Advanced Photon Source

A U.S. Department of Energy, Office of Science,
Office of Basic Energy Sciences national synchrotron x-ray research facility

Publications from year 2004

A study of the nanostructure and tensile properties of ultra-high molecular weight polyethylene. Ultra-high molecular weight polyethylene (UHMWPE) has gained worldwide acceptance as a bearing material used in orthopaedic implants. Despite its widespread use, inherent properties of the polymer continue to limit the wear resistance and the clinical lifespan of implanted knee and hip prosthetics containing UHMWPE components. The degree of crystallinity of UHMWPE is known to strongly influence several of its tensile mechanical properties such as Young's modulus, yield stress, strain-hardening rates, work of fracture and ultimate tensile properties. In this study, medical grade UHMWPE was subjected to four different crystallization conditions resulting in UHMWPE with a range of crystalline morphologies. Thereafter, the crystalline nanostructure was quantitatively characterized using a combination of ultra-small angle X-ray scattering and differential scanning calorimetry. Low-voltage scanning electron microscopy was employed as a supplementary technique to compare the crystalline morphology resulting from each crystallization condition. In addition, uniaxial tensile tests were performed to assess the effects of crystallization conditions on the mechanical properties of UHMWPE. This study showed that while crystallization conditions strongly influenced the morphology of UHMWPE, in most cases the mechanical properties of the material were not significantly affected. (C) 2003 Elsevier Ltd. All rights reserved.

M.B. Turell and A. Bellare. Cited: Biomaterials, 2004, 25 (17), Aug, p 3389-3398.

Hard structured particles: Suspension synthesis, characterization, and compressibility. Hard interactions are developed on three grades of fumed silica by eliminating interparticle forces and sterically stabilizing the particles by attaching an organic coating to the surface of the particles, suspending them in an index-matching solvent and screening the electrostatics. These hard-structured particles are studied to understand the effects of the particle's microstructure on suspension properties without the influence of interparticle forces other than volume exclusion, Brownian, and hydrodynamic interactions. Light and X-ray scattering studies of low-volume-fraction suspensions suggest that the fumed silicas consist of primary particle of radius of gyration R-g1 approximate to 16 nm and aggregate size R-g2 approximate to 50 nm and mass fractal dimension D-f approximate to 2.2. Osmotic compressibilities of these suspensions are measured as a function of particle concentration exploring the packing mechanism of fumed silica. While there is minimal detectable change in the primary particle size, Rg(2) varies by similar to 15%, providing insight into how suspension properties are related to particle size. As expected of hard particles with the same microstructure, the concentration dependence on the osmotic pressure superimposes with volume fraction of solids. The comparison of fumed-silica-suspension measurements to the known behavior of hard-sphere suspensions demonstrates the effects of particle geometry on suspension properties with indications of interpenetration of the fumed silica due to their open geometry.

W.E. Smith and C.F. Zukoski. Cited: Langmuir, 2004, 20 (25), Dec 7, p 11191-11200.

Large-Scale Morphology of Dispersed Layered Silicates. D.W. Schaefer, R.S. Justice, H. Koemer, R.A. Vaia, J. Zhao, M. Yang and J. Vale. Cited: MRS 2004 (Conf. Proc.) Vol. 840 Ed., 2004,

Structure of arylene-bridged polysilsesquioxane xerogels and aerogels. Arylene-bridged polysilsesquioxanes are an interesting class of porous materials prepared by sol-gel processing of ethoxysilane monomers in which there are two or more trialkoxysilyl groups positioned about an arylene bridging group. The majority of these materials are highly porous with surface areas as high as 1880 m(2)/g. In an effort to understand the nature of porosity in these materials, small-angle X-ray and neutron scattering were employed to characterize phenylene-, biphenylene-, and terphenylene-bridged polysilsesquioxanes. Phenylene-bridged polysilsesquioxane xerogels and aerogels were also compared to understand the effect of drying protocol on pore structure. The effect of catalyst concentration is also reported for the base-catalyzed system. In all cases studied here, we find evidence for domains in the nanometer range with distinct fractal character. We associate these domains with porosity rather than microphase separation of organic and inorganic moieties. The nature of this porosity depends on the bridging group in a systematic way, but is only weakly dependent on other synthetic parameters such as catalyst type, catalyst concentration, and drying protocol.

D.W. Schaefer, G. Beaucage, D.A. Loy, K.J. Shea and J.S. Lin. Cited: Chemistry of Materials, 2004, 16 (8), Apr 20, p 1402-1410.

