Thesis (Ph.D.)--Massachusetts Institute of Technology, Dept. of Materials Science and Engineering, 1999. / Includes bibliographical references (leaves 180-191). / A series of ring-opening metathesis (ROMP) polymers functionalized with pendant carborane (C2B10HI2) groups was synthesized. Norbomene-based polymers with the bulky, pseudoaromatic functionality were found to have glass transition temperatures (Tg's) between 29 °C and 290 °C. This variation in Tg can be attributed to structural differences in how the functional group is attached to the polymer backbone. Block copolymerization was used to improve the material processibility. The block copolymers microphase separate into boron-rich and boron-free microdomains. Carborane-functionalized monomers and polymers were used as precursors and models for the synthesis of polyanions with pendant cobalt dicarbollide (Co(C2B9H)2 -l) and carborane anion (CB1 H12-) groups via ROMP. These polyelectrolytes were found to work as hydrophilic ion-exchangers in aqueous acidic solutions. Polymers functionalized with either cobalt dicarbollide or carborane anions demonstrated selective binding of cesium over sodium. Copolymerization and cross-linking were used to reduce the hydrophilicity and solubility of the materials in a stripping solution of strong (8M) nitric acid. / by Alice Man. / Ph.D.

Thesis (Ph. D.)--Massachusetts Institute of Technology, Dept. of Materials Science and Engineering, 2005. / Includes bibliographical references. / Proton spin lattice (T1) relaxation time constants were used to monitor changes in the molecular motion and architecture of polyisoprene, polyisoprene-clay composites and polyhedral oligomeric silsesquioxane (POSS) nanofillers. The high frequency relaxations monitored by NMR are sensitivity to changes in the environment of polyisoprene chains as a function of compressive strain. These are the first experiments to use magic angle spinning nuclear magnetic resonance techniques in situ with compression measurements to identify changes in the chain environment during compressive strain. For the polyisoprene composites, in situ compression measurements were made during the acquisition of NMR relaxation measurements. Therefore, the architecture of polyisoprene-clay composites was monitored as a function of strain. Clay aggregates, composed of stacked clay platelets, were identified in the nanocomposites. Increases in strain resulted in an irreversible, increase in interfacial area between clay and the polymer as the aggregate broke apart. This increase in area could be easily quantified by NMR (- 230%) and was verified with optical microscopy (- 150%). The correlation between NMR and optical microscopy indicates, with certainty, that NMR relaxation measurements can be used to quantify differences in interfacial area of nanocomposites. With this being established, the techniques developed in this thesis could be applied to analyze strain induced changes in interfacial area for samples which are not optically clear or samples in which the particle dimensions make microscopy techniques difficult. The quantitative discrepancy between the two techniques suggests that NMR captures changes in the bulk whereas microscopy is confined to surface effects. Finally, these results point to the potential to design a composite in which this mechanism is halted, such as crosslinking the clay directly to the polymer matrix, in hopes of creating a higher energy mechanism of deformation and thereby improving the mechanical properties. Octaethyl POSS was found to exhibit characteristics exemplified by plastic crystals. Phase transitions were identified with NMR and differential scanning calorimetry at -258 K and -253 K for partially deuterated and fully protonated ethyl POSS, respectively. For both derivatives at temperatures above the phase transition, the molecular motions of POSS were found to be on the order of nanoseconds (-30 ± 2 ns) and associated with molecular tumbling of the POSS molecule. After the phase transition, the molecular tumbling of POSS molecules slowed ( -530 ± 15 ns ) and became more asymmetric. These phase changes were characterized by a change in entropy of 20.2 ± 5 Jmol-'K', a typical value for plastic crystals. This plastic crystalline behavior suggests that in the high temperature phase, the POSS molecules will undergo plastic flow at relatively low levels of stress. Therefore, in the high temperature phase POSS will not enhance mechanical behavior in the same manner as other inorganic fillers, such as silica. In addition, the trends in the transition temperature suggest that the derivatives can be chemically altered to achieve the desired phase at a given operation temperature. Finally, a compression device suitable for fitting inside the rotor of a magic angle spinning NMR probe was built. Although in situ NMR compression experiments have previously been investigated, these experiments were the first to be done while magic angle spinning. This allowed for increased specificity for assigning molecular mobility. Additionally, the magic angle spectra doubled the signal to noise, as compared to static proton NMR spectra. Thus, more rapid spectral acquisition was possible, allowing "snapshots" to be acquired under dynamic processes such as mechanical deformation. This led to a more detailed analysis of deformation than that possible from static spectra. For instance, using magic angle spinning the behavior of bulk polymer was separated from that adjacent to the clay. For this reason, the effect of the changes on the architecture of nanocomposites could be monitored through those protons in closest proximity to the clay surface. This enhanced selectivity resulted in an unambiguous determination of change in composite architecture and its time dependence. / by Georgia Michelle Poliskie. / Ph.D.

