Dissertations / Theses: 'Mechanical properties of nanomaterials'

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Ghorai, Suman. "Chemical, physical and mechanical properties of nanomaterials and its applications." Diss., University of Iowa, 2013. https://ir.uiowa.edu/etd/2501.

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The contribution of atmospheric aerosols towards radiative forcing has a very high uncertainty due to their short atmospheric lifetime. The aerosol effects are largely controlled by the density, elemental composition, and hygroscopic properties of the aerosol particles. Therefore, we have performed designed new methodology using Scanning Transmission X-ray Microscopy (STXM), Atomic force spectroscopy (AFM), micro-FTIR spectroscopy and Scanning Electron Microscopy (SEM) to quantify these important aerosol properties. Hygroscopic properties are quantified by plotting the mass of water on a single particle basis, calculated from STXM, as a function of relative humidity. Alternatively, micro-FTIR spectra have been used to study the effect of composition of aerosol particles on the hygroscopic properties of NaCl. Moreover, a unique combination of STXM and AFM has been utilized to quantify density and elemental composition of micrometer dimensional particles. This method has also been extended towards exploring mixing state of particles, consisting of heterogeneously mixed inorganic and organic compounds. In addition to these above mentioned properties, the fate of an atmospheric particle is often altered by chemical transformation and that in turn is influenced by the atmospheric RH. Therefore, we have studied an unusual keto-enol tautomerism in malonic acid particles at high RH, which is not observed in bulk. This observation could potentially be utilized to significantly improve the models to estimate Secondary Organic Aerosols (SOA). Using STXM and micro-FTIR technique, RH dependent equilibrium constant of the tautomerism reaction has been quantified as well. Organic nanocrystals capable of undergoing solid state photochemical changes in a single-crystal-to-single-crystal (SCSC) manner have been particularly important in fabricating molecular switches, data storage devices etc. Mechanical properties of these nanomaterials may control its SCSC reactivity. In addition, investigation of mechanical stiffness is important to define allowable limit of stiffness towards device application. Therefore, we studied mechanical properties of series organic nano cocrystals primarily consisting of trans-1,2-bis(4-pyridyl)ethylene and substituted resorcinol using AFM nanoindentation technique. Dependence of mechanical properties and SCSC reactivity on the resorcinol structure is also investigated as well. Moreover, photolithography on the thin film of these organic cocrystals has been performed to demonstrate its applicability as a photoresist.

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Rupasinghe, R.-A. Thilini Perera. "Probing electrical and mechanical properties of nanoscale materials using atomic force microscopy." Diss., University of Iowa, 2015. https://ir.uiowa.edu/etd/2268.

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Studying physical properties of nanoscale materials has gained a significant attention owing to their applications in the fields such as electronics, medicine, pharmaceutical industry, and materials science. However, owing to size constraints, number of techniques that measures physical properties of materials at nanoscale with a high accuracy and sensitivity is limited. In this context, development of atomic force microscopy (AFM) based techniques to measure physical properties of nanomaterials has led to significant advancements across the disciplines including chemistry, engineering, biology, material science and physics. AFM has recently been utilized in the quantification of physical-chemical properties such as electrical, mechanical, magnetic, electrochemical, binding interaction and morphology, which are enormously important in establishing structure-property relationship. The overarching objective of the investigations discussed here is to gain quantitative insights into the factors that control electrical and mechanical properties of nano-dimensional organic materials and thereby, potentially, establishing reliable structure-property relationships particularly for organic molecular solids which has not been explored enough. Such understanding is important in developing novel materials with controllable properties for molecular level device fabrication, material science applications and pharmaceutical materials with desirable mechanical stability. First, we have studied electrical properties of novel silver based organic complex in which, the directionality of coordination bonding in the context of crystal engineering has been used to achieve materials with structurally and electrically favorable arrangement of molecules for an enhanced electrical conductivity. This system have exhibited an exceptionally high conductivity compared to other silver based organic complexes available in literature. Further, an enhancement in conductivity was also observed herein, upon photodimerization and the development of such materials are important in nanoelecrtonics. Next, mechanical properties of a wide variety of nanocrystals is discussed here. In particular, an inverse correlation between the Young’s modulus and atomic/molecular polarizability has been demonstrated for members of a series of macro- and nano-dimensional organic cocrystals composed of either resorcinol (res) or 4,6-di-X-res (X = Cl, Br, I) (as the template) and trans-1,2-bis(4-pyridyl)ethylene (4,4’-bpe) where cocrystals with highly-polarizable atoms result in softer solids. Moreover, similar correlation has been observed with a series of salicylic acid based cocrystals wherein, the cocrystal former was systematically modified. In order to understand the effect of preparation method towards the mechanical properties of nanocrystalline materials, herein we have studied mechanical properties of single component and two component nanocrystals. Similar mechanical properties have been observed with crystals despite their preparation methods. Furthermore, size dependent mechanical properties of active pharmaceutical ingredient, aspirin, has also been studied here. According to results reduction in size (from millimetre to nanometer) results in crystals that are approximately four fold softer. Overall, work discussed here highlights the versatility of AFM as a reliable technique in the electrical, mechanical, and dimensional characterization of nanoscale materials with a high precision and thereby, gaining further understanding on factors that controls these processes at nanoscale.

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Weaver, Abigail. "Mechanical and electrical properties of 3D-printed acrylonitrile butadiene styrene composites reinforced with carbon nanomaterials." Thesis, Kansas State University, 2017. http://hdl.handle.net/2097/35413.

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Master of Science
Department of Mechanical and Nuclear Engineering
Gurpreet Singh
3D-printing is a popular manufacturing technique for making complex parts or small quantity batches. Currently, the applications of 3D-printing are limited by the material properties of the printed material. The processing parameters of commonly available 3D printing processes constrain the materials used to a small set of primarily plastic materials, which have relatively low strength and electrical conductivity. Adding ﬁller materials has the potential to improve these properties and expand the applications of 3D printed material. Carbon nanomaterials show promise as ﬁller materials due to their extremely high conductivity, strength, and surface area. In this work, Graphite, Carbon Nanotubes, and Carbon Black (CB) were mixed with raw Acrylonitrile Butadiene Styrene (ABS) pellets. The resulting mixture was extruded to form a composite ﬁlament. Tensile test specimens and electrical conductivity specimens were manufactured by Fused Deposition Method (FDM) 3D-printing using this composite ﬁlament as the feedstock material. Weight percentages of ﬁller materials were varied from 0-20 wt% to see the eﬀect of increasing ﬁller loading on the composite materials. Additional tensile test specimens were fabricated and post-processed with heat and microwave irradiation in attempt to improve adhesion between layers of the 3D-printed materials. Electrical Impedance Spectroscopy tests on 15 wt% Multiwalled Carbon Nanotube (MWCNT) composite specimens showed an increase in DC electrical conductivity of over 6 orders of magnitude compared to neat ABS samples. This 15 wt% specimen had DC electrical conductivity of 8.74x10−6 S/cm, indicating semi-conducting behavior. MWCNT specimens with under 5 wt% ﬁller loading and Graphite specimens with under 1 wt% ﬁller loading showed strong insulating behavior similar to neat ABS. Tensile tests showed increases in tensile strength at 5 wt% CB and 0.5 wt% MWCNT. Placing the specimens in the oven at 135 °C for an hour caused increased the stiﬀness of the composite specimens.

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Saggar, Richa. "Processing and Properties of 1D and 2D Boron Nitride Nanomaterials Reinforced Glass Composites." Doctoral thesis, Vysoké učení technické v Brně. Fakulta strojního inženýrství, 2016. http://www.nusl.cz/ntk/nusl-263205.

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Glasses and ceramics offer several unique characteristics over polymers or metals. However, they suffer from a shortcoming due to their brittle nature, falling short in terms of fracture toughness and mechanical strength. The aim of this work is to reinforce borosilicate glass matrix with reinforcements to increase the fracture toughness and strength of the glass. Boron nitride nanomaterials, i.e. nanotubes and nanosheets have been used as possible reinforcements for the borosilicate glass matrix. The tasks of the thesis are many fold which include: 1. Reinforcement of commercially derived and morphologically different (bamboo like and cylinder like) boron nitride nanotubes in borosilicate glass with the concentration of 0 wt%, 2.5 wt% and 5 wt% by ball milling process. Same process was repeated with reinforcing cleaned boron nitride nanotubes (after acid purification) into the borosilicate glass with similar concentrations. 2. Production of boron nitride nanosheets using liquid exfoliation technique to produce high quality and high aspect ratio nanosheets. These boron nitride nanosheets were reinforced in the borosilicate glass matrix with concentrations of 0 wt%, 2.5 wt% and 5 wt% by ball milling process. The samples were consolidated using spark plasma sintering. These composites were studied in details in terms of material analysis like thermo-gravimetric analysis, detailed scanning electron microscopy and transmission electron microscopy for the quality of reinforcements etc.; microstructure analysis which include the detailed study of the composite powder samples, the densities of bulk composite samples etc; mechanical properties which include fracture toughness, flexural strength, micro-hardness, Young’s modulus etc. and; tribological properties like scratch resistance and wear resistance. Cleaning process of boron nitride nanotubes lead to reduction in the Fe content (present in boron nitride nanotubes during their production as a catalyst) by ~54%. This leads to an improvement of ~30% of fracture toughness measured by chevron notch technique for 5 wt% boron nitride nanotubes reinforced borosilicate glass. It also contributed to the improvement of scratch resistance by ~26% for the 5 wt% boron nitride nanotubes reinforced borosilicate glass matrix. On the other hand, boron nitride nanosheets were successfully produced using liquid exfoliation technique with average length was ~0.5 µm and thickness of the nanosheets was between 4-30 layers. It accounted to an improvement of ~45% for both fracture toughness and flexural strength by reinforcing 5 wt% of boron nitride nanosheets. The wear rates reduced by ~3 times while the coefficient of friction was reduced by ~23% for 5 wt% boron nitride nanosheets reinforcements. Resulting improvements in fracture toughness and flexural strength in the composite materials were observed due to high interfacial bonding between the boron nitride nanomaterials and borosilicate glass matrix resulting in efficient load transfer. Several toughening and strengthening mechanisms like crack bridging, crack deflection and significant pull-out were observed in the matrix. It was also observed that the 2D reinforcement served as more promising candidate for reinforcements compared to 1D reinforcements. It was due to several geometrical advantages like high surface area, rougher surface morphology, and better hindrance in two dimensions rather than just one dimension in nanotubes.

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Wang, Xudong. "Large-Scale Patterned Oxide Nanostructures: Fabrication, Characterization and Applications." Diss., Available online, Georgia Institute of Technology, 2005, 2005. http://etd.gatech.edu/theses/available/etd-11212005-142143/.

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Thesis (Ph. D.)--Materials Science and Engineering, Georgia Institute of Technology, 2006.
Wang, Zhong Lin, Committee Chair ; Summers, Christopher J., Committee Co-Chair ; Wong, C. P., Committee Member ; Dupuis, Russell D., Committee Member ; Wagner, Brent, Committee Member

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Salavati, Mohammad [Verfasser], Timon [Akademischer Betreuer] Rabczuk, Tom [Gutachter] Lahmer, Almeida Areias Pedro [Gutachter] Miguel, Klaus [Gutachter] Gürlebeck, Mark [Gutachter] Jentsch, and Volkmar [Gutachter] Zabel. "Multi-Scale Modeling of Mechanical and Electrochemical Properties of 1D and 2D Nanomaterials, Application in Battery Energy Storage Systems / Mohammad Salavati ; Gutachter: Tom Lahmer, Pedro Miguel Almeida Areias, Klaus Gürlebeck, Mark Jentsch, Volkmar Zabel ; Betreuer: Timon Rabczuk." Weimar : Bauhaus-Universität Weimar, 2020. http://d-nb.info/1212798716/34.

