Subnanometric Stacking of Two-Dimensional Nanomaterials: Insights from the Nanotexture Evolution of Dense Reduced Graphene Oxide Membranes.

Assembling two-dimensional (2D) nanomaterials into laminar membranes with a subnanometer (subnm) interlayer spacing provides a material platform for studying a range of nanoconfinement effects and exploring the technological applications related to the transport of electrons, ions and molecules. However, the strong tendency for 2D nanomaterials to restack to their bulk crystalline-like structure makes it challenging to control their spacing at the subnm scale. It is thus necessary to understand what nanotextures can be formed at the subnm scale and how they can be engineered experimentally. In this work, with dense reduced graphene oxide membranes as a model system, we combine synchrotron-based X-ray scattering and ionic electrosorption analysis to reveal that their subnanometric stacking can result in a hybrid nanostructure of subnm channels and graphitized clusters. We demonstrate that the ratio of these two structural units, their sizes and connectivity can be engineered by stacking kinetics through the reduction temperature to allow the realization of high-performance compact capacitive energy storage. This work highlights the great complexity of subnm stacking of 2D nanomaterials and provides potential methods to engineer their nanotextures at will.

SAXS data modelling for the characterisation of ion tracks in polymers.

Here, we present new models to fit small angle X-ray scattering (SAXS) data for the characterization of ion tracks in polymers. Ion tracks in polyethylene terephthalate (PET), polycarbonate (PC), polyimide (PI) and polymethyl methacrylate (PMMA) were created by swift heavy ion irradiation using 197Au and 238U with energies between 185 MeV and 2.0 GeV. Transmission SAXS measurements were performed at the Australian Synchrotron. SAXS data were analysed using two new models that describe the tracks by a cylindrical structure composed of a highly damaged core with a gradual transition to the undamaged material. First, we investigate the 'Soft Cylinder Model', which assumes a smooth function to describe the transition region by a gradual change in density from a core to a matrix. As a simplified and computational less expensive version of the 'Soft Cylinder Model', the 'Core Transition Model' was developed to enable fast fitting. This model assumes a linear increase in density from the core to the matrix. Both models yield superior fits to the experimental SAXS data compared with the often-used simple 'Hard Cylinder Model' assuming a constant density with an abrupt transition.

Preferred orientation and its effects on intensity-correlation measurements.

Intensity-correlation measurements allow access to nanostructural information on a range of ordered and disordered materials beyond traditional pair-correlation methods. In real space, this information can be expressed in terms of a pair-angle distribution function (PADF) which encodes three- and four-body distances and angles. To date, correlation-based techniques have not been applied to the analysis of microstructural effects, such as preferred orientation, which are typically investigated by texture analysis. Preferred orientation is regarded as a potential source of error in intensity-correlation experiments and complicates interpretation of the results. Here, the theory of preferred orientation in intensity-correlation techniques is developed, connecting it to the established theory of texture analysis. The preferred-orientation effect is found to scale with the number of crystalline domains in the beam, surpassing the nanostructural signal when the number of domains becomes large. Experimental demonstrations are presented of the orientation-dominant and nanostructure-dominant cases using PADF analysis. The results show that even minor deviations from uniform orientation produce the strongest angular correlation signals when the number of crystalline domains in the beam is large.

Local symmetry predictors of mechanical stability in glasses.

The mechanical properties of crystals are controlled by the translational symmetry of their structures. But for glasses with a disordered structure, the link between the symmetry of local particle arrangements and stability is not well established. In this contribution, we provide experimental verification that the centrosymmetry of nearest-neighbor polyhedra in a glass strongly correlates with the local mechanical stability. We examine the distribution of local stability and local centrosymmetry in a glass during aging and deformation using microbeam x-ray scattering. These measurements reveal the underlying relationship between particle-level structure and larger-scale behavior and demonstrate that spatially connected, coordinated local transformations to lower symmetry structures are fundamental to these phenomena. While glassy structures lack obvious global symmetry breaking, local structural symmetry is a critical factor in predicting stability.