Thesis (S.B.)--Massachusetts Institute of Technology, Dept. of Materials Science and Engineering, June 2007. / Includes bibliographical references ( p. 22). / Positionally-sensitive nanoindentation was carried out in the freshly-cleaved nacre found in the shell of the gastropod mollusk Trochus niloticus. Nacre is a hierarchical biocomposite composed of mineral tablets of 95 weight % calcium carbonate (CaCO3) in the aragonite mineral form and a biomacromolecular organic matrix. Nanoindentation was carried out in a pattern of square grids of 256 indents at maximum loads of 1 mN and 500 gN. The average elastic modulus and hardness for the 1 mN indents were found to be 97.8 GPa + 6.41 GPa and 5.41 GPa ± 0.49 GPa, respectively, and for the 500 gN indents average elastic modulus of 94.8 GPa ± 7.28 GPa and hardness of 4.89 GPa ± 0.53 GPa. Maps of the 2-D spatial distribution of elastic modulus and hardness for the indent areas were generated. Tapping mode Atomic Force Microscopy was performed on the indented nacre after a treatment of surface etching, which revealed the tablet boundaries in order to correlate qualitatively the topographical features with the properties distribution. The properties distribution maps revealed a non-uniform distribution of nanomechanical properties as well as highly-localized regions in which the values of the properties differed from the average values. Future studies may point to a direct correlation between structural heterogeneity and the properties distribution. / by Julián Enrique Villarreal. / S.B.

Thesis (M. Eng.)--Massachusetts Institute of Technology, Dept. of Materials Science and Engineering, 2008. / Includes bibliographical references (leaves 36-40). / Ferromagnetic shape memory alloys (FSMAs) are a new class of magnetic field-actuated active materials with no current commercial applications. By applying a magnetic field of around 0.4 T, they can exert a stress of approximately 1.5 MPa, exhibiting a strain of up to 6%. This thesis evaluates their technical and commercial feasibility in orthopaedic applications. Remote actuation is a key advantage FSMAs have over current implant materials. Also, the human body temperature is constant, providing a stable environment for FSMAs to operate. A number of potential orthopaedic applications are proposed and evaluated. Out of these, the most prominent application is the spinal traction device. It is a temporary implantable device, intended to perform internal spinal traction. A design has been proposed, with suggestions of suitable materials for its various components and appropriate device dimensions. Preliminary market and cost analyses have been conducted. This orthopaedic technology is currently in its infant stage. To commercialize this device, more trials are needed. / by Weimin Guo. / M.Eng.

