24 results on '"Thomas R. Gengenbach"'
Search Results
2. Tunable Biogenic Manganese Oxides
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Alexandr N. Simonov, Christine A. Romano, Hannah J. King, Lisandra L. Martin, Lizhi Tao, William H. Casey, Leone Spiccia, Shannon A. Bonke, Bradley M. Tebo, Tim Williams, Thomas R. Gengenbach, Rosalie K. Hocking, Xi-Ya Fang, and Dijon A. Hoogeveen
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Birnessite ,Morphology (linguistics) ,Absorption spectroscopy ,Inorganic chemistry ,chemistry.chemical_element ,02 engineering and technology ,Manganese ,010402 general chemistry ,01 natural sciences ,Catalysis ,Reactivity (chemistry) ,biogenic materials ,tunable morphology ,MnxEFG protein complex ,structure elucidation ,Organic Chemistry ,General Chemistry ,021001 nanoscience & nanotechnology ,Manganese oxide ,0104 chemical sciences ,chemistry ,structural disorder ,Transmission electron microscopy ,Chemical Sciences ,manganese ,0210 nano-technology - Abstract
Influence of the conditions for aerobic oxidation of Mn2+(aq) catalysed by the MnxEFG protein complex on the morphology, structure and reactivity of the resulting biogenic manganese oxides (MnOx ) is explored. Physical characterisation of MnOx includes scanning and transmission electron microscopy, and X-ray photoelectron and K-edge Mn, Fe X-ray absorption spectroscopy. This characterisation reveals that the MnOx materials share the structural features of birnessite, yet differ in the degree of structural disorder. Importantly, these biogenic products exhibit strikingly different morphologies that can be easily controlled. Changing the substrate-to-protein ratio produces MnOx either as nm-thin sheets, or rods with diameters below 20 nm, or a combination of the two. Mineralisation in solutions that contain Fe2+(aq) makes solids with significant disorder in the structure, while the presence of Ca2+(aq) facilitates formation of more ordered materials. The (photo)oxidation and (photo)electrocatalytic capacity of the MnOx minerals is examined and correlated with their structural properties.
- Published
- 2017
3. Thiol surface functionalization via continuous phase plasma polymerization of allyl mercaptan, with subsequent maleimide-linked conjugation of collagen
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George Kiroff, Wayne A. Morrison, Gil D. Stynes, Mark A. Kirkland, and Thomas R. Gengenbach
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chemistry.chemical_classification ,Glow discharge ,Metals and Alloys ,Biomedical Engineering ,02 engineering and technology ,010402 general chemistry ,021001 nanoscience & nanotechnology ,01 natural sciences ,Plasma polymerization ,0104 chemical sciences ,Biomaterials ,chemistry.chemical_compound ,Monomer ,chemistry ,Polymerization ,Polymer chemistry ,Ceramics and Composites ,Thiol ,Surface modification ,Allyl Mercaptan ,0210 nano-technology ,Maleimide - Abstract
Thiol groups can undergo a large variety of chemical reactions and are used in solution phase to conjugate many bioactive molecules. Previous research on solid substrates with continuous phase glow discharge polymerization of thiol-containing monomers may have been compromised by oxidation. Thiol surface functionalization via glow discharge polymerization has been reported as requiring pulsing. Herein, continuous phase glow discharge polymerization of allyl mercaptan (2-propene-1-thiol) was used to generate significant densities of thiol groups on a mixed macrodiol polyurethane and tantalum. Three general classes of chemistry are used to conjugate proteins to thiol groups, with maleimide linkers being used most commonly. Here the pH specificity of maleimide reactions was used effectively to conjugate surface-bound thiol groups to amine groups in collagen. XPS demonstrated surface-bound thiol groups without evidence of oxidation, along with the subsequent presence of maleimide and collagen. Glow discharge reactor parameters were optimized by testing the resistance of bound collagen to degradation by 8 M urea. The nature of the chemical bonding of collagen to surface thiol groups was effectively assessed by colorimetric assay (ELISA) of residual collagen after incubation in 8 M urea over 8 days and after incubation with keratinocytes over 15 days. The facile creation of useable solid-supported thiol groups via continuous phase glow discharge polymerization of allyl mercaptan opens a route for attaching a vast array of bioactive molecules. © 2016 Wiley Periodicals, Inc. J Biomed Mater Res Part A: 105A: 1940-1948, 2017.