Stability, flow alignment and a phase transition of the lipidic cubic phase during continuous flow injection.

Continuous flow injection is a key technology for serial crystallography measurements of protein crystals suspended in the lipidic cubic phase (LCP). To date, there has been little discussion in the literature regarding the impact of the injection process itself on the structure of the lipidic phase. This is despite the fact that the phase of the injection matrix is critical for the flow properties of the stream and potentially for sample stability. Here we report small-angle X-ray scattering measurements of a monoolein:water mixture during continuous delivery using a high viscosity injector. We observe both an alignment and modification of the LCP as a direct result of the injection process. The orientation of the cubic lattice with respect to the beam was estimated based on the anisotropy of the diffraction pattern and does not correspond to a single low order zone axis. The solvent fraction was also observed to impact the stability of the cubic phase during injection. In addition, depending on the distance traveled by the lipid after exiting the needle, the phase is observed to transition from a pure diamond phase (Pn3m) to a mixture containing both gyriod (Ia3d) and lamellar (Lα) phases. Finite element modelling of the observed phase behaviour during injection indicates that the pressure exerted on the lipid stream during extrusion accounts for the variations in the phase composition of the monoolein:water mixture.

Bovine Meniscus Middle Zone Tissue: Measurement of Collagen Fibril Behavior During Compression.

BACKGROUND: Type I collagen is the major component of the extracellular matrix of the knee's meniscus and plays a central role in that joint's biomechanical properties. Repair and reconstruction of tissue damage often requires a scaffold to assist the body to rebuild. The middle zone of bovine meniscus is a material that may be useful for the preparation of extracellular matrix scaffolds. METHODS: Here, synchrotron-based small-angle X-ray scattering (SAXS) patterns of bovine meniscus were collected during unconfined compression. Collagen fibril orientation, D-spacing, compression distance and force were measured. RESULTS: The collagen fibrils in middle zone meniscal fibrocartilage become more highly oriented perpendicular to the direction of compression. The D-spacing also increases, from 65.0 to 66.3 nm with compression up to 0.43 MPa, representing a 1.8% elongation of collagen fibrils perpendicular to the compression. CONCLUSION: The elasticity of the collagen fibrils under tension along their length when the meniscus is compressed, therefore, contributes to the overall elastic response of the meniscus only under loads that exceed those likely to be experienced physiologically.

Structural relationships for the design of responsive azobenzene-based lyotropic liquid crystals.

Light-responsive binary (azobenzene + solvent) lyotropic liquid crystals (LCs) were investigated by structural modification of simple azobenzene molecules. Three benzoic acid-containing azobenzene molecules 4-(4-(hydroxyphenyl)diazenyl)benzoic acid (AZO1), 3-(4-(hydroxyphenyl)diazenyl)benzoic acid (AZO2) and 5-(4-(hydroxyphenyl)diazenyl)isophthalic acid (AZO3) were produced with various amide substitutions to produce tectons with a variety of hydrophobicity, size and branching. The LC mesophases formed by binary (azobenzene + solvent) systems with low volatility solvents dimethylsulfoxide (DMSO) and N,N-dimethylformamide (DMF) as well as the protic ionic liquids ethylammonium formate (EAF) and propylammonium formate (PAF), were investigated using a combination of small-angle X-ray and neutron scattering (SAXS and SANS) as well as polarising light microscopy (PLM). Increasing alkyl group length was found to have a strong influence on LC phase spacing, and changes in the position of substitution on the benzene ring influenced the preferred curvature of phases. UV-induced trans to cis isomerization of the samples was shown to influence ordering and optical birefringence, indicating potential applications in optical devices.

Measured collagen fibril response to arterial inflation using SAXS.

