Thesis (Ph. D.)--Massachusetts Institute of Technology, Dept. of Chemical Engineering, 2006. / Vita. / Includes bibliographical references (leaves 97-98). / Fillers are often added to polymers improve stiffness at the cost of reduced toughness, but this tradeoff is not universal. Well-dispersed microscopic particles have been shown to improve toughness and stiffness simultaneously in some cases. The effect depends on interparticle distance as well as interfacial adhesion. This type of toughening has been more successful in semicrystalline than in amorphous systems. An amorphous polymer blend was chosen to elucidate the effect of matrix properties on the toughening mechanism. The ternary blend of PMMA, PVC, and DOP (a common plasticizer) was characterized using TEM, and was found to be miscible over much of the PVC-rich domain. The blend Tg's fit well to an empirical model, which was used to predict a constant-Tg ([approx.] 40°C) blend series. Mechanical testing showed a wide, systematic variation in properties among these blends, although all were brittle in tension. The blend 90% PVC / 10% DOP was mixed with barium sulfate filler and evaluated for toughness in slow tension. In general, the composites showed decreasing toughness with increasing filler content. However, several specimens at 5 vol% filler exhibited a large increase in ductility and toughness ([approx.] 19-fold). / (cont.) SEM examination of tough specimens revealed several important findings: (1) Filler is present both as micron-scale agglomerates and as well dispersed particles. (2) Well-dispersed particles remain bonded to the matrix even for large deformations. (3) Filler agglomerates are prone to debonding and internal fracture, creating void space and enabling deformation. Base blend properties significantly affect the response to filler. The blend 8% PMMA / 80% PVC / 12% DOP showed small increases in ductility for 5 and 10 vol% filler, with the best result being a 10 vol% specimen showing a 6-fold toughness increase over the neat-blend average. This specimen showed similar microscopic behavior to the 90/10 blend, i.e. agglomerate debonding and fracture, but to a lesser degree. The blend 16% PMMA / 70% PVC / 14% DOP, showed no significant toughening. Also investigated were high-Tg ([approx.] 70°C) blends, which were brittle and became weaker with filler, and low-Tg ([approx.] 30°C) blends, which were intrinsically ductile and were not toughened by filler. / by Roger Lockwood Aronow. / Ph.D.

Thesis (Ph. D.)--Massachusetts Institute of Technology, Dept. of Chemical Engineering, 1985. / MICROFICHE COPY AVAILABLE IN ARCHIVES AND SCIENCE. / Bibliography: leaves 255-264. / by Howard Bernstein. / Ph.D.

Thesis (Ph.D.)--Massachusetts Institute of Technology, Dept. of Chemical Engineering, 2000. / Includes bibliographical references. / This electronic version was submitted by the student author. The certified thesis is available in the Institute Archives and Special Collections. / Pulsed plasma enhanced and hot filament chemical vapor deposition have produced fluorocarbon films with the potential use as low dielectric constant interconnect materials in microelectronic circuits. Solid-state nuclear magnetic resonance spectroscopy was demonstrated as a valuable film characterization tool to understand structure-property processing fundamentals, quantifying film bonding environments and tracing structural instabilities. Thermal lability in fluorocarbon films was attributed to terminal end groups and low molecular weight molecules. High temperature thermal stability was achieved by minimizing such labile sources through a clean deposition of high molecular weight chains of poly(tetrafluoroethylene). Poly(tetrafluoroethylene) film porosity was introduced and controlled through the competition between nucleation and growth of film. Porous poly(tetrafluoroethylene) films were further integrated into a bridge layer and air gap dielectric interconnect scheme. With fluorocarbon materials deposited through such chemical vapor deposition methods, dielectric constants ranging from 2.1 to below 1.5 were conceivably attainable, thus potentially satisfying dielectric interconnect requirements to beyond the 0.1 [mu]m technology node. / by Kenneth Ka Shun Lau. / Ph.D.