- Published
- 2017
4. Transdermal Electrochemical Monitoring of Glucose via High‐Density Silicon Microneedle Array Patch
- Author
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Mehmet Şenel, Nicolas H. Voelcker, María D. Alba, Thomas R. Gengenbach, Beatriz Prieto-Simón, Muamer Dervisevic, and Li Yan
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Biomaterials ,Materials science ,Silicon ,chemistry ,Interstitial fluid ,Electrochemistry ,chemistry.chemical_element ,High density ,Nanotechnology ,Condensed Matter Physics ,Electronic, Optical and Magnetic Materials ,Transdermal - Published
- 2021
5. Dual Action Antimicrobial Surfaces: Alternating Photopatterns Maintain Contact‐Killing Properties with Reduced Biofilm Formation
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Lewis D. Blackman, Marion K. Fros, Nicholas G. Welch, Thomas R. Gengenbach, Yue Qu, Paul Pasic, Pathiraja A. Gunatillake, Helmut Thissen, Peter Cass, and Katherine E. S. Locock
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Polymers and Plastics ,General Chemical Engineering ,Organic Chemistry ,Materials Chemistry - Published
- 2020
6. Catalytic Activity and Impedance Behavior of Screen-Printed Nickel Oxide as Efficient Water Oxidation Catalysts
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Leone Spiccia, Udo Bach, Zheng Hu, Mathias Uller Rothmann, Archana Singh, Qiang Wu, Shery L. Y. Chang, Rosalie K. Hocking, Dongchuan Fu, Yi-Bing Cheng, Satvasheel Powar, Thomas R. Gengenbach, Monika Fekete, and Alexandr N. Simonov
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Materials science ,Anodizing ,General Chemical Engineering ,Nickel oxide ,Non-blocking I/O ,Inorganic chemistry ,Water ,chemistry.chemical_element ,Nanoparticle ,Overpotential ,Catalysis ,Dielectric spectroscopy ,Nickel ,General Energy ,chemistry ,X-ray photoelectron spectroscopy ,Electric Impedance ,Nanoparticles ,Printing ,Environmental Chemistry ,General Materials Science ,Oxidation-Reduction - Abstract
We report that films screen printed from nickel oxide (NiO) nanoparticles and microballs are efficient electrocatalysts for water oxidation under near-neutral and alkaline conditions. Investigations of the composition and structure of the screen-printed films by X-ray diffraction, X-ray absorption spectroscopy, and scanning electron microscopy confirmed that the material was present as the cubic NiO phase. Comparison of the catalytic activity of the microball films to that of films fabricated by using NiO nanoparticles, under similar experimental conditions, revealed that the microball films outperform nanoparticle films of similar thickness owing to a more porous structure and higher surface area. A thinner, less-resistive NiO nanoparticle film, however, was found to have higher activity per Ni atom. Anodization in borate buffer significantly improved the activity of all three films. X-ray photoelectron spectroscopy showed that during anodization, a mixed nickel oxyhydroxide phase formed on the surface of all films, which could account for the improved activity. Impedance spectroscopy revealed that surface traps contribute significantly to the resistance of the NiO films. On anodization, the trap state resistance of all films was reduced, which led to significant improvements in activity. In 1.00 m NaOH, both the microball and nanoparticle films exhibit high long-term stability and produce a stable current density of approximately 30 mA cm(-2) at 600 mV overpotential.
