Master of Sciences (Engineering), Case Western Reserve University, 2024, Biomedical Engineering

Healthcare associated infections (HAIs) in the United States cost $28.4 to $33.8 billion a year and 25.6% of HAIs come from the use of medical devices. There is a need for a strategy to decrease infection rates to prevent further surgeries in patients. An electrosprayed polymerized cyclodextrin (pCD) coating of crosslinked polymer can provide affinity-based release Minocycline that prolongs its efficacy. The parameters of the electrospraying solution and process were tailored to provide spherical droplets. Spherical droplets were fabricated in multiple different formulations through SEM analysis and ATR-FTIR confirmed the success of crosslinking. The drug loading and release study did not have the expected results. Through further analysis it was shown that the coating was not strongly adhered to the stainless steel. Therefore, future work is proposed on surface modification and functionalization to create a stronger bond between the polymer coating and the stainless steel surface.

Committee: Horst von Recum (Committee Chair); Samuel Senyo (Committee Member); Colin Drummond (Committee Member) Subjects: Biomedical Engineering

PhD, University of Cincinnati, 2021, Engineering and Applied Science: Materials Science

Aluminum 7xxx series alloys exhibit a combination of high mechanical strength as well as decent corrosion resistance and are widely utilized in aircraft structures. However, high strength 7xxx series alloys, like AA7075 in the T6 heat-treated condition, is susceptible to failures from fatigue, corrosion, stress corrosion cracking and corrosion-fatigue from the mechanical loading and saline environments these structures are exposed to during service. To address these shortcomings, the effects of advance surface treatment processes of Laser Shock Peening without coating (LSPwC) and Ultrasonic Nanocrystal Surface Modification (UNSM) on the mechanical behavior, corrosion properties and near-surface microstructure changes of Al 7075-T6 alloy were investigated. These treatments induce high compressive residual stresses which results in enhancement of the fatigue life of the material and has a positive impact on the corrosion resistance. A series of experiments were conducted to study the impact of these surface treatments on residual stress, microstructural evolution and, in turn, their effects on strengthening, fatigue, corrosion, and corrosion-fatigue properties. The near-surface microstructure in Al 7075-T6 alloy after these surface treatments were characterized by advanced electron microscopy techniques. LSPwC led to remarkable near-surface microstructure composed of a ~2 µm wide newly solidified matrix recast surface layer embedded with O-rich Al nanoparticles (NPs) with the same close-packed orientation relationship (OR) as the surrounding Al matrix, together with a nano-scale aluminum oxide layer formed on the outermost surface. The formation mechanism is associated with high-pressure surface ablation leading to melting, vaporization, and shock-assisted rapid solidification during the LSPwC process. The close-packed OR between NPs and matrix is believed to be due to surface energy minimization. These unique near-surface microstructural changes induced by LSPw (open full item for complete abstract)

Committee: Vijay Vasudevan Ph.D. (Committee Chair); Yao Fu Ph.D. (Committee Member); Ashley Paz y Puente Ph.D. (Committee Member); Matthew Steiner Ph.D. (Committee Member) Subjects: Materials Science

Doctor of Philosophy, University of Akron, 2021, Mechanical Engineering

In 2016 it was estimated that corrosion related costs were 3.4% of global GDP. Coatings are widely used for preventing or controlling corrosion. However, none of the currently used corrosion resistant coatings provides enough wear resistance for gears and bearing applications. Poor surface morphology of the corrosion resistant coatings cause increased wear and friction, resulting in early failure of the rolling element. Developing electrodeposited alloy coatings that promote synergy with additives used in gear and engine oils, while providing corrosion resistance can be a viable solution. Alloyed metals provides superior properties (like hardness, physical, chemical, magnetic) compared to pure metals, even at a nanoscale. Ni-W alloy was recently been reported to have unique contribution to mechanical, tribological and corrosion resistant performance. In addition, Ni was found to promote the formation of a thicker and durable lubricating layer. However, careful evaluation of in-service life of these alloy coatings are needed. Composite nanoparticles in many cases can also improve tribological performance of the component. Researchers have studied the effect of such nanoparticles on the tribological performance of oils. Both beneficial and detrimental effect of such nanoparticles has been reported. In this study NiW alloy and NiW-TiO2 composite coatings were electrodeposited on SAE 52100 steel coupons. Pulsed reversed current (PRC) electrodeposition technique is used due to its capability of producing more dense and uniform coating. Also, incorporating TiO2 nanoparticles on the NiW matrix is hypothesized to enhance the hardness and corrosion resistance. Both NiW alloy and NiW-TiO2 coated disks were tested in fully formulated oil and mineral oil provided by John Deere. Tribological performance was evaluated in both sliding and rolling condition. Corrosion resistance property were measured in 3.5% NaCl. Sliding performance were tested using High Frequency Reciproc (open full item for complete abstract)

