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Michael H Bartl

Publications and source records attributed to Michael H Bartl.

10 recordsLinked to original sources
PubMed2005

Structural analysis of hybrid titania-based mesostructured composites.

High-optical-quality titania-based mesostructured films with cubic or 2D-hexagonal symmetry were fabricated by combining trifluoroacetate (TFA)-modified titanium precursors with amphiphilic triblock poly(ethylene oxide)-poly(propylene oxide)-poly(ethylene oxide) (PEO-PPO-PEO) copolymers. The distribution, dynamics, and local environments of the TFA-modified titania, PEO, and PPO components of the hybrid were investigated. IR/Raman spectroscopy, in situ small-angle X-ray scattering, and transmission electron microscopy studies indicate that TFA coordinates the titanium center and forms a stable complex that is subsequently organized by the block copolymer species into ordered mesostructures. Solid-state NMR (19)F-->(1)H cross-polarization, (13)C{(1)H} two-dimensional heteronuclear correlation, and (1)H relaxation techniques were used to determine that PEO is predominantly incorporated within the TFA-modified titania, and that PPO environments encompass both microphase separated regions and interfacial regions composed of mixed PPO and TFA-modified titania. NMR (19)F multiple-quantum spin counting measurements suggest that -CF(3) groups of the trifluoroacetate ligands do not form clusters but instead randomly distribute within the inorganic component of the hybrid.

Journal Article↗
PubMed2005

3-D molecular assembly of function in titania-based composite material systems.

Various examples of composite titania-based nanostructured materials exhibiting cooperative functionalities between different active components are presented. The fabrication of these integrated composite materials is based on one-pot supramolecular templating techniques combined with acidic sol-gel chemistry. The defined 3-D nanoscale organization and integration of various functional components results in advanced optoelectronic and photonic applications such as visible light sensitization of mesoporous titania photocatalysts with cadmium sulfide nanocrystals acting as sensitizing integral part of the mesopore wall structure, narrow bandwidth emission from rare earth ion activated nanocrystalline mesoporous titania films, and mirrorless lasing in dye-doped hybrid organic/inorganic mesostructured titania waveguides.

Journal Article↗
PubMed2004

Dye-activated hybrid organic/inorganic mesostructured titania waveguides.

A room-temperature synthesis route for the fabrication of a new type of hybrid organic/inorganic mesostructured material based on titania instead of silica as the inorganic component has been developed. This approach enables facile processing of the titania/block copolymer surfactant precursor solution into optically activated, transparent, and crack-free fibers and planar waveguides with adjustable thickness. Stabilization of the structures occurs upon solvent evaporation by formation of a solid, glasslike material without heat treatment. These dye-activated, high refractive index, titania-based composites show efficient waveguiding and mirrorless lasing at low thresholds without the need of an ultralow refractive index support layer.

Journal Article↗
PubMed2003

Spontaneous formation of nanoparticle vesicles from homopolymer polyelectrolytes.

Nanoparticle vesicles were spontaneously assembled from homopolymer polyamine polyelectrolytes and water-soluble, citrate-stabilized quantum dots. The further addition of silica nanoparticles to a solution of quantum dot vesicles generated stable micrometer-sized hollow spheres whose walls were formed of a thick, inner layer of close-packed quantum dots followed by an outer layer of silica. The method employed here to assemble both the nanoparticle vesicles and the hollow spheres is in direct contrast to previous syntheses that use either tailored block copolymers or oil-in-water emulsion templating. We propose that the formation of charge-stabilized hydrogen bonds between the positively charged amines of the homopolymer polyelectrolytes and the negatively charged citrate molecules stabilizing the quantum dots is responsible for the macroscopic phase separation in this completely aqueous system. The ease and processibility of the present approach gives promise for the production of a diverse array of materials ranging in applications from drug delivery to catalysis to micrometer-scale optical devices.

Journal Article↗
PubMed2002

Benzyl alcohol and transition metal chlorides as a versatile reaction system for the nonaqueous and low-temperature synthesis of crystalline nano-objects with controlled dimensionality.

The reaction of transition metal chlorides with benzyl alcohol leads at low temperatures to oxidic nanostructures with low-dimensional particle shapes such as nearly spherical titania anatase nanoparticles, vanadium oxide nanorods, and tungsten oxide nanoplatelets. The process is simple, allows a scale-up in gram quantities, and leads to highly crystalline materials. Ethanol solutions containing tungsten oxide nanoparticles exhibit blue luminescence upon UV irradiation at room temperature.

Journal Article↗
PubMed2002

High abrasion resistance with sparse mineralization: copper biomineral in worm jaws.

Biominerals are widely exploited to harden or stiffen tissues in living organisms, with calcium-, silicon-, and iron-based minerals being most common. In notable contrast, the jaws of the marine bloodworm Glycera dibranchiata contain the copper-based biomineral atacamite [Cu2(OH)3Cl]. Polycrystalline fibers are oriented with the outer contour of the jaw. Using nanoindentation, we show that the mineral has a structural role and enhances hardness and stiffness. Despite the low degree of mineralization, bloodworm jaws exhibit an extraordinary resistance to abrasion, significantly exceeding that of vertebrate dentin and approaching that of tooth enamel.

Animals↗