Browsing by Author "Cookson, DJ"

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    Application of SAXS to the study of particle-size-dependent thermal conductivity in silica nanofluids.
    (Springer, 2008-10) Chen, G; Yu, WH; Singh, D; Cookson, DJ; Routbort, J
    Knowledge of the size and distribution of nanoparticles in solution is critical to understanding the observed enhancements in thermal conductivity and heat transfer of nanofluids. We have applied smallangle X-ray scattering (SAXS) to the characterization of SiO2 nanoparticles (10-30 nm) uniformly dispersed in a water-based fluid using the Advanced Photon Source at Argonne National Laboratory. Size distributions for the suspended nanoparticles were derived by fitting experimental data to an established model. Thermal conductivity of the SiO2 nanofluids was also measured, and the relation between the average particle size and the thermal conductivity enhancement was established. The experimental data contradict models based on fluid interfacial layers or Brownian motion but support the concept of thermal resistance at the liquid-particle interface. © 2008, Springer.
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    The Australian National Beamline Facility at the Photon Factory
    (American Institute of Physics, 1994) Garrett, RF; Cookson, DJ; Foran, G; Creagh, DC; Wilkins, SW
    The Australian National Beamline Facility has been installed at the Photon Factory, Tsukuba, Japan. The construction and operation of the facility has been funded by a consortium of Australian research organizations, universities, and government funding agencies, with the aim of providing Australian scientists with routine access to synchrotron radiation in the hard‐x‐ray region. The first experiments were performed at the ANBF in November 1992. The facility consists of a general purpose x‐ray‐beamline, including a simple two‐crystal monochromator, delivering either monochromatic x rays (range 5–20 keV) or white radiation to the experimental hutch. The main experimental instrument, a multiconfiguration diffractometer, has recently been installed at the beamline. This unique instrument combines vacuum operation and imaging plate detectors, and can be configured for high‐resolution powder diffraction (including a time resolved mode), protein crystallography, and triple‐axis experiments. In addition, the white or monochromatic beam can pass through the diffractometer to a secondary experimental table, where experiments such as EXAFS, Laue diffraction, topography, and microbeam measurements are performed. Details of the beamline, monochromator, and diffractometer optics and performance will be described, and an overview will be given of the experimental capabilities of the facility. © 1995 American Institute of Physics.
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    Changes in metal nanoparticle shape and size induced by swift heavy-ion irradiation
    (Elsevier, 2009-03) Ridgway, MC; Kluth, P; Giulian, R; Sprouster, DJ; Araujo, LL; Schnohr, CS; Llewellyn, DJ; Byrne, AP; Foran, GJ; Cookson, DJ
    Changes in the shape and size of Co, Pt and An nanoparticles induced by swift heavy-ion irradiation (SHII) have been characterized using a combination of transmission electron microscopy, small-angle X-ray scattering and X-ray absorption near-edge Structure. Elemental nanoparticles of diameters 2-15 nm were first formed in amorphous SiO2 by ion implantation and thermal annealing and then irradiated at room temperature with 27-185 MeV Au ions as a function of fluence. Spherical nanoparticles below a minimum diameter (4-7 nm) remained spherical under SHII but progressively decreased in size as a result of dissolution into the SiO2 matrix. Spherical nanoparticles above the minimum diameter threshold were transformed to elongated rods aligned with the ion beamdirection. The nanorod width saturated at an electronic energy deposition dependent value, progressively increasing from 4-6 to 7-10nm (at 518 keV/nm, respectively) while the nanorod length exhibited a broad distribution consistent with that of the unirradiated spherical nanoparticles. The threshold diameter for spherical nanoparticle elongation was comparable to the saturation value of nanorod width. We correlate this saturation value with the diameter of the molten track induced in amorphous SiO2 by SHII. In summary, changes in nanoparticle shape and size are governed to a large extent by the ion irradiation parameters. © 2009, Elsevier Ltd.
