Small-angle X-ray Scattering Results Research Articles

THE PAYNE EFFECT: PRIMARILY POLYMER-RELATED OR FILLER-RELATED PHENOMENON?

ABSTRACT The hysteretic softening at small dynamic strains (Payne effect)—related to the rolling resistance and viscoelastic losses of tires—was studied as a function of particle size, filler volume fraction, and temperature for carbon black (CB) reinforced uncrosslinked styrene–butadiene rubber (SBR) and a paste-like material composed of CB-filled paraffin oil. The low-strain limit for dynamic storage modulus was found to be remarkably similar for CB-filled oil and the CB-filled SBR. Small-angle X-ray scattering (SAXS) measurements on the simple composites and detailed data analysis confirmed that the aggregate structures and nature of filler branching/networking of carbon black were virtually identical within oil compared to the high molecular weight polymer matrix. The combined dynamic rheology and SAXS results provide clear evidence that the deformation-induced breaking (unjamming) of the filler network—characterized by filler–filler contacts that are percolated throughout the material—is the main cause for the Payne effect. However, the polymer matrix does play a secondary role as demonstrated by a reduction in Payne effect magnitude with increasing temperature for the CB-reinforced rubber, which was not observed to a significant extent for the oil–CB system.

Electrostatic Interactions between Barium Hexaferrite Nanoplatelets in Alcohol Suspensions

In a room-temperature liquid magnet, barium hexaferrite (BHF) nanoplatelets suspended in 1-butanol spontaneously order and form a ferromagnetic nematic phase. In such concentrated suspension, the nanoplatelets align in large macroscopic regions, forming magnetic domains. The key parameter for the suspension stability and the formation of the ferromagnetic nematic phase is electrostatic interaction, which can be influenced by the solvent and the concentration of surfactant, i.e., dodecylbenzenesulfonic acid (DBSA). In this study, we investigated electrostatic interactions of the DBSA-functionalized nanoplatelets’ suspensions in different alcohols. We prepared suspensions in tert-butanol, 1-hexanol, 1-butanol, and 2-propanol and measured conductivity, small-angle X-ray scattering (SAXS), dynamic light scattering (DLS), and electrophoretic mobility. SAXS results and electrophoretic mobility measurements confirmed the colloidal stability of the suspensions, which was not affected by the variation in concentra...

Four steps for revealing and adjusting the 3D structure of aptamers in solution by small-angle X-ray scattering and computer simulation

Nucleic acid (NA) aptamers bind to their targets with high affinity and selectivity. The three-dimensional (3D) structures of aptamers play a major role in these non-covalent interactions. Here, we use a four-step approach to determine a true 3D structure of aptamers in solution using small-angle X-ray scattering (SAXS) and molecular structure restoration (MSR). The approach consists of (i) acquiring SAXS experimental data of an aptamer in solution, (ii) building a spatial distribution of the molecule's electron density using SAXS results, (iii) constructing a 3D model of the aptamer from its nucleotide primary sequence and secondary structure, and (iv) comparing and refining the modeled 3D structures with the experimental SAXS model. In the proof-of-principle we analyzed the 3D structure of RE31 aptamer to thrombin in a native free state at different temperatures and validated it by circular dichroism (CD). The resulting 3D structure of RE31 has the most energetically favorable conformation and the same elements such as a B-form duplex, non-complementary region, and two G-quartets which were previously reported by X-ray diffraction (XRD) from a single crystal. More broadly, this study demonstrates the complementary approach for constructing and adjusting the 3D structures of aptamers, DNAzymes, and ribozymes in solution, and could supply new opportunities for developing functional nucleic acids. Graphical abstract.

Deformation mechanism of hard elastic polyethylene film during uniaxial stretching: Effect of stretching speed

The effects of stretching speed on the structural evolutions and mechanical behaviors of hard-elastic polyethylene films are studied with in-situ and ex-situ small-angle X-ray scattering (SAXS), scanning electronic microscope (SEM) and tensile tests in a wide stretching speed range (0.04–4 mm/s). Based on the evolutions of structural parameters extracted from SAXS results and the surface morphologies from SEM experiments, the stretching speed space can be divided into two regions with the boundary of 0.8 mm/s. Stress induced microphase separation of amorphous phase triggers the yielding behavior, which distributes more homogeneously with the increase of stretching speed. In region I, microphase separation tends to develop into cavities at smaller strain due to the thorough relaxation process of molecular chains in amorphous phases, which results in the inhomogeneous deformation during further stretching. In region II, the relaxation of molecular chains is not enough to response to the variation of external tensile field, thus inducing the uniform distribution of the occurrence of microphase separation.

