Dissertations / Theses: 'Mechanical engineering. Nanostructured materials'

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Shafiullah, Mohammad. "Synthesis of Nanostructured Silicon - Germanium Thermoelectric Materials by Mechanical Alloying." Thesis, KTH, Skolan för informations- och kommunikationsteknik (ICT), 2015. http://urn.kb.se/resolve?urn=urn:nbn:se:kth:diva-175143.

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Silicon-germanium (SiGe) thermoelectric material is especially suited in power generation operating above 700 °C to 1000 °C to convert heat into electricity. Traditional bulk SiGe alloy thermoelectric materials has the value of dimensionless thermoelectric figure of merit (ZT) at maximum about 0.93 at 900 °C. It corresponds to 8% highest device efficiency to convert heat into electricity for commercial SiGe thermoelectric devices. Recently, many efforts have been made to increase the ZT value of SiGe thermoelectric materials. Among them, nanostructuring of SiGe alloy is an effective mechanism to enhance the ZT value of the thermoelectric material. In this approach, the ZT value increases due to the reduction of thermal conductivity caused by enhanced phonon scattering off the increased density of nanograin boundaries. There are different approaches to make nanostructured SiGe alloy bulk thermoelectric materials. Mechanical alloying of elemental Si and Ge powder is one of them. In this thesis work, different compositions of elemental Si and Ge micro powders have been mechanically alloyed using ball milling technique to produce SiGe alloy nanopowder and then were compacted and sintered by spark plasma sintering (SPS) method. Different characterization techniques have been used to see the effect of compositions, milling parameters and sintering conditions on the properties of the synthesized nanopowders and sintered compact samples.

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Zhao, Qing Ph D. Massachusetts Institute of Technology. "First-principles approaches for accurate predictions of nanostructured materials." Thesis, Massachusetts Institute of Technology, 2019. https://hdl.handle.net/1721.1/121849.

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Thesis: Ph. D. in Mechanical Engineering and Computation, Massachusetts Institute of Technology, Department of Mechanical Engineering, 2019
Cataloged from PDF version of thesis. "February 2019."
Includes bibliographical references (pages 154-180).
Nanostructured materials have attracted increasing interest in recent years due to their unusual mechanical, electrical, electronic and optical properties. First-principles electronic structure calculations (e.g., with density functional theory or DFT) provide unique insights into the structure-property relationships of nanostructured materials that can enable further design and engineering. The favorable balance between efficiency and accuracy of DFT has led to its wide application in chemistry, solid-state physics and biology. However, DFT still has limitations and suffers from large pervasive errors in its predicted properties. For small systems, more accurate methods are available but challenges remain for studying nm-scale materials. In the solid-state, unique challenges arise from both the strong sensitivity of correlated transition metal oxides on approximations in DFT and the periodic boundary condition.
Therefore, a greater understanding of approximations inherent in DFT is needed for nanostructured materials. In this thesis, we study nanostructured semiconducting materials, where conventional DFT can be expected to perform well. We develop methods for sampling amorphous materials, rationalizing periodic table dependence in material stability for materials discovery of ordered materials, and bring a surface reactivity perspective to understanding growth processes during materials synthesis. Within the challenging cases of transition metal oxides, we explore how common approximations (e.g., DFT+U and hybrids) affect key nanoscale properties, such as the nature of density localization, and as a result, key observables such as surface stability and surface reactivity. Observation of divergent behavior between these two methods highlights the limited interchangeability of DFT+U and hybrids in the solid-state community.
Finally, leveraging the understanding developed in the first two parts of the thesis, we employ a multiscale approach to systematically tailor DFT functional choice for challenging condensed phase systems using accurate reference data from higher level methods. The combination of large-scale electronic structure modeling with state-of-the-art methodology will provide important, predictive insight into tailoring the nanoscale properties of useful materials, and further development in approximate DFT.
by Qing Zhao.
Ph. D. in Mechanical Engineering and Computation
Ph.D.inMechanicalEngineeringandComputation Massachusetts Institute of Technology, Department of Mechanical Engineering

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Lenert, Andrej. "Tuning energy transport in solar thermal systems using nanostructured materials." Thesis, Massachusetts Institute of Technology, 2014. http://hdl.handle.net/1721.1/92164.

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Thesis: Ph. D., Massachusetts Institute of Technology, Department of Mechanical Engineering, 2014.
Cataloged from PDF version of thesis.
Includes bibliographical references (pages 137-146).
Solar thermal energy conversion can harness the entire solar spectrum and theoretically achieve very high efficiencies while interfacing with thermal storage or back-up systems for dispatchable power generation. Nanostructured materials allow us to tune the spectral properties and heat transfer behavior to enable such systems. However, under high temperature conditions, thermal management, system optimization and minimization of parasitic losses are necessary to achieve competitive solar power generation. This thesis seeks to achieve spectral control and thermal management through manipulation of nanostructured materials. First, this thesis presents the design and development of a nanophotonic solar thermophotovoltaic (STPV) that harnesses the full spectrum of the sun, in a solid-state and scalable way. Through device optimization and control over spectral properties at high temperatures (~1300 K), a device that is 3 times more efficient than previous STPVs is demonstrated. To achieve this result, a framework was developed to identify which parts of the spectrum are critical and to guide the design of nanostructured absorbers and emitters for STPVs. The work elucidated the relative importance of spectral properties depending on the operating regime and device geometry. Carbon nanotubes and a silicon/silicon dioxide photonic crystal were used to target critical properties in the high solar concentration regime; and two-dimensional metallic photonic crystals were used to target critical properties in the low solar concentration regime. A versatile experimental platform was developed to interchangeably test different STPV components without sacrificing experimental control. In addition to demonstrating significant improvements in STPV efficiency, an experimental procedure to quantify the energy conversion and loss mechanisms helped improve and validate STPV models. Using these validated models, this thesis presents a scaled-up device that can achieve 20% efficiencies in the near term. With potential integration of thermal-based storage, such a technology can supply power efficiently and on-demand, which will have significant implications for adoption of STPVs. Second, the thesis shifts focus away from solid-state systems to thermal-fluid systems. A new figure of merit was proposed to capture the thermal storage, heat transfer and pumping power requirements for a heat transfer fluid is a solar thermal system. Existing and emerging fluids were evaluated based on the new metric as well as practical issues. Finally, sub-micron phase change material (PCM) suspensions are investigated for simultaneous enhancement of local heat transfer and thermal storage capacity in solar thermal systems. A physical model was developed to explain the local heat transfer characteristics of a flowing PCM suspension undergoing melting. A mechanism for enhancement of heat transfer through.control over the distribution of PCM particles inside a channel was discovered and explained. Together, this thesis makes significant contributions towards improving our understanding of the role and the effective use of nanostructured materials in solar thermal systems.
by Andrej Lenert.
Ph. D.

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Kuryak, Chris A. (Chris Adam). "Nanostructured thin film thermoelectric composite materials using conductive polymer PEDOT:PSS." Thesis, Massachusetts Institute of Technology, 2013. http://hdl.handle.net/1721.1/79270.

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Thesis (S.M.)--Massachusetts Institute of Technology, Dept. of Mechanical Engineering, 2013.
Cataloged from PDF version of thesis.
Includes bibliographical references (p. 65).
Thermoelectric materials have the ability to convert heat directly into electricity. This clean energy technology has advantages over other renewable technologies in that it requires no sunlight, has no moving parts, and is easily scalable. With the majority of the unused energy in the United States being wasted in the form of heat and the recent mandates to reduce greenhouse gas emissions, thermoelectric devices could play an important role in our energy future by recovering this wasted heat and increasing the efficiency of energy production. However, low conversion efficiencies and the high cost of crystalline thermoelectric materials have restricted their implementation into modem society. To combat these issues, composite materials that use conductive polymers have been under investigation due to their low cost, manufacturability, and malleability. These new composite materials could lead to cheaper thermoelectric devices and even introduce the technology to new application areas. Unfortunately, polymer composites have been plagued by low operating efficiencies due to their low Seebeck coefficient. In this research, we show an enhanced Seebeck coefficient at the interface of poly(3,4- ethylenedioxythiophene) poly(styrenesulfonate) (PEDOT:PSS) spin coated onto silicon substrates. The maximum Seebeck coefficient achieved was 473 uV/K with a PEDOT:PSS thickness of 7.75 nm. Furthermore, the power factor of this interface was optimized with a 15.25 nm PEDOT:PSS thickness to a value of 1.24 uV/K2-cm, which is an order of magnitude larger than PEDOT:PSS itself. The effect of PEDOT:PSS thickness and silicon thickness on the thermoelectric properties is also discussed. Continuing research into this area will attempt to enhance the power factor even further by investigating better sample preparation techniques that avoid silicon surface oxidation, as well as creating a flexible composite material of PEDOT:PSS with silicon nanowires..
by Chris A. Kuryak.
S.M.

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Choi, Hyungryul. "Nanostructured multifunctional materials for control of light transport and surface wettability." Thesis, Massachusetts Institute of Technology, 2014. http://hdl.handle.net/1721.1/92156.

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Thesis: Ph. D., Massachusetts Institute of Technology, Department of Mechanical Engineering, 2014.
Cataloged from PDF version of thesis.
Includes bibliographical references (pages 221-234).
Biological surfaces have evolved to optimize their structures and physical and chemical properties at the micro/nanoscale for adaptation to different environments, exhibiting a wide variety of beneficial functions, ranging from optical properties to wettability, such as anti-reflection coatings in moth eyes and self-cleaning surfaces of lotus leaves. Combining optical and wetting functions in multifunctional materials is critical for practical engineering applications such as energy harvesting, color generation, and operation of optical instrumentation in humid conditions. However, analyses of the functional design constraints of specified optical and wetting functions followed by integrative optimization have been rare, and limited to simple pairwise combinations from two distinct research disciplines. Furthermore, fabricating the desired multifunctional nanostructured materials remains a difficult engineering challenge due to the limitations of existing nanofabrication methods. The work in this thesis focuses on the joint control of light transport and surface wettability. It starts with analysis and design, followed by implementation of new multifunctional nanostructured materials using novel nanolithographic fabrication techniques. We first consider multifunctional silica surfaces consisting of conical nanostructures (nanocones) for enhanced omnidirectional broadband transmissivity in conjunction with structural superhydrophilicity or robust superhydrophobicity. This is achieved through a systematic approach to concurrent design of nanostructures in both domains and an innovative fabrication procedure that achieves the desired aspect-ratios and periodicities in the nanocones with few defects, high feature repeatability, and large pattern area. Enhanced optical transmissivity exceeding 98% has been achieved over a broad bandwidth and range of incident angles independent of the polarization state. These nanotextured surfaces also demonstrate robust anti-fogging or self-cleaning properties, offering potential benefits for applications such as photovoltaic solar cells. As an extended function of this silica nanocone surface, we propose the systematic design and development of nanostructured transparent anti-fingerprint surface coatings that degrade fingerprint oils using photocatalytic effects. The TiO₂-based porous nanoparticle surfaces exhibit short timescales for decomposition of fingerprint oils under ultraviolet light, plus they have transparency comparable to typical glass with low optical haze (< 1%), and are mechanically robust. These TiO₂ nanostructured surfaces are anti-fogging, anti-bacterial, compatible with flexible glass substrates, and remain photocatalytically active in natural sunlight Lastly, instead of eliminating all reflections over the broadband wavelengths of light for enhanced super-transmissivity, 2-dimensional (2D) periodic nanorod surfaces capable of generating vivid colors by wavelength-selective reflection have also been designed and developed. The geometry of the nanorod structures on top of a silicon substrate is optimized to obtain high contrast of colors while still allowing for scalable nanopatterning with the help of newly invented nanofabrication processes. By developing an integrated understanding of optical and wetting properties of nanostructured materials, we have been able to realize novel functionalities using nanostructured surfaces conceived by concurrent design in the two domains and created by new nanofabrication techniques.
by Hyungryul Choi.
Ph. D.

