Electronic Theses and Dissertations (2010 - Present)
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The University of Houston Libraries collect and make publicly available all electronic theses and dissertations (ETDs) produced in UH graduate and PhD programs through the UH institutional repository. ETDs become available after the student submits them to the UH Graduate School, the document is approved by all appropriate parties, and any embargo on the document expires.
Collection Scope
UH Libraries began publishing ETDs from several UH Colleges in 2010. As of Summer 2014, all UH Colleges that require a thesis or dissertation for graduation began submitting these documents in electronic format. Below is a list of UH Colleges that currently participate in the ETD program and their coverage dates in this repository.
UH College | Coverage Dates |
---|---|
C.T. Bauer College of Business | 2010-Present |
Cullen College of Engineering | 2012-Present |
Conrad N. Hilton College of Hotel and Restaurant Management | 2015-Present |
College of Education | 2010-Present |
College of Liberal Arts and Social Sciences | 2012-Present |
College of Natural Sciences and Mathematics | 2012-Present |
College of Optometry | 2010-Present |
College of Pharmacy | 2010-Present |
College of Technology | 2012-Present |
K. G. McGovern College of the Arts | 2016-Present |
G. D. Hines College of Architecture & Design | 2016-Present |
Graduate College of Social Work | 2012-Present |
Additional Information
- Online access for content outside these coverage dates may be available electronically through ProQuest.
Note: As of Fall 2017, all theses and dissertations produced at UH will be submitted to ProQuest. Additionally, some UH Colleges have contributed content to ProQuest at different periods of time in the past. - For print theses and dissertations found outside these coverage dates, please consult UH Libraries’ catalog.
- Additional information on submitting ETDs can be found at the UH Graduate School.
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Browsing Electronic Theses and Dissertations (2010 - Present) by Department "Chemical and Biomolecular Engineering, William A. Brookshire Department of"
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Item A Proposal on the Alleviation of Textile Mass in the Long Term Interplanetary Travel and Cosmos Habitation Through On Board Unsalable Resource Utilization(2020-12) von Slomski, Kirinina Sascha; Bannova, Olga; Bell, Larry; Kennedy, Kriss J.; Toups, LarryThis thesis expresses the use of textile electrospinning as a means to alleviate economic concerns for long term space missions such as the upcoming missions to Mars. The proposal consists of evaluations of the plants most likely to be considered in a Martian greenhouse module. The possibility of using the inedible parts of the plants as the basis for a solution for textile electrospinning. This will ease the burdens of stowage and mass for textiles as well as trash or waste products that must be brought back from Mars. This is imperative as the Planetary Protection Agency requires no biological contamination of Mars, thus eliminating the ability to leave biologically contaminates be left behind on Mars. As well, it notes the hygienic issues concerning textiles and usage to the point of being considered soiled. This thesis contains the amounts associated with textiles needed for a twenty-six-month long journey to Mars and back to Earth if it were four astronauts. Also, the differences in common FDM (fused deposition modeling) and electrospinning, and the ability to create a textile electrospinner. Ending with what is needed to further peruse this study of how to economically ease stowage and mass costs for long-duration missions.Item ANALYSIS AND DESIGN OF STRUCTURED MULTI-FUNCTIONAL TRAPPING CATALYSTS FOR CONVERSION OF HYDROCARBONS AND NOX FROM DIESEL AND ADVANCED COMBUSTION ENGINES(2022-08-09) Gupta, Abhay; Harold, Michael P.; Grabow, Lars C.; Rimer, Jeffrey D.; Brankovic, Stanko R.; Louie, Stacey M.Multifunctional automotive catalysts can help abate harmful emissions, such as NOx (x=1, 2), CO, and hydrocarbons (HCs) and provide a potential solution to meet the need of increasingly stringent vehicle fuel economy standards and emissions regulations. The proposed LHCNT (lean hydrocarbon NOx trap) concept involves the combination of NOx trapping with HC trapping and oxidation for conversion of NOx, HC, and CO during sustained, low-temperature exhaust drive cycles and engine cold-start. In the first part of the work, we focus on NOx uptake and release features on Pd-exchanged SSZ-13 (PNA- Passive NOx Adsorber) catalyst to trap NOx in the absence and presence of several diesel exhaust components (CO, C2H4, H2, C7H8, and C12H26). We identified two prospective mechanistic schemes which are consistent with the uptake/release and DRIFTS (diffuse reflectance infrared Fourier transform spectroscopy) data. Second, we focused on DOC (Diesel Oxidation Catalyst) which is an essential component of modern vehicle emissions control systems. A new Pd-Cu alloy catalyst ((Pd+Cu/SiO2-Al2O3), prepared in-house, exhibited higher resilience to increased light-off temperature, resultant of mutual inhibition between the various pollutants, in comparison with the commercial DOC (Pt+Pd/Al2O3-CeO2). The benefit of eliminating the inhibition effect of NO on CO oxidation is clearly demonstrated in the juxtaposition of the two catalyst and reactor configurations using a CO and NO containing feed. Next, we investigate the spatiotemporal features of a multifunctional monolith lean hydrocarbon NOx trap (LHCNT) for eliminating NOx and C2H4 in simulated diesel exhaust. Spatially-resolved mass spectrometry (SpaciMS) is used to measure the temporal species concentration profiles spanning the sequentially- positioned PNA (Pd/SSZ-13), HCT (Hydrocarbon Trap; Pd/BEA) and DOC (Pt/Al2O3-CeO2) zones. The working concept of the LHCNT is demonstrated through measured integral trapping efficiency profiles, which show NO and C2H4 trapping followed by delayed NO release along with NO and ethylene oxidation during the simulated warmup. Finally, we utilized the same sequential configuration system to identify the impact of CO on NO trapping. Conditions are identified which lead to CO induced deactivation. We conclude our study with the scope of future work based on our results and observations.Item ANOMALOUS DYNAMICS IN GLASSY COLLOIDAL LIQUIDS(2020-12) Roberts, Ryan Cedric; Conrad, Jacinta C.; Palmer, Jeremy C.; Morrison, Greg; Sharma, Pradeep; Grabow, Lars C.A liquid that is slowly cooled below the melting temperature usually undergoes a first-order transition to a crystal with long-range periodic order. Rapid cooling, by contrast, may suppress nucleation and result in a glass transition, in which the liquid viscosity and relaxation time appear to diverge despite the structure remaining liquid-like. With decreasing temperature, liquid dynamics become spatially and temporally heterogeneous as the system segments into ephemeral regions of relatively mobile and immobile particles. In this work, we use molecular dynamics