Página 11 dos resultados de 2573 itens digitais encontrados em 0.142 segundos

‣ Experimental and finite element analysis of high pressure packer elements

Berger, Stephanie, 1981-
Fonte: Massachusetts Institute of Technology Publicador: Massachusetts Institute of Technology
Tipo: Tese de Doutorado Formato: 30 leaves; 1846862 bytes; 1847692 bytes; application/pdf; application/pdf
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Packer elements are traditionally rubber seals that can operate under specified downhole conditions and provide a seal for either a short-term, retrievable, or a long-term, permanent, completion. In this case a retrievable 19.7cm (7-3/4") packer element for a high-pressure high-temperature (HPHT) environment was designed and tested. The element created a seal between the mandrel, or tubing, and the casing. At high temperature and pressure rubber needs to be contained so that it will create and maintain an energized seal. In this study only Aflas rubber was tested. Various backup systems were examined; some more traditional designs such as the carbon steel foldback ring were compared to more experimental ideas. Results of theoretical simulations were compared to actual test results in order to gain a greater understanding of element behavior. Experiments were also performed to study the process of element setting, which is difficult to observe due to the high pressures and temperatures required. In a related study alternative materials to rubber such as annealed high-conductivity oxygen-free copper were tested to determine if the properties could be applied for packer element applications. The most successful design was the foldback ring with an anti-extrusion PEEK ring under the gage ring. This design passed a liquid test at 134 MPa (19.5k psi) differential pressure and a gas test at 87.6 MPa (12.7k psi) differential pressure. New designs such as the split ring with mesh and the garter spring with mesh did not pass fixture tests but could be successful with further modifications. FEA was used as an analytical tool to create simulations of the element after a setting force is applied. The modeling was shown to correlate to the actual test results and therefore it would be a good tool to use in future studies.; by Stephanie Berger.; Thesis (S.M.)--Massachusetts Institute of Technology...

‣ Continuum models for intergranular films in silicon nitride and comparison to atomistic simulations

Bishop, Catherine M. (Catherine Mary), 1975-
Fonte: Massachusetts Institute of Technology Publicador: Massachusetts Institute of Technology
Tipo: Tese de Doutorado Formato: 155 leaves; 5623325 bytes; 9943528 bytes; application/pdf; application/pdf
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A continuum thermodynamic model is developed for the treatment of interfaces in materials. This phase-field model includes energetic contributions from chemical, structural and electrostatic effects. A small parameter set is introduced in the model. These parameters should be adjusted based on the relation of equilibrated phase-field structures to atomistic simulations and experimental observations. To compare the continuum fields to discrete data sets, coarse-graining methods are proposed. Two methods of measuring local atomic structure are developed, one based on Voronoi tessellations and the other based on bond-angle distribution functions. A coarse-graining method based on volume averaging over Voronoi tessellations is employed to continuize both structure and composition information. These fields give insight into the local atomic environment that is necessary for devising continuum models. The stability of intergranular films in CaO-doped Si₃N₄ is examined. A modified associate model that incorporates bulk-thermodynamic Gibbs free energy functions and treats non-bulk equilibrium compositions is developed. Kinetic equations are derived to solve for the equilibrium fields. While the simulations do not reach equilibrium, some trends can be observed. Locally charged domains are kinetically stable near the film. Non-uniform calcium distributions in the doped films indicate that calcium is preferentially located near the film-grain interface. The structural width of the film can be tuned by altering appropriate model parameters.; (cont.) Future avenues of research suggested by this thesis include: developing algorithms for measuring local structure and orientation in multi-component systems and devising atomistic simulations of intergranular pockets that couple experimental information with interatomic potentials.; by Catherine M. Bishop.; Thesis (Ph. D.)--Massachusetts Institute of Technology...