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Garg, Jivtesh. "Thermal conductivity from first-principles in bulk, disordered, and nanostructured materials." Thesis, Massachusetts Institute of Technology, 2011. http://hdl.handle.net/1721.1/65280.

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Thesis (Ph. D.)--Massachusetts Institute of Technology, Dept. of Mechanical Engineering, 2011.
Cataloged from PDF version of thesis.
Includes bibliographical references (p. 133-138).
Thermal conductivity is an important transport property that plays a vital role in applications such as high efficiency thermoelectric devices as well as in thermal management of electronics. We present a first-principles approach based on density-functional perturbation theory (DFPT) to predict the thermal conductivity of semiconducting materials. Heat in these materials is conducted by lattice vibrations (phonons). The most important ingredients in the prediction of thermal conductivity in such materials are the second- and third-order derivatives of energy with respect to atomic displacements. Typically, these are derived using empirical potentials which do not produce the correct harmonic and anharmonic behavior, necessary to accurately compute phonon frequencies and relaxation times. We obtain these derivatives from quantum mechanics through DFPT, and use them along with the solution of the phonon Boltzmann transport equation to predict thermal conductivity. We apply the approach to isotopically pure silicon and germanium as well as materials with disorder such as silicon-germanium alloys and show how this leads to excellent agreement between computed and experimentally measured values. The approach is also applied to predict thermal transport in nanostructured materials such as superlattices. In isotopically pure silicon and germanium, phonons scatter only through the three-phonon anharmonic scattering processes. Using the single-mode relaxation time approximation and estimating the scattering rate of these processes based on the force constants derived from DFPT, excellent agreement is obtained between computed and measured values of thermal conductivity. The approach predicts that in isotopically pure silicon, more than 90% of the heat is conducted by phonons of mean free path larger than 40 nm, providing avenues to lower thermal conductivity through nanostructuring. To predict thermal transport in disordered silicon-germanium alloys of any composition, we make use of the phonon modes of an average crystal which has the two atom unit cell and average mass and force constants appropriate for that composition. The disorder is taken to lead to elastic two-phonon scattering in addition to the three-phonon scattering present in pure materials. The idea was first proposed by Abeles in 1963; however we are able to compute all the ingredients from firstprinciples. The force constants for the composition Sio.5 Geo.5 are obtained by using the virtual crystal where the atomic potential at each site is an average of the silicon and germanium potentials. We demonstrate how this approach can be used to guide design of nanostructured materials to further lower thermal conductivity. In superlattices, we again use the virtual crystal to obtain the second-order and third-force constants. Computed thermal conductivity is found to lower with increase in superlattice period; however, the predicted values are higher than experimentally measured values, and we discuss the cause of this discrepancy. In the limit of very small period superlattice, we find that thermal conductivity can increase dramatically and can exceed that of isotopically pure silicon. This cause of this unexpected result is discussed, and its implications for high thermal conductivity materials, important for applications in thermal management of electronics.
by Jivtesh Garg.
Ph.D.

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Zhang, Liang. "Stability analysis of atomic structures." Diss., University of Iowa, 2006. http://ir.uiowa.edu/etd/70.

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Izadi, Sina. "Al/Ti Nanostructured Multilayers: from Mechanical, Tribological, to Corrosion Properties." Scholar Commons, 2016. https://scholarcommons.usf.edu/etd/6265.

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Nanostructured metallic multilayers (NMMs) are well-known for their high strength in smaller bilayer thicknesses. Six Al/Ti (NMM) with different individual layer thickness were tested for their mechanical hardness using a nanoindentation tool. Individual layer thicknesses were chosen carefully to cover the whole confined layer slip (CLS) model. Nano-hardness had a reverse relation with the square root of individual layer thickness and reached a steady state at ~ 5 nm bilayer thickness. Decreasing the layer bilayer thickness from ~ 104 nm to ~ 5 nm, improved the mechanical hardness up to ~ 101%. Residual stresses were measured using grazing incident X-ray diffraction (GIXRD). Effect of residual stress on atomic structure and dislocation propagation was then investigated by comparing the amount and type of stresses in both aluminum and titanium phases. Based on the gathered data from GIXRD scans tensile stress in Ti phases, and compressive stress in Al would increase the overall coherency of structure. Wear rate in coatings is highly dependent on design and architect of the structure. NMM coatings are known to have much better wear resistance compare to their monolithic constituent phases by introducing a reciprocal architect. In current study wear rate of two Al/Ti NMMs with individual layer thicknesses of ~ 2.5 nm and ~ 30 nm were examined under normal loads of 30 µN, 60 µN, and 93 µN. Wears strokes were performed in various cycles of 1, 2, 3, 4 5 and 10. Wear rates were then calculated by comparing the 3D imaging of sample topology before and after tests. Nano-hardness of samples was measured pre and post each cycle of wear using a nanoindentation tool. The microstructure of samples below the worn surface was then characterized using scanning electron microscopy (SEM), transmission electron microscopy (TEM), atomic force microscopy (AFM), focus ion beam (FIB) and an optical profilometer. Orientation mapping was performed to analyze the microstructure of layers beneath the nano indents. TEM imaging from the cross section of worn samples indicated severely plastically deformed layer (SPDL) below the worn surface. Shear bands and twins are visible after wear and below the worn surface. Decreasing the layer thickness from 30 nm to 2.5 nm resulted in ~ 5 time’s better wear resistance. Nanowear caused surface hardening which consequently increased nano hardness up to ~ 30% in the sample with 2.5 nm individual layer thickness. Increasing the interfaces density of NMMs will significantly improve the corrosion resistance of coating. Reciprocal layers and consequently interfaces will block the path of aggressive content toward the substrate. Corrosion rate evolution of Al/Ti multilayers was investigated through DC corrosion potentiodynamic test. Results seem to be very promising and demonstrate up to 30 times better corrosion resistance compared to conventional sputtered monolithic aluminum. Corrosion started in the form of pitting and then transformed to the localized galvanic corrosion. Decreasing the bilayer thickness from ~ 10.4 nm to ~ 5 nm will decrease the corrosion current density (icorr) of ~ 5.42 × 10-7 (A/cm2) to ~ 6.11 × 10-10 (A/cm2). No sign of corrosion has been seen in the sample with ~ 2.5 nm individual layer thickness. Further AFM and TEM analysis from surface and cross section of NMMs indicate that a more coherent layer by layer structure improves the corrosion rate. Interfaces have a significant role in blocking the pores and imperfections inside coating.

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Basnayaka, Punya A. "Development of Nanostructured Graphene/Conducting Polymer Composite Materials for Supercapacitor Applications." Scholar Commons, 2013. http://scholarcommons.usf.edu/etd/4864.

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The developments in mobile/portable electronics and alternative energy vehicles prompted engineers and researchers to develop electrochemical energy storage devices called supercapacitors, as the third generation type capacitors. Most of the research and development on supercapacitors focus on electrode materials, electrolytes and hybridization. Some attempts have been directed towards increasing the energy density by employing electroactive materials, such as metal oxides and conducting polymers (CPs). However, the high cost and toxicity of applicable metal oxides and poor long term stability of CPs paved the way to alternative electrode materials. The electroactive materials with carbon particles in composites have been used substantially to improve the stability of supercapacitors. Furthermore, the use of carbon particles and CPs could significantly reduce the cost of supercapacitor electrodes compared to metal oxides. Recent developments in carbon allotropes, such as carbon nanotubes (CNTs) and especially graphene (G), have found applications in supercapacitors because of their enhanced double layer capacitance due to the large surface area, electrochemical stability, and excellent mechanical and thermal properties. The main objective of the research presented in this dissertation is to increase the energy density of supercapacitors by the development of nanocomposite materials composed of graphene and different CPs, such as: (a) polyaniline derivatives (polyaniline (PANI), methoxy (-OCH3) aniline (POA) and methyl (-CH3) aniline (POT), (b) poly(3-4 ethylenedioxythiophene) (PEDOT) and (c) polypyrrole (PPy). The research was carried out in two phases, namely, (i) the development and performance evaluation of G-CP (graphene in conducting polymers) electrodes for supercapacitors, and (ii) the fabrication and testing of the coin cell supercapacitors with G-CP electrodes. In the first phase, the synthesis of different morphological structures of CPs as well as their composites with graphene was carried out, and the synthesized nanostructures were characterized by different physical, chemical and thermal characterization techniques, such as Scanning Electron Microscopy (SEM), Transmission Electron Microscopy (TEM), UV-visible spectroscopy, Fourier Transform Infrared (FTIR) spectroscopy, Raman spectroscopy, BET surface area pore size distribution analysis and Thermogravimetric Analysis (TGA). The electrochemical properties of G-CP nanocomposite-based supercapacitors were investigated using Cyclic Voltammetry (CV), galvanostatic charge-discharge and Electrochemical Impedance Spectroscopy (EIS) techniques in different electrolytes, such as acidic (2M H2SO4 and HCl), organic ( 0.2 M LiClO4) and ionic liquid (1M BMIM-PF6) electrolytes. A comparative study was carried out to investigate the capacitive properties of G-PANI derivatives for supercapacitor applications. The methyl substituted polyaniline with graphene as a nanocomposite (G-POT) exhibited a better capacitance (425 F/g) than the G-PANI or the G-POA nanocomposite due to the electron donating group of G-POT. The relaxation time constants of 0.6, 2.5, and 5s for the G-POT, G-PANI and G-POA nanocomposite-based supercapacitors were calculated from the complex model by using the experimental EIS data. The specific capacitances of two-electrode system supercapacitor cells were estimated as 425, 400, 380, 305 and 267 F/g for G-POT, G-PANI, G-POA, G-PEDOT and G-PPy, respectively. The improvements in specific capacitance were observed due to the increased surface area with mesoporous nanocomposite structures (5~10 nm pore size distribution) and the pseudocapacitance effect due to the redox properties of the CPs. Further, the operating voltage of G-CP supercapacitors was increased to 3.5 V by employing an ionic liquid electrolyte, compared to 1.5 V operating voltage when aqueous electrolytes were used. On top of the gain in the operating voltage, the graphene nano-filler of the nanocomposite prevented the degradation of the CPs in the long term charging and discharging processes. In the second phase, after studying the material's chemistry and capacitive properties in three-electrode and two-electrode configuration-based basic electrochemical test cells, coin cell type supercapacitors were fabricated using G-CP nanocomposite electrodes to validate the tested G-CPs as devices. The fabrication process was optimized for the applied force and the number of spacers in crimping the two electrodes together. The pseudocapacitance and double layer capacitance values were extracted by fitting experimental EIS data to a proposed equivalent circuit, and the pseudocapacitive effect was found to be higher with G-PANI derivative nanocomposites than with the other studied G-CP nanocomposites due to the multiple redox states of G-PANI derivatives. The increased specific capacitance, voltage and small relaxation time constants of the G-CPs paved the way for the fabrication of safe, stable and high energy density supercapacitors.

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Trelewicz, Jason R. "Nanostructure stabilization and mechanical behavior of binary nanocrystalline alloys." Thesis, Massachusetts Institute of Technology, 2008. http://hdl.handle.net/1721.1/46679.