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    Conceptual design of the small angle scattering beamline at the Australian Synchrotron
    (American Institute of Physics, 2009-01-19) Kirby, N; Boldeman, JW; Gentle, IR; Cookson, DJ
    A high performance small angle and wide angle x‐ray scattering (SAXS/WAXS) beamline is one of the initial suite of beamlines to be built at the 3 GeV Australian Synchrotron. This beamline will be ready for use in 2008, for structural analysis across a wide range of research applications over length scales of ∼ 1 to greater than 5000 Å. The instrument is intended for advanced analysis capabilities only possible using synchrotron radiation, such as time, space and energy resolved analysis, and for weak scattering systems. Photon energies will be readily variable between 5.2 and 20 keV. © 2007 American Institute of Physics.
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    Cortactin adopts a globular conformation and bundles actin into sheets
    (American Society for Biochemistry and Molecular Biology, 2008-06-06) Cowieson, NP; King, GJ; Cookson, DJ; Ross, I; Huber, T; Hume, DA; Kobe, B; Martin, JL
    Cortactin is a filamentous actin-binding protein that plays a pivotal role in translating environmental signals into coordinated rearrangement of the cytoskeleton. The dynamic reorganization of actin in the cytoskeleton drives processes including changes in cell morphology, cell migration, and phagocytosis. In general, structural proteins of the cytoskeleton bind in the N-terminal region of cortactin and regulatory proteins in the C-terminal region. Previous structural studies have reported an extended conformation for cortactin. It is therefore unclear how cortactin facilitates cross-talk between structural proteins and their regulators. In the study presented here, circular dichroism, chemical cross-linking, and small angle x-ray scattering are used to demonstrate that cortactin adopts a globular conformation, thereby bringing distant parts of the molecule into close proximity. In addition, the actin bundling activity of cortactin is characterized, showing that fully polymerized actin filaments are bundled into sheet-like structures. We present a low resolution structure that suggests how the various domains of cortactin interact to coordinate its array of binding partners at sites of actin branching. © 2008, American Society for Biochemistry and Molecular Biology
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    Crystal growth through progressive densification identified by synchrotron small-angle x-ray scattering
    (American Chemical Society, 2008-05) Li, J; Cookson, DJ; Gerson, AR
    For the first time, evolution of the interfacial structure of aluminum hydroxide nuclei forming within concentrated caustic solutions has been examined in situ in real time. In both dilute and concentrated caustic aluminate solutions (NaOH = 1.0 and 3.0 M, respectively, [NaOH]/[Al] = 1.22), the measured synchrotron small-angle X-ray scattering data indicate distinctly different surface structures throughout the maturation process. In the dilute solution, the data are consistent with a thin layer of less dense, recently accreted material on the surface of large fully dense particles-consistent with the familiar model process of species attachment to well-faceted surfaces. In contrast to this, the data for the concentrated solution are consistent with large diffuse particles growing with a mass fractal dimension of approximately 2.5 which density to form rough surface fractal particles on maturation. This unusual densification crystallization mechanism may occur in analogous concentrated systems where the fractal structures may be entropically stablized. © 2008, American Chemical Society
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    Delineating the first few seconds of supramolecular self-assembly of mesostructured titanium oxide thin films through time-resolved small angle x-ray scattering
    (American Chemical Society, 2008-10-07) Luca, V; Bertram, WK; Sizgek, GD; Yang, B; Cookson, DJ
    The early stages of evaporation induced self-assembly of titanium oxide mesophases from a precursor solution containing TiCl4 and the Pluronic triblock copolymer F-127 in HCl-water-ethanol solution have been studied using time-resolved SAXS techniques. Two experimental protocols were used to conduct these experiments. In one of these, the precursor solution was pumped around a closed loop as solvent was allowed to evaporate at a constant humidity-controlled rate. In the second protocol, a film of precursor solution was measured periodically as it dried completely to a residue under a stream of dry air. This permitted the detailed monitoring of changes in solution chemistry as a function of the elimination of volatile components followed