Electronic Theses and Dissertations (2010 - Present)
Permanent URI for this communityhttps://hdl.handle.net/10657/1
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.
Questions?
Feel free to contact us should you have any questions or comments.
Browse
Browsing Electronic Theses and Dissertations (2010 - Present) by Department "Chemical and Biomolecular Engineering, Department of"
- Results Per Page
- Sort Options
Item A Compact and Efficient Steam Methane Reformer for Hydrogen Production(2012-08) Quon, Willard; Richardson, James T.; Harold, Michael P.; Jacobson, Allan J.; Epling, William S.; Rixey, William G.; Fleischer, MiguelA small-scale steam-methane reforming system for localized, distributed production of hydrogen offers improved performance and lower cost by integrating the following technologies developed at the University of Houston; (1) Catalyzed steam-methane reforming on ceramic foam catalyst substrates. (2) Coupling of reformers to remote heat sources via heat pipes instead of heating by direct-fired heaters. (3) Catalytic combustion of methane with air on ceramic foam substrates as the heat source. Each of these three technologies confer benefits improving the efficiency, reliability, or cost of an integrated compact steam-methane reforming system. A prior 2-D computer model was adapted from existing FORTRAN code for a packed-bed reactor and successfully updated to better reflect heat transfer in the ceramic foam bed and at the reactor wall, then validated with experimental heat transfer and reaction data for use in designing commercial-scale ceramic foam catalytic reactors. Different configurations and sizes of both reformer and combustor reactors were studied to arrive at a best configuration for an integrated system. The radial and axial conversions and temperatures of each reactor were studied to match the heat recovery capability of the reformer to the heat generation characteristics of the combustor. The vetted computer model was used to size and specify a 500 kg/day hydrogen production unit featuring ceramic foam catalyst beds integrated into heat pipe reactors that can be used for multiple end users, ranging from small edible fats and oils hydrogenators to consumer point of sale hydrogen fueling stations. The estimated investment for this 500 kg/day system is $2,286,069 but is expected to drop to less than $1,048,000 using mass production methods. Economic analysis of the 500 kg/day hydrogen production system shows that it is not presently competitive with gasoline as a transportation fuel, but the system is still economically attractive to stationary fuel cell applications or small chemical users with a delivered hydrogen price as low as $1.49/kg, even with a 10% IRR that includes investment recovery, depreciation, taxes, etc.Item A Free Heme Perspective to Sickle Hemoglobin Polymerization(2015-05) Aich, Anupam; Vekilov, Peter G.; Rimer, Jeffrey D.; Lubchenko, Vassiliy; Varadarajan, Navin; Dinu, Bogdan R.Sickle cell hemoglobin (HbS) polymerization is considered to be the primary pathogenic event in the sickle cell anemia. Many cellular and molecular factors have been identified so far as contributor towards the polymerization event. The free heme, prosthetic group of hemoglobin, is one such small molecule which has been previously shown to enhance the polymerization by orders of magnitude and removal of free heme from the supersaturated HbS solution stops the polymerization completely. In the present study we set out to investigate the free heme concentrations in normal adult and sickle cell erythrocytes. We used an enzymatic chemiluminescence assay for the determination of free heme in erythrocytes. The average free heme concentration in sickle cell patients is 44±9 M, in sickle trait individuals—33±4 M, and in healthy adults—20±2 M. We also found that heme release is autocatalytic and results from spectral determination of methemoglobin percentages over time indicate towards well known higher susceptibility of sickle hemoglobin to autoxidation as mechanism for the release. We propose a link between physiological oxidative stress and autocatalytic heme release through imbalance in the reductase homeostasis in the erythrocytes. Inherent kinetic instability of autocatalytic processes may contribute to the known variability of the patients. Looking at the previous polymerization experiments and combining the current results we propose free heme and its release factors to be new targets for therapeutic and drug discovery for sickle cell anemia disease. We also provide a preliminary design of a cell separation device based on deformability induced margination flow for fractionating sickled and unsickled cells in 100% deoxygenated condition. If completed in future, this device promises a biomarker detection platform for sickle cell disease.Item A MICROFLUIDICS APPROACH TOWARDS THE INVESTIGATION OF FREE HEME EFFECTS ON SICKLE CELL HEMOGLOBIN POLYMERIZATION(2012-05) Aich, Anupam; Vekilov, Peter G.; Rimer, Jeffrey D.; Lubchenko, VassiliySickle cell hemoglobin (HbS) polymerization is considered to be the primary pathogenic event in sickle cell anemia. In this work we aim at fabricating an integrated microfluidic device with a localized microheater for the study of HbS polymerization kinetics. We developed fabrication recipes for both an SU-8 based microchannel and a thin film resistive Cu-Cr microheater. We calibrated the heater with both infrared camera and Peltier element and found that a limit exists on the power input to the heater. Computer simulations were carried out to find time resolution of heating process and also the temperature field. Bonding recipe for chip integration has been developed. Surface characterization techniques such as AFM and measuring contact angle with goniometer were used to confirm that oxygen plasma enhances hydrophilicity in SU-8 layer. We found the bonding temperature from differential scanning calorimetry data. Plug flow of liquid in channel has been observed.Item A physical approach for drug delivery: magnetically-driven nanospearing(2016-08) Yang, Zhen; Ren, Zhifeng; Willson, Richard C.; Nikolaou, MichaelDrug delivery that enables spatial and temporal control is essential to improve pharmacotherapy. The emergence of nanotechnology has spurred the development of