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Thesis (Ph. D.)--Massachusetts Institute of Technology, Dept. of Materials Science and Engineering, February 2009.
Includes bibliographical references (leaves 131-145).
The unique mechanical behavior of nanocrystalline metals has become of great interest in recent years, owing to both their remarkable strength and the emergence of new deformation physics at the nanoscale. Of particular interest has been the breakdown in Hall-Petch strength scaling, which is frequently attributed by atomistic simulations to a mechanistic shift to interface dominated plasticity. Experimental validation has been less abundant, primarily due to the processing challenges associated with achieving homogeneous nanocrystalline samples suitable for mechanical testing. Alloying has been proposed as a potential route to high-quality nanocrystalline metals, although choice of an appropriate alloy system, based on available thermodynamic data, remains elusive. In this thesis, we propose a thermodynamic model for nanostructure stabilization that derives from the energetic state variables characteristic of binary alloys. These modeling results motivate the study of Ni-W alloys in particular, which may be synthesized via aqueous electrodeposition, accessing grain sizes across the entire Hall-Petch breakdown regime as characterized by x-ray diffraction and transmission electron microscopy. Ambient temperature nanoindentation testing is employed to evaluate the mechanical behavior of the as-deposited alloys, assessing the nature of flow, the rate sensitivity, and pressure sensitivity of deformation, with emphasis on property inflections required to bridge the behavior of nanocrystalline metals to amorphous solids. The rate sensitivity, in particular, demonstrates an inherent dependence on nanocrystalline grain size, exhibiting a maximum in the vicinity of the Hall-Petch breakdown as a consequence of a shift to glass-like shear localization. In light of this finding, we study the Hall-Petch breakdown at high strain rates, and show that an "inverse Hall-Petch" weakening regime emerges at high rates. Additional effects from structural relaxation are investigated, and illustrated to strongly influence the strength scaling behavior and shift to inhomogeneous flow. Relaxed samples are also subjected to elevated temperature indentation tests, and the results discussed in the context of thermally-activated plasticity, thus providing a more quantitative analysis of the nanoscale deformation mechanisms.
by Jason R. Trelewicz.
Ph.D.

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Rezaei, Seyed Emad. "Defect Engineering: Novel Strengthening Mechanism for Low- Dimensional Zinc Oxide Nanostructures." Wright State University / OhioLINK, 2018. http://rave.ohiolink.edu/etdc/view?acc_num=wright1532902032338622.

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Epstein, Alexander. "Bioinspired, Dynamic, Structured Surfaces for Biofilm Prevention." Thesis, Harvard University, 2012. http://dissertations.umi.com/gsas.harvard:10505.

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Bacteria primarily exist in robust, surface-associated communities known as biofilms, ubiquitous in both natural and anthropogenic environments. Mature biofilms resist a wide range of biocidal treatments and pose persistent pathogenic threats. Treatment of adherent biofilm is difficult, costly, and, in medical systems such as catheters, frequently impossible. Adding to the challenge, we have discovered that biofilm can be both impenetrable to vapors and extremely nonwetting, repelling even low surface tension commercial antimicrobials. Our study shows multiple contributing factors, including biochemical components and multiscale reentrant topography. Reliant on surface chemistry, conventional strategies for preventing biofilm only transiently affect attachment and/or are environmentally toxic. In this work, we look to Nature’s antifouling solutions, such as the dynamic spiny skin of the echinoderm, and we develop a versatile surface nanofabrication platform. Our benchtop approach unites soft lithography, electrodeposition, mold deformation, and material selection to enable many degrees of freedom—material, geometric, mechanical, dynamic—that can be programmed starting from a single master structure. The mechanical properties of the bio-inspired nanostructures, verified by AFM, are precisely and rationally tunable. We examine how synthetic dynamic nanostructured surfaces control the attachment of pathogenic biofilms. The parameters governing long-range patterning of bacteria on high-aspect-ratio (HAR) nanoarrays are combinatorially elucidated, and we discover that sufficiently low effective stiffness of these HAR arrays mechanoselectively inhibits ~40% of Pseudomonas aeruginosa biofilm attachment. Inspired by the active echinoderm skin, we design and fabricate externally actuated dynamic elastomer surfaces with active surface microtopography. We extract from a large parameter space the critical topographic length scales and actuation time scales for achieving nearly ~80% attachment reduction. We furthermore investigate an atomically mobile, slippery liquid infused porous surface (SLIPS) inspired by the pitcher plant. We show up to 99.6% reduction of multiple pathogenic biofilms over a 7-day period under both static and physiologically realistic flow conditions—a ~35x improvement over state-of-the-art surface chemistry, and over a far longer timeframe. Moreover, SLIPS is shown to be nontoxic: bacteria simply cannot attach to the smooth liquid interface. These bio-inspired strategies significantly advance biofilm attachment prevention and promise a tremendous range of industrial, clinical, and consumer applications.
Engineering and Applied Sciences

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Guan, Juan. "Investigations on natural silks using dynamic mechanical thermal analysis (DMTA)." Thesis, University of Oxford, 2013. http://ora.ox.ac.uk/objects/uuid:c16d816c-84e3-4186-8d6d-45071b9a7067.

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This thesis examines the dynamic mechanical properties of natural silk fibres, mainly from silkworm species Bombyx mori (B. mori) and spider species Nephila edulis, using dynamic mechanical thermal analysis, DMTA. The aim is not only to provide novel data on mechanical properties of silk, but also to relate these properties to the structure and morphology of silk. A systematic approach is adopted to evaluate the effect of the three principal factors of stress, temperature and hydration on the properties and structure of silk. The methods developed in this work are then used to examine commercially important aspects of the ‘quality’ of silk. I show that the dynamic storage modulus of silks increases with loading stress in the deformation through yield to failure, whereas the conventional engineering tensile modulus decreases significantly post-yield. Analyses of the effects of temperature and thermal history show a number of important effects: (1) the loss peak at -60 °C is found to be associated the protein-water glass transition; (2) the increase in the dynamic storage modulus of native silks between temperature +25 and 100 °C is due simply to water loss; (3) a number of discrete loss peaks from +150 to +220°C are observed and attributed to the glass transition of different states of disordered structure with different intermolecular hydrogen bonding. Excess environmental humidity results in a lower effective glass transition temperature (Tg) for disordered silk fractions. Also, humidity-dynamic mechanical analysis on Nephila edulis spider dragline silks has shown that the glass transition induces a partial supercontraction, called Tg contraction. This new finding leads to the conclusion of two independent mechanisms for supercontraction in spider dragline silks. Study of three commercial B. mori cocoon silk grades and a variety of processed silks or artificial silks shows that lower grade and poorly processed silks display lower Tg values, and often have a greater loss tangent at Tg due to increased disorder. This suggests that processing contributes significantly to the differences in the structural order among natural or unnatural silks. More importantly, dynamic mechanical thermal analysis is proposed to be a potential tool for quality evaluation and control in silk production and processing. In summary, I demonstrate that DMTA is a valuable analytical tool for understanding the structure and properties of silk, and use a systematic approach to understand quantitatively the important mechanical properties of silk in terms of a generic structural framework in silk proteins.

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Hubbard, Joshua A. "A study of aerodynamic deaggregation mechanisms and the size control of NanoActive™ aerosol particles." Thesis, Kansas State University, 2006. http://hdl.handle.net/2097/173.

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Master of Science
Department of Mechanical and Nuclear Engineering
Steven J. Eckels
Christopher M. Sorensen
Large specific surface areas and high concentrations of reactive edge and defect sites make NanoActive™ metal oxide powders ideal chemical adsorbents. These powders are dispersed in aerosol form to remediate toxic wastes and neutralize chemical and biological warfare agents. In the destructive adsorption of toxic chemicals, effective application requires particles be as small as possible, thus, maximizing surface area and number of edge and defect sites. Other applications, e.g. smoke clearing, require particles be large so they will settle in a timely manner. Ideally, particle size control could be engineered into powder dispersion devices. The purpose of this study was to explore particle cohesion and aerodynamic deaggregation mechanisms to enhance the design of powder dispersion devices. An aerosol generator and four experimental nozzles were designed to explore the most commonly referenced deaggregation mechanisms: particle acceleration, particles in shear and turbulent flows, and particle impaction. The powders were then dispersed through the nozzles with increasing flow rates. A small angle light scattering device was used to make in situ particle size measurements. The nozzle designed for impaction deaggregated the NanoActive™ MgO particles to a lesser degree than the other three nozzles, which deaggregated the particles to a similar degree. Flows in three of the four nozzles were simulated in a commercial computational fluid dynamics package. Theoretical particle and aggregate stresses from the literature were calculated using simulated data. These calculations suggest particle acceleration causes internal stresses roughly three orders of magnitude larger than shear and turbulent flows. These calculations, coupled with experimental data, lead to the conclusion that acceleration was the most significant cause of particle deaggregation in these experiments. Experimental data also identified the dependence of deaggregation on primary particle size and agglomerate structure. NanoActive™ powders with smaller primary particles exhibited higher resistance to deaggregation. Small primary particle size was thought to increase the magnitude of van der Waals interactions. These interactions were modeled and compared to theoretical deaggregation stresses previously mentioned. In conclusion, deaggregation is possible. However, the ideas of particle size control and a universal dispersion device seem elusive considering the material dependent nature of deaggregation.

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Gunti, Srikanth. "Enhanced Visible Light Photocatalytic Remediation of Organics in Water Using Zinc Oxide and Titanium Oxide Nanostructures." Scholar Commons, 2017. http://scholarcommons.usf.edu/etd/6852.

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The techniques mostly used to decontaminate air as well as water pollutants have drawbacks in terms of higher costs, require secondary treatment, and some methods are very slow. So, emphasis has been given to water though the use of photocatalysts, which break organic pollutants to water and carbon dioxide and leave no trace of by-products at the end. Photocatalytic remediation aligns with the waste and wastewater industries’ zero waste schemes with lower cost, eco-friendly and sustainable treatment technology. The commonly used photocatalysts such as titanium oxide (TiO2), zinc oxide (ZnO), tungsten oxide (WO3) have band gap of nearly 3.2 eV. The lower energy band-gap of a semiconductor makes it a better photocatalyst. The major drawbacks of photocatalysts are its inefficiency to work under visible light and high photocorrosion which limits its uses. These limitations can be mitigated through dopants and the formation of varying morphologies like nanowires, nanoparticles, nanotubes etc. Several organic pollutants are insoluble in water, which inhibits the pollutant (insoluble) to come in contact with photocatalytic material thus hindering remediation characteristic of a photocatalyst. Binder material used to immobilize the photocatalytic material tends to decompose due to oxidative and reduction reactions around the photocatalyst which causes the loss of photocatalytic material. This investigation displays the advantage of organic remediation in visible radiation using graphene (G) doped TiO2 nanoparticles and nanowires. The nanostructured G-TiO2 nanoparticles and G-TiO2 nanowires were synthesized using sol-gel and hydrothermal methods. The nanostructured materials were characterized using scanning electron microscopy (SEM), Transmission electron microscopy (TEM), X-ray diffraction (XRD), UV-visible spectroscopy (UV-vis), Fourier transform infrared spectroscopy (FTIR) and particle analyser procedures. The remediation of organic compounds (methyl orange) in water was achieved under visible radiation using graphene doped nanostructured photocatalytic materials. The sol-gel synthesized G-TiO2 nanoparticles has shown complete remediation of methyl orange (MO) in less than four hours, thus displaying enhanced photocatalytic activity achieved through graphene doping on TiO2 nanostructures The dopant and structure introduced in zinc oxide (ZnO) nanomaterials bring foundation for enhanced photocatalytic activity due to lowering of the band gap, and decreasing of photocorrosion through delaying of electron-hole recombination. The challenge to synthesize both nanowire and nanoparticle structures of ZnO doped with graphene (G) are carried out by simple and cost effective hydrothermal as well as super saturation precipitation techniques, respectively. Various nanostructures of ZnO have been synthesized using precipitation and hydrothermal methods are ZnO nanoparticles, G doped ZnO nanoparticles, ZnO nanowires, G doped ZnO nanowires, TiO2 seeded ZnO nanowires and G doped TiO2 seeded ZnO nanowires The synthesized ZnO based nanostructures were characterized using SEM, TEM, XRD, UV-vis, FTIR and particle analyser methods respectively. The standard organic pollutant methyl orange (MO) dye was employed in the water to understand the effective remediation using ZnO nanostructured materials under visible light radiation. The G-ZnO NW structure has shown effective remediation of MO in water in three hours compared to other synthesized nanostructured ZnO materials. The petroleum compounds were photocatalytically remediated from water using G- TiO2 nanoparticles material in visible light radiation. The G-TiO2 nanoparticle was synthesized using sol-gel technique and used on various petroleum-based chemicals (toluene, naphthalene and diesel) were remediated, and samples were analysed using optical and gas chromatography (GC) techniques. The importance of pollutant to come in contact with photocatalyst have been demonstrated by employing surfactant along with G-TiO2 nanoparticles to remediate naphthalene. Earlier studies in this investigation have shown that graphene (G) doping in both titanium oxide (TiO2) and zinc oxide (ZnO), has brought about a reduction in photocorrosion, and an increase in the photocatalytic efficiency for remediation of organics under visible light (λ > 400nm). However, the graphene doped photocatalysts have proven to be hard to coat on a surface, due to the strong hydrophobic nature of graphene. So, attempts have been made to use polyaniline (PANI), a conducting polymer, as a binder material by insitu polymerization of aniline over G-TiO2 nanoparticles (G-TiO2 NP) and G-ZnO nanowires (G-ZnO NW) & characterized using SEM, XRD, UV-vis and FTIR techniques. The photocatalytic, as well as photoelectrochemical catalytic performance of PANI:G-TiO2 NP and PANI:G-ZnO NW, were investigated. The standard MO in water was used for both PANI:G-TiO2 NP and PANI:G-ZnO NW electrodes on conducting substrates. 1:1 PANI:G-TiO2 NP shows an increase of 31% in the remediation of MO in water at potential of +1000 mV, and with the ease in coating PANI:G-TiO2 NP and PANI:G-ZnO NW on various substrates, on top of the visible light remediation allows for the use of these materials and process to be used for practical applications of remediation of organics from water.