Committee: Gary L. Doll (Advisor); Gregory N. Morscher (Committee Member); K.T. Tan (Committee Member); Rajeev K. Gupta (Committee Member); Robert Mallik (Committee Member) Subjects: Chemistry; Materials Science; Mechanical Engineering

Master of Sciences (Engineering), Case Western Reserve University, 2020, Chemical Engineering

A novel approach to hydrophobic surface modifications of cotton fabric using the vapor deposition of hexadecyltrimethoxysilane (HDTMS) was developed. The method does not involve the use of any solvent, offering a less time-intensive, more economical, and more environmentally friendly approach to waterproof surface modifications. There was not a statistical difference in resulting contact angle measurements from the vapor deposition procedure and the solvent-based procedure from the literature. The hydrophobicity of the HDTMS monolayer due to the combination of surface free energy and surface roughness was verified with contact angle measurements and scanning electron microscope (SEM) images in concordance with the Wenzel and Cassie-Baxter models of wetting.

Committee: Daniel Lacks Professor (Advisor); Christine Duval Professor (Committee Member); Julie Renner Professor (Committee Member) Subjects: Chemical Engineering; Chemistry; Materials Science

Master of Science, Miami University, 2019, Mechanical and Manufacturing Engineering

In this work, the condensation heat transfer performance of silica nanospring-coated horizontal aluminum tubes is assessed. Coated samples with varying nanospring mat thicknesses, dependent on growth time, were evaluated against a baseline aluminum sample. Condensation heat transfer testing with water was performed in an evacuated environmentally controlled chamber at flowrates ranging from 1.5 to 5.5 LPM and subcooling temperatures of 1.5, 5.5, and 9.5℃ (Tsat ≈ 20℃). During this testing, the nanospring-coated samples exhibited similar condensation heat transfer coefficients to the baseline sample and the SN15 sample (15-min. growth) increased the heat transferred to the cooling fluid by 60% as compared to the baseline. A patterned sample with alternating hydrophobic and hydrophilic rings was created with 15 minutes of growth, which offered similar heat transfer performance to the SN15 sample. Video analysis determined that the SN15 and SN20 (20-min. growth) experienced an 84% increase in the condensate removal rate over the baseline, while the patterned sample experiences a 96% increase. SEM imaging revealed that the coating withstood the condensation environment. Additional work needs to be performed to further evaluate the coating, but these findings suggest that the coating may be capable of improving condensation heat transfer performance.

Committee: Andrew Sommers Dr. (Advisor); Giancarlo Corti Dr. (Advisor); Carter Hamilton Dr. (Committee Member); Edgar Caraballo Dr. (Committee Member) Subjects: Mechanical Engineering

Doctor of Philosophy, University of Akron, 2018, Polymer Science

Significant efforts have been made to understand corrosion since it is important both scientifically and technologically, as the direct cost resulting from corrosion and its prevention has become a non-negligible portion of the gross domestic product. While considerable effort has been made to understand the macroscopic corrosion behavior and empirical knowledge of effective corrosion mitigation strategies is available, a nanoscale description of corrosion processes is still lacking. This dissertation describes efforts to establish a fundamental understanding of the corrosion process at the coating/metal interface on the nanoscale. The dissertation is divided into three parts. In the first part, a nanoscale depiction of the influence of ions on the diffusion of water is garnered from the analysis of X-ray and neutron reflectivity (XR/NR) and electrochemical impedance spectroscopy (EIS) data since metal, water and oxygen are three key ingredients in corrosion and ions play an important part in accelerating corrosion. The diffusion of water or electrolyte in thin polymeric films in different directions, parallel to the film or perpendicular to it, was distinguished. XR/NR measurements were used to probe the diffusion parallel to the film using a customized diffusion cell and that rate was found to be orders of magnitude larger than the diffusion rate in bulk epoxy. In contrast, when EIS data were analyzed using equivalent electrical circuit (EEC) model fitting, the penetration (diffusion perpendicular to the film) rate was found to be orders of magnitude smaller than the diffusion rate in bulk epoxy. Consistent results from XR, NR and EIS showed that the diffusion rates of electrolyte in both the lateral and perpendicular directions are lower than those of water (H2O/D2O), and that the higher the ion concentration, the lower the rate of diffusion. Reflectivity measurements probing at small (nm) length scales and also comparatively short times (hours) (open full item for complete abstract)

