Partial Structure Functions Research Articles

Microscopic Interaction of Oleated Cellulose and Silica in Dual-Filled Elastomers

The quantification of interactions between fillers and filler with elastomers in nanocomposites relies on the combination of different microscopy techniques. Small Angle X-ray scattering is a key method for the identification of the filler network morphology at the nanoscale. Hybrid nanocomposites containing fillers with diverse morphology and reinforcing ability represent considerable complexity thereby justifying ongoing research in this area, as a consequence of the multiple interactions between fillers and also the filler with the elastomer. Therefore, a microscopic structural investigation of a dual-filled elastomer for tire applications is presented. Chemically modified micro-fibrillated cellulose in combination with traditional silica filler dispersed by melt processing in a styrene-butadiene (SBR) random copolymer were investigated. Small-Angle-X-ray Scattering and Scanning-transmission-electron-microscopy (STEM) revealed non-mixing of the two fillers on the silica scale and the predominant formation of individual filler clusters. Through a novel data deconvolution procedure, partial structure functions corresponding to the contribution of each filler to the scattering function were extracted. This approach offers a suitable methodology to identify the compatibility between morphologically different fillers and their mutual effect on the dispersion.

How hydrogen bond donor acceptor ratio and water content impact heterogeneity in microstructure and dynamics of N,N-diisooctylacetamide and decanol based hydrophobic deep eutectic solvent

Recently hydrophobic deep eutectic solvents (HDESs) have emerged as a potential green alternative media for the extraction of compounds from aqueous environment, and their increased importance as water immiscible solvent has attracted researchers to gain more insights into this domain. The present study employs atomistic molecular dynamics simulations to elucidate the microscopic structural organization, dynamics, and crucial interactions in N,N-diisooctylacetamide (DOA) plus decanol (DEO) based HDES at different mole ratios of the hydrogen bond donor (HBD) and acceptor (HBA). The analysis of simulated X-ray and neutron scattering structure functions reveals a nanoscale heterogeneous structural organization in the HDES at all compositions. The genesis for this heterogeneity can be derived from the polarity alternation peaks of partial structure functions in the low-q region. Polarity ordering in DOA:DEO (1:2) HDES is observed at longer length-scales in comparison to that in DOA:DEO (1:1) and DOA:DEO (2:1) HDESs. Moreover, the liquid morphologies are portrayed by nano-polar domains ingrained into the apolar environment depicting polar and apolar self-segregation. The analysis of angle-resolved radial distribution functions suggests that the microstructures of these HDESs are dominated by a strong DEO-DEO and DEO-DOA hydrogen bonding interactions. Slower decay of the hydrogen bond autocorrelation function corresponding to DOA-DEO suggests stronger hydrogen bonding in DOA-DEO than DEO-DEO. The translational mobility of both the components decreases as the DOA concentration increases. The DEO molecules exhibit faster diffusion in bulk HDES than the DOA molecules. A small water content in the HDES leads to slightly enhanced segregation of polar and apolar environments in the HDESs. We observe that water molecules interfere with the hydrogen bonding network of DOA and DEO by establishing hydrogen bond with them, thereby reducing the strength of DEO-DEO and DOA-DEO hydrogen bond interactions. The hydration also causes slightly faster hydrogen bond relaxation dynamics, indicating the weakening of hydrogen bond interactions between the constituent species of the HDESs.

Local structures and optical properties of As-Se-Te(S) chalcogenide glasses

The partial, total and average coordination number of atoms and, their neighbor distributions have been determined by the neutron diffraction method and application of the Reverse Monte Carlo modeling for experimental data in As40Se60, As40Se30S30 and As40Se30Te30 chalcogenide glasses. The total coordination number of the arsenic and chalcogen atoms is 3 and 2 for all compounds. The average coordination number is 2.4, i.e. the 8-N rule is performed and main structural element is AsSe3 type pyramids, where depending on the chemical composition Se atom is replaced by S or Te atoms. The proportion of homopolar bonds is significant in As40Se60 and As40Se30S30 compositions, but sharply decreases in As40Se30Te30. In all compositions the neighbor distances between arsenic and selenium atoms are the same within error: 2.35 Å (SeSe); 2.45 Å (AsAs) and 2.40 Å (AsSe). The existence of medium range order (MRO) is proved by the analysis of the total and partial pair structural factors and correlation functions in above mentioned compositions. The geometric dimensions of the MRO area, i.e. the quasi-periodicity of density fluctuations in the MRO area and the size of nano-voids have determined within Elliott's void-based model. The change of the optical parameters by variation of the chemical composition has been established from the analysis of the optical transmission spectra.

