MS, University of Cincinnati, 2013, Engineering and Applied Science: Mechanical Engineering

The discovery of Carbon Nanotubes (CNTs) has sparked tremendous interest among the scientific community due to its extraordinary mechanical properties like high strength and elastic modulus and semiconductor like properties. Though spinning the CNTs into continuous yarns enabled the use of CNTs at macroscale, current spinning techniques are not able to reproduce the properties comparable to those observed at nanoscale. Motivated by this gap, a modeling approach is established to address the subject of transferability of the high strength properties from individual CNT to carbon nanotube (CNT) yarns. More specifically, a number of key factors that contribute to the reduced strength of the twisted CNT yarns are investigated. First of all, the effects of Stone-Wales defects on the strength of individual nanotubes are studied. It is found that the tensile strength of the individual CNT is not highly sensitive to the Stone-Wales defects even with relatively high ratio of defects percentage. Subsequently, molecular dynamics and mechanics simulation are performed to evaluate the load transfer mechanism and tensile strength in a bundle of CNTs. The goal is to find the most favorable twist angle for maximum tensile strength and maximum load transfer ability in between the CNTs in CNT bundles. Both small and large bundles have been studied to examine whether the results are scalable. This thesis concludes with a comparison of the simulation results with the analytical studies based on the mechanics of ropes.

Committee: Dong Qian Ph.D. (Committee Chair); Yijun Liu Ph.D. (Committee Member); Mark Schulz Ph.D. (Committee Member) Subjects: Nanotechnology

MS, University of Cincinnati, 2010, Engineering and Applied Science: Electrical Engineering

Carbon nanotubes have excellent electrical and mechanical properties, which are ideally suited for field emission and sensor/actuator applications. The catalyst layer needed for CNT growth (Fe, Ni or Co) once coated on the substrate is subject to an annealing step, which results in the formation of tiny globules of randomly aligned particles. CNTs finally grow on these randomly placed catalyst particles after the substrate annealing. The disadvantage of the bottom-up approach is that the catalyst globules are susceptible to migration on the substrate during thermal annealing and the CNT growth process. The scope of this thesis includes: (1) Patterning arrays of nano-/micro- features by e-beam lithography, (2) shallow etches of the holes by plasma etching in these features (3) deposition of the catalyst material into the shallow holes, (4) CNT growth, and (5) characterization of the patterned nano/micro-scale CNT catalysts and CNT growth. The main objective in this thesis is to immobilize the catalysts on the substrate at a specific location with an array of shallow holes. We believe this will localize and anchor the catalyst producing patterned arrays of CNT's. This method process will also be compared with the current methods of catalyst immobilization developed by Dr. Shanov's group where an alumina layers acts as the catalyst anchor layer. Also CNT growth is compared and with a substrate with no immobilization of the catalyst. The differences in catalyst morphology between annealing the substrate in air and nitrogen will also be compared. All the comparisons are done across different diameters of patterned features on the substrate. This new process will allow for the controlled patterning of CNT growth and enable CNT's to be integrated into manufacture able devices.

Committee: Marc Cahay PhD (Committee Chair); Vesselin Shanov PhD (Committee Member); Robert Jones PhD (Committee Member) Subjects: Materials Science

Doctor of Philosophy, University of Akron, 2014, Polymer Engineering

Two ultrasonic twin screw extrusion systems were designed and manufactured for the ultrasonic dispersion of multi-walled carbon nanotubes in viscous polymer matrices at residence times of the order of seconds in the ultrasonic treatment zones. The first design consisted of an ultrasonic slit die attachment in which nanocomposites were treated. A second design incorporated an ultrasonic treatment section into the barrel of the extruder to utilize the shearing of the polymer during extrusion while simultaneously applying treatment. High performance, high temperature thermoset phenylethynyl terminate imide oligomer (PETI-330) and two different polyetherether ketones (PEEK) were evaluated at CNT loadings up to 10 wt%. The effects of CNT loading and ultrasonic amplitude on the processing characteristics and rheological, mechanical, electrical, thermal and morphological properties of nanocomposites were investigated. PETI and PEEK nanocomposites showed a decrease in resistivity, an increase in modulus and strength and a decrease in strain at break and toughness with increased CNT loading. Ultrasonically treated samples showed a decrease in die pressure and extruder torque with increasing ultrasonic treatment and an increase in complex viscosity and storage modulus at certain ultrasonic treatment levels. Optical microscopy showed enhanced dispersion of the CNT bundles in ultrasonically treated samples. However, no significant improvement of mechanical properties was observed with ultrasonic treatment due to lack of adhesion between the CNT and matrix in the solid state. A curing model for PETI-330 was proposed that includes the induction and curing stages to predict the degree of cure of PETI-330 under non-isothermal conditions. Induction time parameters, rate constant and reaction order of the model were obtained based on differential scanning calorimetry (DSC) data. The model correctly predicted experimentally measured degrees of cure of compression molded (open full item for complete abstract)