simulations of model, colloidal glass-formers to probe anomalous dynamics of glassy liquids. In one investigation, we probe anomalous dynamics of dilute, hard sphere tracers within supercooled liquid and glass matrices with varying interparticle attraction strength. We find that tracers with diameters that are 35\% of the matrix diameter exhibit anomalous dynamics indicative of competing relaxation mechanisms. This competition is associated with particular time and length scales that increase as the dominant interactions within the matrix are modulated from repulsive to attractive. As a result, tracer trajectories in attractive systems are more compact than trajectories in repulsive systems, reflecting the underlying rearrangements of the matrices. Further, we simulate tracers of this characteristic size in glasses with no long-time matrix rearrangement and find that vitrification does not prohibit tracer rearrangement. In fact, tracers are delocalized in repulsive glasses but localized in attractive glasses. This localization in attractive systems is heterogeneous in space and time because of the smaller matrix fluctuations in attractive systems, allowing the matrix structure to more strongly determine tracer dynamics. In another investigation, we examine the dynamics of polydisperse hard spheres confined between parallel hard walls separated by varying length $H$. We find a minimum in relaxation time at an intermediate $H$ that is incommensurate with average particle size, coinciding with a change from square to hexatic crystalline ordering in confined monodisperse hard spheres. Glassy slowdown in systems with commensurate $H$ is correlated with growing hexatically ordered domains, whereas no strong correlation between dynamics and crystalline ordering is observed for incommensurate $H$. Thus, dynamics can be driven by local ordering, but this relation is sensitive to confinement.Item Bacterial Adhesion and Motility at Oil-Water Interfaces(2020-12) Dewangan, Narendra Kumar; Conrad, Jacinta C.; Willson, Richard C.; Cirino, Patrick C.; Rodrigues, Debora F.; Louie, Stacey M.Degradation of hydrocarbons by bacteria is one of the most important processes in oil spill cleanup. In attempt to increase the rate of biodegradation, chemical dispersants have been deployed in many oil spill scenarios to increase the surface area per unit volume available to bacteria. Biofilm formation is one of the important pathways in degradation of oil by bacteria. Because adhesion of bacteria to surface is one of the important steps in biofilm formation. It is important to study what factors affect the bacterial adhesion on oil/water interfaces. Adhesion of bacteria on solid surfaces is widely studied but surprisingly, how bacteria adhere on oil/water interface, and the effect of surfactants and bacterial motility on adhesion of bacteria on oil/water interface is not well studied. First, we designed and fabricated a microfluidic device to produce denser monodispersed oil in water emulsion. We developed a method to be able to capture 3D images of bacteria adhering to oil droplets with minimal number of cells attached to imaging chamber and with minimizing the wetting (~ 180° contact angle) of oil droplet to the imaging chamber. We developed tracking algorithms to visualize the cells adhering on the droplet and to calculate the contact angle that each bacterium makes to the droplet surface. In the first part of the project, we studied the effect of surfactant chemistries (anionic [dioctyl sodium sulfosuccinate, dicyclohexyl sodium sulfosuccinate, dibutyl sodium sulfosuccinate], cationic [cetyltrimethylammonium bromide], and nonionic [Tween 20]) and surfactant concentration on adhesion of nonmotile Marinobacter hydrocarbonoclasticus SP17 on dodecane droplets. Secondly, we found that motile bacteria Halomonas titanicae adhering to dodecane droplets were able to move the droplets in aqueous suspension. We explored the physics of droplet rotation driven by bacteria. Droplets rotate in clockwise direction when viewed from the liquid side, due to symmetry-breaking hydrodynamic interactions of bacteria with the surface. We examined the effect of droplet size on angular speed of droplets. We further investigated the effect of surfactant concentration and interfacial affinity of bacteria (by using three different bacteria species Escherichia coli, Shewanella haliotis, and Halomonas titanicae) on droplet rotation. Thirdly, we investigated the effect of bacterial motility on adhesion of bacteria on hexadecane droplets. Here, we show that bacterial motility enhances adhesion to surfactant-decorated oil droplets dispersed in artificial sea water. Motile Halomonas titanicae adhered to hexadecane droplets stabilized with dioctyl sodium sulfosuccinate (DOSS) more rapidly and at greater surface densities compared to nonmotile H. titanicae, whose flagellar motion was arrested through addition of a proton decoupler. Increasing the concentration of DOSS reduced the surface density of both motile and nonmotile bacteria as a result of the reduced interfacial tension. Finally, we investigated the effect of concentration of anionic surfactant dioctyl sodium sulfosuccinate (DOSS) and calcium chloride on aggregation of nonmotile Marinobacter hydrocarbonoclasticus and Halomonas titanicae in synthetic seawater. Bacteria aggregation may occur due to environmental stresses as a protective mechanism or it can occur as a first step towards biofilm formation and subsequent biodegradation. There are two physical mechanisms known in aggregation of bacteria: (1) aggregation by depletion attraction, and (2) aggregation by bridging attraction due to EPS or polymers. In our study, we found that aggregation (size and number density) increases with increase in DOSS concentration and calcium chloride concentration. Motile Halomonas titanicae showed higher aggregation compared to nonmotile bacteria. Together, we studied bacteria motility and adhesion interactions on cell-solid surface, on cell-liquid interfaces, and on cell/cell interfaces. Broadly, this research contributes to the fields of bioremediation and antifouling.Item Bifurcation and Stability Analysis of Temperature Patterns in Shallow-bed Catalytic Reactors(2022-08-09) Shah, Meet Vipulkumar; Balakotaiah, Vemuri; Harold, Michael P.; Mountziaris, Triantafillos J.; Dindoruk, Birol; Auchmuty, GilesPacked-bed catalytic reactors are widely used in industry to carry out many exothermic reactions. Reaction induced flow instabilities can lead to temperature patterns and localized hot spots through multiple mechanisms in these reactors. This work examines two of these mechanisms that lead to the formation of complex temperature patterns that bifurcate from the uniform state using continuum and discrete models. In the first part of the work, a two-phase finite dispersion continuum model is utilized to analyze the instabilities arising due to coupling between momentum, species and energy balances and variation of fluid physical properties with temperature. It is found that multiple flow rates through the reactor are possible for the same pressure drop. Linear stability analysis