Browsing by Author "Woodward, RC"

Now showing 1 - 6 of 6
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    Experimental validation of proton transverse relaxivity models for superparamagnetic nanoparticle MRI contrast agents.
    (Institute of Physics, 2010-01-22) Carroll, MRJ; Woodward, RC; House, MJ; Teoh, WY; Amal, R; Hanley, TL; St Pierre, TG
    Analytical models of proton transverse relaxation rate enhancement by magnetic nanoparticles were tested by making measurements on model experimental systems in a field of 1.4 T. Proton relaxivities were measured for five aqueous suspensions of iron oxide (maghemite) nanoparticles with nominal mean particle sizes of 6, 8, 10, 11, and 13 nm. Proton relaxivity increased with mean particle size ranging from 13 s(-1) mM Fe-1 for the 6 nm sample, up to 254 s(-1) mM Fe-1 for the 13 nm sample. A strong correlation between the measured and predicted values of the relaxivity was observed, with the predicted values being consistently higher than the measured values. The results indicate that the models give a reasonable agreement with experimental results and hence can be used as the basis for the design of new magnetic resonance imaging contrast and labelling agents. © 2010, Institute of Physics
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    Investigation of field-induced ferromagnetism in Pd-Ni-Fe-P metallic glass by x-ray magnetic circular dichroism
    (American Institute of Physics, 2009-01-12) Yu, DH; Duriavig, J; Loh, NA; Woodward, RC; Lin, HJ; Chang, FH; Kilcoyne, SH; Stampfl, APJ; Robinson, RA
    We have applied x-ray magnetic circular dichroism to investigate the field-induced ferromagnetism in Pd40Ni22.5Fe17.5P20 alloy. The experiment revealed that both Ni and Fe were in a divalent state and that the magnetic properties of the material were determined by the localized 3d electrons of the transition metals. No clear evidence of Ruderman–Kittel–Kasuya–Yosida-type interaction among magnetic clusters was observed. It is believed that the detailed balance of fundamental spin-orbit and exchange interactions as a function of temperature and applied magnetic field determine the different magnetic properties of the alloy. © 2009, American Institute of Physics
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    Lanthanoid “bottlebrush” clusters: remarkably elongated metal–oxo core structures with controllable lengths
    (Journal of the American Chemical Society, 2014-10-04) D'Alessio, D; Sobolev, AN; Skelton, BW; Fuller, RO; Woodward, RC; Lengkeek, NA; Fraser, BH; Massi, M; Ogden, MI
    Large metal–oxo clusters consistently assume spherical or regular polyhedral morphologies rather than high-aspect-ratio structures. Access to elongated core structures has now been achieved by the reaction of lanthanoid salts with a tetrazole-functionalized calixarene in the presence of a simple carboxylate co-ligand. The resulting Ln19 and Ln12 clusters are constructed from apex-fused Ln5O6 trigonal bipyramids and are formed consistently under a range of reaction conditions and reagent ratios. Altering the carboxylate co-ligand structure reliably controls the cluster length, giving access to a new class of rod-like clusters of variable length. © 2014 American Chemical Society
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    Nanostructure of PEO-polyurethane-PEO triblock copolymer micelles in water.
    (Elsevier, 2010-04-01) Caba, BL; Zhang, Q; Carroll, MRJ; Woodward, RC; St Pierre, TG; Gilbert, EP; Riffle, JS; Davis, RM
    Novel hydrophilic triblock copolymers which form micelles in aqueous solution were studied by static and dynamic light scattering (SLS and DLS), small angle neutron scattering (SANS) and densitometry. The polymers were symmetric A–B–A block copolymers having two poly(ethylene oxide) (PEO) tail blocks and a polyurethane (PU) center segment that contained pendant carboxylic acids. The aggregation number of the micelles decreased with increasing PEO mass content. When attempting to fit the SANS data it was found that no single model was suitable over the entire range of block lengths and PEO mass concentrations investigated here. For the polymer with the highest aggregation number, the data were fitted with a triblock model consisting of a homogeneous core with a corona of non-interacting Gaussian chains for which only two free parameters were required: the radius of the core and the radius of gyration of the corona. In this case, the core was found to be effectively dry. At lower aggregation numbers, a star polymer model generated significantly better fits, suggesting the absence of any identifiable central core structure. Good agreement was found between the sizes measured by DLS, SANS and theoretical predictions of micelle size from a density distribution theory. These results show that when significant changes in aggregation number occur, the nanostructure of the micelle can change substantially even for polymers that are remarkably similar. © 2010, Elsevier Ltd.
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    Neutron depolarisation studies on Pd-Ni-Fe-P alloy
    (The Bragg Institute, Australian Nuclear Science and Technology Organisation, 2005-11-27) Yu, DH; Robinson, RA; Fitzsimmons, MR; Woodward, RC; Gilbert, EP
    Magnetic metallic glasses have enormous technological importance in, for example, magnetic recording, magnetic refrigeration and the construction of electrical transformers and motors. Traditionally these amorphous materials were prepared by melt spinning to form ribbons. Bulk magnetic metallic glasses based on the quaternary alloy Pd-Ni-Fe-P exhibit interesting phase behaviour depending on temperature and applied magnetic field. For the alloy of Pd40Ni22.5Fe17.5P20, paramagnetic, superparamagnetic, ferromagnetic and spin glass regions are all evidenced (Shen et al. J. Appl. Phys. 85, 4110, (1999)). It is proposed that the complex phase transitions may be due to the frustration caused by competing interactions between magnetic clusters presented in the material. We will present preliminary findings from neutron depolarization studies on the alloy of Pd40Ni22.5Fe17.5P20 as a function of temperature (RT to 10K) and applied magnetic field up to 11T. © The Authors
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    Neutron depolarization studies of Pd-Ni-Fe-P alloy
    (Elsevier, 2007-07-15) Yu, DH; Fitzsimmons, MR; Gilbert, EP; Woodward, RC; Kilcoyne, SH; Robinson, RA
    Bulk metallic glasses based on the quaternary alloy Pd-Ni-Fe-P exhibit interesting phase behavior depending on temperature and applied magnetic field. Previous work has suggested that a range of magnetic phases, including paramagnetic, superparamagnetic, ferromagnetic and spin glass, can be observed in this system. We have applied one-dimensional neutron depolarization to explore the correlation of magnetic moments in Pd40M22.5Fe17.5P20 alloy as a function of temperature and applied magnetic field. The results provided evidence for correlation lengths of similar to 200A. The nature of the correlations and the formation mechanism of the induced ferromagnetic phase are discussed. © 2007, Elsevier Ltd.