Thesis (Ph.D.)--Massachusetts Institute of Technology, Dept. of Materials Science and Engineering, 2002. / Includes bibliographical references. / Dendrimers are three-dimensional, hyperbranched macromolecules that possess a uniform size and shape. Most dendrimers are spherical in shape; however, the shape of the dendrimer can be adjusting using the number and the position of the branching groups in the core. For example, dendritic rods have been prepared by assembling a dendron around each repeat unit of a linear polymer core, and hybrid-linear dendritic diblock copolymers have been prepared by attaching a dendron to the end functional group of a linear polymer. This linear block in the diblock copolymers also adds physical integrity and an assembly mechanism for arrangement of the polymer. Nonetheless, no one has combined the unique shape of the dendritic rod with that of the linear dendritic diblock copolymer. The objective of this research was to prepare a linear-dendritic rod diblock copolymer, and to examine its assembly behavior in solution, at the air/water interface, and in the bulk. These polymers consisted of a linear poly(ethylene oxide)-poly(ethylene imine) diblock copolymer around which poly(amido amine) branches were divergently synthesized. The dendritic branches were terminated with amine and ester groups, as well as alkyl chains of various lengths in order to "tune" the amphiphilic nature of the polymer. / (cont.) A fundamental change in the assembly behavior of the polymers was observed at generation 4.0 (eight end-groups). In solution, the hydrodynamic and viscometric radii were found to increase to a much greater extent than expected for the generation 4.0 and 4.5 polymers, consistent with a breakdown of the spherical approximation as the dendritic block extended into a rod-like shape. Similarly, at the air/water interface, the dendritic block of generation 4.0-alkyl terminated polymers all adopted a horizontal rod configuration, while the dendritic block of the lower generation polymers took on a random coil configuration, whose shape depended on the length of the terminal alkyl groups as well as the generation number of the dendritic block. Finally, in the bulk, direct observation of the generation 4.0-dodecyl terminated polymer with TEM indicated that the polymer was adopting a rod- or worm-like conformation, while the lower generation polymers only exhibited traditional diblock copolymer or polymer brush behavior. / by Catherine Marie Bambenek Santini. / Ph.D.

Thesis (S.M.)--Massachusetts Institute of Technology, Dept. of Materials Science and Engineering, 2007. / Includes bibliographical references (leaves 98-100). / Internal surgical intervention necessitates the intentional wounding of tissue. In certain clinical procedures, the desired wound healing response requires the use of closure techniques, such as suturing or stapling of disjoined tissues. Risk factors associated with these techniques are largely attributed to the discrete nature of the mechanical forces arising in the tissues. Adhesive sealants can mitigate risk by imparting a continuous stress distribution to tissues upon closure, as opposed to destructive stress concentrations. A novel class of dextran:polyethylene glycol hydrogels are a potential alternative to the limited selection of available adhesive sealants. Multiple compositional variations are available for both the dextran and polyethylene glycol components, making a wide range of clinically relevant material properties achievable. Key material properties determining sealant efficacy include hydration and degradation in an aqueous medium, elastic modulus, adhesion strength to tissue, and biocompatibility. Relationships between these pertinent properties and available compositional variations are determined for dextran:polyethylene glycol materials. / (cont.) Gravimetric, mechanical and biological testing reveal the following compositional determinants of material properties in dextran:polyethylene glycol copolymers: constituent molecular complexity dictates material hydration and degradation, solid content dictates elastic modulus, available aldehyde groups dictate adhesion strength, and material solid content and reactive group ratio dictate induced cell proliferation and cytotoxicity. Knowledge of these property determinants facilitates development of an optimal dextran:polyethylene glycol material in a small bowel resection model for adhesive sealants, and furthers the understanding of these complex copolymers for other sealant applications. Generalization of the identified property determinants to other material classes provides a vehicle for advancement of adhesive sealant technologies. / by Tarek Shazly. / S.M.