drug delivery. Herein, we develop a physics-derived approach, magnetically-driven nanospearing to address challenges associated in drug delivery. Template wetting is employed to formulate a poly-ε-caprolactone nanorod-based spear system that incorporates functional agents including amine groups, magnetic nanoparticles, fluorescein molecules, and gold nanorods. The multifunctional polymeric nanospear provides a promising delivery system for drug delivery. Overall, the amine-group-functionalized surface favors loading of negatively charged molecules, and cellular delivery of ATP is successfully achieved. Gold nanorods functions to enable a photothermally-responsive release behavior for the polymeric spear system. It is also found that the photothemal heating only induces localized structural changes in the polymeric matrix thus triggers surrounded encapsulant release. This localized heating is beneficial to maintain stability of the whole spear system. This work provides an alternative way for cell internalization and a promising delivery system for targeted delivery and controlled release.Item A Rational Design Approach for Tailoring Zeolite Crystal Morphology(2013-12) Lupulescu, Alexandra I. 1987-; Rimer, Jeffrey D.; Harold, Michael P.; Shantz, Daniel F.; Jacobson, Allan J.; Epling, William S.Over the last century, zeolites have become ubiquitous materials in a wide array of applications due to properties such as high acidity, large surface area, and size/shape restriction. Although they have a longstanding precedent of exceptional performance, further optimization has been limited due in part to a lack of fundamental understanding of their growth mechanism(s). Knowledge of these processes can be used to address key issues, such as diffusion limitations, that arise from the suboptimal orientation of pores along the longest crystal dimension. Despite advances toward this goal, an efficient and inexpensive technique capable of producing zeolite crystals with tailored morphology remains elusive. To this end, silicalite-1 (MFI framework type) was chosen as the platform for a novel synthesis scheme that employs zeolite growth modifiers (ZGMs), or molecules that selectively bind crystallographic faces and minimize growth in the normal direction by blocking the attachment of incoming building units, resulting in a tuned zeolite crystal habit. ZGMs that bind to each of the three silicalite-1 faces were indentified. Furthermore, this study revealed several highly potent molecules capable of reducing MFI [010] thickness (preferred pathway for sorbate diffusion) by more than an order of magnitude. This design approach was extended to a 1-dimensional zeolite (LTL framework type). In this study, systematic testing of ZGMs aimed to identify key aspects responsible for selective ZGM-LTL crystal surface binding, such as the spatial distribution and density of terminal silanol groups, and hydrophobic and electrostatic interactions. The analysis of polyols resulted in the identification of two heuristic guidelines that can lead to enhanced ZGM-crystal affinity: an optimal C3 carbon length, as well as 1-3 alcohol group spacing. Lastly, we developed a new in situ AFM protocol capable of observing the silicalite-1 growth mechanism under realistic synthesis conditions (elevated temperature, high pH, and long times). This technique provided the first direct confirmation that nanoparticle and silica molecule attachment, as well as surface restructuring due to Ostwald ripening, are the dominant silicalite-1 growth modes. Furthermore, the information gleaned here will be used to guide future optimization of ZGM design in order to produce zeolites with enhance physicochemical properties.Item A Simulation Approach to Thermodynamics in Interfacial Phenomena(2013-05) Pandey, Yogendra Narayan 1982-; Doxastakis, Manolis; Krishnamoorti, Ramanan; Stein, Gila E.; Ardebili, Haleh; Kulkarni, YashashreeIndustrial applications such as production of high performance polymer-nanocomposites, semiconductor fabrication, and catalysis involve molecular level phenomena governed by interfacial interactions. Precise control of these interactions will leverage the performance of materials in these applications. However, the ability to tailor the molecular characteristics is hindered by incomplete understanding of the controlling factors. This dissertation is broadly divided in three parts discussing the development and application of modern computational methods to elucidate such characteristics. In the first part, detailed atomistic simulations of polymer-nanoparticle systems are performed by coupling preferential sampling techniques with connectivity-altering Monte Carlo algorithms to address the challenges in modeling polymer melts in proximity to a solid. The results reveal that polymer architecture holds a prominent role in systems with nanoscopic particles. Furthermore, a scheme for developing coarse-grained models of polymers with specific chemistry in contact with the solid surface is presented and quantitatively evaluated. These models are necessary to address the larger length scales required for study of polymer-particle mixtures. Interfaces and substrate interactions play an important role for increasingly thinner polymer films employed in the semiconductor industry. There is a clear need to develop predictive models capable of describing reaction-diffusion phenomena in chemically-amplified resists and analyze their performance as a function of film thickness. In this dissertation, using mesoscopic models it is found that a central aspect governing reactions is the anomalous diffusion of the photogenerated acid. The anomalous diffusion coupled with a simple second-order acid annihilation scheme quantitatively captures experimental data for all practical conditions - with only two adjustable parameters. The need to combine the developed scheme with substrate interactions is demonstrated. Finally, the mechanism of zeolite crystal growth in solutions in the presence of growth modifiers is probed by employing atomistic simulations. It is hypothesized that molecules preferentially bind to specific crystal surfaces, which alters the crystal morphology. Using free energy calculations, the affinity of these molecules to interact with model zeolite surfaces