- Published
- 2015
7. Flash-Assisted Processing of Highly Conductive Zinc Oxide Electrodes from Water
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Anthony S. R. Chesman, Enrico Della Gaspera, Danielle F. Kennedy, Jacek J. Jasieniak, Karl Weber, Thomas R. Gengenbach, and Joel van Embden
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Resistive touchscreen ,Materials science ,business.industry ,Doping ,02 engineering and technology ,010402 general chemistry ,021001 nanoscience & nanotechnology ,Condensed Matter Physics ,7. Clean energy ,01 natural sciences ,0104 chemical sciences ,Electronic, Optical and Magnetic Materials ,law.invention ,Biomaterials ,law ,Electrode ,Electrochemistry ,Optoelectronics ,Deposition (phase transition) ,Thin film ,0210 nano-technology ,business ,Chemical bath deposition ,Light-emitting diode ,Transparent conducting film - Abstract
Fabricating high-quality transparent conductors using inexpensive and industrially viable techniques is a major challenge toward developing low cost optoelectronic devices such as solar cells, light emitting diodes, and touch panel displays. In this work, highly transparent and conductive ZnO thin films are prepared from a low-temperature, aqueous deposition method through the careful control of the reaction chemistry. A robotic synthetic platform is used to explore the wide parameter space of a chemical bath system that uses only cheap and earth abundant chemicals for thin film deposition. As-deposited films are found to be highly resistive, however, through exposure to several millisecond pulses of high-intensity, broadband light, intrinsically doped ZnO films with sheet resistances as low as 40 Ω □-1 can be readily prepared. Such values are comparable with state-of-the-art-doped transparent conducting oxides. The mild processing conditions (
- Published
- 2015
8. Dual Action Antimicrobial Surfaces: Alternating Photopatterns Maintain Contact‐Killing Properties with Reduced Biofilm Formation
- Author
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Peter Cass, Katherine E. S. Locock, Paul Pasic, Helmut Thissen, Marion K. Fros, Pathiraja A. Gunatillake, Thomas R. Gengenbach, Nicholas G. Welch, Yue Qu, and Lewis D. Blackman
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Materials science ,Polymers and Plastics ,General Chemical Engineering ,Organic Chemistry ,Biofilm ,Antimicrobial ,Biofouling ,chemistry.chemical_compound ,Chemical engineering ,chemistry ,Dual action ,Materials Chemistry ,Benzophenone ,Surface modification - Published
- 2020
9. Improving the Stability of Ambient Processed, SnO 2 ‐Based, Perovskite Solar Cells by the UV‐Treatment of Sub‐Cells
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Doojin Vak, Aaron Seeber, Andreas Hinsch, Gayathri Mathiazhagan, Thomas R. Gengenbach, Anthony S. R. Chesman, Dechan Angmo, Mei Gao, and Simone Mastroianni
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Materials science ,Energy Engineering and Power Technology ,02 engineering and technology ,010402 general chemistry ,021001 nanoscience & nanotechnology ,01 natural sciences ,7. Clean energy ,Atomic and Molecular Physics, and Optics ,0104 chemical sciences ,Electronic, Optical and Magnetic Materials ,Chemical engineering ,Electrical and Electronic Engineering ,0210 nano-technology ,Uv treatment ,Perovskite (structure) - Published
- 2020
10. Blending chitosan‐g‐poly(caprolactone) with poly(caprolactone) by electrospinning to produce functional fiber mats for tissue engineering applications
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Dominik de Cassan, Thomas R. Gengenbach, Robert Hänsch, Andrea Hoffmann, Birgit Glasmacher, Yvonne Roger, Christopher D. Easton, Alexander Becker, and Henning Menzel
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Materials science ,Polymers and Plastics ,Scanning electron microscope ,General Chemistry ,Electrospinning ,Surfaces, Coatings and Films ,Chitosan ,chemistry.chemical_compound ,Crystallinity ,chemistry ,Chemical engineering ,X-ray photoelectron spectroscopy ,Tissue engineering ,Materials Chemistry ,Fiber ,Caprolactone - Published
- 2019
11. Silver Bismuth Sulfoiodide Solar Cells: Tuning Optoelectronic Properties by Sulfide Modification for Enhanced Photovoltaic Performance
- Author
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Narendra Pai, Thomas R. Gengenbach, Alexandr N. Simonov, Aaron Seeber, Anthony S. R. Chesman, Yi-Bing Cheng, Liangcong Jiang, Philip C. Andrews, Dimuthu C. Senevirathna, Jianfeng Lu, and Udo Bach
