Small-angle X-ray Scattering Investigations Research Articles

Structural and mechanical analysis on mannuronate-rich alginate gels and xerogels beads based on Calcium, Copper and Zinc as crosslinkers

Beads based on a mannuronate(M)-rich alginate (86 % M units) were prepared by adding the polysaccharide solution to a crosslinking bath containing different concentrations (0.5, 2 and 10 wt%) of XCl2 where X = Ca, Cu or Zn. Primarily focus was on Zn, due to its antioxidant, anti-inflammatory and anti-microbial capabilities. The beads were characterized by Field-Emission Scanning Electron Microscopy (FESEM), Fourier-Transform Infra-Red spectroscopy (FT-IR), Thermogravimetric Analysis (TGA), Small-Angle X-ray Scattering (SAXS) and compression tests. The crosslinking agent significantly influenced the properties of the resulting beads. Specifically, Ca-based beads exhibited a smoother surface, while Cu- and Zn-based beads appeared rougher. Interestingly, Zn-based beads displayed a core-shell structure. Young moduli ranged from 3500 and 7000 MPa, with the highest values observed for Zn-beads. SAXS investigation at 0.5 wt% XCl2 suggested increase in the densely packed domains amount in the order: Ca < Cu < Zn. Extended X-ray Absorption Fine Structure (EXAFS) showed that the coordination number was 4.3 ± 0.4 for Cu, and 4.0 ± 0.2 and 1.1 ± 0.1 for Zn in 0.5 wt% XCl2 alginate xerogels, in agreement with reported Density Functional Calculations on Cu2+– and Zn2+–MM complexes. The results from FT-IR, compositional analysis and EXAFS collectively suggested a bridging coordination for these systems.

In Operando Small-Angle X-ray Scattering Investigation of Nanostructured Polymer Electrolyte for Lithium-Ion Batteries

Electrochemical energy storage still presents one of the biggest challenges that society has to face by developing alternative lithium-ion batteries (LIBs) as they already satisfy important preconditions by providing the highest energy and power densities of all battery systems. Nowadays, the employed liquid electrolytes in LIBs do not merge the world’s increasing demand of safely working batteries. Here, we use a lithium salt-doped diblock copolymer electrolyte:poly(styrene)-block-poly(ethylene oxide)/bis(trifluoromethane) lithium salt, denoted PS-b-PEO/LiTFSI, as a solid-state electrolyte. The evolving nanoscale morphology of the electrolyte material in a capillary-based LIB cell is investigated using in operando small-angle X-ray scattering (SAXS). The electrolyte is sandwiched between two opposing electrodes inside of a glass capillary and investigated during cycling at 90 °C while the X-ray beam is oriented orthogonally to the ionic current. Lithium iron phosphate (LFP) is used as a cathode, while bo...

Cubic Liquid Crystalline Gels Based on Glycerol Monooleate for Intra-articular Injection.

In situ gels containing sinomenine hydrochloride (SMH) for intra-articular (IA) administration to treat rheumatoid arthritis (RA) were designed and investigated in this study. Glycerol monooleate (GMO) was used due to the potential to generate viscous crystalline phase structures upon water absorption. The gels were evaluated using different parameters: syringeability, gelation, viscosity, and drug release. And, polarized light microscopy (PLM), small-angle X-ray scattering investigation (SAXS), and rheological studies were used to analyze their internal structures. In vitro drug release studies were performed by the dialysis membrane diffusion method. The syringeability, viscosity, gelation time, and water for gelation of the obtained preparation met the requirements of IA injection. PLM, SAXS, and rheological analysis showed that all samples had transformed from flowable isotropic solution phases to the inverse cubic (V2) phases upon excess water. And, the gels were found to be able to maintain the drug release for more than 1week. Results showed that in situ gels based on GMO liquid crystalline could provide a sustained system for SMH. Due to its sustained release, the in situ cubic gels were suitable for IA injection to treat RA.