Arteries are elastic structures containing both elastin and collagen. While the high content of elastin is understood to be important for the elasticity of arteries with systolic and diastolic pressure pulses, the role of collagen in the elastic properties of arteries is less understood. Here we use small angle X-ray scattering to investigate the changes in arrangement of collagen fibrils and the strain experienced by collagen fibrils as arteries are inflated. Collagen fibrils re-orient to become more aligned in both the annular direction and radially as arteries inflate. With arterial pressures up to 32 kPa there is no observable increase in D-spacing of the collagen fibrils (<0.1%) indicating that there is no extension of straightened fibrils and therefore no change in stress on the collagen fibrils. This is in contrast to tissue such as skin where stress of the tissue may induce strains in collagen fibrils of >6%. In arteries the collagen fibril elasticity (strain at the scale of fibrils) is not the main elastic component of the arterial walls. This indicates that wall elasticity is dominated by other factors such as the structural arrangement of the collagen fibers.

Rich liquid crystal phase behavior of novel alkyl-tri(ethylene glycol)-glucoside carbohydrate surfactants.

Carbohydrates are appealing non-ionic surfactant head-groups as they are naturally abundant, generally biocompatible and biodegradable, and readily functionalized. Herein, we explore the phase behavior of seven novel carbohydrate-based surfactants (CBS) containing a tri-ethylene glycol (TEG) linker between a glucose head-group and alkyl tail-group, with linear saturated (C8-18) and cis-unsaturated (C18:1) alkyl chains. At high aqueous concentrations, these glycolipid-like surfactants transition into a variety of lyotropic liquid crystalline phases following an expected concentration phase sequence: hexagonal (H1) → bicontinuous cubic (V1) → lamellar (Lα). Using polarizing light microscopy (PLM), a binary (surfactant-water) phase diagram for each surfactant was constructed across a temperature range (25-80 °C) revealing thermotropic behavior and a broadening of liquid crystal phase regions with increasing alkyl chain length. There was also a significant difference between saturated and unsaturated alkyl chains, due to the cis-unsaturated 'statistical bend' lowering the melting point. Small-angle X-ray scattering (SAXS) measurements were performed to characterize the liquid crystal phases, identifying highly-ordered p6m,Ia3d, and Lα crystallographic space-groups with up to 7 resolved Bragg peaks, likely due to the highly anisometric nature of the TEG-linked surfactants. The phases were shown to be more numerous and exhibited greater thermal-stability compared to well-characterized alkyl glucoside surfactants lacking an oligoethylene spacer in the literature. Finally, the characteristic dimensions of each phase were determined to enable visualization of the internal microstructures, providing insight into the impact of molecular shape and the distribution of hydro-philicity/phobicity on the formation and stability of liquid crystalline mesophases.

Solid State Characterization of Ciprofloxacin Liposome Nanocrystals.

Liposomes have been widely researched as drug delivery systems; however, the solid state form of drug inside the liposome, whether it is in solution or in a solid state, is often not studied. The solid state properties of the drug inside the liposomes are important, as they dictate the drug release behavior when the liposomes come into contact with physiological fluid. Recently, a new approach of making liposomal ciprofloxacin nanocrystals was proposed by the use of an additional freeze-thawing step in the liposomal preparation method. This paper aims to determine the solid state properties of ciprofloxacin inside the liposomes after this additional freeze-thawing cycle using cryo-TEM, small-angle X-ray scattering (SAXS), and cross-polarized light microscopy (CPLM). Ciprofloxacin precipitated in the ciprofloxacin hydrate crystal form with a unit cell dimension of 16.7 Å. The nanocrystals also showed a phase transition at 93 °C, which represents dehydration of the hydrate crystals to the anhydrate form of ciprofloxacin, verified by temperature-dependent SAXS measurements. Furthermore, the dependence of the solid state form of the nanocrystals on pH was investigated in situ, and it was shown that the liposomal ciprofloxacin nanocrystals retained their crystalline form at pH 6-10. Understanding the solid state attributes of nanocrystals inside liposomes provides improved understanding of drug dissolution and release as well as opening avenues to new applications where the nanosized crystals can provide a dissolution benefit.

