Thesis: Ph. D., Massachusetts Institute of Technology, Department of Chemical Engineering, September 2017. / Cataloged from PDF version of thesis. "February 2018." Handwritten on title page: [September 2017]. / Includes bibliographical references (pages 105-117). / Quantum dots, also called semiconductor nanocrystals, are an interesting class of materials because their band gap is a function of the quantum dot size. Their optical properties are not determined solely by the atomic composition, but may be engineered. Advances in quantum dot synthesis have enabled control of the ensemble size dispersity and the creation of monodisperse quantum dot ensembles with size variations of less than one atomic layer. Quantum dots have been used in a variety of applications including solar cells, light-emitting diodes, photodetectors, and thermoelectrics. In many of these applications, understanding charge transport in quantum dot solids is crucial to optimizing efficient devices. We examine charge transport in monodisperse, coupled quantum dot solids using spectroscopic techniques explained by hopping transport models that provide a complementary picture to device measurements. In our monodisperse quantum dot solids, the site-to-site energetic disorder that comes from size dispersity and the size-dependent band gap is very small and spatial disorder in the quantum dot superlattice often has a greater impact on charge transport. In Chapter 2, we show that improved structural order from self-assembly in monodisperse quantum dots reduces the interparticle spacing and has a greater impact than reduced energetic disorder on increasing charge carrier hopping rates. In Chapter 3, we present temperature-dependent transport measurements that demonstrate again that when energetic disorder is very low, structural changes will dominate the dynamics. We find increasing mobility with decreasing temperature that can be explained by a 1-2 Å contraction in the edge-to-edge nearest neighbor quantum dot spacing. In Chapter 4, we study optical states that are 100-200 meV lower in energy than the band gap. Because we work with monodisperse quantum dots, we are able to resolve this trap state separately from the band edge state and study its optical properties. We identify the trap state as dimers that form during synthesis and ligand exchange when two bare quantum dot surfaces fuse. The findings of this thesis point to the importance of minimizing the structural disorder of the coupled quantum dot solid in addition to the energetic disorder to optimize charge carrier transport. / by Rachel Hoffman Gilmore. / Ph. D.

Thesis (Ph. D.)--Massachusetts Institute of Technology, Dept. of Chemical Engineering, 1991. / Includes bibliographical references (leaves 160-172). / by Dimitrios P. Petridis. / Ph.D.

Thesis (Ph. D.)--Massachusetts Institute of Technology, Dept. of Chemical Engineering, 2004. / Includes bibliographical references. / (cont.) reducing agent than propane in the SCR of NO. Pt-Rh/CuO/A1₂O₃ nanocomposites capable of adsorbing SO₂ in oxygen-rich environment as metal sulfates and releasing SO₂ in reducing atmosphere were synthesized with sequential precipitation technique. These CuO-based sorbents possessed excellent SO₂ adsorption capacity and superior regenerability by CO compared to those produced by the impregnation method due to higher surface area and dispersion of Cu species. A gram of sorbent with 30 wt% Cu could adsorb over 50 mg of SO2 before SO₂ breakthrough was observed. The rate of SO₂ desorption from the CuO/A1₂O₃ sorbents could be enhanced through the incorporation of noble metals. With the use of 0.1 wt% Pt, the CuO/A1₂O₃ sorbent with 30 wt% Cu could be regenerated twice as quickly. Also, on average only 8 ppm of SO₂ were detected downstream of this sorbent over each adsorption cycle at 400⁰C. The excellent sorbent regeneration was attributed to better CO adsorption and lower sulfate decomposition temperature as a result of Pt addition. The nature of sulfur deactivation of these sorbents was highly dependent on the composition of noble metals used. By employing both Rh and Pt, sorbent regeneration rate and stability could be optimized. Rh/CuO-MgO/A1₂O₃ nanocomposites capable of adsorbing NOx and SO₂ in oxygen-rich environment and releasing N₂ and SO₂ in reducing atmosphere were successfully prepared by sequential precipitation ... / Over the past few years, increase in environmental concern has led to a demand for more effective pollution control strategies that would satisfy the new EPA standards regarding automotive emissions of nitrogen oxides (NOx). In particular, the removal of NOx from lean-burn and diesel engines operating under an oxygen-rich atmosphere presents a significant challenge as conventional three-way catalysts are ineffective in this environment. Moreover, the presence of water vapor and sulfur oxides (SOx) in the exhaust stream both inhibits catalyst activity and results in long-term catalyst instability. Thus, it is necessary to develop novel technologies for the removal of NOx from the exhaust of lean-bum engines. This thesis examined three metal oxide nanocomposite systems to serve as (i) catalysts for the selective catalytic reduction (SCR) of NOx by propene, (ii) sorbents for SO₂ storage, and (iii) catalysts for NOx storage-reduction (NSR). In₂O₃-Ga₂O₃/A1₂O₃ nanocomposite catalysts have been synthesized using the sequential precipitation technique. These alumina-based catalysts exhibited superior NO reduction activity to those produced by the impregnation and sol-gel methods due to their higher surface area and dispersion of active components. In fact, an excellent N2 yield of 80% was achieved at 450⁰C over the In₂O₃-Ga₂O₃/A1₂O₃ nanocomposite with 2 wt% In and 8 wt% Ga. The high catalytic activity was attributed to better propene activation by In and improved NOx adsorption on the high surface area Ga₂O₃/A1₂O₃. The In₂O₃-Ga₂O₃/A1₂O₃ nanocomposite remained active even in the presence of SO2. The NO reduction activity of this catalyst system depended on the hydrocarbons that were used as the reducing agents. Propene was found to be a more effective / by Pemakorn Pitukmanorom. / Ph.D.