Thesis (Ph. D.)--Massachusetts Institute of Technology, Dept. of Chemical Engineering, 2009. / Includes bibliographical references. / This thesis explores how tablet performance is affected by microstructure, and how microstructure can be controlled by selection of excipients and compaction parameters. A systematic strategy for formulation and process design of pharmaceutical tablets is proposed. A modified nanoindenter method was used to test the mechanical behavior of diametrally compressed excipient granules. X ray micro computed tomography and Terahertz pulsed spectroscopy (TPS) and imaging (TPI) were used to analyze the microstructure of the tablet core and detect internal defects. Granule failure mechanisms are found to be consistent with tablet microstructure. MCC granules deform plastically when tested and X ray images show individual granules undergoing increasing deformation in tablets as higher compaction forces are used. A highly interconnected pore-structure limited tablet hardness and led to bursting behavior during dissolution. No effect of compaction force or speed was observed in dissolution profiles. Lactose granules fracture at strains less than 5%, forming monolithic structures with no evidence of initial granule shape or size. Pore size decreases as compaction force is increased for DCL 11 tablets. A decreasing pore size corresponds to increasing THz refractive index, tablet hardness and dissolution time. DCL 11 and DCL 14 tablets compacted under the same conditions have the same pore size distributions and hardness, although DCL 14 granules are weaker than DCL 11, and DCL 14 tablets dissolve up to four times slower than DCL 11 tablets. No difference was observed between the THz spectra of tablets made from the two grades of lactose. / (cont.) Further work is needed to understand the physical significance of the THz measurements. TPI can detect laminated tablets and is faster than X ray micro CT. In order to develop a rational design methodology, two key areas for future research are building a process model for compaction and developing quality testing methods that can be analyzed mechanistically. The capstone project explores strategic decision making for innovator firms and generic drug manufacturers in the period surrounding patent expiry. Statin products were used as an illustrative case of a pharmaceutical technology experiencing commoditization. A system dynamics model was used to simulate historic results and explore options for products still under patent protection. Current models of technology market dynamics apply to statins, but regulation and legislation play a large role in controlling market entry, leading to strong sequencing effects. / by Mridula Pore. / Ph.D.

Thesis (Ph. D.)--Massachusetts Institute of Technology, Dept. of Chemical Engineering, 2011. / Cataloged from PDF version of thesis. / Includes bibliographical references (p. 113-119). / The transition from traditional batch blending to continuous blending is an opportunity for the pharmaceutical industry to reduce costs and improve quality control. This operational shift necessitates a deeper understanding of the mixing process informed by particle dynamics and variable interdependencies. The thesis aims to establish a framework for characterizing and improving continuous pharmaceutical blending using a tiered experimental methodology and multivariate analysis. This parameter space exploration attempts to reconcile previous research within the context of cohesive pharmaceutical powders and develop general design principles for maximizing blender performance. A design of experiments was conducted to determine mixing performance with respect to three factors - physical design, operating parameters, and material properties. Multivariate analysis using projections to latent structures was employed to quantify the effect of raw and intermediate variables on the variance reduction ratio. Significant parameters identified included the choice of API, fill fraction, the number of blade passes, the mean residence time, the Bodenstein number, and the period of input feed fluctuations. The results highlight the importance of shear and radial mixing for cohesive powders, which suggest that one-dimensional axial models common in blending literature may not be a sufficient theoretical framework for pharmaceutical applications. The research yielded several insights into design principles for optimizing blending performance. Increasing mean residence time and radial mixing create more robust processing by reducing the impact of material properties and fluctuations in feed consistency. The variance reduction ratio can be improved in a cost-effective manner by determining the fill fraction which maximizes intermediate metrics such as space time, mean residence time, and the number of blade passes. Multivariate analysis was demonstrated to be a practical tool for parameter space optimization and a promising technique for characterizing the effect of material properties on processing. / by Ben Chien Pang Lin. / Ph.D.

Thesis (Ph. D. in Chemical Engineering Practice)--Massachusetts Institute of Technology, Dept. of Chemical Engineering, February 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. "December 2012." / Includes bibliographical references. / Omniphobicity refers to a property of surfaces which are not wetted by water, oils, alcohols and other low surface tension liquids. Robust omniphobic surfaces can be applied in many areas including fabrics with chemical / biological protection and dirt / fingerprint resistant touch screens. The main aim of this thesis is to develop rules for the systematic design of omniphobic surfaces with a focus on textiles. First, a design chart is developed to help us understand the impact of surface chemistry and surface topography on the wettability of a textured surface. A smaller characteristic length scale of a re-entrant surface topography, tighter weave and a coating with inherently low wettability are better for producing omniphobic surfaces that resist wetting by liquids with low surface tension. This framework is applied to textile fabrics and bird feathers to test their wettability. Using this framework, wettability of low surface tension liquids on a polyester fabric is tuned or switched using either thermal annealing or biaxial stretching. Army Combat Uniform fabrics are rendered oleophobic, thus opening the way to optimize omniphobic army uniforms. The wettability of molecules similar to fluorodecyl POSS is investigated by measuring the contact angles with liquids of a broad range of surface tension and polarity. Of the molecules tested so far, fluorodecyl POSS has the lowest solid surface energy (9.3 mN/m) and the lowest increment in solid surface energy (7 mN/m). The wetting aspects of the hierarchical topography of bird feathers are captured using contact angle measurements in terms of a spacing ratio. Thermodynamics of the wetting of feathers and the robustness against wetting during the course of a dive are correlated to the wing spreading behavior. Our understanding of surface wettability of woven meshes is applied to optimize their fog collection ability. A business case for fog harvesting is developed and strategies to decrease asset and cash flow risks are proposed. The contributions presented here provide means to better characterize surfaces with complex topography, tune and a priori predict their wettability and recommend a design strategy both at a molecular and a macroscopic level to maximize their non-wettability. / by Shreerang S. Chhatre. / Ph.D.in Chemical Engineering Practice