is estimated. Distinct free energy minima and orientations of the inhibitor molecule in these minima are characterized and quantified providing a unique molecular understanding of the phenomena.Item Acid Transport in Chemically Amplified Photoresists(2015-05) Patil, Abhijit; Stein, Gila E.; Harold, Michael P.; Balakotaiah, Vemuri; Ruchhoeft, Paul; Baldelli, StevenChemically amplified resists (CARs) are a class of lithographic materials that enable high-throughput semiconductor patterning. CARs are comprised of a glassy polymer resin (reactant) loaded with a photoacid generator (inactive catalyst). Patterns are formed by locally activating a strong acid catalyst with light, and then heating the film to promote catalyst diffusion coupled to polymer deprotection. While CARs have been studied for more than 40 years, there are no quantitative models that predict spatial extent of reaction with nanoscale resolution. This poses a significant roadblock for materials design and optimization, as next generation manufacturing processes will target sub-10 nm feature sizes. We studied reaction kinetics in a model CAR using infrared absorbance spectroscopy and spatially-resolved stochastic simulations. CAR formulas were based on poly(4-hydroxystyrene-co-tertbutyl acrylate) resin, onium salt photoacid generator, and an inert plasticizer. Deprotection rates were measured as a function of catalyst loading, plasticizer loading, and temperature (always below the polymer’s glass transition). Experimental data were interpreted with a simple and efficient model based on anomalous acid diffusion and a phenomenological second-order acid loss. This model predicted key aspects of the macroscopic deprotection rates, such as fast reaction at short times, slow reaction at long times, and a nonlinear dependence on acid loading. Reducing the size of the acid-counterion pair, adding an inert plasticizer, or increasing the temperature will enhance acid transport rates and reduce the anomalous character. These behaviors suggest that acid diffusion is coupled to dynamical properties of the glassy polymer resin. To complement analysis of bulk kinetics, we simulated nanopattern formation using the anomalous acid transport model, and then compared predictions with experimental line widths. The simulations include a spatial distribution of acid catalyst that reflects the exposure statistics in electron beam lithography experiments. However, while experiments include a pattern development step that dissolves the reacted polymer, the simulations do not yet have this module. Nevertheless, the predicted and measured pattern dimensions are in qualitative agreement, suggesting that lithographic resolution in CARs might be predicted from simple spectroscopy measurements coupled to spatially-resolved simulations.Item Advanced Control of Ion and Electron Energy Distributions and Investigation of in-situ Photo-Assisted Etching(2014-05) Zhu, Weiye 1987-; Donnelly, Vincent M.; Economou, Demetre J.; Stein, Gila E.; Wolfe, John C.; Ruchhoeft, PaulPrecise control of ion energy distribution (IED) is critical to achieve highly selective, low damage etching. A novel approach to control IED using pulsed plasma with synchronously pulsed dc bias on a boundary electrode in Ar gas is first presented. Synchronization of the dc bias applied during the afterglow of a pulsed plasma and the plasma rf power resulted in a double-peaked IED. The mean energies of the two peaks, as well as the peak separation, were controlled by adjusting the applied dc bias and the discharge pressure. Nearly mono-energetic IEDs can be extracted in the afterglow of a pulsed plasma. With precisely controlled IEDs, a new, important phenomenon is reported: photo-assisted etching of p-type Si in chlorine-containing plasmas. This mechanism was first discovered in mostly Ar plasmas with a few percent added Cl2. A substantial etching rate was observed, independent of ion energy, when the ion energy was below the ion-assisted etching threshold. Experiments were carried out with light and ions from the plasma either reaching the surface or being blocked, showing conclusively that the “sub-threshold” etching was due to photons. Sub-threshold etching rates scaled with the product of surface halogen coverage and Ar emission intensity. Etching rates measured under MgF2, quartz, and opaque windows showed that sub-threshold etching is due to photon-stimulated processes on the surface, with VUV photons being much more effective than longer wavelengths. In an effort to manipulate the electron energy distribution function (EEDF) and plasma density, a plasma reactor incorporating dual tandem plasma sources separated by a grid is presented. As feature sizes shrink to the nanometer scale, tuning the EEDF becomes increasingly important for both plasma etching and deposition. By pulsing the main plasma source, while maintaining the tandem source in continuous wave mode, a low electron temperature of ~1 eV at high plasma density (1011 cm-3) was realized. This was achieved by applying a dc bias to a boundary electrode in the tandem source. The electron temperature in the afterglow period could be controlled by changing that bias voltage.Item Advanced Pulsed Plasma Techniques(2018-08) List, Tyler Lee; Donnelly, Vincent M.; Economou, Demetre J.; Nikolaou, Michael; Ruchhoeft, Paul; Wolfe, John C.A method for controlling ion energies on insulating surfaces using pulsed plasmas is presented. DC pulses are periodically applied to the chuck holding the substrate in the afterglow of a pulsed plasma to attract an electron swarm to the sample surface. Surface potential measurements validated the proposed method and helped investigate the effect of changing pulse width, amplitude, and frequency of the chuck bias on the resulting surface potential waveform. Retarding field energy analyzer measurements were performed and corrected for the non-uniform charge distribution that prevailed at an applied RF frequency less than the ion sheath transit frequency. Etching of quartz discs and 1000nm-thick SiO2 films on Si wafers was also performed. An etching threshold was found at 100 V chuck bias for both types of substrates, beyond which the etching rate increased proportionally with the square root of chuck bias. No clear effect of the boundary bias