Microstructures and dynamics of tetraalkylphosphonium chloride ionic liquids.

Atomistic simulations have been performed to investigate the effect of aliphatic chain length in tetraalkylphosphonium cations on liquid morphologies, microscopic ionic structures, and dynamical quantities of tetraalkylphosphonium chloride ionic liquids. The liquid morphologies are characterized by sponge-like interpenetrating polar and apolar networks in ionic liquids consisting of tetraalkylphosphonium cations with short aliphatic chains. The lengthening aliphatic chains in tetraalkylphosphonium cations lead to polar domains consisting of chloride anions and central polar groups in cations being partially or totally segregated in ionic liquid matrices due to a progressive expansion of apolar domains in between. Prominent polarity alternation peaks and adjacency correlation peaks are observed at low and high q range in total X-ray scattering structural functions, respectively, and their peak positions gradually shift to lower q values with lengthening aliphatic chains in tetraalkylphosphonium cations. The charge alternation peaks registered in the intermediate q range exhibit complicated tendencies due to a cancellation of peaks and anti-peaks in partial structural functions for ionic subcomponents. The particular microstructures and liquid morphologies in tetraalkylphosphonium chloride ionic liquids intrinsically contribute to distinct dynamics characterized by mean square displacements, van Hove correlation functions, and non-Gaussian parameters for ionic species in the heterogeneous ionic environment. Most tetraalkylphosphonium cations have higher translational mobilities than their partner anions due to strong coordination of chloride anions with central polar groups in tetraalkylphosphonium cations through strong Coulombic and hydrogen bonding interactions. The increase of aliphatic chain length in tetraalkylphosphonium cations leads to a concomitant shift of van Hove correlation functions and non-Gaussian parameters to larger radial distances and longer time scales, respectively, indicating the enhanced translational dynamical heterogeneities of tetraalkylphosphonium cations and the corresponding chloride anions.

Molecular dynamics study of nanoscale organization and hydrogen bonding in binary mixtures of butylammonium nitrate ionic liquid and primary alcohols.

Molecular dynamics simulations are utilized here to explore the nanoscale morphology and the nature of hydrogen bonding in the equimolar mixtures of butylammonium nitrate protic ionic liquid with ethanol, propanol, and butanol. The X-ray scattering experimental study of Greaves et al. [Phys. Chem. Chem. Phys. 13, 13 501 (2011)] has evidenced that alkylammonium nitrate plus alcohol mixtures possess nanoscale structural order which becomes more pronounced as the chain length of the alcohol increases. Our analysis carried out using simulated total and partial X-ray scattering structure functions quantifies the basis of these observations. The partial structure functions highlight the off-phase density correlations of alcohol with both cation and anion in the low-q region. We demonstrate that the chain lengthening of alcohols offers significant variation in the structuring of the polar and apolar moieties in the mixtures. The inspection based on radial distribution functions manifests the non-linear hydrogen bonds of cations with nitrate anions as well as alcohol molecules. The alcohol's hydroxyl group prefers to form linear hydrogen bonds with anions and with other alcohol molecules. Incremented chain length of alcohol improves the extent of hydrogen bonding but does not alter their geometry. Spatial distribution functions delineate similar preferences. It shows stronger directional preferences of the hydroxyl group of alcohols than cation in the vicinity of an anion. Enhanced pair correlations associated with the terminal methyl carbons suggest aggregation of butanol chains in apolar domains. Triplet correlation functions (TCFs) are also used to evaluate the orientational preferences of the present polar moieties in the mixtures. Information based on TCFs for distribution of polar head group of cations and anions unveils the dominance of equilateral configurations over the less frequent isosceles configurations in all the three mixtures.