Committee: Avraam Isayev Dr. (Advisor); Sadhan Jana Dr. (Committee Member); Alamgir Karim Dr. (Committee Member); Shing-Chung Wong Dr. (Committee Member); Wieslaw Binienda Dr. (Committee Member) Subjects: Materials Science; Polymers

Master of Science, The Ohio State University, 2005, Graduate School

Committee: Not Provided (Other) Subjects:

PhD, University of Cincinnati, 2023, Engineering and Applied Science: Materials Science

Although relatively recently discovered, Carbon nanotubes (CNTs) have gained popularity as one of the most exotic materials known due to their extraordinary electronic, thermal, and mechanical properties. CNTs have a very high aspect ratio and they exhibit a very high electrical conductivity and a good mechanical strength. Individually at the nanotube scale, CNTs have extraordinary properties, however, it is challenging to attain these properties when CNTs are used to form macroscopic yarns, tapes, and sheets. Individual single-walled nanotubes (SWNTs) exhibit electrical conductivities and tensile strength of 10^6 S/cm and 30 GPa whereas multi-walled nanotubes (MWNTs) have corresponding values in the range of 10^4 S/cm and 30 GPa. For macroscopic CNT sheet assemblies, the reported electrical conductivity and tensile strength are in the range of 103 S/cm and 102 MPa respectively. This is primarily because of the non – woven nature of macroscopic CNT sheet assemblies along with defects within the individual CNTs that form these macroscale entities. Additionally, the continuous synthesis of CNT sheets itself introduces impurities like amorphous carbon and residual catalyst into the material. These defects and impurities could lead to weak inter-tube interactions and poor alignment of the CNTs and have a significant impact on the final properties. In this dissertation research, CNTs were synthesized using a combination of transition metal catalyst precursors. B and N doped CNTs were synthesized to study the influence of varying catalyst composition and doping on the structure, electronic properties, and purity of CNT sheets produced using the floating catalyst chemical vapor deposition (CVD) method. A second method involving a post processing salt treatment was also developed to improve the properties and purity of CNT sheets. Both the doping and salt treatment methods were successful in improving the electrical conductivity of CNT sheets. Various characterizat (open full item for complete abstract)

Committee: Mark Schulz Ph.D. (Committee Chair); Dinc Erdeniz Ph.D. (Committee Member); Jing Shi Ph.D. (Committee Member); Vesselin Shanov Ph.D. (Committee Member); Ashley Paz y Puente Ph.D. (Committee Member) Subjects: Nanotechnology

Doctor of Philosophy, Case Western Reserve University, 2022, Macromolecular Science and Engineering

The oxygen reduction reaction (ORR), oxygen evolution reaction (OER), and hydrogen evolution reaction (HER) are critical electrocatalytic reactions for clean and renewable energy technologies, such as fuel cells, metal-air batteries, and water-splitting. Current commercial applications of these reactions utilize noble-metal-based catalysts (e.g., Pt, Pd, RuO2, IrO2). The high cost of these precious metal-based catalysts and their limited reserve have precluded these renewable energy technologies from large-scale applications. Therefore, research efforts have focused on the development of alternative catalysts that are readily available and cost-effective, with superior electrocatalytic performance compared to noble-metal-based catalysts. In 2009, nitrogen-doped carbon nanotubes (N-CNTs) were discovered to demonstrate electrocatalytic ORR activity attributed to the doping-induced charge transfer from carbon atoms adjacent to the nitrogen atoms to change the chemisorption mode of O2. More recent studies have further demonstrated that certain heteroatom-doped carbon nanomaterials can even act as multi-functional metal-free electrocatalysts for ORR/OER/HER, leading to the potential development of low-cost, highly efficient, and multi-functional electrocatalysts for advanced clean and renewable energy technologies. The work presented herein develops new carbon-based metal-free electrocatalysts (C-MFECs) by utilizing different design strategies. Chapter two demonstrates carbonization of a newly-synthesized pair of enantiotopic chiral metal-organic frameworks (MOFs) to produce Co-coordinated N-doped carbon materials with a hierarchical rod-like morphology and remarkable bi-functional electrocatalytic activity and stability for both OER and ORR – comparable to both commercial RuO2 for OER and Pt/C electrocatalysts for ORR. The observed excellent electrocatalytic activities were attributed to their unique hierarchical rod-like structure with homogeneously distributed cob (open full item for complete abstract)