Effect of Molecular Orientation to Proton Conductivity in Sulfonated Polyimides with bent backbones

Two organized sulfonated polyimides (ASPIs) with bent polymer backbones were synthesized to study a relation between structure and proton conductivity. Proton conductivity exhibited different values between the thin film and bulk pelletized forms. Results from small-angle X-ray scattering (SAXS) and attenuated total reflection measurements suggest that the orientation of backbones is different between the thin film and bulk forms. SAXS results suggest excess amount of water uptake in the bulk samples compared to the thin film form. These structure and water uptake property could contribute the difference of the proton conductivity between the thin film and bulk pelletized forms.

Structural analysis of hydrogenated nano-crystalline silicon suboxide (nc-SiOx:H, x < 1) thin films with SAXS for a potential application as phase change material

Hydrogenated nano-crystalline silicon suboxide (nc-SiOx:H; x < 1) is a two-phase material in which nanometer-sized silicon (nc-Si) region enclosed by hydrogenated amorphous silicon suboxide (a-SiOx:H) matrix. nc-SiOx:H thin films are produced by using highly hydrogen-diluted (dH ≥ 90%) plasma of silane and carbon-dioxide mixture, in a Plasma Enhanced Chemical Vapor Deposition (PECVD) system. The high concentration of the H-atoms in the plasma assist the silicon atoms on the growing film surface to crystallize. Small Angle X-Ray Scattering (SAXS) method was used to determine the nano-scale structures of nc-SiOx:H thin films, for varying hydrogen dilution ratios. The size, shape and the distribution of the nano-formations are found to depend strongly on the preparation conditions. From FTIR absorption and Raman scattering experiments, atomic oxygen and hydrogen contents and also the crystal ratio of the samples are evaluated. As results of nano-structural analyses, the morphologies, sizes and distributions of the nano-aggregations are found to be closely related to the crystallization of the films. From the SAXS results of the samples prepared at the hydrogen dilution ratio of 90%, the nano-aggregations are found to form in uniformly distributed core-shells. However, as the hydrogen dilution is increased to higher ratios to 95% and further to 99%, the nano-scaled fractals are deduced to form. The oxygen and hydrogen contents in nc-SiOx:H are strictly related to the crystal ratio of the samples. The crystal ratio is determined by the hydrogen dilution ratio during the deposition. The two-phase structure of nc-SiOx:H samples and the dependence on the hydrogen dilution ratio may suggest these materials are candidates for phase change materials. Depending on the deposition parameters, smaller nc-Si structures may be prepared which may have different (lower) electron densities required to melt the amorphous region and make the phase change possible due to explosive crystallization.

Commonly used FRET fluorophores promote collapse of an otherwise disordered protein

The dimensions that unfolded proteins, including intrinsically disordered proteins (IDPs), adopt in the absence of denaturant remain controversial. We developed an analysis procedure for small-angle X-ray scattering (SAXS) profiles and used it to demonstrate that even relatively hydrophobic IDPs remain nearly as expanded in water as they are in high denaturant concentrations. In contrast, as demonstrated here, most fluorescence resonance energy transfer (FRET) measurements have indicated that relatively hydrophobic IDPs contract significantly in the absence of denaturant. We use two independent approaches to further explore this controversy. First, using SAXS we show that fluorophores employed in FRET can contribute to the observed discrepancy. Specifically, we find that addition of Alexa-488 to a normally expanded IDP causes contraction by an additional 15%, a value in reasonable accord with the contraction reported in FRET-based studies. Second, using our simulations and analysis procedure to accurately extract both the radius of gyration (Rg) and end-to-end distance (Ree) from SAXS profiles, we tested the recent suggestion that FRET and SAXS results can be reconciled if the Rg and Ree are "uncoupled" (i.e., no longer simply proportional), in contrast to the case for random walk homopolymers. We find, however, that even for unfolded proteins, these two measures of unfolded state dimensions remain proportional. Together, these results suggest that improved analysis procedures and a correction for significant, fluorophore-driven interactions are sufficient to reconcile prior SAXS and FRET studies, thus providing a unified picture of the nature of unfolded polypeptide chains in the absence of denaturant.