Relationship between electrical conductivity and spatial arrangements of carbon nanotubes in polystyrene nanocomposites: The effect of thermal annealing and plasticization on electrical conductivity

The effect of both thermal annealing and plasticization of the polymeric matrix by low molecular weight compounds on the electrical conductivity of the polystyrene based carbon nanotubes (CNTs) composites were investigated. It was found that the electrical conductivity of the samples filled with 3 wt% of CNTs increased by nearly 2 orders of magnitude after thermal annealing for 10 h at 150 °C, and it further increased with increasing plasticizer content. The effect of the hierarchical CNT morphology on the electrical conductivity of composites was elucidated by in-situ Raman and Synchrotron Radiation Small Angle X-ray Scattering investigations. The synergistic effect between thermal treatment and matrix plasticization contributes to efficiently eliminate the residual stress at the interface between polymeric matrix and carbon nanotubes. This leads to the formation of a more effective CNTs network featured by more dense bundles, exhibiting a larger number of contacts between the CNTs which contributes to significantly enhance the electrical conductivity of composites.

Microcapsules for Confining Fluids: Prediction of Shell Stability from Advanced SAXS Investigations

Polymeric microcapsules represent an effective tool to confine a broad range of materials for diverse applications. Melamine-formaldehyde capsules have been extensively used to encapsulate fragrances (or other substances) in order to control the perfume release and to extend its efficacy. Capsule properties can be controlled and tuned by varying synthesis conditions, such as batch composition, pH and temperature. Their stability is certainly related to structural features such as mechanical, thermal and morphological characteristics. Nevertheless, to the best of our knowledge, a quantitative correlation between capsules leakage profiles and structural features has never been attempted. We report on a model based on the small angle X-ray scattering (SAXS) to describe the relationship between the homogeneous wall structure and the leakage properties of melamine capsules. SAXS is a suitable technique to investigate the structure of capsule shell at the nanometer scale and has been employed here to disclose t...

Relationship between temperature-induced changes in internal microscopic structures of poly(N-isopropylacrylamide) microgels and organic dye uptake behavior.

Temperature-induced changes in the internal structures of poly(N-isopropylacrylamide) (pNIPAm) microgels were evaluated by small-angle X-ray scattering (SAXS), and the results were used to explain organic dye uptake by the microgels. The dye uptake experiments were conducted using two organic dyes: cationic rhodamine 6G (R6G) and anionic erythrosine. In the SAXS investigation, the internal structures of the microgels were characterized in terms of the correlation length, ξ, and the distance, d*, which originated from the local packing of the isopropyl groups of two neighboring chains. With increasing temperature up to the volume phase transition temperature (VPTT) of the microgels, the correlation length, ξ, was increased and the distance, d*, was decreased. At the same time, the amounts of the dyes taken up by the pNIPAm microgels were increased, despite a decrease in the volume of the microgels. The results indicated that the pNIPAm chains were closer to each other due to the hydrophobic association of isopropyl groups, which resulted in the growth of the hydrophobic domains. Thus, the hydrophobic interactions between the dyes and pNIPAm were probably accompanied by the domain formation. With a further increase of temperature above the VPTT, the correlation length, ξ, was decreased and then not defined because the Ornstein-Zernike type contribution disappeared, and the distance, d*, was not largely changed. At the same time, the uptake amounts of the dyes per unit volume of the microgels were also not largely changed, which behaved similar to the distance, d*. It was probably due to the fact that the internal structures of the microgels were not largely changed because the isopropyl groups were in contact with each other. The view was supported by the result of the uptake study of the nonthermoresponsive microgels which did not have the hydrophobic isopropyl groups.