on etching rate was seen. Time-resolved UV absorption of pulsed electronegative fluorocarbon and chlorine inductively-coupled plasmas is presented. The time-dependent variation of Si-byproducts were verified against previous publications as well as the limits of the current apparatus. The lack of decay of CF2 in 100 Hz and 500 Hz pulsed C4F8 plasmas was also seen. Time-dependent studies of power-modulated chlorine inductively-coupled plasmas are presented. Power at 13.56 MHz applied to the plasma was modulated between high and low power states. Time-resolved optical emission, power delivery, and Langmuir probe measurements revealed at least two periodic steady-state conditions upon switching from high to low power: a “normal” mode in which electron temperature (Te) remains constant, while electron and ion number densities (ne and n+) and optical emission spectroscopic (OES) intensities smoothly drop to a level roughly equal to the fractional drop in power, and an “abnormal” mode in which ne, n+ and OES intensities plummet before rising to values commensurate with the drop in power. Whether the plasma operates in the normal or abnormal mode is sensitive to settings on the matching network and is also a function of pressure and pulsing parameters.Item Applications of Inverse Theory and Machine Learning in Rate/Pressure Transient Analysis(2015-08) Chaudhary, Nitinkumar Lalitkumar; Lee, W. John; Dindoruk, Birol; Weglein, Arthur B.The applicability of decline relations (empirical or analytical) in rate transient analysis (RTA) to forecast the production of an unconventional reservoir depends on the validity of assumptions made during the development of these decline relations. None of the present rate decline relations used to estimate the ultimate recovery (EUR), are conceptually applicable in a reservoir where hydrocarbon production exhibits variable rate and pressure. We propose a new methodology based on an inverse deconvolution problem formulation to accurately forecast performance in such reservoirs. To handle the instability in deconvolution, we propose the use of elastic net regularization and a new weighting scheme in our deconvolution algorithm. In this work, we propose a non-parametric density-based outlier detection method, which identifies outliers by classifying the data into clusters and assigning local outlier factors to the individual data points. We validate our method using synthetic examples generated using numerical models of multi-stage hydraulically fractured wells in unconventional reservoirs. Upon validation we demonstrate our method using field examples. Our work demonstrates that this new methodology integrating, pressures into decline curve analysis is theoretically and practically more robust than the analysis of pressure normalized decline curves currently used to solve the problem.Item Applied and Fundamental Studies of LNT-SCR Dual-layer Monolithic Catalysts for Lean NOx Emission Control(2015-12) Zheng, Yang; Harold, Michael P.; Luss, Dan; Epling, William S.; Jacobson, Allan J.; Brankovic, Stanko R.The increasingly stringent both greenhouse gas (GHG) and tailpipe NOx emission standards have driven the continuous improvement of commercial deNOx technologies, NOx reduction & storage (NSR, also referred to as lean NOx trap (LNT)) and selective catalytic reduction (SCR) technologies. This dissertation conducts applied and fundamental studies of coupled LNT-SCR dual-layer catalysts with the aim of expanding the operating temperature window of a conventional NSR system at lower cost. This is accomplished by a systems approach to identify the influencing factors such as catalyst composition and architecture, types of reducing agents, operating and regeneration strategies, as well as synergistic interactions between the LNT and SCR. We start with performance evaluation of dual-layer catalysts under different regeneration conditions such as H2 alone, CO/H2 mixture and a simulated diesel exhaust containing the CO/H2/C3H6 mixture. Spatial analyses of NH3 yield and NOx conversion along the LNT monolith identify the upstream zone as major NH3 generator and NOx reducer, especially at temperatures exceeding 300 oC. Zoning of either or both the SCR and LNT having a dual-layer structure enables an increase in the low-temperature (200-250 oC) NOx conversion, and minimizes the high temperature (300-400 oC) conversion loss caused by the SCR diffusion resistance and undesired NH3 oxidation by the LNT. The hydrocarbon (HC) reductant leads to an alternative LNT-SCR synergy to classical NH3-pathway; a LNT-assisted HC-SCR pathway. The LNT promotes the formation of partially oxidized HC intermediates during the rich purge which are otherwise difficult to be generated by the Cu-zeolite layer at low temperatures. These activated intermediates can be captured and utilized by the SCR catalyst via HC-SCR during the ensuing lean phase. This pathway plays a major role at low temperatures (<= 225 oC) using the simulated diesel exhaust feed. We investigated the steady-state and transient effects of reductants (CO, H2 and C3H6) on Cu-SSZ-13 catalyzed NH3-SCR as the SCR component in the combined system is periodically exposed to a rich exhaust. The three reductants affect to different extent the NH3-SCR reactions. Propylene is most effective in promoting NO2 reduction to NO by formation of organic intermediates. CO effectively reduces nitrates to nitrites that react with NO2, releasing NO. H2 follows a similar pathway as CO but is less effective. Finally, the effects of the lean/rich cycling frequency on both LNT and combined catalysts are investigated. Rapid C3H6 pulsing into a lean exhaust steam expands the operating temperature window of a conventional NSR system in both low and high-temperature regions. The combination of rapid propylene pulsing and the dual-layer catalyst architecture achieves the highest low-temperature NOx conversion. The working mechanisms of rapid propylene pulsing on both LNT and LNT-SCR catalysts are elucidated. Optimization of top-layer material and catalyst configuration like SCR and PGM zoning can improve system performance at lower cost.Item Bacterial Adhesion and Motility on Silanized Glass Surfaces(2016-08) Sharma, Sumedha; Conrad, Jacinta C.; Willson, Richard C.; Robertson, Megan