‣ An analytic solution for magnetization distribution in multigrain ferromagnetic materials in an applied magnetic field

Sunter, Kristen A. (Kristen Ann), 1982-
Fonte: Massachusetts Institute of Technology Publicador: Massachusetts Institute of Technology
Tipo: Tese de Doutorado Formato: 22, [20] leaves; 1987029 bytes; 1985521 bytes; application/pdf; application/pdf
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The magnetic behavior of a material is governed by the variation in anisotropy direction from grain to grain as well as the changes in ferromagnetic parameters at grain boundaries and other defect regions. For example, transmission electron microscopy results show that chromium segregation occurs at the grand boundaries in CoCrTa films, which are used in hard disk drives. In this paper, we model the case of two adjacent semi-infinite grains with arbitrary crystalline orientations with respect to each other. A Gaussian distribution is used to model the change in magnetic properties at the interface, and boundary conditions are imposed on the direction of magnetization deep within the grains and at the interface. The effects due to the diffuse interface are included using perturbation theory. The sum of the exchange, anisotropy and Zeeman energies is minimized, and the resulting Euler equation is solved analytically. A profile of the magnetization orientation in an inhomogeneous medium in an applied field is obtained to show the extent of the effects of grain boundary segregation. These results can direct future large-scale computer calculations and media improvement.; by Kristen A. Sunter.; Thesis (S.B.)--Massachusetts Institute of Technology...

‣ Determination of special boundary coordination at quadruple nodes using EBSD

Ng, Christopher, 1983-
Fonte: Massachusetts Institute of Technology Publicador: Massachusetts Institute of Technology
Tipo: Tese de Doutorado Formato: 35 leaves; 1912222 bytes; 1911566 bytes; application/pdf; application/pdf
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Grain boundaries are known to play an important role in materials properties including corrosion and cracking resistance. Some grain boundaries are resistant to corrosion and cracking and are known as "special" boundaries. While the structure of individual grain boundaries is important, the connectivity of the grain boundaries largely determines the properties of a bulk material. The coordination and connectivity of special grain boundaries have previously been studied in two dimensional grain boundary networks and are quantified by the triple junction distribution (TJD), which has been found to be non-random. The study of connectivity has been extended to three dimensions and simulations have previously been done to obtain a quadruple node distribution (QND) which was also non-random. Using Electron Back-Scattered Diffraction to characterize grain boundaries in copper and aluminum, this project obtains an experimental quadruple node distribution and verifies that it too is non-random.; by Christopher Ng.; Thesis (S.B.)--Massachusetts Institute of Technology, Dept. of Materials Science and Engineering, 2005.; Includes bibliographical references (leaf 21).

‣ Anomalous solubility behavior of mixed monolayer protected metal nanoparticles

Myerson, Jacob W
Fonte: Massachusetts Institute of Technology Publicador: Massachusetts Institute of Technology
Tipo: Tese de Doutorado Formato: 32 leaves; 1399518 bytes; 1398494 bytes; application/pdf; application/pdf
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The solubility of mixed monolayer protected gold nanoparticles was studied. Monolayer protected metal nanoparticles are attractive materials because of the optical and electronic properties of their metal cores and because of the surface properties of their ligand coating. Recently, it was discovered that a mixture of ligands phase separate into ordered domains of single nanometer or subnanometer width on the surface of metal nanoparticles. The morphology and length of the ligand domains (which take the form of ripples on the particle surface) has given these nanoparticles novel properties. Because monolayer protected nanoparticles can be dissolved and dried many times, they can be handled and processed in ways not available to other nanomaterials. Understanding the solubility of mixed monolayer protected metal nanoparticles could help in implementing their unique new properties. This study demonstrates that the solubility of these particles in organic solvents cannot be explained only in terms of the composition of the ligand shell. Instead, solubility is also closely linked to morphology of the ligand shell via relationships between the size of the solvent molecule and the size of the features in the morphology.; by Jacob W. Myerson.; Thesis (S.B.)--Massachusetts Institute of Technology...