Structure analysis for Fe-based and Ni-based metal-metalloid amorphous alloys

Transition metal-metalloid amorphous systems such as Fe-B and Ni-B are usually applied for the soft magnetic metallic glassy alloys and are counted as one of prominent categories in the field of amorphous alloy technology. Since glass forming ability of these systems correlates closely with the atomic level structure depending on chemical species of metal and metalloid, the local structure analysis for these glassy alloys is strongly required. In order to obtain the reliable structural model for these metal (Fe, Ni)-metalloid (B) amorphous samples, we determined the partial structural functions by combinational use of neutron diffraction (ND) and anomalous X-ray scattering (AXS). The amorphous ribbon samples were produced by the single-roller melt-spinning technique. The AXS measurements at Fe and Ni absorption edges were carried out at BL-7C of Photon Factory, KEK. The ND experiment was performed by using the time-of-flight technique and high intensity total diffractometer, NOVA at MLF, J-PARC. The figure shows the g(r)s for Fe80B20, Ni81B19, and Ni60B40calculated by the interference functions obtained by ND measurements. The dashed lines in the figure indicate the interatomic distances estimated from Goldschmidt atomic radii (Fe: 1.28 Å, Ni: 1.25 Å, B: 0.97 Å). At the nearest neighbor region up to about 3 Å, the first peak could be accounted for a harmony of metal (M)–B and B–B pair correlations and the second peak is mainly contributed by the M-M pair correlation. As for the three dimensional structural modeling of the amorphous samples, reverse Monte Carlo simulation has been performed starting from an initial model of 2,000 atoms with the b.c.c. structure. The present simulation results are found to reproduce the experimental interference functions obtained by the ND, ordinary X-ray diffraction, and AXS measurements. We will present the obtained structural model and local structural units around B including their arrangement.

The Structure of Hydrated Poly (D, L - Lactic Acid) Studied With X-Ray Diffraction and Molecular Simulation Methods.

The effect of hydration on the molecular structure of amorphous poly (D, L-lactic acid) (PDLLA) with 50:50 L-to-D ratio has been studied by combining experiments with molecular simulations. X-ray diffraction measurements revealed significant changes upon hydration in the structure functions of the copolymer. Large changes in the structure functions at ~ 10 days of incubation coincided with the large increase in the water uptake from ~1 to ~40% and the formation of voids in the film. Computer modeling based on the recently developed TIGER2/TIGER3 mixed sampling scheme was used to interpret these changes by efficiently equilibrating both dry and hydrated models of PDLLA. Realistic models of bulk amorphous PDLLA structure were generated as demonstrated by close agreement between the calculated and the experimental structure functions. These molecular simulations were used to identify the interactions between water and the polymer at the atomic level including the change of positional order between atoms in the polymer due to hydration. Changes in the partial O-O structure functions, about 95% of which were due to water-polymer interactions, were apparent in the radial distribution functions. These changes, and somewhat smaller changes in the C-C and C-O partial structure functions, clearly demonstrated the ability of the model to capture the hydrogen bonding interactions between water and the polymer, with the probability of water forming hydrogen bonds with the carbonyl oxygen of the ester group being about four times higher than with its ether oxygen.

Short-range order and collective dynamics of poly(vinyl acetate): A combined study by neutron scattering and molecular dynamics simulations

The structure and collective dynamics at local length scales of poly(vinyl acetate) (PVAc) have been investigated by combining neutron scattering on a deuterated sample and fully atomistic molecular dynamics simulations. The experimental data have provided microscopic information at molecular level and a critical check to validate the simulated cell. In order to gain deep insight on the structure factor, we have grouped the simulation results in terms of three molecular substructures: the main chain, the carboxyl group, and the methyl group. The study of the resulting static partial structure functions has revealed the origin of the diffraction peaks, and a real-space evaluation of the characteristic radial distribution functions has allowed separating intra- and interchain contributions to the total correlation functions. The extension of this study to the dynamic structure factor has revealed a coupling between the side-group motions and the main-chain dynamics at intermolecular distances. Moreover, a decrease in coherency of the main-chain motions at intermolecular level is observed with increasing temperature, leading to a rather decoupled behavior between the main chains at 200 K above the glass transition.

Partial Pair Correlation Functions of Low-Density Supercritical Water Determined by Neutron Diffraction with the H/D Isotopic Substitution Method

Neutron diffraction measurements were carried out on H/ D isotopically substituted water in the low-density supercritical condition (T = 673 K, P = 26.3 MPa, and rho = 0.0068 molecules.A-3) in order to obtain direct information on the intermolecular partial structure functions, gHH inter(r), gOH inter(r), and gOO inter(r). In correspondence to the high-density supercritical water previously reported, the intermolecular nearest neighbor peaks in gHH inter(r), gOH inter(r), and gOO inter(r) are diffuse compared with the ambient ones. The nearest neighbor O...O distance (3.3 A) and its coordination number (2.6) were determined from the observed gOO inter(r). These results indicate that the orientational correlation between neighboring water molecules is considerably lost in low-density supercritical water. Small clusters involving a few water molecules are preferentially formed in low-density supercritical water, which is consistent with results obtained by previous IR and NMR studies.