L.; Agrawal, Ashutosh; Hu, Yandi; Arora, Dinesh K.Attachment of bacteria to surfaces is the first step in the formation of biofilms. Medical, industrial, and technological applications require effective control over biofilm formation, and control of initial bacterial attachment is a potential alternate approach to conventional techniques to promote or suppress biofilm formation. Conventional use of antibiotics and bactericidal agents as antifouling techniques has adverse environmental implications1 and potentially lead to evolution of antibiotic resistant strains of bacteria.2 Controlling the initial attachment step in biofilm formation circumvents these disadvantages associated with conventional approaches. Rational design of surfaces to control bacterial attachment, however, requires fundamental understanding of bacteria-surface interactions and adhesion mechanisms. In this work, we investigate the adhesion of bacteria on surfaces of controlled physical properties to obtain a mechanistic understanding of adhesion and near surface mobility of bacteria. First, we study the deposition behavior of Escherichia coli from flow on surfaces of controlled charge, wettability, and energy created by self-assembly of organosilanes on glass. We use high throughput bacteria tracking algorithms to analyze the trajectories for hundreds of bacteria. We characterize surface-associated motion of attached cells and find that a motility metric based on extent of motion mediated by flagella is inversely correlated with rate of bacterial deposition, whereas conventional surface characterization metrics are not well correlated. The transition from transient initial attachment to irreversible attachment is also correlated to deposition rate. Our results suggest that the techniques and methods presented here to characterize transient surface motility can potentially serve as a metric to rapidly determine the efficacy of surfaces to reduce fouling by bacteria. Next, we characterize the near-surface mobility associated with adhesion in E. coli bacteria deposited from flow at varying shear stresses on glass substrates bearing self-assembled alkylsilane and fluoroalkylsilane layers. We find that deposition of bacteria decreases with shear stress and increases with surface roughness. Bacteria also exhibit mobile adhesion on very smooth surfaces resulting in large linear displacements in the direction of flow which is independent of flagellar expression but requires absence of fimbriae on the cell surface. Speed of mobile adhesion decreases and residence time of cells increases as a function of increasing shear stress. Since surface roughness determines the transition from immobile to mobile adhesion, we suggest that strategies to reduce frictional interactions between cells and surfaces, either by engineering nanoscale-smooth surfaces or by suppressing expression of cell surface adhesins such as fimbriae, may help to reduce fouling during initial deposition. Finally, we investigate the competing effects of surface chemistry, solution ionic strength, and medium viscoelasticity on near-surface attachment and motion of E. coli. We vary solution viscoelasticity by adding xanthan gum, a model polysaccharide; solution chemistry by adding a monovalent salt NaCl; and surface chemistry by using a hydrophobic silanized glass and hydrophilic cleaned glass. We sort cells between two types of near-surface behavior: surface-associated non-swimming and near-surface swimming. We characterize the dynamics of each population of cells and find that the swimming cells show near ballistic motion; and the non-swimming cells show near diffusive behavior on short time scales and sub-diffusive behavior on long times. Of the three variables in the experiment (ionic strength, surface chemistry, and polymer concentration) the last has the most pronounced effect on dynamics and average speed of swimming cells. We show that high polymer concentrations in semi-dilute entangled regime present obstacles to bacteria locomotion and cells exhibit reversals in swimming trajectories without angular reorientation of the cell body axis. Our results suggest that characterizing the rheological properties of ambient environment is important for effective design of surfaces for applications such as medical implants and sensors in oil exploration where bacterial attachment occurs under moderate to highly viscous and Newtonian to highly non-Newtonian environments.Item Bacteriophage Imaging Immunoassay for Point of Care Diagnostics(2016-08) Kim, Jinsu; Conrad, Jacinta C.; Willson, Richard C.; Vekilov, Peter G.; Varadarajan, Navin; Shih, Wei-Chuan; Ghasemi, HadiPoint-of-care (PoC) devices are used for medical testing at or near the site of patient care. Due to its low cost, simple assay operation, and ease of mass production, the lateral flow immunoassay (LFA) is one of the most widely used and commercially available PoC tests. Nevertheless, traditional LFAs remain limited by two main issues: lack of sensitivity and difficulties in quantification. To develop sensitive and quantitative LFAs, we can consider three strategies (1) new LFA reaction membranes, (2) new reporter materials, and/or (3) new read-out methods. Here, we developed functionalized phage nanoparticles as a new sensitive reporter for LFAs. The use of phage as a scaffold for attachment of multiple bio-recognition and read-out-signal molecules constitutes a novel and innovative approach in LFAs. We first developed fluorescently labeled M13 phage that also are functionalized with anti-analyte antibodies. Individual phage bound to the target analyte (here MS2 virus as a model) and captured on an LFA membrane strip were imaged using epi-fluorescence microscopy. Using automated image processing, we counted the number of bound phage in micrographs as a function of target concentration. The resultant assay was more sensitive than enzyme-linked immunosorbent assays and traditional colloidal-gold nanoparticle LFAs for direct detection of viruses. Next, to understand the high sensitivity, we characterized the binding modes of the phage reporter to targets in the fibrous glass LFA membrane using microscopy and image analysis. We found that the elongated shape of M13 phage coupled with the complex flow promotes reorientation and facilitates the