‣ Multifaced stone and ceramic moulds from Bronze Age Anatolia : building an analytical protocol of mould properties and behavior during the process of metal casting

Biçer, Katherine K. (Katherine Kershen)
Fonte: Massachusetts Institute of Technology Publicador: Massachusetts Institute of Technology
Tipo: Tese de Doutorado Formato: 193 leaves; 15895523 bytes; 15903739 bytes; application/pdf; application/pdf
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A three phase analytical protocol is developed to systematize the study of multifaceted serpentinite bronze-casting moulds from Bronze Age Anatolia (ca. 3500-1700 B.C.). These moulds represent a class of metal processing tools that reflect material properties and perhaps also social concerns in their development and use. In phase I of the protocol, standard serpentinite tiles are heated to known temperatures and the crack density and ineral changes at each temperature are determined using scanning electron microscopy (SEM) and energy dispersive x-ray (EDX) analysis. These results then serve to calibrate the cracking and mineralogical behaviors of serpentinite replica moulds used in controlled casting experiments during phase II. Metallography on several phase II cast objects provides additional information on heat flow through the stone. In phase III, the protocol is modified appropriately for the non-destructive study of four archaeological moulds using x-ray diffraction (XRD), x-ray fluorescence (XRF), and SEM. The applicability of the protocol to other stone and ceramic materials is discussed.; by Katherine K. Biçer.; Thesis (S.M.)--Massachusetts Institute of Technology, Dept. of Materials Science and Engineering, 2005.; Includes bibliographical references (leaves 91-96).

‣ Evaluation of the commercial potential of novel organic photovoltaic technologies

Barr, Jonathan (Jonathan Allan)
Fonte: Massachusetts Institute of Technology Publicador: Massachusetts Institute of Technology
Tipo: Tese de Doutorado Formato: 49 leaves; 2581086 bytes; 2583036 bytes; application/pdf; application/pdf
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Photovoltaic cells based on organic semiconducting materials have the potential to compete with the more mature crystalline and thin film based photovoltaic technologies in the future primarily due to the expectation of significantly reduced manufacturing costs. Stabilized power conversion efficiencies of organic photovoltaics are still well below those of crystalline Si photovoltaics, however a continuous, high throughput, roll-to-roll manufacturing process involving low temperature deposition or printing techniques is expected to partially account for their reduced efficiency and boost their commercial attractiveness. In addition, organic photovoltaics are flexible, light weight, and not fragile which makes them particularly suitable for transportation and portable electronics applications. Four organic photovoltaic technologies as well as the advantages and setbacks of each are described including Graetzel (wet) cells, blended photovoltaics, asymmetric tandem cells with hybrid planar-mixed molecular heterojunctions, and external antenna photovoltaics. A variety of start-up companies in various stages of commercialization of these technologies as well as the intellectual property related to these technologies is also discussed.; (cont.) A simplified cost model is presented to quantitatively estimate the possible cost reductions that continuous roll-to-roll production could entail for three different scenarios. Finally...

‣ Analysis of potential applications for the templated dewetting of metal thin films

Frantzeskakis, Emmanouil
Fonte: Massachusetts Institute of Technology Publicador: Massachusetts Institute of Technology
Tipo: Tese de Doutorado Formato: 125 leaves; 5431197 bytes; 5436361 bytes; application/pdf; application/pdf
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Thin films have a high surface-to-volume ratio and are therefore usually morphologically unstable. They tend to reduce their surface energy through transport of mass by diffusion. As a result, they decay into a collection of small isolated islands or particles. This solid-state process, known as thin film dewetting, can be initiated by grooving at grain boundaries or triple junctions. Dewetting of thin films on topographically modified substrates has many interesting characteristics. It is a novel self-assembly process for the formation of well-ordered nanoparticle arrays with narrow size distributions and uniform crystallographic orientation. Potential applications of particles resulting from templated thin film solid-state dewetting are reviewed. Applications in patterned magnetic information-storage media, plasmon waveguides, and catalytic growth of ordered arrays of semiconducting nanowires and carbon nanotubes are discussed. Templated dewetting technology has not been fully developed, and technological barriers are identified for all of the commercial applications considered.; (cont.) However, the self-assembly characteristics of templated dewetting may ultimately offer advantages in the manufacture of both patterned media and catalytic nanomaterial growth technologies.; by Emmanouil Frantzeskakis.; Thesis (M. Eng.)--Massachusetts Institute of Technology...