Committee: Mark Foster (Advisor); Mark Soucek (Advisor); Mesfin Tsige (Committee Chair); Ali Dhinojwala (Committee Member); Qixin Zhou (Committee Member) Subjects: Polymers

Doctor of Philosophy, University of Akron, 2015, Civil Engineering

Spherical roller bearings (SRBs) utilized in the gearboxes of wind turbine generators are known to be especially susceptible to premature failure due to low cycle micropitting of the raceways. Micropitting in rolling element bearings is believed to arise from significant roller/raceway sliding in thin film lubrication conditions. Roller/raceway sliding occurs in SRBs as a consequence of their geometry, and almost all the bearings in wind turbine gearboxes operate in thin film (or low lambda) lubrication conditions. There is currently no accepted solution to mitigate micropitting in wind turbine gearboxes that are equipped with SRBs. Since WC/a-C:H coatings on rolling elements have been effectively used to solve wear issues encountered by SRBs in other industrial applications, these coatings have been offered as a solution to low cycle micropitting in wind turbine gearbox SRBs. This research plan has been developed to test the hypothesis that a WC/a-C:H coating will mitigate or eliminate micropitting such as that experienced by SRBs in wind turbine gearboxes. The laboratory tool that is used to create micropitting on test specimens is the PCS Instruments Micropitting Rig (PCS MPR). The MPR is a three-contact disc machine in which there are three rings of equal diameter positioned at 120 degrees apart with a smaller diameter roller located in the middle and in contact with all the rings. This arrangement allows the test roller to be subjected to a large number of rolling contact cycles in a short period of time and hence significantly reduces testing time. At a typical entrainment speed of 3.5m/s, the central test roller will experience approximately one million contact cycles per hour. Since the controls of the PCS MPR allow the speed, slide-roll ratio, temperature, and load to be automatically and independently controlled, the thin film lubrication and slide/roll ratio conditions that generate micropitting on SRBs can be reproduced in the laboratory. Mo (open full item for complete abstract)

Committee: Gary Doll Professor (Advisor); Evans Ryan Doctor (Committee Member); Binienda Wieslaw Doctor (Committee Member); Dong Yalin Doctor (Committee Member); Menzemer Craig Doctor (Committee Member); Sancaktar Erol Doctor (Committee Member) Subjects: Aerospace Engineering; Aerospace Materials; Materials Science; Mechanical Engineering

PhD, University of Cincinnati, 2009, Engineering : Materials Science

The film structure and surface morphology of a novel one-step epoxy-silane coating system were revealed by neutron reflectivity, Atomic Force Microscope (AFM) and Environmental Scanning Electron Microscope (ESEM). The bis-sulfur silane is enriched at the coating-substrate interface instead of uniformly distributed, which leads to a layered structure. The phase separation within bulk coating films was investigated by Ultra Small Angle X-ray Scattering (USAXS) and Small Angle Neutron Scattering (SANS). The epoxy-silane network forms branched morphologies without significant interface. No phase separation on scale range from 0.5 nm to 10.3 nm were observed. The protection mechanisms of the epoxy-silane coating system were studied in terms of coating structure, water response behavior, salt exclusion and hydrothermal stability. By comparing pure epoxy and epoxy-silane mixtures in various aqueous environments, the effects of the addition of silane were determined. The key mechanisms of silane-enhanced protection are: 1. Bis-sulfur silane is enriched at the substrate-coating interface and forms a SiO2-like interface region, which ensures excellent adhesion between coating and substrate. The addition of silane also increases the roughness of the epoxy-silane film. 2. The silane serves as a crosslinker, resulting in a denser and less hydrophilic bulk film compared to the neat epoxy. The hydrophobic nature of bis-sulfur silane also increases the overall hydrophobicity of the mixed film. 3. The salt exclusion effect is introduced to epoxy-silane film due to the addition of bis-sulfur silane fines the molecular-level free space. 4. The epoxy-silane film shows improved hydrothermal stability. The addition of bis-sulfur silane eliminates the hydroxyl groups formed during the cure process. The absence of hydroxyl group prevents the bond scission effect. The addition of silane also introduces the immunity of hydrothermal degradation to the film-substrate interface by the forma (open full item for complete abstract)