binding. The binding efficiency was also influenced by other assay parameters, such as the length of the phage and their flux through the LFA membrane. The number of bound phage increased as the phage length increased; similarly the number of bound phage increased with the flux [within a particular flow regime]. These results suggested that the increased length and flux of phage increased the chance that phage encountered fibers, thereby enhancing binding efficiency. Next, as a first step towards practical phage LFAs we characterized the stability and durability of phage at elevated temperatures. To reveal the mechanism of temperature-tolerant mutant stability, we characterized the mutant genomes using next-generation sequencing technology. Three potential mechanisms were suggested for the apparent increase in temperature tolerance: gene replication enhancement (due to mutations in gp2); formation of miniphage; and mutations in the p7 coat protein. Finally, as a first step towards a user-friendly and handheld system compatible with PoC use, we incorporated two photon detectors, a multi-pixel photon counter (MPPC) and a photomultiplier tube (PMT), into a smartphone accessory. The sensitivities of those detectors were compared by determining a low level of 1,5-anhydroglucitol (AHG) as a model test reaction in a chemiluminescence assay. The assay sensitivity depended on the detector performance; the PMT detector exhibited ten-fold better sensitivity than the MPPC. These results raise the promising possibility that the developed detectors could be applied to our phage LFA by inserting the appropriate light source and optical filters.Item Bifurcation Analysis of Homogeneous-Heterogeneous Combustion(2016-08) Alam, Imran; Balakotaiah, Vemuri; Luss, Dan; Grabow, Lars C.; Auchmuty, Giles; Schreiber, IgorWe present theory and comprehensive bifurcation analysis of thermally coupled homogeneous-heterogeneous combustion of propane and methane in short monolith, fibermat or gauze type reactors with a focus on the dependence of the ignition, extinction, hysteresis, double and boundary limit loci on the various design and operating parameters. We analyze the impact of inlet fuel mole fraction, inlet temperature, residence time and channel hydraulic radius on the relative position of the homogeneous and catalytic ignition and extinction points and identify the parameter regions in which either catalytic or homogeneous reaction dominates. We also identify the regions in which catalytic ignition leads either to an intermediate branch on which the homogeneous reaction rate is negligible or directly to a high conversion and temperature state thereby facilitating homogeneous ignition. For the case of methane oxidation, we examine both the lean and rich feeds with the operating pressure as the bifurcation variable and compare the predicted results with available experimental data and numerical simulations using detailed CFD models. We then study the impact of the Lewis number, 〖Le〗_f (thermal diffusivity of the reaction mixture to the molecular diffusivity of the limiting reactant) and the Peclet numbers on the maximum temperature attained for coupled homogeneous-heterogeneous combustion process in a parallel plate reactor using one, two and three-dimensional models. For the case of 1-D models, we find that the maximum temperature never exceeds the adiabatic value for physically consistent boundary conditions. For 2-D models, we find that for 〖Le〗_f<1, the hot spot temperature can exceed the adiabatic value, it is always located on the wall and its distance from the inlet and magnitude increase with increasing radial Peclet number. However, for 〖Le〗_f>1, contrary to some literature claims, the peak temperature never exceeds the adiabatic value, though the temperature can be non-monotontic across the channel. We show that 3-D solutions can bifurcate either from 1-D or 2-D solutions irrespective of the value of the Lewis number. The implications of these observations for catalyst and process design in systems in which both homogeneous and catalytic reactions occur are discussed.Item Blending PLA(Poly-lactic acid) with layered silicates(2013-05) Heo, Yoo Rang 1986-; Krishnamoorti, Ramanan; Robertson, Megan L.; Ardebili, HalehLayered silicates are used for organic/inorganic hybrid fillers to reinforce the polymers. Dispersion of polymer and layered silicate is important because phase separation leads to weak interaction which makes poor property at polymer-layered silicate nanocomposites. In this work, PLA(Poly-lactic acid) is synthesized from cyclic L-lactide with layered silicates through in-situ ring opening reaction with varying concentrations of layered silicate. PLA is an attractive biomaterial and is used for packaging due to high strength and high-modulus properties. Its shortcomings such as barrier property, brittleness can be enhanced by mixing it with organic modified layered silicate. The polymer-layered silicate nanocomposites are characterized by x-ray diffraction, thermal gravimetric analysis and optical microscopy. In this work, intercalated or exfoliated polymer layered silicate nanocomposites could be achieved. The analysis of samples shows that crystallinity is decreased with increasing inorganic concentration. In addition, thermal stability and morphology also depend on dispersibility and inorganic concentration.Item Bottlebrush Polymers: A Pathway to Engineering Surfaces and Interfaces(2018-05) Mah, Adeline; Ruchhoeft, Paul; Stein, Gila E.; Robertson, Megan L.; Ardebili, Haleh; Verduzco, RafaelBottlebrush polymers are macromolecules with a linear backbone and densely-grafted polymeric side-chains. Steric repulsion between the side chains forces the backbone to extend, leading to a rod or wormlike conformation. Therefore, bottlebrush polymers resemble both comb polymers and polymer-grafted particles. Our goal is to develop an in-depth understanding on the thermodynamics of bottlebrush polymer additives for linear hosts, with an emphasis on understanding interface and surface attraction for the design of compatibilizers and functional coatings. First, we studied the phase behavior of bottlebrush polymers with random copolymer poly (styrene-r-methyl methacrylate) side-chains in a blend of two immiscible homopolymers, polystyrene