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Salavati, Mohammad [Verfasser], Timon [Akademischer Betreuer] Rabczuk, Tom [Gutachter] Lahmer, Almeida Areias Pedro Gutachter] Miguel, Klaus [Gutachter] [Gürlebeck, Mark [Gutachter] Jentsch, and Volkmar [Gutachter] Zabel. "Multi-Scale Modeling of Mechanical and Electrochemical Properties of 1D and 2D Nanomaterials, Application in Battery Energy Storage Systems / Mohammad Salavati ; Gutachter: Tom Lahmer, Pedro Miguel Almeida Areias, Klaus Gürlebeck, Mark Jentsch, Volkmar Zabel ; Betreuer: Timon Rabczuk." Weimar : Bauhaus-Universität Weimar, 2020. http://d-nb.info/1212798716/34.

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Ilyas, Muhammad. "Development of nano-graphene cementitious composites (NGCC)." Thesis, Brunel University, 2016. http://bura.brunel.ac.uk/handle/2438/15828.

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Ordinary Portland cement (OPC) is the main constituent of concrete works as a principal binder for aggregates and intrinsically transmits the brittleness into concrete through the formation of hydration crystals in the cement microstructure. A number of nano cementitious composites were developed in recent years to offset the brittleness with newly discovered nanomaterials and the most prevalent among those is the graphene oxide (GO). The main objective of this PhD research work is to develop nano graphene cementitious composites (NGCC) using low cost, two dimensional (2D) graphene nanoplatelets (GNPs) and one dimensional (1D) graphited carbon nanofibres (GCNFs) with unique conical surface morphology. The GNPs were sourced synthesised in an environmental friendly way via plasma exfoliation whereas, GCNFs were manufactured through catalytic vapour grown method. The project further investigated the effect of these nanomaterials in regulating the distinctive microstructure of cement matrix leading to enhance its mechanical properties. Three different types of high-performance NGCC namely NGCC-Dot, NGCC-Fnt and NGCC-CNF, are developed by activating pristine GNPs (G-Dot), functionalised GNPs (G-Fnt) and graphited nanofibers (G-CNFs) into the cement matrix respectively. It is found through various characterization and experimental techniques that both GNPs and GCNFs regulated the cement microstructure and influenced the mechanical properties of NGCC uniquely. A remarkable increase in the flexural and the tensile strength of newly developed NGCC has been achieved and that could be attributed to the formation of distinctive microstructure regulated by catalytic activation of these nanomaterials. The shape (1D, 2D) and unique morphology of these nanomaterials played a vital role in the mechanism of crystal formation to regulate the cement microstructure. Based on the observations of test results and comprehensive characterization, the possible mechanisms of crystal formation and development of distinctive microstructure of NGCC has been established which has then proceeded to the development of a physical model for NGCC development.

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Ok, Sinan. "Surface Properties Of Carbon Nanomaterials." Master's thesis, METU, 2005. http://etd.lib.metu.edu.tr/upload/12606671/index.pdf.

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Carbon can be in several forms. Amorphous, graphite and diamond. Fullerenes are accepted as the fourth form of solid carbon. They are basically, large carbon cage molecules. By far the most common one is C60. Nanotubes are actually longer forms of fullerenes. If a voltage is applied between two carbon rods, an arc will develop between them. If the arc is maintained in helium or argon (instead of air) clouds of black carbon powder is produced. Although many studies have been performed on cathodic deposits, (i.e. nanotubes first seen in this section) very few studies on the carbon sooth are found in the literature. Only around 10% of the black soot is fullerene, the composition of the remainder varies depending on the working conditions. But it is assumed to contain parts of various fullerene particles even higher fullerenes up to C300. This fraction is abbreviated as FES through the thesis. This work comprises the production of FES (fullerene extracted soot), soot, cathodic deposit produced under nanotube conditions and cathodic deposit produced under fullerene conditions and characterization of these in terms of their specific surface areas
pore volume distribution, porosity and as a second part, adsorption capacity of gases H2 and NH3 have been found. Both physical and chemical adsorption analyses were done using Quantichrome Autosorb 1-C surface analyzer. Obtained isotherms for nitrogen adsorption were found to be in between type II and type IV. BET surface areas for the samples of FES and soot prepared under nanotube conditions and cathodic deposit prepared under fullerene and nanotube conditions were found 240, 180, 14.6 and 29.7 m2/g of surface area respectively. Micropore volumes were calculated from Horwath - Kowazoe and Saito - Foley methods were found 0.045, 0.034, 2.38*10-3 and 1.19*10-3 cc/g respectively. Active surface areas for NH3 adsorption were found for FES, soot and Norit active carbon sample are found to be 39.2, 49.6, 32.5 m2/g at 300 C and 6.35, 14.65, 6.59 m2/g at 3000 C respectively. As a result of this work, it is concluded that although not superior to NORIT CN1 active carbon sample, FES is as active as that material and able to adsorb as much hydrogen as active carbon. This is important because FES is already a side product of the arc-evaporation fullerene production technique and has no known uses at all.

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Baimpas, Nikolaos. "'Hybrid' non-destructive imaging techniques for engineering materials applications." Thesis, University of Oxford, 2014. http://ora.ox.ac.uk/objects/uuid:1aa00fed-34e6-4a5e-951b-c710e21ac23c.

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The combination of X-ray imaging and diffraction techniques provides a unique tool for structural and mechanical analysis of engineering components. A variety of modes can be employed in terms of the spatial resolution (length-scale), time resolution (frequency), and the nature of the physical quantity being interrogated. This thesis describes my contributions towards the development of novel X-ray “rich” imaging experimental techniques and data interpretation. The experimental findings have been validated via comparison with other experimental methods and numerical modelling. The combination of fast acquisition rate and high penetration properties of X-ray beams allows the collection of high-resolution 3-D tomographic data sets at submicron resolution during in situ deformation experiments. Digital Volume Correlation analysis tools developed in this study help understand crack propagation mechanisms in quasi-brittle materials and elasto-plastic deformation in co-sprayed composites. For the cases of crystalline specimens where the knowledge of “live” or residual elastic strain distributions is required, diffraction techniques have been advanced. Diffraction Strain Tomography (DST) allows non-destructive reconstruction of the 2-D (in-plane) variation of the out-of-plane strain component. Another diffraction modality dubbed Laue Orientation Tomography (LOT), a grain mapping approach has been proposed and developed based on the translate-rotate tomographic acquisition strategy. It allows the reconstruction of grain shape and orientation within polycrystalline samples, and provides information about intragranular lattice strain and distortion. The implications of this method have been thoroughly investigated. State-of-the-art engineering characterisation techniques evolve towards scrutinising submicron scale structural features and strain variation using the complementarity of X-ray imaging and diffraction. The first successful feasibility study is reported of in operando stress analysis in an internal combustion engine. Finally, further advancement of ‘rich’ imaging techniques is illustrated via the first successful application of Time-of-Flight Neutron Diffraction Strain (TOF-NDST) tomography for non-destructive reconstruction of the complete strain tensor using an inverse eigenstrain formulation.

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Yang, Rusen. "Oxide nanomaterials synthesis, structure, properties and novel devices /." Diss., Available online, Georgia Institute of Technology, 2007, 2007. http://etd.gatech.edu/theses/available/etd-06212007-161309/.

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Thesis (Ph. D.)--Materials Science and Engineering, Georgia Institute of Technology, 2008.
Peter J. Hesketh, Committee Member ; Zhong Lin Wang, Committee Chair ; C.P. Wong, Committee Member ; Robert L. Snyder, Committee Member ; Christopher Summers, Committee Member.

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Quintero, Pinzón Carlos Mario. "Luminescent spin crossover nanomaterials : physical properties and applications." Toulouse 3, 2012. http://thesesups.ups-tlse.fr/1899/.

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L'objectif principal de cette thèse est de fournir un nouveau protocole qui permet la détection de la transition de spin (TS) dans un nano-objet unique. Dans ce but, nous proposons d'utiliser la luminescence comme sonde très sensible qui peut être employée à des échelles où d'autres méthodes conventionnelles ne sont plus efficaces. Nous avons cherché à développer des nano-matériaux à TS avec des propriétés de luminescence dans le but d'isoler ces objets et ensuite sonder leurs propriétés via la détection luminescente. Sur la base de techniques de lithographie douce, plusieurs méthodes allant de l'assemblage aléatoire jusqu'à l'assemblage capillaire dirigé de nanoparticules à TS et également la synthèse in situ d'objets isolés luminescents à TS (ca. 150 nm) ont été explorées. Dans le même temps, leur étude en microscopie de fluorescence est présentée et les défis expérimentaux que cette tâche a imposée sont discutés. En outre, l'application potentielle de ces matériaux hybrides en microthermométrie est étudiée. Comme preuve de concept, des films minces de systèmes luminescents à TS ont été déposés sus des micro / nanofils chauffés par effet Joule afin de cartographier leur température
The main objective of this thesis is to provide a new protocol that permits the detection of the spin crossover (SCO) phenomenon in a single nano-object. To accomplish this, we propose luminescence as a highly sensitive technique that may be employed at scales where other conventional methods are no longer effective. We aimed to develop SCO nano-materials with luminescence properties in order to isolate these objects, address them and then probe their properties via luminescent detection. Methods ranging from random to directed microcappilary assembly of SCO nanoparticles and also in situ synthesis of isolated luminescent SCO objects (ca. 150 nm) based on soft lithographic techniques were explored. At the same time, their investigation in fluorescence microscopy is shown and the experimental challenges that this task imposed are discussed. Also, the potential application of these hybrid materials in microthermometry is studied. As a proof of concept, thin films of luminescent SCO systems were employed to obtain thermal cartographies of gold micro - nanowires heated by Joule effect

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Mansfield, E. D. H. "Synthesis, characterisation, and diffusive properties of functionalised nanomaterials." Thesis, University of Reading, 2016. http://centaur.reading.ac.uk/68345/.

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The aim of this thesis was to assess the diffusive properties of functionalised and unfunctionalised nanomaterials in a variety of different media. The main goal was to gain an insight into the fundamental mechanisms underpinning nanoparticle diffusion and how the surface properties of nanoparticles alter their net movement through different environments. Initially a library of polymer-functionalised silica nanoparticles were synthesised and characterised. The polymers chosen were; poly(ethylene glycol) (PEG), poly(2-oxazolines) (POZ) and poly(n-isopropyl acrylamide) (PNIPAM). Firstly, the diffusion of different sized gold nanoparticles was assessed in concentrations of Pluronic F-127, in order to determine how the solution properties affected diffusion. It was found that as the solution undergoes a transition in response to environmental stimuli, there is an increase in diffusion coefficient; however the area they move in becomes more confined (assessed using a bespoke python script written for use with NTA). PNIPAM- and PNPOZ-silica nanoparticles were assessed for their aggregation and diffusion using DLS, NTA, and SANS. It was found that the position of a nitrogen atom in the amide group, present in both polymers, plays a key role in governing how the particles aggregate in solution, which in turn affects how they diffuse through solvents of varying polarities. POZ-silica nanoparticles were assessed for mucus penetration against a positive control of PEGylated nanoparticles. It was found that POZ-silica was effective at enhancing nanoparticle mucus penetration, and the hydrophilicity of these polymers plays a key role in determining the degree of permeation (with methylated POZ significantly more diffusive than propylated POZ). These finding provide valuable insight into some of the molecular mechanisms governing nanoparticle diffusion and how surface chemistry governs these effects.

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Cho, Hansohl. "Atomistic simulations of chemomechanical processes in nanomaterials under extreme environments." Thesis, Massachusetts Institute of Technology, 2009. http://hdl.handle.net/1721.1/57788.

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Thesis (S.M.)--Massachusetts Institute of Technology, Dept. of Mechanical Engineering, 2009.
Cataloged from PDF version of thesis.
Includes bibliographical references (p. 142-146).
The complex chemomechanical behavior of nanomaterials under extreme thermal and mechanical environments is of interest for a range of basic science and defense applications. By the limitation of experimental approaches for objects of nanometer, novel computational methods have been developed to investigate such phenomena in nanomaterials under extreme environments. In this thesis, novel continuum and atomistic mechanical modeling and simulations are implemented and constructed for the analysis of the chemomechanical behavior of the dissimilar nano-scale metals, Nickel and Aluminum under a variety of thermal and mechanical stimuli. These studies form the basis of preliminary research on the predictive design principles for reactive polymer nanocomposites.
by Hansohl Cho.
S.M.