Committee: Dale Schaefer (Committee Chair); Jude Iroh (Committee Member); Vesselin Shanov (Committee Member); William Vanooij (Committee Member) Subjects: Engineering; Materials Science

PhD, University of Cincinnati, 2006, Engineering : Mechanical Engineering

The main objective of this work is to study the surface modification and the mechanics of interfaces in nanocomposites. Investigation of this topic is motivated by the exceptional mechanical properties that have been demonstrated in many nanomaterials. A combined modeling and experimental approach is developed. The systems studied mainly include polystyrene polymers that are reinforced by carbon nanotubes subjected to different surface modifications. In the experimental part of this work, the surfaces of three different types of carbon nanotubes are modified by plasma polymerization technique using a custom-built RF plasma system. Characterization indicates that the surface properties of carbon nanotubes are modified by the process and a thickness of 2-7 nm deposited polymer film is achieved. Results from DSA and TGA measurements provide the evidences for such polymer film existence and uniformity is examined based on above measurements. The thickness of deposited polymer film estimated from TGA measurements matches the thickness observed from HRTEM very well. SIMS and Raman measurement further confirmed the existence of the deposited film and its uniformity. It is found that the chemical structure of carbon nanotube surface can be tailored by changing the monomer in plasma polymerization processing. The deposited polymer films not only significantly improve the dispersion of carbon nanotube in solvent and polymeric matrix, but also significantly improve the interfacial properties between carbon nanotube and polymer matrix. Mechanical testing also indicates that the plasma treatment can improve the mechanical properties of nanocomposite significantly. When the concentration of MWCNT is 3%, the mechanical property of nanocomposite reaches the maximum point. The experimentally observed relation between the mechanical properties and interface motivates the modeling and simulation study. Molecular mechanics and molecular dynamics are two of the primary tools used for (open full item for complete abstract)

Committee: Dr. Dong Qian (Advisor) Subjects: Engineering, Mechanical

PhD, University of Cincinnati, 2002, Pharmacy : Pharmaceutical Sciences

Loop diuretics offer great advantages in treating edematous states associated with congestive heart failure, liver cirrhosis and kidney failure owing to their intense diuretic effect. Evidences suggested the diuretic effect can be exaggerated by careful control of the rate at which loop diuretics are made available to the urinary tubules. If optimally designed, peroral extended release formulation can provide better utilization of the same total dose of loop diuretic, an effect of utmost importance in edematous patients with high resistance to loop diuretics. Bumetanide multiparticulate immediate and extended release formulations were developed and tested in rabbits. A novel multiple response optimization technique based on superimposing contour diagrams was developed and successfully used to optimize bumetanide release. Instability in drug release from multiparticulate formulations after storage warrants in depth investigation of different formulation and processing factors controlling drug release. Curing time, temperature, plasticizer level, coating polymer lipophilicity, and the use of hydrophilic seal coat were explored in this study. The findings proved instability in bumetanide release is attributed to drug migration into the film coat during storage. Careful selection of plasticizer level and curing conditions together with the use of hydrophilic seal coat prevented drug migration and stabilized drug release after storage. When compared to immediate release formulation in rabbits, equivalent amounts of bumetanide were excreted from both formulations yet at different rates. The slow delivery of bumetanide from the extended release formulation improved its diuretic and natriuretic efficiencies within the first day after dosing. The activation of compensatory mechanisms is thought to diminish the response to extended release bumetanide formulation within the second day. While providing comparable diuretic and saliuretic effects to that of immediate release form (open full item for complete abstract)

Committee: Dr. Adel Sakr (Advisor) Subjects: Health Sciences, Pharmacy

Doctor of Philosophy, The Ohio State University, 2004, Industrial and Systems Engineering