Modifying internal organization and surface morphology of siRNA lipoplexes by sodium alginate addition for efficient siRNA delivery

Vectorized small interfering RNAs (siRNAs) are widely used to induce specific mRNA degradation in the intracellular compartment of eukaryotic cells. Recently, we developed efficient cationic lipid-based siRNA vectors (siRNA lipoplexes or siLex) containing sodium alginate (Nalg-siLex) with superior efficiency and stability properties than siLex. In this study, we assessed the physicochemical and some biological properties of Nalg-siLex compared to siLex. While no significant differences in size, ζ potential and siRNA compaction were detected, the addition of sodium alginate modified the particle morphology, producing smoother and heterogeneous particles characterized by transmission electron microscopy. We also noted that Nalg-siLex have surface differences observed by X-ray photoelectron spectroscopy. These differences could arise from an internal reorganization of components induced by the addition of sodium alginate, that is indicated by Small-Angle X-ray Scattering results. Moreover, Nalg-siLex did not trigger significant hepatotoxicity nor inflammatory cytokine secretion compared to siLex. Taken together these results suggest that sodium alginate played a key role by structuring and reinforcing siRNA lipoplexes, leading to more stable and efficient delivery vector.

In situ monitoring of the structural change of microemulsions in simulated gastrointestinal conditions by SAXS and FRET

Microemulsions are promising drug delivery systems for the oral administration of poorly water-soluble drugs. However, the evolution of microemulsions in the gastrointestinal tract is still poorly characterized, especially the structural change of microemulsions under the effect of lipase and mucus. To better understand the fate of microemulsions in the gastrointestinal tract, we applied small-angle X-ray scattering (SAXS) and fluorescence resonance energy transfer (FRET) to monitor the structural change of microemulsions under the effect of lipolysis and mucus. First, the effect of lipolysis on microemulsions was studied by SAXS, which found the generation of liquid crystalline phases. Meanwhile, FRET spectra indicated micelles with smaller particle sizes were generated during lipolysis, which could be affected by CaCl2, bile salts and lecithin. Then, the effect of mucus on the structural change of lipolysed microemulsions was studied. The results of SAXS and FRET indicated that the liquid crystalline phases disappeared, and more micelles were generated. In summary, we studied the structural change of microemulsions in simulated gastrointestinal conditions by SAXS and FRET, and successfully monitored the appearance and disappearance of the liquid crystalline phases and micelles.

Mechanical hysteresis, interface and filler–filler structural breakdowns in ethylene vinyl acetate organoclay composites internally lubricated via radiolytically degraded PTFE microparticles

ABSTRACTInclusion of two or more distinct fillers (hybrid fillers) in a matrix is envisaged to entail synergetic advantages. This study reports synthesis and property evaluation of a novel hybrid filler‐based polymer composite containing two types of fillers with distinct attributes namely mechanical reinforcement and internal lubrication. Poly(tetrafluoroethylene) micro‐particles (PTFEMP) were synthesized via radiolytic‐mechanical degradation and used as an internal lubricant for organoclay (OC) reinforced ethylene vinyl acetate (EVA) matrix. Mechanical hysteresis, nonlinear and linear small amplitude oscillatory shear rheology, morphology, small angle X‐ray scattering (SAXS), dynamic coefficient of friction (DCoF), surface wetting and thermoxidative stability of binary and ternary composites were investigated. In EVA/OC composites, PTFEMP acted as an internal lubricant and reduced DCoF in a volume fraction‐dependent fashion. OC and PTFEMP both increased the mechanical hysteresis of EVA; though the magnitude of hysteresis was much less in PTFEMP. Intriguingly, PTFEMP reduced mechanical hysteresis of EVA/OC composites that is work done during loading and unloading stress–strain cycles was considerably reduced with the inclusion of PTFEMP in EVA/OC composites. SAXS results revealed mass fractals and the presence of an interfacial layer in EVA/OC composites but not in EVA/PTFEMP composites. © 2017 Wiley Periodicals, Inc. J. Polym. Sci., Part B: Polym. Phys. 2018, 56, 509–519