An in-situ small angle x ray scattering analysis of nanopore formation during thermally induced chemical dealloying of brass thin foils.

The development of non-noble nano-porous metal materials is hindered by surface oxidation reactions and from the difficulty to generate long range order pore arrays. Dealloying is a promising route to generate such materials by selective chemical etching of metal alloy materials. This process can generate nano-metal materials with superior plasmonic, catalytic and adsorptive surface properties. Here, the impact of properties of the etching solution on the dealloying process to generate nano-pores across thin film alloys was investigated by in-situ SAXS dealloying experiments. Single phase CuZn alloys were used as model materials to evaluate the influence of the solution temperature on the pore formation kinetics. This novel analysis allowed to visualize the change in surface properties of the materials over time, including their surface area as well as their pore and ligament sizes. The dealloying kinetics at the very early stage of the process were found to be critical to both stable pore formation and stabilization. SAXS in-situ data were correlated to the morphological properties of the materials obtained from ex-situ samples by Rutherford back scattering and scanning electron microscopy.

Tropical Keratopathy (Florida Spots) in Cats.

The authors used microscopy and synchrotron-based small-angle X-ray scattering analysis (SAXS) to describe lesions macroscopically typical of tropical keratopathy ("Florida spots") from 6 cats on St Kitts. Microscopically, there were varying degrees of epithelial hyperplasia and thinning of the cornea (by 4% to 18%) due to loss of corneal stroma associated with dense accumulations of collagen in the superficial stroma. The collagen fibrils in lesions were wider and had more variable diameters (39.5 ± 5.0 nm, mean ± SD) than in normal corneas (25.9 ± 3.6 nm; P < .01). There were occasional vacuoles (<1 µm) in the corneal epithelial basement membrane but no evidence of inflammation, edema, stromal neovascularization, fibrosis, acid-fast organisms, or structures suggestive of a fungal organism. SAXS analysis showed collagen fibril diameters and variation in size were greater in stroma containing the lesions compared to normal corneas (48.8 ± 4.5 nm vs 35.5 ± 2.6; P < .05). The d-spacing of collagen in the stroma of lesions and normal corneas was the same, but the average orientation index of collagen in lesions was greater (0.428 ± 0.08 vs 0.285 ± 0.03; P < .05). A survey revealed Florida spots lesions were static over time and became less obvious in only 1 of 6 affected cats adopted on St Kitts and taken to areas in the US where lesions are not reported. An anterior stromal collagen disorder with various degrees of epithelial hyperplasia is the pathologic hallmark of lesions clinically identical to Florida spots in cats from St Kitts.

Acellular dermal matrix collagen responds to strain by intermolecular spacing contraction with fibril extension and rearrangement.

Acellular dermal matrix (ADM) materials are used as scaffold materials in reconstructive surgery. The internal structural response of these materials in load-bearing clinical applications is not well understood. Bovine ADM is characterized by small-angle X-ray scattering while subjected to strain. Changes in collagen fibril orientation (O), degree of orientation as an orientation index (OI) (measured both edge-on and flat-on to the ADM), extension (from d-spacing changes) and changes to intermolecular spacing are measured as a result of the strain and stress in conjunction with mechanical measurements. As is already well established in similar systems, when strained, collagen fibrils in ADM can accommodate the strain by reorienting by up to 50° (as an average of all the fibrils). This reorientation corresponds to the OI increasing from 0.3 to 0.7. Here it is shown that concurrently, the intermolecular spacing between tropocollagen decreases by 10% from 15.8 to 14.3Å, with the fibril diameter decreasing from 400 to 375Å, and the individual fibrils extending by an average of 3.1% (D-spacing from 63.9 to 65.9nm). ADM materials can withstand large strain and high stress due to the combined mechanisms of collagen reorientation, individual fibril extension, sliding and changes in the molecular packing density.

Artificially modified collagen fibril orientation affects leather tear strength.

