Kim S. Finnie

Electrostatic Self-Assembly of PEG Copolymers onto Porous Silica Nanoparticles

A critical requirement toward the clinical use of nanocarriers in drug delivery applications is the development of optimal biointerfacial engineering procedures designed to resist biologically nonspecific adsorption events. Minimization of opsonization increases blood residence time and improves the ability to target solid tumors. We report the electrostatic self-assembly of polyethyleneimine-polyethylene glycol (PEI-PEG) copolymers onto porous silica nanoparticles. PEI-PEG copolymers were synthesized and their adsorption by self-assembly onto silica surfaces were investigated to achieve a better understanding of structure-activity relationships. Quartz-crystal microbalance (QCM) study confirmed the rapid and stable adsorption of the copolymers onto silica-coated QCM sensors driven by strong electrostatic interactions. XPS and FT-IR spectroscopy were used to analyze the coated surfaces, which indicated the presence of dense PEG layers on the silica nanoparticles. Dynamic light scattering was used to optimize the coating procedure. Monodisperse dispersions of the PEGylated nanoparticles were obtained in high yields and the thin PEG layers provided excellent colloidal stability. In vitro protein adsorption tests using 5% serum demonstrated the ability of the self-assembled copolymer layers to resist biologically nonspecific fouling and to prevent aggregation of the nanoparticles in physiological environments. These results demonstrate that the electrostatic self-assembly of PEG copolymers onto silica nanoparticles used as drug nanocarriers is a robust and efficient procedure, providing excellent control of their biointerfacial properties.

Quantum dot and silica nanoparticle doped polymer optical fibers.

A novel and highly versatile doping method has been developed to allow active dopants, including materials incompatible with the polymer matrix, to be incorporated into microstructured polymer optical fibers through the use of nanoparticles. The incorporation of quantum dots and silica nanoparticles containing Rhodamine isothiocyanate is demonstrated.

Examination of U valence states in the brannerite structure by near-infrared diffuse reflectance and X-ray photoelectron spectroscopies

Abstract The valence state of uranium doped into a f 0 thorium analog of brannerite (i.e., thorutite) has been examined using near-infrared (NIR) diffuse reflectance (DRS) and X-ray photoelectron (XPS) spectroscopies. NIR transitions of U 4+ , which are not observed in spectra of brannerite, have been detected in the samples of U x Th 1− x Ti 2 O 6 , and we propose that strong specular reflectance is responsible for the lack of U 4+ features in UTi 2 O 6 . Characteristic U 5+ bands have been identified in samples in which sufficient Ca 2+ has been added to nominally effect complete oxidation to U 5+ . XPS results support the assignments of U 4+ and U 5+ by DRS. The presence of residual U 4+ bands in the spectra of the Ca-doped samples is consistent with segregation of Ca 2+ to the grain boundaries during high temperature sintering.

Atomic layer deposition of TiO2 and Al2O3 thin films and nanolaminates

We have been developing our capability with atomic layer deposition (ALD), to understand the influence of deposition parameters on the nature of TiO2 and Al2O3 films (high and low refractive index respectively), and multilayer stacks thereof (nanolaminates). These stacks have potential applications as anti-reflection coatings and optical filters. This paper will explore the evolution of structure in our films as a function of deposition parameters including temperature and substrate surface chemistry. A broad range of techniques have been applied to the study of these films, including cross-sectional transmission electron microscopy, spectroscopic ellipsometry and secondary-ion mass spectrometry. These have enabled a wealth of microstructural and compositional information on the films to be acquired, such as accurate film thickness, composition, crystallization sequence and orientation with respect to the substrate. The ALD method is shown to produce single-layer films and multilayer stacks with exceptional uniformity and flatness, and in the case of stacks, chemically abrupt interfaces. We are currently extending this technology to the coating of polymeric substrates.

Atomic Layer Deposition of TiO2 / Al2O3 Films For Optical Applications

Atomic layer deposition (ALD) is an important technology for depositing functional coatings on accessible, reactive surfaces with precise control of thickness and nanostructure. Unlike conventional chemical vapour deposition, where growth rate is dependent on reactant flux, ALD employs sequential surface chemical reactions to saturate a surface with a (sub-) monolayer of reactive compounds such as metal alkoxides or covalent halides, followed by reaction with a second compound such as water to deposit coatings layer-by-layer. A judicious choice of reactants and processing conditions ensures that the reactions are self-limiting, resulting in controlled film growth with excellent conformality to the substrate. This paper investigates the deposition and characterisation of multi-layer TiO2 /Al2O3 films on a range of substrates, including silicon <100>, soda glass and polycarbonate, using titanium tetrachloride/water and trimethylaluminium/water as precursor couples. Structure-property correlations were established using a suite of analytical tools, including transmission electron microscopy (TEM), secondary ion mass spectrometry (SIMS), X-ray reflectometry (XRR) and spectroscopic ellipsometry (SE). The evolution of nanostructure and composition of multi-layer high/low refractive index stacks are discussed as a function of deposition parameters.

