Thesis (Ph. D.)--Massachusetts Institute of Technology, Dept. of Chemical Engineering, 1994. / Includes bibliographical references (leaves 181-186). / by Chun-Hyuk Lee. / Ph.D.

Thesis (Ph. D.)--Massachusetts Institute of Technology, Dept. of Chemical Engineering, 1991. / Includes bibliographical references (leaves 210-215). / by David Charles Guell. / Ph.D.

Thesis (Ph. D.)--Massachusetts Institute of Technology, Dept. of Chemical Engineering, 1991. / Includes bibliographical references (leaves 271-286). / by Narayanan Ramprasad. / Ph.D.

Thesis (Ph. D.)--Massachusetts Institute of Technology, Dept. of Chemical Engineering, 2009. / Includes bibliographical references. / The control of feature profiles in directional plasma etching processes is crucial as critical dimension, line-edge roughening, and other artifacts affect device performance and process yields. A profile simulator is necessary to predictively model the etching processes as well as roughness transfer and artifact evolution. The development of profile simulators has been inhibited by the limited knowledge of the surface kinetic processes and rate coefficients. A mixing-layer surface kinetic model was developed to account for plasma-surface interactions. The simplified reaction set was carefully chosen to reflect the overall etching characteristics and the rate coefficients were fitted to experimental data. After the model was tested for accuracy using poly-Si etching in Cl2 gas plasma, it was incorporated into the 3-Dimensional (3-D) Monte Carlo profile simulator with a cell-based representation. The good match between the profile simulation and the kinetics modeling results verified the capability of incorporating complex chemical processes into the 3-D simulator. The angular dependence on etching yield was modeled based upon the mixing layer kinetics model. All the rate coefficients fitted previously at normal ion incidence were kept constant without any further optimization. The angular curves were assigned to all ion-initiated reactions based upon their characteristics and the overall etching yield was calculated with a combination of individual etching yields. The variation of etching yield with ion bombardment angle for poly-Si in Cl2 plasma was modeled and showed quantitative agreement with the experimental measurements, indicating the angular curves for all the fundamental reactions are sufficient to account for the etching behavior at off-normal angles at different operating conditions. With the modeling of angular dependence, the kinetics model is complete and can be used to explore the surface roughness in the 3-D profile simulator. The roughening of the SiO2 surface in fluorocarbon plasma was explored using the 3-D Monte Carlo profile simulator. / (cont.) The kinetics of SiO2 etching in C4Fs/Ar plasma was first developed in a similar fashion to that for poly-Si etching, with the additional assumption of equal reaction rates among all ionic or neutral radicals. All the ionic and neutral species experimentally measured were taken as inputs and the etching yield were predicted over a range of neutral-to-ion flux ratios and ion energies. Angular dependence on etching yield was also modeled to take into account the etching at off-normal angles. Then the kinetics was incorporated into the 3-D simulator and a good match was found between the experimental and profile simulation results in terms of etching yield and surface composition at various conditions, suggesting the kinetics after incorporation is capable of predicting complex surface chemistry of oxide substrate with fluorocarbon plasma. Then SiO2 surface roughness was simulated as functions of ion bombardment angle and neutral-to-ion flux ratio. The surface patterns, preferential orientation with respect to the ion beam and spatial frequency of the simulated surface showed a qualitative match with the experimental observations. The transition from coarsening to smooth surface with the increase of neutral-to-ion flux ratio was captured and related to the extent of polymerization on the surface. At low neutral-to-ion flux ratio, the modeled surface composition contour confirmed the formation of polymer islands around the roughened area, leading to etching inhomogeneity on the leading and shadowing side of features. The formation of polymer patchiness according to the simulation verified the polymer-induced micro-masking mechanism people proposed mechanistically to explain roughening on dielectric films. At high neutral-to-ion flux ratio, the simulation showed a higher extent of polymerization and yet the polymer deposit fairly uniformly and result in a smooth surface. The 3-D simulator coupled with detailed kinetics provided insights to the surface roughening mechanism on a microscopic basis. / by Wei Guo. / Ph.D.

Thesis (B.S.)--Massachusetts Institute of Technology, Dept. of Chemical Engineering, 1962. / MIT copy bound with: The rheology of blood-effect of hematocrit and temperature on yield value / by Hyunkook Shin [1962] / Includes bibliographical references (leaves 58-59). / by Xavier L. Simon. / B.S.