by the actual drying process itself. The SAXS data were modeled in terms of two Guinier radii for soft nanoparticles while a broad Gaussian feature in the scatter profiles was accounted for by particle-article scattering interference due to close packing. For the initial precursor solution, one Guinier radius was found to be about 17 (A) over circle while the other ranged from 4 to 11 (A) over circle. Changing the rate of evaporation affected the two radii differently with a more pronounced effect on the smaller particle size range. Analysis gave an interparticle distance in the range 55-80 (A) over circle for the initial precursor solution which decreased steadily at both of the humidities investigated as evaporation proceeded and the particle packing increased. These results represent the first attempts to monitor in a precise fashion the growth of nano building blocks during the initial stages of the self-assembly process of a titanium oxide mesophase. © 2008, American Chemical Society
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    Direct current servo motor controlled four‐jaw slits for synchrotron radiation
    (American Institute of Physics, 1994-07-18) Garrett, RF; Cookson, DJ; Davey, P; Janky, S; Wilkins, SW
    A four‐jaw slit assembly and eight‐axis dc servo motor controller have been constructed and are in use at the Australian National Beamline Facility (ANBF) at the Photon Factory. Because of the vacuum operation of the beamline diffractometer, dc servo motors were preferred to stepper motors. Due to the large number of motors to be controlled, commercial dc servo controllers were unsuitable, and an eight‐axis controller was designed to be used in conjunction with the E500 CAMAC stepper motor controller. The system has been in use at the ANBF for about one year, and has allowed the integration of approximately 30 dc servo and stepper motors into a standard control system. © 1995 American Institute of Physics.
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    Effect of molecular weight on the mechanical and electrical properties of block copolymer electrolytes.
    (American Chemical Society, 2007-06-26) Singh, M; Odusanya, O; Wilmes, GM; Eitouni, HB; Gomez, ED; Patel, AJ; Chen, VL; Park, MJ; Fragouli, P; Latrou, H; Hadjichristidis, N; Cookson, DJ; Balsara, NP
    The relationship between ionic conductivity, morphology, and rheological properties of polystyrene-block-poly(ethylene oxide) copolymers (SEO) doped with a lithium salt, Li[N(SO2CF3)(2)], is elucidated. We focus on lamellar samples with poly(ethylene oxide) (PEO) volume fractions, phi, ranging from 0.38 to 0.55, and PEO block molecular weights, M-PEO, ranging from 16 to 98 kg/mol. The low-frequency storage modulus (G') at 90 degrees C increases with increasing M-PEO from about 4 x 10(5) to 5 x 10(7) Pa. Surprisingly, the conductivity of the SEO/salt mixtures with the molar ratio of Li to ethylene oxide moieties of 0.02 sigma, also increases with increasing M-PEO, from 6.2 x 10(-5) to 3.6 x 10(-4) S/cm at 90 degrees C. We compare sigma with the conductivity of pure PEO/salt mixtures, sigma(PEO), and find that sigma/[phi sigma(PEO)] of our highest molecular weight sample is close to 0.67, the theoretical upper limit for transport through randomly oriented lamellar grains. © 2007, American Chemical Society
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    Effects of selected process parameters on the morphology of poly(ethylene terephthalate) preforms and bottles
    (Wiley-Blackwell, 2007-10-05) Hanley, TL; Sutton, D; Karatchevtseva, I; Cookson, DJ; Burford, RP; Knott, RB
    Small-angle X-ray scattering (SAXS) studies and polarized optical microscopy were undertaken to explore possible morphological explanations for the poor mechanical strength in the petaloid bases of poly(ethylene terephthalate) bottles. With a standard commercial production line, one set of injection-molded preforms was over-packed by 1.1 wt % to investigate the effect on the molecular morphology with respect to a set of control samples. Both sets of preforms showed highly crystalline and oriented areas corresponding to the injection gate region. The main body of the control preform was amorphous, and although the overpacked preform was essentially amorphous, there was some evidence for weak crystallinity. The SAXS patterns of the bottle petaloid base blown from the corresponding preforms produced similar SAXS patterns for overpacked and control bottle bases, indicating that the commercial process is robust at least to this degree of overpacking. Optical microscopy showed detailed crystalline features around the gate region and thin crystalline layers sandwiched between a quenched skin layer in direct contact with the cold mold walls and the main flow of material into the mold. © 2007, Wiley-Blackwell.