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Samarakoon, Duminda K. "Structural, electronic, and magnetic properties of graphene-based nanomaterials." DigitalCommons@Robert W. Woodruff Library, Atlanta University Center, 2013. http://digitalcommons.auctr.edu/dissertations/708.

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The binding of radical groups such as hydrogen, hydroxyl, epoxide, or fluorine to the graphene surface, forms covalent bonds and transforms the trigonal sp2 orbital to the tetragonal sp3 orbital. Such a transformation drastically modifies electronic properties, which leads to the opening of a bandgap through the removal of the bands near the Fermi level of the pristine graphene. We have investigated the structural, electronic, magnetic, and vibrational properties of functionalized graphene based on first-principles densityfunctional calculations. A twist-boat conformation is identified as the energetically most favorable nonmetallic configuration for fully oxidized graphene. The calculated Raman G-band blue shift is in very good agreement with experimental observations. A detailed analysis of fluorographene membranes indicates that there exist prominent chair and stirrup conformations, which correlate with the experimentally observed in-plane lattice expansion contrary to a contraction in graphane. The optical response of fluorographene is investigated using the GW-Bethe-Salpeter equation approach. The results are in good conformity with the experimentally observed optical gap and reveal predominant chargetransfer excitations arising from strong electron-hole interactions. The appearance of bounded excitons in the ultraviolet region can result in an excitonic Bose-Einstein condensate in fluorographene. Hydrogenated epitaxial graphene has distinctive electronic properties compared to the two-sided hydrogenated graphene. The stability of a given hydrogenation pattern is strongly influenced by the amount of sp2-hybridized bonding in the structure. A trigonal planar networked hydrogenation pattern is identified as an intrinsic ferromagnetic semiconductor, which is in good conformity with experimental observations. The electronic structure of graphite and rotational-stacked multilayer epitaxial graphene as a function of the applied electric bias is investigated using dispersion-corrected density-functional theory. The tailoring of electronic band structure correlates with the interlayer coupling tuned by the applied bias. The implications of controllable electronic structure of rotationally fault-stacked epitaxial graphene grown on the C-face of SiC for future device applications are discussed. We have also investigated the electronic properties of fully hydrogenated boron-nitride (BN) layer and zigzag-edged nanoribbons using dispersion-corrected density-functional calculations. Among various low-energy hydrogenated membranes referred to as chair, boat, twist-boat, and stirrup, the stirrup conformation is the most energetically favorable one. The zigzag-edged BN nanoribbon, prominently fabricated in experiments, possesses intrinsic half-metallicity with full hydrogenation. The half-metallicity can be tuned by applying a transverse electric bias, thereby providing a promising route for spintronics device applications.

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Herring, Natalie. "Formation Mechanisms and Photocatalytic Properties of ZnO-Based Nanomaterials." VCU Scholars Compass, 2013. http://scholarscompass.vcu.edu/etd/494.

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Zinc Oxide (ZnO) is one of the most extensively studied semiconductors because of its unique properties, namely, its wide band gap (3.37 eV) and high excitation binding energy (60 meV). These properties make ZnO a promising material for uses in a broad range of applications including sensors, catalysis and optoelectronic devices. The presented research covers a broad spectrum of these interesting nanomaterials, from their synthesis and characterization to their use as photocatalyts. A new synthetic approach for producing morphology controlled ZnO nanostructures was developed using microwave irradiation (MWI). The rapid decomposition of zinc acetate in the presence of a mixture of oleic acid (OAC) and oleylamine (OAM) results in the formation of hexagonal ZnO nanopyramids and ZnO rods of varying aspect ratios. The factors that influence the morphology of these ZnO nanostructures were investigated. Using ligand exchange, the ZnO nanostructures can be dispersed in aqueous medium, thus allowing their use as photocatalysts for the degradation of malachite green dye in water. Photocatalytic activity is studied as a function of morphology; and, the ZnO nanorods show enhanced photocatalytic activity for the degradation of the dye compared to hexagonal ZnO nanopyramids. After demonstrating the catalytic activity of these ZnO nanostructures, various ways to enhance photocatalytic activity were studied by modification of this MWI method. Photocatalytic activity is enhanced through band gap modulation and the reduction of electron-hole recombination. Several approaches were studied, which included the incorporation of Au nanoparticles, N-doping of ZnO, supporting ZnO nanostructures on reduced graphene oxide (RGO), and supporting N-doped ZnO on N-doped RGO. ZnO-based nanostructures were studied systematically through the entire process from synthesis and characterization to their use as photocatalysis. This allows for a thorough understanding of the parameters that impact these processes and their unique photocatalytic properties.

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Li, Guangqin. "Studies on Hydrogen-Storage Properties of Palladium Based Nanomaterials." 京都大学 (Kyoto University), 2014. http://hdl.handle.net/2433/193566.

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Panzer, Matthew James. "Experimental study on the impact of carbon nanomaterials on coke formation." Thesis, University of Iowa, 2016. https://ir.uiowa.edu/etd/2256.

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Thermal management is a major concern of jet engine development. During flight, engine components reach extreme temperatures as a result of frictional heating due to elevated airflow velocities. Jet fuel is used as a coolant to dissipate heat throughout the engine. This cooling process induces temperature and pressure increases within the fuel. At temperatures above 325°F, hydrocarbon fuels start to become thermally unstable, leading to the formation of solid deposits, known as coke. This paper outlines an experimental study that was conducted to further examine the coking mechanism. Specifically, a complete experimental setup and procedure was designed to simulate coke deposit formation in a controlled laboratory environment. Fuel was thermally stressed up to 330°C at 10 Bar for approximately 6 hours. Tests were conducted using plain Jet-A fuel and Jet-A fuel with 0.1% carbon nanoparticle and nanotube additives. Deposit formation on stainless steel samples were analyzed using Scanning Electron Microscopy imaging. Results showed that the introduction of nano-additives into the fuel yielded less deposit formation and build up on stainless steel surfaces. Both nanoparticles (100 nm diameter) and nanotubes (8 – 15 nm diameter, 0.5 – 2 μm length) were found to be effective at suppressing coke deposits above 300°C.

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Conca, Luca. "Mechanical properties of polymer glasses : Mechanical properties of polymer glasses." Thesis, Lyon, 2016. http://www.theses.fr/2016LYSE1050/document.

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Ce manuscrit présente des récentes extensions au modèle PFVD, basé sur l'hétérogénéité de la dynamique des polymères vitreux à l'échelle de quelques nanomètres et résolu par simulation en 3D, afin de fournir une description physique unifiée des propriétés mécaniques et dynamiques des polymères vitreux soumis à déformation plastique. Trois sujets principaux sont traités : La plastification. Sous déformation, les polymères atteignent le seuil de plasticité (yield) à quelques pourcents de déformation et quelques dizaines de MPa. Nous proposons que l'énergie élastique absorbée à l'échelle des hétérogénéités dynamiques accélère la dynamique locale. On observe contraintes ultimes de quelques dizaines de MPa à quelques pourcents de déformation et que la plastification est due à un nombre relativement petit d'événements locaux. Il a été observé que la dynamique devient plus rapide et homogène dans le régime plastique et que la mobilité moyenne atteint une valeur stationnaire, linéaire avec le taux de déformation. Nous proposons que la contrainte locale stimule la diffusion de monomères des domaines lents à ceux rapides (mécanisme de facilitation) et accélère dynamique locale. Ceci permets d'observer l'homogénéisation de la dynamique, avec des caractéristiques proches de l'expérience. L'écrouissage, dans les polymères enchevêtrés ou réticulés. A grande déformation, la contrainte augmente avec une pente caractéristique d'ordre 10 – 100 MPa au-dessous de la transition vitreuse. De manière analogue à une théorie récente, nous proposons que la déformation locale oriente les monomères dans la direction d'étirage et ralentie la dynamique, suite à l'intensification des interactions locales. Les modules d'écrouissage mesurés, les effets de la réticulation et du taux de déformation sont comparables aux données expérimentales. En outre, on trouve que l'écrouissage a un effet stabilisateur sur les phénomènes de localisation et sur les bandes de cisaillement
This manuscript presents recent extensions to the PFVD model, based on the heterogeneity of theh dynamics of glassy polymers at the scale of a few nanometers et solved by 3D numerical simulation, which aim at providing a unified physical description of the mechanical and dynamical properties of glassy polymers during plastic deformation. Three main topics are treated: Plasticization. Under applied deformation, polymers undergo yield at strains of a few percent and stresses of some 10 MPa.We propose that the elastic energy stored at the scale of dynamical heterogeneities accelerates local dynamics. We observe yield stresses of a few 10 MPa are obtained at a few percent of deformation and that plastification is due to a relatively small amount of local yields. It has been observed that dynamics becomes faster and more homogeneous close to yield and that the average mobility attains a stationary value, linear with the strain rate. We propose that stress-induced acceleration of the dynamics enhances the diffusion of monomers from slow domains to fast ones (facilitation mechanism), accelerating local dynamics. This allows for obtaining the homogeneisation of the dynamics, with the same features observed during experiments. Strain-hardening, in highly entangled and cross-linked polymers. At large strain, stress increases with increasing strain, with a characteristic slope (hardening modulus) of order 10 – 100 MPa well below the glass transition. Analogously to a recent theory, we propose that local deformation orients monomers in the drawing direction and slows dows the dynamics, as a consequence of the intensification of local interactions. The hardening moduli mesured, the effect of reticulation and of strain rate are comparable with experimental data. In addition, strain-hardening is found to have a stabilizing effect over strain localization and shear banding

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Hatting, Benjamin [Verfasser]. "Optical and Vibrational Properties of Doped Carbon Nanomaterials / Benjamin Hatting." Berlin : Freie Universität Berlin, 2017. http://d-nb.info/1123998760/34.

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Li, Ling. "Structural and optical properties of nanomaterials produced using template technique /." View abstract or full-text, 2004. http://library.ust.hk/cgi/db/thesis.pl?PHYS%202004%20LI.

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Williams, Brent M. "Synthesis, characterization, and enhanced magnetic properties of iron carbide nanomaterials." VCU Scholars Compass, 2017. http://scholarscompass.vcu.edu/etd/5007.

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Permanent magnets are classified as hard magnetic materials with the main purpose of generating flux for applications such as electric motors, turbines, and hard drives. High coercivity, magnetic remanence, and saturation values with high stability are some of the requirements for permanent magnets. Rare-earth magnets including neodymium and samarium based magnets are known to have superior magnetic properties due to their high magnetocrystalline anisotropy. However, due to the price of rare-earth materials development of alternate permanent magnets composed of inexpensive materials is an ongoing process. Previously cobalt carbide (CoxC) have shown promise as a potential rare-earth free magnet alternative with magnetic properties comparable to that of hexaferrite materials. Unfortunately, CoxC magnets have a low magnetic saturation (50 emu g-1) which drastically lowers its energy product. Alternatively, iron carbide has a rather high bulk magnetization value of 140 emu g-1 and is composed of naturally abundant materials. The sole issue of iron carbide is that it is considered an intermediate magnet with properties between those of a hard and a soft magnetic material. The main focus of this work is the enhancement of the hard magnetic properties of iron carbide through size effect, shape anisotropy, magnetocrystalline anisotropy and exchange anisotropy. First a wet synthesis method was developed which utilized hexadecyltrimethylammonium chloride to control particle size, shape, and crystal structure to manipulate the magnetic properties of iron carbide. With this method a semi-hard 50 nm orthorhombic Fe3C phase and a magnetically soft single crystal hexagonal Fe7C3 structure with texture-induced magnetic properties were developed. The properties for both materials were further enhanced through formation of exchange bias Fe3C/CoO nanoaggregates and spring exchange coupling of the ferromagnetically hard and soft phases of Fe7C3/SrFe12O19. A 33% increase in coercivity was observed at room temperature for the antiferro/ferromagnetic Fe3C/CoO in comparison to the bare Fe3C. While iron carbide enhanced the magnetic saturation and remanence of strontium ferrite. This work concludes that with further development of iron carbide nanocomposites they may be employed as future alternative permanent magnets.