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16

Daugherty, Timothy J. "Computational Fluid Dynamics Modeling and Experimental Investigation of a Chemical Vapor Deposition Synthesis of ZnO Nanostructures." Youngstown State University / OhioLINK, 2016. http://rave.ohiolink.edu/etdc/view?acc_num=ysu1464802505.

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17

Yang, Weixuan. "Temperature-dependent homogenization technique and nanoscale meshfree particle methods." Diss., University of Iowa, 2007. http://ir.uiowa.edu/etd/147.

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18

Hartschuh, Ryan D. "Optical Spectroscopy of Nanostructured Materials." University of Akron / OhioLINK, 2007. http://rave.ohiolink.edu/etdc/view?acc_num=akron1195016254.

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19

Zhang, Jin. "Mechanical behaviours of piezoelectric nanostructures." Thesis, Swansea University, 2014. http://ethos.bl.uk/OrderDetails.do?uin=uk.bl.ethos.678635.

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The objective of this thesis is to present a modelling and simulation study for the mechanics of PNs with an emphasis placed on the unique features of PNs due to the piezoelectric and small scale effects.

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Yan, Kun. "Size effects on the thermo-mechanical behavior on nano-structures/ materials." Click to view the E-thesis via HKUTO, 2008. http://sunzi.lib.hku.hk/hkuto/record/B41290513.

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Choi, Jongwon Ph D. Massachusetts Institute of Technology. "Selective transport properties in nanostructured materials." Thesis, Massachusetts Institute of Technology, 2017. http://hdl.handle.net/1721.1/111322.

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Thesis: Ph. D., Massachusetts Institute of Technology, Department of Materials Science and Engineering, 2017.
Cataloged from PDF version of thesis.
Includes bibliographical references.
Nanostructuring is an established method in engineering materials due to exciting new properties that manifest only in the nano-regime. When investigating nanomaterials, atom-scale simulations can be powerful tools. Through computational approach, one can 1) understand the underlying physics of a materials property, 2) propose new design principles for certain applications and 3) evaluate the performance of the material. In this thesis, we explore new materials and engineering approaches for various fields of application through a number of computational methods - molecular dynamics, density functional theory, semi-classical Boltzmann theory and Monte Carlo simulations. We first investigate the thermal and electrical transport properties of rippled graphene structures. Here we focus on the rippled textures formed by topological defects of graphene, namely Stone-Wales defects and graphene nanobuds. By exploring different configuration of Stone-Wales defects, the effect of rippling on the thermal conductivity is isolated. We also calculated the thermal and electrical transport properties of rippled graphene nanobuds and evaluate their thermoelectric efficiency. While looking into practical approaches to achieve two-dimensional materials with periodic nanostructures, our interest has extended to covalent organic frameworks (COFs) and their desalination properties. Through classical calculations, we show that COF membranes can achieve high salt rejection rate while enhancing the water permeability up to two to three orders of magnitude compared to conventional desalination membranes. The COF membrane was also shown to have decent mechanical properties although further modification may be needed to ensure its mechanical integrity in practical settings. Another type of self-assembled frameworks is the metal-organic frameworks (MOFs). Here the gas adsorption properties of MOF in defective and strained structures have been explored. We first look into water adsorption properties of MOF-801 and explore the role of defects. The defect sites contribute to preferential adsorptive behavior, which changes the water adsorption isotherm significantly. In addition, we look into strained UiO-66 structures and reveal that compressed, asymmetrical pores can affect the adsorptive behaviors of methane and carbon dioxide. This dissertation consists of five chapters. Chapter 1 first covers the general overview of the fields of application in concern: thermal and electrical properties of graphene-based systems, desalination, gas adsorption. Chapter 2 focuses on theoretical methods used for calculating thermal transport properties, electrical properties, desalination properties, and adsorption properties of materials of interest. Our results for the thermal and electrical transport properties of rippled graphene structure are presented in Chapter 3. In Chapter 4, we switch gears to calculate the desalination properties of two-dimensional covalent organic frameworks. Lastly, the gas adsorption of metal organic frameworks is discussed in Chapter 5.
by Jongwon Choi.
Ph. D.

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22

Gunawidjaja, Ray. "Organic/inorganic nanostructured materials towards synergistic mechanical and optical properties /." Diss., Atlanta, Ga. : Georgia Institute of Technology, 2009. http://hdl.handle.net/1853/29733.

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Thesis (Ph.D)--Industrial and Systems Engineering, Georgia Institute of Technology, 2010.
Committee Chair: Tsukruk, Vladimir; Committee Member: Bucknall, David; Committee Member: Kalaitzidou, Kyriaki; Committee Member: Shofner, Meisha; Committee Member: Tannenbaum, Rina. Part of the SMARTech Electronic Thesis and Dissertation Collection.

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23

Xu, Wei-Hua. "Mechanical properties of materials at micro/nano scales /." View abstract or full-text, 2003. http://library.ust.hk/cgi/db/thesis.pl?MECH%202003%20XU.

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24

Évora, Victor Manuel Fortes. "Fabrication and dynamic mechanical behavior of nanocomposites /." View online ; access limited to URI, 2004. http://0-wwwlib.umi.com.helin.uri.edu/dissertations/dlnow/3135902.

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25

Gordon, Jeremy B. "Thermorheological properties of nanostructured dispersions." Thesis, Massachusetts Institute of Technology, 2007. http://hdl.handle.net/1721.1/39866.

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Thesis (S.M.)--Massachusetts Institute of Technology, Dept. of Mechanical Engineering, 2007.
Includes bibliographical references (p. 143-149).
Nanostructured dispersions, which consist of nanometer-sized particles, tubes, sheets, or droplets that are dispersed in liquids, have exhibited substantially higher thermal conductivities over those of the liquids alone. While it is desirable to synthesize a fluid that has improved heat transfer characteristics, it is necessary that the viscosity remain low, so as not to appreciably increase the pumping power needed to employ these fluids in "real world" applications. To this end, the theological and thermal properties of twenty-six different nanostructured dispersions were examined. In terms of rheometry, both steady flow and creep tests were employed, while the transient hot wire technique was utilized to perform measurements of the thermal conductivity of each fluid. Characterization of the dispersed phase was completed using dynamic light scattering and transmission electron microscopy. In particular, the dispersion properties examined were nanostructure material, nanoparticle size, base fluid material, nanostructure concentration, and presence of a surfactant. It was observed that several of the fluids or nanopowders obtained from commercial manufacturers either contained no particles, had the presence of a relatively large proportion of water in ethylene glycol-based fluids, or were composed of particles with sizes far in excess of those claimed by the manufacturer.
(cont.) Ultimately, it was determined that while most of the fluids studied demonstrated Newtonian or slightly shear thinning behavior, several of the fluids exhibited undesirable yield stresses that could be attributed to the formation of a network structure of aggregated nanoparticles. However, it was observed that the addition of a surfactant helped to keep the nanoparticles from clustering to the same degree, thereby eliminating the presence of a yield stress, and reducing the viscosity of the fluid over the entire range of shear rates. The surfactant also contributed to an increase in thermal conductivity enhancement, thereby producing a highly desirable behavior.
by Jeremy B. Gordon.
S.M.

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26

Zhu, Ronghua (Richard). "Atomistic Simulation of Nanostructured Materials." University of Akron / OhioLINK, 2006. http://rave.ohiolink.edu/etdc/view?acc_num=akron1164059775.

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27

Yan, Kun, and 閆琨. "Size effects on the thermo-mechanical behavior on nano-structures/ materials." Thesis, The University of Hong Kong (Pokfulam, Hong Kong), 2008. http://hub.hku.hk/bib/B41290513.

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28

Wang, Benjamin Ning-Haw. "Rheological and morphological characterization of hierarchically nanostructured materials." Thesis, Massachusetts Institute of Technology, 2007. http://hdl.handle.net/1721.1/38975.

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Thesis (Ph. D.)--Massachusetts Institute of Technology, Dept. of Chemical Engineering, 2007.
Vita.
Includes bibliographical references (leaves 154-168).
Hierarchically nanostructured materials exhibit order on multiple length scales, with at least one of a few nanometers. The expected enhancements for applications using these materials include improved mechanical, thermal and electrical properties; however, control of the morphology which governs material performance and fabrication remains a challenge. The development of novel quantitative characterization techniques is important to connect the underlying morphology to relevant processing parameters and macroscopic behavior. Rheological and morphological analysis can illustrate these governing structure-property relationships for hierarchically nanostructured materials based on "O-D" polyhedral oligomeric silsesquioxane (POSS) particles, "l-D" carbon nanotubes (CNTs), and "2-D" clay nanoparticles. We develop a technique, using small-angle X-ray scattering, which provides quantitative measurements of the morphological characteristics of CNT films, including shape, orientation, CNT diameter, and spacing between CNTs. The method reflects a locally averaged measurement that simultaneously samples from millions of CNTs while maintaining the necessary precision to resolve spatial morphological differences within a film.
(cont.) Using this technique we elucidate spatial variation in pristine films and study changes in the film structure as a result of mechanical manipulations such as uniaxial compression and capillarity-induced densification. We study the rheological properties of blends formed from POSS and clay nanoparticles incorporated into PMMA in shear and extensional flow fields. Relevant morphological parameters, such as volume fraction, aspect ratio of the clay particles, and POSS miscibility are determined using wide angle X-ray scattering and transmission electron microscopy. The interdependence between melt rheology and morphology are understood within a theoretical framework for percolated physical networks, providing for comprehensive guidance regarding the performance and processing of POSS and clay based nanocomposites.
by Benjamin Ning-Haw Wang.
Ph.D.

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29

Bassett, David. "Synthesis and applications of bioinspired inorganic nanostructured materials." Thesis, McGill University, 2011. http://digitool.Library.McGill.CA:80/R/?func=dbin-jump-full&object_id=97064.