Detecting structural orientation in isoprene rubber/multiwall carbon nanotube nanocomposites at different scales during uniaxial deformation

AbstractEnhanced strain‐induced crystallization (SIC) behavior in isoprene rubber/multiwall carbon nanotube (IR/MWCNT) nanocomposites was analyzed in terms of structural orientation during uniaxial deformation. In situ synchrotron wide‐angle X‐ray diffraction and small‐angle X‐ray scattering (SAXS) reveal the molecular orientation in IR/MWCNT composites at different scales. The inclusion of MWCNTs leads to a decrease in the molecular orientation at small strain due to the promotion of SIC. Meanwhile, the presence of MWCNTs induces a large‐scale orientation within the vulcanized rubber network based on SAXS results. Considering the heterogeneous nature of the vulcanized network, the nucleation process during SIC is discussed from the viewpoint of thermodynamics. The oriented large‐scale structure in IR/MWCNT composites is composed of local rubber chains stretched up MWCNTs, from which the additional nuclei are induced. By forming a bound rubber layer around MWCNTs through attractive interactions, MWCNTs can amplify the local strain of rubber segments and form a highly oriented large‐scale structure, but without altering the overall molecular orientation level. The evolution of detailed structural orientation in MWCNT‐filled rubber composites during deformation is revealed for the first time. © 2017 Society of Chemical Industry

Full-scale use of X-ray scattering techniques to characterize aged Al-2wt.%Cu alloy

In this work X-ray scattering techniques are used in full scale to characterize the microstructure of Al-2wt.%Cu alloy in order to state common and diverse features between artificial and dynamic ageing. Artificial ageing of the alloy is implemented via T6 regime, dynamic ageing occurs during high pressure torsion. X-ray phase analysis of diffraction patterns obtained in the transmission regime has for the first time identified and quantified the nanodisperse phases of precipitates in the both aged states. Lattice parameters, coherent scattering domains distribution over sizes, averaged dislocation density, fractions of edge and screw dislocations of Al phase after artificial and dynamic ageing are determined via the diffraction patterns obtained in the reflection regime. Small angle X-ray scattering (SAXS) technique has established quantitative characteristics of size, shape and distribution of precipitates in the mentioned states. In order to confirm the results of SAXS, transmission electron microscopy studies are performed on the same foils. Peculiarities of mechanisms of artificial and dynamic ageing in the studied alloy are discussed on the basis of the obtained data.

Multiscale structures of Zr-based binary metallic glasses and the correlation with glass forming ability

Thermal behaviors and structures of three Zr-based binary glass formers, Zr50Cu50, Zr64Cu36 and Zr64Ni36, were investigated and compared using differential scanning calorimetry (DSC), transmission electron microscopy (TEM), high energy X-ray diffraction (XRD) and small angle X-ray scattering (SAXS). The high energy XRD results show that the bulk glass former Zr50Cu50 has a denser atomic packing efficiency and reduced medium-range order than those of marginal glass formers Zr64Cu36 and Zr64Ni36. Based on TEM observations for the samples after heat treatment at 10K above their crystallization onset temperatures, the number density of crystals for Zr50Cu50 was estimated to be 1023–1024m−3, which was four-orders higher than that in Zr64Cu36 and Zr64Ni36 metallic glasses. SAXS results indicate that Zr50Cu50 has higher degree of nanoscale inhomogeneities than those in Zr64Cu36 and Zr64Ni36 at as-cast state. The observed multiscale structures are discussed in terms of the phase stability and glass-forming ability of Zr-based binary glass formers.

