Thesis (Ph. D.)--Massachusetts Institute of Technology, Dept. of Materials Science and Engineering, 2008. / Includes bibliographical references. / Guiding electro-magnetic radiation is fundamental to optics. Lenses, mirrors, and photonic crystals all accomplish this task by different routes. Understanding the interaction of light with materials is fundamental to improving and extending optical science and engineering as well as producing novel optical elements. Improvement in this understanding should not only include work to understand the interaction with traditional engineering materials but also should target the understanding of the interaction of electromagnetic radiation with biological structures as millions of years of evolution have sorted out numerous ways to modulate light (e.g. the fish eye or the skin of the octopus). The goal of this thesis work is to fabricate novel optical elements by taking cues from nature and extending the state of the art in light guiding behavior. Here, optical elements are defined as structured materials that guide or direct electromagnetic radiation in a predetermined manner. The work presented in this thesis encompasses biologically inspired tunable multilayer reflectors made from block copolymers and improvements to liquid filled lenses which mimic the human eye.In this thesis a poly(styrene)-poly(2-vinylpyridine) block copolymer was used to create a bio-mimetic, one-dimensional, multilayer reflector. The wavelengths of light reflected from this multilayer reflector or Bragg stack were tuned by the application of stimuli which included temperature, change in the solvent environment, pH, salt concentration in the solvent, and electrochemistry. / (cont.) A linear-shear rheometer was also built to investigate the mechanochromic color change brought about through the shearing of a one-dimensional, high molecular-weight, block-copolymer, photonic gel. Biologically inspired lenses were also studied through the construction of a finite element model which simulated the behavior of a liquid-filled lens. Several tunable parameters, such as the modulus, internal residual stress, and thickness of the membrane were studied for their influence on the shape of the lens membrane. Based on these findings, suggestions for the reduction of spherical aberration in a liquid filled lens were made. A gradient in the elastic modulus of the membrane was also investigated for use in the reduction of spherical aberration. / by Joseph John Walish. / Ph.D.

Thesis (Ph. D.)--Massachusetts Institute of Technology, Dept. of Materials Science and Engineering, 1998. / Includes bibliographical references (leaves 93-95). / by Stephan P. Mangin. / Ph.D.

Thesis: S.B., Massachusetts Institute of Technology, Department of Materials Science and Engineering, 2015. / Cataloged from PDF version of thesis. / Includes bibliographical references (pages 34-36). / Alkali activated bricks offer an alternative to traditional clay fired bricks for use in construction in the developing world. Previous work in this lab focused on creating a robust mix formulation to create these bricks, but they faced high water absorption and were not optimized under pressure molding conditions. The motivation for the work on alkali-activated bricks is based on the claim that they have a lower environmental burden, but this claim has not yet been verified for this formulation. Thus, this thesis focused on the effects of controlled testing of formation pressure and particle size distribution on brick performance and understanding the relative environmental impacts of clay fired bricks and alkali activated bricks. It was found that water absorption and compressive strength have a strong dependence on forming pressure, with 3-day compressive strengths ranging from 7MPa to 27MPa and water absorption from 35% to as high as 60% as forming pressure increased from 5 to 35Mpa. Sieving of the ash used in the bricks to control for particle size distribution had a minimal effect on performance, but the similarity is attributed to the fact that packing density within the selected particle size ranges were similar. Further testing on controlled mixing of particle sizes is needed to see if better performance can be obtained. Life cycle assessment results verify the claim that the bricks perform better from an environmental perspective, but also show the dependence of that performance on variables such as lime content or kiln efficiency. / by Cecilio Aponte. / S.B.