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chemistry.chemical_classification ,Materials science ,Sulfide ,Renewable Energy, Sustainability and the Environment ,business.industry ,Band gap ,Photovoltaic system ,chemistry.chemical_element ,02 engineering and technology ,010402 general chemistry ,021001 nanoscience & nanotechnology ,01 natural sciences ,0104 chemical sciences ,Bismuth ,chemistry ,Valence band ,Optoelectronics ,General Materials Science ,0210 nano-technology ,business - Published
- 2018
12. Dynamically Gas‐Phase Switchable Super(de)wetting States by Reversible Amphiphilic Functionalization: A Powerful Approach for Smart Fluid Gating Membranes
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Antonio Tricoli, Hieu T. Nguyen, Thomas R. Gengenbach, Vincent S. J. Craig, William S. Y. Wong, and Xiang Gao
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Materials science ,Microfluidics ,Nanotechnology ,02 engineering and technology ,Gating ,010402 general chemistry ,021001 nanoscience & nanotechnology ,Condensed Matter Physics ,01 natural sciences ,0104 chemical sciences ,Electronic, Optical and Magnetic Materials ,Biomaterials ,Membrane ,Superhydrophilicity ,Amphiphile ,Electrochemistry ,Surface modification ,Wetting ,0210 nano-technology ,Smart fluid - Abstract
In nature, cellular membranes perform critical functions such as endocytosis and exocytosis through smart fluid gating processes mediated by nonspecific amphiphilic interactions. Despite considerable progress, artificial fluid gating membranes still rely on laborious stimuli-responsive mechanisms and triggering systems. In this study, a room temperature gas-phase approach is presented for dynamically switching a porous material from a superhydrophobic to a superhydrophilic wetting state and back. This is realized by the reversible attachment of bipolar amphiphiles, which promote surface wetting. Application of this reversible amphiphilic functionalization to an impermeable nanofibrous membrane induces a temporary state of superhydrophilicity resulting in its pressure-less permeation. This mechanism allows for rapid smart fluid gating processes that can be triggered at room temperature by variations in the environment of the membrane. Owing to the universal adsorption of volatile amphiphiles on surfaces, this approach is applicable to a broad range of materials and geometries enabling facile fabrication of valve-less flow systems, fluid-erasable microfluidic arrays, and sophisticated microfluidic designs.
- Published
- 2017
13. Enhancing neurite outgrowth from primary neurones and neural stem cells using thermoresponsive hydrogel scaffolds for the repair of spinal cord injury
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David Finkelstein, Thomas R. Gengenbach, John S. Forsythe, David Moses, Malcolm K. Horne, and David R. Nisbet
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Materials science ,Neurite ,Polymers ,Biomedical Engineering ,Biocompatible Materials ,Hydrogel, Polyethylene Glycol Dimethacrylate ,Neural tissue engineering ,Biomaterials ,Mice ,chemistry.chemical_compound ,Tissue engineering ,Materials Testing ,Neurites ,Animals ,Polylysine ,Glucans ,Cells, Cultured ,Spinal Cord Injuries ,Neurons ,Aniline Compounds ,Molecular Structure ,Tissue Engineering ,Tissue Scaffolds ,biology ,Multipotent Stem Cells ,Temperature ,Metals and Alloys ,Cell Differentiation ,Neural stem cell ,Nerve Regeneration ,Cell biology ,Mice, Inbred C57BL ,Xyloglucan ,nervous system ,chemistry ,Self-healing hydrogels ,Ceramics and Composites ,biology.protein ,Xylans ,Stem cell ,Azo Compounds ,Biomedical engineering ,Neurotrophin - Abstract
In this study, thermoresponsive xyloglucan hydrogel scaffolds were investigated as candidates for neural tissue engineering of the spinal cord. The hydrogels were optimized to provide similar mechanical properties to that of native spinal cord, although also being functionalized through the immobilization of poly-D-lysine to promote neurone adhesion and neurite outgrowth. Under 2D and 3D culture conditions, xyloglucan scaffolds supported the differentiation of primary cortical neurones. Furthermore, functionalization provided a means of controlling and optimizing the cell diameter, number, migration and the neurite density, and the direction of growth. The interaction of neural stem cells (NSCs) was also investigated on the xyloglucan scaffolds in vitro. The survival of the NSCs and the axonal extensions on the scaffolds were similar to that of the primary cortical neurones. These findings suggest that xyloglucan-based materials are suitable for providing a neurotrophic milieu.