BACKGROUND: Ovine leather has around half the tear strength of bovine leather and is therefore not suitable for high-value applications such as shoes. Tear strength has been correlated with the natural collagen fibril alignment (orientation index, OI). It is hypothesized that it could be possible to artificially increase the OI of the collagen fibrils and that an artificial increase in OI could increase tear strength. RESULTS: Ovine skins, after pickling and bating, were strained biaxially during chrome tanning. The strain ranged from 2 to 15% of the initial sample length, either uniformly in both directions by 10% or with 3% in one direction and 15% in the other. Once tanned, the leather tear strengths were measured and the collagen fibril orientation was measured using synchrotron-based small-angle X-ray scattering. CONCLUSION: The OI increased as a result of strain during tanning from 0.48 to 0.79 (P = 0.001) measured edge-on and the thickness-normalized tear strength increased from 27 to 43 N mm-1 (P < 0.001) after leather was strained 10% in two orthogonal directions. This is evidence to support a causal relationship between high OI (measured edge-on), highly influenced by thickness, and tear strength. It also provides a method to produce stronger leather. © 2017 Society of Chemical Industry.

Favored local structures in amorphous colloidal packings measured by microbeam X-ray diffraction.

Local structure and symmetry are keys to understanding how a material is formed and the properties it subsequently exhibits. This applies to both crystals and amorphous and glassy materials. In the case of amorphous materials, strong links between processing and history, structure and properties have yet to be made because measuring amorphous structure remains a significant challenge. Here, we demonstrate a method to quantify proportions of the bond-orientational order of nearest neighbor clusters [Steinhardt, et al. (1983) Phys Rev B 28:784-805] in colloidal packings by statistically analyzing the angular correlations in an ensemble of scanning transmission microbeam small-angle X-ray scattering (µSAXS) patterns. We show that local order can be modulated by tuning the potential between monodisperse, spherical colloidal silica particles using salt and surfactant additives and that more pronounced order is obtained by centrifugation than sedimentation. The order in the centrifuged glasses reflects the ground state order in the dispersion at lower packing fractions. This diffraction-based method can be applied to amorphous systems across decades in length scale to connect structure to behavior in disordered systems with a range of particle interactions.

Deer leather: analysis of the microstructure affecting pebble.

BACKGROUND: Deer leather has a characteristic pattern, referred to as 'pebble', which is accorded such importance that a lack of it renders a leather defective. Synchrotron-based small-angle X-ray scattering (SAXS), ultrasonic imaging, scanning electron microscopy, and tear tests were used to investigate the structural characteristics of well-pebbled and poorly pebbled cervine leathers. RESULTS: Poorly pebbled leather has a less open structure in the upper grain region than well-pebbled leather. The orientation index (OI) of leather with a poor pebble is less than that of the well-pebbled leather, particularly in the corium. The tear strength is also less for the poorly pebbled leather. CONCLUSIONS: The differences in structure between well- and poorly pebbled cervine leathers are not the same as the structural differences between tight and loose bovine leathers, to which they are sometimes compared. On the contrary, good pebble may reflect an internal structure similar to that of looseness. It is hoped that methods to prevent a reduction in pebbling during the processing of cervine leather may be developed by applying this knowledge of cervine leather's structural characteristics. © 2017 Society of Chemical Industry.

A small angle X-ray scattering study of the structure and development of looseness in bovine hides and leather.

BACKGROUND: Some bovine hides produce poor quality leather, termed loose leather. The structural characteristics of hides and the intermediate processed stages that lead to loose leather are not well understood. In the present study, synchrotron-based small angle X-ray scattering (SAXS) is used to investigate collagen fibril orientation at the different stages of processing (i.e. from hide through to leather) that result in both tight and loose leathers. RESULTS: Tight leather of a relatively isotropic texture has a lower orientation index (OI) than loose leather of a more pronounced stratified texture; conversely, tight pickled hide and wet blue have a higher OI than loose pickled hide and wet blue. There is a greater increase in OI on processing from pickled hide to dry crust (leather) for loose material. This is largely the result of a greater increase in hide thickness prior to pickling for loose hide than tight hide, followed by a greater decrease at the dry crust stage. The collagen fibrils in loose leather and wet blue more readily orient under stress than do those in tight leather. Loose leather has a more pronounced layered structure than tight leather, although this difference is not apparent from SAXS measurements of hide prior to the dry crust stage; it develops during processing. CONCLUSION: The greater swelling of the loose hide during processing disrupts the structure and leads to a more layered collagen arrangement on shrinking at the final dry crust stage. © 2016 Society of Chemical Industry.