Thesis (Ph. D.)--Massachusetts Institute of Technology, Dept. of Chemical Engineering, 2009. / 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. / Stimuli-responsive polymer thin films provide the ability to control the interaction of a surface with its environment. Synthetic techniques with fine compositional control are required to engineer specific responses to stimuli. Initiated chemical vapor deposition (iCVD) is a novel vacuum deposition technique in which polymer films are synthesized bottom-up as monomer and initiator vapors are introduced into a vacuum coating chamber. iCVD can conformally coat nanoscale, three-dimensional geometries with a high level of compositional control. Such coating capabilities are difficult by solution-based film synthesis techniques, and compositional control is difficult by other CVD techniques. In this thesis work, the synthesis and application of stimuli-responsive and reactive polymer thin films by iCVD have been studied. First, functionally versatile alternating copolymers of poly(styrene-alt-maleic anhydride) were synthesized. This was the first demonstration of alternating copolymer synthesis by CVD. Fourier transform infrared spectroscopy, x-ray photoelectron spectroscopy, and 13C NMR characterization verified that well-defined alternating structure was present, as predicted from standard solution phase polymerizations. Next, polymer crosslinking was tuned in the synthesis of pH-responsive hydrogel thin films composed of poly(maleic anhydride-co-dimethylacrylamide-co-di(ethylene glycol) divinyl ether). These films had swelling ratios, defined as the thickness in the water-swollen state over the thickness in the dry state, in excess of 11. These films were employed as ultrathin permeable, size-selective skin layers in composite membranes. / (cont.) The final two projects involved the synthesis of polymer thin films as chemically selective layers in microscale chemical sensors. In a sensing system based on the detection of amine compounds through their reaction with reactive polymer coatings on microcantilevers, it was shown that increased crosslinking of the polymer layer leads to greater cantilever deflection. This increased deflection enabled the design of simple, resistance-based signal readout schemes with low power requirements. New polymer compositions and sensing strategies were also developed for the detection of nitroaromatic explosives vapors. Poly(4-vinylpyridine) was shown to swell when exposed to nitroaromatics, while showing little response to common interferents. In contrast to conventional nitroaromatic-selective layers, it was shown that poly(4-vinylpyridine) does not interact with nitroaromatics through hydrogen bonding, which is important for multicomponent sensor arrays. A new microscale sensing concept utilizing this swelling was designed, fabricated, and characterized. / by Wyatt E. Tenhaeff. / Ph.D.

Thesis (B.S.)--Massachusetts Institute of Technology, Dept. of Chemical Engineering, 1939. / MIT copy bound with: Vulcanization of rubber under stretch / Irving N. Smith. 1939. / Includes bibliographical references (leaves 31-32). / by M. C. Sze. / B.S.

Thesis (B.S.) Massachusetts Institute of Technology. Dept. of Chemical Engineering, 1948. / MIT copy bound with: Galvanic cells as electric filter capacitors / Frank E. Guptill, Jr. 1948. / Bibliography: leaf xviii. / by Edward J. Hobaica, Robert F. Lovezzola. / B.S.