Committee: Liming Dai (Advisor); Gary Wnek (Committee Chair); Lei Zhu (Committee Member); Hatsuo Ishida (Committee Member); Chung-Chiun Liu (Committee Member) Subjects: Chemistry; Materials Science

Doctor of Philosophy (PhD), Wright State University, 2020, Engineering PhD

The goal of this project is to investigate fabrication approaches and structure-property relationships of porous and flexible hierarchical hybrid solids suitable for advanced surface-active devices. Multi-scale hierarchical carbon materials are being fabricated by strong covalent attachment of multiwall carbon nanotube(MWCNTs) arrays on flexible carbon fabric substrates in order to enhance the surface area per unit volume. This was done using chemical vapor deposition (CVD) after functionalizing the surface with a plasma-derived nano-oxide coating. Structural and chemical characterization is performed using scanning electron microscope(SEM), energy dispersive spectroscopy(EDS) and x-ray photoelectron spectroscopy(XPS). Surface area estimates have been made by building structural models from Electron Microscopy data and subsequently validated with direct measurement with BET isotherm analyses. It is seen that calculated specific surface area (SSA) of the material via mass increase during the CVD process is in good agreement with BET gas adsorption measurement of the SSA. It has been shown that further modification of these surfaces is very effective for tailoring their wettability for selective infiltration of different fluids. These structures have been infiltrated with responsive polymers such as Poly(N-isopropylacrylamide(PNIPAM)s to fabricate smart stimuli-responsive composites. In addition, palladium nanoparticles(PdNPs) have been attached onto the nanotube carpets. Particle distribution, size variation, and structures have be investigated using Scanning Electron Microscopy (SEM) & Energy Dispersive Spectroscopy (EDS). X-ray photo spectroscopy (XPS) was employed for bonding state analysis. In-depth understanding of catalytic behavior of these hybrid nanocatalysts (Fabric-CNT-Pd system) has been performed by investigating the catalytic reduction of a model water contaminant triclosan(TCS). The reaction rates, efficiency, and durability have been studied (open full item for complete abstract)

Committee: Sharmila M. Mukhopadhyay Ph.D. (Advisor); Nadagouda N. Mallikarjuna Ph.D. (Committee Member); Willie F. Harper, Jr. Ph.D. (Committee Member); Hong Huang Ph.D. (Committee Member); H. Daniel Young Ph.D. (Committee Member) Subjects: Engineering; Materials Science; Nanotechnology

Doctor of Philosophy, Case Western Reserve University, 2019, Macromolecular Science and Engineering

This dissertation has a primary focus on design and development of composites by employing processing methods aimed at improving filler dispersion in polymers. Mixing elements taking advantage of extensional dominated flows are adopted. Several such mixing elements, extensional mixing elements (EMEs) to be specific, with varying degree of ability to impose extensional dominated flows, have been experimentally validated. A first attempt is made to enhance the dispersion of carbon black (CB), graphene nano platelets (GNP) and carbon nano tubes (CNT) in polypropylene (PP). Enhanced dispersion does translate into improved mechanical properties. A more comprehensive approach is adopted with an integrated computational and processing method on thermoplastic polyurethane (TPU) graphene oxide (GO) composites. The role of filler functionalization in exfoliation and TPU hard block crystallization is established. A difference in anisotropy and phase separation is observed between material processed with EME and kneading blocks. A significantly enhanced ductility is obtained by employing EME during processing. Improved abrasion and strength is also observed. A secondary focus of the thesis includes synthesis of composites by wet chemical and other processes to end up with composite materials with enhanced properties and/or improved material behavior. Hydrogels of poly(ethylene glycol) methyl ether methaycrylate filled with graphene oxide are made via a reversible assisted fragmentation termination (RAFT) approach. Reinforcement and lubrication effects are studied with the incorporation of covalent bonds between filler and matrix. Aerogels obtained from hydrogels of graphene oxide (GO) and montmorillonite (MMT) clay nanocomposites in poly(vinyl alcohol) are synthesized. Hence, obtained aerogels have improved compressive strength and further silylation makes them functional materials for oil-water separation. Twin-screw reactive extrusion of Thermoplastic polyureth (open full item for complete abstract)