Thesis: S.B., Massachusetts Institute of Technology, Department of Materials Science and Engineering, 2011. / Cataloged from PDF version of thesis. / Includes bibliographical references (page 35). / We examined the feasibility of using the resonant frequency of magnetic bead-domain wall (DW) couples in a host fluid to measure particle size. Nickel-Iron (Permalloy) rings, made using electron beam lithography, served as the tracks for nucleating and moving DWs, and Invitrogen Dynabeads M-270 magnetic beads were used for the experiment. Tween-20 surfactant in solution and SiO2 capping layers for the structures were used to overcome substrate-bead interaction and maintain bead mobility. The resonant frequency of 40 bead-DW couples was measured and found to lie in a range between 18.3 and 42.7 Hz with a median of 31.1 Hz. In addition, sets of resonance experiments were performed to examine the dependence of the resonant frequency on driving amplitude, DW type, and position on the permalloy (Py) ring. The resonant frequency populations of beads bound to head-head and tail-tail DWs overlapped, but each DW type seemed to be centered around a different frequency. Examining different positions on a ring showed that a large contribution to the spread in resonant frequencies may come from DW pinning due to structural defects or remanent surfacebead interaction. Finally, the resonant frequency is independent of the driving amplitude, a finding which supports the linear spring model for DW-bead interaction. We conclude that resonance measurements made with optical methods reliably distinguish particles of different hydrodynamic radius. This work has also helped identify and address some of the obstacles to improve the reliability of these resonance measurements as indicators of particle size. By demonstrating this detection capability, we can proceed with the development of spin-valve -based resonance devices suitable for clinical applications. / by Daniel Mauricio Montana Fernandez. / S.B.

Thesis (Ph. D.)--Massachusetts Institute of Technology, Dept. of Materials Science and Engineering, 1997. / Vita. / Includes bibliographical references. / by Harold D. Ackler. / Ph.D.

Thesis (S.M.)--Massachusetts Institute of Technology, Dept. of Materials Science and Engineering, 2000. / Includes bibliographical references (leaves 56-57). / YBa2Cu3O7-x (YBCO) thin films were prepared on lanthanum aluminate (LAO) single crystals and buffered (5000 Y20 3, 500 Ce02) Ni-single crystal substrates by metal organic deposition (MOD) process. Glassy films were converted to epitaxial YBCO films, by heating in wet atmosphere of N2/02 mixture. A novel technique was used to determine the rate of conversion of films from glassy state to crystalline YBCO films. In this approach, the concentration of residual fluoride in the partially converted films was examined using fluoride ion selective electrode. Results obtained by this method were compared to results obtained by such methods as X-ray analysis and in-situ resistivity measurements. Analysis of data obtained by different methods showed that fluoride concentration measurement method is a fast and very accurate method. The influence of different factors on conversion rate was investigated by this approach, including high and low vapor pressure of water in the processing atmosphere, temperature and influence of substrate material on conversion. A simple model was proposed to describe the growth of crystalline YBCO film for diffusion controlled and reaction controlled growth kinetics. Results obtained by in-situ resistivity measurements were compared to results predicted by the model. The obtained data fits the model that describes interface reaction limited growth kinetics. / by Igor L. Seleznev. / S.M.

Thesis (M.S.)--Massachusetts Institute of Technology, Dept. of Materials Science and Engineering, 1997. / Includes bibliographical references (p. 87-88). / by Elicia M.A. Maine. / M.S.

Thesis (Ph. D.)--Massachusetts Institute of Technology, Dept. of Materials Science and Engineering, 1988. / Includes bibliographical references. / by Jiro Kawamoto. / Ph.D.