CHARACTERIZATION OF Y2O3-DOPED La2Zr207 BASED EB-PVD THERMAL BARRIER COATINGS USING X-RAY MICROTOMOGRAPHY (CMT) AND SMALL ANGLE NEUTRON DIFFRACTION (SAND). B. Saruhan, A.F. Renteria, F. De Carlo, A. Kulkarni and J. Ilavsky. Cited: Cocoa Beach 2004 (Conf. Proc.) (Cocoa Beach), Vol. Ed., 2004,

Elasticity and clustering in concentrated depletion gels. X-ray scattering and rheology are employed to study the volume fraction dependence of the collective structure and elastic moduli of concentrated nanoparticle-polymer depletion gels. The nonequilibrium gel structure consists of locally densified nonfractal clusters and narrow random interfaces. The elastic moduli display a power law dependence on volume fraction with effective exponents that decrease with increasing depletion attraction strength. A microscopic theory that combines local structural information with a dynamic treatment of gelation is in good agreement with the observations.

S. Ramakrishnan, Y.L. Chen, K.S. Schweizer and C.F. Zukoski. Cited: Physical review E, 2004, 70 (4), Oct, p -.

Effect of silica nanoparticles on morphology of segmented polyurethanes. Two series of segmented polyurethanes having soft segment concentration of 50 and 70 wt%, and different concentrations of nanometer-diameter silica were prepared and tested. Atomic force microscopy revealed a strong effect of nanoparticles on the large-scale spherulitic morphology of the hard domains. Addition of silica suppresses fibril formation in spherulites. Filler particles were evenly distributed in the hard and soft phase. Nano-silica affected the melting point of the hard phase only at loadings > 30 wt% silica. A single melting peak was observed at higher filler loadings. There is no clear effect of the filler on the glass transition of soft segments. Wide-angle X-ray diffraction showed decreasing crystallinity of the hard domains with increasing filler concentration in samples with 70 wt% soft segment. Ultra small-angle X-ray scattering confirms the existence of nanometer phase-separated domains in the unfilled sample. These domains are disrupted in the presence of nano-silica. The picture that emerges is that nano-silica suppresses short-scale phase separation of the hard and soft segments. Undoubtedly, the formation of fibrils on larger scales is related to short-scale segment segregation, so when the latter is suppressed by the presence of silica, fibril growth is also impeded. (C) 2004 Elsevier Ltd. All rights reserved.

Z.S. Petrovic, Y.J. Cho, I. Javni, S. Magonov, N. Yerina, D.W. Schaefer, J. Ilavsky and A. Waddon. Cited: Polymer, 2004, 45 (12), May 20, p 4285-4295.

Non-agglomerated dry silica nanoparticles. Silica nanoparticles for polymer nanocomposites are made by oxidation of hexamethyldisiloxane (HMDSO) in methane/oxygen diffusion flames. The flame temperature is measured by in-situ Fourier transform infrared (FTIR) spectroscopy while the degree of agglomeration of the product powder is quantitatively determined by ultra small angle X-ray scattering (USAXS) and is confirmed by transmission electron microscopy (TEM). Precisely controlled, non-agglomerated silica particles having an average primary particle diameter of 18-85 nm, as determined by N-2 adsorption and TEM, are made at low silica production rates of 9 g/h or at low O-2 flow rates at silica production rates of 17 g/h, while smaller and highly agglomerated particles are made at high O-2 flow rates at silica production rates of 17 g/h. The differences in morphology result from the completion of gas-to-particle conversion and from the onset of steep cooling in the flames that determines the duration of full coalescence. Nanocomposites with dimethylacrylate polymers are made using non-agglomerated silica particles and compared to the ones made with commercially available silicas. (C) 2004 Elsevier B.V. All rights reserved.

R. Mueller, H.K. Kammler, S.E. Pratsinis, A. Vital, G. Beaucage and P. Burtscher. Cited: Powder Technology, 2004, 140 (1-2), Feb 16, p 40-48.

X-ray imaging with ultra-small-angle X-ray scattering as a contrast mechanism. A new transmission X-ray imaging technique using ultra-small-angle X-ray scattering (USAXS) as a contrast mechanism is described. USAXS imaging can sometimes provide contrast in cases where radiography and phase-contrast imaging are unsuccessful. Images produced at different scattering vectors highlight different microstructural features within the same sample volume. When used in conjunction with USAXS scans, USAXS imaging provides substantial quantitative and qualitative three-dimensional information on the sizes, shapes and spatial arrangements of the scattering objects. The imaging technique is demonstrated on metal and biological samples.