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Although the study of biominerals may be traced back many centuries, it is only recently that biological principles have been applied to synthetic systems in processes termed "biomimetic" and "bioinspired" to yield materials syntheses that are otherwise not possible and may also reduce the expenditure of energy and/or eliminate toxic byproducts. Many investigators have taken inspiration from interesting and unusual minerals formed by organisms, in a process termed biomineralisation, to tailor the nanostructure of inorganic materials not necessarily found biogenically. However, the fields of nanoparticle synthesis and biomineralisation remain largely separate, and this thesis is an attempt to apply new studies on biomineralisation to nanomaterials science.Principally among the proteins that influence biomineralisation is a group comprised largely of negatively charged aspartic acid residues present in serum. This study is an investigation determining the ability of these serum proteins and other anolagous biomolecules to stabilise biologically relevant amorphous minerals and influence the formation of a variety of materials at the nanoscale. Three different materials were chosen to demonstrate this effect; gold was templated into nanosized single crystals by the action of bioorganic molecules, and the utility of these nanoparticles as a biosensor was explored. The influence of bioorganic molecules on the phase selection and crystal size restriction of titanium dioxide, an important semiconductor with many applications, was explored. The use of bioorganically derived nanoparticles of titanium dioxide was then demonstrated as a highly efficient photocatalyst. Finally, calcium carbonate, a prevalent biomineral was shown to form highly ordered structures over a variety of length scales and different crystalline polymorphs under the influence of a templating protein. In addition, an alternative route to producing calcium phosphate nanoparticle dispersions by mechanical filtration was explored and use as a transfection vector was optimised in two cell lines.Several significant achievements are presented: (i) the assessment of the relative ability of serum, serum derived proteins and their analogues to stabilize the amorphous state, (ii) the formation of single crystalline gold templated by an antibody, (iii) the formation of highly photocatalytically active nanoparticulate anatase by a phosphorylated cyclic esther, (iv) the formation of conical structures at the air liquid interface by the templating ability of a protein and (v) the optimisation of calcium phosphate nanoparticle mediated transfection in two cell lines by mechanical filtration.
Malgré le fait que l'étude des biomatériaux remonte à plusieurs siècles, ce n'est que récemment que des principes biologiques furent appliqués à des systèmes synthétiques dans des procédés de "biomimetic" et "bioinspirés", permettant ainsi de nouveaux matériaux de synthèses tout en réduisant l'expansion d'énergie et/ou d'éliminer les résultantes toxiques. Plusieurs chercheurs se sont inspirés des formes inusuelles dès plus intéressantes créées par des organismes, formés par un procédé de biominéralisation, qui modifie la nanostructure des matériaux synthétiques. Toutefois, les champs d'études des synthèses de nanoparticules et de la biominéralisation demeurent grandement à part, et cette thèse tente d'appliquer de nouvelles études de biominéralisation par rapport à la science des nanomatériaux.Les protéines sériques qui influencent la biominéralisation sont chargées négativement de résidus d'aspartate. Cette recherche déterminera l'habileté de ces protéines et des diverses molécules bio–organiques qui stabilisent biologiquement d'important minéraux aux multiples formes qui influencent la formation de matériaux non biogènes sur une nano échelle; l'or et le dioxyde de titane ont permis de démontrer ce résultat. L'or fut transformé en nanoparticules de cristal par l'action des protéines sériques, et c'est l'utilité de ces nanoparticules en tant que biocapteurs qui fut explorée. L'influence des molécules bios-organiques sur le choix de la phase ainsi que sur la restriction de la grosseur du cristal de dioxyde de titane, un important semi-conducteur dans plusieurs applications, fut explorée. Les nanoparticules dérivant bio-organiquement du dioxyde de titane ont dès lors démontrées leur action hautement efficace comme photo catalyseur. Le carbonate de calcium, un biominéral commun, a su démontré sa capacité à auto-former des structures à multiples échelles ainsi que différents polymorphes cristallins sous l'influence d'une protéine modèle. De plus, la manipulation des structures à former divers arrangements est une variable qui fut démontrée. Finalement, la stabilité des nanoparticules du phosphate de calcium à se disperser dans le sérum de culture fut modifiée afin d'optimiser l'efficacité du transfert dans deux lignes de cellules.Plusieurs grandes recherches ont accomplis de façon significative; (i) l'évaluation de l'habileté relative du sérum, le dérivé des protéines sériques et de leur capacité à stabiliser les phases de leurs multiples formes, (ii) la formation simple cristalline de l'or former par un anticorps, (iii) la formation de nanoparticules très actives photocatalytiquement d'anatase formées par un ester cyclique phosphorylée, (iv) la formation de structures coniques à l'interface air liquide par la capacité de gabarits d'une protéine, (iv) l'optimisation de transfection médiation par des nanoparticules de phosphate de calcium dans deux lignées cellulaires par filtration méchanique.

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Stellman, Paul Steven. "Kinematic and dynamic modeling of Nanostructured Origami." Thesis, Massachusetts Institute of Technology, 2006. http://hdl.handle.net/1721.1/35639.

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Thesis (S.M.)--Massachusetts Institute of Technology, Dept. of Mechanical Engineering, 2006.
Includes bibliographical references (leaves 85-88).
Nanostructured Origami is a manufacturing process that folds nanopatterned thin films into a desired 3D shape. This process extends the properties of 3D design and connectivity found in origami artwork to the bulk fabrication of 3D nanostructures. Our technique is a two-step procedure that first patterns the devices in 2D and then folds the membranes to the final 3D shape along pre-defined creases. This thesis describes theoretical methods that have been developed to model the actuation of origami devices. The background of origami mathematics and advances in robotics are presented in the context of modeling Nanostructured Origami. Unfolding of single-vertex origami is discussed, and an algorithm is implemented to calculate the unfolding trajectories of several devices. Another contribution of this thesis is the presentation of a methodology for modeling the dynamics of two classes of origami: accordion origamis and single-vertex origamis. The forward dynamics and equilibrium analysis of a useful bridge structure and the corner cube origami are simulated. The response of a model of an experimental actuation technique is well-behaved, and it is shown that the final folded state of these devices is at a stable equilibrium.
by Paul Steven Stellman.
S.M.

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31

Yiu, Stephen Cheuk Bun. "Crystallization, structure and mechanical characteristics of polymer-silicate nanocomposites." access abstract and table of contents access full-text, 2005. http://libweb.cityu.edu.hk/cgi-bin/ezdb/dissert.pl?msc-ap-b21175329a.pdf.

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Thesis (M.Sc.)--City University of Hong Kong, 2005.
At head of title: City University of Hong Kong, Department of Physics and Materials Science, Master of Science in materials engineering & nanotechnology dissertation. Title from title screen (viewed on Sept. 4, 2006) Includes bibliographical references.

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32

Kwok, Yee Shan. "Crystallization, structure and mechanical characteristics of polymer-silicate nanocomposites." access abstract and table of contents access full-text, 2005. http://libweb.cityu.edu.hk/cgi-bin/ezdb/dissert.pl?msc-ap-b21174386a.pdf.

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Thesis (M.Sc.)--City University of Hong Kong, 2005.
At head of title: City University of Hong Kong, Department of Physics and Materials Science, Master of Science in materials engineering & nanotechnology dissertation. Title from title screen (viewed on Sept. 1, 2006) Includes bibliographical references.

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33

Zhao, Hongxia. "Studies of thermal, mechanical and fracture behaviors of rigid nanoparticulates filled polymeric composites /." access full-text access abstract and table of contents, 2005. http://libweb.cityu.edu.hk/cgi-bin/ezdb/thesis.pl?phd-ap-b19887589a.pdf.

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Thesis (Ph.D.)--City University of Hong Kong, 2005.
"Submitted to Department of Physics and Materials Science in partial fulfillment of the requirements for the degree of Doctor of Philosophy" Includes bibliographical references.

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34

Chen, Yanshuang. "The Effect of Inorganic Nanostructured Materials on Neurogenesis." Master's thesis, Temple University Libraries, 2016. http://cdm16002.contentdm.oclc.org/cdm/ref/collection/p245801coll10/id/421454.

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Bioengineering
M.S.
Damage and/or loss of functional neurons can lead to detrimental cognitive and paralyzing effects in humans. Prime examples of such negative situations are well documented in patients with Parkinson's and Alzheimer's disease. In recent years, the utilization of neural stem cells and their derivation into neurons have been the focus of many research endeavors. The main reason for this is because neural stem cells are multi-potent and can differentiate into neurons, astrocytes, and oligodendrocytes. The research that will be detailed in this thesis involves the potential use of inorganic nanostructured materials to efficiently deliver bioactive molecules (i.e., retinoic acid, kinase inhibitors) to cells that can modulate the differentiation potential of certain cells into neurons. Specifically, PC12 (derived from rat pheochromocytoma) cells, as a neural model, was treated with select nanostructured materials with and without neuron inducers (molecules and ions) and the results were analyzed via biochemical assays and live-cell fluorescence microscopy. This thesis will include an in depth look into the cytocompatibility of the tested nanostructured materials that include silica nanoparticles, titanate nanotube microspheres, and carbon microparticles.
Temple University--Theses

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35

Zhang, Yan. "Relationship between morphology, crystallization behavior and mechanical properties of polypropylene micro- and nanocomposites /." View abstract or full-text, 2004. http://library.ust.hk/cgi/db/thesis.pl?CENG%202004%20ZHANG.

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36

Huang, Ting-Yun Sasha. "Stability of nanostructured : amorphous aluminum-manganese alloys." Thesis, Massachusetts Institute of Technology, 2016. http://hdl.handle.net/1721.1/104107.

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Thesis: Ph. D., Massachusetts Institute of Technology, Department of Materials Science and Engineering, 2016.
This electronic version was submitted by the student author. The certified thesis is available in the Institute Archives and Special Collections.
Cataloged from student-submitted PDF version of thesis.
Includes bibliographical references (pages 113-122).
Nanocrystalline alloys have attracted interest for decades because of their improved mechanical strength without sacrificing ductility, but structural stability has always been an issue. In this work, bulk aluminum-manganese (Al-Mn) nanocrystalline alloys have been synthesized using room temperature ionic liquid electrodeposition, by which various nanostructures and dual-phase structures can be created by controlling the Mn solute incorporation level. The manganese exhibits grain boundary segregation in the Al-Mn solid solution in the as-deposited condition, which contributes to enhanced stability of the nanostructure. The grain boundary properties of the nanostructured alloys were studied via three dimensional atom probe tomography and aberration-corrected scanning electron microscopy. The segregation energies were calculated based on the experimental results and compared with the values calculated from a thermodynamic-based segregation model. Upon heating of the nanostructured and dual-phase alloys, a variety of complex phase transformations occur. A combination of X-ray diffraction, transmission electron microscopy, as well as differential scanning calorimetry were employed to understand the phase transformation mechanisms and grain growth processes. A Johnson-Mehl-Avrami-Kolmogorov analytical model was proposed as a descriptive method to explain the phase transformation sequence. Using the parameters extracted from the analytical model, predictive time-temperature transformation diagrams were constructed. The stability region of the alloy in time-temperature space is thus established, providing a simple way to evaluate nanostructure stability.
by Ting-Yun Sasha Huang.
Ph. D.

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37

Beets, Nathan James. "Computational Studies of the Mechanical Response of Nano-Structured Materials." Diss., Virginia Tech, 2020. http://hdl.handle.net/10919/98468.