Binary and Ternary Phase Behaviors of Short Double-Chain Quaternary Ammonium Amphiphiles: Surface Tension, Polarized Optical Microscopy, and SAXS Investigations

A series of short chain dialkyldimethylammonium amphiphiles ([DiC(n)][X] and [DiC(n)]2[X] with n = 6, 8, or 10) has been investigated as a function of the nature of the counteranion [X] (Cl(-) and Br(-) as classical references and MoO4(2-) and WO4(2-) as catalytic anions). Critical aggregation concentrations (CACs) in water were determined by surface tension measurements, and the binary phase diagrams of the surfactant/water systems were established using polarized optical microscopy (POM) and small angle X-ray scattering (SAXS). The evolution of microstructures and lyotropic phases were discussed in terms of surfactant chain length and counterion effect. A cubic phase region was observed for the divalent counteranions associated with the intermediate chain length, i.e., [DiC8]2[MoO4] and [DiC8]2[WO4]. Finally, the fish diagrams reflecting the polyphasic microemulsion phase behavior of the water/amphiphile/oil ternary systems were established using the carbon number of mono- and dichlorinated n-alkanes as a scan variable. The amphiphile efficiency was also discussed according to the chain length and the nature of the counterions. The hydrophilic-lipophilic behavior of the amphiphiles was evaluated on the basis of the fish diagrams allowing their classification according to the Hofmeister anion sequence. The unusual behavior of [DiC8][Cl] and [DiC8]2[MO4] (M = W or Mo) is highlighted by all experiments: these compounds are clearly intermediates between hydrotropes, [DiC6] cation, and surfactants, [DiC10] cation.

Small-Angle X-ray Scattering Investigations of Biomolecular Confinement, Loading, and Release from Liquid-Crystalline Nanochannel Assemblies.

This Perspective explores the recent progress made by means of small-angle scattering methods in structural studies of phase transitions in amphiphilic liquid-crystalline systems with nanochannel architectures and outlines some future directions in the area of hierarchically organized and stimuli-responsive nanochanneled assemblies involving biomolecules. Time-resolved small-angle X-ray scattering investigations using synchrotron radiation enable monitoring of the structural dynamics, the modulation of the nanochannel hydration, as well as the key changes in the soft matter liquid-crystalline organization upon stimuli-induced phase transitions. They permit establishing of the inner nanostructure transformation kinetics and determination of the precise sizes of the hydrophobic membraneous compartments and the aqueous channel diameters in self-assembled network architectures. Time-resolved structural studies accelerate novel biomedical, pharmaceutical, and nanotechnology applications of nanochannel soft materials by providing better control of DNA, peptide and protein nanoconfinement, and release from diverse stimuli-responsive nanocarrier systems.

Structural aspects of alkali treated sisal fiber — A SAXS investigation

The present work emphasizes the effect of alkali (NaOH) solution on macromolecular parameters of sisal fiber. The macromolecular parameters of alkali treated sisal fiber were computed along with air-dried sisal fiber by treating fiber as a non-ideal two-phase system characterized by continuous variation of electron density at the phase boundary. Small angle Xray scattering (SAXS) technique was employed to evaluate the macromolecular parameters, using correlation functions, applying the theories of Vonk, Ruland and Misra et al. The finite value of width of transition layer suggests to treat the fiber to be a non-ideal two-phased system. The evaluated macromolecular parameters are: transversal periodicity, specific inner surface, volume fractions of matter and void phases, transversal lengths in both phases, range of inhomogeneity, volume fraction of transition layer and length of coherence.

Long-Living Intermediates during a Lamellar to a Diamond-Cubic Lipid Phase Transition: A Small-Angle X-Ray Scattering Investigation

To generate nanostructured vehicles with tunable internal organization, the structural phase behavior of a self-assembled amphiphilic mixture involving poly(ethylene glycol) monooleate (MO-PEG) and glycerol monooleate (MO) is studied in excess aqueous medium by time-resolved small-angle X-ray scattering (SAXS) in the temperature range from 1 to 68 degrees C. The SAXS data indicate miscibility of the two components in lamellar and nonlamellar soft-matter nanostructures. The functionalization of the MO assemblies by a MO-PEG amphiphile, which has a flexible large hydrophilic moiety, appears to hinder the epitaxial growth of a double diamond (D) cubic lattice from the lamellar (L) bilayer structure during the thermal phase transition. The incorporated MO-PEG additive is found to facilitate the formation of structural intermediates. They exhibit greater characteristic spacings and large diffusive scattering in broad temperature and time intervals. Their features are compared with those of swollen long-living intermediates in MO/octylglucoside assemblies. A conclusion can be drawn that long-living intermediate states can be equilibrium stabilized in two- or multicomponent amphiphilic systems. Their role as cubic phase precursors is to smooth the structural distortions arising from curvature mismatch between flat and curved regions. The considered MO-PEG functionalized assemblies may be useful for preparation of sterically stabilized liquid-crystalline nanovehicles for confinement of therapeutic biomolecules.