Committee: Joao Maia (Advisor); Manas-Zloczower Ica (Committee Member); Dai Liming (Committee Member); Lewandowski John (Committee Member) Subjects: Analytical Chemistry; Chemistry; Design; Engineering; Materials Science; Nanoscience; Nanotechnology; Polymer Chemistry; Polymers

PhD, University of Cincinnati, 2019, Medicine: Industrial Hygiene (Environmental Health)

Carbon nanotubes and carbon nanofibers (CNT/F) are cylindrical-shaped nanomaterials made of carbon atoms. These materials offer the potential for vast technological breakthroughs in various industrial applications in biomedicine, electronics, as well as high-performance intermediates such as coatings and composites for aerospace, automobiles, and construction. However, as CNT/F have emerged in manufacturing, evidence of potential health effects from animal studies has linked these nanomaterials to effects such as pulmonary inflammation, fibrosis, and granulomas. Although limited human evidence of adverse effects from occupational exposures to CNT/F currently exist, it is recognized that longitudinal studies will be needed due to the long latency periods for many of the health effects of concern. Therefore, the overarching goals of this dissertation, which includes chapters 1-3, were to develop consensus sampling methods to characterize U.S. workplace exposures to CNT/F as well as evaluate alternative methods to estimate exposures for future uses in longitudinal epidemiologic studies. In chapter 1, we measured CNT/F exposures among U.S. workers for use in a dose-response analysis. Full-shift exposures were assessed from participants at 12 facilities for the mass of elemental carbon (EC) at the respirable and inhalable aerosol size fractions, along with the quantitative characterization of CNT/F exposures with transmission electron microscopy (TEM) analysis. The results of this study demonstrated the occurrence of a broad range of workplace exposures to CNT/F. EC mass exposures were generally below the current occupational exposure limit (OEL) of 1 µg/m^3 (as respirable EC mass), but generally above 1 µg/m^3 as inhalable EC mass, which currently does not have an OEL. In chapter 2, we identified workplace determinants that contribute to exposure and developed predictive models to estimate CNT/F exposures for future use in longitudinal studies. An exposure da (open full item for complete abstract)

Committee: Sergey Grinshpun Ph.D. (Committee Chair); Stephen Bertke Ph.D. (Committee Member); Tiina Reponen Ph.D. (Committee Member); Mary Schubauer-Berigan Ph.D. (Committee Member); Glenn Talaska Ph.D. (Committee Member) Subjects: Occupational Safety

Master of Science in Engineering, University of Akron, 2015, Chemical Engineering

The internal susceptibility and corrosion of pipelines has widely been minimized by the use of inhibitors which mitigate and control degradation effects due to flow conditions and to aggressive environments created inside the pipeline. However, environmental hazard might constitute a problem due to the chemical substances forming the inhibitors. A very specific application of pipeline integrity occurs in offshore facilities for oil recovery production where a mixture of pressurized water-CO2 is injected to almost depleted oil wells in order to enhance recovery. As CO2 injection is very common in marine environments, the effect of chloride ions is added to the corrosive variables of the system is considered. Environmental aggressiveness is set due to a paired effect of environmental conditions: the formation of carbonic acid in the water-CO2 mixture and the presence of chloride ions as part of the marine environment. Here we aimed to electrochemically characterize a zinc-rich epoxy nanocoating primer (ZREP), as well as a composite variation incorporating carbon nanotubes (CNT-ZREP), on an API X52 pipeline grade steel substrate. A rotating cylinder electrode (RCE) was used to incorporate the flow regime and equivalent shear stress conditions. The selected electrolyte for testing was 3% (wt.) NaCl saturated with CO2. The anti-corrosion properties of these nanocomposite coatings are a result of the combined effects of Zn and C nanoelements, which impart special properties not initially inherent in the matrix or in the nanoelements. The effects of these medium conditions on the performance of the substrate/coating system were characterized in real-time by electrochemical impedance spectroscopy. The damage evolution concept was adopted to analyze the current stages and to propose possible mechanisms for the roles of the CNTs and Zn cathodic in providing enhanced protection to the substrate.