Thesis (Ph. D.)--Massachusetts Institute of Technology, Dept. of Materials Science and Engineering, 2009. / Includes bibliographical references (p. 161-170). / In the search for new materials for energy conversion and storage technologies such as solid oxide fuel cells, nano-ionic materials have become increasingly relevant because unique physical and transport properties that occur on the nanoscale may potentially lead to improved device performance. Nanocrystalline cerium oxide, in particular, has been the subject of intense scrutiny, as researchers have attempted to link trends in electrical conductivity with the properties of space charge layers within the material. In this thesis, efforts designed to intentionally modify the space charge potential, and thus the space charge profiles and the macroscopic conductivity, are described.Nanocrystalline CeO2 thin films with a columnar microstructure were grown by pulsed laser deposition. A novel heterogeneous doping technique was developed in which thin NiO and Gd203 diffusion sources were deposited on the ceria surface and annealed in the temperature range of 7008000C in order to diffuse the cations into the ceria layer exclusively along grain boundaries. Time-offlight secondary ion mass spectrometry (ToF-SIMS) was utilized to measure the diffusion profiles. A single diffusion mechanism, identified as grain boundary diffusion, was observed. Using the constant source solution to the diffusion equation, grain boundary diffusion coefficients on the order of 10-15 to 10-13 cm2/s were obtained for Ni, as well as Mg diffusion emanating from the underlying substrate. Microfabricated Pt electrodes were deposited on the sample surface, and electrical measurements were made using impedance spectroscopy and two-point DC techniques. The asdeposited thin films displayed a total conductivity and activation energy consistent with reference values in the literature. After in-diffusion, the electrical conductivity decreased by one order of magnitude. Novel electron-blocking electrodes, consisting of dense yttria-stabilized zirconia and porous Pt layers were fabricated in order to deconvolute the ionic and electronic contributions to the total conductivity. In the as-deposited state, the ionic conductivity was determined to be pO2-independent, and the electronic conductivity displayed a slope of -0.30. The ionic transference number in the as-deposited state was 0.34. / (cont.) After annealing either with or without a diffusion source at temperatures of 700-8000C, both the ionic and electronic partial conductivities decreased. The ionic transferene numbers with and without a diffusion source were 0.26 and 0.76, respectively. Based on the existing framework of charge transport in polycrystalline materials, carrier profiles associated with the Mott-Schottky and Gouy-Chapman models were integrated in order to predict conductivity values based on parameters such as grain size and the space charge potential. Mott-Schottky profiles with a space charge potential of 0.44V were used to describe the behavior of the ceria thin films in the as-deposited state. It is proposed that annealing at temperatures of 700TC and above resulted in segregation of acceptor impurity ions to the grain boundary, resulting in GouyChapman conditions. The best fit to the annealed data occurred for a space charge potential of 0.35 V: a decrease of approximately 90 mV from the as-deposited state. In addition, a high-conductivity interfacial layer between the CeO2 and substrate was detected and was determined to influence samples with no surface diffusion source to a greater degree than those with NiO or Gd203. / by Scott J. Litzelman. / Ph.D.

Thesis (Ph.D.)--Massachusetts Institute of Technology, Dept. of Materials Science and Engineering, 1999. / Includes bibliographical references (p. 253-258). / by John Jason Sprague. / Ph.D.

Thesis (M.Eng.)--Massachusetts Institute of Technology, Dept. of Materials Science and Engineering, 2002. / Includes bibliographical references (p. 45-49). / The layer-by-layer assembly of polyelectrolytes into multilayered films is an attractive approach for fabricating novel biomaterials, as it offers tremendous control over the internal composition and surface properties of their layered architectures. In this work, polyelectrolyte multilayers (PEMs) were evaluated as a platform for applications in controlling the spatial adhesion of living cells. An overview is presented on current developments and competing technologies within research and industry with respect to cell patterning and cell-based devices. Interviewed individuals in research and industry suggested a variety of potential applications of PEMs in cell patterning technology. A patent search on the core technologies (i.e. PEMs and patterning methods) and on applications in cell patterning, cell-based screening, and cell-based biosensors revealed ample opportunity for starting a new venture with a platform based on the layer-by-layer assembly of PEMs. A brief business plan for starting a new venture with a platform based on the layer-by-layer assembly of PEMs is proposed to initially target the high throughput screening and cell-based biosensor markets. / by Aleksandr John White. / M.Eng.