Time-resolved Small-angle X-ray Scattering Investigation of the Folding Dynamics of Heme Oxygenase: Implication of the Scaling Relationship for the Submillisecond Intermediates of Protein Folding

Polypeptide collapse is generally observed as the initial folding dynamics of proteins with more than 100 residues, and is suggested to be caused by the coil-globule transition explained by Flory's theory of polymers. To support the suggestion by establishing a scaling behavior between radius of gyration (Rg) and chain length for the initial folding intermediates, the folding dynamics of heme oxygenase (HO) was characterized by time-resolved, small-angle X-ray scattering. HO is a highly helical protein without disulfide bridges, and is the largest protein (263 residues) characterized by the method. The folding process of HO was found to contain a transient oligomerization; however, the conformation within 10 ms was demonstrated to be monomeric and to possess Rg of 26.1(+/-1.1) A. Together with the corresponding data for proteins with different chain lengths, the seven Rg values demonstrated the scaling relationship to chain length with a scaling exponent of 0.35+/-0.11, which is close to the theoretical value of 1/3 predicted for globules in solutions where monomer-monomer interactions are favored over monomer-solvent interactions (poor solvent). The finding indicated that the initial folding dynamics of proteins bears the signature of the coil-globule transition, and offers a clue to explain the folding mechanisms of proteins with different chain lengths.

SAXS Investigation of ABC Triblock Star Terpolymers in Aqueous Solution

The structure of three different ABC triblock star terpolymers in aqueous solution has been investigated by small‐angle x‐ray scattering (SAXS). The form factor was modeled using an analytical expression for a Gaussian homopolymer star since the SAXS data were not sensitive to the electron density differences between blocks. The interparticle structure factor could be described by the hard sphere model. The radius of gyration of the stars is obtained by modeling of the SAXS data. The overall size of the stars is sensitive to the degree of hydrophobicity of the block located in the center of the star. The dimensions of the starblock terpolymers are compared with those obtained from light‐scattering experiments.

Time-Resolved WAXD and SAXS Investigations on Butyl Branched Alkane at Elevated Pressures

The crystallization behavior and the morphological aspect of the butyl branched alkane C96H193CH(C4H9)C94H189 have been investigated using time-resolved wide-angle X-ray diffraction (WAXD) and small-angle X-ray scattering (SAXS) at atmospheric and elevated pressures. The solution crystallized sample shows pronounced crystalline reflections in WAXD with a lamellar thickness of 127 A, corresponding to a once-folded structure in SAXS at atmospheric pressure. Cooling the sample from the melt at 4 °C/min at atmospheric pressure results in a lamellar thickness of 104 A with chains having a tilt angle of 35°. The crystallization of the branched alkane at pressures of ca. 4 kbar and the same cooling rate of 4 °C/min reveals a new crystal reflection emerging between the (100) monoclinic and the (110) orthorhombic reflections. Simultaneous to the appearance of the new reflection, a sudden shift in the Bragg d value of the (110) orthorhombic reflection occurs, indicating densification of the orthorhombic unit cell. ...