- Published
- 2009
14. Colloid Probe AFM and XPS Study of Time-Dependent Aging of Amine Plasma Polymer Coatings in Aqueous Media
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Paul Hamilton-Brown, Laurence Meagher, Hans J. Griesser, Anna Tarasova, Thomas R. Gengenbach, Tarasova, Anna, Hamilton-Brown, P, Gengenbach, Thomas Reinhold, Griesser, Hans Joerg, and Meagher, Laurence
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Aqueous solution ,Polymers and Plastics ,X-ray photoelectron ,Plasma polymerization ,Analytical chemistry ,Condensed Matter Physics ,Polyelectrolyte ,Allylamine ,Surface Change ,Ageing ,chemistry.chemical_compound ,Colloid ,X-ray photoelectron spectroscopy ,chemistry ,Chemical engineering ,Atomic force microscopy (AFM) ,DLVO theory ,Surface charge ,Amine - Abstract
Effects of surface oxidation on the properties of amine plasma polymer (pp) films in aqueous media have not been widely studied, despite their use to control bio-interfacial properties. Changes in the surface composition of allylamine and heptylamine pp films, on water exposure, were followed by XPS. The surface potential was monitored via AFM measurements and comparison to DLVO theory. Analysis of XPS data implied high initial oxidation rates (rapid quenching of surface radicals). Oxidation of the pp films followed evolution of carbon-based rather than nitrogen-based species. Analysis of AFM force data showed changes in the sign of the surface potential with aging from positive to negative. Implications, for example for surface immobilization of molecules in aqueous environments, are also discussed.
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- 2008
15. Scanning Probe Nanolithography and Protein Patterning of Low-Fouling Plasma Polymer Multilayer Films
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Michael Abdo, Thomas R. Gengenbach, Benjamin W. Muir, Andrew Fairbrother, Keith M. McLean, Patrick G. Hartley, and Florian Rovere
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chemistry.chemical_classification ,Materials science ,Fouling ,Mechanical Engineering ,Biomolecule ,Nanotechnology ,Polymer ,Plasma ,Protein patterning ,Plasma polymerization ,Nanolithography ,chemistry ,Mechanics of Materials ,Dip-pen nanolithography ,General Materials Science - Published
- 2006
16. Elimination of stick-slip of elastomeric sutures by radiofrequency glow discharge deposited coatings
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George Jessup, Ronald C. Chatelier, Chris Martin, Zoran R. Vasic, Thomas R. Gengenbach, and Hans J. Griesser
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Hexamethyldisiloxane ,Glow discharge ,Materials science ,Biomedical Engineering ,Slip (materials science) ,engineering.material ,Elastomer ,Biomaterials ,Contact angle ,chemistry.chemical_compound ,X-ray photoelectron spectroscopy ,Coating ,chemistry ,Ultimate tensile strength ,engineering ,Composite material - Abstract
Fine elastomeric sutures intended for cardiovascular surgery can exhibit “stick-slip” behavior as they are pulled through tissue; the resulting oscillatory force can damage delicate tissue or cause sutures to snap. To eliminate this undesirable effect, sutures were surface-modified using a radiofrequency glow discharge in a vapor of either hexamethyldisiloxane or hexamethyldisilazane, to produce a thin polymeric coating on the suture. The same coatings were also deposited onto aluminized tape to facilitate their characterization by measurement of air/water contact angles and by X-ray photoelectron spectroscopy. Coatings from both monomers were found to be very hydrophobic. The hexamethyldisiloxane glow discharge coatings underwent negligible oxidation when stored in air, and thus remained stable over a shelf-life period akin to what may be required of sutures. The hexamethyldisilazane glow discharge coatings, in contrast, incorporated substantial amounts of oxygen over a 3-month period. The coatings did not measurably alter the tensile properties of the sutures. The frictional properties of coated sutures were assessed by measuring the dynamic friction between the suture and ovine myocardium. Both coatings were effective in removing the inherent stick-slip behavior of polybutester sutures in this model. The coatings remained intact after several passes and proved to be robust and efficacious under various strain regimes. © 2000 John Wiley & Sons, Inc. J Biomed Mater Res (Appl Biomater) 53: 235–243, 2000
