MS, University of Cincinnati, 2023, Engineering and Applied Science: Mechanical Engineering

Ultrasonic Nanocrystal Surface Modification (UNSM) is a relatively new surface modification technique caused by severe plastic deformation,. UNSM involves scanning a CNC-controlled Tungsten Carbide ball tip across the surface of the specimen whilst it vibrates at an ultrasonic frequency backed by a static load. The ultrasonic vibration backed by the static load coupled with the scanning action have an overall effect that can be considered analogous to a hybrid of micro-cold forging and burnishing. Numerous studies have been undertaken toward understanding the underlying principles governing the outcome of the process, however, a comprehensive investigation into the effects of different processing parameters on the surface properties of the processed specimen has been missing from the literature. The objective of this study was to perform a comprehensive investigation of the effects of different processing parameters of UNSM on the surface properties of 300M steel, a material that is widely used for numerous applications such as aircraft landing gears and high-performance drive shafts. Experiments were performed using combinations of the following three processing parameters: scanning speed, scanning interval, and static load. The resulting surfaces were evaluated for surface hardness, roughness, wettability, appearance, and residual stresses. After analyzing the results, it was observed that the sliding action of the scanning motion caused trenches, visible under a microscope, to form on the surface of the specimen that was found to be one scanning interval apart. It was found that as the scanning speed is decreased the micro-cold forging action of the vibratory motion becomes the dominant governing mechanism of the process and the surface roughness increases as a result of decreasing scanning speed. The increase in static load was observed to intensify the peening action of the vibratory motion of the tungsten carbide tip resulting in surface damage, visible (open full item for complete abstract)

Committee: Murali Sundaram Ph.D. (Committee Chair); Manish Kumar Ph.D. (Committee Member); Dinc Erdeniz Ph.D. (Committee Member) Subjects: Mechanical Engineering

Doctor of Philosophy, The Ohio State University, 2012, Chemical and Biomolecular Engineering

The field of nucleic acid based therapeutics offers treatments for diseases at the most basic level of cellular biochemistry and its potential is boundless. Oligonucleotide therapeutics is also an invaluable tool in studying cellular processes and the precise effect certain genes have on disease models. Since passive cellular uptake of these highly charged molecules is low, an effective delivery method is imperative in order to achieve an observable effect. Lipid based nanoparticles with their numerous, well-documented advantages are often used for delivery and in this work, both pharmaceutical and engineering based approaches were explored to construct lipoplex nanoparticles. From the pharmaceutical side, the effect of lipid chirality on transfection efficiency was investigated. From an engineering perspective, even though liposomal nanoparticles represent an especially promising class of drug delivery vectors, conventional bulk mixing preparation methods have room for improvement with regards to yield and consistent control over structure and composition. Therefore, a device-based approach using arrays of microwells was studied to not only deliver particles directly to cells in a more controlled way but also to introduce control over the typically uncontrolled complexation process of lipids and nucleic acids. DOTAP, as a racemic mixture, is a cationic lipid and a widely used transfection reagent. In this study, racemic and enantiomerically pure DOTAP were used in lipoplex formulations to deliver siRNA to MCF-7 cells, targeting the aromatase enzyme. The R enantiomer of DOTAP was found to be more efficacious than the S enantiomer or the racemate when used in combination with cholesterol. Specifically, the aromatase activity of cells treated with R-DOTAP lipoplexes was 50% lower than those treated with S-DOTAP or racemic lipoplexes at a 10 nM siRNA concentration. In other words, R-DOTAP lipoplexes were twice as effective at the low concentration. Amongst the DOTAP en (open full item for complete abstract)

Committee: L. James Lee (Advisor); Robert J. Lee (Advisor); Jeffrey J. Chalmers (Committee Member); Zhonga Liu (Committee Member) Subjects: Chemical Engineering