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Demko, Michael Thomas. "Novel Thermal Characterization Methods for Micro/Nanomaterials." Case Western Reserve University School of Graduate Studies / OhioLINK, 2008. http://rave.ohiolink.edu/etdc/view?acc_num=case1215008098.

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Kellie, Benjamin M. "Carbon Nanomaterials Deposition in an Alumina Microcombustor." The Ohio State University, 2012. http://rave.ohiolink.edu/etdc/view?acc_num=osu1338319539.

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McCrory, Michael S. "Synthesis, Characterization, and Application of Molybdenum Oxide Nanomaterials." Scholar Commons, 2017. https://scholarcommons.usf.edu/etd/7424.

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Nanostructured molybdenum trioxide (MoO3) was synthesized and used as a precursor in a comparative study, along with commercial MoO3, to synthesize molybdenum dioxide (MoO2) nanoparticles. Scanning electron microscope (SEM) images revealed the particles to be approximately 30-50 nm in diameter. X-ray diffraction (XRD) confirmed MoO3 was fully reduced to MoO2 in all cases. Time dependent experiments showed that within two hours no traces of MoO3 are present. All of the experiments showed the materials were excellent absorbent materials, as well as photocatalysts. Both MoO2 materials performed almost exactly the same, with both samples being able to remove 100% of the methylene blue (MB) in one minute with light, and in two minutes without light. The morphology of MoO2 was controlled in a comparative study by varying the concentration of cetyltrimethylammonium bromide (CTAB) present during the hydrothermal reaction. As the concentration of CTAB increased, the morphology of the material changed from nanoparticles, to nanospheres, to microspheres, to hollow microspheres, and finally a highly agglomerated version of microspheres and particles combined, as confirmed by SEM images. A formation mechanism for the formation of the various sized spheres was proposed with a combination of aggregation and Ostwald ripening. XRD confirmed that all of the MoO3 was reduced to MoO2, along with no residual peaks from the CTAB that was present during the reaction. Upon trying to mix some of the materials into the MB solutions, it became obvious that some of the materials were hydrophobic. The decontamination results once again showed that the synthesized MoO2 materials were not only photocatalysts, but adsorbents as well. Samples synthesized with 0.1-5 mM CTAB were able to remove 100% of the MB in 10 minutes or less. Samples synthesized with 10 mM CTAB were able to remove 54.4% and 35% of the MB in 10 minutes, with and without light, respectively. Samples synthesized with 15 mM CTAB were able to remove 29.4% and 26.3% of the MB in 10 minutes, with and without light, respectively. The apparent decrease in decontamination performance was proposed to be caused by surface morphology induced hydrophobicity. A mechanism to describe why the hydrophobic particles were still able to decontaminate the water was proposed to be caused by coming into direct contact with the magnetic stirrer as the water level dropped due to sample collection. MoO2 nanoparticles were successfully synthesized onto a copper substrate, in a single step, via a hydrothermal synthesis technique. It is believed to be the first report of such a synthesis method. XRD confirmed all of the MoO3 had been reduced to MoO2, and also confirmed that no other compounds had formed between the molybdenum and copper. SEM images of the MoO2 coated copper substrate showed uniform nanoparticles ranging from 30-50 nm. The MoO2 coated copper substrate was able to decontaminate 57.5% of the MB from water in 10 minutes without exposure to light, while it was able to decontaminate 71.7% of the MB from water in 10 minutes with exposure to light.

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Zagaynova, Valeria. "Carbon-based magnetic nanomaterials." Doctoral thesis, Umeå universitet, Institutionen för fysik, 2012. http://urn.kb.se/resolve?urn=urn:nbn:se:umu:diva-53568.

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Magnetism of carbon-based materials is a challenging area for both fundamental research and possible applications. We present studies of low-dimensional carbon-based magnetic systems (fullerene-diluted molecular magnets, carbon nanotubes, graphite fluoride, and nanoporous carbon) by means of SQUID magnetometer, X-ray diffraction and vibrational spectroscopy, the latter techniques used as complementary instruments to find a correlation between the magnetic behaviour and the structure of the samples.In the first part of the thesis, characteristic features of the magnetization process in aligned films of carbon nanotubes with low concentration of iron are discussed. It is shown that the magnetism of such structures is influenced by quantum effects, and the anisotropy behaviour is opposite to what is observed in heavily doped nanotubes.In the second part, Mn12-based single molecular magnets with various carboxylic ligands and their 1:1 fullerene-diluted complexes are studied. We prove that magnetic properties of such systems strongly depend on the environment, and, in principle, it is possible to design a magnet with desirable properties. One of the studied compounds demonstrated a record blocking temperature for a single molecular magnet. Both fullerene-diluted complexes demonstrated “magnetization training” effect in alternating magnetic fields and the ability to preserve magnetic moment.The third and the fourth parts of the thesis are dedicated to the analysis of various contributions to the magnetic susceptibility of metal-free carbon-based systems – intercalated compounds of graphite fluorides and nanoporous oxygen-eroded graphite. The magnetic properties of these systems are strongly dependent on structure, and can be delicately tuned by altering the π-electron system of graphite, i. e. by degree of fluorination of intercalated compounds and by introduction of boron impurity to the host matrix of nanoporous graphite.
Magnetism av kolbaserade material är ett utmanande område för både grundforskning och möjliga tillämpningar. Vi presenterar studier med låg-dimensionella kolbaserade magnetiska system (fulleren-utspädda molekylära magneter, kolnanorör, grafit fluorid och nanoporösa kol) med hjälp av SQUID magnetometer, röntgendiffraktion och vibrerande spektroskopi, de senare tekniker som används som komplement instrument för att finna sambandet mellan den magnetiska uppträdande och strukturen hos proven. I den första delen av avhandlingen är egenheter från magnetisering processen i linje filmer av kolnanorör med låg koncentration av järn diskuteras. Det visas att magnetism av sådana strukturer påverkas av kvantmekaniska effekter och anisotropin beteende är motsatsen till vad som observerats i kraftigt dopade nanorör. I den tvåa delen är Mn12-baserade enda-molekyl magneter med olika karboxylsyror ligander och deras 1:1 fulleren-utspädda komplex studeras. Vi visar att magnetiska egenskaperna hos sådana system beror i hög grad på miljön, och i princip är det möjligt att utforma en magnet med önskvärda egenskaper. En av de studerade föreningarna visade en post blockeringstemperaturen för en enda molekylär magnet. Både fulleren-utspädda komplex visade "magnetisering utbildning" effekt i alternerande magnetfält och möjligheten att bevara magnetiskt moment. Den tredje och fjärde delarna av avhandlingen är avsedda för inneboende magnetism av analys av olika bidrag till magnetisk susceptibilitet av metall-fritt kol-baserade system -inskjutna föreningar grafit fluorider och nanoporösa O2-eroderade grafit. Magnetiska egenskaperna hos dessa system är starkt beroende av strukturen, och kan fint avstämmas genom att man ändrar π-elektronsystem av grafit, i. e. med graden av fluorering av inskjutna föreningar och genom införandet av bor föroreningar till värd matris av nanoporösa grafit.

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Gupta, Maneesh Kumar. "Stimuli-responsive hybrid nanomaterials: spatial and temporal control of multifunctional properties." Diss., Georgia Institute of Technology, 2012. http://hdl.handle.net/1853/45920.

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Recently, technological advancement and the promise of next-generation devices have created an overwhelming push for the continued miniaturization of active systems to the micro- and nanometer scale. In this regime, traditional mechanical systems are largely inaccessible and as a result new active or stimuli-responsive materials are required. The work presented in this dissertation provides an understanding of the responsive nature of polymer and biopolymer interfaces especially in contact with metal nanoparticles. This understanding was utilized in conjunction with top-down template-based and self-assembly fabrication strategies to create hybrid protein based films and active polymer-metal hybrids that exhibit large and well-defined modulation of mechanical and optical properties. These materials processing developments represent advancement in the current state of the art specifically in three major areas: 1. template-based top-down control of protein chain conformation, 2. high-throughput synthesis and assembly of strongly coupled plasmonic nanoparticles with modulated optical properties (both near- and far-field), 3. field-assisted assembly of highly mobile and non-close packed magnetic nanorods with capabilities for rapid actuation.

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Vonnemann, Jonathan [Verfasser]. "Multivalency associated properties of polysulfated nanomaterials in biomedical applications / Jonathan Vonnemann." Berlin : Freie Universität Berlin, 2015. http://d-nb.info/1067442294/34.

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Karakoti, Ajay. "Tuning the properties of nanomaterials as function of surface and environment." Doctoral diss., University of Central Florida, 2010. http://digital.library.ucf.edu/cdm/ref/collection/ETD/id/4688.

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It is demonstrated that in this PEGyltaed CNPs system, the PEG essentially forms a complex with CNPs in the presence of hydrogen peroxide to facilitate this electron transfer process. The superoxide dismutase (SOD) and catalase mimetic ability of CNPs is described and special emphasis is given to its biocompatibility. The second half of the thesis emphasizes the role of synthesis and surface modification in influencing the catalytic performance of cerium oxide modified titanium dioxide catalysts for decomposition of methanol. Noble metals supported on oxide nanoparticles have been an area of active research in catalysis. It is demonstrated that the modification of surface of the oxide nanoparticles by noble metals is a function of the synthesis process. By keeping the size of the nanoparticles constant, it was demonstrated that the differences in the oxidation state of noble metals can lead to change in the activity of noble metals. This contribution adds to the already existing controversy in the open literature about the role of the oxidation state of platinum in catalysis. The core level shifts in the binding energy of the 4f electrons of platinum was used as a guide to the gauge the oxidation state. Results from an in-house built catalytic reactor coupled to mass spectrometer and in-situ diffuse reflectance infra-red spectroscopy are used to quantify the catalytic performance and identify the mechanism of reaction as well as products of methanol decomposition.; Nanotechnology has shaped the research and development in various disciplines of science and technology by redefining the interdisciplinary research. It has put the materials science at the forefront of technology by allowing the researchers to engineer materials with properties ranging from electronics to biomedical by using materials as diverse as ceramics to just plain carbon. These exceptional properties are achieved by minimizing the dimension of particles in such smaller domains that the boundary between the individual atoms, ions or cluster of particles is very small. This results in a change in conventional properties of particles from continuum physics to quantum physics and hence the properties of nanoparticles can be tuned based upon their size, shape and dimensionality. One of the most apparent changes upon decreasing the particle size is the increase in surface area to volume ratio. Thus nanoparticles possess greater tendency to interact with the environment in which they are present and similarly the environment can affect the properties of nanomaterials. The environment here is described as the immediate solid, liquid or gaseous material in immediate contact with the external surface of the nanoparticles. In order to control the physico-chemical properties of nanoparticles it is important to control the surface characteristics of nanoparticles and its immediate environment. The current thesis emphasizes the role of tuning the surface of nanoparticles and/or the environment around the nanoparticles to control their properties. The current approach in literature uses nanoparticles as a platform that can be used for a myriad of applications by just changing the surface species which can tune the properties of nanoparticles. Such surface modification can provide nanomaterials with hydrophilic, hydrophobic, biocompatible, sensing, fluorescence and/or electron transfer properties.; The current thesis demonstrates the interaction between nanoparticles and the environment by changing the surface characteristics of nanomaterials through the use of oxide nanoparticles as examples. The first part of the thesis discusses the synthesis, modification and properties of cerium oxide nanoparticles (CNPs), a versatile material used in wide range of applications from catalysis to glass polishing, for their potential use in biomedical applications as a function of medium. The thesis starts by projecting the effect of environment on the properties of nanomaterials wherein it is shown that simple medium, such as, water can influence the optical properties of nanoparticles. It was shown that the strong polarizing effect of water on the non-bonding f electrons can cause a blue shift in the optical properties of CNPs as a function of increase in trivalent oxidation state of cerium in CNPs. This phenomenon, contradictory to existing literature in solid state where a red shift is observed upon increasing the trivalent oxidation state of cerium in CNPs, is purely attributed to the medium-inflicted change in properties of nanoparticles. This concept is built upon in the first half of thesis by increasing the colloidal stability of nanoparticles by surface and/or medium modification. It is shown that the narrow range of pH in which the colloidal CNPs are stable can be extended by changing the medium from water to polyhydroxy compounds such as glucose and dextran. The synthesis was designed specially to avoid the traditional precipitation and re-dispersion strategy of synthesis of nanoparticles to preserve the surface activity. The complex forming ability of cerium with polysaccharides was employed to synthesize the CNPs in a one step process and the pH stability of the NPs was extended between 2.0 to 9.5.; The difference in the complexing ability of the monomer - glucose and its anhydro glucose polymer - dextran is reflected in the ability of cerium to form super-agglomerates with the monomer while anhydro gluco polymer forms extremely disperse 3-5 nm nanoparticles through steric modification. It is shown that the antioxidant activity of nanoparticles remain unchanged by surface modification by demonstrating the cycling of the oxidation state of cerium in CNPs, with time, through hydrogen peroxide mediated transition of oxidation states of cerium. It is demonstrated that the polymeric coatings, generally considered as passive surface coatings, can also play an active role in tuning the properties of nanomaterials and increasing their biocompatibility as well as bio-catalytic activity. It is demonstrated that the antioxidant activity of CNPs can be increased as a function of polyethylene glycol (PEG) while the biocompatibility is unaltered due to the biocompatible nature of PEG. The antioxidant activity of CNPs involves an electron transfer (ET) from the CNPs to the reactive oxygen species or vice versa. This heterogeneous ET system is further complicated by the presence of surface adsorbed species. Interfacial charge/electron transfer (ET) between a particle and adsorbed (or covalently bonded) molecule presents significant complexity as it involves a solid state electron transfer over long distance. Unlike a free ion, in solid state, the conducting electrons can be temporarily trapped by the coupling lattice sites. Adsorption/attachment of surface species to nanoparticle can disturb the electronic levels by further polarizing the electron cloud thereby localizing the electron and facilitating the charge transfer. Such an interfacial electron transfer between NPs and adsorbed organic species can be compared to the single electron transfer carried by organometallic systems with a metal ion core modified with electron delocalizing porphyrin ligands.
ID: 028732931; System requirements: World Wide Web browser and PDF reader.; Mode of access: World Wide Web.; Thesis (Ph.D.)--University of Central Florida, 2010.; Includes bibliographical references.
Ph.D.
Doctorate
Department of Mechanical, Materials and Aerospace Engineering
Engineering and Computer Science