Local Structure of Syndiotactic Poly(methyl methacrylate). A Combined Study by Neutron Diffraction with Polarization Analysis and Atomistic Molecular Dynamics Simulations

The local structure of syndiotactic poly(methyl methacrylate) (PMMA) has been investigated by combining neutron scattering and fully atomistic molecular dynamics simulations. Selectively deuterating parts of the PMMA monomer, we have accessed five different partial structure factors in the glassy state by neutrons, and polarization analysis has allowed isolating the coherent contribution to the total scattering. In addition, the temperature dependence of the static structure factor has been determined on the fully deuterated sample. The different measured partial structure factors show qualitatively different features with respect to peak positions and heights and provide a very critical check to validate the simulated structure. To gain deep insight into the structure, we have grouped the simulation results in terms of three molecular substructures: the main chain, the α-methyl group, and the ester side group. The study of the resulting partial structure functions has revealed the origin of the diffraction peaks, including those in the X-rays pattern reported in the literature. In addition, a real-space evaluation of the characteristic radial distribution functions has allowed separating intra- and interchain contributions to the total correlation functions. We have found that (i) PMMA exhibits a strong local order with an average main-chain distance of ≈8.6 Å, (ii) this is the only average interchain distance and thus no precursor effect of a layered structure is found, (iii) the main chain shows a persisting all-trans structure, and (iv) a strong anticorrelation between the main chain and the ester side groups, together with an interdigitation of the side groups, suggests a marked separation between the backbone and the side-group spatial arrangements.

Neutron as a Probe of Structural Investigation of Solutions

Neutron diffraction technique plays an important role in investigation of the solution structure. The isotopic substitution method is widely used as one of the most powerful tools that provide information on the partial structure functions of the solution system with highly complexity.High-performance total scattering spectrometers installed at J-PARC will make it possible to extend the research field to the next stage, involving more dilute solution systems with biological importance, possibly, living organs etc. It may also be important for the further progress of the neutron science community in Japan that the community admits many active researchers who are not familiar to the neutron scattering.

Static structure of liquid alloys of alkali metals

Abstract The transferability of Fiolhais et al. (Phys. Rev. B 51 (1995) 14001; 53 (1996) 13193(E)) pseudopotential to liquid alloys is assessed. Molecular dynamics simulations are performed to predict the static structure of Na–K, Na–Cs, and K–Cs alloys at equiatomic composition. Comparison with experimental results confirms the ability of the so-called individual version of the potential to be used in the case of alloys of alkali components. The partial structure functions, experimentally unreachable, are presented and the behaviours of each system are discussed.

Determination of displacements from nanoprecipitates in a Cu–Ni–Fe single crystal using anomalous small-angle and large-angle X-ray scattering

Single crystals of Cu–41.5 at.% Ni–16 at.% Fe have been studied by small-angle and large-angle X-ray scattering in order to determine the displacements induced by the disc-like precipitates formed during decomposition. The small-angle X-ray scattering (SAXS) patterns gave information on the size and the organization of the precipitates, while the scattering near Bragg peaks allows a determination of the distortions of the lattice created by these precipitates. The variations of the atomic scattering factors of Fe, Ni and Cu (for the large-angle measurements) were used to determine both the partial structure functions (`chemical' data) and the partial displacements. The precipitates were found to be enriched in Fe and Ni, which induced a contraction of the lattice, while the depleted matrix (mainly Cu) was dilated. This succession of compressed and dilated regions is very stable and prevents a single precipitate from growing much in this direction during coarsening. This can explain why a single precipitate tends to grow mainly in the orthogonal directions, where the extension of the displacements is smaller than the precipitated region.

Anomalous X-ray scattering for determining the partial structural functions of binary liquids

The availability of intense white X-rays from synchrotron radiation sources has greatly improved both acquisition and quality of anomalous X-ray scattering (AXS) measurements. A demonstration is given of the usefulness of the AXS method for determining three partial structural functions of liquid matter by some selected examples of molten salts such as CuBr and RbBr.

Partial structural functions of molten copper halides CuX (X = Br, I) estimated from the anomalous x-ray scattering measurements

The three partial structural functions of molten copper halides CuX (X = Br, I) have been estimated from anomalous x-ray scattering (AXS) measurements coupled with the reverse Monte Carlo (RMC) simulation technique. For both cases of molten CuBr and CuI, the Cu-Cu partial structure factor of aCuCu(Q) was found to be rather structureless and the closest Cu-Cu distance was significantly smaller than that for X-X, indicating like-ion penetration into the first unlike-ion coordination shell, similar to the molten CuCl case. We then suggest a disordered close packing of anions where Cu ions meander so as to take a strongly disordered distribution by penetrating through the tetrahedral holes.