L.E. Levine and G.G. Long. Cited: Journal of Applied Crystallography, 2004, 37 Oct, p 757-765.

Microstructure-property correlations in industrial thermal barrier coatings. This paper describes the results from multidisciplinary characterization/scattering techniques used for the quantitative characterization of industrial thermal barrier coating (TBC) systems used in advanced gas turbines. While past requirements for TBCs primarily addressed the function of insulation/ life extension of the metallic components, new demands necessitate a requirement for spallation resistance/strain tolerance, i.e., prime reliance, on the part of the TBC. In an extensive effort to incorporate these TBCs, a design-of-experiment approach was undertaken to develop tailored coating properties by processing under varied conditions. Efforts focusing on achieving durable/high-performance coatings led to dense vertically cracked (DVC) TBCs, exhibiting quasi-columnar microstructures approximating electron-beam physical-vapor-deposited (EB-PVD) coatings. Quantitative representation of the microstructural features in these vastly different coatings is obtained, in terms of porosity, opening dimensions, orientation, morphologies, and pore size distribution, by means of small-angle neutron scattering (SANS) and ultra-small-angle X-ray scattering (USAXS) studies. Such comprehensive characterization, coupled with elastic modulus and thermal conductivity measurements of the coatings, help establish relationships between microstructure and properties in a systematic manner.

A.A. Kulkarni, A. Goland, H. Herman, A.J. Allen, J. Ilavsky, G.G. Long, C.A. Johnson and J.A. Ruud. Cited: Journal of the American Ceramic Society, 2004, 87 (7), Jul, p 1294-1300.

Structure of flame-made silica nanoparticles by ultra-small-angle X-ray scattering. Ultra-small-angle X-ray scattering (USAXS) of agglomerated and nonagglomerated flame-made silica nanoparticles is investigated systematically for ubiquitous characterization of particle size and degree of agglomeration. Primary particle diameters determined from the USAXS particle volume to surface ratio were compared to those obtained from nitrogen adsorption (Brunauer-Emmett-Teller (BET)) measurements. Independent of the silica precursor state (vapor or liquid), production rate (5-1100 g/h), degree of agglomeration, or flame conditions (premixed, diffusion, or spray flame), there is excellent agreement between BET and USAXS for the average primary particle diameter. Furthermore, the USAXS data reveal the effect of the fuel and precursor flow rate for various vapor- and liquid-fed flame reactors on product primary particle diameter and agglomerate size.

H.K. Kammler, G. Beaucage, R. Mueller and S.E. Pratsinis. Cited: Langmuir, 2004, 20 (5), Mar 2, p 1915-1921.

Versatile USAXS (Bonse-Hart) facility for advanced materials research. The USAXS facility at UNICAT Sector 33 at the Advanced Photon Source (APS) is a world-class resource for advanced materials research emphasizing full-range characterization of nanometer-scale to micrometer-scale microstructures. Receiving photons from an APS Undulator A X-ray source, the instrument delivers approximate to 10(13) ph s(-1) incident in a 0.4 mm x 2.5 mm area at the sample position for 10 keV photons, has an incident photon energy range from 7 keV to 19 keV, a single-scan Q range (where Q = 4pi/lambda sin theta, lambda is the photon wavelength, and 2theta is the angle of scatter) from 0.0001 Angstrom(-1) to 1 Angstrom(-1), over 10 decades of detector intensity range, absolute intensity calibration by primary methods, fluorescence rejection in the scattered beam, excellent energy resolution (Deltalambda/lambda) for anomalous USAXS, and a maximum unfocused beam size of 0.4 mm x 2.5 mm, with useful beams as small as 20 mum x 20 mum. The facility offers semi-automated data reduction, rapid and rigorous data analysis using state-of-the-art structure factors and models, and radiographic and USAXS-imaging. Both 1-D collimated (slit-smeared configuration) and 2-D collimated configurations are routinely available. Ongoing development of this facility continues in an active partnership between the instrument scientists and the user community.

