concentrations

Rheological responses of hydrophobic fumed silica powders, whose surface silanol groups were modified by hexadecane, suspended in 1,4-dioxane at lower silica concentrations than 6.8 vol% have been investigated as a function of the silica concentration. Transient shear stress behavior before attaining the steady-state shear stress could be classified into three regimes as follows, irrespective of the silica concentration: at the lower shear rates than ca. 0.3 s−1 a stress overshoot was observed, at the shear rate ranges from 0.3 to 30 s−1 sustained oscillations in shear stresses were exhibited and these oscillations were first observed for the suspensions at the low particle concentrations, and beyond the shear rate of 30 s−1 a sigmoid decrease of the shear stress with increasing time, that is, structural breakdown, was observed. At the steady state the silica suspensions showed shear thickening. Small angle neutron scattering (SANS) measurements of the silica suspension under shear flow provided that changes in the SANS intensities were well correlated with the shear thickening behavior. However, shear thinning behavior at higher shear rates did not cause any changes in the SANS intensities.

Effects of Nitrogen Concentration and Plastic Deformation on Small Angle Neutron Scattering for Austenitic Stainless Steels

The small angle neutron scattering (SANS) profile has been found to be influenced by nitrogen addition and plastic deformation for austenitic stainless steels. In solution-treated specimens, the slope of plots for SANS intensity versus the magnitude of scattering vector, q, becomes larger than −4 in the Porod region, suggesting the influence of short range N ordering. The change in scattering intensity profile with tensile deformation was in situ measured and it is found that SANS intensity becomes larger with increasing of plastic strain except a q region around 0.6 nm−1 for N bearing steel, where the intensity decreases in the beginning and then increases with increasing of plastic strain. This temporary decrease in SANS intensity is confirmed for cold rolled specimens. Severe deformation given by swaging to a N free steel brings larger increase in SANS intensity than a N bearing steel. The influence of plastic deformation on SANS intensity is larger in austenitic steels than in ferritic steels.

SANS simulation of aggregated protein in aqueous solution

Small-angle neutron scattering (SANS) of aggregated protein in an aqueous solution is simulated based on the crystallographic data of the protein. After obtaining the crystallographic data of the target protein, hydrogen atoms are added to the data and then some hydrogen atoms are replaced with deuterium atoms. The structure models are made with this data and then their gyration radii and SANS intensities are calculated. Compared the calculated SANS data with the experimental one, the most probable structure is determined. With this analysis method, the aggregate structure of proteasome α7-subunit (PRSα) in an aqueous solution was investigated. Three structural models, a simple monomer and two types of dimers, were supposed as the aggregated structure of PRSα. The analysis showed that the best compromised structure was the dimer, which was consistent with electron microscopy observation.

Determination of Intervesicular Transfer of Lipids by SANS-U

We applied a time-resolved small-angle neutron scattering (SANS) technique to the vesicle system of phospholipids to determine the lipid dynamics. This technique takes advantage of the large difference in the scattering length density between hydrogenated and deuterated lipids, and the exchange of these lipids between vesicles results in a decrease in the scattering intensity, which can be detected by time-resolved SANS measurements. Vesicles consisting of deuterated (D-LUV) or hydrogenated phospholipid (H-LUV) with a diameter of ca. 100nm were prepared using Tris-buffered saline of D2O/H2O mixture that has a mean scattering length density between D-LUV and H-LUV. The SANS intensity from the mixtures of D-LUV and H-LUV was reduced over time, and the observed kinetics could be explicitly represented by a simple model that includes two independent kinetic parameters, i. e., the rates of transbilayer and interbilayer exchange. In addition, these dynamics were found to depend strongly on acyl chain length of the lipids and the presence of cholesterol.

