Ultra-small-angle X-ray Scattering Research Articles

Polymer electrolyte membranes from fluorinated polyisoprene-block-sulfonated polystyrene: Structural evolution with hydration and heating

Small-angle neutron scattering (SANS) and ultra-small-angle X-ray scattering (USAXS) have been used to study the structural changes in fluorinated polyisoprene/sulfonated polystyrene (FISS) diblock copolymers as they evolved from the dry state to the water swollen state. A dilation of the nanometer-scale hydrophilic domains has been observed as hydration increased, with greater dilation occurring in the more highly sulfonated samples or upon hydration at higher temperatures. Furthermore, a decrease in the order in these phase separated structures is observed upon swelling. The glass transition temperatures of the fluorinated blocks have been observed to decrease upon hydration of these materials, and at the highest hydration levels, differential scanning calorimetry (DSC) has shown the presence of tightly bound water. A precipitous drop in the mechanical integrity of the 50% sulfonated materials is also observed upon exceeding the glass transition temperature (Tg), as measured by dynamic mechanical analysis (DMA).

Non-destructive characterization of structural hierarchy within aligned carbon nanotube assemblies.

Understanding and controlling the hierarchical self-assembly of carbon nanotubes (CNTs) is vital for designing materials such as transparent conductors, chemical sensors, high-performance composites, and microelectronic interconnects. In particular, many applications require high-density CNT assemblies that cannot currently be made directly by low-density CNT growth, and therefore require post-processing by methods such as elastocapillary densification. We characterize the hierarchical structure of pristine and densified vertically aligned multi-wall CNT forests, by combining small-angle and ultra-small-angle x-ray scattering (USAXS) techniques. This enables the nondestructive measurement of both the individual CNT diameter and CNT bundle diameter within CNT forests, which are otherwise quantified only by delicate and often destructive microscopy techniques. Our measurements show that multi-wall CNT forests grown by chemical vapor deposition consist of isolated and bundled CNTs, with an average bundle diameter of 16 nm. After capillary densification of the CNT forest, USAXS reveals bundles with a diameter >4 μm, in addition to the small bundles observed in the as-grown forests. Combining these characterization methods with new CNT processing methods could enable the engineering of macro-scale CNT assemblies that exhibit significantly improved bulk properties.

Particle Restabilization in Silica/PEG/Ethanol Suspensions: How Strongly do Polymers Need To Adsorb To Stabilize Against Aggregation?

We study the effects of increasing the concentration of a low molecular weight polyethylene glycol on the stability of 44 nm diameter silica nanoparticles suspended in ethanol. Polymer concentration, c(p), is increased from zero to that characterizing the polymer melt. Particle stability is accessed through measurement of the particle second-virial coefficient, B(2), performed by light scattering and ultrasmall angle X-ray scattering (USAXS). The results show that at low polymer concentration, c(p) < 3 wt %, B(2) values are positive, indicating repulsive interactions between particles. B(2) decreases at intermediate concentrations (3 wt % < c(p) < 50 wt %), and particles aggregates are formed. At high concentrations (50 wt % < c(p)) B(2) increases and stabilizes at a value expected for hard spheres with a diameter near 44 nm, indicating the particles are thermodynamically stable. At intermediate polymer concentrations, rates of aggregation are determined by measuring time-dependent changes in the suspension turbidity, revealing that aggregation is slowed by the necessity of the particles diffusing over a repulsive barrier in the pair potential. The magnitude of the barrier passes through a minimum at c(p) ≈ 12 wt % where it has a value of ∼12 kT. These results are understood in terms of a reduction of electrostatic repulsion and van der Waals attractions with increasing c(p). Depletion attractions are found to play a minor role in particle stability. A model is presented suggesting displacement of weakly adsorbed polymer leads to slow aggregation at intermediate concentration, and we conclude that a general model of depletion restabilization may involve increased strength of polymer adsorption with increasing polymer concentration.

