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 2005

Integrated chemical systems: The simultaneous formation of hybrid nanocomposites of iron oxide and organo silsesquioxanes. A sol-gel approach for the synthesis of hybrid nanocomposites of iron oxide and bridged polysilsesquioxanes has been established. The procedures allow for the simultaneous formation of iron oxide and poly silsesquioxane networks in monolithic xerogels and aerogels. These hybrid nanocomposites are synthesized from FeCl(3)center dot 6H(2)O and functionalized silsesquioxane monomers in a one-pot reaction using epoxides as a gelation agent. The porosity and microstructure of the materials have been determined by nitrogen porosimetry, electron microscopy, and ultra small-angle X-ray scattering. The hybrid nanocomposites exhibit a uniform dispersion of both components with no evidence for phase separation at length scales >5 nm. At this limit of resolution, it is not possible to distinguish between two independent interpenetrating networks integrated at molecular length scales or a random copolymer or mixtures of both.

L.H. Zhao, B.J. Clapsaddle, J.H. Satcher, D.W. Schaefer and K.J. Shea. Cited: Chemistry of Materials, 2005, 17 (6), Mar 22, p 1358-1366.

How does surface modification aid in the dispersion of carbon nanofibers? Small-angle light scattering is used to assess the dispersion behavior of vapor-grown carbon nanofibers suspended in water. These data provide the first insights into the mechanism by which surface treatment promotes dispersion. Both acid-treated and untreated nanofibers exhibit hierarchical morphology consisting of small-scale aggregates (small bundles) that agglomerate to form fractal clusters that eventually precipitate. Although the morphology of the aggregates and agglomerates is nearly independent of surface treatment, their time evolution is quite different. The time evolution of the small-scale bundles is studied by extracting the size distribution from the angle-dependence of the scattered intensity, using the maximum entropy method in conjunction with a simplified tube form factor. The bundles consist of multiple tubes possibly aggregated side-by-side. Acid oxidation has little effect on this bundle morphology. Rather acid treatment inhibits agglomeration of the bundles. The time evolution of agglomeration is followed by fitting the scattering data to a generalized fractal model. Agglomerates appear immediately after cessation of sonication for untreated fibers but only after hours for treated fibers. Eventually, however, both systems precipitate.

J. Zhao, D.W. Schaefer, D.L. Shi, J. Lian, J. Brown, G. Beaucage, L.M. Wang and R.C. Ewing. Cited: Journal of Physical Chemistry B, 2005, 109 (49), Dec 15, p 23351-23357.

Calcium alginate barrier films modified by montmorillonite clay. The goal of decreasing the permeation of small molecules through calcium alginate films is addressed by incorporating small amounts of montmorillonite clay into the polymer. Incorporation is achieved by (i) blending up to 3 wt% pre-exfoliated montmorillonite into sodium alginate polymer solutions, (ii) casting thin films, (iii) cross-linking the chains with calcium chloride solution into insoluble calcium alginate, and (iv) drying the resulting cross-linked materials. Exfoliation and dispersion of the montmorillonite platelets is assessed by light scattering and small-angle X-ray scattering. The barrier properties of the impregnated films were gauged by permeation of benzaldehyde using a Hanson-Research diffusion cell. Decreased permeability is found at clay loadings below 3 wt%.

J.M. Vale, R.S. Justice, D.W. Schaefer and J.E. Mark. Cited: Journal of Macromolecular Science-Physics, 2005, B44 (6), p 821-831.