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30

Yang, Xiaofang. "Development of hybrid surface mechanical attrition treatment : formation of carbon and nitride nanomaterials." Troyes, 2009. http://www.theses.fr/2009TROY0009.

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Un procédé dénommé SMAT (Surface Mechanical Attrition Treatment) a été développé pour la fabrication des structures nanocristallines à la surface des matériaux cristallins. Les propriétés mécaniques ainsi que les propriétés de diffusion avec une réactivité exceptionnelle sont nettement améliorées pour l’échantillon SMATé. Par conséquent, les métaux SMATés sont considérés pour la fabrication de nanomatériaux de carbone. Des échantillons en acier inoxydable (AISI 316L), Co, Ni et Ti SMATés ont été soumis au procédé CVD simple pour la synthèse des nanomatériaux de carbone. Les nanomatériaux de carbone sont obtenus en surface de ces échantillons. Ces produits sont caractérisés par MET, MEB, DRX et spectrométrie RAMAN, indiquant une présence de CNFs sur les échantillons SMATés en acier inoxydable 316 L, Co, Ti ainsi qu’une présence de CNFs et MWNTs sur Ni SMATé. Le mécanisme de la croissance de CNFs sur les métaux de transition traités par le SMAT a été illustré schématiquement. Les effets de différents paramètres sont ainsi discutés. La seconde partie de la thèse concerne un nouveau développement de la machine SMAT. Pour former une couche nanostructurée plus épaisse en surface de matériaux, un nouveau système de SMAT a été développé. Les échantillons en l’acier inoxydable 316 ont été traités sous traction et à haute température en utilisant le nouveau système de SMAT. Puis, ces échantillons ont été nitrurés par un procédé de nitruration assisté par plasma. Les échantillons ont été caractérisés par microscopie optique, DRX, nanoindentation, et la machine de micro-dureté
Since the development of the new technique SMAT (Surface Mechanical Attrition Treatment), great success has been achieved. The mechanical properties and the diffusion properties of materials treated by SMAT are greatly improved. Carbon nanomaterials such as carbon nanofibers (CNFs) and carbon nanotubes (CNTs) have attracted special attention due to their unique properties and potential application. Since the diffusion properties of materials have been improved after the SMAT process, a SMAT process followed by a CVD process, i. E. Hybrid SMAT, is tailored for synthesizing carbon nanomaterials in-situ on the surface of bulk metallic materials. 316L stainless steel, pure Co, pure Ni and pure Ti plate were subjected to hybrid SMAT process to synthesize carbon nanomaterials. The effects of main parameters are discussed. The products were investigated by SEM, TEM, XRD and RAMAN characterizations. Growth mechanism was proposed. The second part of work concerns the development of SMAT machine and the formation of nitride nanomaterials on bulk metallic materials. A new SMAT system that can provide various treating conditions was developed to form a thicker nanostructured surface layer. 316 stainless steel samples were subjected to the new system, treating under traction and under thermal stress respectively. The treated samples were investigated by optical micros-copy, XRD and nanoindentation. Treated samples were submitted to the nitriding process to form nitride nanomaterials. The nitride samples were investigated by optical microscopy and microhardness tester

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Meyer, Jörg. "Electronic Properties of Organic Nanomaterials Studied by Scanning Tunneling Microscopy and Spectroscopy." Doctoral thesis, Saechsische Landesbibliothek- Staats- und Universitaetsbibliothek Dresden, 2016. http://nbn-resolving.de/urn:nbn:de:bsz:14-qucosa-200781.

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In this work organic molecules, namely derivatives of BODIPY and poly-para-phenyls are investigated on different metal surfaces by means of LT-STM. These molecule are important for the development of molecular electronics and spintronics. I show that aza-BODIPY molecules form a weak chemical bond with the Au(111) substrate and the molecular structure significantly changes upon adsorption. Due to the low corrugation of the Au(111) surface, diffusion of the molecule is observed for applied bias in excess of ±1 V. The temperature dependent formation of different molecular nanostructures formed by polyparaphenyls and Au adatoms is discussed. The diffusing Au adatoms act as coordination centers for the cyano groups present on one end of the molecules. The structure of the super molecular assemblies completely changes in a temperature range of only 60 K. Furthermore, I investigate in this work the hybridization of atomic orbitals within the molecular ligand. The Kondo resonance of a Co atom incorporated into an other aza-BODIPY derivative is investigated in detail on Ag(100). The hybridization of the atomic Co orbital with the organic ligands molecular orbitals is shown by spectroscopy measurements with submolecular resolution. The changing line shape of the Kondo resonance for the molecule-substrate system is discussed. This data is compared to measurements of Co incorporated in another molecular binding motive and on different metal samples to show the importance of the local environment for molecular materials
In dieser Arbeit werden organische Moleküle, Derivate von BODIPY und poly-para-Phenyl, auf verschiedenen Metalloberflächen mittels Tief-Temperatur Rastertunnelmikroskopie (LT-STM) untersucht. Diese Moleküle sind wichtig für die Entwicklung von molekularer Elektronik und Spintronik. Ich zeige, dass aza-BODIPY-Moleküle eine schwache chemische Bindung mit dem Au(111)- Substrat eingehen und die molekulare Struktur bei der Adsorption deutlich verändert wird. Wegen der geringen Rauigkeit der Au(111)-Oberfläche wird bereits bei einer angelegten Spannungen über ±1 V die Diffusion der Moleküle beobachtet. Die temperaturabhängige Bildung verschiedener molekularer Nanostrukturen aus poly-para-Phenyl und frei beweglichen Goldatomen wird diskutiert. Die diffundierenden Goldatome agieren hierbei als Koordinationszentren für die Cyanogruppen am einen Ende der Moleküle. Die Struktur der supramolekularen Anordnungen verändert sich dabei in einem Temperaturbereich von nur 60 K vollkommen. Außerdem beschäftige ich mich in dieser Arbeit mit der Hybridisierung atomare Orbitale im molekularen Verbund. Die Kondo-Resonanz eine Co-Atoms, welches in einem anderen aza-BODIPY-Derivat gebunden ist, wird detailliert auf der Ag(100)-Oberfläche untersucht. Die Hybridisierung des atomaren Co-Orbitals mit den molekularen Orbitalen des organischen Liganden wird an Hand von Spektroskopiemessungen mit submolekularer Auflösung gezeigt. Die veränderte Form der Kondo-Resonanz für dieses Molekül-Substrat-System wird diskutiert. Diese Daten werden mit Messungen an Co-Atomen in anderen molekularen Bindungsschemen und auf anderen Substraten verglichen um dieWichtigkeit der lokalen Umgebung für molekulare Materialien zu verdeutlichen

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Navarrete, Gatell Eric. "Synthesis and gas sensing properties of inorganic semiconducting, p-n heterojunction nanomaterials." Doctoral thesis, Universitat Rovira i Virgili, 2021. http://hdl.handle.net/10803/672438.

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En aquesta tesis utilitzant principalment Aerosol Assited Chemical Vapor Deposition, AACVD, com a metodologia de síntesis d'òxid de tungstè nanoestructurat s'han fabricat diferents sensors de gasos. Per tal d'estudiar la millora en la selectivitat i la sensibilitat dels sensors de gasos basats en òxid de tungstè aquest s'han decorat, via AACVD, amb nanopartícules d'altres òxids metàl·lics per a crear heterojuncions per tal d'obtenir un increment en la sensibilitat electrònica, les propietats químiques del material o bé ambdues. En particular, s'han treballat en diferents sensors de nanofils d'òxid de tungstè decorats amb nanopartícules d'òxid de níquel, òxid de cobalt i òxid d'iridi resultant en sensors amb un gran increment de resposta i selectivitat cap al sulfur d'hidrogen, per a l'amoníac i per a l'òxid de nitrogen respectivament a concentracions traça. A més a més, s'han estudiat els mecanismes de reacció que tenen lloc entre les espècies d'oxigen adsorbides a la superfície del sensor quan interactua amb un gas. I també s'ha treballat en intentar controlar el potencial de superfície de les capes nanoestructurades per tal de controlar la deriva en la senyal al llarg del temps, quan el sensor està operant, a través d'un control de temperatura.
En esta tesis utilizando principalmente Aerosol Assited Chemical Vapor Deposition, AACVD, como metodología de síntesis de óxido de tungsteno nanoestructurado se han fabricado diferentes sensores de gases. Para estudiar la mejora en la selectividad y la sensibilidad de los sensores de gases basados en óxido de tungsteno estos se han decorado, vía AACVD, con nanopartículas de otros óxidos metálicos para crear heterouniones para obtener un incremento en la sensibilidad electrónica, las propiedades químicas del material o bien ambas. En particular, se han trabajado en diferentes sensores de nanohilos de óxido de tungsteno decorados con nanopartículas de óxido de níquel, óxido de cobalto y óxido de iridio resultante en sensores con un gran incremento de respuesta y selectividad hacia el sulfuro de hidrógeno, para el amoníaco y para el óxido de nitrógeno respectivamente a concentraciones traza. Además, se han estudiado los mecanismos de reacción que tienen lugar entre las especies de oxígeno adsorbidas en la superficie del sensor cuando interactúa con un gas. Y también se ha trabajado en intentar controlar el potencial de superficie de las capas nanoestructuradas para controlar la deriva en la señal a lo largo del tiempo, cuando el sensor está trabajando, a través de un control de temperatura.
In this thesis, using mainly Aerosol Assited Chemical Vapor Deposition, AACVD, as a synthesis methodology for nanostructured tungsten oxide, different gas sensors have been manufactured. To study the improvement in the selectivity and sensitivity of gas sensors based on tungsten oxide, they have been decorated, via AACVD, with nanoparticles of other metal oxides to create heterojunctions to obtain an increase in electronic sensitivity, in the chemical properties of the material or at the same time in both. Particularly, we have worked on different tungsten oxide nanowire sensors decorated with nanoparticles of nickel oxide, cobalt oxide and iridium oxide resulting in sensors with a large increase in response and selectivity towards hydrogen sulfide, for ammonia. and for nitrogen oxide respectively at trace concentrations. In addition, the reaction mechanisms that take place between oxygen species adsorbed on the sensor surface when it interacts with a gas have been also studied. Furthermore, efforts have been put on trying to control the surface potential of the nanostructured layers to control the drift in the signal over time, when operating the sensors, through temperature control.

