Ultra-small-angle X-ray Scattering Research Articles

From Nucleation to Fat Crystal Network: Effects of Stearic-Palmitic Sucrose Ester on Static Crystallization of Palm Oil.

Palm oil (PO), a semi-solid fat at room temperature, is a popular food ingredient. To steer the fat functionality, sucrose esters (SEs) are often used as food additives. Many SEs exist, varying in their hydrophilic-to-lipophilic balance (HLB), making them suitable for various food and non-food applications. In this study, a stearic-palmitic sucrose ester with a moderate HLB (6) was studied. It was found that the SE exhibited a complex thermal behavior consistent with smectic liquid crystals (type A). Small-angle X-ray scattering revealed that the mono- and poly-esters of the SE have different packings, more specifically, double and single chain-length packing. The polymorphism encountered upon crystallization was repeatable during successive heating and cooling cycles. After studying the pure SE, it was added to palm oil, and the crystallization behavior of the mixture was compared to that of pure palm oil. The crystallization conditions were varied by applying cooling at 20 °C/min (fast) and 1 °C/min (slow) to 0 °C, 20 °C or 25 °C. The samples were followed for one hour of isothermal time. Differential scanning calorimetry (DSC) showed that nucleation and polymorphic transitions were accelerated. Wide-angle X-ray scattering (WAXS) unraveled that the α-to-β' polymorphic transition remained present upon the addition of the SE. SAXS showed that the addition of the SE at 0.5 wt% did not significantly change the double chain-length packing of palm oil, but it decreased the domain size when cooling in a fast manner. Ultra-small-angle X-ray scattering (USAXS) revealed that the addition of the SE created smaller crystal nanoplatelets (CNPs). The microstructure of the fat crystal network was visualized by means of polarized light microscopy (PLM) and cryo-scanning electron microscopy (cryo-SEM). The addition of the SE created a finer and space-filling network without the visibility of separate floc structures.

Orientational ordering and assembly of silica-nickel Janus particles in a magnetic field.

The orientation ordering and assembly behavior of silica-nickel Janus particles in a static external magnetic field were probed by ultra small-angle X-ray scattering (USAXS). Even in a weak applied field, the net magnetic moments of the individual particles aligned in the direction of the field, as indicated by the anisotropy in the recorded USAXS patterns. X-ray photon correlation spectroscopy (XPCS) measurements on these suspensions revealed that the corresponding particle dynamics are primarily Brownian diffusion [Zinn, Sharpnack & Narayanan (2023). Soft Matter, 19, 2311-2318]. At higher fields, the magnetic forces led to chain-like configurations of particles, as indicated by an additional feature in the USAXS pattern. A theoretical framework is provided for the quantitative interpretation of the observed anisotropic scattering diagrams and the corresponding degree of orientation. No anisotropy was detected when the magnetic field was applied along the beam direction, which is also replicated by the model. The method presented here could be useful for the interpretation of oriented scattering patterns from a wide variety of particulate systems. The combination of USAXS and XPCS is a powerful approach for investigating asymmetric colloidal particles in external fields.

Design of Carbon Aggregation Structure in Polymer Electrolyte Fuel Cell Catalyst Ink by Solvent Hydrophilicity