Clustering and mechanics in dense depletion and thermal gels. We report on the microstructure and mechanical properties (elastic modulus) of concentrated depletion and thermal gels of octadecyl-coated silica particles for different values of the strength of interaction-polymer concentration for depletion gels and temperature for thermal gels. The depletion gels are composed of dense clusters and voids, while the thermal gels are devoid of clusters. Shear breaks up clusters in depletion gels while it induces clustering in the thermal gels. In both of these gels, the microstructure recovers to the presheared state upon cessation of shear. The recovery of the elastic modulus mimics the microstructure in the sense that the elastic modulus recovers to the presheared sheared state after shearing is stopped. Calculations of the gel boundary by modeling the interactions with an effective one-component square-well model reveals that suspensions with similar ranges of attraction gel at the same volume fraction at a fixed strength of attraction. Calculations of the elastic modulus using the naive mode coupling theory for depletion gels are in good agreement with experimental measurements provided clustering is taken into account and have the same magnitude as the elastic moduli of thermal gels with similar strengths of attraction. These calculations, in addition to the experimental observations reinforce the point that the microscopic parameter determining the elastic modulus of dense gels and its recovery is the localization length which is only a fraction of the particle diameter and not the structure on the length scale of the particle diameter and larger.

S. Ramakrishnan, V. Gopalakrishnan and C.F. Zukoski. Cited: Langmuir, 2005, 21 (22), Oct 25, p 9917-9925.

Soy-oil-based segmented polyurethanes. Segmented polyurethanes were prepared from soy polyol, diphenyl methane diisocyanate (MDI), and ethylene glycol or butane diol as chain extenders. Samples were prepared with true hard-segment concentrations (HSC) of about 0, 10, and 40%. Both the soft MDI-polyol and hard MDI/diol segments are glassy at room temperature. These samples were also crosslinked through the polyfunctional polyol soft segment. Partial crystallinity and phase separation were detected in samples with 40% HSC, on the basis of DSC data. Small-angle X-ray scattering shows the existence of phase separation with domain sizes of about 10 nm in the 40% HSC samples, but not in the others. The distribution of domain sizes is considerably broader for the ethylene-glycol extended system compared with that for the butane-diol case. Although the presence of hard segments lowers the crosslink density, samples with higher HSC had higher glass transition temperatures, higher strengths, higher moduli, lower swelling, lower elongation at break, and lower impact strengths. (c) 2005 Wiley Periodicals, Inc.

Z.S. Petrovic, M.J. Cevallos, I. Javni, D.W. Schaefer and R. Justice. Cited: Journal of Polymer Science Part B-Polymer Physics, 2005, 43 (22), Nov 15, p 3178-3190.

Plasma spray coatings for producing next-generation supported membranes. Ceramic systems as membranes play a critical role in synthesis gas production as well as gas separation technologies. This paper presents, the potential for thermal spray technology in natural gas-related programs, with a special emphasis on the production Of ceramic membranes for oxygen gas separation processes. Yttria-stabilized zirconia (YSZ) coatings were deposited Under different environments (air and vacuum) resulting in altered pore and crack distributions introduced during the spray process. We report on the characterization of these coatings using small-angle neutron Scattering (SANS) and ultrasmall-angle X-ray scattering (USAXS) to explain the different pore structures observed for the two coating conditions. A quantitative representation of the microstructural features in these coatings is presented in terms of porosity, anisotropic void surface area and pore size distribution. Also. thermal and mechanical properties, complemented with impedance spectroscopy measurements, help Understand coating behavior. Such comprehensive characterization, coupled with property measurements of the coatings, successfully demonstrates the potential of thermal spray technology in membrane production.

A.A. Kulkarni, S. Sampath, A. Goland, H. Herman, A.J. Allen, J. Ilavsky, W.Q. Gong and S. Gopalan. Cited: Topics in Catalysis, 2005, 32 (3-4), Mar, p 241-249.

Advanced microstructural characterization of plasma-sprayed zirconia coatings over extended length scales. Achieving control of the microstructure of plasma-sprayed thermal barrier coating (TBC) systems offers an opportunity to tailor coating properties to demanding applications. Accomplishing this requires a fundamental understanding of the correlations among processing, microstructure development, and related TBC properties. This article describes the quantitative characterization of the microstructure of plasma-sprayed partially stabilized zirconia (PSZ) coatings by means of x-ray and neutron-scattering imaging techniques. Small-angle neutron scattering, ultra-small-angle x-ray scattering, and x-ray microtomography were used to characterize and visualize the nature and structure of the features in these material systems. In addition, the influence of processing parameters on microstructure development is discussed along with thermal cycling effects on the pore morphology, and their resultant influence of the porosity on the thermal conductivity and elastic modulus of plasma-sprayed PSZ TBCs.