and polymethyl methacrylate. We determined that bottlebrush composition and architecture will control the morphology of the blends and identified the conditions that lead to the formation of a bottlebrush-rich interphase that suppresses coarsening of the blend microstructures. Second, we studied the segregation behavior of bottlebrush polystyrene in a blend with linear polystyrene by systematically changing the bottlebrush side-chain length, bottlebrush backbone length, and length of the linear host. We developed a scaling law and generated a phase diagram that describes the segregation behaviors of bottlebrush polymers in a thin film. Finally, we investigated the stability and swelling response of bottlebrush networks that were crosslinked using atom beam lithography. We found that swelling declines as the number of side-chains is increased, which is consistent with a simple Flory model for equilibrium swelling of networks.Item Building Models of Process Systems: Applications in Control and Design(2017-12) Misra, Shobhit; Nikolaou, Michael; Grabow, Lars C.; Palmer, Jeremy C.; Qin, Guan; Darby, Mark L.Traditional or new methods for building models of process systems can combine physical understanding with statistical analysis so that models can be developed for use in many fields of engineering. This work focusses on developing models that can be used for system design (e.g., cementing of hydrocarbon wells), process control (e.g., in manufacturing of chemicals or pharmaceuticals), and simulation purposes (e.g., to study the robustness of automatic control system). Availability of large amounts of data that is recorded during hydrocarbon well construction makes it possible to apply data-driven modeling methods to address the problem of natural gas leakage from cemented section of hydrocarbon wells – a problem that is too complex to investigate using the existing modeling and experimental methods. The problem has significant operational and environmental implications as leaking wells pose serious pollution threats to both groundwater and the atmosphere. Design of wellbore preparation and cementing recipes involve decisions on over two dozen design variables that affect the quality of hydrocarbon well cementing. Given historical data of these design variables, data-driven models are developed to successfully classify wells into “leak” and “no leak” categories in cross-validation tests. In addition, these models identify and rank the most important factors for preventing leakages. The quality of data generated in experiments can also be improved by designing experiments in such a way that the resulting model identified from the data fulfills certain requirements of the application for which the model is identified. Controller design for multivariable system is one such application where design of experiments can be modified to generate good quality data. The controller designed using the model built from the resulting data can be used to better control the processes, such as production of chemicals. The model building method consists of two steps, namely estimation of (a) model order i.e., structure of model, and (b) values of model parameters. Of the two steps, the first one is far more challenging and more strongly dependent on the quality of data generated in the identification experiment. A new design of experiments (DOE) is proposed that accurately estimates the model order even for the most challenging systems. Comparison of the proposed DOE with other currently practiced DOEs using simulation studies on two process systems validates the effectiveness of the proposed design to accurately estimate model order when other DOEs fail to do so. A rigorous mathematical analysis is also provided to further confirm the claim. Simulating process systems before the actual installation of the systems in the field is a useful and cost-effective way to foresee the problems that may occur after installation and analyze the effects of these problems in advance. Automatic control system of a novel directional drilling technology is simulated and effects of changing drill bit torque on controller performance are studied.Item Catalysis of Imperfections: Importance of the Nature and Abundance of Defects in Oxides and Chalcogenides for Diverse Applications(2017-12) Kasiraju, Sashank; Grabow, Lars C.; Harold, Michael P.; Bollini, Praveen; Epling, William S.; Wong, Michael S.Catalysis is ubiquitous in modern civilization, with far-reaching applications in the chemical, energy, automobile, electronic and pharmaceutical industries. Recent advances in computational infrastructure and state-of-the-art experimental techniques are leading to an exponential growth of our understanding of catalysis. Active sites in catalysts provide its essential functionality and are analogous to the role of mitochondria for life functions. This thesis aims to provide case-studies of synergistic combinations of experimental spectroscopic techniques, and computationally efficient ab-initio methods such as Density Functional Theory (DFT)to study and predict the intrinsic nature of these active-sites, and in turn their catalytic activity. The first example relates to the abatement of nitrate and nitrite ions, which are globally detected surface and ground water contaminants with adverse health effects. In/In2O3 deposited on Pd nanoparticles (NPs) shows excellent room temperature nitrate catalytic reduction activity to nitrogen gas. We provide evidence that metallic Pd active sites are responsible for H2 activation and spillover to reduce In2O3 and form the active sites for nitrate ion adsorption and reduction to nitrite. A volcano-type activity relation exists for the overall nitrate reduction activity and the In surface content of the bimetallic catalysts particles. Next, a hybrid Mo2C/MoS2 catalyst prepared via carburization of vertically aligned nanosheets of MoS2 was investigated. It exhibits exceptional electrochemical performance for the hydrogen evolution reaction (HER) and outperforms the parent electrocatalysts (Mo2C and MoS2). Experimental and computational evidence points towards the introduction of CHX species at the S defects on the S-edge of MoS2, and we attribute the remarkable catalytic activity to these novel active sites that exhibit a