Controlling the porous structure of the cathode catalyst layer in a polymer electrolyte fuel cell is essential to reduce the reaction and mass transport resistance of the oxygen reduction reaction. As the catalyst layer is a coating of a catalyst ink, the aggregation structure of platinum-supported carbon (Pt/C) and ionomer in ink is a key property for achieving the optimal catalyst layer.1 Previous studies reported that the weight fraction of water in solvents could control aggregation structure in ink.2-4 For example, Kumano et al.2 reported that increasing the water ratio to 1-propanol enhances the ionomer adsorption on Pt/C (Γ) and dispersion of Pt/C, causing the lowering of the viscosity of the inks. Based on the results, they speculated that water repels ionomers and promotes their adsorption on Pt/C particles. They further speculated that the ionomers adsorbed on the Pt/C particles induce repulsive interactions between Pt/C particles via electrostatic repulsive interactions among sulfonate groups of adsorber ionomers. By the enhanced repulsive interactions, Pt/C particles are dispersed, and viscosity decreases. The discussion in the previous study likely indicates that the hydrophilicity of the solvent is an essential factor controlling the aggregation structure of catalyst ink. Here, we verify this hypothesis. As a universal indicator of the hydrophilicity, we adopt the hydrogen-bond term HSP-δH of the Hansen solubility parameters. We examined how HSP-δH is correlated to the ionomer adsorption ratio to Pt/C (Γ), viscoelasticity of ink, and structural properties of ink measured by ultra-small angle X-ray scattering (USAXS).The catalyst inks were prepared by mixing Pt/C (TEC10V30E, TKK), Nafion 20 wt% solution (DE2020, Chemours), ultrapure water, and three different alcohols [ethanol (EtOH), 1-propanol (PrOH) and diacetone alcohol (DAA)]. The water weight fraction in the solvents was set to 25 - 85 wt%. Γ is plotted as a function of HSP-δH in Fig. 1. Regardless of the alcohol species, Γ increases with increasing HSP-δH. The trend is consistent with the previously reported trend observed in the mixtures of water and 1-propanol. Figures 2 (a) and (b) show the equilibrium storage modulus G’0 obtained by the rheometer and the fractal dimension D 2 of agglomerates of Pt/C particles in ink as functions of Γ. Here, D 2 is determined by fitting the unified model5 to the USAXS spectrum obtained by the synchrotron radiation (Spring-8, Japan). Both decreases with the increase of Γ. The lowering of D 2 indicates that the agglomerates of Pt/C particles are dispersed and turn to less-structured particles, as schematically shown in Fig. 2 (c). By the dispersion, G’0 decreases. Accordingly, the hydrophilicity, indeed, promotes the ionomer adsorption, and the adsorption induces the dispersion. The hydrophilicity is a key factor controlling the structure and rheology of the catalyst ink, and HSP-δH is a universal descriptor of hydrophilicity. Reference K. B. Hatzell, M. B. Dixit, S. A. Berlinger, and A. Z. Weber, J. Mater. Chem. A, 5 (39), 20527-20533 (2017). N. Kumano, K. Kudo, Y. Akimoto, M. Ishii, and H. Nakamura, Carbon, 169 429-439 (2020). S. Takahashi, T. Mashio, N. Horibe, K. Akizuki, and A. Ohma, ChemElectroChem, 2 (10), 1560-1567 (2015). T. Van Cleve, S. Khandavalli, A. Chowdhury, S. Medina, S. Pylypenko, M. Wang, K. L. More, N. Kariuki, D. J. Myers, A. Z. Weber, S. A. Mauger, M. Ulsh, and K. C. Neyerlin, ACS Appl Mater Interfaces, 11 (50), 46953-46964 (2019). G. Beaucage, H. K. Kammler, and S. E. Pratsinis, J. Appl. Crystallogr., 37 (4), 523-535 (2004). Figure captions Figure 1 Dependence of the ionomer adsorption ratio Γ on the HSP-δH of the catalyst ink solvent. Figure 2 (a) Γ dependence of the equilibrium storage modulus G’0 of the catalyst inks. G’0 is plotted on a logarithmic scale. G’0 values of inks that are not measurable due to being less than the measurable lower limit are conventionally described as 0. (b) Γ dependence of the mass fractal D 2 of Pt/C aggregates in the inks. (c) Schematic illustration of the aggregation structure of Pt/C in the solvents. Figure 1