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Ozdemir, Gokhan. "Mechanical Properties Of Cfrp Anchorages." Master's thesis, METU, 2005. http://etd.lib.metu.edu.tr/upload/12605890/index.pdf.

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Due to inadequate lateral stiffness, many reinforced concrete buildings are highly damaged or collapsed in Turkey after the major earthquake. To improve the behavior of such buildings and to prevent them from collapse, repair and/or strengthening of some reinforced concrete elements is required. One of the strengthening techniques is the use of CFRP sheets on the existing hollow brick masonry infill. While using the CFRP sheets their attachment to both structural and non-structural members are provided by CFRP anchor dowels. In this study, by means of the prepared test setup, the pull-out strength capacities of CFRP anchor dowels are measured. The effects of concrete compressive strength, anchorage depth, anchorage diameter, and number of fibers on the tensile strength capacity of CFRP anchor dowel are studied.

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34

Virues, Delgadillo Jorge Octavio. "Mechanical properties of arterial wall." Thesis, University of British Columbia, 2008. http://hdl.handle.net/2429/923.

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The incidence of restenosis has been shown to be correlated with the overstretching of the arterial wall during an angioplasty procedure. It has been proposed that slow balloon inflation results in lower intramural stresses, therefore minimizing vascular injury and restenosis rate. The analysis of the biomechanics of the arterial tissue might contribute to understand which factors trigger restenosis. However, few mechanical data are available on human arteries because of the difficulty of testing artery samples often obtained from autopsy while arteries are still considered "fresh". Various solutions mimicking the physiological environment have been used to preserve artery samples from harvesting to testing. In vitro mechanical testing is usually preferred since it is difficult to test arteries in vivo. Uniaxial and biaxial testing has been used to characterize anisotropic materials such as arteries, although methodological aspects are still debated. Several objectives were formulated and analyzed during the making of this thesis. In one study, the effect of deformation rate on the mechanical behavior of arterial tissue was investigated. The effect of several preservation methods, including cryopreservation, on the mechanical properties of porcine thoracic aortas was also analyzed. Finally, the differences in the mechanical behavior between three different types of sample geometry and boundary conditions were compared under uniaxial and equi-biaxial testing. Thoracic aortas were harvested within the day of death of pigs from a local slaughterhouse. Upon arrival, connective tissue was removed from the external wall of the artery. Then the artery was cut open along its length and cut out in rectangular samples for uniaxial testing, and square and cruciform samples for biaxial testing. Samples belonging to the freezing effect study were preserved for two months at -20°C and -80°C in isotonic saline solution, Krebs-Henseleit solution with 1.8 M dimethylsulfoxide, and dipped in liquid nitrogen. Samples belonging to the deformation rate effect study were tested uniaxially and equi-biaxially at deformation rates from 10 to 200 %/s. The uniaxial and biaxial experiments were simulated with the help of an inverse finite element software. The use of inverse modeling to fit the material properties by taking into account the non-uniform stress distribution was demonstrated. A rate-dependent isotropic hyperelastic constitutive equation, derived from the Mooney-Rivlin model, was fitted to the experimental results (i.e. deformation rate study). In the proposed model, one of the material parameters is a linear function of the deformation rate. Overall, inverse finite element simulations using the proposed constitutive relation accurately predict the mechanical properties of the arterial wall. In this thesis, it was found that easier attachment of samples (rectangular and cruciform) is accomplished using clamps rather than hooks. It was also found that the elastic behavior of arteries is nonlinear and non-isotropic when subjected to large deformations. Characterization of the arterial behavior at large deformations over a higherdeformation range was achieved using cruciform samples. The mechanical properties of arteries did not significantly change after preservation of arteries for two months. Under uniaxial and biaxial testing, loading forces were reduced up to 20% when the deformation rate was increased from 10 to 200 %/s, which is the opposite to the behaviour seen in other biological tissues. The differences observed in the mechanical behavior of fresh and thawed samples were not significant, independently of the storing medium or freezing temperature used. The lack of significant differences observed in the freezing study was likely due to the small number of samples tested per storing group. Further studies are required to clarify the impact of cryopreservation on extracellular matrix architecture to help tailor an optimized approach to preserve the mechanical properties of arteries. From the results obtained in the deformation rate study, it is concluded that the stiffness of arteries decreases with an increase in the deformation rate. In addition, the effect of deformation rate was observed to be higher than the effect of anisotropy. The inverse relationship between stiffness and deformation rate raises doubts on the hypothesized relationship between intramural stress, arterial injury, and restenosis.

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Choi, Hwa-Soon. "Mechanical properties of canine pericardium." Diss., Georgia Institute of Technology, 1989. http://hdl.handle.net/1853/15492.

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Puaud, Max. "Mechanical properties of biopolymer films." Thesis, University of Nottingham, 2000. http://eprints.nottingham.ac.uk/11624/.

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Hard gelatin capsules have been used for drug delivery for a long time. The current production process takes advantage of the very unusual properties of gelatin: gelation, very low viscosity, film mechanical properties and film solubility. Although the hard gelatin capsules present many advantages compared to other drug delivery systems, their uses are restricted because of the animal origin of the gelatin. A HPMC gelling agent system is currently used for producing animal product free hard capsules. This work examines the possibility of using a different system in a similar production process. The gelling conditions of the mixed system, the potential of various film formers and the mechanical properties of some films are considered. Gelling agent filler mixed systems were prepared, and the limit concentration of filler that allowed gelation was noted. It was shown that none of the gelling agents would always gel and gelation was never prevented by the maltodextrin (up to a concentration of 14%). The gelation inhibition obtained is likely to be due to phase separation. The charge densities of the various products were also measured. It showed that when there is little charge density difference, gelation is inhibited. Polymer compatibility is increased by increasing the charge density differences. However, an asymmetry is observed. This is explained by the necessary shift of the binodal that would predict prevention of incompatibility. Many films were cast from various biopolymers. The films were screened via sensory analysis. The process allowed to define terms that discriminate the films. The results showed that cellulose derivatives, alginate and alginate derivative films had sensory analysis scores similar to gelatin. Although none of the starch derivatives had such good scores, some presented some promising results. Alginate and caseinate films were selected for further analysis. The mechanical properties of gelatin and HPMC films were compared by puncture tests. The results at a relative humidity of 44% are similar. However, the effect of the moisture content on both films' mechanical properties showed differences. The fracture patterns and polarised microscopy observation were also very different. Alginate films' mechanical properties were similar to gelatin. However, alginate films are not soluble in acidic environments. The effects of molecular weight on the mechanical properties of cellulose derivatives and alginates films were different. Increasing the calcium content of the alginate sample gave similar results to those obtained by increasing the molecular weight. It is proposed that ultimate deformation occurs through different processes in various films. Alginate/gelatin films are thought to deform through crazing, and the fracture process generates many surfaces (lines). Molecular weight and crosslinking would stabilise the crazes. On the other hand, cellulose derivative would deform through slippage and the energy is dissipated during deformation. This is consistent with the orientation observed after fracture, the lack of new surfaces and the high hydrophobicity of these polymers. Caseinate films of sodium, potassium, calcium and magnesium were studied. Sodium caseinate presented the best mechanical properties. Glycerol proved to be the best plasticiser. Glyoxal crosslinking or increase in pH did not improve the mechanical properties of these films. Caseinate films are poorer than alginate, HPMC or gelatin films. Caseinate deformation processes might occur through both slippage and crazing owing to the low molecular weight and high hydrogen bonding ability. Overall, different deformation processes can lead to similar mechanical behaviour. None of the films studied is likely to replace gelatin or HPMC. More complex systems are proposed for further study.

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Bidasaria, Sanjay K. "Electronic and mechanical properties of." Diss., Atlanta, Ga. : Georgia Institute of Technology, 2008. http://hdl.handle.net/1853/28101.

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Thesis (M. S.)--Physics, Georgia Institute of Technology, 2009.
Committee Chair: Marchenkov, Alexei; Committee Member: Callen, William Russell; Committee Member: First, Phillip; Committee Member: Kindermann, Marcus; Committee Member: Riedo, Elisa.

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Salisbury, S. T. Samuel. "The mechanical properties of tendon." Thesis, University of Oxford, 2008. http://ora.ox.ac.uk/objects/uuid:97b73cf6-53bc-4606-b974-a1cdc662e9e8.

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Although the tensile mechanical properties of tendon have been well characterised, the viscoelastic and anisotropic properties remain uncertain. This thesis addresses the anisotropic and viscoelastic material properties of tendon. A method to characterise the three-dimensional shape of tendon is reported and experiments to characterise the fibre-aligned and fibre-transverse viscoelastic properties of tendon are presented. The cross-sectional profiles of bovine digital extensor tendons were determined by a laser-slice method. Linear dimensions were measured within 0.15 mm and cross-sectional areas within 1.7 mm². Tendons were compressed between two glass plates in creep loading at multiple loads. Compression was then modelled in a finite element environment. Tendon was found to be nearly incompressible and reproduction of its isochronal load-displacement curve was achieved with a neo-Hookean material model (E ≃ 0.3 MPa). The fibre-aligned tensile mechanical properties were described using a Quasi-Linear Viscoelastic model. The model was effective at reproducing cyclic loading; however, it was ineffective at predicting stress relaxation outside the scope of data used to fit the model. When all experimental results are considered together, two significant conclusions are made: (1) tendon is much stiffer in fibre-aligned tension than in fibre-transverse compression and (2) the fibre-aligned tensile response is strain dependant, while the transverse response is not.

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McCullough, Kieran. "Mechanical properties of metallic foams." Thesis, University of Cambridge, 1999. https://www.repository.cam.ac.uk/handle/1810/272153.

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King, Raymond John. "Dynamic Mechanical Properties of Resilin." Thesis, Virginia Tech, 2010. http://hdl.handle.net/10919/33677.

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Resilin is an almost perfect elastic protein found in many insects. It can be stretched up to 300% of its resting length and is not affected by creep or stress relaxation. While much is known about the static mechanical properties of resilin, it is most often used dynamically by insects. Unfortunately, the dynamic mechanical properties of resilin over the biologically relevant frequency range are unknown. Here, nearly pure samples of resilin were obtained from the dragonfly, Libellua luctuosa, and dynamic mechanical analysis was performed with a combination of time-temperature and time-concentration superposition to push resilin through its glass transition. The tensile properties for resilin were found over five different ethanol concentrations (65, 70, 82, 86 and 90% by volume in water) between temperatures of -5Â°C and 60Â°C, allowing for the quantification of resilinâ s dynamic mechanical properties over the entire master curve. The glass transition frequency of resilin in water at 22Â°C was found to be 106.3 Hz. The rubber storage modulus was 1.6 MPa, increasing to 30 MPa in the glassy state. At 50 Hz and 35% strain over 98% of the elastic strain energy can returned each cycle, decreasing to 81% at the highest frequencies used by insects (13 kHz). However, despite its remarkable ability to store and return energy, the resilin tendon in dragonflies does not act to improve the energetic efficiency of flight or as a power amplifying spring. Rather, it likely functions to passively control and stabilize the trailing edge of each wing during flight.
Master of Science

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41

Kappiyoor, Ravi. "Mechanical Properties of Elastomeric Proteins." Diss., Virginia Tech, 2014. http://hdl.handle.net/10919/54563.

