Browsing by Author "Finnie, KS"

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    Biodegradability of sol-gel silica microparticles for drug delivery
    (Springer, 2009-01) Finnie, KS; Waller, DJ; Perret, FL; Krause-Heuer, AM; Lin, HQ; Hanna, JV; Barbé, CJ
    The biodegradability of porous sol–gel silica microparticles in physiological buffers has been investigated using a USP4 flow-through dissolution tester. In the open configuration, which most closely models in-vivo conditions, the particles dissolved rapidly at pH 7.4, with a rate dependent on the surface area and media flow rate. In the closed configuration, the fastest dissolving 4 mg silica sample was almost completely dissolved in 100 mL of buffer after 36 h. The initial dissolution rates appeared relatively linear but dropped off as dissolved SiO2 concentrations approached 20–25 ppm. Addition of serum proteins acted to slow dissolution by 20–30%, suggesting a slower degradation in vivo. Silica microparticles administered for controlled release drug delivery would therefore be expected to be eliminated relatively rapidly from the body, depending on the sample size and local fluid flow conditions. © 2009, Springer. The original publication is available at www.springerlink.com
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    Crystallization of TiO2 powders and thin films prepared from modified titanium alkoxide precursors
    (Wiley-Blackwell, 2008-06) Karatchevtseva, I; Cassidy, DJ; Zhang, Z; Triani, G; Finnie, KS; Cram, SL; Barbé, CJ
    The modification of titanium alkoxides by chemical reactions with ligands yields complexes or molecular clusters that are substantially different from those of the parent alkoxides. In this study, we investigate the structural evolution of powders and thin films prepared from two titanium oxo-alkoxyacylate clusters with different oxo-core structures [Ti6(μ3-O)2(μ2-O)2](CH3COO)8(μ2-OiPr)2(OiPr)6 and [Ti6(μ3-O)6](μ-RCOO)6(OiPr)6 ([6,4] and [6,6], respectively) as a function of annealing temperature. The structural evolution of powders and thin films prepared from the corresponding parent alkoxide Ti(OiPr)4 (TiP) were also investigated for comparison. In all powders, the amorphous-to-anatase transformation occurred upon heating to 400°C. In sharp contrast, the anatase-to-rutile transformation of the powder prepared from the [6,6] cluster was significantly inhibited compared with the conventionally derived powder, with no rutile being detected even after annealing at 800°C for 1 h. This was attributed to the small crystallite size in the [6,6]-derived powder, which is lower than the critical size previously reported for the anatase-to-rutile transformation in similar sol–gel-derived materials. In thin films, the amorphous-to-anatase phase transition also occurred at temperatures as low as 400°C for coatings deposited from conventional TiP precursor and [6,4] cluster solutions. However, in contrast to the corresponding powders no rutile nucleation occurred even at 800°C in either film. © 2008, Wiley-Blackwell.
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    Effect of sol-gel encapsulation on lipase structure and function: a small angle neutron scattering study
    (Springer, 2005-01) Rodgers, LE; Holden, PJ; Knott, RB; Finnie, KS; Bartlett, JR; Foster, LJR
    The application of small angle neutron scattering (SANS) to the characterisation of sol–gel hosts containing biomolecules offers the opportunity to explore the relationship between gel structure and catalyst. A model system involving the immobilisation of Candida antarctica lipase B (CALB) was investigated. Gels were produced by fluoride-catalysed hydrolysis of fixed ratios of tetramethylorthosilicate (TMOS) and methyltrimethoxysilane (MTMS). Phase separation between the enzyme and the evolving sol–gel matrix was minimised by incorporating glycerol into the sol–gel precursor solution. The potential stabilising effect of the NaF catalyst upon the enzyme was also investigated. Scattering studies were conducted on both immobilised lipase, and lipase in free solution. Scattering studies on free enzyme provided evidence of multiple populations of enzyme aggregates and showed that choice of solvent affected the degree of aggregation. Both NaF and glycerol affected neutron scattering, indicating changes in lipase conformation. Increasing glycerol concentration increased the degree of aggregation and produced differences in solvent packing on the surface of protein molecules. Initial evidence from SANS data indicated that the presence of the enzyme during gel formation conferred structural changes on the gel matrix. Modelling the effect of sol–gel encapsulation on lipase requires comparison of data from free enzyme to the immobilised form. Removal of the enzyme from the sol–gel structure, post gelation, is necessary to better characterise the modified matrix. This methodological problem will be the subject of future investigations. © 2005, Springer.