A physics-driven Σ-Y atomization model for heavy-duty engine simulations

The atomization of a liquid jet is a multi-scale and multi-physics problem of interest for many engineering applications. Particularly, it drives the fuel-oxidizer mixing and dictates the efficiency of combustion engines. High-fidelity multi-phase simulations remain challenging due to the excessive computational cost required to capture all the atomization scales. Thus, atomization models are necessary to represent sub-grid liquid structures. In this work, a modified Σ-Y model in the context of Eulerian-Lagrangian Spray Atomization (ELSA) is used to transport the surface area density of the spray. The model's predictive performance is assessed under various operating conditions relevant to heavy-duty engines using the Engine Combustion Network (ECN) Spray C and Spray D research-grade injectors. The classic droplet collision formulation of the Σ-Y model alone does not replicate the response of the measured spray surface area to changes in injector, ambient pressure, and injection pressure, requiring individual tuning of the model's parameters. Instead, a transition between dense and dilute spray breakup mechanisms is proposed in terms of the average droplet spacing. The collision breakup mechanism represents the dilute spray, whereas the droplet size in the dense spray is driven by a competition between the integral scale of turbulence and the balance between the turbulent kinetic energy and the surface energy of the droplets. Such an approach minimizes the requirements for model tuning. Moreover, the role of the constants of a compressible standard k-ε RANS model is assessed in the injector's internal flow and external spray simulation framework, and an updated set is proposed. The results are validated against x-ray radiography and Ultra-Small Angle X-ray Scattering (USAXS) data and highlight the predictive capabilities of the proposed physics-driven Σ-Y model, which is compatible with engine simulation turnaround times.

On the equivalence of the X-ray scattering retrieval with beam tracking and analyser-based imaging using a synchrotron source

X-ray phase contrast imaging (XPCI) methods give access to contrast mechanisms that are based on the refractive properties of matter on top of the absorption coefficient in conventional x-ray imaging. Ultra small angle x-ray scattering (USAXS) is a phase contrast mechanism that arises due to multiple refraction events caused by physical features of a scale below the physical resolution of the used imaging system. USAXS contrast can therefore give insight into subresolution structural information, which is an ongoing research topic in the vast field of different XPCI techniques. In this study, we quantitatively compare the USAXS signal retrieved by the beam tracking XPCI technique with the gold standard of the analyzer based imaging XPCI technique using a synchrotron x-ray source. We find that, provided certain conditions are met, the two methods measure the same quantity.

Photonic Amorphous I‐WP‐Like Networks Create Angle‐Independent Colors in Sternotomis virescens Longhorn Beetles

AbstractStructural color originates from the interference of light with periodic structures that feature characteristic length scales on the order of the wavelength of visible light. Long‐range order in photonic structures usually causes iridescence, and increasing disorder renders colors angle‐independent. Random disorder distributes scattering intensity over all wavelengths, producing white in the absence of absorption. Various non‐iridescent, vivid color patterns are found in Sternotomini longhorn beetles. Herein, Sternotomis virescens is investigated, where elytral scales produce a green‐blue color pattern on otherwise black elytra. Combining focused ion beam scanning electron microscopy (FIB‐SEM) tomography, ultra‐small‐angle X‐ray scattering (USAXS), structural modeling, and full‐wave optical simulations, it is found that the color originates from amorphous photonic networks based on sub‐units resembling the I‐WP unit cell, a triply‐periodic minimal surface with body‐centered‐cubic symmetry. This work provides insights into how quasi‐order produces stable colors in S. virescens longhorn beetles, highlights the advantages of volumetric imaging using FIB‐SEM tomography of porous nanostructured materials, and raises interesting questions about the formation mechanisms of amorphous structures in vivo.

Deformation Mechanism of Amorphous Plasticized Poly(vinyl butyral)

Understanding the deformation mechanism of amorphous polymeric materials is indispensable for their applications but is quite challenging. Here, with amorphous plasticized poly(vinyl butyral) (PVB) as a model system, we studied its structural change in situ during uniaxial deformation with ultrasmall-angle X-ray scattering (USAXS). We observed a stretch-induced phase separation behavior characterized by a butterfly scattering pattern in plasticized PVB for the first time. This phase separation, featured by a concentration fluctuation along the stretch direction, is a result of stress–concentration coupling under stretch. The phase size at its formation is around 100 nm, which increases almost linearly with strain. The strain rate has a weak effect on the phase size. This suggests that the elastic deformation of the network, cross-linked by entanglements and hydrogen-bonding clusters, governs the phase size. We proposed a tentative model to explain the deformation behavior of plasticized PVB, where the breaking and reforming of hydrogen bonds, the formation and growth of phase separation against osmotic pressure, and the plastic deformation and rupture of phase structure dissipate a large amount of energy and endow the plasticized PVB with excellent mechanical performance. We believe our findings are general and should be applicable to other amorphous polymers with solvents or plasticizers.