A.A. Kulkarni, A. Goland, H. Herman, A.J. Allen, J. Ilavsky, G.G. Long and F. De Carlo. Cited: Journal of Thermal Spray Technology, 2005, 14 (2), Jun, p 239-250.

Monitoring simultaneously the growth of nanoparticles and aggregates by in situ ultra-small-angle x-ray scattering. Ultra-small-angle x-ray scattering can provide information about primary particles and aggregates from a single scattering experiment. This technique is applied in situ to flame aerosol reactors for monitoring simultaneously the primary particle and aggregate growth dynamics of oxide nanoparticles in a flame. This was enabled through the use of a third generation synchrotron source (Advanced Photon Source, Argonne IL, USA) using specialized scattering instrumentation at the UNICAT facility which is capable of simultaneously measuring nanoscales to microscales (1 nm to 1 mu m). More specifically, the evolution of primary-particle diameter, mass-fractal dimension, geometric standard deviation, silica volume fraction, number concentration, radius of gyration of the aggregate, and number of primary particles per aggregate are measured along the flame axis for two different premixed flames. All these particle characteristics were derived from a single and nonintrusive measurement technique. Flame temperature profiles were measured in the presence of particles by in situ Fourier transform infrared spectroscopy and thermophoretic sampling was used to visualize particle growth with height above the burner as well as in the radial direction. (C) 2005 American Institute of Physics.

H.K. Kammler, G. Beaucage, D.J. Kohls, N. Agashe and J. Ilavsky. Cited: Journal of Applied Physics, 2005, 97 (5), Mar 1, p -.

Interface morphology and phase separation in polymer-dispersed liquid crystal composites. It is widely appreciated that electro-optic activity in polymer-dispersed liquid crystals (PDLCs) depends on separation of the polymer and liquid crystal (LC) phases. Since the phase structure develops in a non-equilibrium system, the morphology of the LC domains depends on the details of the chemical and physical processes active during domain formation. The nature of the interface between the polymer and liquid crystal phases is of particular interest. This work discusses the two-phase morphology in an acrylate-based system that develops during polymerization-induced phase separation (PIPS). Using small-angle X-ray scattering (SAXS) and ultra-small-angle X-ray scattering (USAXS), we find that interfaces in PDLCs developed from an acrylate-based recipe are more disordered than generally appreciated. Information gained from SAXS and USAXS is compared to data from scanning electron microscopy (SEM) and transmission electron microscopy (TEM). To elucidate the apparent discrepancies between imaging and scattering, we investigated the effects of SEM sample preparation. We observe significant alteration of the interface morphology due to the leaching of the LC phase. © 2005 Elsevier Ltd. All rights reserved.

R.S. Justice, D.W. Schaefer, R.A. Vaia, D.W. Tomlin and T.J. Bunning. Cited: Polymer, 2005, 46 (12), May 26, p 4465-4473.

Morphological characterization of carbon-nanofiber-reinforced epoxy nanocompsites using ultra-small angle scattering. R.S. Justice, D.P. Anderson, J.M. Brown, K. Lafdi and D.W. Schaefer. Cited: Abstracts of Papers of the American Chemical Society, 2005, 230 Aug 28, p U3511-U3511.

Versatile USAXS (Bonse-Hart) facility for advanced materials research. P.R. Jemian. Cited: Abstracts of Papers of the American Chemical Society, 2005, 230 Aug, p 74-PMSE.