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    Low temperature bonding of ceramics by sol-gel processing
    (Springer Nature, 2001-12) Barbé , CJ; Cassidy, DJ; Triani, G; Latella, BA; Mitchell, DRG; Finnie, KS; Bartlett, JR; Woolfrey, JL; Collins, GA
    Sol-gel bonds were produced between smooth, clean silicon or polycrystalline alumina substrates by spin-coating solutions containing partially hydrolysed silicon alkoxides onto both substrates. The two coated substrates were assembled and the resulting sandwich was fired at temperatures ranging from 300 to 600°C. The influence of the sol-gel chemistry on the film microstructure and interfacial fracture energy was investigated using a wide range of techniques, including ellipsometry, FTIR, TG-DTA, rheology, TEM and micro-indentation. For silicon wafers, an optimum water-alkoxide molar ratio of 10 and hydrolysis water pH of 2 were found. Such conditions led to relatively dense films (>90%), resulting in bonds with significantly higher fracture energy (3.5 J/m2) than those obtained using classical water bonding (typically 1.5 J/m2). Aging of the coating solution was found to decrease the bond strength. Poly-crystalline alumina substrates were similarly bonded at 600°C; the optimised silica sol-gel chemistry yielded interfaces with fracture energy of 4 J/m2. © 2000 Kluwer Academic Publishers.
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    New duplex process for corrosion protection by PI3.
    (Elsevier, 2008-06-30) Short, KT; Zhang, Z; Finnie, KS; Collins, GA; Figueroa, CA
    In this work, we report a study of a novel duplex process for corrosion protection using a CNx coating on a nitrided martensitic stainless steel by plasma immersion ion implantation (PI3). The morphology, chemical composition and electronic properties of the coating and the interface between the coating and nitrided metal were studied by SEM, EDS, Raman and XPS techniques. The corrosion behaviour of the samples was studied by electrodynamics measurements. The degradation of the corrosion resistance introduced by the PI3 plasma nitriding treatment of commercial metal alloy AISI 420 is reverted by coating the surface with an additional CNx film. © 2008, Elsevier Ltd.
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    Sol-gel tungsten oxide/titanium oxide multilayer nanoheterostructured thin films: structural and photoelectrochemical properties
    (American Chemical Society, 2007-12-20) Luca, V; Blackford, MG; Finnie, KS; Evans, PJ; James, M; Lindsay, MJ; Skyllas-Kazacos, M; Barnes, PRF
    Multilayer structures of alternating thin titanium and tungsten oxide layers having dimensions of similar to 20 nm have been fabricated from titanium alkoxide and various tungstate precursor solutions using the dip coating technique. Single, double, and triple layer titanate and tungstate thin films were deposited on silicon substrates, and these films were initially annealed at 400°C. Structural and microstructural aspects of the films were investigated using a variety of techniques, including X-ray reflectometry, grazing incidence X-ray absorption spectroscopy (GIXAS), cross-sectional transmission electron microscopy (TEM), and secondary ion mass spectrometry. The dimensions of the films and the character of the interfaces were principally gauged by cross-sectional TEM and X-ray reflectometery. All films were continuous on a local scale and had relatively low surface roughness. At the treatment temperature of 400°C, only the tungsten oxide component showed appreciable crystallinity. The multilayer films had relatively diffuse interfaces, even after annealing in air at this temperature. At these temperatures, easily measurable diffusion of tungsten into the titanium oxide component was observed, whereas the diffusion of titanium into the tungsten oxide component occurred to a lesser degree. At higher temperatures, interdiffusion of components was found to be significant. TEM, X-ray diffraction, and Ti K-edge GIXAS measurements indicated that annealing at 400°C generated films in which the titanate component remained amorphous while the tungstate component crystallized in the tetragonal modification Of WO3, which is normally stable only at high temperatures. Grazing incidence X-ray absorption spectroscopy allowed the degree of distortion of the tungsten oxygen polyhedra to be monitored as a function of depth into the film. The photoelectrochernical activity of the multilayer film electrodes was investigated, and the activity for water photo-oxidation was assessed. The photoelectrochernical response was greatest when crystalline WO3 was bounded on both sides by amorphous TiO2 layers. In this bounded state, WO3 had unique structural characteristics. © 2007, American Chemical Society
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    Structure and dehydration of the pyrochlore system NaW2−yMoyO6+δ·nH2−zO between 10 and 675 K
    (Elsevier, 2008-07) Thorogood, GJ; Kennedy, BJ; Luca, V; Blackford, MG; van de Geeste, SK; Finnie, KS; Hanna, JV; Pike, KJ
    The temperature dependence of the structure of the pyrochlore NaW2−yMoyO6+δ·nH2−zO has been investigated using a variety of diffraction and spectroscopic methods. The positions of OH−/H2O molecules in the structure have been determined. Increases in temperature induce small lattice parameter changes, which are thought to result from movement of the H2O molecules in the pyrochlore lattice. Crown Copyright © 2008 Published by Elsevier Ltd.