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In this dissertation, simulation techniques are used to understand the role of surfaces, interfaces, and capillary forces on the deformation response of bicontinuous metallic composites and porous materials. This research utilizes atomistic scale modeling to study nanoscale deformation phenomena with time and spatial resolution not available in experimental testing. Molecular dynamics techniques are used to understand plastic deformation of metallic bicontinuous lattices with varying solid volume fraction, connectivity, size, surface stress, loading procedures, and solid density. Strain localization and yield response on nanoporous gold lattices as a function of their solid volume fraction are investigated in axially strained periodic samples with constant average ligament diameter. Simulation stress results revealed that yield response was significantly lower than what can be expected form the Gibson-Ashby formalism for predicting the yield response of macro scale foams. It was found that the number of fully connected ligaments contributing to the overall load bearing structure decreased as a function of solid volume fraction. Correcting for this with a scaling factor that corrects the total volume fraction to "connected, load bearing" solid fraction makes the predictions from the scaling equations more realistic. The effects of ligament diameter in nanoporous lattices on yield and elastic response in both compressive and tensile loading states are reported. Yield response in compression and tension is found to converge for the two deformation modes with increasing ligament diameter, with the samples consistently being stronger in tension, but weaker in compression. The plastic response results are fit to a predictive model that depends on ligament size and surface parameter (f). A modification is made to the model to be in terms of surface area to volume ratio (S/V) rather than ligament diameter (1/d) and the response from capillary forces seems to be more closely modeled with the full surface stress parameter rather than surface energy. Fracture response of a nanoporous gold structure is also studied, using the stress intensity-controlled equations for deformation from linear elastic fracture mechanics in combination with a box of atoms, whose interior is governed by the molecular dynamics formalism. Mechanisms of failure and propagation, propagation rate, and ligament-by-ligament deformation mechanisms such as dislocations and twin boundaries are studied and compared to a corresponding experimental nanoporous gold sample investigated via HRTEM microscopy. Stress state and deformation behavior of individual ligaments are compared to tensile tests of cylinder and hyperboloid nanowires with varying orientations. The information gathered here is used to successfully predict when and how ligaments ahead of the crack tip will fracture. The effects of the addition of silver on the mechanical response of a nanoporous lattice in uniaxial tension and compression is also reported. Samples with identical morphology to the study of the effects of ligament diameter are used, with varying random placement concentrations of silver atoms. A Monte Carlo scheme is used to study the degree of surface segregation after equilibration in a mixed lattice. Dislocation behavior and deformation response for all samples in compression and tension are studied, and yield response specifically is put in the context of a surface effect model. Finally, a novel bicontiuous fully phase separated Cu-Mo structure is investigated, and compared to a morphologically similar experimental sample. Composite interfacial energy and interface orientation structure are studied and compared to corresponding experimental results. The effect of ligament diameter on mechanical response in compressive stress is investigated for a singular morphology, stress distribution by phase is investigated in the context of elastic moduli calculated from the full elastic tensor and pure elemental deformation tests. Dislocation evolution and its effects on strain hardening are put in the context of elastic strain, and plastic response is investigated in the context of a confined layer slip model for emission of a glide loop. The structure is shown to be an excellent, low interface energy model that can arrest slip plane formation while maintaining strength close to the theoretical prediction. Dislocation content in all samples was quantified via the dislocation extraction algorithm. All visualization, phase dependent stress analysis, and structural/property analysis was conducted with the OVITO software package, and its included python editor. All simulations were conducted using the LAMMPS molecular dynamics simulation package. Overall, this dissertation presents insights into plastic deformation phenomena for nano-scale bicontinuous metallic lattices using a combination of experimentation and simulation. A more holistic understanding of the mechanical response of these materials is obtained and an addition to the theory concerning their mechanical response is presented.
Doctor of Philosophy
Crystalline metals can be synthesized to have a sponge-like structure of interconnected ligaments and pores which can drastically change the way that the material chemically interacts with its environment, such as how readily it can absorb oxygen and hydrogen ions. This makes it attractive as a catalyst material for speeding up or altering chemical reactions. The change in structure can also drastically change how the material responds when deformed by pressing, pulling, tearing or shearing, which are important phenomena to understand when engineering new technology. High surface or interface area to volume ratios can cause a massive surface-governed capillary force (the same force that causes droplets of water to bead up on rain coat) and lead to a higher pressure within the material. The effect that both structure and capillary forces have on the way these materials react when deformed has not been established in the context of capillary force theory or crystalline material plasticity theory. For this reason, we investigate these materials using simulation methods at the atomic level, which can give accurate and detailed data on the stress and forces felt atom-by-atom in a material, as well as defects in the material, such as dislocations and vacancies, which are the primary mechanisms that cause the crystal lattice to permanently deform and ultimately break. A series of parameters are varied for multiple model systems to understand the effects of various scenarios, and the understanding provided by these tests is presented.

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Hong, Yan. "Encapsulated nanostructured phase change materials for thermal management." Doctoral diss., University of Central Florida, 2011. http://digital.library.ucf.edu/cdm/ref/collection/ETD/id/4929.

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A major challenge of developing faster and smaller microelectronic devices is that high flux of heat needs to be removed efficiently to prevent overheating of devices. The conventional way of heat removal using liquid reaches a limit due to low thermal conductivity and limited heat capacity of fluids. Adding solid nanoparticles into fluids has been proposed as a way to enhance thermal conductivity of fluids, but recent results show inconclusive anomalous enhancements in thermal conductivity. A possible way to improve heat transfer is to increase the heat capacity of liquid by adding phase change nanoparticles with large latent heat of fusion into the liquid. Such nanoparticles absorb heat during solid to liquid phase change. However, the colloidal suspension of bare phase change nanoparticles has limited use due to aggregation of molten nanoparticles, irreversible sticking on fluid channels, and dielectric property loss. This dissertation describes a new method to enhance the heat transfer property of a liquid by adding encapsulated phase change nanoparticles (nano-PCMs), which will absorb thermal energy during solid-liquid phase change and release heat during freeze. Specifically, silica encapsulated indium nanoparticles, and polymer encapsulated paraffin (wax) nanoparticles have been prepared using colloidal method, and dispersed into poly-alpha]-olefin (PAO) and water for high temperature and low temperature applications, respectively. The shell, with a higher melting point than the core, can prevent leakage or agglomeration of molten cores, and preserve the dielectric properties of the base fluids. Compared to single phase fluids, heat transfer of nanoparticle-containing fluids have been significantly enhanced due to enhanced heat capacities. The structural integrity of encapsulation allows repeated uses of nanoparticles for many cycles.; By forming porous semi crystalline silica shells obtained from water glass, supercooling has been greatly reduced due to low energy barrier of heterogeneous nucleation. Encapsulated phase change nanoparticles have also been added into exothermic reaction systems such as catalytic and polymerization reactions to effectively quench local hot spots, prevent thermal runaway, and change product distribution. Specifically, silica-encapsulated indium nanoparticles, and silica encapsulated paraffin (wax) nanoparticles have been used to absorb heat released in catalytic reaction, and to mitigate the gel effect during polymerization, respectively. The reaction rates do not raise significantly owing to thermal buffering using phase change nanoparticles at initial stage of thermal runaway. The effect of thermal buffering depends on latent heats of fusion of nanoparticles, and heat releasing kinetics of catalytic reactions and polymerizations. Micro/nanoparticles of phase change materials will open a new dimension for thermal management of exothermic reactions.
ID: 029809237; System requirements: World Wide Web browser and PDF reader.; Mode of access: World Wide Web.; Thesis (Ph.D.)--University of Central Florida, 2011.; Includes bibliographical references (p. 164-191).
Ph.D.
Doctorate
Mechanical Materials and Aerospace Engineering
Engineering and Computer Science

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39

Rubin, Julia G. (Julia Grace). "Selective solar absorber materials : nanostructured surfaces via scalable synthesis." Thesis, Massachusetts Institute of Technology, 2017. http://hdl.handle.net/1721.1/111347.

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Thesis: S.B., Massachusetts Institute of Technology, Department of Materials Science and Engineering, 2017.
Cataloged from PDF version of thesis.
Includes bibliographical references (page 32).
Current solar to thermal energy conversion technologies, including concentrated solar power (CSP) and solar water heaters (SWH) utilize absorber surfaces that collect incident solar radiation. However, these absorber surfaces emit thermal energy (at their temperature) in the infrared (IR) spectrum, resulting in decreased overall efficiency for solar-to-thermal conversion. Selective absorber surfaces are highly absorptive in the solar spectrum, yet highly reflective in the infrared spectrum and therefore have the potential to minimize thermal energy loss. Copper Oxide (CuO) nanostructures are a candidate selective absorber material due to high absorptivity in the solar spectrum (about 95%), relatively high reflectance in the IR spectrum, scalability, and ease of fabrication. The aim of this study was to analyze optical properties and thermal stability of CuO surfaces in order to assess its feasibility as a selective absorber material. CuO nanostructures were synthesized on copper via chemical wet processing. Samples were thermally cycled to simulate day/night cycles in a typical SWH application. A cycle consisted of 12 hours of heating at 200°C and 12 hours of cooling to ambient temperature. Samples were cycled 1, 2, 3, 8, and 10 times. Surface optical properties were characterized using Ultraviolet-Visible Spectroscopy (UV-Vis) and Fourier Transform Infrared Spectroscopy (FTIR) and compared to optical properties of Pyromark®, the industry standard. Reflectance in the IR spectrum of CuO samples was found to increase after initial heating, whereas the absorptivity decreased. This tradeoff in optical performance resulted in an overall efficiency that remained relatively stable between 0 and 10 cycles (69.5±1.6%, 70.2±1.6%, respectively). CuO samples were found to be roughly 10% more efficient (optical conversion) than Pyromark® (npyromark,3x = 59.5±0.7%), indicating that CuO samples have the potential to be an efficient selective absorber material.
by Julia G. Rubin.
S.B.

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40

Osswald, Sebastian Gogotsi IU G. Scharff Peter. "In situ raman spectroscopy study of oxidation of nanostructured carbons /." Philadelphia, Pa. : Drexel University, 2008. http://hdl.handle.net/1860/2972.

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Kim, Jeong-Gil. "Nanomanufacturing of functional nanostructured surfaces for efficient light transport." Thesis, Massachusetts Institute of Technology, 2015. http://hdl.handle.net/1721.1/100128.

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Thesis: Ph. D., Massachusetts Institute of Technology, Department of Mechanical Engineering, 2015.
Cataloged from PDF version of thesis.
Includes bibliographical references.
Nanostructured surfaces have given rise to many unique optical properties, such as broadband anti-reflectivity, structural coloring effects, and enhanced light extraction from high refractive index materials due to their potential to modulate optical behavior on their surfaces. This thesis focuses on design, analysis, and fabrication of functional nanostructured surfaces for efficient light transport, seeking optimized optical performance, high mechanical robustness, and manufacturability, with the aim of increasing the practicality of the photonic nanostructures. First, for the case when light propagates from a low-index material to a high-index material, I designed and fabricated an array of inverted nanocones that realizes anti-reflectivity with robust mechanical strength. The surface exhibits broadband, omnidirectional anti-reflectivity due to the axially varying effective refractive index of the inverted nanocone arrays. The surface also maintains its optical performance after being externally loaded, thanks to low stress concentration and small deflection of the inverted nanocone structure. In addition, for multi-optical interfacial surfaces, double-gradient- index nanostructures are proposed and demonstrated in order to achieve ultimate anti-reflectivity. The top surface, textured with inverted nanocones, maintains high mechanical robustness. Second, for the case where light has to be extracted from high-index materials, a conical photonic crystal is proposed and demonstrated. The tapered conical geometry suppresses Fresnel reflections at the optical interfaces due to adiabatic impedance matching. Periodicity of the arrays of cones diffracts light into higher-order modes with different propagating angles, enabling certain photons to overcome total internal reflection (TIR). After optimizing the structural geometries to balance Fresnel reflection and TIR, light yield efficiency is characterized experimentally on scintillator surfaces. In order to enhance the adaptability to industrial manufacturing, the fabrication methods are based on replicating the photonic nanostructures into a UV-curable polymer, with the help of laser interference lithography as a method of fabricating a master mold. Advanced techniques such as vacuum assisted-filling and a selective delaminating method are also developed to produce nanostructures more effectively. The novel nanostructured surfaces designed in the thesis, and the ability to imprint these topographies through several generations, are promising for large-scale commercial applications where efficient light transport is important.
by Jeong-Gil Kim.
Ph. D.

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Choi, Hyungryul. "Fabrication of anti-reflective and imaging nanostructured optical elements." Thesis, Massachusetts Institute of Technology, 2011. http://hdl.handle.net/1721.1/106723.