‣ Incorporation of silica into baroplastic core-shell nanoparticles

Hewlett, Sheldon A
Fonte: Massachusetts Institute of Technology Publicador: Massachusetts Institute of Technology
Tipo: Tese de Doutorado Formato: 33 p.; 1356517 bytes; 1355580 bytes; application/pdf; application/pdf
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Core-shell baroplastics are nanophase materials that exhibit pressure-induced flow at low temperatures and high pressures. Core-shell baroplastics used in this work are comprised of a low Tg poly(butyl acrylate) (PBA) core and a high Tg polystyrene (PS) shell. These novel polymer systems can be molded into fully formed, 3-D shapes with the application of high pressure at room temperature. While the mechanical properties are equivalent to or better than those of commercial thermoplastic elastomers, more can be done to improve upon individual aspects of the mechanical properties, such as elastic modulus. This work looks at creating baroplastic nanocomposites with the goal of improving upon the mechanical properties. To accomplish this goal, two incorporation strategies for introducing silica nanoparticles were developed. The pre-emulsion strategy incorporated hydrophobized silica nanoparticles inside the core-shell nanoparticles to create core-shell-shell nanoparticles. The post-emulsion strategy incorporated charged silica nanoparticles after core-shell emulsion, with the intention of creating crystalline structures with silica and core-shell nanoparticles.; (cont.) The pre-emulsion strategy resulted in a decrease in particle size for the core-shell-shell nanoparticles...

‣ Boundary element modeling of elasticity in materials in terms of distribution of second phase structures

Lok, Yi Cheung
Fonte: Massachusetts Institute of Technology Publicador: Massachusetts Institute of Technology
Tipo: Tese de Doutorado Formato: 113 p.
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The Boundary Element Method is used to study the interaction of second phase objects in a material. In particular, this study examines the relationship between stress parameters, such as stress concentration and normal traction, and geometrical parameters such as separation distance and orientation. The use of BEM enables easy manipulation of internal objects and rapid re-calculation in a series of simulations. Additional library functions are added to Julian, a general BEM solver, to expand its functionality to include elasticity calculation, inclusion modeling, and shape optimization with parallel processing. With a few thousand nodes, it is found that computation time scales as O(V), where N is the resolution of the mesh in each direction. An accuracy of over 99% is achieved in many benchmarks. A spherical cavity next to an inclusion is found to have higher stress concentration when aligned parallel to the loading direction. Stress analysis on a pair of neighboring cavities shows relatively small (less than 10%) increase in stress concentration beyond a separation of 0.5 diameter.; (cont.) While highest stress is observed when two cavities are aligned perpendicular to loading direction at very close separation, the highest stress configuration deviates from that alignment to almost +/- 30 degrees as separation increases. The radius of interaction is found to be determined by the larger of two second phase objects and is larger for a cavity surrounded by eight cavities in three dimensions. Our result suggests that a 15% weight saving is possible in a closed-cell foam for less than 10% increase in stress concentration due to the presence of immediate neighbors.; by Yi Cheung Lok.; Thesis (Ph. D.)--Massachusetts Institute of Technology...

‣ Acoustic assisted actuation of Ni-Mn-Ga ferromagnetic shape memory alloys

Peterson, Bradley William
Fonte: Massachusetts Institute of Technology Publicador: Massachusetts Institute of Technology
Tipo: Tese de Doutorado Formato: 115 p.
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Ferromagnetic shape memory alloys (FSMA) have been shown in recent work to exhibit large magnetic field induced strains. The material generally requires a large threshold field (of order 3-4 kOe) to initiate the strain. Thus, the power requirements are large and actuators based on these materials could tend to be large. This thesis reports on the effect on the actuation properties of Ni-Mn-Ga single crystals of the use of a sinusoidal stress wave generated by a piezoelectric stack actuator. The piezoelectric drive causes a time varying stress wave in the FSMA that resolves as a shear across the twin-boundaries and aids the twin boundary in overcoming defect-related obstacles. The FSMA shows increased strain and a reduction in threshold field. The effect is most pronounced for crystals showing large initial threshold fields which are associated with high defect strengths or concentrations. For crystals with a large threshold, 4.7 kOe, actuated at 1 Hz, the piezoelectric drive reduces the threshold field by as much as 21% for a piezoelectric driven at 5 kHz and 20 Vrms. As a result of this large threshold reduction, strain output can be more than doubled for magnetic drive amplitudes near the threshold field.; (cont.) Strain improvement is modest...