Doctor of Philosophy, University of Akron, 2006, Chemical Engineering

The importance of polymer thin films (< 100 nm) in microelectronics, coatings/paints, adhesives, nanofabrication, or biodevices has promoted extensive studies on the dewetting phenomenon of these thin films. Most of the studies have been focused on the effects of polymer properties on the dewetting and the associated kinetics while the effects of substrates on the dewetting behaviors, which could be crucial in some cases, have rarely been reported. For the few experimental studies that utilized modified substrates, none has systematically varied substrate surface energy (γS) to examine its effects on the dewetting. Therefore, in this study, the effects of γS on the dewetting process of supported polystyrene (PS, Mn of 63k and 9.3k) thin films were studied. The substrates were modified using various organosilanes under different preparation conditions to systematically vary γS, ranging from 13 to 63 mJ/m2. In particular, the preparation methods included (1) contact printing of octadecyltrichlorosilane on oxidized silicon wafers for different contact times, (2) vapor phase deposition of mixed CF3- and CH3-terminated organosilanes with different ratios, and (3) solution deposition of polar organosilanes with functional groups of -COOH, -CH2Cl, -NH2, or -SH. On these substrates, the kinetics of dewetting was first investigated as a function of γS. Empirical relationships between the rate of hole growth (dewetting velocity, VR) and γS, VR ≈ 530 exp(-0.13γS) and 310 exp(-0.10γS), were obtained from the dewetting of PS-63k thin films on the -CH3 and -CF3/-CH3 covered surfaces, respectively. For PS-9.3k on the OTS surfaces, VR ≈ 1.1 x 104 exp(-0.13γS) was obtained. In analogous to a desorption process, the exponential relationship between VR and γS was hypothesized to be originated from the energy required to overcome the free energy of adhesion in the dewetting process, which is proportional to γS1/2. Second, an origin of the instability of the rim, formed around the dewe (open full item for complete abstract)

Committee: Bi-min Zhang Newby (Advisor) Subjects: Engineering, Chemical

Master of Science in Engineering, University of Akron, 2024, Mechanical Engineering

Additively manufacturing (AM), which is also referred to as 3D printing, is a collection of innovations that generate 3D parts by printing materials in a layer-wise pattern. In comparison to subtractive manufacturing (SM), which includes the removal of material from a compact block or workpiece to produce a desired framework or structure, additive manufacturing (AM) uses adding a material to print out another material. Creating an effective and inexpensive 17-4 PH technology is crucial. A conventional 17-4 PH synthesis method is material extrusion additive manufacturing process. Data collection and aggregation are not done properly in large parts of the globe. The material extrusion additive manufacturing process operates on the premise of layer-by-layer framework and manufacturing of stainless steel. An extensive study into the development of stainless steel, its strength and weaknesses, and its behavior under various conditions has to be researched. The aim of this research was to implement the post processing techniques, using the Ultrasonic Nanocrystal Surface Modification (UNSM), and conventional grinding methods to improve the surface characteristics and mechanical properties of the additively manufactured 17-4 PH stainless steel. 17-4 PH stainless steel was produced using additive manufacturing, successfully. In addition, the microstructure of 17-4 PH stainless steel was characterized using optical microscopy. To satisfy the specific requirement of surface integrity, a finishing process was conducted for the manufacture of stainless steels. The article suggests that the use of Laser and UNSM (LA-UNSM) to improve on this technology should be considered for future works. Furthermore, targeted grinding cooling (TGC) fluid application should be considered for future studies on surface modification.

Committee: Manigandan Kannan (Advisor); Tanmay Tiwari (Committee Member) Subjects: Materials Science; Mechanical Engineering

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

In polymeric nanocomposites like automobile tire, nanofiller reinforcement are responsible for diverse mechanical property enhancements. Dispersion (aggregate break-up) and even distribution of the nanofiller in the matrix is a prerequisite for excellent reinforcement. Diverse factors impact homogeneous dispersion and distribution of these fillers in the polymeric matrixes. Moreover, formation of conductive networks in these systems is of utmost importance due to tear mitigation and static charge dissipation. Hence a great inter-play between homogenous dispersion and distribution plus formation of conductive network of nano-fillers is indispensable. Diverse factors affect dispersion, distribution, and the formation of conductive networks in polymeric nanocomposites. Surface properties and mixing conditions are factors that play a prominent role in the dispersion of silica fillers in polymers matrixes. When surface charges are present in the silica, they can induce aggregate-aggregate repulsions, which is not beneficial to the formation of conductive networks. Surface modification of silica can shield these repulsive interactions of aggregates. In this work, surface modification of silica was achieved by carbon coating during flame synthesis and by the means of silane coupling agents. The effect of mixing conditions on dispersion and distribution of nano aggregates was also studied. Ultra-small-angle X-ray scattering (USAXS) and microscopy were employed in the analysis of the results. The impact of surface carbon, silane coupling agents and mixing conditions on the van der Waals enthalpic attraction, a*, the excluded volume b* and molar excluded volume per aggregate B2 is determined. These parameters all describe and quantify the extent of dispersion in the studied systems.