Thesis (Ph. D.)--Massachusetts Institute of Technology, Dept. of Chemical Engineering, 2005. / Includes bibliographical references (p. 225-240). / Recombinant human glycoproteins produced by Chinese Hamster Ovary (CHO) cells are an important class of therapeutic molecules and investigating means of improving the production rate and product quality of these glycoproteins is therefore of great interest. Culturing CHO cells under mild hypothermia (30-33 ⁰C) leads to growth arrest in the G₀/G₁ phase of the cell cycle and, in some cases, causes an increase in specific productivity of recombinant protein, as was shown here for the model CHO cell line producing human interferon-gamma (IFN-[gamma]). Controlled proliferation, achieved by inducing growth arrest in the G₀/G₁ phase by chemical, environmental or genetic means, is commonly used to increase CHO specific productivity and thus there is speculation that enhanced hypothermic productivity is due to growth arrest. However, it was proven here that the positive effect of hypothermia on recombinant protein production is due to elevated IFN-[gamma] mRNA levels instead. At both 32 ⁰C and 37 ⁰C, specific productivity is growth-associated, increasing as the percentage of cells in the S phase increased, demonstrating that a cell line can be both a growth-associated producer and have enhanced productivity under hypothermic conditions. It was hypothesized that the best production platform would be cells actively growing at low temperature and this was proven to be the case using two different methods, namely growth factor supplementation and selection of cells capable of hypothermic growth. Both methods gave multi-fold increases in total IFN-y production compared to the 32 ⁰C and 37 ⁰C controls, thereby validating the novel culture strategy of active hypothermic growth. / (cont.) Cells capable of achieving significant hypothermic growth were also isolated for the non-recombinant CHO-KI cell line and are now available for the future production of any recombinant protein. Glycoprotein quality is partially assessed by the level of glycosylation and IFN-[gamma] contains two potential N-linked glycosylation sites. This thesis gives the first report of a detrimental effect of hypothermic culture on glycosylation, showing a 4-5% decrease in the end-of-batch percentage of 2-sites occupied glycoforms relative to the 37 ⁰C control. However, this negative effect is completely eliminated by culturing under perfusion conditions. / by Stephen Richard Fox. / Ph.D.

Thesis (Ph. D.)--Massachusetts Institute of Technology, Dept. of Chemical Engineering, 1991. / Includes bibliographical references (p. 277-286). / by Ian C. Yates. / Ph.D.

Thesis (Ph.D.)--Massachusetts Institute of Technology, Dept. of Chemical Engineering, 2000. / Includes bibliographical references. / This thesis develops modeling techniques for chemical vapor deposition processes, specifically metalorganic vapor phase epitaxy (MOVPE). The difficulty in creating an overall modeling strategy for the MOVPE process is that important processes occur on a wide range of length and time scales. Gas phase heat and mass transfer affect the flux of species to the surface, while atomic processes affect the morphology of the growing film. In this thesis, new computational models are developed that work on specific length scales, models are linked together, and combined models are used to study the physics of actual deposition processes. A Kinetic Monte Carlo (KMC) model is developed in order to simulate surface morphology during epitaxial growth. Computational methods, such as binary trees, are used to improve the computational efficiency of the KMC algorithm. To extend the computationally accessible length and time scales, a new parallel algorithm is developed based on ideas from Parallel Discrete Event Simulations (PDES). Superlinear speedup is achieved using this algorithm. The methodology is used along with optimization routines to fit Temperature Programmed Desorption (TPD) spectra to experimental data of methyl desorption off Ga-rich GaAs and determine consistent desorption mechanisms. Physically based reactor scale models are linked to KMC models to gain an overall understanding of the MOVPE system. Initially reactor models that include surface unknowns are flux-split; the surface model is separated from the gas phase model and linked together through the flux to the surface. It is shown that flux-split models exactly match coupled models and in some cases offer better convergence. This linking methodology is extended with the use of a KMC model for the surface. A test case using GaAs growth is modeled, and both accurate growth rate and surface morphology estimates are achieved using the linked model. Neither model separately could predict both flux and surface morphology, but the linked models can be used to make a range of predictions from gas phase concentrations to surface morphology. A reactor used for Grazing-Incidence X-ray Scattering (GIXS) experiments is analyzed using the linked model. The linked model matches both gas-phase concentrations and surface morphology estimates in the reactor. The surface model is compared to experimental GIXS diffuse scattering. The model predicts that the complex reactions on the surface (As dimer and organic group adsorption and desorption from the surface) cause the surface morphology evolution to differ from that observed in molecular beam epitaxy. / by Rajesh Venkataramani. / Ph.D.

Thesis (Sc. D.)--Massachusetts Institute of Technology, Dept. of Chemical Engineering, 1960. / Vita. / Includes bibliographical references (leaves 203-208). / by Charles Albert Homsy. / Sc.D.