Controlling Aggregation of Nonionic Surfactants Using Mixed Glycol Media

The extent of aggregation of nonionic surfactants can be controlled by the composition of mixed solvents with two miscible glycols, ethylene glycol (EG)/propylene glycol (PG). Three nonionic surfactants bearing a common E8 ethoxylated headgroup, but with variations in the hydrocarbon chain, have been investigated: octaethylene monododecyl ether (C12E8), octaethylene monotetradecyl ether (C14E8), and octaethylene monohexadecyl ether (C16E8). The hydrogen-bonding solvents were EG/PG mixtures at different PG levels, defined in terms of the concentration (mol %) of PG. Aggregation was investigated using small-angle neutron scattering (SANS) with h-CiE8 surfactants, at 10 and 5 wt %, in deuterated glycol solvents to improve contrast. Increasing PG concentration (mol %) in the background EG/PG solvent leads to a consistent decrease in the SANS intensity, until in pure d-PG only very weak scattering is observed. These SANS data were analyzed using cylinder or ellipsoidal form factors for the EG-rich and PG-rich systems, respectively, hence demonstrating an aggregate shape change as a function of solvent composition. The results show that aggregation of nonionic surfactants occurs in glycol solvents and that the EG:PG ratio may be used as an effective means to switch aggregation "on" or "off", as required.

The Solution Structure of Stilbenoid Dendrimers: A Small‐Angle Scattering Study

The spatial structure of a stilbenoid dendrimer is investigated by small-angle X-ray scattering (SAXS) and small-angle neutron scattering (SANS) in dilute solution. All measurements are performed in toluene. The dendrimer consists of a stilbenoid scaffold with appended hexyloxy chains. SAXS is mainly sensitive to the dendrimer scaffold whereas SANS intensity, measured in fully deuterated toluene, derives from the solute molecules. The resulting SAXS and SANS intensities are analyzed by comparison with various models. It is found that the model of a circular disk gives the best description of the data. SAXS data demonstrate that the stilbenoid scaffold is flat as expected for benzene rings conjugated through vinylene units. Thus, it can be described by a circular disk with a radius of 1.6 nm and a thickness of 0.7 nm. SANS, on the other hand, shows that the hexyloxy chains are not confined in the plane defined by the core. This is derived from modeling the SANS data with a much thicker circular disk (radius: 2.4 nm, thickness: 1.8 nm). The structure factor S(q), describing the interaction of the dendrimers at higher concentrations, is modeled quantitatively with the "polymer reference interaction site model" (PRISM) integral equation formalism for hard plates such as particles. Here the structural data obtained from the analysis of the SANS data are used so that no new adjustable parameter is necessary for this description.

Observation of Liquid-to-Glass and Glass-to-Glass Transitions in L64/D2O Triblock Copolymer Micellar System

We report photon correlation spectroscopy (PCS), low shear viscosity and small angle neutron scattering (SANS) studies of a Pluronic L64 micellar system in aqueous solutions at high polymer concentrations (wt%), 35.0%<c<54.4%, in a temperature range where a kinetic glass transition (KGT) has been observed. We analyze SANS intensity distributions in the liquid state assuming that the micelles are spherical and interact among themselves via an effective pair-potential consisting of a hard core plus a narrow attractive square-well, the depth of which is temperature dependent. Comparison of the potential parameters so obtained with the phase diagram predicted recently by mode coupling theory (MCT) allows us to verify the existence of the so-called “liquid to attractive glass” KGT line. We then use scaling plots of SANS intensity distributions to show the existence of another branch of the KGT line where transitions from a repulsive glass to an attractive glass occur. In particular, we show an evidence of the existence of the so-called A3 singularity end point where two glasses become identical in local structure [Sow-Hsin Chen, Wei-Ren Chen, Francesco Mallamace, “The glass–glass transition and its end point in a co-polymer micellar system”, to be published].

Interaction of hydrogen and deuterium with dislocations in palladium as observed by small angle neutron scattering

Small angle neutron scattering (SANS) measurements on Pd samples containing dislocations with a density of a few 10 11 cm −2 reveal an additional intensity for a scattering vector of 0.02 Å −1 to 0.2 Å −1 after loading with hydrogen (H) or deuterium (D). The corresponding net cross section is inversely proportional to the scattering vector as expected for line type scattering objects with a superimposed exponential decrease stemming from scattering within the Guinier-regime. This experimental finding is in accordance with a model where extended segregation of H or D within the dilated regions of edge dislocations occurs. In a first order approximation this corresponds to a precipitation of cylindrically shaped hydrides along the dislocation line and can be treated quantitatively yielding radii in agreement with SANS data. Whereas gas volumetric measurements at the same total concentration reveal no difference for the amount of H- and D-segregation, there is a pronounced effective difference in SANS intensities which cannot be explained by the different scattering lengths alone. However, the different sign of the latter quantity in combinations with an expected volume expansion within the hydride/deuteride region provides a reasonable explanation of the intensity difference observed. Knowing the amount of segregated H or D from gas volumetry and the dislocation density from electron microscopy the SANS results can be explained in a self consistent way.