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Thesis (S.M.)--Massachusetts Institute of Technology, Dept. of Mechanical Engineering, 2011.
Cataloged from PDF version of thesis.
Includes bibliographical references (p. 69-73).
Moth eyes minimize reflection over a broad band of angles and colors and lotus leaves minimize wetting over a broad range of breakthrough pressures by virtue of subwavelength structures patterned on their respective surfaces; similar examples of organisms exploiting geometry to attain properties unavailable in bulk materials are abundant in nature. These instances have inspired applications to man-made structures, collectively known as functional materials: for example, self-cleaning/anti-fogging surfaces, and solar cells with increased efficiency. I fabricated a functional surface where both wetting and reflectivity are controlled by geometry. Using a periodic array of subwavelength-sized high aspect ratio cones, patterned on glass and coated with optimized surfactants, I have experimentally shown that we can significantly enhance transmission from the surfaces of a glass slab, and at the same time make the surfaces either superhydrophobic or superhydrophilic, depending on the applications, such as antifogging and self-cleaning glass. Novel lithographic techniques result in high patterning accuracy over large surface areas, and is easily adaptable to nanoimprinting for future mass replication. In addition, an all-dielectric subwavelength-patterned Luneburg lens was fabricated for operation at free-space wavelength of A =1.55 um.
by Hyungryul Choi.
S.M.

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Mortazavi, Bohayra, and Bohayra Mortazavi. "Multiscale modeling of thermal and mechanical properties of nanostructured materials and polymer nanocomposites." Phd thesis, Université de Strasbourg, 2013. http://tel.archives-ouvertes.fr/tel-00961249.

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Nanostructured materials are gaining an ongoing demand because of their exceptional chemical and physical properties. Due to complexities and costs of experimental studies at nanoscale, computer simulations are getting more attractive asexperimental alternatives. In this PhD work, we tried to use combination of atomistic simulations and continuum modeling for the evaluation of thermal conductivity and elastic stiffness of nanostructured materials. We used molecular dynamics simulations to probe and investigate the thermal and mechanical response of materials at nanoscale. The finite element and micromechanics methods that are on the basis of continuum mechanics theories were used to evaluate the bulk properties of materials. The predicted properties are then compared with existing experimental results.

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Mortazavi, Bohayra. "Multiscale modeling of thermal and mechanical properties of nanostructured materials and polymer nanocomposites." Thesis, Strasbourg, 2013. http://www.theses.fr/2013STRAD007/document.

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Les matériaux nanostructurés suscitent un intérêt qui va croissant en raison de leurs propriétés chimiques et physiquesexceptionnelles. A cause de la complexité et du coût des développements expérimentaux à l’échelle nano, la simulationnumérique devient une alternative de plus en plus populaire aux études expérimentales. Dans ce travail de thèse, nous avons essayé de combiner des simulations à l’échelle atomique avec de la modélisation en milieu continu pour évaluer la conductivité thermique et la réponse élastique de matériaux nanostructurés. Nous avons utilisé des simulations de dynamique moléculaire pour calculer la réponse mécanique et thermique des matériaux sur des volumes à l’échelle nano. Des méthodes de micromécanique et la méthode des éléments finis, qui utilisent la mécanique des milieux continus, ont permis d’évaluer les propriétés mécaniques des matériaux à l'échelle macroscopique. Les résultats obtenus par ces simulations numériques ont été ensuite comparés avec ceux issus de l’expérience
Nanostructured materials are gaining an ongoing demand because of their exceptional chemical and physical properties. Due to complexities and costs of experimental studies at nanoscale, computer simulations are getting more attractive asexperimental alternatives. In this PhD work, we tried to use combination of atomistic simulations and continuum modeling for the evaluation of thermal conductivity and elastic stiffness of nanostructured materials. We used molecular dynamics simulations to probe and investigate the thermal and mechanical response of materials at nanoscale. The finite element and micromechanics methods that are on the basis of continuum mechanics theories were used to evaluate the bulk properties of materials. The predicted properties are then compared with existing experimental results

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Zarur, Jury Juan Andrey 1970. "Catalytic combustion of methane with nanostructured barium hexaaluminate-based materials." Thesis, Massachusetts Institute of Technology, 1999. http://hdl.handle.net/1721.1/9116.

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Thesis (Ph.D.)--Massachusetts Institute of Technology, Dept. of Chemical Engineering, February 2000.
Includes bibliographical references.
Catalytic combustion of methane has been widely studied as an alternative to gasphase homogeneous combustion. It allows combustion to occur at high levels of excess air, leading to more complete reaction and reduced hydrocarbon emissions. It further enables combustion to proceed at lower temperatures, significantly reducing the NO" production. Noble metal systems, such as platinum and palladium, have been studied as combustion catalysts. However, noble metal clusters tend to sinter or vaporize at the high combustion temperatures. Recently, complex oxides have been examined for methane combustion due to their enhanced thermal resistance. Barium hexaaluminate (BHA) was chosen for this research, since its unique crystalline structur~ has the potential to suppress grain growth at high temperatures. A novel reverse microemulsion-mediated sol-gel processing technique was developed to synthesize non-agglomerated BHA nanoparticles with high surface areas and thermal stability. The reverse microemulsion also provided a unique medium to achieve highly dispersed active species on BHA nanoparticles to enhance the catalytic performance for methane combustion. Reverse microemulsions of water/i30-octane and water/cyclohexane were successfully stabilized with a non-ionic surfactant system consisting of polyethoxylated and linear alcohols. The water/iso-octane system was found to be ideal for the sol-gel mediated synthesis, since it required only a small amount of surfactants for stabilization. Quasi-elastic light scattering and small-angle neutron scattering showed that at low water contents, the reverse microemulsions consisted of slightly polydisperse discrete aqueous domains with a core-shell structure. Systems with higher water contents could be best described with a bicontinuous structure with intermixed water and oil domains. The water/iso-octane system was found to possess excellent stability under the conditions required for reverse microemulsion-mediated sol-gel processing of BHA materials. The composition of the reverse microemulsion governed the morphology of the aqueous domains, which in tum determined the shape and aggregation of the BHA particles derived. Non-agglomerated nanospheres were recovered from reverse microemulsions with water volume fractions of 0.05-0.15. At higher water contents, percolation between aqueous domains in the system became significant, yielding BHA particles with filament-like morphologies. The water:alkoxide ratio in the sol-gel process determined the relative rates of hydrolysis and polycondensation reactions. At a relatively high water:alkoxide ratio of ~100 times the stoichiometric value, the stability of the reverse microemulsion was preserved throughout the aging process. Well-defined, high surface area BHA nanoparticles were successfully recovered from the medium by freeze drying. Residual surfactants and volatiles were best removed by supercritical drying. The resulting materials were crystallized at a relatively low temperature of 1050°C due to their superb chemical homogeneity. Surface areas of >160 m2/g and ultrafine grain sizes of S30 nm were retained by these BHA nanoparticles after calcination at l 300°C. Active transition metal and rare earth oxides could be deposited with ultrahigh dispersion on BHA nanoparticles during their aging in the reverse microemulsion medium. BHA nanoparticles coated with Mn02 and Ce02 clusters showed light-off (defined as 10% conversion of an air stream containing 1 vol% CH4) at remarkably low temperatures of ~400°C, rivaling noble metal systems. These novel materials sustained their activity for extended periods at temperatures in excess of 1000°C, demonstrating a thermal stability superior to other existing combustion catalysts. The performance of BHA-based materials was evaluated in an atmospheric burner operated under realistic industrial conditions. Catalyst systems were washcoated onto monoliths of different compositions and microstructures. Nickel foams and fiber reinforced honeycombs demonstrated excellent thermal shock resistance; the latter were preferred for high-temperature operations since they would give rise to negligible pressure drops. In our catalytic combustor design, nanocrystalline PdO/Ce02-BHA was used as the low-temperature ignition catalyst to initiate the reaction by 250°C. A mid temperature catalyst, such as MnOi-BHA or Ce02-BHA nanocomposite, was utilized to promote reaction in the range of 600-1000°C. A flame-supporting catalyst, consisting of pure nanostructured BHA was employed to stabilize the flame at temperatures up to 1300°C. Using this multi-stage catalyst design, flames of ultra-lean methane:oxygen ratios (0.2S~0.5) were ignited and sustained for extended periods over multiple heating-cooling- restarting cycles. This system successfully eliminated NOx production with no unburned hydrocarbon emissions in an effective catalytic methane combustion process.
by Juan Andrey Zarur Jury.
Ph.D.

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46

Das, Kaushik. "Synthesis and characterization of nanostructured thin films for microsystems." Thesis, McGill University, 2012. http://digitool.Library.McGill.CA:80/R/?func=dbin-jump-full&object_id=110607.

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Integration of nanomaterials (in the form of quantum dots, nanotubes, nanowires, nanocrystalline thin films, and nanocomposite films) with micromachined devices can lead to improved performance and new functionalities; however, it has to confront many difficult scientific and engineering challenges. Addressing some of these challenges is the overarching goal of this thesis. The first major challenge is to develop versatile methods for synthesizing nanomaterials and integrating them with micromachined structures and devices. An approach that combines spray-coating of electron beam resist, direct-write electron beam lithography, physical vapour deposition of thin films, and lift-off processes was developed for integrating nanomaterials directly on fragile micromachined structures. Polymeric and metallic structures in the form of arrays of holes, arrays of lines, and concentric circles were patterned directly on various micromachined structures including commercial metal-coated silicon microcantilevers used for atomic force microscopy,and commercial plate-mode SiC/AlN microresonators used for sensing. The critical lateral dimensions of the nanostructured materials ranged from 135 nm to 500 nm. Once the practical difficulties of material synthesis and integration have been addressed, it is necessary to confront the challenges of predicting the behaviour, performance, and reliability of the integrated system. As a step towards that goal, this thesis established process-structure-property relationships for three different nanomaterials. The first study focused on the elastic properties of polyimide nanocomposite films reinforced with single-walled carbon nanotubes. Both computational (Eshelby-Mori-Tanaka micromechanics) and experimental (nanoindenter-based bending tests of freestanding nanocomposite films) approaches were utilized to this end. Using results from microstructural examination, a link was found between the elastic properties of the nanocomposite and the dispersion, alignment and bundle size of the single-walled carbon nanotubes. The second study focused on energy dissipation by internal friction in nanofabricated structures. A novel method was developed for measuring internal friction using a silicon microcantilever platform that is calibrated against thermoelastic damping. The use of this method was demonstrated by obtaining the first calibrated measurements of internal friction in aluminium nanowires with thickness ranging from 50 nm to 100 nm and widths ranging from 110 nm to 396 nm. At room temperature, the internal friction in these nanowires ranged from 0.026 to0.035 for frequencies between 6.5 kHz and 21 kHz. Combining these measurements with microstructural examination of the grain size of the nanowires provided useful insights into the effects of patterning on dissipation. The third study explored the relationships between processing parameters and elastic properties for a novel nanocomposite architecture which consists of an interconnected carbon nanotube network that is conformally coated with a thin layer of titanium nitride. Taken together, the contributions of this thesis - processes for patterning and integration, techniques for measuring material properties, and results for process-structure-property relationships - establish a foundation for the rational integration of nanomaterials with MEMS.
L'intégration des nanomatériaux (dans le forme de points quantum, nanotubes, nanofils, minces films nanocristallins et films nanocomposites) avec des dispositifs micro-fabriqués a le potentiel de permettre le développement de systèmes micro électromécaniques (SMEM) ayant des fonctionnalités et performances accrues. Toutefois, plusieurs défis scientifiques et d'ingénierie doivent être surmontés. Cette thèse a comme objectif de résoudre certains de ces défis. Le premier défi majeur est de développer des méthodes versatiles pour synthétiser des nanomatériaux et les intégrer aux dispositifs et structures micro-fabriquées. Une approche qui combine le revêtement par atomisation de résine, la lithographie à écriture-directe par faisceau d'électrons, le dépôt de films minces et des procédés de soulèvement a été développé pour intégrer des nanomatériaux directement sur la fragilité des structures micro-usinées. Des structures polymériques et métalliques de différentes formes (trous, lignes et cercles concentriques) ont été fabriquées directement sur les micro-poutres de silicium commercialement disponibles et utilisées pour la microscopie à force atomique ainsi que des micro-résonateurs commerciaux de type "plate-mode SiC/AlN" utilisés à des fins de détection. Les dimensions critiques latérales des matériaux nanostructurés varient de 135 nm à 500 nm. Une fois que les difficultés pratiques de synthèse et d'intégration des matériaux ont été maîtrisées, il a été nécessaire de comprendre et prédire le comportement, la performance et la fiabilité du système intégré. Cette thèse a établi des relations fabrication-structure-propriétés pour trois différents nanomatériaux. La première étude s'est concentrée sur les propriétés élastiques de films polymériques renforcés de nanotubes de carbone. Les propriétés élastiques de films nanocomposites de polyimide (PI) et renforcés par des nanotubes de carbone à simple paroi (SWNT) ont été étudiées par une étude numérique (via la micromécanique Eshelby-Mori-Tanaka) et expérimentale (par des tests de flexion de films nanocomposites non-contraints basés sur la nanoindentation). En utilisant des résultats d'inspections microstructurales, un lien a été établi entre les propriétés élastiques du nanocomposite et la dispersion, l'alignement et la taille des agglomérats de nanotubes de carbone. La seconde étude s'est concentrée sur la dissipation d'énergie par friction interne dans les structures nano-fabriquées. Une méthode originale a été développée pour mesurer la friction interne en utilisant une plateforme pour des micro-poutres de silicium qui est calibrée en fonction de l'amortissement thermoélastique. L'utilisation de cette méthode a été démontrée en obtenant les premières mesures calibrées de friction interne dans des nanofils d'aluminium ayant des épaisseurs de 50 à 100 nm et des largeurs de 110 nm à 396 nm. À température ambiante, la friction interne de ces nanofils a varié de 0.026 à 0.035 pour des fréquences entre 6.5 kHz et 21 kHz. La combinaison de ces mesures avec une inspection microstructurale de la taille des grains des nanofils a fourni des indices des effets produits par la forme des motifs sur la dissipation. La troisième étude a exploré les relations entre les paramètres de fabrication et les propriétés élastiques pour une architecture nanocomposite originale consistant d'un réseau de nanotubes de carbone interconnecté recouvert d'une mince couche de nitrure de titane. Dans leur ensemble, les contributions de cette thèse - les procédés de fabrication de motifs et d'intégration, les techniques pour mesurer les propriétés des matériaux, et les résultats pour les relations fabrication-structure-propriétés - établissent une fondation pour l'intégration rationnelle des nanomatériaux avec les SMEM.