Microstructure Characterization of Thermal Barrier Coating Deposits - Practical Models from Measurements. J. Ilavsky, A. Allen, T. Dobbins, A. Kulkarni and H. Herman. Cited: Thermal Spray Connects: Explore its surfacing potential! Proceedings of the ITSC 2005 (Conf. Proc.) (Basel, Switzerland), Vol. Ed., ASM International, 2005,

Cage melting and viscosity reduction in dense equilibrium suspensions. Zero-shear viscosities of dense colloidal suspensions are strongly correlated with the dynamics of particles in cages produced by nearest neighbors. At a given volume fraction, repulsive or attractive interparticle forces are expected to enhance cages, slow dynamics, and increase zero-shear rate viscosities. However, recent studies have shown that hard sphere glasses melt when depletion attractions are introduced, and this is correlated with the break up of local cages and enhancentent of density fluctuation relaxation rates. Glass formation in hard sphere suspensions is attributed to the loss of free volume and the entropic localization of particles. Melting is associated with the ability of depletion attractions to increase the local free volume due to a decrease in nearest-neighbor cages. Here, we report evidence for the reduction in the zero-shear viscosity of dense hard and near-hard sphere suspensions, as the strength of depletion attractions increases, at Volume fractions well below the experimental glass and gel transitions. Increasing the strength of depletion attractions is found to drive suspension viscosities through a minimum. The magnitude of the drop in zero-shear viscosity grows in magnitude as the volume fraction is increased. These results suggest that the localization and cage effects that characterize glass formation originate at volume fractions below those associated with glass formation. Experimental results are compared with models that incorporate the effects of microstructure on suspension dynamics. (c) 2005 The Society of Rheology.

V. Gopalakrishnan, S.A. Shah and C.F. Zukoski. Cited: Journal of Rheology, 2005, 49 (2), Mar-Apr, p 383-400.

Hierarchical morphology of carbon single-walled nanotubes during sonication in an aliphatic diamine. Dispersion of single-walled carbon nanotubes (SWNTs) by sonication into diamine curing agents is studied as a means to improve the dispersion of SWNTs in cured epoxy. Cured and uncured specimens are analyzed by light microscopy, electron microscopy, light scattering (LS), ultra small-angle X-ray scattering (USAXS), electrical conductivity and Raman spectroscopy. A flexible diamine (D2000) forms a stable SWNT suspension leading to good homogeneity in both the diamine and the cured epoxy. High resolution transmission electron microscopy (TEM) shows that small ropes of SWNTs (mostly under 15 nm) are present despite the sample's visual homogeneity. Further morphological investigation of cured and uncured D2000 resins using light and small-angle X-ray scattering indicates that the SWNTs are networked into fractal clusters that electrically percolate at low SWNTs loadings (0.05 wt%). Published by Elsevier Ltd.

J.M. Brown, D.P. Anderson, R.S. Justice, K. Lafdi, M. Belfor, K.L. Strong and D.W. Schaefer. Cited: Polymer, 2005, 46 (24), Nov 21, p 10854-10865.

X-ray scattering and spectroscopy studies on diesel soot from oxygenated fuel under various engine load conditions. Diesel soot from reference diesel fuel and oxygenated fuel under idle and load engine conditions was investigated with X-ray scattering and X-ray carbon K-edge absorption spectroscopy. Up to five characteristic size ranges were found. Idle soot was generally found to have larger primary particles and aggregates but smaller crystallites, than load soot. Load soot has a higher degree of crystallinity than idle soot. Adding oxygenates to diesel fuel enhanced differences in the characteristics of diesel soot, or even reversed them. Aromaticity of idle soot from oxygenated diesel fuel was significantly larger than from the corresponding load soot. Carbon near-edge X-ray absorption fine structure (NEXAFS) spectroscopy was applied to gather information about the presence of relative amounts of carbon double bonds (C=C, C=O) and carbon single bonds (C-H, C-OH, COOH). Using scanning X-ray transmission microspectroscopy (STXM), the relative amounts of these carbon bond states were shown to vary spatially over distances approximately 50 to 100 nm. The results from the X-ray techniques are supported by thermo-gravimetry analysis and high-resolution transmission electron microscopy. (C) 2005 Elsevier Ltd. All rights reserved.

A. Braun, N. Shah, F.E. Huggins, K.E. Kelly, A. Sarofim, C. Jacobsen, S. Wirick, H. Francis, J. Ilavsky, G.E. Thomas and G.P. Huffman. Cited: Carbon, 2005, 43 (12), Oct, p 2588-2599.