Thesis (Ph. D.)--Massachusetts Institute of Technology, Dept. of Chemical Engineering, 1974. / Vita. / Includes bibliographical references (leaves 262-267). / An investigation has been performed to determine the conditions at the onset of surface tension-driven instability, in gas-liquid systems, as characterized by the critical value of a dimensionless Marangoni number. A theoretical analysis, for the case in which a surface tension-lowering solute transfers from a liquid according to penetration theory, shows that adsorption of the solute in the Gibbs layer, at the gas-liquid interface, has a strong ability to retard convective instability. Theories which ignore Gibbs adsorption predict the onset of convection at Marangoni numbers as much as ten thousand times higher than the values found experimentally. With Gibbs adsorption included in the new theory, the discrepancy is very substantially reduced, to a factor of ten or less. Frequently, the residual disagreement has been blamed on the presence of minute amounts of impurities, adsorbed in the Gibbs layer, in the experimental liquids. The revised theory confirms that this influence can be strong under some circumstances. However, new experimental determinations of the critical Marangoni number, during triethylamine desorption from water, show that in typical systems the presence of trace contaminants is inconsequential. It is suggested that further efforts, to resolve the data-theory discrepancy, should focus on the relation between predictions of the critical Marangoni number and assumptions made in the stability theory concerning the size of the convective disturbance cells. / by John Richard Ross. / Ph.D.

Thesis (Ph. D.)--Massachusetts Institute of Technology, Dept. of Chemical Engineering, 2008. / Includes bibliographical references. / Biodegradable polymer particles have diverse applications in drug delivery. The main objective of this thesis was to apply these delivery systems to modulating the immune system. We optimized particle formulations for the delivery of three novel immune modulating compounds, small inhibiting RNA, immunostimulatory RNA, and 3-1,6-glucan. Because microparticles formulated from PLGA and Poly(3-amino-ester) have been shown to target and transfect DNA in antigen presenting cells we studied their ability to knock down genes with siRNA. We discovered ways to improve particle morphology, encapsulation efficiency, and buffer the acidic microenvironment of degrading microparticles, all significant challenges with siRNA. We next used fluorescent nanoparticles as imaging agents to study these siRNA delivery challenges. Cationic polymers were deposited on the surface of fluorescent core-shell silica nanoparticles electrostatically; the resulting particles were complexed with a nucleic acid and delivered to cells. We screened a library of 60 unique formulations to identify an optimal protocol for DNA transfection demonstrating efficiency equal to PEI. We screened a library of 30 unique formulations for siRNA delivery and demonstrated knockdown of 25%. Confocal imaging showed that polymer coating increased localization of the nanoparticles to the cell membrane, endosomes and nucleus. Polycation surface-modification seemed broadly extendable to a biodegradable polymer particle delivery system for siRNA. Cationic lipids or lipidoids were promising polycations to apply to biodegradable particle surface-modification because they efficiently deliver siRNA. We screened 30 lipidoid formulations for optimal knockdown in P388-D1 macrophage cells, and isolated formulations that demonstrated up to 40% knockdown in P388-D1, 80% knockdown in primary macrophage, and 65% knockdown in mouse macrophage in vivo. / (cont.) We formulated microparticles from PLGA/lipidoid blends that demonstrated nearly 80% knockdown in P388-D1. This same formulation also induced sequence specific interferon response to immunostimulatory RNA in human peripheral blood mononuclear cells. Finally we used PLGA microparticles to deliver a novel fungal cell wall component, 3-1,6-glucan, to neutrophils. This approach induced neutrophil expression of reactive oxygen species in vitro. In a mouse model of blood stream Candida albicans infection 60% of mice survived lethal doses when treated with the particles. / by Jason E. Fuller. / Ph.D.