Comparison of nanocomposite dispersion and distribution for several melt mixers

Breakup (dispersion) and distribution of nanoparticles are the chief hurdles towards taking advantage of nanoparticles in polymer nanocomposites for reinforcement, flame retardancy, conductivity, chromaticity, and other properties. Microscopy is often used to quantify mixing, but it has a limited field of view, does not average over bulk samples, and fails to address nano-particle hierarchical structures. Ultra-small-angle X-ray scattering (USAXS) can provide a macroscopic statistical average of nanoscale dispersion (breakup) and emergent hierarchical structure, as well as the distribution on the nanoscale. This work compares several common mixer geometries for carbon black-polystyrene nanocomposites. Two twin-screw extruder geometries, typical for industrial processing of melt blends, are compared with a laboratory-scale single screw extruder and a Banbury mixer. It is found that for a given mixer, nanoscale distribution increases following a van der Waals function using accumulated strain as an analogue for temperature while macroscopic distribution/dispersion, using microscopy, does not follow this dependency. Breakup and aggregation in dispersive mixing follow expected behavior on the nanoscale. Across these drastically different mixing geometries an unexpected dependency is observed for nanoscale distributive mixing (both nano and macroscopic) as a function of accumulated strain that may reflect a transition from distributive turbulent to dispersive laminar mixing as the mixing gap is reduced.

Cryogels loaded with nanostructured fluids studied by ultra-small-angle X-ray scattering

The combination of nanostructured fluids (NSFs), such as micellar solutions or microemulsions and highly-retentive hydrogels, such as PVA-based cryogels, represents nowadays a promising and innovative approach in the field of conservation of cultural heritage, as it enables the highest control available during cleaning interventions. However, at present, little is known about the confinement of NSFs into PVA-based cryogels. In the present work, small-angle X-ray scattering (SAXS) and ultra-small-angle X-ray scattering (USAXS), combined with fluorescence correlation spectroscopy (FCS), were used to address this issue. Two significantly different NSFs were selected for this purpose, based on anionic or nonionic surfactants, and they were confined into four different gels: two single PVA and two PVA/PVA “twin-chain polymer networks” (TC-PNs). The analysis of the experimental results shows that surfactant nature is crucial in determining the interaction of NSFs with the gels’ polymer network. Moreover it was demonstrated that loading NSFs on PVA-based cryogels does not significantly affect the short-range nanostructure of neither the NSFs nor the gels, preserving the cleaning performances of the combined system.

Anisotropic flocculation in shear thickening colloid-polymer suspension via simultaneous observation of rheology and X-ray scattering

A shear thickening fluid, showing a significant increase in viscosity under shear stress, is a promising material for shock absorption applications. Colloidal dispersions of silica nanoparticles and polyethylene oxide polymers with large molecular weights also exhibit a shear thickening phenomenon, which is manifested by a transformation from liquid to gel, called shake-gel. To understand the gelation mechanism, small-angle X-ray scattering (SAXS) and ultra-small-angle X-ray scattering (USAXS) were performed with an X-ray transmission cell, which was used as a Couette cell in a rheometer. This setup enables simultaneous rheological measurements with SAXS and USAXS, providing real-time observation of the change from liquid to gel. An anisotropic increase of the scattering spectra indicated the formation of aligned floc structures. This result implies that a polymer chain recombined the network and transformed into the large flocs aligned in the flow direction. Additionally, the shifted peaks from the silica cluster indicated that the aligned flocs were compressed by the shear stress. The present work paves the way for the advanced design of shake-gel materials.