‣ Role of bit patterned media in future of hard disk drives

Aravindakshan, Vibin
Fonte: Massachusetts Institute of Technology Publicador: Massachusetts Institute of Technology
Tipo: Tese de Doutorado Formato: 61 p.
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The hard disk industry has traditionally stayed competitive by competing on the means of price alone by cutting down aggressively on cost via increase of areal density. Continuing increases in the areal density of hard disk drives will be limited by thermal instability of the thin film medium and is estimated to be limited to about 500Gb/in2. Patterned media, in which data are stored in an array of single.domain magnetic particles, have been suggested as a means to overcome this limitation and to enable recording densities greater than ITb/in2. However, the implementation of patterned media requires fabrication of sub-50-nm features over large areas and the design of recording systems that differ from those used in conventional hard drives. This report discusses the challenges facing patterned media, the fabrication of arrays of ́small magnetic particles and their magnetic properties. The practical implementation of patterned media recording schemes is assessed via technology estimates and cost analysis.; by Vibin Aravindakshan.; Thesis (M. Eng.)--Massachusetts Institute of Technology, Dept. of Materials Science and Engineering, 2007.; Includes bibliographical references (p. 60-61).

‣ Assessment of in vitro engineered microvascular networks and their application in the treatment of chronic wounds

King, Connie Hong-Yee
Fonte: Massachusetts Institute of Technology Publicador: Massachusetts Institute of Technology
Tipo: Tese de Doutorado Formato: 72 p.
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As the number of individuals suffering from tissue loss and end-stage organ failure continues to grow, researchers are turning to tissue engineering to provide better methods of treatment. The field, however, still faces many technical challenges that are limiting its applications. One challenge faced in engineering more complex tissues and organs is the need for inherent microvasculature to supply the tissue with nutrients and oxygen. Researchers at The Charles Stark Draper Laboratory have developed a method for engineering microvascular networks in vitro using various microfabrication techniques. This paper discusses the current state of the research and technical challenges to overcome before commercializing the technology. The feasibility of using the networks in the nearer term application of treating chronic wounds will also be assessed, and a potential business strategy will be laid out.; by Connie Hong-Yee King.; Thesis (M. Eng.)--Massachusetts Institute of Technology, Dept. of Materials Science and Engineering, 2007.; "September 2007."; Includes bibliographical references (p. 67-72).

‣ Thermoelectrics : material advancements and market applications

Monreal, Jorge
Fonte: Massachusetts Institute of Technology Publicador: Massachusetts Institute of Technology
Tipo: Tese de Doutorado Formato: 83 leaves
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Thermoelectric properties have been known since the initial discovery in 1821 by Thomas Seebeck, who found that a current flowed at the junction of two dissimilar metals when placed under a temperature differential. This was followed by the discovery in 1834 by John Peltier, that the inverse was also true. That is, that a current applied to two dissimilar metals would yield a temperature differential. Interest in thermoelectrics laid dormant for almost 100 years and were primarily a laboratory curiosity. That interest was revived in the early 1900s with applications for remote power generation aboard satellites and several military applications. Thermoelectric devices, such as beverage coolers or thermocouples for temperature sensors, that tried to make use of these characteristics shortly followed. However, commercial success soon slowed down as efficiencies of the materials were not conducive to profitability. The effectiveness of a thermoelectric was described by a dimensionless figure of merit given by ZT=(S2a/ke+kp)T, where S is the Seebeck coefficient, T is the operational temperature, a is the electrical conductivity, ke is the electron contribution to thermal conductivity, and kp is the thermal conductivity due to phonon propagation across a crystal lattice. From the mid-1940s until the 1970s there was very slow progress in increased thermoelectric material efficiency...