is used to determine the impact of catalyst particle size (bed permeability), reactor aspect ratio and reaction parameters on the stability boundary under different boundary conditions. The second part of the work examines temperature patterns due the existence of multiple steady states at the catalyst particle scale. Generalized cell models are developed to understand the impact of multiple length scales in the reactor and their impact on stable temperature patterns. Transverse arrangement of cells is used to examine pattern formation due to thermokinetic multiplicity occurring at smaller length scales of the reactor. Linear stability and bifurcation analysis are utilized to compute various stable and unstable patterned branches, and the impact of various parameters. Transient analysis is performed to determine the basins of attraction of various patterned states in the phase space. The third part of the work examines transverse 2D arrangement of cells to understand the pattern formation behavior in shallow bed reactors. The boundaries of stable patterns for different reactor geometries and scaling of the bed conductivity at which stable patterns are eliminated with reactor size are determined. Models with 2D arrangement of cells with axial variation in temperature and concentrations and multiple reactions are analyzed to further explain the experimentally observed patterns.Item Biomimetic Active Sites in Metal-Organic Framework Catalysts for Hydrocarbon Transformations(2022-05-10) Hall, Jacklyn Noel; Bollini, Praveen; Harold, Michael P.; Rimer, Jeffrey D.; Shaffer, Devin L.; Chiang, HsuMetal-organic frameworks (MOFs) are a class of crystalline materials featuring uniform distributions of inorganic nodes interconnected within well-defined organic porous environments. For applications in catalysis, the homogeneity of active centers attainable within MOFs enables achieving a level of clarity into structure-catalytic property relationships and reaction mechanisms beyond which can be realized in synthetic catalysts delimited by a high degree of heterogeneity in active site speciation – a feature of particular importance in the development of biomimetic catalysts. Herein, we demonstrate MIL-100 (MIL = Materials of Institut Lavoisier), a prototypical MOF featuring mixed-valent trinuclear metal nodes [M2+(M3+)2O], features an active site pool which is uniform in structure and catalytic performance. A combination of in-situ infrared spectroscopic characterization and probe molecule adsorption experiments with H2O, NO, and CO evidence the accessibility of the near theoretical density of coordinatively unsaturated divalent and trivalent open-metal sites within the Cr- and Fe-analogues of MIL-100 through facile thermal activation protocols (≤ 523 K, inert or vacuum). Furthermore, we demonstrate the activated catalysts effectuate the gas-phase stoichiometric oxidation of CH4 with N2O to partial oxygenates (methanol and acetaldehyde) through the involvement of every potentially available M2+ open-metal site. Carbon monoxide is applied as a reductant to further elucidate reaction steps that mediate redox turnovers with N2O over MIL-100. Transient, steady-state, and isotopic kinetic analyses provide novel insight into levers for tuning the kinetic relevance of specific reduction and oxidation elementary reaction steps through second-sphere coordination effects and identity of the active metal.Item Biomolecular Detection Assays(2022-05-10) Hlavinka, Victoria; Willson, Richard C.; Orman, Mehmet A.; Kourentzi, Katerina; Shevkoplyas, Sergey S.; Mohan, ChandraIn the present work, three methods for the detection or monitoring of biomolecules are outlined in detail. The first study describes the development of a saliva-based enzymatic screening assay for diabetes mellitus. In the second study, lateral flow assays (LFAs) utilizing commercial colloidal gold and blue latex nanoparticle reporters are compared to persistent luminescence nanoparticle (PLNP; “nanophosphor”) LFAs to assess the sensitivity of nanophosphors as a reporter system. The final study demonstrates the utility of a nanophosphor-based LFA for detecting low concentrations of dengue virus (DENV) biomarker non-structural protein 1 (NS1). 1,5-Anhydroglucitol (AHG) is a naturally occurring monosaccharide and a clinically validated blood biomarker for diabetes. The blood concentration of AHG falls during periods of hyperglycemia, as glucose outcompetes AHG for kidney reuptake. Salivary AHG quantification has been suggested to be useful for diabetes screening but has not been implemented in any widely applicable fashion. We have developed a chemiluminescence assay to quantify AHG in saliva and demonstrated that the assay could distinguish between healthy and diabetic individuals (N = 265; p < 0.0001, ROC AUC = 0.82). These findings suggest that, with further validation, this approach may serve as the basis of a non-invasive tool for diabetes screening. Commercially-available LFAs commonly use colloidal gold or blue latex nanoparticles reporter systems that lack sensitivity and are prone to human error when interpreted visually. We have developed nanophosphors that can detect low levels of antigen. In a comparison study, a nanophosphor-based human immunoglobulin G (IgG) LFA had a limit of detection of 0.625 ng/mL, an 81-fold and 58-fold increase in sensitivity over colloidal gold and blue latex nanoparticles, respectively. Current DENV diagnostic methods are commonly unspecific and cannot detect early infection. We have developed an inexpensive, rapid LFA to detect DENV NS1, a known marker of early dengue infection. Using strontium aluminate nanophosphors as reporters, we achieved a limit of detection of 1 ng/mL DENV serotype 1 NS1 antigen. Our assay is comparable to a laboratory-based NS1 ELISA with a 1 ng/mL limit of detection.Item Control of Photo-Assisted Etching of Si in Chlorine Containing Plasmas(2021-05) Du, Linfeng; Donnelly, Vincent M.; Economou, Demetre J.; Grabow, Lars C.; Ruchhoeft, Paul; Wolfe, John C.Plasma etching is critical for the fabrication of very large-scale integration (VLSI) microelectronic devices. In-plasma photo-assisted etching (PAE) with ion energy below the ion-assisted etching (IAE) was discovered in our laboratory several years ago. PAE may be advantageous or detrimental, depending on the situation. Thus, it is desirable to be able to control PAE. This thesis reports fundamental studies of PAE suppression using oxygen additions to the plasma and PAE enhancement by extra VUV flux irradiating the Si substrate. O2 addition to a baseline plasma was used to control PAE of p-type Si (100) and poly-Si in a high density, Faraday-shielded, Ar/Cl2 (225/25 sccm) inductively coupled plasma. The etching rate of samples etched under PAE condition was not affected by 0.1 or 0.25 sccm O2 addition to the base case Ar/Cl2 plasma, while etching stopped with more than 0.5 sccm O2 addition. Ion assisted etching, was not affected by up to 2 sccm of oxygen addition, but decreased rapidly when more than 5 sccm O2 was added to the plasma. Thus, there was a window of O2 additions that completely suppressed