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47

Gallagher, Jamie Brian. "Synthesis of nanostructured materials with potential renewable energy generation applications." Thesis, University of Glasgow, 2015. http://theses.gla.ac.uk/7040/.

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The work in this thesis is concerned with growth of low dimensional materials in a variety of morphologies which have potential renewable energy generation applications. The work described within demonstrates synthesis methods for the production of materials with thermoelectric applications and materials for photovoltaic purposes. Products are characterised using a range of techniques including: scanning and transmission electron microscopy; energy dispersive X-ray spectroscopy and powder X-ray diffraction. Presented here is an investigation into the growth of bismuth telluride on silicon surfaces via chemical vapour deposition (CVD). Resultant particle morphology is reported in relation to experimental conditions such as surface conditions (silicon, gold/palladium on silicon and disordered silicon surfaces), temperature and reagent concentration. Successful synthesis of Bi2Te3 plates is presented starting from elemental precursors via a closed vessel CVD process. Plates with sub-micron thickness (but up to 40 μm diameter) are produced template free on a silicon surface and without the need for transport gases or expensive precursors. Using modification of silicon surfaces the growth of 2-4 μm tetragonal pyramids of Bi2Te3 are demonstrated. CVD is also used to produce bismuth rich nanowires up to 40 μm but <100 nm in diameter, these were produced by increasing the bismuth concentration in comparison to other methods. This thesis also details an investigation into the suitability of a range of substrates for CVD. Alumina is demonstrated to be a suitable surface for Bi2Te3 CVD with nanostructured Bi2Te3 spheres of 5-20 μm diameter presented. Additionally vertically aligned arrays of copper telluride are presented using a single step CVD process. Arrays consist of hexagonal plates <500 nm in thickness but up to 25 μm in diameter. Due to preferential reaction with tellurium GaAs is demonstrated to be a poor facilitator for Bi2Te3 growth as is cobalt. The production of nanostructured sphere of TiO2 is also presented. Spheres with tuneable diameter are produced in <60 s in multi-mode microwave reactors using a hydrothermal process. The spheres are comprised of radially aligned nanorods producing spheres of 1-3 μm. Spheres are demonstrated to be a single rutile TiO2 phase. Spheres are characterised with phase, band gap and morphology presented and influence of experimental parameters such as time and reagent concentration is discussed. 2 Finally this work investigates the doping and conversion of TiO2 structures to TiN and TiO2-xNx structures. Using ammonolysis TiO2 is converted to a TiN structure while retaining its original its original spherical morphology. Using the same ammonolysis process TiO2 is doped and the demonstrational shift in band gap to the visible region is presented.

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48

Stolfi, Michael Anthony. "Optical properties of nanostructured silicon-rich silicon dioxide." Thesis, Massachusetts Institute of Technology, 2006. http://hdl.handle.net/1721.1/37583.

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Thesis (Ph. D.)--Massachusetts Institute of Technology, Dept. of Materials Science and Engineering, 2006.
Includes bibliographical references (p. 190-195).
We have conducted a study of the optical properties of sputtered silicon-rich silicon dioxide (SRO) thin films with specific application for the fabrication of erbium-doped waveguide amplifiers and lasers, polarization sensitive devices and devices to modify the polarization state of light. The SRO thin films were prepared through a reactive RF magnetron sputtering from a Si target in an O2/Ar gas mixture. The film stoichiometry was controlled by varying the power applied to the Si target or changing the percentage of 02 in the gas mixture. A deposition model is presented which incorporates the physical and chemical aspects of the sputtering process to predict the film stoichiometry and deposition rate for variable deposition conditions. The as-deposited films are optically anisotropic with a positive birefringence (nTM > nTE) that increases with increasing silicon content for as-deposited films. The dependence of the birefringence on annealing temperature is also influenced by the silicon content. After annealing, samples with high silicon content (>45 at%) showed birefringence enhancement while samples with low silicon content (<45 at%) showed birefringence reduction. A birefringence of more than 3% can be generated in films with high silicon content (50 at% Si) annealed at 11000C.
(cont.) We attribute the birefringence to the columnar film morphology achieved through our sputtering conditions. Er was incorporated through reactive co-sputtering from Er and Si targets in the same O2/Ar atmosphere in order to investigate the energy-transfer process between SRO and Er for low annealing temperatures. By studying the photoluminescence (PL) intensity of Er:SRO samples annealed in a wide range of temperatures, we demonstrated that the Er sensitization efficiency is maximized between 600°C and 700°C. Temperature-resolved PL spectroscopy on SRO and Er:SRO samples has demonstrated the presence of two different emission sensitizers for samples annealed at 6000C and 1 100°C. This comparative study of temperature-resolved PL spectroscopy along with energy Filtered Transmission Electron Microscopy (EFTEM) has confirmed that the more efficient emission sensitization for samples annealed at 6000C occurs through localized centers within the SRO matrix without the nucleation of Si nanocrystals. Er-doped SRO slab waveguides were fabricated to investigate optical gain and loss for samples annealed at low temperatures.
(cont.) Variable stripe length gain measurements show pump dependent waveguide loss saturation due to stimulated emission with a maximum modal gain of 3 ± 1.4 cm-1 without the observation of carrier induced losses. Pump and probe measurements on ridge waveguides also confirms the presence of SRO sensitized signal enhancement for samples annealed at 6000C. Transmission loss measurements demonstrate a significant loss reduction of 1.5 cm-1or samples annealed at 600°C compared to those annealed at 1000°C. These results suggest a possible route for the fabrication of compact, high-gain planar light sources and amplifiers with a low thermal budget for integration with standard Si CMOS processes.
by Michael Anthony Stolfi.
Ph.D.

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Chao, Michelle (Michelle L. ). "Hydrophobic nanostructured glass surfaces using metal dewetting process." Thesis, Massachusetts Institute of Technology, 2017. http://hdl.handle.net/1721.1/111342.

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Thesis: S.B., Massachusetts Institute of Technology, Department of Materials Science and Engineering, 2017.
Cataloged from PDF version of thesis.
Includes bibliographical references (page 18).
This project aims to create a hydrophobic surface through a top down fabrication process of a nanostructure surface on a glass surface. The nanostructure is created through reactive ion etching utilizing silver as a mask. The silver mask is the result of a solid state thermal dewetting process which is controlled by varying the temperature and time of the process. Using this fabrication process, contact angles up to 137 degrees was achieved. Further surface modification resulted in contact angles exceeding 150 degrees. Superhydrophobic surfaces were made with the addition of a secondary roughness feature and the a PDMS coating.
by Michelle Chao.
S.B.

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Chu, Kuang-Han Ph D. Massachusetts Institute of Technology. "Micro and nanostructured surfaces for enhanced phase change heat transfer." Thesis, Massachusetts Institute of Technology, 2013. http://hdl.handle.net/1721.1/79311.

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Thesis (Ph. D.)--Massachusetts Institute of Technology, Dept. of Mechanical Engineering, 2013.
Cataloged from PDF version of thesis.
Includes bibliographical references (p. 61-65).
Two-phase microchannel heat sinks are of significant interest for thermal management applications, where the latent heat of vaporization offers an efficient method to dissipate large heat fluxes in a compact device. However, a significant challenge for the implementation of microchannel heat sinks is associated with flow instabilities due to insufficient bubble removal, leading to liquid dry-out which severely limits the heat removal efficiency. To address this challenge, we propose to incorporate micro/nanostructures to stabilize and enhance two-phase microchannel flows. Towards this goal, this thesis focuses on fundamental understanding of micro/nanostructures to manipulate liquid and vapor bubble dynamics, and to improve overall microchannel heat transfer performance. We first investigated the role of micro/nanostructure geometry on liquid transport behavior. We designed and fabricated asymmetric nanostructured surfaces where nanopillars are deflected with angles ranging from 7 -52'. Uni-directional liquid spreading was demonstrated where the liquid propagates in a single preferred direction and pins in all others. Through experiments and modeling, we determined that the spreading characteristic is dependent on the degree of nanostructure asymmetry, height-to-spacing ratio of the nanostructures, and intrinsic contact angle. The theory, based on an energy argument, provides excellent agreement with experimental data. This work shows a promising method to manipulate liquid spreading with structured surfaces, which potentially can also be used to manipulate vapor bubble dynamics. We subsequently investigated the effect of micro/nanostructured surface design on vapor bubble dynamics and pool boiling heat transfer. We fabricated micro-, nano-, and hierarchically-structured surfaces with a wide range of well-defined surface roughness factors and measured the heat transfer characteristics. The maximum critical heat flux (CHF) was ~250 W/cm2 with a roughness factor of~-13.3. We also developed a force-balance based model, which shows excellent agreement with the experiments. The results demonstrate the significant effect of surface roughness at capillary length scales on enhancing CHF. This work is an important step towards demonstrating the promising role of surface design for enhanced two-phase heat transfer. Finally, we investigated the heat transfer performance of microstructured surfaces incorporated in microchannel devices with integrated heaters and temperature sensors. We fabricated silicon micropillars with heights of 25 [mu]m, diameters of 5-10 [mu]m and spacings of 5- 10 [mu]m in microchannels of 500 [mu]m x 500 [mu]m. We characterized the performance of the microchannels with a custom closed loop test setup. This thesis provides improved fundamental understanding of the role of micro/nanostructures on liquid spreading and bubble dynamics as well as the practical implementation of such structures in microchannels for enhanced heat transfer. This work serves as an important step towards realizing high flux two-phase microchannel heat sinks for various thermal management applications.
by Kuang-Han Chu.
Ph.D.

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Dissertations / Theses on the topic 'Mechanical engineering. Nanostructured materials'

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