Thesis (Ph. D.)--Massachusetts Institute of Technology, Dept. of Chemical Engineering, 2005. / Includes bibliographical references. / Initiated chemical vapor deposition (iCVD) is a novel technique for depositing polymeric thin films. It is able to deposit thin films of application-specific polymers in one step without using any solvents. Its uniqueness of in situ surface polymer synthesis distinguishes iCVD from conventional processes such as spin-on deposition and plasma-enhanced chemical vapor deposition. It allows engineering polymers to be made with specific microscale properties translating to well-defined macroscale behaviors. In this thesis work, two application-specific polymers based on poly(2-hydroxyethyl methacrylate) (PHEMA) and poly(cyclohexyl methacrylate) (PCHMA) were synthesized using iCVD. PHEMA thin films with specific degrees of cross-linking leading to well-defined structural, thermal, wetting, and swelling properties were made in a single vacuum step by simply adjusting chamber conditions. Cross-linked PCHMA thin films were synthesized for use as sacrificial layers for microfabrication. Such films of engineering polymers cannot be made using conventional methods. A study of the polymerization mechanism was included to serve as a groundwork for increased understanding of iCVD as a thin- film deposition method. / (cont.) Growth rates and molecular weights, crucial parameters for polymeric thin films, were found to be highly dependent on the surface concentrations of monomers, leading to the conclusion that polymer formation occurs predominantly on the surface of the substrate. This conclusion also infers that controlling the surface concentrations of monomers can lead to copolymers/terpolymers with well-defined compositions, which was demonstrated in the iCVD of PHEMA-based thin films. iCVD therefore can be extended to complex polymer systems with multiple monomeric building blocks. Photo- initiatied chemical vapor deposition (piCVD) using a volatile photoinitiator is introduced for the first time in this thesis. piCVD possesses all the benefits of iCVD over conventional processes but uses a photochemical initiation mechanism that simplifies chamber design and potentially allows self-patterning during deposition. / by Kelvin Chan. / Ph.D.

Thesis (Ph. D.)--Massachusetts Institute of Technology, Dept. of Chemical Engineering, 1997. / Includes bibliographical references (p. 191-192). / by Friedrich K. von Gotberg. / Ph.D.

Thesis (Sc. D.)--Massachusetts Institute of Technology, Dept. of Chemical Engineering, February 2002. / Includes bibliographical references (p. 165-178). / Antisense oligonucleotides have the potential to selectively inhibit the expression of any gene with a known sequence. Antisense-based therapies are under development for the treatment of infectious diseases as well as complex genetic disorders. Although there have been some remarkable successes, realizing this potential is proving difficult because of problems with oligonucleotide stability, specificity, affinity, and delivery. Each of these limitations has been addressed experimentally through the use of chemically-modified oligonucleotides and oligonucleotide conjugates, with much success in enhancing oligonucleotide efficacy. These early studies have shown that selection of target site, once considered a trivial problem, is critical to the success of antisense strategies. It has become clear that the efficacy of antisense oligonucleotides is a strong function of the structure of the target mRNA. Though single-stranded, RNA molecules are typically folded into complex three-dimensional structures, formed primarily by intramolecular Watson-Crick base-pairing. If an oligonucleotide is complementary to a sequence embedded in the three dimensional structure, the oligonucleotide may not be able to bind to its target site and exert its therapeutic effect. Because the majority of the structure of RNA molecules is due to Watson-Crick base-pairing, relatively accurate predictions of these folding interactions can be made from algorithms that locate the structure with the most favorable free energy of folding. / (cont.) Taking advantage of the predictability of RNA structures, this thesis addresses the problem of antisense target site selection, first from a theoretical and subsequently an experimental standpoint. A thermodynamic model to predict the binding affinity of oligonucleotides for their target mRNA is described and validated using multiple in vitro and cell-culture based experimental data sets. Subsequently, direct experimental comparisons with theoretical predictions are made on the well-characterized rabbit-[beta]-globin (RBG) mRNA, using a novel, centrifugal, binding affinity assay. The importance of the hybridization kinetics is also explored, as is the role of association kinetics in defining the rate of cleavage by the enzyme ribonuclease H (RNase H). Finally, the applicability of the model in identifying biologically active oligonucleotides is demonstrated. / by S. Patrick Walton. / Sc.D.

Thesis (Ph. D.)--Massachusetts Institute of Technology, Dept. of Chemical Engineering, 1998. / Includes bibliographical references (leaves 168-186). / by Melody A. Swartz. / Ph.D.