Mechanical behaviour of nano composite aerogels

In order to improve the mechanical properties of silica aerogels, we propose the synthesis of nano composite aerogels. Silica particles (20–100 nm) are added in the monomer solution, just before gelling and supercritical drying. The silica particles addition increases the mechanical properties, but also affects the aggregation process, the aerogel structure and the pore sizes. We discuss the different parameters which infer in the mechanical behaviour of silica aerogel such as: brittle behaviour, load bearing fraction of solid (pore volume), internal stresses (shrinkage), size and distribution of flaws, subcritical flaws propagation (chemical susceptibility). With silica particles addition, the mechanical properties rapidly increase, stiffening and strengthening the structure by a factor 4–8. Moreover, the mechanical strength distribution and the Weibull modulus characterizing the statistical nature of flaws size in brittle materials show a more homogeneous strength distribution. The composite structure is made of two imbricate networks, the polymeric silica and the particles silica networks. Ultra Small Angle X-ray Scattering experiments show that besides the fractal network usually built up by the organosiloxane, the silica particles is forming another fractal structure at a higher scale. The fractal structure could be related to the low Weibull parameter characteristic of a large flaws size distribution, pores being the critical flaws.

Mechanical reinforcement of polymer nanocomposites: theory and ultra-small angle X-ray scattering (USAXS) studies

The microstructure of polymer-grafted nanoparticles in polymer melts that are chemically identical to the brush was investigated using ultra-small angle X-ray scattering (USAXS). The dispersions were thermodynamically stable. Particle size and melt molecular weight were varied such that the particle softness, L*, or the ratio of the brush thickness to the particle radius ranged from L* = 0.02–0.29. The experimentally extracted structure factors and radial distribution functions from USAXS show stronger particle interactions in lower molecular weight melts due to brush stretching corresponding to an enhancement in bulk properties at particle concentrations above the jamming transition. Good agreement was found between the measured structure factors and those predicted using the Percus–Yevick closure. Further, enhancement in the storage modulus, previously observed with rheology, was predicted through the Zwanzig–Mountain relation and Monte Carlo simulations. Overall, the use of USAXS and rheology enables the connection between experiment and theory to predict, and ultimately control the interactions of polymer-grafted nanoparticles in polymer melts.

Shear ordered diblock copolymers with tuneable optical properties

A series of high molecular weight poly(styrene-b-isoprene) block copolymers with optical properties defined by composition in a non-selective solvent were studied using simultaneous ultra small angle X-ray scattering (USAXS) and optical spectrometry. A small magnitude shear produces ordered and oriented states in the copolymer solutions that persist for extended periods of time, and also have superior optical properties that are directly attributable to the mesoscopic block copolymer (BCP) morphology. We have demonstrated that the optical transmission of these materials can be tuned by the addition of low molecular weight poly(isoprene) and poly(styrene) to swell their respective domains within the diblock copolymer. The optical transmission peak for the diblocks could be tuned; from 380 nm-440 nm for the 670k diblock, 425 nm-540 nm for the 850k diblock and 541 nm-625 nm for the 1 million diblock by altering the solution concentration and composition. The full width at half maximum that can be achieved for the optical transmission peaks is as small as 15 nm at 473 nm with a Δλ/λ of 0.03, highlighting the high quality ordering in these systems. Also a small shift in the transmission peak wavelength was observed across a wide angle of view (15 nm at 30°) suggesting that these materials could be used for large area narrow band optical filters.