Static and dynamic scattering from ternary polymer blends: Bicontinuous microemulsions, Lifshitz lines, and amphiphilicity

Ternary polymer blends, comprising two homopolymers and the corresponding diblock copolymer, have been examined by small-angle neutron scattering (SANS) and dynamic light scattering (DLS). Two chemical systems have been employed: one consisting of polyethylethylene, polydimethylsiloxane, and poly(ethylethylene-b-dimethylsiloxane), and another containing polyethylenepropylene, polyethyleneoxide, and poly(ethylenepropylene-b-ethylene oxide). The molecular weights and compositions were chosen to emphasize the region of the phase prism dominated by the bicontinuous microemulsion (BμE) phase; the homopolymer molecular weights and volume fractions were approximately equal. The SANS intensity was compared quantitatively with the Teubner–Strey structure factor, and interpreted via the amphiphilicity factor fa. The transition from a fully disordered mixture at higher temperatures to a well-developed BμE upon cooling did not correlate well with either the disorder line (fa=+1) or the total monomer Lifshitz line (fa=0). However, DLS provided a clear signature of this transition, via a distinct maximum in the temperature dependence of the dynamic correlation length. We hypothesize that this maximum is closely correlated to the homopolymer/homopolymer Lifshitz line. The structure of the interfaces in the BμE was further examined in terms of the curvature and the copolymer coverage, as functions of copolymer concentration and temperature.

Concentration Fluctuation and Salt-Induced Percolation in 1-Propanol Aqueous Solution

Temperature dependent Kirkwood-Buff parameters G p p , G w w and G p w have been evaluated for the 1-propanol-water solution (1:5 in mole ratio) from S c c (0) obtained by small angle neutron scattering (SANS) experiments. Structural model for the concentration fluctuation for the solution at 25°C has been constructed based on the value of G p p . Characteristic feature of the SANS intensity and fractal nature of the concentration fluctuation can be explained qualitatively by the model structure. The volume fraction w of propanol-rich regions in the solution has been estimated as a function of temperature. Salt-induced phase separation phenomena observed on the current solution is discussed based on the temperature-dependent percolation theory.

Interface between a Polysulfone and Polyamide As Studied by Combined Neutron Reflectivity and Small-Angle Neutron Scattering Techniques

Interfaces between the two phases formed in immiscible polymer pairs were studied by means of neutron reflectivity (NR) combined with small-angle neutron scattering (SANS). The interfacial widths evaluated by the two methods were compared for two systems: a nonreactive system composed of polyamide (PA) and polysulfone (PSU) and a reactive system composed of PA and PSU with a phthalic anhydride reactive end group (PSU-R) in which PSU-b-PA block copolymers can be formed at the interface. SANS measurements were made on bulk mixtures, and the NR measurements were performed on thin film bilayer stacks of PA and PSU or PSU-R. The intrinsic interfacial widths, WI,diffuse, obtained from the two methods were compared for the samples that underwent similar annealing protocols and were quenched below the glass transition temperatures Tg's to room temperature. A consistent result for WI,diffuse can be obtained for the two methods only after taking into account the following important factors: (i) the SANS intensity should be corrected for the frozen density heterogeneities within each phase as well as the frozen thermal composition fluctuations; (ii) the contribution of capillary wave fluctuations to a net (or observed) interfacial width, WI,obs, is more significant for NR than SANS. Without the former correction, the SANS profiles at high scattering vector, q, showed asymptotic behavior of q-n (n < 4), giving an erroneous conclusion on WI,obs. The WI,obs values obtained for the reactive system were found to be larger than those for the nonreactive system for both methods, reflecting block copolymer formation at the interfaces. The interfacial area density, Σ, for the bulk mixture of the reactive system rapidly decreased with time and reached a constant value within ca. 2 min after annealing above the Tg's, while Σ for the nonreactive system kept decreasing with time. This elucidates that the growth of the phase-separating domains in the reactive system was pinned by the formation of block copolymers at the interfaces during early annealing times.

The effects of the electronic structure of micropores on the small angle scattering of X-rays and neutrons

The effects of the electronic structure of micropores on the small angle scattering of X-rays and neutrons