PAE but allowed IAE to proceed unobstructed. Vacuum transferred X-ray photoelectron spectroscopy (XPS) showed that PAE-treated samples had a thicker surface oxide and lower chlorine concentration (SiCl). In contrast, the surface of IAE samples contained Si dangling bonds and higher silicon chlorides (SiCl2 and SiCl3). The PAE rate of p-type Si was enhanced by extra vacuum ultraviolet (VUV) photon flux. Etching was carried out in the Ar/Cl2 ICP used above (main ICP). Additional photon flux was provided by a compact Ar/He (2.5/47.5 sccm) plasma source (auxiliary ICP), in tandem with the main ICP. The auxiliary ICP was also used as a standalone plasma source to determine (using VUV spectroscopy) the composition of the Ar/He gas mixture that maximized the 106.7 nm line (1s4) of the resonant state of argon. Most PAE-treated samples had a rough surface under the scanning electron microscope (SEM). A significant etching enhancement of 51% was found at a pressure of 15 mTorr, where the PAE rate with only the 60 W main ICP ON was 0.069 μm/min, increasing to 0.104 μm/min when the 200 W auxiliary ICP was also turned ON. XPS survey results showed that PAE with only the main ICP ON resulted in the same [Cl]/[Si] surface concentration ratio of about 0.15, when both ICPs were ON, suggesting that the chemical composition of the silicon surface was not affected by the additional VUV photon flux. High resolution XPS indicated that the extra VUV photon flux from the auxiliary ICP may induce surface conversion of lower chlorides to higher chlorides. Surprisingly large PAE yields 356 and 135 Si/photon were found at neutral-to-photon flux ratios of 19 × 104 and 0.9 × 104, respectively.Item Controlling Pathological Mineralization Using Molecular Modifiers(2021-08) Kim, Do Young; Rimer, Jeffrey D.; Vekilov, Peter G.; Palmer, Jeremy C.; Rodrigues, Debora F.; Lee, T. RandallThe development of new methods to prevent mineral scale formation can have significant impact on natural, biological, and industrial process. A ubiquitous approach to regulating crystal formation is through the use of modifiers, which are (macro)molecules that interact with crystals to inhibit nucleation and/or growth. Understanding the fundamental mechanisms of crystallization inhibitors is relevant to a broad range of fields, including their frequent use in crystal engineering and biomineralization. This dissertation focuses on two types of pathological crystals: calcium oxalate monohydrate (COM), the primary component of kidney stones, and magnesium ammonium phosphate hexahydrate (struvite). Struvite is a key constituent of infection stones (e.g., kidney stones); and it is also a common scale in water purification and transport. Despite considerable interest in this material, the fundamental understanding of struvite growth is still at its infancy due to the lack of appropriate platforms to assess growth over multiple length scales. The use of flow systems to study infection stone formation is promising, as they can simulate the flow conditions where struvite naturally forms (e.g., urinary tract systems, catheter, pipelines, etc.). This dissertation has established a new method of evaluating struvite crystal growth under flow using a combination of microfluidics and in situ atomic force microscopy (AFM). Through these synergistic approaches, we quantified anisotropic kinetics of crystallization over a broad range of conditions and resolved the molecular mechanism of growth and its inhibition whereby layers on crystal surfaces advance from either screw dislocations or 2-dimensional generation and spreading of islands – both of which are classical pathways. Growth modifiers range from small ions and molecules to large macromolecules. Here, we examined the impact of bio-inspired small molecules on both struvite and COM crystallization. Several phosphate-based molecules exhibit an unparalleled dual mode of action capable of suppressing both nucleation and growth of crystals. Time-resolved AFM images of struvite surface at varying inhibitor concentration revealed a unique mode of crystal growth inhibition, wherein surfaces become laden with an amorphous layer that leads to roughened interfaces and growth succession through dynamic sequences that are not commonly witnessed for other minerals. In studies of COM, we observed that modifiers irreversibly stunt crystal growth in timescales that are relevant to pathological COM kidney stone formation. Comparisons between phosphate-based modifiers and two reference compounds previously identified as highly effective COM inhibitors, carboxylate-based hydroxycitrate and the urinary protein osteopontin, revealed that phosphate-based inhibitors suppress COM crystallization at substantially lower concentrations than both conventional modifiers, thus highlighting the unique efficacy of these newly evaluated bio-inspired molecules. In addition, the results presented in this dissertation address knowledge gaps that are beneficial to the development of effective inhibitors with the potential to replace existing therapeutics for these widespread maladies. Collectively, this dissertation presents research efforts aimed at inhibiting the formation of pathological crystals, focusing on an understanding of crystal growth under dynamic conditions and pathways to arrest growth via modifiers (i.e., inhibitors) that may serve as model compounds for preventative drugs.Item DECIPHERING THE MOLECULAR INTERACTIONS BETWEEN ANTIMALARIALS AND HEMATIN CRYSTAL SURFACES(2021-05) Ma, Wenchuan; Vekilov, Peter G.; Rimer, Jeffrey D.; Miljanić, Ognjen Š.; Donnelly, Vincent M.; Karim, Alamgir; Palmer, Jeremy C.; Hadjiev, Viktor G.Crystallization is the central process of materials synthesis in biological, geological, and extraterrestrial systems. Nature achieves remarkable diversity of shapes, patterns, compositions, and functions of the arising crystalline structures by combining simple strategies to control the number of nucleated crystal and the sizes to which they grow. In recent years, organic and mixed inorganic-aqueous liquids have received greater attention as alternative solvents for preparation of crystalline materials and separation (or purification) by crystallization, in particular for high-value materials such as pharmaceuticals and fine chemicals. In contrast to crystallization from purely aqueous solvents, the level of understanding of the fundamental processes of crystal growth from such liquids is severely limited. Issues that have been addressed are solvent selection, control of nucleation and growth (including seeding), solubility, transport regimes, and effects of ongoing solute synthesis, among others. In most cases, the optimization of the growth processes is carried out by trial-and-error or by mimicking pathways developed for other compounds. The lack of insight into the relevant fundamental mechanisms has emerged as a major obstacle to a rational approach to optimization and control of crystallization in organic and mixed solvents. Approximately 3.2 billion people are at risk of malaria. Hematin is released as a byproduct of hemoglobin catabolism during the malaria parasite