Effect of Aging Treatment on the Microstructure and Resistivity of a Nickel-Base Superalloy

The γ′ precipitation behavior of age-hardened WASPALOY, aged at 998 K, 1073 K, and 1148 K (725 °C, 800 °C, and 875 °C) for times ranging from 0.5 to 263.5 hours, were evaluated via analysis of ultra small angle X-ray scattering (USAXS) curves and scanning electron microscopy (SEM) micrographs. The USAXS spectra revealed a single precipitate size distribution at the earliest aging times, which evolves into a bimodal precipitate size distribution at later aging times. The primary precipitate radius displayed t 1/3 coarsening dependence for aging at 1073 K and 1148 K (800 °C and 875 °C); however, the primary radius increased with t 0.4 dependence at 998 K (725 °C), most likely due to mixed growth and coarsening. A figure of merit, η′, consisting of two terms, one associated with precipitate size and volume fraction and the other with compositional fluctuations, was proposed. η′ shows direct empirical correlations with changes in the measured electrical resistivity.

Investigation of a Catalyst Ink Dispersion Using Both Ultra-Small-Angle X-ray Scattering and Cryogenic TEM

The dispersion of Nafion ionomer particles and Pt/C catalyst aggregates in liquid media was studied using both ultra-small-angle X-ray scattering (USAXS) and cryogenic TEM. A systematic approach was taken to study first the dispersion of each component (i.e., ionomer particles and Pt/C aggregates), then the combination of the components, and last the catalyst ink. Multiple-level curve fitting was used to extract the particle size, size distribution, and geometry of the Pt/C aggregates and the Nafion particles in liquid media from the scattering data. The results suggest that the particle size, size distribution, and geometry are not uniform throughout the systems but rather vary significantly. It was found that the interaction of each component (i.e., the Nafion ionomer particles and the Pt/C aggregates) occurs in the dispersion. Cryogenic TEM was used to observe the size and geometry of the particles in liquid directly and to validate the scattering results. The TEM results showed excellent agreement.

Quantification of void network architectures of suspension plasma-sprayed (SPS) yttria-stabilized zirconia (YSZ) coatings using Ultra-small-angle X-ray scattering (USAXS)

Suspension plasma spraying (SPS) is able to process a stabilized suspension of nanometer-sized feedstock particles to form thin (from 20 to 100 μm) coatings with unique microstructures. The void (pore) network structure of these ceramic coatings is challenging to characterize and quantify using commonly used techniques due to small sizes involved. Nevertheless, the discrimination of these pores in terms of their size and shape distribution, anisotropy, specific surface area, etc., is critical for the understanding of processing, microstructure, and properties relationships. We will show that one of suitable combinations of techniques providing sufficient detail is ultra-small-angle X-ray scattering (USAXS) and helium pycnometry, combined with scanning electron microscopy (SEM). Yttria-partially stabilized zirconia (YSZ) coatings were manufactured by plasma processing of suspension of particles with average diameter of ∼50 nm. Several sets of spray parameters (plasma gas mixture, spray distance, electric arc intensity, etc.) were used to generate plasma jets with different mass enthalpies and coefficients of thermal transfer and different heat fluxes transferred to the substrate. Free-standing coatings were studied as-sprayed and annealed at 800 and 1100 °C for 10 and 100 h (non-constrained sintering). Results indicate that the SPS coatings exhibit nanosized pore microstructure: average void size was about the same size scale as the feedstock size; i.e., nanometer sizes with multimodal void size distribution. About 80% of the pores (by number) exhibited characteristic dimensions smaller than 30 nm. Total void content of as-sprayed SPS coatings varies between 13% and 20%. Most of the voids were found to be opened with only between one-tenth to one-third of voids volume being inaccessible by intrusion (not connected to either surface). During annealing, even at temperatures as low than 800 °C, the microstructure transformed: while the total void content did not change significantly, the void size distribution evolved toward larger sizes. This unique void system, together with the nanometer scale of the particulate matrix itself, gave these coatings very low apparent thermal conductivity (in the order of 0.1 W m −1 K −1), as rarefaction effect and phonon scattering mechanisms are very likely emphasized.

