Thesis (Ph. D.)--Massachusetts Institute of Technology, Dept. of Materials Science and Engineering, 2002. / Includes bibliographical references (p. 125-135). / This electronic version was submitted by the student author. The certified thesis is available in the Institute Archives and Special Collections. / Fretting fatigue is defined as damage resulting from small magnitude (0.5-50 microns) displacement between contacting bodies where at least one of the bodies has an applied bulk stress. The applicability and limits of a fracture mechanics based life prediction is explored. Comparisons are made against highly controlled experiments and less controlled but more realistic experiments using a novel dovetail attachment fixture. Surface engineering approaches are examined from a mechanics perspective. Using a new tool, depth sensing indentation, the mechanical properties of an aluminum bronze coating are determined. Fretting fatigue experiments are performed on specimens coated with aluminum bronze and on specimens treated with low plasticity burnishing. Low plasticity burnishing is a new method of introducing beneficial compressive residual stresses without significant cold work at the surface. A mechanics based approach to the selection of palliatives is addressed. / by Brett P. Conner. / Ph.D.

Thesis (B.S.)--Massachusetts Institute of Technology, Dept. of Materials Science and Engineering, 1998. / Includes bibliographical references (leaf 32). / by Douglas J. Harris. / B.S.

Thesis (M. Eng.)--Massachusetts Institute of Technology, Dept. of Materials Science and Engineering, 2008. / Includes bibliographical references (leaves 56-58). / With the increasing demanding of bandwidth in information technology, electronic connections meet the limitation in high speed processing in shorter and shorter reach. In the work, three markets for optical connection with different reach, which range from 10km down to 1 meter, have been discussed. The 10km market denotes for the LAN standard and would mature soon. For the 100m range, active cable has emerged to meet the requirement and would penetrate the market soon. The detail analysis would be addressed on 1-10 meet market, where electronic cables have just met the limitation. Cost modeling and business plan has been conducted. After that, the conclusion and suggestions would be made on that reach. / by Jia Luo. / M.Eng.

Thesis (S.B.)--Massachusetts Institute of Technology, Dept. of Materials Science and Engineering, 2013. / Cataloged from PDF version of thesis. / Includes bibliographical references (p. 29). / MIT policies set forth by the Department of Environment, Health, and Safety (EHS) require that all laboratories maintain a chemical inventory to properly document the use of hazardous chemicals. While EHS has provided a chemical inventory management tool called ChemTracker to help labs to do so, it is estimated that less than 20% of laboratories utilize the software. As a result, an EHS committee has been formed to re-evaluate ChemTracker and explore other options for inventory management. RFPs have been sent to potential vendors to determine if alternatives can better satisfy the goals of EHS and attain the benefits of effective chemical management. To analyze the problem of low usage rates of ChemTracker, interviews were conducted with research groups within the Department of Materials Science & Engineering (DMSE). These revealed that the largest variables were the number of chemicals used by the lab and the user-friendliness of the software. The initial time investment to switch from current, simpler methods to ChemTracker discouraged many smaller labs from pursuing that option. Current users of ChemTracker also expressed frustration with auto-fill features that weren't comprehensive and thus hindered the process of entering and updating inventory. Future work should expand into other departments to observe usage behavior and concerns and compare to those within DMSE. Any chemical inventory management software should be user-tested prior to full Institute implementation to ensure adoption by a larger proportion of groups around campus. While compulsory software would also ensure adoption, a one-size-fits-all approach is not appropriate for chemical tracking due to the hassle it could create and the potential impact on productivity of research itself. Thus, further analysis of user concerns and better marketing of the tools to address those concerns are required for a successful solution to the problem. / by Valerie Jing-chi Chia. / S.B.

Thesis (S.B.)--Massachusetts Institute of Technology, Dept. of Materials Science and Engineering, 2013. / "June 2013." Cataloged from PDF version of thesis. / Includes bibliographical references (p. 29-30). / This research investigates the copolymerization of divinylbenzene and 4- vinylpyridine into organic thin films that exhibit conformal, stable, and uniform surface properties. Thin films were grown using initiated chemical vapor deposition, a variant of hot-wire deposition using a chemical initiator. Readily variable monomer flow into the active stage of the reactor allows for directly tunable copolymer composition. This tunability extends onto the control of material surface properties of a substrate that is coated with these organic thin films. The conditions of iCVD allow a variety of delicate substrates to be coated and for the full retention of pendant functional groups. This leads to their application to many industries including water desalination membranes, microfluidics, photolithography, sensors, among many others. The focus of this paper is on the facilitated control of surface modification using iCVD techniques and some of its future applications are also discussed. / by Ernesto Martinez. / S.B.