The main theme of the proposed research was centered on a broad scope of surface finishing processes, including conventional finish cutting to ball burnishing. In finish cutting, the effects of edge preparation and tool wear of the cutting tool are considered most critical, as they directly determine surface finish and properties of the subsurface layer (residual stress, microstructure, microhardness). Understanding of tool wear and the capability of predicting it enable successful process optimization. To work towards this goal, the effect of cutting edge designs (hone and chamfer) on the cutting variables and process mechanics was investigated using Finite Element Method (FEM) simulations. An FEM-based methodology involving nodal wear rate calculations was developed for uncoated carbide to predict the progression of tool wear geometry during cutting. Cutting inserts with multilayer coatings are used in every category of industrial cutting applications. The analysis of the wear behavior of coated tools largely relies on extensive experimental tests. To supplement reliable process data and reduce the required experimental costs, an FEM simulation model for coated tools was developed by modeling the coating structure as an effective composite layer. The thermal insulation effect of the hard coatings (ex. Al2O3) was evaluated using the model and qualitatively compared with the experimental data in literature. The developed analysis model for coated tools was applied to a selected industrial case in which a comparative study of tool wear was required. The wear characteristics of the 1mm-TiN/9.5mm-Al2O3/4mm-TiCN coated tool against AISI 1080 and 8219 were analyzed through conventional turning experiments. Correspondingly, an approximated 2-D simulation model was developed based on fresh tool geometry. This model predicted the initial wear rate at the start of cutting and allowed differentiation of the tool wear at distinct cutting conditions. Another focus of this resea (open full item for complete abstract)

Committee: Taylan Altan (Advisor) Subjects:

Master of Sciences (Engineering), Case Western Reserve University, 2010, Materials Science and Engineering

Five types of zinc coated sheet steels were evaluated for their surface friction, coating adhesion properties and formability under different strain states. The coefficient of friction values found under biaxial tensile strain were significantly larger than those associated with the drawing strain states. It was found that surface morphology, strain state, and shear yield strength of the zinc coating were direct factors affecting surface friction. The η- phase based coatings exhibited the lowest coating adhesion either at the plane strain condition or at the stretching condition whereas the δ- phase based coating exhibited that at the drawing condition. It was found that coating adhesion depends directly on the microstructure of the zinc coating and the strain state. It was also found that surface friction and coating adhesion could affect the formability of a zinc coated steel sheet by influencing its strain state and fracture mechanism, respectively.

Committee: Gary Michal Prof./PhD (Committee Chair); Gerhard Welsch Prof./PhD (Committee Member); John Lewandowski Prof./PhD (Committee Member) Subjects: Materials Science

Doctor of Philosophy, University of Akron, 2012, Polymer Science

A key means of creating an interface able to withstand all kinds of stresses developed during processing and device operation is to achieve substantial interdiffusion of the two polymers at the interface. There have been many studies of the structure of model polymer/polymer interfaces at thermodynamic equilibrium where detailed comparisons can be made with predictive theories. Also the connection between adhesion and interface width for these equilibrium interfaces has been investigated by others. Non-equilibrium interfaces are more complicated than their equilibrium analogs, but much more common, and therefore important, in practice. One example is the interface between direct solution cast polyimide (PI) films used as compensation layers and the films used for their support in liquid crystal displays (LCDs). We consider specifically PI copolymers that are soluble in common organic solvents and therefore suitable for solution casting on a substrate film, e.g. cellulose triacetate. To obtain high quality bilayers with excellent durability, sufficient interlayer adhesion strength is needed. This adhesion directly correlates with the structure of the interface between the polyimide layer and the cellulose triacetate substrate. It is important to understand how the non-equilibrium interface structure in such systems involving polymer layers of limited miscibility can be adjusted during the direct coating process to achieve better adhesion. Polyimide/cellulose triacetate bilayer structures for interfacial width measurements are deposited by first spin coating the cellulose triacetate layer and then spin coating or solution casting the polyimide layer on top of the cellulose triacetate layer, while corresponding bilayers for adhesion measurements are deposited by sequential solution casting. Two fluorinated polyimides are studied: IN1 with 12.5 atomic wt% of fluorine and IN3 with 31.3 atomic wt% of fluorine content. Estimation of the segment-segment interaction paramete (open full item for complete abstract)

Committee: Mark Foster Dr. (Advisor); Gary Hamed Dr. (Committee Member); Darrell Reneker Dr. (Committee Member); Sadhan Jana Dr. (Committee Member); Bi-min Newby Dr. (Committee Member) Subjects: Engineering; Materials Science; Physics; Plastics; Polymer Chemistry; Polymers; Technology