lifecycle in human erythrocytes and detoxified by sequestration as innocuous hemozoin crystals. Hematin crystallization has been the most effective target for antimalarial drugs. Previous studies have found that the formation of hematin crystals follows a classical mechanism whereby new crystal layers are nucleated on top of existing ones and spread to cover the entire face. Direct observations established two classes of quinoline inhibition mechanisms. Amodiaquine and mefloquine were found to largely only bind to kink growth sites, where molecular units add to a step. This is the least effective mechanism of heme crystal growth inhibition. In a second mechanism, known as “step-pinning,” chloroquine and quinine bind on a flat surface face, inhibited new layer growth over broad areas of the crystal surface. We employed atomic force microscopy to monitor in real time the growth of steps on the (100) surface under the influence of varied drug combinations. This molecular-level view revealed that the action of quinine and amodiaquine is additive, indicating the lack on interaction between the action of each of these two drugs. Chloroquine and mefloquine weaken each other’s action, indicting antagonism in their suppression of hematin growth. These findings may serve as a basis for a lock-and-key approach to targeted drug development that is rooted in the physical basis for hemozoin crystal growth inhibition. One of the most relevant, yet the least investigated pathological crystal is cholesterol crystal, which is a principle component of gallstones(1-5) and atherosclerosis (6, 7). Prior studies have largely focused on the effects of phospholipids and bile salts on the formation of cholesterol crystals;(8) however, few groups have examined the mechanism(s) of crystallization. To this end, we conducted preliminary studies revealing cholesterol crystal growth occurs by a combination of classical and nonclassical (9) pathways involving the addition of monomer and precursors (i.e. clusters), respectively.Item Deciphering the Molecular Mechanisms of Organic Crystallization(2021-05) Chakrabarti, Rajshree; Vekilov, Peter G.; Rimer, Jeffrey D.; Palmer, Jeremy C.; Hadjiev, Viktor G.; Miljanić, Ognjen Š.Crystallization is a central part of several physiological, pathological processes, in the manufacturing of pharmaceuticals, fine chemicals, semiconductors, and many other engineered materials. Organic solvents are extensively used for crystallization of organic small molecules such as active pharmaceutical ingredients and organic molecules like porphyrins. Fundamental studies on organic crystallization are important as solution thermodynamics plays an important role in crystal growth rates. Solvent structuring and solute–solvent interactions are yet unexplored realms of organic crystallization, whereas aqueous crystallization where the H-bonds of water molecules play an important role of controlling the solution thermodynamics is relatively well understood. In this work we address the effects of factors like solute-solvent interactions, solvent viscosity, and solvent size. We determine the solution thermodynamics of etioporphyrin I crystallization from a line of five organic solvents highlighting the role of several solute- solvent interactions. We use these solubility measurements and complement them with X-ray diffraction and UV-vis spectroscopy of the solution phase. From the thermodynamics data we shed light on the solute-solvent interactions. For organic solvents with weak solvent -solvent bonds, solvent structuring at the crystal interface is weak resulting in a lower activation energy barrier for solute incorporation into the growth sites. We showed that the solute-solvent interactions govern the mode of solute incorporation into the growth sites. Results on the growth mechanism of etioporphyrin I reveal that an incoming solute molecule occupies a state where it is only partially attached to the kink and this state precedes full incorporation. The stability of this intermediate state dictates the activation barrier for growth and, ultimately, the crystal growth rate. We explored the composition of the solute species that exist in the solution and incorporate in the crystal and found out that, at least in one case, that of etioporphyrin I, a continuum of solute dimers are present in the solution and reform on their way to a kink into a growth competent conformation. This latter mechanism fully deviates from the assumption of the classical theories of crystal nucleation and growth, which posit that only solute monomers can associate to the kinks. On exploring the mechanisms employed by foreign additives to impact the propagation of steps on a crystal surface we demonstrate that certain modifiers may exert dual action, by blocking both the kinks and the steps. These novel finding will help us control crystallization process development with desired end product features like crystal shape, size and from.Item Developing Organic Free Crystallization Pathways for the Optimization of Zeolite Catalysts(2021-12) Jain, Rishabh; Rimer, Jeffrey D.; Bollini, Praveen; Robertson, Megan L.; Jacobson, Allan J.; Zones, Stacey I.Zeolites are an essential class of crystalline porous materials with a wide range of applications. A core objective of optimizing zeolites is to produce materials with physicochemical properties and corresponding performances that exceed conventional counterparts. This places an impetus on elucidating and controlling processes of crystallization where one of the most critical design criteria is the ability to prepare zeolite crystals with ultrasmall dimensions to mitigate the deleterious effects of mass transport limitations. Zeolite crystallization predominantly occurs by nonclassical pathways involving the attachment of complex (alumino)silicate precursors to crystal surfaces, yet recurrent images of fully crystalline materials with layered surfaces comprised of nanometer-sized steps are evidence that growth also occurs by a classical route of molecule (monomer) attachment. Recent studies have shown that a controlled switch from nonclassical to classical pathways can alter the anisotropic rates of crystallization with concomitant impact on material properties that affect their performance in commercial applications; however, few studies identify conditions under which zeolites grow by a purely classical mechanism. Seed-assisted approaches in zeolite synthesis differ from classical processes in that the seeds tend to dissolve, giving rise to an unknown memory of the parent crystal structure that facilitates the nucleation of the daughter. It has been hypothesized in literature that a shared structural feature, such as a composite building unit, between the parent and the crystals produced from a non-seeded growth solution results in identical parent-daughter framework types. This Thesis focuses on how seed-assisted syntheses impact zeolite properties such as size, morphology, structure, and defects. We observe that the molar composition of the growth mixture and the properties of the seed crystals play a significant role in controlling the kinetics of nucleation