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When we stretch and contract a rubber band a hundred times, we expect the rubber band to fail. Yet our heart stretches and contracts the same amount every two minutes, and does not fail. Why is that? What causes the significantly higher elasticity of certain molecules and the rigidity of others? Equally importantly, can we use this information to design materials for precise mechanical tasks? It is the aim of this dissertation to illuminate key aspects of the answer to these questions, while detailing the work that remains to be done. In this dissertation, particular emphasis is placed on the nanoscale properties of elastomeric proteins. By better understanding the fundamental characteristics of these proteins at the nanoscale, we can better design synthetic rubbers to provide the same desired mechanical properties.
Ph. D.

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42

Dimitriu, Radu. "Complex mechanical properties of steel." Thesis, University of Cambridge, 2009. https://www.repository.cam.ac.uk/handle/1810/218319.

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Whereas considerable progress has been reported on the quantitative estimation of the microstructure of steels as a function of most of the important determining variables, it remains the case that it is impossible to calculate all but the simplest of mechanical properties given a comprehensive description of the structure at all conceivable scales. Properties which are important but fall into this category are impact toughness, fatigue, creep and combinations of these phenomena. The work presented in this thesis is an attempt to progress in this area of complex mechanical properties in the context of steels, although the outcomes may be more widely applied. The approach used relies on the creation of physically meaningful models based on the neural network and genetic programming techniques. It appears that the hot-strength, of ferritic steels used in the powerplant industry, diminishes in concert with the dependence of solid solution strengthening on temperature, until a critical temperature is reached where it is believed that climb processes begin to contribute. It is demonstrated that in this latter regime, the slope of the hot-strength versus temperature plot is identical to that of creep rupture-strength versus temperature. This significant outcome can help dramatically reduce the requirement for expensive creep testing. Similarly, a model created to estimate the fatigue crack growth rates for a wide range of ferritic and austenitic steels on the basis of static mechanical data has the remarkable outcome that it applies without modification to nickel based superalloys and titanium alloys. It has therefore been possible to estimate blindly the fatigue performance of alloys whose chemical composition is not known. Residual stress is a very complex phenomenon especially in bearings due to the Hertzian contact which takes place. A model has been developed that is able to quantify the residual stress distribution, under the raceway of martensitic ball bearings, using the running conditions. It is evident that a well-formulated neural network model can not only be extrapolated even beyond material type, but can reveal physical relationships which are found to be informative and useful in practice.

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43

Drodge, Daniel Ryan. "Mechanical properties of energetic composites." Thesis, University of Cambridge, 2010. https://www.repository.cam.ac.uk/handle/1810/265501.

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This thesis presents research into the mechanical response of particulate polymer composites, both energetic and inert, that contributes towards the wider understanding of deformation and damage mechanisms in Polymer Bonded Explosive (PBXs). Specifically, high and low strain-rate compression experiments were performed on several composites, with a view to measuring their elastic properties. A brief review of PBXs, polymers and particulate composites forms chapter 1. A key piece of mechanical testing apparatus, the Split Hopkinson Pressure Bar (SHPB), is critically assessed in chapters 2 and 3. The gauge calibration procedure was critically evaluated; the necessity of dispersion correction was investigated; and a method for allowing for the finite specimen transit time was introduced. Chapter 4 presents a comparison of methods of estimating a high strain-rate elastic modulus, including ultrasonic and pulse-shaped SHPB measurements. All methods returned moduli within the expected range and in broad agreement with each other. Chapter 5 describes SHPB and ultrasonic transducer experiments performed on a UK PBX and binder at temperatures ranging from -100�C to 30�C. Results build upon and agree with published findings, demonstrating a lower glass transition temperature in the binder than in the PBX, implying that the binder in the PBX experiences a higher strain-rate. Chapter 6 reports experiments performed on three cast RDX-HTPB composites, where quantifiable damage was introduced at high strain-rate using a Direct Impact Hopkinson Bar, and the resulting composite modulus was measured quasi-statically. The most abrupt decrease in modulus due to damage was measured for the composite containing bimodally distributed filler particles. Finally, in chapter 7, two sets of sugar-HTPB composites were produced: one with fixed particle size distribution with varying particle separation, and the other vice-versa. Microstructural properties, including the distribution of intergranular separations, were measured using X-ray microtomography. Quasi-static and SHPB compression experiments were performed. Particle size and separation were found to be secondary to fill-fraction in governing material properties. A Porter-Gould modulus decay function was fitted to the stress-strain curves. The binder elastic modulus and crystal-binder adhesion energy were estimated at high and low strain-rates.

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44

Rains, Jeffrey K. "Mechanical properties of tracheal cartilage." Thesis, University of British Columbia, 1989. http://hdl.handle.net/2429/27994.

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Large airways collapse has been implicated as one of the causes of maximal expiratory flow limitation. Since cartilage plays an important role in maintaining the form of these airways, an understanding of the mechanical properties of the cartilage is necessary for a better understanding of the mechanisms which limit maximal expiratory flow. This work establishes a technique whereby the tensile stiffness of human tracheal cartilage can be determined using uniaxial equilibrium tensile tests. A technique was developed in which standard shaped specimens were cut from tracheal cartilage rings and tested in a specially designed tensile tester in order to determine the stress-strain relationship of the specimen. The stress-strain relationship of the cartilage test specimens was found to be linear up to approximately 10 % strain. However, irreversible disruption of the cartilage matrix occurred at strains greater than 10 %. The tensile stiffness of the tracheal cartilage fell in the range 1-20 MPa and was found to decrease with increasing depth from the outer surface of the tissue. This layer-wise variation in tensile stiffness reflected the orientation of the collagen fibrils in the tissue. An age-related increase in the tensile stiffness of tracheal cartilage was found. This age-related change in tensile stiffness may reflect an increase in collagen cross-linking in specimens from older individuals. A possible bias of the test method toward the measurement of the mechanical properties of the collagen fibrils, as opposed the combined effects of the collagen and proteoglycans, was suspected. However, to the extent that equilibrium tensile testing reflects the ability of tracheal cartilage to bend in response to alterations in transmural pressure, these results suggest that age-related changes in large airway cartilage stiffness are not the cause of the age-related decrease in maximal expiratory flow.
Applied Science, Faculty of
Chemical and Biological Engineering, Department of
Graduate

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45

Root, Samuel E. "Mechanical Properties of Semiconducting Polymers." Thesis, University of California, San Diego, 2018. http://pqdtopen.proquest.com/#viewpdf?dispub=10745535.

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Mechanical softness and deformability underpin most of the advantages offered by semiconducting polymers. A detailed understanding of the mechanical properties of these materials is crucial for the design and manufacturing of robust, thin-film devices such as solar cells, displays, and sensors. The mechanical behavior of polymers is a complex function of many interrelated factors that span multiple scales, ranging from molecular structure, to microstructural morphology, and device geometry. This thesis builds a comprehensive understanding of the thermomechanical properties of polymeric semiconductors through the development and experimental-validation of computational methods for mechanical simulation. A predictive computational methodology is designed and encapsulated into open-sourced software for automating molecular dynamics simulations on modern supercomputing hardware. These simulations are used to explore the role of molecular structure/weight and processing conditions on solid-state morphology and thermomechanical behavior. Experimental characterization is employed to test these predictions—including the development of simple, new techniques for rigorously characterizing thermal transitions and fracture mechanics of thin films.

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Lintzén, Nina. "Mechanical properties of artificial snow." Licentiate thesis, Luleå tekniska universitet, Geoteknologi, 2013. http://urn.kb.se/resolve?urn=urn:nbn:se:ltu:diva-16798.

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Mechanical properties of snow have been a subject of research since the mid-20th century. Theresearch done is based on natural snow. During the last decades the winter business industryhas been growing and also the interest for constructing buildings and artwork of snow. Suchconstructions are generally built using artificial snow, i.e. snow produced by snow guns. Up tothe present constructions of snow are designed based on knowledge by experience. Only minorscientific studies on artificial snow and its properties has been published. Hence it is ofimportance to investigate material properties for artificial snow.A survey of current state of the art knowledge of properties for natural snow was done andbasic material properties for different qualities of artificial snow were investigated. Strengthand deformation properties for artificial snow were evaluated through uniaxial compressivetests where cylindrical test specimens were subjected to different constant deformation rates.The results show that artificial snow at low deformation rates will have a plastic deformationbehavior where the initial deformation will cause a hardening of the snow structure. At higherdeformation rates brittle failure may occur. For artificial snow with a homogeneous and finegrained structure the deformation behavior was found to change from plasticity to brittleness ata certain critical deformation rate. Artificial snow with coarse grained structure was found to bebrittle giving unstructured results independent of the load level.Four point loading was applied on beams of artificial snow to study creep deformation, bendingstrength and to determine the ultimate load for the different snow qualities. The results showedcoarse grained artificial snow underwent relatively small creep deformations. Both the creepbehavior and the ultimate strength varied randomly at the same applied load. Large plasticdeformations were observed with the fine grained artificial without any failure of the beams.The ultimate load was relatively high and repeatable results were achieved for all test.Previous presumptions that coarse grained artificial snow with high density would have highstrength and were not confirmed by the experiments performed on different qualities ofartificial snow. The performed tests indicate that fine grained artificial snow of lower densityhave more predictable strength properties of equally high or higher magnitude as for coarsegrained artificial snow. The plastic deformations were however higher for the fine grainedartificial snow. High deformations are not favorable for structures which should maintain theshape during the winter season. When designing constructions of snow both strength anddeformation properties should be taken into account.
Godkänd; 2013; 20131002 (ninlin); Tillkännagivande licentiatseminarium 2013-10-23 Nedanstående person kommer att hålla licentiatseminarium för avläggande av teknologie licentiatexamen. Namn: Nina Lintzén Ämne: Geoteknik/Soil Mechanics and Foundation Engineering Uppsats: Mechanical Properties of Artificial Snow Examinator: Professor Sven Knutsson, Institutionen för samhällsbyggnad och naturresurser, Luleå tekniska universitet Diskutant: Tekn. lic. Lars Vikström, LKAB, Luleå Tid: Fredag den 15 november 2013 kl 10.00 Plats: F1031, Luleå tekniska universitet

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47

Loveless, Thomas A. "Mechanical Properties of Kenaf Composites Using Dynamic Mechanical Analysis." DigitalCommons@USU, 2015. https://digitalcommons.usu.edu/etd/4310.

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Natural fibers show potential to replace glass fibers in thermoset and thermoplastic composites. Kenaf is a bast-type fiber with high specific strength and great potential to compete with glass fibers. In this research kenaf/epoxy composites were analyzed using Dynamic Mechanical Analysis (DMA). A three-point bend apparatus was used in the DMA testing. The samples were tested at 1 hertz, at a displacement of 10 μm, and at room temperature. The fiber volume content of the kenaf was varied from 20%-40% in 5% increments. Ten samples of each fiber volume fraction were manufactured and tested. The flexural storage modulus, the flexural loss modulus, and the loss factor were reported. Generally as the fiber volume fraction of kenaf increased, the flexural storage and flexural loss modulus increased. The loss factor remained relatively constant with increasing fiber volume fraction. Woven and chopped fiberglass/epoxy composites were manufactured and tested to be compared with the kanaf/epoxy composites were manufactured and tested to be compared with the kenaf/epoxy composites. Both of the fiberglass/epoxy composites reported higher flexural storage and flexural loss modulus values. The kenaf/epoxy composites reported higher loss factor values. The specific flexural storage and specific flexural loss modulus were calculated for both the fiberglass and kenaf fiber composites. Even though the kenaf composites reported a lower density, the fiberglass composites reported higher specific mechanical properties.

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48

Hos, James Pieter. "Mechanochemically synthesized nanomaterials for intermediate temperature solid oxide fuel cell membranes." University of Western Australia. School of Mechanical Engineering, 2005. http://theses.library.uwa.edu.au/adt-WU2006.0016.