- Published
- 2000
17. Aging of 1,3-diaminopropane plasma-deposited polymer films: Mechanisms and reaction pathways
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Hans J. Griesser and Thomas R. Gengenbach
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chemistry.chemical_classification ,Degree of unsaturation ,Reaction mechanism ,Polymers and Plastics ,Radical ,Organic Chemistry ,Polymer ,Hydrogen atom abstraction ,Redox ,Hydrocarbon ,chemistry ,Polymer chemistry ,Materials Chemistry ,Amine gas treating - Abstract
In the course of plasma deposition of organic–polymeric thin films, radicals are incorporated into the growing film. These radicals initiate spontaneous oxidation reactions that continue over many weeks when the plasma polymers are stored in air. These reactions and their products have been previously studied in detail for spectroscopically simple, hydrocarbon-based plasma polymers. In this investigation, the aging of 1,3-diaminopropane (DAP) plasma polymer samples was monitored by XPS and FTIR in order to study how the oxidative reaction pathways might differ in a plasma-deposited material that is initially rich in amine groups. The freshly deposited DAP plasma polymer consisted of a random hydrocarbon network with a considerable amount of unsaturation and a high concentration of nitrogen-containing functional groups, mainly primary/secondary amines and imines. These groups strongly influenced the aging reactions: in contrast to hydrocarbon-based material where hydrogen abstraction and reaction of carbon-centered radicals with in-diffusing oxygen result in a wide range of oxidative products, both XPS and FTIR identified a rather narrow range of products (mainly amides and similar groups) in DAP plasma polymers even after extensive aging for more than 2 years. Reaction routes based on oxidation and/or hydrolysis of nitrogen functional groups, and involving primary as well as secondary reactions, are proposed to account for the spectroscopic data. The structure of the aged DAP plasma polymer appeared to be stable, and did not undergo more extensive oxidation, in contrast to hydrocarbon plasma polymers. In particular, carboxylic acid groups and carbamates were not detected. © 1999 John Wiley & Sons, Inc. J Polym Sci A: Polym Chem 37: 2191–2206, 1999
- Published
- 1999
18. Compositional changes in plasma-deposited fluorocarbon films during ageing
- Author
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Thomas R. Gengenbach and Hans J. Griesser
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chemistry.chemical_classification ,Radical ,Surfaces and Interfaces ,General Chemistry ,Polymer ,Condensed Matter Physics ,Surfaces, Coatings and Films ,Contact angle ,Hydrocarbon ,chemistry ,X-ray photoelectron spectroscopy ,Chemical engineering ,Materials Chemistry ,Organic chemistry ,Wetting ,Thin film ,Fourier transform infrared spectroscopy - Abstract
Plasma polymer coatings were deposited from perfluoro-1,3-dimethylcyclohexane (PFDMCH) and their composition and surface properties studied by XPS, grazing-angle Fourier transform infrared spectroscopy and contact angle measurements as a function of time after fabrication as they were stored under ambient conditions for more than 2 years. The spontaneous ambient oxidation of PFDMCH plasma polymers was found to be multi-step process. The rapid initial oxygen uptake, assigned to reaction between carbon-centred radicals incorporated into the coating during deposition and in-diffusing atmospheric O 2 , was similar to that of plasma polymers deposited from hydrocarbon-based monomers (alkanes, alkylamines, alcohols), suggesting that the density of radicals incorporated during deposition was similar. Subsequently, however, the extent of oxidation was much lower for PFDMCH coatings. This can be attributed to the lack of availability of hydrogen abstraction reactions, which are important for radical propagation in hydrocarbon-based plasma polymers. While XPS recorded a continuous incorporation of oxygen for more than 2 years, the air/water contact angles decreased only during the first 2 months and on further storage remained stable. There appeared to be only a small extent of surface restructuring as assessed from the small depth variations of compositions. The surface was enriched in CF 3 groups at all times.