and the trajectory of interzeolite transformations. Furthermore, we observe that seeds offer unique routes to achieve small crystal sizes and distinct morphologies in comparison to many conventional syntheses. Advantages of seeding include shorter synthesis time and the ability to reduce or eliminate the need for organic structure-directing agents, thereby providing a facile and efficient route to design zeolites for various industrial applications. The fundamental mechanisms underlying zeolite seed-assisted crystallization are complex and elusive; however, our study provides new insight into these processes and highlights the important role of kinetics in governing parent-daughter (or seed-product) relationships. Furthermore, we use high temperature atomic force microscopy (AFM) to image zeolite crystal surface growth in situ. We report time-resolved images of 2-dimensional growth demonstrating layer generation by three distinct mechanisms, including nucleation from the edges of surface defects. Our findings reveal that silica nanoparticles in the growth medium incorporate into advancing steps on crystal surfaces to generate defects (i.e., amorphous silica occlusions) that largely go undetected in literature. In situ AFM measurements also show the dominance of gel mediated crystal growth in the case of faujasite zeolite syntheses.Item Development and Characterization of Magnetoelectric Nanocomposites and Thin-Film Laminates for Biosensor Applications(2022-05-12) Safi Samghabadi, Farnaz; Litvinov, Dmitri; Chang, Long; Ruchhoeft, Paul; Bao, Jiming; Robles Hernandez, Francisco C.Magnetoelectric (ME) effect has a number of promising applications in sensors, energy harvesting, antennas, drug delivery, etc. In ME materials the electric polarization can be controlled by varying the material’s magnetization state and, conversely, varying the electric polarization affects the material’s magnetization state. The ME effect has been observed in a few single-phase multiferroic materials; however, the effect is relatively weak at room temperature, which hampers useful applications. More robust ME behavior has been achieved in composites that combine mechanical coupled magnetostrictive and piezoelectric materials arranged in a matrix. These composites can be produced in versatile connectivity configurations/matrices with a wide choice of materials, volume fraction, and microstructure and can exhibit several orders of magnitude stronger ME effect than single-phase ME materials. In this work, the development and characterization of two different types of multi- phase ME materials, nanocomposites, and thin-film laminates are investigated. Mag- netoelectric composites of CoFe2O4-BaTiO3 are synthesized using commercially avail- able CoFe2O4 and BaTiO3 precursors with employing the inexpensive and scalable process based on ball-milling and high-temperature sintering/annealing for drug de- livery applications. ME thin film laminates of AlN and FeGaZr also are developed and utilized as the building block for fabrication of a suspended ME sensor for integration into a magnetic field sensor.Item DEVELOPMENT OF FLEXIBLE TRIBOELECTRIC NANOGENERATORS AND SOLID-STATE LITHIUM-ION POLYMER BATTERIES FOR ENERGY CONVERSION AND STORAGE PURPOSES(2022-12) Cheng, Kuan; Ardebili, Haleh; Karim, Alamgir; Ghasemi, Hadi; Bao, Jiming; Ryou, Jae-HyunConventional techniques to harvest and store energy are challenged by the ever-increasing demand for versatile forms of electrical energy caused by the rapid expansion of the Internet of Things (IoTs). As emergent solutions, flexible triboelectric nanogenerators (TENGs) and lithium-ion batteries (LIBs) have been invented and extensively studied in recent years. Different TENGs are fabricated to scavenge mechanical energy from most natural sources and human motions, making them portable solutions to energy generation on-demand. On the other hand, rechargeable LIBs play critical roles in the evolution of energy over 50 years, owing to its abilities to store massive amount of energy, lay the foundation for portable smart devices, and make possible a fossil fuel-free world. At the beginning of this dissertation, latest efforts that incorporating low-dimension carbon materials with TENG systems will be systematically reviewed. Carbon materials, including graphene and carbon nanotube, can bring many synergistic properties to TENGs, such as output enhancement and multifunctionality. They are poised to further the reach of TENG applications and make a positive impact on common issues related to TENG technology. The second section is to present a robust route to fabricate flexible TENGs with multifunctionality by nano-patterning thermoplastic polyurethane (TPU) thin films. Topographically optimized TENGs could promote higher power generation while preventing biofilm formation without using any chemical additives. Analysis of pattern amplitude and wavelength correlation to output power is uniquely provided for a deeper understanding of how patterned TENGs enable peak performance. The last part of this work presents the fabrication and characterization of lithium-ion batteries based on solid-state polymer electrolytes. Efforts made to substitute conventional liquid electrolyte and plastic separators make a great accomplishment on mechanical properties and safety aspects of LIBs. Fluoroethylene carbonate (FEC) has been proved as an effective electrolyte additive, which helps building LIB systems with ultra-high capacity and low self-discharge. Comprehensive electrochemical properties along with thermal properties of LIBs will be closely scrutinized in this work.Item Diagnostic Studies of Silicon and Silicon Dioxide Etching in Fluorine and Chlorine-Containing Inductively Coupled Plasmas(2021-05) Arora, Priyanka; Donnelly, Vincent M.; Economou, Demetre J.; Nikolaou, Michael; Ruchhoeft, Paul; Bao, JimingPlasma etching processes are widely used to produce patterns in the fabrication of microelectronic devices. The recent development of micro-/nano- technologies for micro-electro-mechanical systems, as well as the reduction of critical dimensions in transistors towards 7 nm and below, has brought out the need to control plasma etching processes. The very severe requirements in terms of etch rate, selectivity, profile control and surface damage caused by ion bombardment have been at the origin of the development of mechanistic studies by means of plasma diagnostics and surface analysis. In the present study, chemical reaction probabilities, defined as the number of silicon atoms removed per incident fluorine atom, have been investigated in mixtures of NF3 and SF6 plasmas in an inductively-coupled plasma reactor. Fluorine atom densities were measured by optical emission actinometry, and isotropic etching rates were measured by the degree of undercutting of SiO2-masked silicon, using cross-sectional scanning electron microscopy (SEM). The F atom reaction probabilities derived from isotropic etching rates indicate a ~30-fold higher reaction probability in SF6 plasmas compared with values in NF3 plasmas. This surprising enhancement of reaction probabilities for F with