Thesis (Ph. D.)--Massachusetts Institute of Technology, Dept. of Materials Science and Engineering, 2010. / Includes bibliographical references (p. 164-168). / In situ deposition of high-k materials to passivate the GaAs in metal organic chemical vapor deposition (MOCVD) system was well demonstrated. Both atomic layer deposition (ALD) and chemical vapor deposition (CVD) methods were applied in this research. The CVD aluminum nitride (AIN) was first selected to be in situ deposited on GaAs surface by using trimethlyaluminum(TMA) and dimethylhydrazine (DMHy). However, the frequency dispersion of Capacitance-Voltage (C-V) curves for in situ AIN/GaAs samples are always large because of the existence of high interfacial defect state density (Dit) due to the nitridization of the GaAs surface during the AIN deposition. In order to avoid the surface reaction, in situ ALD of aluminum oxide (A1₂O₃) on GaAs in MOCVD system was proposed. Isopropanol (IPA) was chosen as the oxygen source for A1₂O₃ ALD and the mechanism was investigated. Pure A120 3 thin film was obtained and no arsenic or gallium oxide was observed at the interface. Both frequency dispersion of C-V curve and the Di, of oxide/p-GaAs interface are low for this process. In situ CVD A1₂O₃ on GaAs was also performed. Gallium oxide (Ga₂O₃) was observed at the interface. The Ga₂O₃ was enriched in the A1₂O₃ above the interface during the deposition process and a possible mechanism was proposed. This layer reduces the frequency dispersion of the C-V characteristics and lowers the Dit of n-type GaAs sample. After the in situ method had been successfully established, ex situ experiments was also performed to compare the results with in situ process in the same MOCVD system. Annealing native oxide covered GaAs samples in Arsine (AsH 3) prior to ALD A1₂O₃ results in C-V characteristics of the treated samples that resemble the superior C-V characteristics of p-type GaAs. Besides, both TMA and IPA show self-cleaning effect on removing the native oxide in ex situ process. The discrepancy in the C-V characteristics was observed in in situ p- and n-type GaAs samples. Finally, the entire Dit energy distributions of interfaces from different processes were determined by conductance frequency method with temperature-variation C-V measurement. The existence of Ga₂O₃ at interface was found to be the possible source to lower the density of mid-gap defect state. From the C-V simulation, the mid-gap defect states are acceptor-like (Gallium Vacancies) and the source to cause high frequency dispersion of the C-V curves for n-type substrate. The relation between the interfacial defect state distribution and the processes was correlated. / by Cheng-Wei Cheng. / Ph.D.

Thesis (S.M.)--Massachusetts Institute of Technology, Dept. of Materials Science and Engineering, 1999. / Includes bibliographical references (leaf 53). / by Kim-Marie Levis. / S.M.

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 137-160). / We investigate how the external quantum efficiency (EQE) of colloidal quantum-dot light emitting devices (QD-LEDs) can be enhanced by addressing in situ QD photoluminescence (PL) quenching mechanisms occurring with and without applied bias. QD-LEDs promise efficient, high colour-quality solid-state lighting and displays, and our cost analysis of industrial-scale QD synthesis suggests they can be cost competitive. Efficiency 'roll-off' at high biases is among the most enduring challenges facing all LED technologies today. It stands in the way of high efficiencies at high brightness, yet it has not previously been studied in QD-LEDs. Simultaneous measurements of QD electroluminescence (EL) and PL in an operating device allow us to show for the first time that EQE roll-off in QD-LEDs derives from the QD layer itself, and that it is entirely due to a bias-driven reduction in QD PL quantum yield. Using the quantum confined Stark Effect as a signature of local electric fields in our devices, the bias-dependence of EQE is predicted and found to be in excellent agreement with the roll-off observed. We therefore conclude that electric field-induced QD PL quenching fully accounts for roll-off in our QD-LEDs. To investigate zero-bias PL quenching, we fabricate a novel near-infrared (NIR)-emitting device based on core-shell PbS-CdS QDs synthesised via cation exchange. QDs boast high PL quantum yield at wavelengths beyond 1 [mu]m, making them uniquely suited to NIR applications such as optical telecommunications and computing, bio-medical imaging, and on-chip bio(sensing) and spectroscopy. Core-shell PbS-CdS QDs enhance the peak EQE of core-only PbS control devices by 50- to 100-fold, up to 4.3 %. This is more than double the efficiency of previous NIR QD-LEDs, making it the most efficient thin-film NIR light source reported. PL measurements reveal that the efficiency enhancement is due to passivation of the PbS core by the CdS shell against a non-radiative recombination pathway caused by a neighboring conductive layer within the device architecture. / by Geoffrey James Sasajima Supran. / Ph. D.