Committee: Gregory Beaucage Ph.D. (Committee Chair); Jude Iroh Ph.D. (Committee Member); Russell Schwartz Ph.D M.A B.A. (Committee Member); Kabir Rishi Ph.D M.A B.A. (Committee Member); Jonathan Nickels Ph.D. (Committee Member) Subjects: Materials Science

Doctor of Philosophy (Ph.D.), Bowling Green State University, 2024, Photochemical Sciences

R-alkoxysilanes are the monomer workhorses of silicon-based sol-gel chemistry and are used as the building blocks for materials from silicas to silicones. However, since their inception, the sol-gel and siloxanes communities have struggled with uncontrolled hydrolysis, premature condensation, and overall polymerization and functionalization control. This dissertation focuses on the development of new silicon sol-gel chemistry methodologies which utilize photocaged R-alkoxysilanes and siloxane polymers to aid in synthetic control towards distinct silicon-based materials. We started our investigation with the synthesis and characterization of 2-nitrobenzyloxy photocage systems from ethyl and phenyl derivatives of Rx-(alkoxy)silanes, with x=0-3 and y=1-4, end group photocaged polydimethylsiloxanes, as well as photocaged polyhedral oligomeric silicon-based cage systems. Furthermore, we have also developed Rx-(alkoxy)silanes, with x=0-3 and y=1-4 that contain the 3-dimethylaminobenzyloxy photocage as a more stable alternative to the 2-nitrobenzyloxy based compounds. We have explored the photochemical responses for photo removal including kinetics, efficiency, stability, and tin catalyzed coupling of products to induce polymerization and surface functionalization. We have found that sufficient removal of the photocage groups was achieved, giving a new avenue to generate silicon-based materials. For this dissertation, Chapter 1 describes the background photochemical and silicon-based chemistries needed to understand these processes and their challenges. Chapter 2 details the extensive work on Rx-(alkoxy)silanes containing 2-nitrobenzyloxy groups and their performance in photochemical processes. Chapter 3 defines the work on 2-nitrobenzyloxy polymeric/oligomeric versions of silicon-based materials. Chapter 4 gives an overview of our preliminary work on 3-dimethylaminobenzyloxy photocaged Rx-(alkoxy)silanes. Finally, Chapter 5 gives conclusions and connections for this resea (open full item for complete abstract)

Committee: Joseph Furgal Ph.D. (Committee Chair); Ellen Gorsevski Ph.D. (Other); Jayaraman Sivaguru Ph.D. (Committee Member); Alexander Tarnovsky Ph.D. (Committee Member) Subjects: Chemistry; Organic Chemistry

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, Miami University, 2021, Chemistry and Biochemistry

Construction of well-defined polyurethane dendrimers is challenging due to the high reactivity of externally added or in-situ formed isocyanates leading to the formation of side products. For this reason, the synthesis of dendritic polyurethanes is limited to very few reports. With a primary focus of dendrimer research on the interaction of the periphery and the core, we report the synthesis of a common polyurethane dendron, which allows for late-stage variation of both the periphery and the core. The periphery can be varied simply by installing a clickable unit in the dendron and then attaching to the core and vice-versa. Thus, a common dendron allows for varying both the periphery and the core in the final two steps. To accomplish this, protecting-group-free one-pot multicomponent Curtius reaction was utilized to afford a robust and versatile AB2 type polyurethane dendron employing commercially available simple molecules 5-hydroxyisophthalic acid, 11-bromoundecanol, and 4-penten-1-ol (or 4-pentyn-1-ol). Subsequent late-stage modification of either dendrons or dendrimers via thiol-ene or azide-alkyne click reaction gave surface-functionalized alternating aromatic-aliphatic polyurethane homodendrimers to generation-three (G3). A bifunctional AB2 type dendritic monomer demonstrated this approach's versatility by undergoing a click reaction followed by attachment to the core or attachment to the core followed by click reaction at the periphery to generate surface-functionalized polyurethane dendrimers. This approach enables the incorporation of functionalities at the periphery and the core that may not withstand the dendrimer growth for the synthesis of polyurethane dendrimers and other dendritic macromolecules. While 1-octanethiol was used in the late-stage modification of G1-G3 dendrimers using thiol-ene click chemistry, organic azides (7-diethyl-3-azidocoumarin, 9-azido-2,3,5,6-tetrahydro-1H, 4H-11-oxa-3a-aza-benzo[de]anthracene-10-one, and 4-azido-N-ethyl-1, (open full item for complete abstract)