Thesis (Ph. D.)--Massachusetts Institute of Technology, Dept. of Materials Science and Engineering, 2013. / 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. / Electrostatic fiber formation, or electrospinning, offers a particularly simple and robust method to create polymeric nanofibers of various sizes and morphologies. In electrospinning, a viscoelastic fluid is charged so that a liquid jet is ejected from the surface of the fluid (typically in the form of a drop supplied by a needle or spinneret) and collected on a grounded plate, creating a nonwoven fiber mat. Modification of the diameter of the fibers as well as the porosity, specific surface area, and mechanical properties of the mat allows one to tailor electrospun mats for specific applications. Despite the widespread and rapidly growing use of electrospinning in the fabrication of novel nanomaterials, there are no simple, universal methods of predicting, a priori, the properties of electrospun fibers from knowledge of the polymer solution properties and electrospinning operating conditions alone. Changing a single fluid or processing parameter can affect the jet and fiber formation through several mechanisms. For example, using a different solvent can change several properties of the electrospinning fluid, such as the dielectric constant, conductivity, surface tension, and solute-solvent interaction. The work in this thesis seeks to develop a simple relation for predicting terminal jet diameter during electrospinning, which accounts for solution viscoelasticity as well as solution conductivity and operating parameters that can be easily measured and controlled. The mechanical and tribological properties of electrospun fiber mats are of paramount importance to their utility as components in a variety of applications. Although some mechanical properties of these mats have been investigated previously, reports of their tribological properties are essentially nonexistent. In this thesis, electrospun nanofiber mats of poly(trimethyl hexamethylene terephthalamide) (PA 6(3)T) and poly(hexamethylene adipamide) (PA 6,6) are characterized mechanically and tribologically. Post-spin thermal annealing was used to modify the fiber morphology, inter-fiber welding, and crystallinity within the fibers. Morphological changes, in-plane tensile response, friction coefficient, and wear rate were characterized as functions of the annealing temperature. The Young's moduli, yield stresses and toughnesses of the PA 6(3)T nonwoven mats improved by two- to ten-fold when annealed slightly above the glass transition temperature, but at the expense of mat porosity. The mechanical and tribological properties of the thermally annealed PA 6,6 fiber mats exhibited significant improvements through the Brill transition temperature, comparable to the improvements observed for amorphous PA 6(3)T electrospun mats annealed near the glass transition temperature. The wear rates for both polymer systems correlate with the yield properties of the mat, in accordance with a modified Ratner-Lancaster model. The variation in mechanical and tribological properties of the mats with increasing annealing temperature is consistent with the formation of fiber-to-fiber junctions and a mechanism of abrasive wear that involves the breakage of these junctions between fibers. A mechanically robust proton exchange membrane with high ionic conductivity and selectivity is an important component in many electrochemical energy devices such as fuel cells, batteries, and photovoltaics. The ability to control and improve independently the mechanical response, ionic conductivity, and selectivity properties of a membrane is highly desirable in the development of next generation electrochemical devices. In this thesis, the use of layer-by-layer (LbL) assembly of polyelectrolytes is used to generate three different polymer film morphologies on highly porous electrospun fiber mats: webbed, conformal coating, and pore-bridging films. Specifically, depending on whether a vacuum is applied to the backside of the mat or not, the spray-LbL assembly either fills the voids of the mat with the proton conducting material or forms a continuous fuel-blocking film. The LbL component consists of a proton-conducting, methanolimpermeable poly(diallyl dimethyl ammonium chloride)/sulfonated poly(2,6-dimethyl 1,4- phenylene oxide) (PDAC/sPPO) thin film. The electrospun fiber component consists of PA 6(3)T fibers of average diameter between 400 and 800 nm, in a nonwoven matrix of 60-90% porosity depending on the temperature of thermal annealing utilized to improve the mechanical properties. This thesis demonstrates the versatility and flexibility of this fabrication technique, since any ion conducting LbL system may be sprayed onto any electrospun fiber mat, allowing for independent control of functionality and mechanical properties. The mechanical properties of the spray coated electrospun mats are shown to be superior to the LbL-only system, and possess intrinsically greater dimensional stability and lower mechanical hysteresis than Nafion under hydration cycling. The electrochemical selectivity of the composite LbL-electrospun membrane is found to be superior to Nafion, which makes them a viable alternative proton exchange membrane for fuel cell applications. The composite proton exchange membranes fabricated in this work were tested in an operational direct methanol fuel cell, with results showing the capability for higher open circuit voltages (OCV) and comparable cell resistances when compared to Nafion. / by Matthew Marchand Mannarino. / Ph.D.