‣ Commercialization of germanium based nanocrystal memory

Seow, Kian Chiew
Fonte: Massachusetts Institute of Technology Publicador: Massachusetts Institute of Technology
Tipo: Tese de Doutorado Formato: 100 p.
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This thesis explores the commercialization of germanium-based nanocrystal memories. Demand for smaller and faster electronics and embedded systems supports the development of high-density, low-power non-volatile electronic memory devices. Flash memory cells designed for ten years of data retention require the use of a thick tunneling oxide. This compromises writing and reading speed as well as endurance. A smaller device size can be achieved and speed and can be improved by decreasing the oxide thickness. However, significant charge leakage will occur if the oxide is too thin, which will reduce the data retention time dramatically. This imposes a limit to the amount by which the oxide thickness can be decreased in conventional devices. Research has shown that by incorporating nanocrystals in the tunnel oxide, charge traps are created which reduce charge leakage and improve endurance through charge-storage redundancy. By replacing the conventional floating gate memory with one using Si or Ge nanocrystals, the nonvolatile memory exhibits high programming speed with low programming voltage and superior retention time, and yet is compatible with conventional silicon technology. This thesis provides an analysis of competing technologies...

‣ Substrate engineering for monolithic integration of III-V semiconductors with Si CMOS technology

Dohrman, Carl Lawrence
Fonte: Massachusetts Institute of Technology Publicador: Massachusetts Institute of Technology
Tipo: Tese de Doutorado Formato: 172 p.
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Ge virtual substrates, fabricated using Si1-xGex-.Ge, compositionally graded buffers, enable the epitaxial growth of device-quality GaAs on Si substrates, but monolithic integration of III-V semiconductors with Si CMOS using this platform is hampered by the large thickness of the Si1-xGex graded region. To address this issue, the Silicon on Lattice-engineered Silicon (SOLES) was developed, consisting of a silicon-on-insulator (SOI) structure fabricated on a Ge virtual substrate. Placement of the Si device layer at the surface makes it possible to process this platform similarly to typical SOI wafers, with the added functionality of a buried III-V template which can be used for GaAs device fabrication. This platform was fabricated using a scalable layer transfer technique. AlInGaP LEDs were also demonstrated on a SOLES substrate. In addition, an alternative growth process was investigated for Si1-xGex virtual substrates with lower threading dislocation density (TDD) and thickness. This process, the thermally relaxed ultra-thin (TRUT) buffer process, consists of coherent growth of lattice-mismatched Si1.xGex layers, followed by post-growth annealing. Growth of TRUT buffers over the Si0.5Ge0.5 to Si0.3Ge0.7 alloy range with high strain levels resulted in the nucleation of surface defects which appear to limit the maximum strain rate of compositionally graded buffers. However...

‣ Structural, magnetic, and optical properties of orthoferrite thin films

Supplee, William Wagner
Fonte: Massachusetts Institute of Technology Publicador: Massachusetts Institute of Technology
Tipo: Tese de Doutorado Formato: 43 leaves
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Pulsed laser deposition was used to create thin films of Ce-Fe-O and Y-Fe-O systems. Deposition temperature and ambient oxygen pressure were varied systematically between samples to determine which deposition conditions were most favorable to the formation of cerium/yttrium orthoferrite. The structure and composition of each film were then determined using X-ray diffraction and wavelength dispersive spectroscopy respectively. In addition, the magnetic and optical properties of the yttrium films were characterized to determine the suitability of these materials as Faraday isolators at A=1550 nm. Results show that orthoferrite crystal structures in these systems are not stable in the temperature and oxygen ranges tested. It was also found that increasing oxygen pressure caused exponential decay in the deposition rate. Most films were amorphous, exhibiting a paramagnetic M-H plot and a Verdet coefficient between 0.37 and 0.89 deg cm-1 Gauss-1; by William Wagner Supplee, Jr.; Thesis (S.B.)--Massachusetts Institute of Technology, Dept. of Materials Science and Engineering, 2007.; Includes bibliographical references (leaves 41-43).