Multi-scale pore morphology in directed vapor deposited yttria-stabilized zirconia coatings

A high pressure, electron-beam directed-vapor deposition process has been used to deposit partially stabilized zirconia containing 7% mass yttria at deposition pressures of 7.5–23 Pa. Anisotropic, ultra-small-angle X-ray scattering (USAXS) was then used to determine the surface area, shape and orientation of pores within the coatings. The total surface area of the ellipsoidal shaped pores was found to increase with deposition pressure. However, the through-thickness thermal conductivity measurements reveal the existence of a minimum thermal conductivity in coatings deposited at an intermediate pressure. Observations of the anisotropic X-ray scattering intensity at this intermediate pressure indicated greater proportions of both feather-like (oblate) pores with their major dimension at about 60° to the plane of the coating and fine columnar (prolate) pores oriented perpendicular to the coating plane. Since these oblate pore orientations are most efficient at impeding conductive thermal transport through the coating, it is believed that the change in preferred pore orientations with pressure is responsible for the higher thermal resistance of coatings grown in the intermediate pressure regime.

Quantification of void networks of as-sprayed and annealed nanostructured yttria-stabilized zirconia (YSZ) deposits manufactured by suspension plasma spraying

Suspension plasma spraying (SPS) allows processing a stabilized suspension of nanometer-sized feedstock particles to form thick (from 20 to 100 μm, average values) deposits. The void content and porous network of such deposits are difficult to quantify (in terms of void and size distributions, anisotropy, etc.) using conventional techniques due to their low resolution. The combination of ultra-small-angle X-ray scattering (USAXS) and helium pycnometry permits to address some of the characteristics of this void network. Deposits of yttria-partially stabilized zirconia (YSZ) were manufactured by plasma spraying a suspension made of solid sub-micrometer-sized particles (50 and 400 nm) with several sets of spray operating parameters. Results indicate that the average void size exhibits the same scale as the solid structure; i.e., nanometer sizes and multimodal size distribution which varies with spray operating parameters. About 90% of voids (by number) exhibit characteristic dimensions smaller than 40 nm. The cumulative void volume fraction of such as-sprayed deposits varies between about 13 and 20%, depending upon operating parameters. The void network architecture evolves also with annealing conditions: the void size distribution evolves toward higher void characteristic dimensions as a result of sintering of smallest voids but the cumulative void content does not decrease significantly.

Communications: Complete description of re-entrant phase behavior in a charge variable colloidal model system

In titration experiments with NaOH, we have determined the full phase diagram of charged colloidal spheres in dependence on the particle density n, the particle effective charge Z(eff) and the concentration of screening electrolyte c using microscopy, light and ultrasmall angle x-ray scattering (USAXS). For sufficiently large n, the system crystallizes upon increasing Z(eff) at constant c and melts upon increasing c at only slightly altered Z(eff). In contrast to earlier work, equilibrium phase boundaries are consistent with a universal melting line prediction from computer simulation, if the elasticity effective charge is used. This charge accounts for both counterion condensation and many-body effects.

Ultra-Small-Angle X-ray Scattering of Polymers

Ultra-small-angle X-ray scattering (USAXS) is capable of probing structural inhomogeneities in the size range of 1 to 1000 nm. Recent developments of X-ray sources and optics make USAXS increasingly relevant to polymer research. In this review, we examine the current technical state of USAXS instrumentation, and briefly introduce the method of data reduction and analysis. We emphasize USAXS's application in areas such as polymer nanocomposites, polymer gels and solutions, polymer blends, polymer micelles and microemulsions, and colloidal sciences. Finally, we predict more USAXS studies on polymeric systems, especially those with large-scale structures or hierarchical microstructures.