Quantitative determining interface information of nano composite by synchrotron radiation small-angle X-ray scattering

Abstract The interface plays a decisive role on the performance of nano dielectric composite films, and researchers have made tremendous efforts to confirm the existence of the interface in nano dielectric composite films. However, establishing quantitative determining interface information of nano composites is very difficult. In this paper, a typical nano dielectric, PI/SiO 2 composite film with content of 10% SiO 2 was prepared by an in-situ method and the microstructures of PI/SiO 2 and pure PI were obtained by the small-angle X-ray scattering (SAXS), which is a non-destructive testing method. The TEM results show that the average grain diameter of SiO 2 particles and the thicknesses of the interfaces are about 7.5 nm and 2.2 nm, respectively. The SAXS results are confirmed by direct TEM imaging method, in which SiO 2 particles adsorb the surrounding PI molecular chains, and form the interfaces. The average grain diameters of SiO 2 (not including the absorbed PI) particles and the thicknesses of interfaces are about 6.8 nm and 2.6 nm respectively. From this paper, we have proved that SAXS is a new effective means for the quantitative determining of interface information of nano composites.

Pore Model in the Melting Regime of a Lyotropic Biomembrane with an Anionic Phospholipid.

Aqueous dispersions of the anionic phospholipid dimyristoyl phosphatidyl glycerol (DMPG) exhibit an unusual "melting regime", at the phase transition between the ordered (gel) and the disordered (fluid liquid crystal) state of hydrocarbon chains, depending on the ionic strength and DMPG concentration, previously attributed to the pore formation. Dispersions with 150 mM DMPG present a lamellar phase above 23 °C, within the melting regime. In this study, we present a detailed pore model for the analysis of small-angle X-ray scattering (SAXS) results and their variation with temperature, focused on the surface fractions of pores in the bilayers. Large and small toroidal pores are necessary to explain the SAXS results. Pores have DMPG in the fluid conformation, whereas the flat region of the bilayer has DMPG molecules in fluid and in gel conformations. A particular strategy was developed to estimate the charges due to the localization of mobile ions in the system, which is based on the calculation of electron densities by duly considering all molecular and ionic species that characterize the system, and the temperature dependency of their volumes. The best fit to the model of SAXS curves defines that the gel phase transforms initially, at 19.4 °C, in uncoupled bilayers with large pores (radius 93.2 ± 0.5 Å, with water channel diameter 137 ± 1 Å), which transform into small pores along the lamellar phase. The minimum intensity of the SAXS bilayer peak at 30 °C corresponds to a maximum number of small pores, and above 35 °C, the system enters into the normal lamellar fluid phase, without pores. The charge is estimated and shows that the regions with pores contains less Na+ ions per polar head; hence, when they are forming, there is a release of Na+ ions toward the bulk.

Coarse‐grained modeling of the intrinsically disordered protein Histatin 5 in solution: Monte Carlo simulations in combination with SAXS

Monte Carlo simulations and coarse-grained modeling have been used to analyze Histatin 5, an unstructured short cationic salivary peptide known to have anticandidical properties. The calculated scattering functions have been compared with intensity curves and the distance distribution function P(r) obtained from small angle X-ray scattering (SAXS), at both high and low salt concentrations. The aim was to achieve a molecular understanding and a physico-chemical insight of the obtained SAXS results and to gain information of the conformational changes of Histatin 5 due to altering salt content, charge distribution, and net charge. From a modeling perspective, the accuracy of the electrostatic interactions are of special interest. The used coarse-grained model was based on the primitive model in which charged hard spheres differing in charge and in size represent the ionic particles, and the solvent only enters the model through its relative permittivity. The Hamiltonian of the model comprises three different contributions: (i) excluded volumes, (ii) electrostatic, and (iii) van der Waals interactions. Even though the model can be considered as gross omitting all atomistic details, a great correspondence is obtained with the experimental results. Proteins 2016; 84:777-791. © 2016 Wiley Periodicals, Inc.