In-Situ X-Ray Scattering Study of Iridium Oxide Catalyst for Polymer Electrolyte Membrane Water Electrolyzer during Ink Sonication and Drying Process

Polymer electrolyte membrane water electrolyzers (PEMWEs) offer greenhouse gas emission-free hydrogen production for fuel cell vehicles and other industrial uses when using renewable energy sources [1]. Unsupported iridium oxide (IrO2) is the most active stable oxygen evolution reaction (OER) catalyst utilized in the anode of the PEMWE [2]. The atomic and microstructure of IrO2 catalysts and electrodes and interactions between and ionomer and catalyst can affect the ultimate performance of the PEMWE anode. These properties and phenomena may be controlled by the interactions of the ionomer in the catalyst-ionomer ink, by the effect of ink solvent composition on those interactions, and by the ink mixing and coating procedures. The microstructure evolution of the IrO2 catalyst during ink processing has not yet been identified. This presentation will describe relationships between ink formulation, electrode morphology, and performance for the IrO2-based PEMWE anodes. Moreover, the results of the evolution of the catalyst layer during the ink drying process as a function of solvent removal rate and solvent identity will be discussed. This study uses the in-situ technique of ultra-small angle X-ray scattering (USAXS) combined with small angle X-ray scattering to determine particle size distributions and the extent of IrO2 agglomeration in the inks and electrodes during the ink mixing/settling and drying processing. The effects of ionomer concentration, catalyst concentration, and solvent composition on the microstructure of the catalyst inks and electrode are correlated with the PEMWE performance and operando diagnostic data. Acknowledgements This work was supported by the U.S. Department of Energy, Energy Efficiency and Renewable Energy, Hydrogen and Fuel Cell Technologies Office under the H2NEW Consortium. This work was authored in Argonne National Laboratory, a U.S. Department of Energy (DOE) Office of Science laboratory operated for DOE by UChicago Argonne, LLC under contract no. DE-AC02-06CH11357. This research used the resources of the Advanced Photon Source (APS), a U.S. Department of Energy (DOE) Office of Science User Facility operated for the DOE Office of Science by Argonne National Laboratory under Contract No. DE-AC02-06CH11357.

Understanding the Nanostructures in the Electrolytes By Small-Angle X-Ray Scattering

The solution solvation structure of the liquid electrolyte directly affects transport properties, which ultimately determines the performance of batteries. It has been predicted that the nanoscale aggregates in the liquid electrolytes, especially as the salt concentrations increase. However, little is known about these structures due to the limitation of the traditional methods. Herein, we demonstrate that small-angle X-ray scattering-wide angle X-ray scattering (SAXS-WAXS), even ultra-small-angle X-ray scattering (USAXS) could be applied to capture these larger aggregates in the electrolytes, including conventional organic electrolytes, high concentration electrolytes, water-in-slat electrolytes, and redox-active electrolytes. Raman, neutron scattering, IR, and molecular dynamics (MD) simulations further support the proposed structures. This work highlights the fundamental structure analysis in nanoscale, which will prompt better electrolytes in the future.

Self-Assembled glycerol monooleate demixes miscible liquids through selective hydrogen bonding to water