極小角散乱法によるナノ〜メゾスケール構造の評価

Introduction to small-angle X-ray scattering (SAXS) and ultra small-angle X-ray scattering (USAXS) is presented. SAXS is useful for microstructure analysis of age-hardenable alloys containing precipitates with several to several tens of nanometers in size. On the other hand, USAXS is appropriate to examine much larger microstructural heterogeneities, such as inclusions, voids, and large precipitates whose size is typically around one micrometer. Combining these two scattering methods, and sometimes also with diffractions, it is possible to assess the hierarchical structure of the samples in-situ and nondestructively, ranging from phase identification, quantitative analysis of precipitation structures upto their mesoscopic aggregates, large voids and inclusions. From technical viewpoint, USAXS requires some specific instrumentation for its optics. However, once a reasonable measurement was made, the analysis for the intensity is the same as that for conventional SAXS. In the present article, short introduction of conventional SAXS is presented, and then, the analysis is applied for a couple of USAXS data obtained for well-defined oxide particles whose average diameters are expected to be about 0.3 micrometers.

Correlating Small Angle Scattering Spectra to Electrical Resistivity Changes in a Nickel-base Superalloy

AbstractWaspaloy specimens aged at 800°C from 0.5h to 88.5h were evaluated via small angle neutron scattering (SANS), ultra small angle X-ray scattering (USAXS), electrical resistivity, and SEM. The average γ' precipitate size and volume fraction, obtained from modeling the small angle scattering data, was used to calculate a figure of merit of electron scattering. This figure of merit is designed to correlate the electron scattering ability of the material to the precipitate microstructure. The USAXS data shows a secondary precipitate population at smaller diameters that is absent from the SANS data, since the SANS measurements were not obtained at high enough values of Q. It is believed that this secondary population makes the USAXS-derived figure of merit more sensitive to the actual measured resistivity response than the SANS-derived values; however, the SANS derived primary precipitate sizes are believed to more accurate due to a larger sample volume.

Structure and viscoelastic properties of hybrid ferrogels with iron oxide nanoparticles synthesized in situ

Ultra small angle X-ray scattering (USAXS) experiments in the q-range (10−4–0.2 Å) were performed to determine the structure of iron oxide NPs in situ synthesized inside semi-interpenetrating polymer networks (semi-IPNs) of linear alginate and crosslinked poly(N-isopropylacrylamide) (PNiPAAm). Results from the fitting of USAXS experiments were related with the reinforcement and swelling properties exhibited by the hybrid semi-IPNs which, in turn, were found to be highly dependant on the alginate concentration and the volume fraction of iron oxide nanoparticles. The USAXS findings, along with those from rheological and swelling measurements, allow determining whether iron oxide nanoparticles are bonded to the polymer matrix or if they are simply ‘packed’ inside the polymer network without interaction with the polymer chain.

低燃費タイヤを指向した末端変性溶液重合ＳＢＲに関する研究

In recent, the reduction of rolling resistance of tires has become more significant in the tire industry, because it has close relation to the fuel consumption efficiency and CO2 emission of motor vehicles. Rolling resistance of tire is closely related to hysteresis loss properties of tire tread compounds. Dispersibility of filler is considered to affect hysteresis loss. Some styrene-butadiene rubbers with functional groups at chain ends have been developed by solution polymerization system (S-SBRs) to achieve good interaction with silica filler. They showed significant reduction in the hysteresis loss of silica reinforced compounds. Especially, the modified S-SBR with both primary amino group and alkoxysilyl group exhibited excellently lower hysteresis loss properties. In order to observe the dispersibility of silica in compounds with this modified S-SBR directly, the measurements of transmission electron microscopy (TEM) and ultra small angle X-ray scattering (USAXS) were carried out. As the results, the excellent dispersion states of silica in the compounds with this modified S-SBR was observed, and we found that smaller size of silica aggregates could reduce the hysteresis loss to much lower level. This result coincided with those obtained by dynamic viscoelstic measurement.