Insights into the Morphology and Kinetics of Growth of Silver Metal–Organic Nanotubes

The kinetics of the formation of novel porous metal organic nanotubes, [Ag2(4,4′-(1,4-(xylene)diyl)bis(1,2,4-triazole) (NO3)2]·NMP, was investigated by means of ex-situ time-resolved small-angle X-ray scattering (SAXS) and scanning electron microscopy (SEM). The SAXS results were modeled using the Gualtieri model, which decouples the nucleation and growth processes giving additional insight into the crystal formation mechanism. The results show that the semirigid 4,4′-(1,4-(xylene)diyl)bis(1,2,4-triazole) ligand (L) binds with silver ions, adopting a seesaw geometry to form a polydisperse isotropic framework immediately after mixing the ligands and metal ions. In addition, the SEM imaging demonstrates that the microcrystals grow anisotropically, with nucleation along the edge of the 3D aggregate. These combined data demonstrate that the growth of this MONT occurs in two steps: a rapid formation of an isotropic porous structure immediately after mixing the reactant, which then develops anisotropically as t...

CNS myelin structural modification induced in vitro by phospholipases A2

Myelin is the self-stacked membrane surrounding axons; it is also the target of several pathological and/or neurodegenerative processes like multiple sclerosis. These processes involve, among others, the hydrolytic attack by phospholipases. In this work we describe the changes in isolated myelin structure after treatment with several secreted PLA2 (sPLA2), by using small angle x-ray scattering (SAXS) measurements. It was observed that myelin treated with all the tested sPLA2s (from cobra and bee venoms and from pig pancreas) preserved the lamellar structure but displayed an enlarged separation between membranes in certain zones. Additionally, the peak due to membrane asymmetry was clearly enhanced. The coherence length was also lower than the non-treated myelin, indicating increased disorder. These SAXS results were complemented by Langmuir film experiments to follow myelin monolayer hydrolysis at the air/water interface by a decrease in electric surface potential at different surface pressures. All enzymes produced hydrolysis with no major qualitative difference between the isoforms tested.

Plasma column and nano-powder generation from solid titanium by localized microwaves in air

This paper studies the effect of a plasma column ejected from solid titanium by localized microwaves in an ambient air atmosphere. Nanoparticles of titanium dioxide (titania) are found to be directly synthesized in this plasma column maintained by the microwave energy in the cavity. The process is initiated by a hotspot induced by localized microwaves, which melts the titanium substrate locally. The molten hotspot emits ionized titanium vapors continuously into the stable plasma column, which may last for more than a minute duration. The characterization of the dusty plasma obtained is performed in-situ by small-angle X-ray scattering (SAXS), optical spectroscopy, and microwave reflection analyses. The deposited titania nanoparticles are structurally and morphologically analyzed by ex-situ optical and scanning-electron microscope observations, and also by X-ray diffraction. Using the Boltzmann plot method combined with the SAXS results, the electron temperature and density in the dusty plasma are estimated as ∼0.4 eV and ∼1019 m−3, respectively. The analysis of the plasma product reveals nanoparticles of titania in crystalline phases of anatase, brookite, and rutile. These are spatially arranged in various spherical, cubic, lamellar, and network forms. Several applications are considered for this process of titania nano-powder production.

Polystyrene-block-Polybutadiene-block-Polystyrene Triblock Copolymer Meets Silica: From Modification of Copolymer to Formation of Mesoporous Silica

In this work, we reported a facile preparation of mesoporous silica materials assisted by a commercial polystyrene-block-polybutadiene-block-polystyrene (PS-b-PB-b-PS) triblock copolymer. For this purpose, the PS-b-PB-b-PS triblock copolymer was first functionalized with (3-mercaptopropyl)triethoxysilane via a thiol-ene radical addition approach, and then the functionalized triblock copolymer with the midblock bearing triethoxysilane moieties was employed to perform intercomponent sol–gel reactions with tetraethoxysilane (TEOS) to obtain the organic–inorganic gels. The organic–inorganic gels with variable compositions were then used as precursors to obtain mesoporous silica via pyrolysis at elevated temperatures. The functionalized triblock copolymer was characterized by means of Fourier transform infrared spectroscopy, nuclear magnetic resonance spectroscopy, and small-angle X-ray scattering (SAXS). The results of SAXS, transmission electron microscopy, and Brunauer–Emmett–Teller measurements indicate that the mesoporous silica materials were successfully obtained and the porosity of the materials can be modulated with the mass ratios of the functionalized triblock copolymer to the precursor of silica (viz. TEOS).