- Published
- 1998
19. Deposition conditions influence the postdeposition oxidation of methyl methacrylate plasma polymer films
- Author
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Thomas R. Gengenbach and Hans J. Griesser
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chemistry.chemical_classification ,Reaction mechanism ,Polymers and Plastics ,Organic Chemistry ,Polymer ,Plasma ,chemistry.chemical_compound ,Monomer ,chemistry ,X-ray photoelectron spectroscopy ,Chemical engineering ,Polymer chemistry ,Materials Chemistry ,Molecule ,Fourier transform infrared spectroscopy ,Methyl methacrylate - Abstract
Plasma polymer films were deposited from methyl methacrylate (MMA) vapor under various plasma conditions and XPS and FTIR used to study the changes to the compositions of the films as they were stored in air for longer than 1 year. The plasma power input per monomer mass unit (W/FM) markedly affected the composition of the freshly deposited MMA plasma polymers. A low value of W/FM led to a high degree of retention of the original monomer structure, whereas a high value of W/FM resulted in substantial monomer fragmentation and the formation of a partially unsaturated material considerably different to conventional PMMA. As the MMA plasma coatings were stored in ambient air after fabrication, all showed spontaneous oxidative changes to their composition, but the extents and reaction products differed substantially. Deposition at low W/FM led to moderate oxidative changes, whereas high power led to a pronounced increase in the oxygen content over time and resulted in a wide range of carbon–oxygen functionalities in the aged material. As the initial compositions/plasma deposition conditions thus influenced the oxidative postdeposition reactions, MMA plasma polymers deposited under different conditions not only varied in their initial composition but then became even more diverse as they aged. © 1998 John Wiley & Sons, Inc. J Polym Sci A: Polym Chem 36: 985–1000, 1998
- Published
- 1998
20. Incorporation of Surface Topography in the XPS Analysis of Curved or Rough Samples Covered by Thin Multilayers
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Ronald C. Chatelier, Hans J. Griesser, Heather A. W. St John, Thomas R. Gengenbach, and Peter Kingshott
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Surface (mathematics) ,Elemental composition ,Materials science ,Atomic force microscopy ,Analytical chemistry ,Conformal map ,Surfaces and Interfaces ,General Chemistry ,Surface finish ,Condensed Matter Physics ,Curvature ,Surfaces, Coatings and Films ,X-ray photoelectron spectroscopy ,Materials Chemistry ,Thin film ,Composite material - Abstract
Approaches are described for the analysis of XPS signals from samples comprising thin conformal coatings on substrates with non-ideal surface topography. In particular, attention is focused on arbitrarily shaped rough or curved substrates. Relations are derived for the relative x-ray photoelectron intensities emitted from various elements in such non-ideal samples. The surface topography of arbitrarily rough samples is analysed by atomic force microscopy to provide a frequency histogram of the local slopes, which is incorporated into a global, multi-element analysis method for interpretation of the observed XPS elemental intensities. An analogous approach is used for the analysis of curved samples. Our algorithms also enable simultaneous analysis of successively coated multilayer structures. When the elemental composition of the individual layers is known, the fit procedure enables determination of the thickness values of single-layer and multilayer coatings. The range of validity of the theory is discussed. © 1997 by John Wiley & Sons, Ltd.
- Published
- 1997
21. Correlation of the Nitrogen 1s and Oxygen 1s XPS Binding Energies with Compositional Changes During Oxidation of Ethylene Diamine Plasma Polymers
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Hans J. Griesser, Thomas R. Gengenbach, and Ronald C. Chatelier
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chemistry.chemical_classification ,Radical ,Binding energy ,chemistry.chemical_element ,Surfaces and Interfaces ,General Chemistry ,Polymer ,Condensed Matter Physics ,Photochemistry ,Nitrogen ,Oxygen ,Redox ,Surfaces, Coatings and Films ,chemistry ,X-ray photoelectron spectroscopy ,Polymer chemistry ,Materials Chemistry ,Carbon - Abstract
In the course of plasma deposition of organic-polymeric thin films, radicals are incorporated into the growing film. These radicals initiate spontaneous oxidation reactions that continue over many weeks when the plasma polymers are stored in air. The resultant changes to the composition with time were monitored by XPS for ethylene diamine plasma polymer samples in order to improve understanding of the products of the oxidative reactions. The broadness of all the peaks, and the multitude of functional groups expected to be present, precluded the obtainment of detailed compositional information by curve fitting for components, but shifts in the binding energies (BEs) of the N 1s and O 1s peaks with time provided useful evidence of compositional changes. As the oxygen content of the plasma polymer increased upon oxidation, the binding energy of the N 1s photoelectrons increased from 399.1 to 399.8 eV. Concurrently, the amount of nitrogen in relation to carbon (N/C) decreased from 0.42 to 0.34. As the nitrogen content of the plasma polymer decreased, the binding energy of the O 1s photoelectrons increased from 531.1 to 531.8 eV. The BE values and their shifts with time/compositional changes suggested that the oxidation process predominantly caused oxidation of the carbon atoms that had amine groups attached to them, leading to the formation of amide groups and perhaps also some imides.