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    High‐resolution triple‐crystal x‐ray‐diffraction experiments performed at the Australian National Beamline Facility in Japan
    (American Institute of Physics, 1994-07-18) Nikulin, AY; Stevenson, AW; Hashizume, H; Wilkins. SW; Cookson, DJ; Foran, G; Garrett, RF
    The x‐ray‐diffraction results reported here are from the first high‐resolution triple‐crystal experiments to be performed at the Australian National Beamline Facility at the Photon Factory. The heart of the facility is a multipurpose two‐axis high‐resolution vacuum diffractometer (BIGDIFF) Z. Barnea et al., Rev. Sci. Instrum. 63, 1069 (1992) capable of use for high‐resolution powder diffraction (using both conventional scintillation detectors and imaging plates), protein crystallography, reflectometry, as well as single‐crystal diffractometry. The present experiments were conducted on BIGDIFF in triple‐crystal diffraction mode with a monolithic channel‐cut Si monochromator (supplied by Professor M. Hart), a single‐crystal Si sample, and a four‐reflection monolithic channel‐cut Si analyzer crystal. The Si(111) sample is a part of a wafer which had been implanted with 100 keV B+ ions (doses 1×1015 and 5×1015 cm−2) through a one‐dimensional 0.5 μm thick oxide strip pattern with a 5.83 μm period and 4 μm open region. The triple‐crystal data were collected in the form of two‐dimensional intensity maps in the vicinity of the 111 Bragg peak, varying the sample rotation (ω) and the analyzer/scintillation detector rotation (2θ). The first results were collected in air both with the as‐described sample and after the oxide layer had been removed. Certain slice scans (one‐dimensional sections of the two‐dimensional intensity maps) were also collected with a vacuum of 1 Torr and reveal considerable improvement in signal to background. The data will be compared with a recent similar study A. Yu. Nikulin et al., J. Appl. Cryst. 27, 338 (1994) performed on BL‐14B at the Photon Factory. The new data collected in air indicate that lattice distortion may be mapped with a resolution of approximately 160 Å, to a depth of approximately 1.0 μm, providing valuable quantitative information on ion diffusion in such implanted materials. The slice scans collected in vacuum indicate that a depth resolution of 50 Å is certainly achievable using BIGDIFF. The data show the excellent potential of BIGDIFF for extremely good signal to noise and very high resolution in such experiments, and the advantages of working entirely in vacuum. © 1995 American Institute of Physics.
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    Humidity-induced phase transitions in ion-containing block copolymer membranes.