Si in SF6 plasmas is further investigated based on the mechanism of adsorbed sulfur acting as a catalyst to greatly enhance the etching rate of Si. Further, we discussed the use of glow discharge optical emission spectroscopy (GD-OES) for in-situ, real-time characterization of surfaces exposed to plasmas. A small coupon piece was mounted on an rf-biased electrode and inserted into an opening in the reactor wall. Silicon or SiO2 substrates on a separately rf-biased electrode were etched in an inductively-coupled plasma (ICP) of Cl2/Ar/O2 or C4F8/O2, respectively. Pulsed bias was applied to sputter the surface of the coupon piece. Optical emission from the region above the coupon surface was collected and spectrally resolved. The difference in intensity between the coupon bias on and off condition was used to determine what species were present on the surface. A quantification method for converting emission intensities into atomic composition depth profiles is presented.Item DIELECTRIC POLYMERS AND NANOCOMPOSITE THIN FILMS FOR HIGH ENERGY STORAGE CAPACITORS(2022-08-09) Veerasamy, Jagadesh; Karim, Alamgir; Shaffer, Devin L.; Ghasemi, HadiImproving the present technology's energy storage capacity and efficiency is crucial for society's sustainable development and progress. The different forms of energy storage devices include fuel cells, batteries, supercapacitors, and electrostatic capacitors. Batteries and fuel cells have high energy density but low power density. Capacitors have high power density but low energy density. If the energy density of capacitors increases, they will be suitable energy storage devices with better performance and high efficiency. Also, capacitors are more compact than batteries and fuel cells for unit energy density. Polymer dielectrics are suitable for pulsed power applications due to their high breakdown strength, low cost, low loss, flexibility, and good processability. The energy density of the capacitor can be increased by enhancing its breakdown strength and dielectric permittivity. The energy storage capacity of dielectrics has a quadratic dependence on breakdown strength. This study used two strategies to increase polymer dielectric breakdown strength and permittivity. We studied the effect of filler concentration in nanocomposite dielectrics in enhancing dielectric permittivity without compromising its breakdown strength. Polymer-Grafted-Nanoparticles have performed much better than Polymer-Nanoparticle blend films. PGNPs have shown an increase of 40% in breakdown strength due to the creation of well-defined barriers which delay the breakdown propagation. Also, the fillers contribute to the enhancement in permittivity, which is 3.5 times higher than pure PMMA films. Another method employed was free volume reduction of polymers by reducing the chain end density. We used Polystyrene (PS) and Cyclic polystyrene (cPS) for the study. cPS has shown a 50% increase in breakdown strength and almost 80% increase in discharge energy density compared to PS. Also, thermal stability analysis of PS and cPS films with nanopatterned waves shows that cPS films are more thermally stable than PS films. These strategies to enhance the breakdown strength and dielectric permittivity, along with the novel insights into the dielectric failure, will pave the way for the design of high energy and power density dielectric capacitors for fulfilling the energy demand of the next generation.Item Effect of H2 Plasma Conditioning on Anodized Al Chamber and Quartz Discs(2021-05) Zhou, Yingliang; Donnelly, Vincent M.; Economou, Demetre J.; Nikolaou, Michael; Wolfe, John C.; Ruchhoeft, PaulIn this work, two projects related to semiconductor integrated circuit processing are investigated: (1) H2 plasma conditioning of anodized Al walls of a high density remote plasma source; (2) H2 plasma erosion and roughening of quartz discs. In the first project, experiments were performed in a high power-density (10 – 40 W/cm3), purely inductive plasma in an anodized-Al coated, transformer coupled toroidal plasma (TCTP) source at a pressure of 0.8 Torr. Optical emission spectroscopy was employed to monitor the time-resolved evolution of species from the walls. 4%H2/Ar or 3%N2/9%H2/Ar plasmas, alternated with Ar, O2/Ar or NF3/Ar “cleaning” plasmas were investigated. In Ar plasmas, the H-to-Ar intensity ratio decayed to base line in a stretched exponential manner over ~0.5-1.5 min, reflecting out-diffusion of hydrogen from the prior hydrogen-containing plasma exposure, with larger signals observed after longer exposure to the hydrogen-containing plasma. Compared to Ar plasmas, the amount of evolved hydrogen increases up to ten-fold in NF3/Ar plasmas, while it decreases five-fold in O2/Ar plasmas with no dependence on the duration of the hydrogen-containing plasma. It was shown that formation of HF and OH in NF3/Ar and O2/Ar plasmas does not significantly affect H Balmer- emission intensity, and that the enhancement or suppression is due to F and O impingement on and diffusion into the anodized Al. It is proposed that F reacts with H in the layer to for HF, which diffuses out of the film, while O reacts with diffusing H and binds it as immobile AlOH. A time-dependent 1-D diffusion model was developed, and reproduces most of the observed effects with a H and/or H2 diffusion coefficient that increases as a function of distance from the surface, ascribed to the columnar, porous nature of anodized Al. The second project presents a study of the erosion of SiO2 in the same TCTP. At 0.5Torr, quartz samples were exposed to plasma densities of 1-3 x 1013cm-3 and H atom temperatures of 4000-8000K. Short (e.g. 1 min) H2/Ar plasma exposure followed by long (9 min) plasma-off cool-down periods resulted in higher etching rates and increased erosion, compared to long (e.g. 1 hr) continuous plasma operation, and was ascribed to the higher substrate temperatures reached with continuous plasma operation and a negative dependence of the etching rate on temperature. When exposure to H2/Ar plasmas were alternated with O2/Ar plasmas and plasma–off periods, the etching rate was reduced to near-zero and surface roughness was much reduced. N2/Ar plasma treatments were less effective in reducing the etching rate, while surface roughness was nearly eliminated. A proposed mechanism involves penetration of H below the surface and insertion into Si-O-Si linkages to form SiH and SiOH groups, and crack propagation that leads to shedding of small silica particles. Periodic exposure to O atoms hydroxalizes sub-surface and reforms Si-O-Si linkages, and generates H2O that presumably desorbs.Item Electrodeposition of CoNiFeX magnetic Films with Low Magnetic Losses for Power Applications(2023-05-08) Solanki, Dhaivat; Brankovic, Stanko R.; Robles Hernandez, Francisco C.; Ruchhoeft, Paul; Bao, Jiming; Chang, LongElectromagnetic induction is essential for functioning of the analog circuits used in cell phones, MEMS devices and other power related electronics. In order to meet the demand of higher efficiency and minimum magnetic losses in IC devices, we have developed solution chemistry for electrodeposition of