Thesis (Ph.D.)--Massachusetts Institute of Technology, Dept. of Materials Science and Engineering, 1997. / Includes bibliographical references. / Large gap joints are frequently encountered in the manufacturing of massive components as well as in the repairing of damaged parts. Several methods using powder interlayers to produce large clearance transient liquid phase (TLP) joints have been developed and investigated in this work. One of the methods was using a mixture of powders of the melting point depressant (MPD) and the base material, from which a great amount of MPD (>30 vol.%) usually has to be used to eliminate residual porosity. To reduce the MPD in the joint, the liquid infiltrated powder interlayer bonding (LIPB) process was developed. For a material system that has a large mutual solubility between the liquid and the solid at the bonding temperature, a protective coating on the particles of the base material was applied to avoid excessive dissolution and inhibit early diffusional solidification, which can block the infiltration paths and prevent full infiltration. Direct coating of the MPD on the particles of the base material proved highly effective in producing tough and strong joints for certain material systems. The classic liquid phase sintering (LPS) theory was adopted to explain the physical process as occurring in the powder interlayer during joining. Despite the general applicability of the theory, there are several other important factors have to be considered as well. For example, the reaction rate between the MPD and the base material can markedly affect the densification of a mixed powder interlayer. Fast growth of the intermetallic compounds as a result of reaction can significantly retard the liquid flow. For the infiltration process, kinetics of dissolution and diffusional solidification largely depend on the mutual solubility between the liquid (infiltrant) and the solid (powder interlayer). Dissolution is needed to open up closed pores in the powder interlayer. However, excessive dissolution is undesirable due to fast liquid saturation and subsequent diffusional solidification, which may prevent complete infiltration of the interlayer. A protective coating on the particles of the base material provides a way of reducing the dissolution rate, which facilitates full infiltration of the interlayer. The solubility factor is also crucial for direct coating of the MPD on the particles of the base material. Higher solubility of the base material in the MPD is preferred to maintain enough liquid for complete densification. Experiments were performed on joining the materials including titanium alloy, Ti- 6A1-4V, nickel base superalloy, Inconel 625, stainless steel, SS304, and commercially pure copper. Application of the particular joining process depends on careful choice of the MPD, the base powders as well as the geometry of the interlayers. / by Wei-Dong Zhuang. / Ph.D.

Thesis (Ph. D.)--Massachusetts Institute of Technology, Dept. of Materials Science and Engineering, 2008. / Includes bibliographical references. / One major efficiency limiting factor in thin film solar cells is weak absorption of long wavelength photons due to the limited optical path length imposed by the thin film thickness. This is especially severe in Si because of its indirect bandgap. This thesis invents a novel light trapping scheme, the textured photonic crystal (TPC) backside reflector, which can enhance path length by at least several hundred times the film thickness for sufficient absorption. Physical principles and design optimization of TPC are discussed in detail. Thin film Si solar cells integrated with the new back reflector are successfully fabricated and significant efficiency enhancement is demonstrated.The new back reflector combines a one-dimensional photonic crystal as a distributed Bragg reflector (DBR) and reflection grating. The DBR achieves near unity reflectivity in a wide omnidirectional bandgap completely covering the wavelengths needing light trapping, and the grating can diffract light into large oblique angles and form total internal reflection against the front surface of the cell. The unique combination of DBR and grating tightly confines light inside the cell, effectively changing the path length from the thickness of the cell to its width.The back reflector parameters and the antireflection coating are systematically optimized for thin film Si solar cells through simulation and experiments. A 2 [mu]m thick cell can achieve 54% efficiency enhancement using the optimized design.For proof of concept, the TPC back reflector is integrated with thick crystalline Si solar cells (675 [mu]m thick), which demonstrate external quantum efficiency enhancement up to 135 times in the wavelength range of 1000-1200 nm. / (cont.) To prove the theory on the intended application, top-contacted thin film Si solar cells integrated with the TPC back reflector are successfully fabricated using Si-on-insulator material through an active layer transfer technique. All cells exhibit strong absorption enhancement, similar to that predicted by simulation. The 5 [mu]m thick cells gained 19% short circuit current density improvement, despite machine problems during fabrication. The textured photonic crystal back reflector design can be applied directly to single and poly-crystalline Si solar cells, and its principle is broadly applicable to other materials systems. / by Lirong Zeng. / Ph.D.

Thesis (S.B.)--Massachusetts Institute of Technology, Dept. of Materials Science and Engineering, 2005. / Includes bibliographical references (leaf 29). / Vanadium oxide thin film cathodes were analyzed to determine whether smaller average grain size and/or a narrower average grain size distribution affects the capacity-rate performance in lithium-ion batteries. Vanadium oxide thin films were prepared by sputtering onto ITO-coated glass substrates and crystallized in a refined annealing process to generate diverse microstructures. Average grain size and grain size distribution were determined in SEM analysis. No significant difference was observed in capacity rate behavior with changes in microstructure. However, it is speculated that further in situ analysis may show different relative diffusion rates into grains of differing sizes is related to different microstructures. / by Robin M. Davis. / S.B.