Geopolymers for the Immobilization of Radioactive Waste

Geopolymers are made by adding aluminosilicates to concentrated alkali solutions for dissolution and subsequent polymerization to form a solid. They are amorphous to semicrystalline three dimensional aluminosilicate networks. Although they have been used in several applications their widespread use is restricted due to lack of long term durability studies and detailed scientific understanding. Three important tools for the study of geopolymers are transmission electron microscopy (TEM), solid state magic angle spinning nuclear magnetic resonance (MAS NMR) and infra red (IR) spectroscopy. Cs and Sr are two of the most difficult radionuclides to immobilize and are therefore suitable elements to study in assessing geopolymers as matrices for immobilization of radioactive wastes. In this study Cs or Sr was added to geopolymer samples prepared using fly ash precursors. A commercial metakaolinite geopolymer was studied for comparison. The geopolymers were mainly amorphous as shown by TEM, whether they were made from fly ash or metakaolinite. In the fly ash geopolymer, Cs preferentially inhabited the amorphous phase over the minor crystalline phases, whereas Sr was shared in both. The MAS NMR showed that Cs is held mostly in the geopolymer structure for both fly ash and metakaolinite geopolymers. The IR spectra showed a slight shift in antisymmetric Si-O-Al stretch band to a lower wavenumber for the fly ash geopolymer, which implies that more Al is incorporated in this geopolymer structure than in the metakaolinite geopolymer.

The replacement of titanium by zirconium in ceramics for plutonium immobilization

Zirconates and titanates, based on the nominal baseline composition developed for the Plutonium Immobilization Project, have been prepared with and without process impurities. The titanates form pyrochlore as the major phase and the zirconates form a defect-fluorite. Very little, if any, of each impurity is accommodated in the defect-fluorite with powellite, kimzeyite, a spinel and a silicate glass appearing as extra phases in this ceramic. In the titanate ceramics the pyrochlore incorporates more impurities, with the remainder forming zirconolite and a small amount of silicate glass. At extreme levels of impurities, traces of magnetoplumbite, perovskite and loveringite were found. The defect-fluorite zirconate phase is more radiation damage resistant than the titanate pyrochlore, though the secondary phases in the zirconate will reduce the radiation damage resistance of zirconate monoliths. To produce a dense product the oxide-route zirconate required sintering temperatures of about 1550 C, 200 C higher than that required for the titanate. Silicate impurities reduce the sintering temperatures appreciably.

Sol-Gel Synthesis of Complex Titanates in Micro-Emulsions

Amorphous precursor nanopowders of zirconolite (CaZrTi2O7) were prepared using a water-in-oil micro-emulsion synthesis, with Ti(OiC3H7)4, Zr(OnC3H7)4 and either Ca(OC2H5)2 or an aqueous Ca(NO3)2 solution as precursors. The stoichiometry and structural evolution of the nanoparticles were investigated using a range of techniques, including ICP-MS, TEM, gas adsorption and vibrational spectroscopy. The use of Ca(OC2H5)2 led to slightly sub-stoichiometric nanopowders (CaxZrTi2O6+x, x = 0.8), following washing. Lower values of x were obtained in the washed nanopowders when using Ca(NO3)2, with x = 0.004, 0.022 or 0.52 at pH 2, 7 or 13, respectively. In the latter system, a comparison between the washed and unwashed nanopowders revealed that 25% of the calcium was lost during washing. The Ca(NO3)2 was found to form unstable tetraamine complexes within the reverse micelles at high pH, which transformed into Ca(OH)2 on ageing. The Ca(OH)2 can then interact with the hydrolysed titanium/zirconium alkoxides, and thus be integrated chemically into the final nanoparticle structure.

Atomic layer deposition (ALD) of TiO2 and Al2O3 thin films on silicon

The essential features of the ALD process involve sequentially saturating a surface with a (sub)monolayer of reactive species, such as a metal halide, then reacting it with a second species to form the required phase in-situ. Repetition of the reaction sequence allows the desired thickness to be deposited. The self-limiting nature of the reactions ensures excellent conformality, and sequential processing results in exquisite control over film thickness, albeit at rather slow deposition rates, typically <200nm/hr. We have been developing our capability with ALD deposition, to understand the influence of deposition parameters on the nature of TiO2 and Al2O3 films (high and low refractive index respectively), and multilayer stacks thereof. These stacks have potential applications as anti-reflection coatings and optical filters. This paper will explore the evolution of structure in our films as a function of deposition parameters including temperature and substrate surface chemistry. A broad range of techniques have been applied to the study of these films, including cross sectional transmission electron microscopy, spectroscopic ellipsometry, secondary ion mass spectrometry etc. These have enabled a wealth of microstructural and compositional information on the films to be acquired, such as accurate film thickness, composition, crystallization sequence and orientation with respect to the substrate. The ALD method is shown to produce single layer films and multilayer stacks with exceptional uniformity and flatness, and in the case of stacks, chemically abrupt interfaces. We are currently extending this technology to the coating of polymeric substrates.

Characterization of thin metal oxide films grown by atomic layer deposition

Atomic layer deposition (ALD) is a versatile technique for producing a wide variety of thin films. It provides a method for precisely controlling film thickness and composition. In addition films produced by ALD are highly conformal and are therefore excellent for the generation of MEMS devices. In the present study, single and multi layer films of TiO2 and Al2O3 have been deposited on silicon substrates at 200 and 300°C. These films have been characterised by a number of surface analytical techniques including dynamic secondary ion mass spectrometry (SIMS), ion beam analysis, electron microscopy and spectroscopic ellipsometry. These methods have enabled the optical, chemical and structural properties of the films to be accurately assessed. The results obtained to date demonstrate that ALD produces highly uniform single and multi layer films with minimal impurities. These high quality films are being applied to new opportunities for the development of future MEMS devices.