Thesis (Ph. D.)--Massachusetts Institute of Technology, Dept. of Chemical Engineering, 2009. / Includes bibliographical references (p. 119-121). / An essential requirement for the fabrication of future electronic, magnetic, optical and biologically-based devices, composed of constituents at the nanometer length scale, is the precise positioning of the components in the system's physical domain. We introduce the design principles, problems and methods associated with the controlled formation of nanostructures with desired geometries through a hybrid top-down and bottom-up approach: top-down formation of physical domains with externally- imposed controls and bottom-up generation of the desired structure through the self-assembly of the nanoscale constituents, driven by interparticle interactions (short- and long-range) and interactions with the external controls (e.g., electrical, magnetic, chemical). The desired nanoscale structure must be locally stable and robust to a desired level of robustness, and it should be reachable from any initial particle distribution. These two requirements frame the two elements of the design problem: (a) Static Problem: Systematic placement of externally imposed controls and determination of their intensities in order to ensure that the final desired structure is stable with a desired degree of robustness; (b) Dynamic Problem: Time-varying controls in order to ensure that the desired final structure can be reached from any initial particle distribution. The concept of external controls is realized through point conditions, which introduce attractive or repulsive interaction terms in the system potential energy. The locations of the point conditions are found through the solution of a minimum tiling problem. / (cont.) Given these locations, the Static Problem is solved through the solution of combinatorially-constrained optimization problems. The Dynamic Problem is solved through a genetic algorithm search for the appropriate time-varying system degrees of freedom. Crucial to the achievement of the design goals is the necessity to break the ergodicity of the system phase space and control the subset of system states accessible to the system. More specifically, the static approach requires isolating the desired structure from all competing structures in phase space. The dynamic approach involves a multiresolution view of the system particle number, where we successively restrict the accessible volume of phase space based on coarse-grained particle number (i.e., density) specifications. We illustrate the design problems and solution methods through 1- and 2-dimensional lattice models and simulate the self-assembly process with a dynamic Monte Carlo method. / by Earl Osman P. Solis. / Ph.D.

Thesis (Ph. D.)--Massachusetts Institute of Technology, Dept. of Chemical Engineering, 2007. / Includes bibliographical references. / Polymers are known to exhibit strong time-dependent mechanical behavior. In different temperatures or frequency regimes, the rate sensitivities of polymers change as various primary and secondary molecular mobility mechanisms are accessed. The incorporation of nanoparticles can potentially alter the molecular level structure of polymer, offering the opportunity to tailor the rate-dependent mechanical deformation and failure behavior of the polymer. This study focuses on polyhedral oligomeric silsesquioxanes (POSS) enhanced polymeric systems. POSS are hybrid organic-inorganic nano-scale molecules which consist of a silica cage with functional groups attached to the cage comers. Various binary and ternary polymer blends were produced by incorporating methacryl-POSS (C56I88,28Si8) (mPOSS) and dioctyl phthalate (DOP) into poly(vinyl chloride) (PVC) through melt blending. mPOSS was found to be miscible with PVC up to 15 wt% added. Both mPOSS and DOP plasticize PVC and reduce the [alpha]-transition temperature. While mPOSS also reduces the secondary ([beta]) transition temperatures in PVC, DOP was found to restrict the p-relaxation motions. / (cont.) The rate-dependent yield and postyield behavior was characterized in compression testing over a wide range of strain rate (10-4/s to [approx.] 4000/s). Due to the geometric and size distinctions between the two molecules, mPOSS and DOP have different influences on PVC local molecular motions, resulting in dissimilar mechanical behavior. A clear rate-dependent sensitivity transition in yield was observed in the pure PVC and PVC/mPOSS blends in the intermediate strain rate regime, which is attributed to the need for stress-assisted activation of [beta]-motions at high strain rates. A transition in rate sensitivity was also identified in high DOP content compounds; this transition is due to the [alpha]-transition. The potential of using POSS as a plasticizer for PVC was evaluated. Through the use of ternary compositions, the proportion of mPOSS in PVC was increased substantially. The T8 of appropriately formulated ternary PVC/mPOSS/DOP compounds can be reduced to near room temperature, and these materials exhibit desirable ductile behavior. A constitutive model was used to predict the large deformation behavior of the PVC compounds. The two-process model is shown to capture the rate-sensitivity transitions in yield and the large deformation stress-strain behavior at low and high strain rates. / by Sharon Yu-Wen Soong. / Ph.D.

Thesis (Ph. D.)--Massachusetts Institute of Technology, Dept. of Chemical Engineering, 1998. / Includes bibliographical references. / by Suman K. Banerjee. / Ph.D.