Committee: Homero Castaneda-Lopez Dr. (Advisor); Qixin Zhou Dr. (Committee Member); Rajeev Gupta Dr. (Committee Member) Subjects: Chemical Engineering; Chemistry; Engineering

Doctor of Philosophy (PhD), Wright State University, 2012, Engineering PhD

Multi-scale hierarchical carbon structures have been developed by growing strongly attached carbon nanotubes (CNT) on high surface area substrates having open, interconnected porosity. This investigation was developed on cellular carbon foams but the process is equally suitable for other geometries including flat, fibers, and other porous substrates (interconnected). It is also adaptable to other substrate materials such as metals, alloys or ceramic compounds. Multiwalled carbon nanotubes are grown using a floating catalyst chemical vapor deposition (CVD) method after pre-coating the substrate with a silica nano-layer. The silica-coated graphitic substrates are seen to grow 280 times more nanotubes per unit area compared to bare graphite. Detailed spectroscopic and microscopic studies indicate that this significant improvement can be attributed to improved adhesion and distribution of the iron catalysts and enhanced catalytic activity from substrate interactions. Failure analysis of the nanotube layer under several types of loading demonstrates strong adhesion between CNT and substrate, with failure occurring in the underlying substrate. Attachment of carbon nanotubes can result in more than two orders of magnitude increase in specific surface area as independently confirmed by modeling the microstructure and direct surface area measurement using Brunauer-Emmett-Teller (BET) technique. These hierarchical materials are tested as encapsulation structures for phase change materials (PCM). The CNT can act as nanofin radiators enhancing energy exchange between the thermally conductive encapsulation and the PCM, hence improving thermal response time. A heat cell was designed to compare the response times of foam encapsulation with and without CNT. Encapsulation with CNT is found to have and significantly faster thermal response. DSC measurements demonstrate that CNT/foam hierarchical encapsulation provides 15% higher storage of latent heat. The improvements in thermal res (open full item for complete abstract)

Committee: Sharmila M. Mukhopadhyay PhD (Advisor); Raghavan Srinivasan PhD (Committee Member); H. Daniel Young PhD (Committee Member); P.Terry Murray PhD (Committee Member); Ajit K. Roy PhD (Committee Member) Subjects: Materials Science

Doctor of Philosophy (PhD), Wright State University, 2005, Engineering PhD

Pulikollu, Rajasekhar Venkata. Ph.D., Department of Mechanical and Materials Engineering, Wright State University, 2005. Nano-coatings on Carbon Structures for Interfacial Modification. Surface modification of materials is a rapidly growing field as structures become smaller, more integrated and complex. It opens up the possibility of combining the optimum bulk properties of a material with optimized surface properties such as enhanced bonding, corrosion resistance, reactivity, stress transfer, and thermal, optical or electrical behavior. Therefore, surface functionalization or modification can be an enabling step in a wide variety of modern applications. In this dissertation several surface modification approaches on carbon foam and carbon nano-fibers will be discussed. These are recently developed sp 2 graphitic carbon based structures that have significant potential in aerospace, automotive and thermal applications. Influence of surface modification on composite formation and properties have also been investigated. Two types of property changes have been investigated: one for enhancing the surface reactivity and another for surface inertness. Characterization techniques such as X-ray Photoelectron Spectroscopy (XPS), Atomic Force Microscopy (AFM), Contact Angle Measurement, Scanning Electron Microscope (SEM), Transmission Electron Microscope(TEM), and mechanical testing are used in this study to find out the influence of these coatings on surface composition, chemistry, and morphology. Mechanical testing has been performed on composites and stand-alone foam to study the influence of surface modification on physical and mechanical properties of the composite materials. The effectiveness of these coatings on metallic/graphite interface has also been investigated for metal-matrix composite related applications. Additionally, the influence of plasmacoatings on nucleation and growth of nanotubes on larger carbon structures (to produce multiscale, multifunctional mater (open full item for complete abstract)

Committee: Sharmila Mukhopadhyay (Advisor) Subjects: Engineering, Materials Science