    (American Chemical Society, 2008-03-25) Park, MJ; Nedoma, AJ; Geissler, PL; Balsara, NP; Jackson, A; Cookson, DJ
    The phase behavior of ion-containing block copolymer membranes in equilibrium with humidified air is studied as a function of the relative humidity (RH) of the surrounding air, ion content of the copolymer, and temperature. Increasing RH at constant temperature results in both disorder-to-order and order-to-order transitions. In-situ small-angle neutron scattering experiments on the open block copolymer system, when combined with wafer uptake measurement, indicate that the disorder-to-order transition is driven by an increase in the partial molar entropy of the water molecules in the ordered phase relative to that in the disordered phase. This is in contrast to most systems wherein increasing entropy results in stabilization of the disordered phase. © 2008, American Chemical Society
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    Impact of controlled particle size nanofillers on the mechanical properties of segmented polyurethane nanocomposites
    (Inderscience, 2007-08-06) Finnigan, B; Casey, P; Cookson, DJ; Halley, PJ; Jack, KS; Truss, RW; Martin, DJ
    The impact of average layered silicate particle size on the mechanical properties of thermoplastic polyurethane (TPU) nanocomposites has been investigated. At fixed addition levels (3 wt% organosilicate), an increase in average particle size resulted in an increase in stiffness. Negligible stiffening was observed for the smallest particles (30 nm) due to reduced long-range intercalation and molecular confinement, as well as ineffective stress transfer from matrix to filler. At low strain (<= 100%), an increase in filler particle size was associated with an increase in the rate of stress relaxation, tensile hysteresis, and permanent set. At high strain (1200%), two coexisting relaxation processes were observed. The rate of the slower (long-term) relaxation process, which is believed to primarily involve the hard segment rich structures, decreased on addition of particles with an average diameter of 200 nm or less. At high strain the tensile hysteresis was less sensitive to particle size, however the addition of particles with an average size of 200 nm or more caused a significant increase in permanent set. This was attributed to slippage of temporary bonds at the polymer-filler interface, and to the formation of voids at the sites of unaligned tactoids. Relative to the host TPU, the addition of particles with an average size of 30 nm caused a reduction in permanent set. This is a significant result because the addition of fillers to elastomers has long been associated with an increase in hysteresis and permanent set. At high strain, well dispersed and aligned layered silicates with relatively small interparticle distances and favourable surface interactions are capable of imparting a resistance to molecular slippage throughout the TPU matrix. © 2007, Inderscience Enterprises Ltd.
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    Increased water retention in polymer electrolyte membranes at elevated temperatures assisted by capillary condensation
    (American Chemical Society, 2007-11) Park, MJ; Downing, KH; Jackson, A; Gomez, ED; Minor, AM; Cookson, DJ; Weber, AZ; Balsara, NP
    We establish a new systematic methodology for controlling the water retention of polymer electrolyte membranes. Block copolymer membranes comprising hydrophilic phases with widths ranging from 2 to 5 nm become wetter as the temperature of the surrounding air is increased at constant relative humidity. The widths of the moist hydrophilic phases were measured by cryogenic electron microscopy experiments performed on humid membranes. Simple calculations suggest that capillary condensation is important at these length scales. The correlation between moisture content and proton conductivity of the membranes is demonstrated. © 2007, American Chemical Society
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    Inverse hexagonal - inverse ribbon - lamellar gel phase transition sequence in low hydration DOPC:DOPE phospholipid mixtures
    (Elsevier, 2009-01) Kent, B; Garvey, CJ; Cookson, DJ; Bryant, G
    The inverse hexagonal to inverse ribbon phase transition in a mixed phosphatidylcholine-phosphatidylethanolamine system at low hydration is studied using small and wide angle X-ray scattering. It is found that the structural parameters of the inverse hexagonal phase are independent of temperature. By contrast the length of each ribbon of the inverse ribbon phase increases continuously with decreasing temperature over a range of 50 C. At low temperatures the inverse ribbon phase is observed to have a transition to a gel lamellar phase, with no intermediate fluid lamellar phase. This phase transition is confirmed by differential scanning calorimetry. © 2008, Elsevier Ltd.
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    Ion irradiation effects on metallic nanocrystals
    (Taylor & Francis, 2007-07) Kluth, P; Johannessen, B; Giulian, R; Schnohr, CS; Foran, GJ; Cookson, DJ; Byrne, AP; Ridgway, MC
    We have investigated structural and morphological properties of metallic nanocrystals ( NCs) exposed to ion irradiation. NCs were characterized by transmission electron microscopy in combination with advanced synchrotron-based analytical techniques, in particular X-ray absorption spectroscopy and small-angle X-ray scattering. A number of different effects were observed depending on the irradiation conditions. At energies where nuclear stopping is predominant, structural disorder/amorphization followed by inverse Ostwald ripening/dissolution due to ion beam mixing was observed for Au and Cu NCs embedded in SiO2. The ion-irradiation-induced crystalline to amorphous transition in the NCs, which cannot be achieved in the corresponding bulk metals, was attributed to their initially higher structural energy as compared to bulk material and possibly preferential nucleation of the amorphous phase at the NC/SiO2 interface. At very high irradiation energies (swift heavy ion irradiation), where the energy loss is nearly entirely due to electronic stopping, a size-dependent shape transformation of the NCs from spheres to rod like shapes was apparent in Au NCs. Our preliminary results are in good agreement with considerations on melting of the NCs in the ion track as one mechanism involved in the shape transformation. © 2007, Taylor & Francis Ltd.