Committee: Richard Taylor PhD, Professor (Advisor); C. Scott Hartley PhD, Professor (Committee Chair); Dominik Konkolewicz PhD, Associate Professor (Committee Member); David Tierney PhD, Professor (Committee Member); J. Andrew Jones PhD, Assistant Professor (Other) Subjects: Organic Chemistry

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

Doctor of Philosophy, University of Akron, 2020, Mechanical Engineering

In this research, an innovative surface engineering process, ultrasonic nanocrystal surface modification (UNSM), was used to process a 7075-T651 aluminum alloy. It was observed that UNSM led to better surface finish, higher surface hardness, and the generation of an oxide layer on the surface of this alloy, in addition to beneficial compressive residual stresses in the near-surface region. Rotating–bending fatigue tests showed that UNSM processing significantly improved the fatigue performance of 7075-T651 aluminum alloy in both the low-cycle fatigue regimes and high-cycle fatigue regimes. Besides, the oxides that formed in the surface layer after UNSM treatment were found to prevent pitting corrosion of 7075-T651 aluminum alloy in a 3.5 wt% NaCl solution. Therefore, the fatigue performance of the UNSM-treated samples did not deteriorate after corrosion in a 3.5 wt% NaCl solution. These results demonstrate that UNSM is a robust surface modification method that can improve the rotating–bending fatigue resistance and pre-corrosion fatigue resistance of the 7075-T651 aluminum alloy. Furthermore, the fatigue life extension of the pre-damaged 7075-T651 aluminum alloy through UNSM treatment was investigated for the first time. It was found that the fatigue life of 7075-T651 aluminum alloy deteriorates after being immersed in a corrosion solution. However, UNSM treatment significantly recovered the fatigue life of the pre-corroded samples. Removal of corroded surface layer, the introduction of work-hardened surface region and compressive residual stress by UNSM treatment played a compelling role in the restoration of fatigue life of the pre-damaged sample. This result indicated that UNSM is a feasible method for rejuvenation of corrosion-damaged 7075-T651 aluminum alloy. UNSM also showed its powerful effectiveness to rejuvenate pre-fatigued 7075-T651aluminum alloy.

Committee: Yalin Dong (Advisor); Chang Ye (Committee Member); Guo-Xiang Wang (Committee Member); Qixin Zhou (Committee Member); En Cheng (Committee Member) Subjects: Mechanical Engineering

Doctor of Philosophy (Ph.D.), Bowling Green State University, 2020, Photochemical Sciences

We present the study of Fe(III)-carboxylate photochemistry of natural polyuronates in aqueous solutions and in soft hydrogel materials with near UV and violet light. Described in this dissertation are the use of Fe(III)-carboxylate photochemistry for sustainable material applications such as surface modifications and controlled plant nutrient delivery. Quantitative photochemistry of the Fe(III)-alginate system in aqueous solutions was studied using near UV light, and the effect of factors such as alginate composition and solution pH was studied. Degradation of alginate chain with the photochemical reaction was observed by the changes in the solution viscosity. The photochemical reaction seemed to proceed through a radical species and the generation of carbon dioxide anion radical (CO2.-) was identified using Electron Paramagnetic Resonance (EPR) spectroscopy. We present all polysaccharide hydrogels prepared with agarose and carboxylate group containing pectin which showed photoresponsive behavior. Upon Fe(III) coordination and irradiation with 405 nm LED for various time intervals, these gels changed their pH, mechanical properties, porous structure and swelling properties. Based on the radical generation phenomenon, studies on polymerization of selected acrylic monomers using this Fe(III)-carboxylate photochemical system was studied. Other than polyuronate based hydrogels, fabrics with introduced carboxylate functionality showed their ability to polymerize acrylic monomers on their surface, and change their physical and mechanical properties with the use of light. Hydrogel beads prepared with alginate or alginate and other polysaccharide mixtures with Fe(III) showed their ability to absorb phosphate ions from model waste solutions. The solution phosphate concentration dependent phosphate uptake showed a maximum phosphate uptake around 1.5 mgg-1. Phosphate uptake above 1 mgg-1 was seen for a wide pH range of 4.8 - 11.5 due to the strong binding betwe (open full item for complete abstract)