Investigations of morphology of moisture‐cured silicone–urethanes

Results of studies on synthesis and properties of siloxane–urethane prepolymers as well as on selected properties of moisture-cured silicone–urethanes have already been published. In this paper, some results of investigations of the effect of chemical structure of such silicone–urethane polymers on their phase seggregation investigated using mainly (TEM) transmission electron microscopy and small-angle x-ray scattering (SAXS) techniques are presented. It was found in TEM studies that in silicone-urethanes obtained by moisture-curing of NCO-terminated prepolymers prepared from siloxane oligomer diols (SOD) and isophoronediisocyanate (IPDI), two factors determine the morphology of samples: length of siloxane chain and NCO/OH ratio. SAXS investigations showed that these silicone–urethanes had a lamellar structure. It was found that the long period of this structure changed from 4 to 9 nanometers as the siloxane chain length increased nine times. The increase of the long period correlated with the decrease of Young's modulus of the corresponding samples. TEM investigations of silicone–urethanes obtained by moisture-curing of NCO-terminated prepolymers prepared from the blends of SOD and polyoxypropylenediol (PPG) revealed complex morphology which depended on the SOD/PPG ratio. Copyright © 2000 John Wiley & Sons, Ltd.

Direct observation of single domains in poled (111) PZT (PbZr0.25Ti0.75O3) films

Films of (111) oriented poled ferroelectric lead zirconate titanate (PZT) crystallites on (100)Si/SiO2/(111) Pt were investigated by scanning tunneling microscopy (STM), atomic force microscopy (AFM) and small angle X–ray scattering (SAXS).SAXS investigations allowed to estimate a mean value of domain thickness of 17.5nm. Exertion of stress (5.1×104Nm−2) to the film resulted in an increase of domain width of ∼1%.After metallization of the PZT surface with a Cr–Ni film of 5.2nm or a Ti film of 5.0nm thickness, domains were visible by STM measurements as parallel stripes on the surface with a width of 15–20nm. A downward vertical corrugation of 1.0–1.5nm typically occurred at the intersection site of domain walls with the surface. Its presence is ascribed to shear strain originating from coherency defects in the interface.High resolution AFM with electron beam deposited supertips on unmetallized samples revealed areas of typically several micrometers in diameter showing crystallites with perfectly aligned domains of 10–15nm width. The domains formed parallel slabs of twinned-crystallites with their polarization c-axis changing alternately from [001] to [010] direction. For a fully poled (111) PZT film, the c-axis of each (90°) domain is inclined towards the surface by 35° and tilted against the surface normal by +45 or −45°, respectively. These results generally confirm the Speck–Streiffer–Pompe–Romanov domain model which predicts for a (111) PZT film of 500nm thickness a polyvariant with alternating (90°) domains of 16.4nm width.

In situ Observation of Nucleation and Crystal Growth in Zeolite Synthesis. A Small-Angle X-ray Scattering Investigation on Si-TPA-MFI

The formation and consumption of nanometer scale precursor particles during the hydrothermal synthesis of Si-TPA-MFI from a clear solution has been studied in situ using a combination of X-ray scattering techniques and with electron microscpy. The combination of wide-, small-, and ultra-small-angle X-ray scattering allowed us to obtain information on a continuous range of length scales spanning over four orders of magnitude (0.17−6000 nm), covering all particle populations present during the complete course of the crystallization process. The use of high-brilliance synchrotron radiation allows us to perform time-resolved experiments. Two types of precursor particles were observed: 2.8 nm sized primary units and aggregates (≈10 nm). Variation of the alkalinity of the synthesis mixture revealed a strong correlation between the concentration of the aggregates and the rate of the crystal nucleation. The presence of the 2.8 nm sized primary units appears to be independent on the alkalinity. The addition of seed crystals to a synthesis mixture that does not show spontaneous nucleation (no aggregates observed) resulted in normal crystal growth. The size distribution of the growing crystals could be followed in situ by fitting calculated scattering patterns to experimental curves and showed good agreement with electron microscopy results. The apparent activation energy for crystal growth is determined to be 83 kJ/mol by following in situ the crystal growth process at various reaction temperatures. These data show that the formation of aggregates of primary units is an essential step in the nucleation process and suggest that the crystal growth step is the reaction-controlled inclusion of the 2.8 nm sized primary units at the crystal surface.