thermoneutral differential Gibbs free energy of H adsorption. Finally, MoO3 is studied as a potential hydrodeoxygenation (HDO) catalyst to upgrade pyrolysis vapor to value added fuels and chemicals. We propose that O defects on the surface provide the active site for HDO reactions involving C-O scission and H2 splitting. Transition metal promotion and carburization to a mixed oxy-carbide phase greatly enhance the O defect site density and provide additional metallic sites for H2 splitting.Item Chamber Wall Interactions with HBr/Cl2/O2 Plasmas Studied by the “Spinning Wall” Method(2015-05) Srivastava, Ashutosh K.; Donnelly, Vincent M.; Economou, Demetre J.; Stein, Gila E.; Wolfe, John C.; Ruchhoeft, PaulPlasma etching is a widely used method to pattern materials in the fabrication of microelectronic devices. As the minimum feature sizes, or so-called critical dimensions, shrink beyond 14 nm, plasma etching processes need to be ever more tightly controlled. At low pressures in the range of 1-100 mTorr, typical in current plasma processes, the ~cm mean free path of species ranges are comparable to reactor dimensions. Consequently, gas phase reactions (especially three-body processes) become less likely and heterogeneous reactions on chamber walls become increasingly important. The surface layers formed on the reactor walls become a source of production or loss of species. As a result, shifting plasma composition leads to process drifts, leading to changes in etching rates, profiles, selectivity, and yields. Hence, it is of prime importance to understand the interactions of plasmas with the dynamic chamber wall surfaces. HBr plasmas are used to etch Si, as well as GaN, PZT, InP, indium zinc oxide and other materials. In Si etching, HBr plasmas create better anisotropic profiles than Cl2 plasmas, with better selectivity toward SiO2. Selectivity can be further improved by adding oxygen to the plasma. The feed gas composition of HBr/Cl2/O2 plasmas is optimized to best meet the needs of the particular application. Keeping such a complex process stable over time requires tight control over all plasma parameters, including reactor wall conditions. Here, we have studied the interaction of HBr/Cl2/O2 inductively-coupled plasmas with reactor chamber wall deposits, with and without Si etching, using the “spinning wall” technique. The spinning wall is part of the reactor chamber walls, allowing near-real time analysis of the composition of surface layers via Auger electron spectroscopy, and determination of species desorbing off the walls by mass spectrometry. In HBr plasmas with no bias voltage on the Si substrate, and hence no Si etching, HBr is ~30% dissociated and H2 and Br2 form in the plasma. Layers deposited on the reactor chamber contained little if any Br under these conditions. Adding O2 to an HBr plasma leads to formation of Br2 and H2O products that desorb from the spinning wall. H2O has a very long residence time on the surface. With bias voltage applied to the Si substrate in an HBr plasma, SiBr and SiBr3 are prominent mass spectrometer signals, SiBr2 and SiBr4 appear to be the major gas phase components, and a SiOxBry layer deposits on the spinning wall. Adding 20% O2 to HBr stops etching and eliminates Br from the surface layer, indicating that Br on the reactor walls is a result of SiBrx impingement, and not from bromination by impinging Br. With HBr/Cl2 plasmas and no bias on the stage, a SiOxCly layer deposits; no Br is detected. In addition, the mass spectrum of HBr and Cl2 gas mixture without plasma revealed HCl, Br2 and BrCl species. Further experiments revealed that these products were the result of reactions between HBr and Cl2 on the plasma reactor walls. With plasma and bias on the Si substrate, both Br and Cl incorporate in a depositing layer. Adding 20% O2 to a HBr/Cl2 plasma with substrate bias suppresses Br adsorption, but Cl still adsorbs. In 40% O2/HBr/Cl2 plasmas with stage bias, Cl adsorption also ceases.Item Characterization and Optimization of Multifunctional Automotive Catalysts(2019-12) Malamis, Sotirios A.; Harold, Michael P.; Epling, William S.; Rimer, Jeffrey D.; Bollini, Praveen; Brankovic, Stanko R.Multifunctional automotive catalysts provide new opportunities for gasoline and diesel engines to meet the constantly tightening emissions and fuel economy standards from various regulatory agencies. Meeting these demands is important not only for securing industrial compliance but also for improving human health and air quality. Combining multiple functions into a single catalyst saves design space and reduces material cost. Here we conduct steady state and transient experiments on multifunctional catalysts that span the operational range of gasoline and diesel engines including cold start and high-temperature operations in order to reduce NOx and hydrocarbon (HC) emissions. We investigate first the Three-Way NOx Storage Catalyst (TWNSC), a concept that combines three-way and NOx storage functionalities for optimal performance during high-temperature vehicle operation. A series of experiments identifies operating conditions that maximize conversion and performance for application with a downstream selective catalytic reduction (SCR) catalyst. Second, we characterize new catalysts that address the cold start issue of modern engines, namely the Lean Hydrocarbon NOx Trap (LHCNT) concept. The LHCNT is a precious group metal (PGM)-zeolite material that combines low temperature NOx and hydrocarbon storage and catalytic conversion of both species into a single unit. By conducting transient uptake and release experiments we obtain useful insight about competitive adsorption, release temperature, conversion activity, and water impact. We find that hydrocarbon concentration and identity, as well as PGM content and zeolite geometry can affect NOx/HC uptake and release performance. Findings from single catalyst function experiments are used to evaluate sequential and dual-layered configurations that improve the overall LHCNT performance. The final part of this work investigates the feasibility of modeling such a catalyst to predict performance and screen new materials. These results provide guidance for improving catalytic systems in the automotive catalysis industry in order to keep up with emission standards.