Water is miscible with dimethylsulfoxide (DMSO), with which it interacts through hydrogen bonds (H-bonds). Glycerol monooleate (GMO, 53 g/L) demixes water and DMSO, yielding kinetically stable DMSO in water emulsions with up to ≈75 % DMSO (relative to water, v/v), as demonstrated by Fourier Transform Infrared (FTIR) spectromicroscopy, ultra small angle X-ray scattering (USAXS) and light scattering experiments, and optical microscopy. With > 75 % DMSO (relative to water) emulsions reverse and DMSO becomes the continuous phase (as shown by electrical conductivity measurements). The size of emulsified droplets decreases with increasing DMSO ratios (relative to water), as demonstrated by USAXS. Synchrotron X-ray Diffraction (XRD) measurements conducted in the small (SAXS) and wide angle (WAXS) regions show that the DMSO:water ratio affects GMO self-assembly. GMO (53 g/L) self-assembles into cubic crystal mesophases with 40 % DMSO (relative to water) and into disordered lamellar phases with 50 % DMSO. At even higher DMSO percentages, GMO self-assembles into reverse micelles, which contain water and are surrounded by DMSO (as shown by analyzing XRD data with the Steubner and Strey model). Although GMO mainly partitions in the DMSO rich phase, attenuated total reflectance (ATR)-FTIR measurements show that GMO interacts with water through H-bonds. Importantly, it increases the proportion of single H-bond donors (SD, which structure water the most) relative to double donors (DD, which structure water less). H-bonding between the hydrophilic head of GMO and initiates separation between DMSO and water, which would be H-bonded to one another in the absence of GMO. While this study focuses on DMSO, GMO also emulsifies water and tetrahydrofuran (THF), dimethylformamide (DMF) and dioxane. Our findings redefine which solvents can be emulsified with water, and have potential implications for water treatment.

Parametric Study of the Influence of Support Type, Presence of Platinum on Support, and Ionomer Content on the Microstructure of Polymer Electrolyte Fuel Cell Catalyst Layers

Ultra-small angle X-ray scattering (USAXS) was employed to investigate the effects of carbon support type, the presence of platinum on carbon, and ionomer loading on the microstructure of polymer electrolyte fuel cell (PEFC) catalyst layers (CLs). Particle size distributions (PSDs), obtained from fitting the measured scattering data were used to interpret the size of carbon aggregates (40–300 nm) and agglomerates (>400 nm) from two-component carbon/ionomer and three-component platinum/carbon/ionomer CLs. Two types of carbon supports were investigated: high surface area carbon (HSC) and Vulcan XC-72. CLs with a range of perfluorosulfonic acid (PFSA) ionomer to carbon (I/C) ratios (0.2–1.2) and also with perfluoroimide acid (PFIA) ionomer were studied to evaluate the effect of ionomer on CL microstructure. The carbon type, the presence of platinum, and ionomer loading were all found to significantly impact carbon agglomeration. The extent of Pt/C agglomeration in the CL was found to increase with increasing ionomer and platinum concentration and to decrease with increasing carbon surface area. Platinum electrochemically-active surface area (ECSA) and local oxygen transport resistance (RnF) were correlated to the CL microstructure to yield relationships affecting electrode performance.

Heterogeneous Percolation in Poly(methylvinylsiloxane)/Silica Nanocomposites: The Role of Polymer–Particle Interaction

Agglomeration and linking of nanoparticles or aggregates lead to the formation of percolated particle networks and alter the mechanical enhancement in polymer nanocomposites. Although critical behaviors have been widely studied, the solidlike behavior is only well described under the condition of the uniform dispersion of nanoparticles. In this work, we illustrate the role of particle–polymer interaction in the uniformity of particle dispersion and mechanical enhancement. Two types of silica with different interfacial adhesion energies with poly(methylvinylsiloxane) were adopted, resulting in different uniformities of particle dispersion. The critical percolation concentrations from the yield shear stress and yield first normal stress difference are identical. A lower interfacial adhesion energy leads to a higher critical concentration. The preshear stress only affects the critical concentration but does not change the critical exponents, which rely on the particle–polymer interaction. The mechanical enhancement, expressed as the power-law dependence of the yield stresses on the filler content, exhibits extraordinarily large power-law exponents for nanocomposites with lower interfacial adhesion energy, seriously deviating from the theoretical prediction in homogeneous dispersion systems. Based on the structural information from small-angle X-ray scattering (SAXS)/ultrasmall-angle X-ray scattering (USAXS) and transmission electron microscopy (TEM), we propose a model describing the heterogeneous percolation of loose aggregates in the presence of compact aggregates. This model shows that the heterogeneity of aggregates, including the fraction of compact aggregates and their fractal dimension, is the key factor in the scaling relationship between the yield stress and the particle volume fraction.