I. Ilavsky, P. Jemian, A.J. Allen and G.G. Long. Cited: Synchrotron Radiation Instrumentation, 2004, 705

Size-range analysis of diesel soot with ultra-small angle X-ray scattering. Carbonaceous soot produced in a small diesel engine test facility was investigated with ultra-small-angle X-ray scattering. Three soot samples produced using a reference diesel fuel and the reference fuel plus two oxygenate additives were investigated. The presence of objects at three typical size ranges, i.e., aggregates, primary particles, and subunits. was observed. By Studying soot powders and pellets from pressed powder, a separation of scattering contributions front aggregates and primary particles was possible. The scattering curves of soot from oxygenated diesel show significant differences between samples obtained Under idle and load conditions. Soot from regular diesel fuel did not show Such differences. (C) 2004 The Combustion Institute. Published by Elsevier Inc. All rights reserved.

A. Braun, F.E. Huggins, S. Seifert, J. Ilavsky, N. Shah, K.E. Kelly, A. Sarofim and G.P. Huffman. Cited: Combustion and Flame, 2004, 137 (1-2), Apr, p 63-72.

Particle size distributions from small-angle scattering using global scattering functions. Control and quantification of particle size distribution is of importance in the application of nanoscale particles. For this reason, polydispersity in particle size has been the focus of many simulations of particle growth, especially for nanoparticles synthesized from aerosols such as fumed silica, titania and alumina. Single-source aerosols typically result in close to a log-normal distribution in size and micrograph evidence generally supports close to spherical particles, making such particles ideal candidates for considerations of polydispersity. Small-angle X-ray scattering (SAXS) is often used to measure particle size in terms of the radius of gyration, R-g, using Guinier's law, as well as particle surface area, S/V, from the Porod constant B and the scattering invariant Q. In this paper, the unified function is used to obtain these parameters and various moments of the particle size distribution are calculated. The particle size obtained from BET analysis of gas adsorption data directly agrees with the moment calculated from S/V. Scattering results are also compared with TEM particle-counting results. The potential of scattering to distinguish between polydisperse single particles and polydisperse particles in aggregates is presented. A generalized index of polydispersity for symmetric particles, PDI = BRg4/(1.62G), where G is the Guinier prefactor, is introduced and compared with other approaches to describe particle size distributions in SAXS, specifically the maximum-entropy method.

G. Beaucage, H.K. Kammler and S.E. Pratsinis. Cited: Journal of Applied Crystallography, 2004, 37 Aug, p 523-535.

Probing the dynamics of nanoparticle growth in a flame using synchrotron radiation. Flame synthesis is one of the most versatile and promising technologies for large-scale production of nanoscale materials(1-3). Pyrolysis has recently been shown to be a useful route for the production of single-walled nanotubes(4), quantum dots(5) and a wide variety of nanostructured ceramic oxides for catalysis(6) and electrochemical applications(7). An understanding of the mechanisms of nanostructural growth in flames has been hampered by a lack of direct observations of particle growth(8-21), owing to high temperatures (2,000 K), rapid kinetics (submillisecond scale), dilute growth conditions (10-6 volume fraction) and optical emission of synthetic flames. Here we report the first successful in situ study of nanoparticle growth in a flame using synchrotron X-ray scattering. The results indicate that simple growth models, first derived for colloidal synthesis(22), can be used to facilitate our understanding of flame synthesis. Further, the results indicate the feasibility of studies of nanometre-scale aerosols of toxicological(23) and environmental(24) concern.

G. Beaucage, H.K. Kammler, R. Mueller, R. Strobel, N. Agashe, S.E. Pratsinis and T. Narayanan. Cited: Nature Materials, 2004, 3 (6), Jun, p 370-374.

Mechanical behavior of alumina/poly(methyl methacrylate) nanocomposites. Alumina/poly(methyl methacrylate) (PMMA) nanocomposites were synthesized using 38 and 17 nm alumina nanoparticles. At an optimum weight fraction, the resulting nanocomposites display a room-temperature brittle-to-ductile transition in uniaxial tension with an increase in the strain-to-failure that averages 40% strain and the appearance of a well-defined yield point in uniaxial tension. Concurrently, the glass transition temperature (T-g) of the nanocomposites drops by more than 20 degreesC. The brittle-to-ductile transition is found to depend on poor interfacial adhesion between polymer and nanoparticle. This allows the nucleation of voids, typically by larger particles (similar to100 nm), which subsequently expand during loading. This void formation suppresses craze formation and promotes delocalized shear yielding. In addition, the reduction in T-g shrinks the shear yield envelope, further promoting this type of yield behavior. The brittle-to-ductile phenomenon is found to require both larger particles for void growth and smaller particles that induce the lowering of yield stress.

B.J. Ash, R.W. Siegel and L.S. Schadler. Cited: Macromolecules, 2004, 37 (4), Feb 24, p 1358-1369.