MS, University of Cincinnati, 2009, Engineering : Environmental Engineering

Carbon nanofibers (CNFs) and carbon nanotubes (CNTs) have become wonder products for industrial use because of their unique characteristics such as thermal and electrical conductivity, heat distortion resistance, mechanical reinforcement, and high surface area. As a result, engineered carbon nanomaterials are being produced at a rapid rate for use in the aerospace, automotive, environmental, computer, and recreational industries. However, certain characteristics of carbon nanomaterials make them a cause for concern. CNFs and CNTs are tiny, cylindrical or cone-shaped, manufactured forms of carbon and their structure can be similar to that of asbestos. The effects of asbestos exposure include severe lung fibrosis or scarring, lung cancer, including cancer of the lining of the lungs, or pleura, called mesothelioma. In this study, five samples of carbon nanomaterials are aerosolized and sampled through a cascade impactor to determine their size distribution and geometric mean diameter (GMD). The samples are evaluated using a scanning electron microscope with energy dispersive x-ray analysis (SEM/EDS) to determine their morphology and metal content. Seven samples, including three CNFs and four CNTs of different lengths and diameters, are tested for PAH concentration using gas chromatography/mass spectrometry (GC/MS). The carbon nanomaterials used in this study are produced via chemical vapor deposition (CVD), which uses metal catalysts such as Fe, Co, and/or Ni. Inductively coupled plasma atomic emission spectroscopy (ICP-AES) is used to quantify trace metals in the carbon nanomaterials.

Committee: Mingming Lu PhD (Committee Chair); Eileen Birch PhD (Committee Member); Tim Keener PhD (Committee Member); George Sorial PhD (Committee Member); Jagjit Yadav PhD (Committee Member) Subjects: Environmental Engineering

MS, University of Cincinnati, 2008, Engineering : Mechanical Engineering

Carbon nanotubes (CNT) that comprise large clusters referred to as carbon nanotube arrays were discovered in 1991 by Sumio Iijima. Carbon nanotubes are the strongest material known to exist and have amazing electrical and thermal properties. Chemical Vapor Deposition (CVD) is currently the best method for producing relatively pure super-long CNT arrays over large surface areas. The research presented here focuses primarily on new methods for improving the various aspects of the synthesis process with the intent of growing very long CNT arrays over large substrate surface areas. Experiments were conducted to optimize certain aspects of the substrate preparation and CVD processes. In addition, amazing advances in CNT growth were obtained by combining gadolinium with iron catalyst. Research was also conducted in two areas of carbon nano-composite materials.

Committee: Mark Schulz PhD (Committee Chair); Vesselin Shanov PhD (Committee Co-Chair); Jay Kim PhD (Committee Member); Randy Allemang PhD (Committee Member) Subjects: Materials Science

Doctor of Philosophy, The Ohio State University, 2009, Chemical Engineering

In recent years there has been increased interest in the broad areas of micro- and nano-technology due to the potential to create materials with unique properties which were previously unattainable. One area of special interest has been the use of nanoparticles such as nanoclays, nanofibers and carbon nanotubes and microscale carbonyl iron particles. Nanoclays and nanofibers have received attention due to their ability to be incorporated into polymer matrices and impart functionality such as electrical conductivity, increased tensile strength and modulus, and a reduction of gas and moisture permeability at much lower particle loadings when compared to traditional fillers such as carbon black and glass fibers. The addition of these nanoparticles also has a significant effect on the rheological properties of the composite. The rheological behavior of polystyrene/nanoclay composites under steady state shear flow and polystyrene/carbon nanofiber composites under transient shear and uniaxial extension is investigated. A constitutive model is developed that is capable of predicting the shear and extensional rheology of both types of composites and predicts orientation changes to the nanoparticles due to flow. The model is validated through comparison to the experimental rheological measurements of both composite types and experimental measurements of carbon nanofiber orientation in the polystyrene/carbon nanofiber composites under uniaxial extension.The addition of magnetizable carbonyl iron particles to a non-magnetizable carrier fluid has been done to create a smart fluid, known as a magnetorheological fluid, whose rheological properties can be modified through the application of a magnetic field. This added functionality is being utilized in applications such as shock absorbers, dampers, brakes, and clutches. The use of these fluids in engineering applications requires rheological models capable of capturing their complex flow behavior under various flow conditions. Th (open full item for complete abstract)

Committee: Dr. Kurt Koelling (Advisor); Dr. Stephen Bechtel (Committee Member); Dr. L. James Lee (Committee Member) Subjects: Chemical Engineering

Doctor of Philosophy in Clinical-Bioanalytical Chemistry, Cleveland State University, 2009, College of Science