Microstructural evolution of cross-linked polytetrafluoroethylene under gamma irradiation using ultra-small angle X-ray scattering

Cross-linked polytetrafluoroethylene (XPTFE) with excellent wear and radiation resistant is expected to be applied in strong radiation fields. In this study, synchrotron ultra-small angle X-ray scattering (USAXS) techniques combined with in-situ uniaxial stretching were firstly used to study the mechanical property degradation mechanism of XPTFE in terms of micro-structural evolution in real time. As the increase of cross-linking degree, the size and spacing of the scatterers for XPTFE were more unequal. When XPTFE was uniaxially stretched at room temperature, its molecular chains were tilted, and lamellae crystals were elongated and thinned along the stretching direction. When XPTFE was irradiated by γ-rays under air, with increasing absorbed doses, the long period decreased first and then increased, while the gyration radius was reversed. After high-dose irradiation, the mechanical properties of XPTFE were lost, making their stretching processes were dominated by the orientation of some small broken crystals along the stretching direction and accompanied by the formation of voids. But for XPTFE under constant stress uniaxial stretching at variable temperature, its chain segments and molecular chains cannot be oriented even at elevated temperatures, maintaining a degree of thermal stability.

Influence of Carbon Support Type, Presence of Platinum and Ionomer Content on Agglomeration in Catalyst Layers

Polymer electrolyte fuel cell (PEFC) energy conversion systems have found application in transportation applications due to their high power density, low operating temperature, high energy conversion efficiency, and speed of refueling.1 One of the key components of a PEFC is the membrane electrode assembly (MEA), which consists of a proton exchange membrane (PEM), such as a perfluorosulfonic acid (PFSA), sandwiched between two catalyst layers (CLs) serving as anode and cathode. Several studies of CL microstructure−performance relationships suggest that the electrode microstructure characteristics, such as the extent of the catalyst−ionomer interaction, continuity of the ionomer phase, and pore size distribution are critical for performance.2-4 However, successful implementation of novel materials for PEFC electrodes is hindered by the lack of a fundamental understanding of the complex, multicomponent nature of the CL, the interplay of its components, and their independent and cooperative effects on the effective properties and performance.In this work, ultra-small angle X-ray scattering (USAXS) was employed to investigate the effects of carbon support type, presence of platinum, and ionomer loading on catalyst agglomeration in CLs. Particle size distributions (PSDs), obtained from fitting the scattering data using the maximum entropy (MaxEnt) method, were used to determine the size of carbon aggregates and agglomerates from carbon-ionomer and platinum-carbon-ionomer CLs. Three types of carbon supports were chosen for the investigation: high surface area carbon (HSC), Vulcan XC-72, and graphitized Vulcan XC-72. CLs with a range of perfluorosulfonic acid (PFSA) ionomer loadings (0.2-1.0 ionomer to carbon ratio, I/C) were studied in order to evaluate the effect of ionomer on the CL agglomerate structure. The CL agglomerate structure will be correlated with electrochemical performance to reveal the interplay of the components, and their independent and cooperative effects on performance. References B.D. McNicol, D. A. J. Rand, K. R. Williams, J. Power Sources 100 (2001) 47–59.F. C. Cetinbas, X. Wang, R. K. Ahluwalia, N. N. Kariuki, R. P. Winarski, Z. Yang, J. Sharman, and D. J. Myers, J. Electrochem. Soc., 164, (2017) F1596–F1607.Y.-C. Park, H. Tokiwa, K. Kakinuma, M. Watanabe, M. Uchida, J. Power Sources 315 (2016) 179-191.S. Holdcroft, Chem. Mater., 26 (2014) 381−393. This work was supported by the U.S. Department of Energy, Energy Efficiency and Renewable Energy, Hydrogen and Fuel Cell Technologies Office under the auspices of the Fuel Cell Performance and Durability Consortium (FC-PAD). The Advanced Photon Source was supported by the U.S. Department of Energy, Office of Science User Facility. Argonne National Laboratory is managed for the U.S Department of Energy by the University of Chicago Argonne, LLC, also under contract DE-AC-02-06CH11357.