- Published
- 1996
22. Characterization of the Ageing of Plasma-deposited Polymer Films: Global Analysis of X-ray Photoelectron Spectroscopy Data
- Author
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Thomas R. Gengenbach, Hans J. Griesser, and Ronald C. Chatelier
- Subjects
chemistry.chemical_classification ,Photoemission spectroscopy ,Binding energy ,Analytical chemistry ,Surfaces and Interfaces ,General Chemistry ,Polymer ,Condensed Matter Physics ,Spectral line ,Surfaces, Coatings and Films ,Characterization (materials science) ,X-ray photoelectron spectroscopy ,chemistry ,Materials Chemistry ,Deposition (phase transition) ,Thin film - Abstract
A protocol for global analysis of x-ray photoelectron spectra of plasma-deposited polymer films is presented. These materials are difficult to analyse because of the multitude of different chemical groups present. The combination of different primary and secondary binding energy shifts results in relatively broad, featureless photoelectron peaks. The protocol is based on fitting a series of spectra obtained by monitoring the surface composition of a plasma polymer film over extended periods of time after deposition. Information obtained from this first round of curve-fitting is used in the form of additional constraints for a second round of fitting. This leads to a self-consistent procedure which is akin to a global approach to curve-fitting. To illustrate application of this method, results of a study of ann-heptylamine plasma polymer are described. The spectral changes on ageing provided clear evidence for radical-initiated oxidation reactions. These reactions generated additional radicals, which sustained the oxidation process for many months and not only led to substantial incorporation of oxygen into the material (forming a variety of carbon–oxygen functionalities) but also to conversion of most of the existing carbon–nitrogen functionalities to an oxidized form.
- Published
- 1996
23. Robust Sub‐Monolayers of Co 3 O 4 Nano‐Islands: A Highly Transparent Morphology for Efficient Water Oxidation Catalysis
- Author
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Guanyu Liu, Hongjun Chen, Noushin Nasiri, Nhien Hon Le, Adrian Lowe, Monika Fekete, Parvathala Reddy Narangari, Antonio Tricoli, Mykhaylo Lysevych, Alexandr N. Simonov, Leone Spiccia, Siva Krishna Karuturi, Hark Hoe Tan, Chennupati Jagadish, and Thomas R. Gengenbach
- Subjects
Electrolysis ,Aqueous solution ,Materials science ,Renewable Energy, Sustainability and the Environment ,Inorganic chemistry ,Nanoparticle ,02 engineering and technology ,Overpotential ,010402 general chemistry ,021001 nanoscience & nanotechnology ,Electrochemistry ,01 natural sciences ,0104 chemical sciences ,law.invention ,Catalysis ,Chemical engineering ,law ,Water splitting ,General Materials Science ,0210 nano-technology ,Cobalt oxide - Abstract
The scalable synthesis of highly transparent and robust sub-monolayers of Co3O4 nano-islands, which efficiently catalyze water oxidation, is reported. Rapid aerosol deposition of Co3O4 nanoparticles and thermally induced self-organization lead to an ultra-fine nano-island morphology with more than 94% light transmission at a wavelength of 500 nm. These transparent sub-monolayers demonstrate a remarkable mass-weighted water oxidation activity of 2070–2350 A gCo3O4−1 and per-metal turnover frequency of 0.38–0.62 s−1 at an overpotential of 400 mV in 1 m NaOH aqueous solution. This mixed valent cobalt oxide structure exhibits excellent long-term electrochemical and mechanical stability preserving the initial catalytic activity over more than 12 h of constant current electrolysis and 1000 consecutive voltammetric cycles. The potential of the Co3O4 nano-islands for photoelectrochemical water splitting has been demonstrated by incorporation of co-catalysts in GaN nanowire photoanodes. The Co3O4-GaN photoanodes reveal significantly reduced onset overpotentials, improved photoresponse and photostability compared to the bare GaN ones. These findings provide a highly performing catalyst structure and a scalable synthesis method for the engineering of efficient photoanodes for integrated solar water-splitting cells.
- Published
- 2016
24. Inside Back Cover: Scalable Synthesis of Efficient Water Oxidation Catalysts: Insights into the Activity of Flame-Made Manganese Oxide Nanocrystals (ChemSusChem 24/2015)
- Author
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Guanyu Liu, Mun Hon Cheah, Jeremy Hall, Thomas R. Gengenbach, Noushin Nasiri, Antonio Tricoli, and Leone Spiccia
- Subjects
Materials science ,General Chemical Engineering ,chemistry.chemical_element ,Nanotechnology ,Manganese ,Manganese oxide ,Catalysis ,Nanomaterials ,General Energy ,Nanocrystal ,chemistry ,Environmental Chemistry ,General Materials Science ,Cover (algebra) - Published
- 2015
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