Synthesis and Optical Properties of Mn2+-Doped ZnS Nanoparticles in Solutions and Coatings

Mn2+-doped ZnS nanoparticles with different Mn-doping concentrations stabilized by hydroxypropyl cellulose (HPC) have been synthesized in ethanolic solutions and coatings. Their optical and structural properties have been characterized by means of UV-vis spectroscopy, luminescence spectroscopy, high resolution transmission electron microscopy (HRTEM) and small angle X-ray scattering (SAXS). Solutions and coatings exhibit a strong luminescence at 590 nm when excited with UV light showing that Mn2+ is incorporated into the ZnS nanoparticles. The highest luminescence intensity is obtained with an Mn2+ concentration of 2 mol%. HRTEM and SAXS investigations show that the particles are crystalline and are 3 ± 0.5 nm in size. Irradiation of the coatings with UV light leads to a photochemical oxidation of the particles, as shown by the decreasing absorption of the coating with irradiation time and a blue shift of the absorption maximum. Furthermore, the luminescence intensity first strongly increases and then decreases completely with UV-irradiation time. Both phenomena can be explained by the photochemical oxidation of the particles.

Two-Dimensional Small-Angle X-ray Scattering Investigation of Stretched Borosilicate Glasses

A two-dimensional fit of a suitable model for interpreting small-angle X-ray scattering (SAXS) has been shown to be a valuable tool in obtaining quantitative microstructural information. The model is based on the hypothesis that dilute ellipsoidal particles are arranged parallel to each other. The method has been applied to two glasses containing oriented particles. The investigated materials are both alkali aluminoborosilicate glasses, thermally treated and redrawn at a temperature above their softening point. The Ag(Cl, Br) crystalline droplets, formed during the preliminary thermal treatment, assume, after drawing, a cigar-like shape, oriented in the stretching direction, and give the material birefringence properties. The volumetric particle distribution has an average of 22 × 70 nm and is skewed up to length values of about 1200 nm. The composition of the solid solution, determined by X-ray diffraction (XRD), is Ag(Cl0.35, Br0.65). When the Ag(Cl, Br) particles on the surface are chemically reduced to Ag, a material with polarizing properties is obtained (PolarcorTM). For this sample, two distributions of particles have been found: one with an average of 18 x 230 nm and skewed up to 600 nm, and one, very sharp, of much shorter particles (14 × 30 nm).

Cluster Formation in Liquid Lithium Niobate A Small Angle X-ray Scattering Investigation

T Structural analysis of the clustering phenomenon in the LiNbO3 melt was carried out by means of small-angle X-ray scattering using synchrotron radiation in the range of momentum transfer 0.2 nm-1 ≤ k ≤ 14.0 nm-1. Microclusters were present in the melt throughout the entire explored temperature-domain from 1673 K to 1513 K which includes undercooling (melting point 1526 K). The radius of gyration, size, shape and distance of particles were determined. Chains of few NbO6 octahedra and small blocks constituted by two layers of four corner-shared octahedra, interlocked by a lithium atom, could be good models for the microclusters in a large temperature-domain. By lowering the temperature, the particle size increased. Below 1553 K, probable macroclusters would be correlated to the rapid increase of the viscosity. Using the viscosity data and previously published and the present SAXS results, it was possible to evaluate the volume of the clusters. Near the freezing point about a quarter of the volume would be occupied by clusters.

SAXS Investigations on Uniaxially Drawn Fibers Obtained from Polyethylene Reactor Powder

The polyethylene powders studied were synthesized by both slurry and gas-phase processes at temperatures ranging between 30 and 85 °C. Fibers were drawn from these nascent powders under identical processing conditions. The maximum achievable draw ratio was found to be strongly dependent on synthesis conditions. Highest ductilities are obtained for samples synthesized by a slurry process at 85 °C. Small-angle X-ray scattering (SAXS) measurements were performed on fibers coextruded from reactor powders at a draw ratio of 6. No interferential effects were detected in the equatorial profiles. In contrast, the meridional SAXS patterns display interference peaks whose intensities bear definite relationships to both ductility and synthesis conditions. Fibers obtained from samples synthesized by a slurry process at 85 °C display a well-defined interference peak along the meridional direction. Fibers obtained from samples synthesized in the other conditions show only an ill-defined broad shoulder. Results of peak ...