Microstructure Characterization of Catalysis Layers during Ink Drying Process for Polymer Electrolyte Membrane Fuel Cells

A catalyst ink for proton exchange membrane fuel cells (PEMFCs) is generally prepared by various mixing methods by dispersing platinum or platinum alloy nanoparticles supported on carbon blacks with ionomers in a specific solvent or solvent combination. The catalyst ink is deposited on the surface of the membrane or diffusion media and is typically subjected to elevated temperatures to facilitate rapid removal of solvent. Large carbon agglomerates resulting from sub-optimal ink dispersion and drying conditions can limit catalyst utilization, inhibit mass transport in the catalyst layer, and damage the membrane and possibly also the gas diffusion media [1, 2]. Micro-structural evolution of the catalyst ink can be controlled by interactions of the ionomer in the catalyst-ionomer ink and by the effect of ink solvent composition on those interactions during the ink drying process. This presentation will describe the results of in-situ/ex-situ X-ray scattering studies of the evolution of the cathode catalyst layer during the ink drying process to determine the impact of solvent removal rates and solvent identity on the structural evolution of the cathode catalyst layer. These studies also included operando ink drying at room temperature, under an atmosphere containing the solvent, and a high temperature. Ultra-small angle X-ray scattering (USAXS) was used to measure the agglomerate size distribution during the ink drying. A small environmental chamber was used to examine drying phenomena of high solid-content inks and dispersions to determine structural evolution during ink drying. The effects of ionomer concentration, catalyst concentration, and solvent composition on the microstructure of the catalyst inks and electrode are correlated with the MEA performance and operando diagnostic data. The goal of these studies is to guide the MEA fabrication process to optimize MEA performance and durability.

Discussion of Orientation and Performance of Crosslinked Ultrahigh-Molecular-Weight Polyethylene Used for Artificial Joints.

Previously, the orientation structure of ultrahigh-molecular-weight polyethylene (UHMWPE) for artificial joints was considered to be unchanged after irradiation crosslinking. Therefore, much of the research related to the long-term failure of artificial joints has focused on material improvements. In this study, ultrasmall-angle X-ray scattering (USAXS) and the small/wide-angle X-ray scattering (SAXS-WAXS) combined technique reveal that the orientation structures of UHMWPE materials at all scales (nanoscale to microscale) are responsible for the long-term failure of artificial joints. To further illustrate the formation of these hierarchical oriented structures, a simple model is presented. In this model, first, the migration of free radicals plays a vital role, and the different steric hindrances in different directions directly lead to uneven migration behavior of free radicals. Second, the uneven migration of free radicals contributes to an inhomogeneous concentration of free radicals, thus resulting in observable crosslinking nonuniformities. Finally, all the hierarchical structural nonuniformities promote long-term failure of artificial joints after long-term wear.

A spatio-temporal in-situ investigation of the Payne effect in silica-filled rubbers in Large Amplitude Oscillatory Extension

The present work deals with the structural and dynamic characteristics of a silica filler network within an industrial elastomeric composite with time-resolved Ultra-Small-Angle-X-ray Scattering (USAXS), collected for the first time in-situ under periodic uniaxial deformation. The in-situ configuration allows a unique correlation between the x-ray patterns highlighting the structure of the filler and the dynamic-mechanical stress-strain response that characterizes the full composite. A scattering model is applied to quantitatively identify the filler network evolution as a function of dynamic strain. To address the Payne effect and the underlying structural modifications correlated to intra- and inter-filler-aggregate effects, all rubbers were pre-conditioned to suppress stress-softening related to the Mullins effect. Sector-averaged scattering intensities along the parallel strain direction reveal a jamming/de-jamming transition between clusters. The dynamic stress response of the full composite shows onsets of non-linear behavior with contributions assigned to both filler and rubber phase separately. • Scattering analysis of silica-filled SBR elastomers. • Study of the Payne effect through in-situ combination of USAXS and DMA methods. • Relationship between structural and dynamic-mechanical properties. • Identification of jamming/de-jamming transition upon oscillatory deformation.