Thesis: Ph. D., Massachusetts Institute of Technology, Department of Materials Science and Engineering, 2017. / 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 159-169). / Block copolymers (BCPs) are a class of soft materials consisting of two (or more) different chains joint together by covalent bond. This special chemical structure leads to microphase separation and consequently a variety of highly controllable self-assembly patterns. Directed self-assembly (DSA) of BCPs has therefore emerged as one of the most promising technologies to fabricate functional nanostructures and is able to produce patterns with ultra-small resolution (sub-10 nm) while maintaining high throughput and order. However, existing DSA methods depend mostly on carbon or silicon-based BCPs, thus lack functionality for sophisticated applications. This work aims at expanding the capability of DSA techniques by exploring new ways of incorporating functional materials into the BCP matrix and by imposing non-native symmetries on the BCP patterns. First, we focused on constructing nanocomposite thin films composed of BCPs and various types of functional materials (i.e., inorganic ions, inorganic-organic complex, organic compounds and nanoparticles). Based upon this methodology, we developed novel ways of fabricating mesoporous thin film structures with rectangular, triangular and quasicrystalline symmetries by means of graphoepitaxial post array templates. On the other hand, we also examined the limits of DSA by introducing artificial noise to mimic fabrication errors and studied the corresponding responses from BCP. This study demonstrates the potential of DSA of BCP in building thin film nanostructure of unconventional symmetries with functional components. / by Yi Ding. / Ph. D.

Thesis (B.S.)--Massachusetts Institute of Technology, Dept. of Materials Science and Engineering, 1990. / Includes bibliographical references (leaf 41). / by Susan M. Kuhn. / B.S.

Thesis (S.B.)--Massachusetts Institute of Technology, Dept. of Materials Science and Engineering, 2013. / 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 (p. 60-61). / Alloy anodes form a promising path to the use of multi-cation electrolytes by increasing chemical stability. In this study, a lithium-magnesium alloy anode was developed such that lower cost and lower melting temperature multi-cation electrolytes could be incorporated in liquid metal batteries (LMBs). In a first part of this work, Lithium-magnesium was proven to be a viable anode in a standard uni-cation (Li+) Li-Mg/LiCl-LiF-LiI/Sb-Pb battery. SEM and EDS confirmed the stability of this anode with respect to the cathode (Sb-Pb) and the standard uni-cation electrolyte. Performance metrics (voltage, efficiencies, etc.) for the Li-Mg anode cell were found to be comparable to the analogous pure Li anode system. In a second part of this work, using the alloyed Li-Mg anode, we demonstrated successful cycling of cells using multi cation electrolytes in Li-Mg/LiBr-KBr/Sb-Pb and Li-Mg/LiCl-KCl/Sb-Pb LMBs. Each of these multi-cation electrolyte systems boasted an active materials energy cost of (<150$/kWh), which is less expensive than the metric cost to implement storage batteries in the electrical grid.[1] These results open the door to incorporating lower cost and lower melting temperature electrolyte candidates in LMBs by using alloyed anodes. / by Allan Blanchard. / S.B.

Thesis: S.B., Massachusetts Institute of Technology, Department of Materials Science and Engineering, 2017. / Cataloged from PDF version of thesis. / Includes bibliographical references (pages 54-55). / Thermalization losses drastically reduce the efficiency of silicon solar cells. In an age where we need sustainable energy production more than ever, silicon is the best material to target due to its high stake in the sustainable energy market. An organic-inorganic solar cell hybrid of tetracene-covered silicon can reduce thermalization losses through the downconversion process of using a high energy photon to generate two lower energy electron-hole pairs. This occurs through the singlet-triplet fission process that excitons can undertake in tetracene. The effect of the interface quality between tetracene and silicon on successful triplet energy transfer is investigated. RFPCD (Radio Frequency Photoconductive Decay) is used to measure the bulk lifetime as well as the surface recombination lifetime of minority carriers in both n- and p-type Silicon of various doping concentrations. The surface recombination velocity was calculated from the measurement of surface recombination lifetime and analyzed after the silicon underwent RCA clean, RCA clean followed by an HF dip, tungsten nitride ALD, and tetracene evaporation using various combinations of these steps to form appropriate process flows. It was found that the highest surface quality was obtained by the lowest doped wafers. Additionally, similar doping levels were affected similarly by the various processing steps outlined above while the type of dopant did not seem to dictate the surface quality response. Triplet energy transfer was not fully confirmed from tetracene to silicon, but the surface quality turned out to be a very important indication for whether or not this energy transfer could occur. / by Eveline Postelnicu. / S.B.