Nitric oxide (NO) is an important intercellular messenger that acts in many tissues to regulate a diverse range of physiological and pathological processes. The physiologically implications of NO function are far from being completely understood. The multifaceted reactivity of NO prompted the need for accurate determination of the concentration of this molecule. However, it is difficult to detect nitric oxide, particularly in biological media and near live cells due to its short half-life, a result of its reactivity and the low levels of NO produced in vivo. As a result, the accurate and reliable detection of NO under varying experimental conditions has always posed a challenging task. The main goal was to develop ultra-sensitive electrocatalytic sensors for accurate quantification of NO. We report the fabrication and characterization of improved NO sensors based on electrocatalytic platforms such as ruthenium (colloids, nanoparticles, and nanotubes) and carbon (pastes and nanotubes), acting as catalytic sites for NO oxidation. These sensors are characterized using various surface analytical tools. The electrocatalytic oxidation of NO is assessed by cyclic voltammetry and amperometry both in solution phase and gas phase. Excellent sensitivity and linearity are observed for our modified electrodes towards NO quantification. Our new NO detection sensors also show superior limit of detection and selectivity against common interference species. Our NO sensors are tested for various applications including in the measurement of NO released from human umbilical vein endothelial cells (HUVECs).

Committee: Dr. Mekki Bayachou PhD (Advisor); Dr. Lily Ng PhD (Committee Member); Dr. Robert Wei PhD (Committee Member); Dr. John Turner PhD (Committee Member); Dr. Petru Fodor PhD (Committee Member) Subjects: Chemistry

Doctor of Philosophy, University of Akron, 2010, Polymer Engineering

The major objective of this study was to investigate the effect of ultrasonic treatment on the state of dispersion and properties of carbon nanotubes (CNTs) and carbon nanofibers (CNFs) in polymer matrices. In order to achieve this objective, an ultrasonic single screw extruder operating at a frequency of 20 kHz and an amplitude of upto 10 μm and an ultrasonic twin screw extruder operating at a frequency of 40 kHz and an amplitude of upto 6.0 μm, were used to process highly viscous materials and disperse these nanofillers homogeneously in a polymer matrix at residence times of order of seconds. High temperature thermoplastic resins including polyetherimide (PEI), liquid crystalline polymer (LCP) and polyetheretherketone (PEEK) were used. Multiwalled carbon nanotubes (MWNTs) and CNFs were used as reinforcing fillers. The effect of nanofiller loading and ultrasonic amplitudes on rheological, mechanical, electrical, thermal and morphological properties of the nanocomposites was studied. Ultrasonic treatment showed a tremendous decrease in die pressure. Morphological studies showed that ultrasonic treatment improved dispersion of CNFs and CNTs in polymer matrices. PEI/CNFs and PEI/MWNTs nanocomposites were prepared using ultrasound assisted single and twin screw extruder, respectively. A permanent increase in the viscosity, storage and loss modulus and decrease in tan δ was observed with ultrasonic treatment. Ultrasonically treated PEI/CNFs nanocomposites showed a decrease in electrical percolation threshold value as compared to the untreated ones. Breakage of CNFs was observed primarily due to extrusion process alone. In case of PEI/MWNTs nanocomposites, percolation threshold value was found to be between 1 and 2 wt% loading of CNTs for both treated and untreated samples. LCP/CNFs nanocomposites were prepared using ultrasound assisted twin screw extruder with separate feeding of CNFs in the polymer melt. In contrast to behavior of PEI/CNFs and PEI/MWNTs nanocomposites (open full item for complete abstract)

Committee: Avraam Isayev Dr. (Advisor); Erol Sancaktar (Committee Chair); Kevin Cavicchi (Committee Member); Darrell Reneker (Committee Member); Zhenhai Xia (Committee Member) Subjects: Polymers

Doctor of Philosophy, University of Akron, 2007, Polymer Engineering

Chaotic mixing is a novel mixing technique offering high mixing efficiency even under mild shearing conditions. In this work, chaotic mixing was used to prepare composites of carbon nanofibers and two thermoplastic polymers – poly (methyl methacrylate) (PMMA) and thermoplastic polyurethanes (TPU) – and their electrical, mechanical, and thermal properties were evaluated. The TPU systems were based on the reaction products of 4,4'-diphenylmethane diisocyanate, (MDI), soft segment polyol, and 1,4-butanediol as chain extender. Soft segment polyols in the form of poly(propylene glycol) (PPG), and poly(ε-caprolactone)diol (PCL) were used to obtain respectively amorphous and crystalline soft segments. Of these, the TPU system based on crystalline soft segment exhibited shape memory effects. Both, as-received untreated carbon nanofibers (CNF) with a very low amount of atomic oxygen on the surface, and oxidized carbon nanofibers (CNFOX) were used. CNFOX was also modified by esterifying with PPG to produce a third type of carbon nanofiber named CNFOL. These carbon nanofibers were examined by X-ray photoelectron spectroscopy to determine the elemental composition of the surface, and by scanning electron microscopy and transmission electron microscopy to determine the surface morphology.