Thesis (Ph.D.)--Massachusetts Institute of Technology, Dept. of Materials Science and Engineering, 1999. / Includes bibliographical references (leaves 120-124). / This thesis focuses on the use of a new sequential adsorption technique to deposit thin polyelectrolyte multilayer films. This involves alternately dipping a substrate into dilute aqueous solutions of a positively charged polyelectrolyte followed by a negatively charged polyelectrolyte, with a rinsing step in between. By repeating this process an arbitrary number of times, a thin film can be built up due to the electrostatic interaction between the two oppositely charged polyelectrolytes. This technique was used to create thin film electroluminescent devices based on poly(p-phenylene vinylene) (PPV) using a water soluble precursor to PPV and poly(acrylic acid) (PAA). The structure of such films has been shown to be highly dependent on the conditions of the dipping solutions. The pH of the solutions controls the degree of ionization of the PAA which influences the deposition process by affecting both the conformation of the PAA in solution as well as the charge density of the PAA on the surface. These films exhibited a light output of greater than 1000 cd/m 2 (about 10 times the brightness of a computer monitor), significantly higher than that typically reported for films of pure PPV. A time dependent charging process together with a reduction in the turn-on voltage with charging, and a non-rectifying device behavior, suggest an electrochemical mode of operation. In such a case, ions present in the film play an active role by modifying the electrical injection characteristics. More fundamental studies on the impedance and dielectric characteristics of sequentially adsorbed films were performed on layers of poly(allylamine hydrochloride) (PAH) with PAA as well as PAH with sulfonated polystyrene (SPS). This provided some insight into the level of ionic conductivity present in these films. Typically ionic conductivities were observed that ranged from about 10-12 S/cm at room temperature up to about 10-8 to 10-9 S/cm at 1 100°C. The apparent dielectric constant also increased to relatively large values at low frequencies implying the buildup of ions at the interface. The PAH/SPS system required much higher temperatures than the PAHIPAA system before any significant change in the electrical characteristics were observed suggesting that ionic motion is much more hindered in PAH/SPS films. / by Michael Frederick Durstock. / Ph.D.

Thesis (Ph. D.)--Massachusetts Institute of Technology, Dept. of Materials Science and Engineering, 2005. / Includes bibliographical references. / To fabricate living cell-based immunological sensors, we have examined two PEO-based biomaterials that can be patterned to generate cellular array templates: poly(allylamine)-g- poly(ethylene glycol) graft-copolymer and poly(ethylene glycol) dimethacrylate hydrogel. Poly(allylamine)-g-poly(ethylene glycol) polycation graft-copolymers were designed, synthesized, and characterized in order to combine bio-functionality with patternability on charged polyelectrolyte multilayer surfaces. Polymer-on-polymer stamping (POPS) techniques were used to create micron scale patterned regions on negatively charged multilayer surfaces via direct stamping of these graft copolymers. The long PEG side chains effectively resisted adsorption of antibodies or other proteins, and created a bio-inert area when patterned by POPS. On the other hand, desired proteins can be covalently attached to the graft copolymer by introducing proper coupling agents. Arrays of proteins were produced by either simple adsorption or coupling of proteins onto the graft copolymer patterned surfaces. The protein arrays were utilized as templates in fabricating cellular arrays of non-adherent B cells. / (cont.) Poly(ethylene glycol) dimethacrylate hydrogel precursors were photopolymerized into 3D rmicrowell array templates via micromolding. After the floors of microwells were decorated with antibodies, hydrogel microwell array templates were employed in fabrication of cellular arrays. The topology of microwells facilitates the positioning of cells inside microwells and improves the binding stability of cells with protection from mechanical agitations. T cell arrays fabricated on hydrogel microwell array templates were tested as living cell- based immunological sensors. B cells were settled uniformly on T cell arrays to establish contacts between B and T cells over a large area. A level of T cell activation by target peptides were quantified using calcium sensitive fura dyes. A large set of individual T cell response data was acquired from a single T cell array and utilized to obtain average dose-response behavior of T cells. Average T cell responses were suitable as quantitative signal of a living cell-based immunological sensor. In addition, a potential application of T cell arrays in high throughput assay of individual T cell responses was investigated. / (cont.) Analysis of calcium oscillation frequency of individual T cells revealed that there is no clear correlation of calcium oscillation frequency with target peptide dose in this experiment. / by Heejae Kim. / Ph.D.