A secondary graphite crystal spectrometer for anomalous X-ray diffraction experiments

Abstract A new design for implementation of anomalous X-ray diffraction experiments is proposed. The exploitation of a graphite crystal spectrometer with good energy resolution in combination with an acceptable counting rate opens new possibilities to carry out AWAXS experiments and calculate partial structure functions. The proof of this measurement principle is demonstrated by presentation of the partial structure factor and radial distribution function for rubidium germanate glasses around the germanium component.

Partial Structural Functions of Molten AgBr Estimated from the Anomalous X-Ray Scattering Data Coupled with Neutron Diffraction

The three partial structural functions of molten AgBr have been determined by using a combination of the anomalous X-ray scattering (AXS) data and conventional neutron diffraction result. This data processing includes the help of the reverse Monte Carlo (RMC) simulation technique. The partial structure factor of a AgAg ( Q ) in molten AgBr was rather broad than that found in molten alkali halides such as RbBr. The resultant structural parameters suggest that the structure of molten AgBr is quite likely described by disordered close packing of Br ions where Ag ions are distributed in both octahedral and tetrahedral holes.

Partial Structural Functions of Molten RbBr Estimated from the Anomalous X-ray Scattering Data

The anomalous x-ray scattering (AXS) measurements for molten RbBr have been made using the energies close to the Rb K (15.202 keV) and Br K (13.470 keV) absorption edges for estimating three partial structural functions of Rb-Rb, Br-Br and Rb-Br pairs. The data processing for obtaining three partials includes the intensity data obtained at the energy of 17.0 keV, which is far from both edges and the help of the reverse Monte Carlo (RMC) simulation technique. The resultant partial structural functions of molten RbBr suggest that the configuration in the first Rb-Br coordination shell is found to be octahedral, as it is in the crystal.

Reverse Monte Carlo Simulation for Determining the Partial Structural Functions of GeO<SUB>2</SUB> Glass from the Anomalous X-ray Scattering and Neutron Diffraction Data

Reverse Monte Carlo (RMC) simulation has been carried out in order to estimate the partial structural functions of Ge–Ge, O–O and Ge–O pairs for GeO2 glass. Three independent interference functions from the ordinary X-ray diffraction, neutron diffraction and anomalous X-ray scattering measurements near Ge K absorption edge were used in the RMC simulation. The present results clearly indicate that the GeO2 glass structure can be described by a continuous random network of corner-shared GeO4 tetrahedral units as detected in the α-quartz type of GeO2 crystal.

Role of plectin in cytoskeleton organization and dynamics

Plectin and its isoforms are versatile cytoskeletal linker proteins of very large size (>500 kDa) that are abundantly expressed in a wide variety of mammalian tissues and cell types. Earlier studies indicated that plectin molecules were associated with and/or directly bound to subcomponents of all three major cytoskeletal filament networks, the subplasma membrane protein skeleton, and a variety of plasma membrane-cytoskeleton junctional complexes, including those found in epithelia, various types of muscle, and fibroblasts. In conjunction with biochemical data, this led to the concept that plectin plays an important role in cytoskeleton network organization, with consequences for viscoelastic properties of the cytoplasm and the mechanical integrity and resistance of cells and tissues. Several recent findings lent strong support to this concept. One was that a hereditary disease, epidermolysis bullosa simplex (EBS)-MD, characterized by severe skin blistering combined with muscular dystrophy, is caused by defects in the plectin gene. Another was the generation of plectin-deficient mice by targeted inactivation of the gene. Dying shortly after birth, these animals exhibited severe defects in skin, skeletal muscle and heart. Moreover, in vitro studies with cells derived from such animals unmasked an essential new role of plectin as regulator of cellular processes involving actin stress fibers dynamics. Comprehensive analyses of the gene locus in man, mouse, and rat point towards a complex gene expression machinery, comprising an unprecedented diversity of differentially spliced transcripts with distinct 5' starting exons, probably regulated by different promoters. This could provide a basis for cell type-dependent and/or developmentally-controlled expression of plectin isoforms, exerting different functions through binding to distinct partners. Based on its versatile functions and structural diversification plectin emerges as a prototype cytolinker protein among a family of proteins sharing partial structural homology and functions.