Committee: Sadhan Jana (Advisor); Avraam Isayev (Other); Rex Ramsier (Other); Kevin Cavicchi (Other); Shing-Chung Wong (Other) Subjects:

PhD, University of Cincinnati, 2024, Engineering and Applied Science: Electrical Engineering

This dissertation work deals with the development of refined models of field emission (FE) from carbon nanotubes (CNTs). The first project described focuses on an efficient algorithm computing the temperature distribution along a CNT during FE, considering the substrate as a perfect heat sink at temperature T₀. It incorporates Joule heating effects, radiative losses, and recently reported analytical expressions for emission current density and heat exchange at the CNT tip, including Nottingham-Heating and Henderson-Cooling effects. Temperature dependencies of CNT's electrical resistivity and thermal conductivity are also included. Simulation times for calculating CNT FE characteristics and temperature distribution were found to be about two orders of magnitude faster compared to numerical methods accounting for both current and energy exchange at the CNT tip. The algorithm was adapted to analyze the impact of thermal contact resistance on the FE properties of a CNT. Using a boundary condition from literature, thermal contact resistance effects at a CNT/chuck interface were accounted for, with the chuck assumed as a perfect heat sink at temperature T₀. Results demonstrate that current constriction at the CNT/chuck contact point induces self-heating effects, which escalate with higher thermal contact resistance values. Consequently, this increases the temperature profile along the CNT, including its tip temperature, and augments the FE current beyond values presumed with the CNT/chuck interface at T₀. The fractional change of emission current with applied external electric field was calculated for increasing thermal resistivity values of the CNT/chuck interface. Next, the effect of electrostatic forces on the FE properties of flexible emitters as a function of the strength of the applied (macroscopic) external electrostatic field are investigated. Results show that deflection of a flexible metallic CNT due to an externally applied electrostatic field inc (open full item for complete abstract)

Committee: Marc Cahay Ph.D. (Committee Chair); Tao Li Ph.D. (Committee Member); Mark Schulz Ph.D. (Committee Member); Tyson Back Ph.D. (Committee Member); Yeongin Kim Ph.D. (Committee Member); Je-Hyeong Bahk Ph.D. (Committee Member) Subjects: Electrical Engineering

PhD, University of Cincinnati, 2023, Arts and Sciences: Chemistry

Lead contamination can cause serious health effects in humans, especially in young children. While there are various sources of lead contamination, the two major sources are drinking water and paint. The lead in drinking water comes from the lead service lines (LSLs) or lead soldering, while lead was added to paints originally as either pigments or additives. Traditionally, the gold standard for detecting lead in drinking water and paint is inductively coupled plasma-mass spectroscopy (ICP-MS) or atomic absorption spectroscopy (AAS) since these techniques can detect lead ions and insoluble lead compounds. However, these methods are expensive and require trained personnel, so samples must be collected and sent off for analysis. Therefore, homeowners concerned about their water or paint must wait for results. There has been an effort to develop electrochemical sensors that can detect low concentrations of lead in water and paint; however, they require a sample preparation step, typically acidification with nitric acid, to dissolve the insoluble lead compounds before analysis. Again, this makes these methods less user-friendly. This dissertation focuses on using electrochemical methods for acidifying water samples containing drinking water and detecting the lead, either a lead corrosion scale from LSLs or lead paint. The first part of this work focuses on membrane electrolysis, a technique that allows for the in situ generation of nitric acid so that no reagent has to be handled. This technique was used to dissolve the lead corrosion scale and lead paint samples so they could be detected by square wave anodic stripping voltammetry (SWASV). Standard addition is used to estimate the lead concentration from the electrochemical method for either sample, and the results are then compared to ICP-MS. The results show good agreement between the comparisons of the concentrations determined through the electrochemical method and ICP-MS for both the lead corrosion scale a (open full item for complete abstract)

Committee: Noe Alvarez Ph.D. (Committee Chair); Ryan White Ph.D. (Committee Member); Neil Ayres Ph.D. (Committee Member) Subjects: Analytical Chemistry