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[Truncated abstract] In this dissertation an investigation into the utility of mechanochemically synthesized nanopowders for intermediate temperature solid oxide fuel cell components is reported. The results are presented in the following parts: the synthesis and characterisation of precursors for ceramic and cermet components for the fuel cell; the physical and electrical characterisation of the electrolyte and electrodes; and the fabrication, operation and analysis of the resulting fuel cells. Samarium-doped (20 mol%) ceria (SDC) nanopowder was fabricated by the solid-state mechanochemical reaction between SmCl3 with NaOH and Ce(OH)4 in 85 vol% dilution with NaCl. A milling time of 4 hours and heat treatment for 2 hours at 700°C yielded a material with equivalent particle and crystallite sizes of 17 nm. The existence of a complete solid solution was affirmed by electron energy loss spectroscopy and x-ray diffraction analysis. Doped-ceria compacts were sintered for 4 hours at 1350°C forming ceramics of 88% theoretical density. The ionic conductivity in flowing air was 0.009 S/cm, superior to commercially supplied nanoscale SDC. Anode precursor composite NiO-SDC nanopowder was synthesized by milling Ni(OH)2 with the previously defined SDC formulation ... Anode-supported fuel cells were fabricated on a substrate of at least 500 'm 55wt%NiO-SDC with 17vol% graphite pore formers. Suspensions of SDC were deposited by aerosol on the sintered bilayer at a thickness around 5 'm. A cathode of 10% SDC (SmSr)0.5CoO3 was deposited onto the sintered electrolyte and after firing had a thickness of around 25 'm. Operation of fuel cells in single-chamber mixtures of CH4 and air diluted in argon were successful and gave power outputs of 483 'W/cm2. Operation in undiluted 25 vol% CH4:air gave a power output of 5.5 mW/cm2. It was shown that a large polarisation resistance of 4.1 Ω.cm2 existed and this was assigned to losses in the anode, namely mass transport limitation associated with the catalytic combustion of methane and insufficient porosity. The large surface area of Ni appeared to allow more methane to combust and hence prevented its electrochemical reaction from occurring, thus limiting the performance of the cell. The synthesis procedures, ceramic processing and fabrication techniques and testing methods are discussed and contribute significant understanding to the fields of ceramic science and fuel cell technology.

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Alrobei, Hussein. "Synthesis and Characterization of Alpha-Hematite Nanomaterials for Water-Splitting Applications." Scholar Commons, 2018. https://scholarcommons.usf.edu/etd/7661.

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The recent momentum in energy research has simplified converting solar to electrical energy through photoelectrochemical (PEC) cells. There are numerous benefits to these PEC cells, such as the inexpensive fabrication of thin film, reduction in absorption loss (due to transparent electrolyte), and a substantial increase in the energy conversion efficiency. Alpha-hematite ([U+F061]-Fe2O3) has received considerable attention as a photoanode for water-splitting applications in photoelectrochemical (PEC) devices. The alpha-hematite ([U+F061]-Fe2O3) nanomaterial is attractive due to its bandgap of 2.1eV allowing it to absorb visible light. Other benefits of [U+F061]-Fe2O3 include low cost, chemical stability and availability in nature, and excellent photoelectrochemical (PEC) properties to split water into hydrogen and oxygen. However, [U+F061]-Fe2O3 suffers from low conductivity, slow surface kinetics, and low carrier diffusion that causes degradation of PEC device performance. The low carrier diffusion of [U+F061]-hematite is related to higher resistivity, slow surface kinetics, low electron mobility, and higher electro-hole combinations. All the drawbacks of [U+F061]-Fe2O3, such as low carrier mobility and electronic diffusion properties, can be enhanced by doping, which forms the nanocomposite and nanostructure films. In this study, all nanomaterials were synthesized utilizing the sol-gel technique and investigated using Scanning Electron Microscopy (SEM), X-ray Diffractometer (XRD), UV-Visible Spectrophotometer (UV-Vis), Fourier Transform Infrared Spectroscopy (FTIR), Raman techniques, Particle Analyzer, Cyclic Voltammetry (CV), and Chronoamperometry, respectively. The surface morphology is studied by SEM. X-Ray diffractometer (XRD) is used to identify the crystalline phase and to estimate the crystalline size. FTIR is used to identify the chemical bonds as well as functional groups in the compound. A UV-Vis absorption spectral study may assist in understanding electronic structure of the optical band gap of the material. Cyclic voltammetry and chronoamperometry were used to estimate the diffusion coefficient and study electrochemical activities at the electrode/electrolyte interface. In this investigation, the [U+F061]-Fe2O3 was doped with various materials such as metal oxide (aluminum, Al), dichalcogenide (molybdenum disulfide, MoS2), and co-catalyst (titanium dioxide, TiO2). By doping or composite formation with different percentage ratios (0.5, 10, 20, 30) of aluminum (Al) containing [U+F061]-Fe2O3, the mobility and carrier diffusion properties of [U+F061]-hematite ([U+F061]-Fe2O3) can be enhanced. The new composite, Al-[U+F061]-Fe2O3, improved charge transport properties through strain introduction in the lattice structure, thus increasing light absorption. The increase of Al contents in [U+F061]-Fe2O3 shows clustering due to the denser formation of the Al-[U+F061]-Fe2O3 particle. The presence of aluminum causes the change in structural and optical and morphological properties of Al-[U+F061]-Fe2O3 more than the properties of the [U+F061]-Fe2O3 photocatalyst. There is a marked variation in the bandgap from 2.1 to 2.4 eV. The structure of the composite formation Al-[U+F061]-Fe2O3, due to a high percentage of Al, shows a rhombohedra structure. The photocurrent (35 A/cm2) clearly distinguishes the enhanced hydrogen production of the Al-[U+F061]-Fe2O3 based photocatalyst. This work has been conducted with several percentages (0.1, 0.2, 0.5, 1, 2, 5) of molybdenum disulfide (MoS2) that has shown enhanced photocatalytic activity due to its bonding, chemical composition, and nanoparticle growth on the graphene films. The MoS2 material has a bandgap of 1.8 eV that works in visible light, responding as a photocatalyst. The photocurrent and electrode/electrolyte interface of MoS2-[U+F061]-Fe2O3 nanocomposite films were investigated using electrochemical techniques. The MoS2 material could help to play a central role in charge transfer with its slow recombination of electron-hole pairs created due to photo-energy with the charge transfer rate between surface and electrons. The bandgap of the MoS2 doped [U+F061]-Fe2O3 nanocomposite has been estimated to be vary from 1.94 to 2.17 eV. The nanocomposite MoS2-[U+F061]-Fe2O3 films confirmed to be rhombohedral structure with a lower band gap than Al-[U+F061]-Fe2O3 nanomaterial. The nanocomposite MoS2-[U+F061]-Fe2O3 films revealed a more enhanced photocurrent (180 μA/cm2) than pristine [U+F061]-Fe2O3 and other transition metal doped Al-[U+F061]-Fe2O3 nanostructured films. The p-n configuration has been used because MoS2 can remove the holes from the n-type semiconductor by making a p-n configuration. The photoelectrochemical properties of the p-n configuration of MoS2-α-Fe2O3 as the n-type and ND-RRPHTh as the p-type deposited on both n-type silicon and FTO-coated glass plates. The p-n photoelectrochemical cell is stable and allows for eliminating the photo-corrosion process. Nanomaterial-based electrodes [U+F061]-Fe2O3-MoS2 and ND-RRPHTh have shown an improved hydrogen release compared to [U+F061]-Fe2O3, Al-[U+F061]-Fe2O3 and MoS2-[U+F061]-Fe2O3 nanostructured films in PEC cells. By using p-n configuration, the chronoamperometry results showed that 1% MoS2 in MoS2-[U+F061]-Fe2O3 nanocomposite can be a suitable structure to obtain a higher photocurrent density. The photoelectrochemical properties of the p-n configuration of MoS2-α-Fe2O3 as n-type and ND-RRPHTh as p-type showed 3-4 times higher (450 A/cm2) in current density and energy conversion efficiencies than parent electrode materials in an electrolyte of 1M of NaOH in PEC cells. Titanium dioxide (TiO2) is known as one of the most explored electrode materials due to its physical and chemical stability in aqueous materials and its non-toxicity. TiO2 has been investigated because of the low cost for the fabrication of photoelectrochemical stability and inexpensive material. Incorporation of various percentages (2.5, 5, 16, 25, 50) of TiO2 in Fe2O3 could achieve better efficiencies as the photoanode by enhancing the electron concentration and low combination rate, and both materials can have a wide range of wavelength which could absorb light in both UV and visible spectrum ranges. TiO2 doped with [U+F061]-Fe2O3 film was shown as increasing contacting area with the electrolyte, reducing e-h recombination and shift light absorption along with visible region. The [U+F061]-Fe2O3-TiO2 nanomaterial has shown a more enhanced photocurrent (800 μA/cm2) than metal doped [U+F061]-Fe2O3 photoelectrochemical devices.

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Yu-KueiYeh and 葉育魁. "Estimation of Mechanical Properties of Nanomaterials." Thesis, 2017. http://ndltd.ncl.edu.tw/handle/2e8dsg.

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Abstract:

博士
國立成功大學
航空太空工程學系
105
Due to the difficulties of the experimental works on the nanomaterials, many efforts have been recently put on the estimation of their mechanical properties through theoretical and numerical simulations. A semi-analytical method called molecular-continuum (MC) model and a molecular dynamics based (MD-based) nonlinear finite element simulation method are proposed to estimate the stiffness, strength, and fracture toughness of nanomaterials in this thesis. The MC model is developed by combining the concept of molecular dynamics and continuum mechanics, in which the potential energy describing the interactions of atoms is not restricted to the harmonic potential function, and hence its deriving stress-strain relation is not restricted to be linear. Unlike the usual test performed by applying forces, in this model a displacement field is employed in the representative volume element of a specimen. For predicting the stiffness and strength, the uniform strain field is applied. To estimate fracture toughness, a parameter called the strain intensity factor is introduced, and the near tip solution of linear elastic fracture mechanics rewritten in terms of strain intensity factor is used to locate the atoms of the cracked specimen. Through this model, the Young’s moduli, Poisson’s ratios, and shear modulus of graphene and carbon nanotubes (CNTs) for armchair, zigzag, and chiral types can all be written as simple rational functions in which the dependence of radius, chiral angle, and thickness can be observed clearly from the explicit closed-form expressions by using the harmonic potential functions. Moreover, according to the proposed molecular-continuum model, an integrated symbolic and numerical computational scheme (ISNC) is established to deal with the general nanomaterials. The stiffness defined based upon the initial linear region, and the ultimate strength, yield strength and, mode I/mode II toughness occurring at the later period of the materials can all be predicted. Identical results of the closed-form solutions and ISNC verify the correctness of our derivation. Comparison of the results obtained by other methods or different potential energy functions further justifies the simplicity, validity, and efficiency of the proposed model. The MD-based nonlinear finite element simulation method to estimate the mechanical properties of nanomaterials is developed by using a frame-like structure to construct the molecular model. The bond stretching energy and bond angle bending energy in molecular dynamics can be simulated by the analogous concept in finite element approach, that is, these strain energies of a beam element caused by tensile stress and bending moment, respectively. The nonlinear modified Morse potential energy is selected and used to calculate the nonlinear stress-strain relation and sectional area of the beam element in our simulation. As the prediction by the MC model, a prescribed-displacement condition is applied in this method. The energy release rate is used to predict the fracture toughness of nanomaterials. Since the value of crack increment must be extremely smaller than the value of crack length for calculating the energy release rate, the continuum model of nanomaterials with nonlinear elastic property is constructed based upon the properties estimated by the beam element model. The mechanical properties for both graphene and CNTs in different types and sizes are presented to illustrate the feasibility of this method. To verify the correctness of two methods, the existing results provided by the other experimental and numerical methods are compared and discussed in this study. The comparison shows that the results estimated by these models fall in the reasonable range.

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