Thesis (Ph. D.)--Massachusetts Institute of Technology, Dept. of Materials Science and Engineering, 1994. / Includes bibliographical references. / Ph.D.

Thesis (S.M.)--Massachusetts Institute of Technology, Dept. of Materials Science and Engineering, 1998. / Includes bibliographical references (p. 93). / Pharmaceutical grade materials were used in the fabrication of fast-release and extended-release oral dosage forms. Tablets were processed by employing a method of solid freeform fabrication known as three dimensional printingTM (3DPTM). A microcrystalline cellulose powder was used in combination with pH-dependent and permeable polymeric binder solutions. Release studies in acidic media were performed using both dye and drug (antihistamine) as actives. Deposition was performed by micro pipette into concept devices. It was concluded that printing parameters could be used to control the microstructure and release behavior. The performance of a drop-on-demand inkjet printing system was evaluated to be highly accurate, and the system was used in the fabrication of model oral dosage forms. Tablets were constructed with a permeable polymer as binder. Mechanical tests showed that the tablets were comparable to industry references for both strength and friability. A USP dissolution method involving an acid and buffer stage was used for extended-release studies. Release by diffusion was found to depend on device porosity level and drug distribution as defined during fabrication. / by Robert D. Palazzolo. / S.M.

Thesis: Ph. D., Massachusetts Institute of Technology, Department of Materials Science and Engineering, 2016. / Cataloged from PDF version of thesis. / Includes bibliographical references (pages 113-120). / Efficient mechanical energy harvesters enable various wearable devices and may also act as auxiliary energy supply to isolated area. In this thesis, I present a novel class of mechanical energy harvesters based on stress-voltage coupling in electrochemically alloyed electrodes. The device consists of two identical Li-alloyed Si as electrodes, separated by electrolyte-soaked polymer membranes. Bending-induced asymmetric stresses generate chemical potential difference, driving lithium ion flux from the compressed to the tensed electrode to generate electric current. Unbending the device reverses the ion flux, generating electrical current in the opposite direction. The thermodynamic analyses reveal that the ideal energy-harvesting efficiency of this device is dictated by the Poisson's ratio of the electrodes. For the thin-film-based energy harvester used in this study, the device has achieved the overall efficiency of 0.6% and a generating capacity of 15%. The device also presents unique characteristics over the existing type of mechanical energy harvesters. Compared to piezoelectric or triboelectric generators, the prototype demonstrates low internal impedance of the order of 300[omega] as opposed to 100M[omega] in the other two types, and continuous electric current of the order of 3 seconds as opposed to 50ms in the other two types. From kinetics analysis, we show that the device's electric current generation is limited by lithium diffusion inside the LixSi electrode for sufficiently thick electrodes and by electrolyte diffusion for thin electrodes below 400nm. Tuning the current peak widths between 5s and 22s was demonstrated experimentally. The framework developed in the kinetics analyses also suggests that the device may be used as a spectroscopic tool to measure lithium diffusivity inside electrochemical alloys. The experimentally observed kinetics suggests lithium diffusivity on the order of 10-¹⁰cm² /s in Li₃.₁Si. The device demonstrates a practical use of stress-composition coupling in electochemically active alloys to harvest low-grade mechanical energies from various lowfrequency motions, such as everyday human activities. The analyses present the quantitative strategies to optimize the device in terms of its total energy output, kinetic behavior and ultimately the design principles for an energy harvester optimized for harvesting a specifically targeted frequency motion. / by Sangtae Kim. / Ph. D.