Thesis (S.M.)--Massachusetts Institute of Technology, Dept. of Materials Science and Engineering, 2010. / Cataloged from PDF version of thesis. / Includes bibliographical references (p. 108-112). / The behavior of alloy 617 at 650°C in low oxygen partial pressure environments has been studied under static loading. Of particular interest was the crack growth rate in these conditions. For that, tests were conducted at a constant stress intensity factor of 49.45 MPa'm (45 ksidinch) using a direct current potential drop measurement system to determine crack length. High purity argon gas allowed establishing an oxygen partial pressure as low as 10-22 atm and premixed oxygen/argon gases were used to vary the oxygen potential. To go dee er into the understanding of the phenomena involved, a creep test (constant load of 1.21x10 N in argon environment) and a corrosion experiment (50 ppm oxygen in argon for 500 hours without any load) were also added. The crack growth tests led to a particularly unexpected result: whatever the oxygen potential, the crack growth rate increased with time and the plot for the crack length versus time displayed a recurrent parabolic shape without any change in the environment. No unique crack growth rate could be defined in a given environment and the influence of the environment on the crack growth rate was not clearly visible. Multiple features were found to surround the main crack: secondary cracks parallel to the principal one, intergranular cracking ahead of the crack tip, wedge cracks at grain boundaries and aggregates of Cr-rich carbides near the lips of the crack. Moreover no extensive oxide scale was formed on the surface of the sample exposed to the corrosive environment (50 ppm oxygen in argon) for 500 hours. The non-constant crack growth rates, together with the observed cracking features, were attributed to the competition between creep deformation and mechanical fracture, likely environmentally enhanced. An exponential law was found to fit the data for the crack growth rate as a function of time for a K of 49.45 MPalm (45 ksi'inch). The effects of the environment were overcome by mechanical and thermal processes leading to damage accumulation and so, a reaction of alloy 617 to the external stress and temperature highly dependent on time. This behavior was compared with the one of alloys Haynes 230 and Incoloy 908 in the same conditions. / by Fanny Mas. / S.M.

Thesis: S.B., Massachusetts Institute of Technology, Department of Materials Science and Engineering, 2014. / Cataloged from PDF version of thesis. / Includes bibliographical references (pages 337-39). / Aligned arrays of carbon nanotubes (A-CNTs), called CNT forests, are the precursor for controlled-morphology macroscopic nanocomposites and nanoengineered composites due to theirscale-dependent, tunable physicall properties. Applications include polymer and ceramic matrix nanocomposites (PNCs and CMNCs), nanostiching as laminate interply reinforcement, as well as in supercapacitors, MEMS devices and electrodes for ion actuators and sensors. A key component of manufacturing materials comprised of A-CNTs is controlling the morphology and geometry of the CNT forest. Current laboratory findings show significant variability in CNT forest growth characteristics, and an experimental study was conducted to better understand and control for the observd process variations. An exploratory investigation of growth parameters allowed for a local optimization of growth temperature and hydrocarbon flow rates, as well as an acceptable range of sample placement in the CVD furnace to achieve ~1mm tall CNT forests. Results from this investigation led to the conclusion that the significant inconsistencies between consecutive growths must be due to factors out of direct control, mainly humidity. A new system is being developed to better control for and monitor water in the furnace. A second investigation focused on post growth cool down effects, and the possible shortening (deforestation) of CNTs at high temperatures without a renewing source of the carbon precursor. Deforestation conditions did not lead to CNT shortening. / by Hanna Megumi Vincent. / S.B.