The Microstructure of TATB‐Based Explosive Formulations During Temperature Cycling Using Ultra‐Small‐Angle X‐Ray Scattering

AbstractTATB (1,3,5 triamino‐2,4,6‐trinitrobenzene), an extremely insensitive explosive, is used both in polymer‐bound explosives (PBXs) and as an ultra‐fine pressed powder (UFTATB). Many TATB‐based explosives, including LX‐17, a mixture of TATB and Kel‐F 800 binder, experience an irreversible expansion with temperature cycling known as ratchet growth. Additional voids, with sizes hundreds of nanometers to a few micrometers, account for much of the volume expansion. Measuring these voids is important feedback for hot‐spot theory and for determining the relationship between void size distributions and detonation properties. Also, understanding mechanisms for ratchet growth allows future choice of explosive/binder mixtures to minimize these types of changes, further extending PBX shelf life. This paper presents the void size distributions of LX‐17, UFTATB, and PBXs using commercially available Cytop M, Cytop A, and Hyflon AD60 binders during temperature cycling between −55 and 70 °C. These void size distributions are derived from ultra‐small‐angle X‐ray scattering (USAXS), a technique sensitive to structures from about 2 nm to about 2 μm. Structures with these sizes do not appreciably change in UFTATB. Compared to TATB/Kel‐F 800, Cytop M and Cytop A show relatively small increases in void volume from 0.9 to 1.3% and 0.6 to 1.1%, respectively, while Hyflon fails to prevent irreversible volume expansion (1.2–4.6%). Computational mesoscale models combined with experimental results indicate both high glass transition temperature as well as TATB binder adhesion and wetting are important to minimize ratchet growth.

Quantification of the coarsening kinetics of γ′ precipitates in Waspaloy microstructures with different prior homogenizing treatments

We report on quantification of the γ′ precipitate population, and its coarsening behavior, in controlled Waspaloy microstructures synthesized to possess γ matrix grain sizes ranging from 13 to 89 μm. The grain microstructures were produced by initial solution-treatments at 1045, 1090 and 1145 °C. The γ′ precipitates were obtained by aging at 779 and 796 °C for times ranging from 0.1 to 263.5 h. Specimen characterization was conducted via optical microscopy and scanning electron microscopy, DC four-point probe resistivity and ex situ ultra-small-angle X-ray scattering (USAXS) experiments at each aging time. The γ′ size distribution, obtained from the USAXS analysis, transformed from an initial unimodal to an eventual bimodal distribution with continued aging. The overall coarsening kinetics, although non-steady state, followed t 1/3 behavior, when the primary γ′ radius was used as the quantifying precipitate dimension. The coarsening rate constants were primarily determined by the aging temperature used, while the influence of prior homogenizing treatments was minimal to non-existent. A generic correlation was found to exist between a newly proposed figure-of-merit of scattering, η based on the USAXS-derived γ′ precipitate distribution(s) and the measured electrical resistivity.

Information extraction and CT reconstruction of liver images based on diffraction enhanced imaging

X-ray phase-contrast imaging (PCI) is a new emerging imaging technique that generates a high spatial resolution and high contrast of biological soft tissues compared to conventional radiography. Herein a biomedical application of diffraction enhanced imaging (DEI) is presented. As one of the PCI methods, DEI derives contrast from many different kinds of sample information, such as the sample’s X-ray absorption, refraction gradient and ultra-small-angle X-ray scattering (USAXS) properties, and the sample information is expressed by three parametric images. Combined with computed tomography (CT), DEI-CT can produce 3D volumetric images of the sample and can be used for investigating micro-structures of biomedical samples. Our DEI experiments for liver samples were implemented at the topography station of Beijing Synchrotron Radiation Facility (BSRF). The results show that by using our provided information extraction method and DEI-CT reconstruction approach, the obtained parametric images clearly display the inner structures of liver tissues and the morphology of blood vessels. Furthermore, the reconstructed 3D view of the liver blood vessels exhibits the micro blood vessels whose minimum diameter is on the order of about tens of microns, much better than its conventional CT reconstruction at a millimeter resolution. In conclusion, both the information extraction method and DEI-CT have the potential for use in biomedical micro-structures analysis.