‣ Commercial applications of block copolymer photonic gels

Lou, Sally S
Fonte: Massachusetts Institute of Technology Publicador: Massachusetts Institute of Technology
Tipo: Tese de Doutorado Formato: 62 leaves
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Block copolymer photonic gels are a simple and easily processed material which responds rapidly to environmental stimuli through a color change. The diblock copolymer that forms the gel self-assembles into a lamellar structure that has the potential to reflect light over a broad range of wavelengths, from the IR to the UV. Application of a stimulus causes a change in the periodicity and/or index of refraction of layers that result in a shift of the stop band. The types of stimuli include temperature, pressure, pH, electric field, salt concentration, and humidity. Due to the high level of tunability of the polymers, it is possible to tailor the response of the gel to achieve a desired effect. This thesis is an assessment of the commercial applications of the photonic gel technology. First a cost model was developed for the polymerization of the block copolymer, polystyrene-b-poly(2-vinyl pyridine). The results indicate that it is cost effective to invest in a small scale production facility at large production volumes. Next, an evaluation of three potential markets was conducted. The anti-counterfeit market is most promising because of large profit margins and the opportunity for future company growth through R&D of new anti-counterfeit measures. The other two markets in color cosmetics and food preservation present potential opportunities for licensing.; by Sally S. Lou.; Thesis (M. Eng.)--Massachusetts Institute of Technology...

‣ Attractive electrostatic self-assembly of ordered and disordered heterogeneous colloids

Maskaly, Garry R. (Garry Russell), 1978-
Fonte: Massachusetts Institute of Technology Publicador: Massachusetts Institute of Technology
Tipo: Tese de Doutorado Formato: 193 p.; 7064851 bytes; 7064543 bytes; application/pdf; application/pdf
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Ionic colloidal crystals are here defined as multicomponent ordered colloidal structures stabilized by attractive electrostatic interactions. These crystals are colloidal analogues to ionic materials including zincblende, rocksalt, cesium chloride, and fluorite. A thermodynamic study revealed that the screening ratio, charge ratio, and monodispersity are critical parameters in ionic colloidal crystal (ICC) formation. Experimentally, small ordered regions were observed under ideal thermodynamic conditions. However, no larger crystalline regions were found in these samples. The kinetics of ICC formation was studied using a variety of computational techniques, including Brownian dynamics, Monte Carlo, and a Newton's method solver. These techniques have each elucidated properties and processing conditions that are important to crystallization. The Brownian dynamics and Monte Carlo simulations showed that the previous experiments were highly undercooled. Furthermore, a narrow crystallization window was found, demonstrating the need to create particle systems that meet the narrow parameter space where ICCs should be stable. Pair interaction potentials were evaluated for their accuracy using a Poisson-Boltzmann (PB) equation solver. The PB solver was also used to further refine crystalline formation energies so that systems can be more accurately tailored. A surprising result from the PB solver showed that the lowest formation energy occurs when the quantity of surface charges on both particles are equal. Although this result is not predicted by any colloidal pair potentials...

‣ Nano-contact printing of DNA monolayers; Nano-contact printing of deoxyribonucleic acid monolayers

Tong, Angela, 1983-
Fonte: Massachusetts Institute of Technology Publicador: Massachusetts Institute of Technology
Tipo: Tese de Doutorado Formato: 23 leaves; 991795 bytes; 989950 bytes; application/pdf; application/pdf
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Technology today is directed towards building smaller devices. To accommodate this development, printing methods are needed. Some printing methods that are used include lithography, micro-contact printing, and inkjet printing. These methods all require specialized instrumentation, hazardous chemicals, and complicated and tedious steps that increase cost of manufacturing. Nano-contact printing is an alternative solution which relies on the specificity of DNA to direct molecules into precise patterns. This study attempts to find the limitations of nano-contact printing through the printing of oligonucleotide monolayers. Eight pattern transfers were made with one master copy and the oligonucleotide surface coverage was analyzed using tapping mode atomic force microscopy (AFM). The percent coverage of oligonucleotide was then calculated from the tapping mode AFM phase images. Two general trends were found. The oligonucleotide surface coverage on the master increased slightly, while the surface coverage on the pattern transfers decreased. One possible explanation for the trends is that the decrease in contact between master and secondary substrate is due to both the accumulation of dirt and the wear and tear of' the master. By improving the contact between master and secondary substrate...