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    Ion-irradiation-induced amorphization of Cu nanoparticles embedded in SiO2
    (American Physical Society, 2007-11) Johannessen, B; Kluth, P; Llewellyn, DJ; Foran, GJ; Cookson, DJ; Ridgway, MC
    Elemental Cu nanoparticles embedded in SiO2 were irradiated with 5 MeV Sn3+. The nanoparticle structure was studied as a function of Sn3+ fluence by extended x-ray absorption fine structure spectroscopy, small-angle x-ray scattering, and transmission electron microscopy. Prior to irradiation, Cu nanoparticles exhibited the face-centered-cubic structure. Upon irradiation at intermediate fluences (1×1013 to 1×1014 ions/cm2), the first nearest neighbor Cu-Cu coordination number decreased, while the Debye-Waller factor, bondlength, and third cumulant of the bondlength distribution increased. In particular, at a fluence of 1×1014 ions/cm2 we argue for the presence of an amorphous Cu phase, for which we deduce the structural parameters. Low temperature annealing (insufficient for nanoparticle growth) of the amorphous Cu returned the nanoparticles to the initial preirradiation structure. At significantly higher irradiation fluences (1×1015 to 1×1016 ions/cm2), the nanoparticles were dissolved in the matrix with a Cu coordination similar to that of Cu2O. © 2007, American Physical Society
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    Measurement of latent tracks in amorphous SiO2 using small angle x-ray scattering
    (Elsevier, 2008-06) Kluth, P; Schnohr, CS; Sprouster, DJ; Byrne, AP; Cookson, DJ; Ridgway, MC
    In this paper we present preliminary yet promising results on the measurement of latent ion tracks in amorphous, 2 mu m thick SiO2 layers using small angle X-ray scattering (SAXS). The tracks were generated by ion irradiation with 89 MeV An ions to fluences between 3 x 10(10) and 3 x 10(12) ions/cm(2). Transmission SAXS measurements show distinct scattering from the irradiated SiO2 as compared to the unirradiated material. Analysis of the SAXS spectra using a cylindrical model suggests a core-shell like density distribution in the ion tracks with a lower density core and a higher density shell as compared to unirradiated material. The total track radius of similar to 48 angstrom is in very good agreement with previous experiments and calculations based on an inelastic thermal spike model. © 2008, Elsevier Ltd.
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    Multiple-wavelength powder diffraction using imaging plates at the Australian National Beamline
    (International Union of Crystallography, 1997-08-04) Cookson, DJ; Hunter, BA; Kennedy, SJ; Garrett, RF
    The Australian powder diffractometer at the Photon Factory is capable of recording multiple powder-diffraction scans in less than 5 min per pattern using imaging plates in Debye–Scherrer geometry. This, coupled with incrementing the X-ray beam energy in suitably small steps (down to ∼2 eV) between exposures, allows fast collection of anomalous diffraction data. Data collected from a copper oxide-based superconductor at energies near the Cu K-absorption edge are presented, along with an account of the technique used to extract multiple-exposure powder-diffraction data from imaging plates. © International Union of Crystallography
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    Nanowetting of rough superhydrophobic surfaces.
    (American Institute of Physics, 2007-12-17) Zhang, HB; Lamb, RN; Cookson, DJ
    Small angle x-ray scattering has been used to investigate the in situ immersive wetting of ultrarough surfaces which exhibit superhydrophobicity with extreme water contact angle (θA=169°). Reduced scattering contrast observed from rough surfaces when partially or totally wetted reveals significant physical differences between superhydrophobic surfaces not otherwise apparent from conventional contact angle measurements. © 2007, American Institute of Physics