Diesel soot in the light of synchrotron radiation - A review of USAXS, WAXS, and NEXAFS data. A. Braun, S. Seifert, J. Ilavsky, S. Mun, S. Ehrlich, S. Wirick, A. Kubatova, N. Shah, F. Huggins, K. Kelly, M.M. Maricq and G.P. Huffman. Cited: Abstracts of Papers of the American Chemical Society, 2005, 229 Mar 13, p U864-U864.

Deformation of diesel soot aggregates as a function of pellet pressure: A study with ultra-small-angle x-ray scattering. Diesel soot powder generated under idle and load engine conditions was pressed into pellets at pressures ranging up to approximately 8.5 GPa. Soot powder was also immersed in acetone in order to obtain soot aggregates without agglomeration. Small-angle x-ray scattering was carried out on the powder, the pellets, and on the acetone-immersed soot. Powder and pellets show characteristic aggregate structure at small scattering vectors. Scattering curves of the pellets show a shift of the aggregate size-related scattering feature towards larger scattering vectors for increasing pressure. For the highest pressures, this aggregate structure vanished, while the suspected primary particle scattering became visible as the asymptote of the aggregate scattering structure. Soot was immersed and ultrasonicated in acetone to prevent agglomeration of aggregates, which naturally occurs in powders. This can be considered as the simulation of asymptotic behavior for vanishing pressure. Aggregate size of powder was about 290 nm for the idle soot and 240 nm for the load soot. Primary particle sizes were 14.3 and 10.2 nm, respectively. The idle soot showed a higher compressibility (0.9 GPa/nm) than the load soot (12.0 GPa/nm). Pressing the soot into pellets eliminates scattering structures from aggregation of primary particles and provides a good route to reveal the otherwise inaccessible primary particle scattering. In addition, studying the aggregate structure as a function of pellet pressure allows us to derive compacticity data of the soot. (c) 2005 American Institute of Physics.

A. Braun, J. Ilavsky, S. Seifert and P.R. Jemian. Cited: Journal of Applied Physics, 2005, 98 (7), Oct 1, p -.

Ostwald ripening of cobalt precipitates in silica aerogels? An ultra-small-angle X-ray scattering study. Monolithic silica aerogels with radial symmetry were synthesized by supercritical drying, doped to 2% and 10% with cobalt, and reduced with hydrogen. All samples were investigated with ultra-small-angle X-ray scattering. The nondoped aerogels have three populations of scatterers with radii of gyration of about 10, 40 and 60 - 70 Angstrom. The doped aerogels show an additional structure with a radius of gyration ranging from 1050 to 3000 Angstrom. This structure causes intensity oscillations, thus revealing a relatively narrow size distribution. Scattering curves of the 10%-doped aerogels fitted well to a Lifshitz-Slyozov-Wagner particle size distribution, thus revealing that Ostwald ripening might have occurred during aerogel preparation. The same range also shows differences depending on whether the samples were reduced, or in their as-prepared condition. Scattering curves obtained from the cylinder-axis region were different from the scattering curves obtained from the sample boundary, indicating a process-dependent skin effect.

A. Braun, J. Ilavsky, B.C. Dunn, P.R. Jemian, F.E. Huggins, E.M. Eyring and G.P. Huffman. Cited: Journal of Applied Crystallography, 2005, 38 Feb, p 132-138.

Characterization of ceramics by X-ray and neutron small-angle scattering. This paper reviews some recent advances in small-angle X-ray and neutron scattering methods and their application to address complex issues in ceramic systems of technological importance. It is shown how small-angle scattering (SAS) can be applied to ceramic systems in order to extract statistically representative microstructure information (e.g., void volume fraction size distributions, internal surface areas, pore morphologies) that complements the information obtained from diffraction methods, X-ray microtomography, or electron microscopy. It is demonstrated how SAS studies provide insights, not obtainable by other means, on the processing-microstructure-property relationships that frequently govern technological performance.

A.J. Allen. Cited: Journal of the American Ceramic Society, 2005, 88 (6), Jun, p 1367-1381.