Collagen Fibril Intermolecular Spacing Changes with 2-Propanol: A Mechanism for Tissue Stiffness.

Materials composed primarily of collagen are important as surgical scaffolds and other medical devices and require flexibility. However, the factors that control the suppleness and flexibility of these materials are not well understood. Acellular dermal matrix materials in aqueous mixtures of 2-propanol were studied. Synchrotron-based small-angle X-ray scattering was used to characterize the collagen structure and structural arrangement. Stiffness was measured by bend tests. Bend modulus increased logarithmically with 2-propanol concentration from 0.5 kPa in water to 103 kPa in pure 2-propanol. The intermolecular spacing between tropocollagen molecules decreased from 15.3 to 11.4 Å with increasing 2-propanol concentration while fibril diameter decreased from 57.2 to 37.2 nm. D-spacing initially increased from 63.6 to 64.2 nm at 50% 2-propanol then decreased to 60.3 nm in pure 2-propanol. The decrease in intermolecular spacing and fibril diameter are due to removal of water and the collapse of the hydrogen bond structure between tropocollagen molecules causing closer packing of the molecules within a fibril. We speculate this tighter molecular packing may restrict the sliding of collagen within fibrils, and similar disruption of the extended hydration layer between fibrils may lead to restriction of sliding between fibrils. This mechanism for tissue stiffness may be more general.

Collagen Fibril Response to Strain in Scaffolds from Ovine Forestomach for Tissue Engineering.

Scaffold biomaterials are typically applied surgically as reinforcement for weakened or damaged tissue, acting as substrates on which healing tissue can grow. Natural extracellular matrix (ECM) materials consisting mainly of collagen are often used for this purpose, but are anisotropic. Ovine forestomach matrix (OFM) ECM was exposed to increasing strain and synchrotron-based SAXS diffraction patterns and revealed that the collagen fibrils within underwent changes in orientation, orientation index (a measure of isotropy), and extension. Response to the strain depended on the direction the collagen fibrils were oriented. When the ECM was stretched in the direction of collagen fibril orientation, the fibrils become more oriented and begin to take up the strain immediately (as shown by the increased d-spacing). Stretch applied perpendicular to dominant fibril direction caused the fibrils to initially become less oriented as they were pulled away from the original direction, and less force was initially transmitted along the length of the fibrils (i.e., the d-spacing changed less). SAXS analysis of OFM and the starting raw tissue showed there is no difference in the structural arrangement of the collagen fibrils. Understanding the directional structural response of these materials under strain may influence how surgeons select and place the materials in use.

Improved radiation dose efficiency in solution SAXS using a sheath flow sample environment.

Radiation damage is a major limitation to synchrotron small-angle X-ray scattering analysis of biomacromolecules. Flowing the sample during exposure helps to reduce the problem, but its effectiveness in the laminar-flow regime is limited by slow flow velocity at the walls of sample cells. To overcome this limitation, the coflow method was developed, where the sample flows through the centre of its cell surrounded by a flow of matched buffer. The method permits an order-of-magnitude increase of X-ray incident flux before sample damage, improves measurement statistics and maintains low sample concentration limits. The method also efficiently handles sample volumes of a few microlitres, can increase sample throughput, is intrinsically resistant to capillary fouling by sample and is suited to static samples and size-exclusion chromatography applications. The method unlocks further potential of third-generation synchrotron beamlines to facilitate new and challenging applications in solution scattering.