CoNiFeX (X=S,P,B,V) thin films with high magnetic moment (HMM) and permeability with higher than 100μΩ-cm resistivity; higher than 1.7 T magnetic moment. CoNiFeX alloys are fully compatible with existing manufacturing concepts in semiconductor industry. Direct current (DC) and pulse current (PC) deposition methods to produce CoNiFeX alloys is employed to demonstrate control over BCC crystal structure by tuning transport conditions during electrodeposition. The BCC structure of CoNiFeX alloys is characterized with average grain size of 10-20 nm which consequently yields coercivity values of CoNiFeX alloys between 8-15 Oe at 500 nm film thickness. CoNiFe alloys produced by DC and PC deposition have magnetic moment higher than 1.7 T, which is not significantly diminished with addition of X (X=S,P,B,V) as resistivity controlling phase. More than 100% increase in the resistivity of deposited CoNiFeX alloys is demonstrated with controlled concentration of X burring molecules and Fe3+ ions as hydroxide precipitating agent without deterioration in magnetic properties. All samples exhibit shiny surface finish and low stress. Electrodeposition process is scaled up with customized setup to build thin film inductor devices on 4 in wafer, fabricated at Nanofabrication Facility at the University of Houston. Thin film inductor devices with CoNiFeX cores are tested at Intel Corporation facility in wide frequency range (1 MHz to 1 GHz). More than 70% improvement in induction efficiency compared to air core devices is observed when CoNiFeX magnetic cores of various geometry are introduced in device design. Direct measurement of permeability and losses for DC deposited CoNiFeX alloys is performed by resonant cavity setup, which illustrate reduction in losses at 100 MHz frequency due to resistivity improvement by incorporation of X phase in CoNiFeX alloys.Item Elucidating Storage and Oxidation Mechanisms on Pd and Pt Catalysts: From Single Atoms to Nanoparticles(2023-05-08) Solanki, Surya Pratap Singh; Grabow, Lars C.; Harold, Michael P.; Rimer, Jeffrey D.; Epling, William S.; Dauenhauer, Paul J.Metal based catalysts have played a crucial role in the development of industrial catalytic processes, including the Haber-Bosch process for ammonia synthesis that uses metal-based catalyst. Platinum group elements have emerged as exceptional catalysts for various applications, including pollution abatement, battery materials, and the production of value-added chemicals. These metals are often dispersed as isolated single atoms or nanoparticles on a support to increase their effectiveness. The activity of these sites varies depending on the reaction, with Pd single atoms exchanged in zeolite pores being more favorable for NOx adsorption and larger Pt nanoparticles being preferred for methane activation. The automotive industry faces a significant challenge in reducing NOx emissions from diesel exhaust at low temperatures (<200 ℃). Passive NOx adsorber (PNA) emerged as a potential technology that uses Pd-exchanged zeolite materials to reduce NOx in diesel engine exhaust. Density functional theory (DFT) and reaction experiments were used in the current work to understand reaction mechanisms. The findings show that water oxidizes NO to NO2, resulting in the reduction of Pd which acts as storage site with stronger NO binding. However, the combined presence of water and CO can deactivate the catalyst. This understanding offers a new direction for the improvement of PNA material. Recent advancements in dynamic catalysis have demonstrated enhanced catalytic performance compared to static conditions. Dynamic reactor experiments along with DFT were used in this study to explore avenues to maximize hydrogen production during methane partial oxidation on Pt-based catalysts. The study found that feed modulation with varying concentrations of oxygen could enhance hydrogen production, and the mechanistic investigation confirmed the role of hydroxyl groups at the metal support interface in improving hydrogen selectivity. Additionally, DFT calculations were used to understand the electronic properties of Pt-based catalysts subjected to dynamic surface charge environments in catalytic condenser devices. Varying surface charge on the catalyst could help increase reaction rates in dynamic conditions. These findings provide valuable insights for the development of more efficient and effective dynamic catalytic processes, which are critical for sustainable growth while minimizing environmental impact.Item Elucidating the Ligand-induced Phase Behavior of Polymer-grafted Nanoparticle Thin Films(2022-05-11) Wu, Wenjie; Karim, Alamgir; Robertson, Megan L.; Palmer, Jeremy C.; Shaffer, Devin L.; Ghasemi, HadiHigh molecular mass polymer-grafted nanoparticles (PGNPs) have attracted significant attention in the past few decades with the potential to design next-generation polymer nanocomposites with enhanced optical and mechanical properties and thermal stabilities. A critical requirement for these new nanoparticles and their associated applications is the control of their morphology and the dispersion in the system. However, subsequent studies have demonstrated that the mobilities of the high molecular mass PGNPs decrease significantly, which leads to poor or no control over their phase morphologies. In this study, we aim to overcome this scientific problem and control the spatial organization of those materials via the interactions between the grafted polymer layer and the polymer matrix in both smooth and nanopatterned films. We firstly investigate a binary high molecular mass PGNPs blends using a direct immersion annealing method (DIA) that allows for facile tuning of the PGNPs phase boundary, phase separation kinetics, and the ultimate scale of phase separation after a sufficient ‘aging’ time. We show that the phase morphologies could be readily switched between phase-separated and homogenous states by changing the thermodynamic conditions of DIA solution quality. To overcome the low-mobility problem and exert exquisite control over the distribution of high molecular mass PGNPs in a nanopatterned film, we developed a solvent vapor annealing soft lithography (SVA-SL) method. We revealed that the minimization of the entropic free energy from the topographic nanoimprint patterning along with the increased mobilities from solvent vapor drives the high molecular mass PGNPs to the ‘mesa’ region of nanopatterned films. Furthermore, reversible partitioning (selective vs. no partitioning) in a nanopatterned film can be facilely achieved by introducing enthalpic interactions into the system. Both the SVA-SL processing method and the reversible partitioning via tunning the interaction parameter are important. It allows for facile imprint patterning of PGNP materials and large-scale organization of the “sluggish” high molecular mass PGNPs. These approaches, along with the DIA method to control the morphologies of smooth film, have great potential to design the nanocomposite films with the enhanced thermo-mechanical property of the resulting films, and a corresponding extended range of potential nanotech applications.