Committee: Alexis Ostrowski PhD (Advisor); Pavel Anzenbacher PhD (Committee Member); George Bullerjahn PhD (Committee Member); Lewis Fulcher PhD (Other) Subjects: Agriculture; Biogeochemistry; Chemistry; Environmental Science; Geochemistry; Inorganic Chemistry; Materials Science; Polymers

Master of Science (MS), Ohio University, 2020, Mechanical Engineering (Engineering and Technology)

This study evaluated the functionalization of bituminous and sub-bituminous coals via acid and hydrogen peroxide routes to improve interfacial adhesion in coal-plastic composites. Three coals were studied, including Pittsburgh No. 8, Kittanning, and Powder River Basin. Boehm analysis and Fourier-transform infrared spectroscopy were used to study coal surface chemistry. Additionally, the interactions (esterification) between the coal's hydroxyl functional groups and graft-maleic anhydride on four different coupling agents were studied. An investigation of the effect of coal filler content (0-60 wt.%) and coupling agent content (0-3 wt.%) on the tensile and flexure properties of the material was conducted. When the coupling agent was added, the greatest improvement in mechanical properties occurred at 60 wt.% coal content and 3 wt.% coupling agent (maleic anhydride grafted-polypropylene) content.

Committee: Jason Trembly (Advisor); Kerrti Kappagantula (Committee Member); Frank Kraft (Committee Member); Peter Harrington (Committee Member) Subjects: Materials Science; Mechanical Engineering

MS, University of Cincinnati, 2018, Engineering and Applied Science: Materials Science

This study investigates the effects of laser shock peening (LSP) and ultrasonic nanocrystal surface modification (UNSM) on residual stress, near surface modification, and hardness of Inconel 718 (IN718) specimens manufactured by selective laser melting (SLM) techniques. IN718 is a nickel-based Ni-Cr-Fe superalloy. It has a unique set of properties that include good workability, corrosion resistance, high-temperature strength, favorable weldability, and excellent manufacturability. Additive manufacturing (AM) techniques, in particular, the laser assisted AM techniques have been developed and adopted in the industry in the past three decades. The LSP and UNSM are the recently developed mechanical surface treatment techniques that cause the severe plastic deformation on the surface. This in turn induces deep compressive stresses and forms a fine-crystalline surface layer in the specimen that improves the hardness, strength, and fatigue life. In this study, the SLM technique is used to manufacture IN718 super-alloy specimens. SLM parts are well known for their high tensile stresses in the as-built state, in the surface or subsurface region. These stresses have a detrimental effect on the mechanical properties, especially on the fatigue life. LSP and UNSM as a surface treatment method are applied on heat-treated specimens and as-built specimens. Heat-treated specimens are those samples which are fully annealed to relieve all the inbuilt stresses. They are heat treated at 955°C for one hour followed by furnace cooling. After LSP and UNSM treatment, optical microscope and electron back scattered diffraction (EBSD) is used to characterize the microstructures of both heat-treated and as-built specimens. A nanoindentation test is performed to determine the local properties like the hardness of as-built and heat-treated specimens. Afterward, the hardness along the distance from the LSP and UNSM treated surface is also defined. After UNSM treatment, compressive residual str (open full item for complete abstract)

Committee: Jing Shi Ph.D. (Committee Chair); Yao Fu (Committee Member); Vijay Vasudevan Ph.D. (Committee Member) Subjects: Materials Science

MS, University of Cincinnati, 2017, Engineering and Applied Science: Materials Science

Type 316 stainless steel (SS316) is widely used in steam generating plants and water reactor systems due to its superior mechanical properties and corrosion resistance. However, it is still subject to the intergranular corrosion (IGC) and stress corrosion cracking (SCC) in certain environments. To improve the resistance to IGC, grain boundary engineering (GBE) was employed to optimize the grain boundary character distribution (GBCD) of SS316. Multi-cycle of ultrasonic nano-crystal surface modification (UNSM) and subsequent annealing at high temperature was employed in this study to modify the GBCD in the near surface region. The strain induced by UNSM and subsequent annealing modified the GBCD in near surface region until 300um in depth by increasing the population of low Σ coincident site lattice (CSL) grain boundary and by breaking the connection of high angle grain boundaries (HAB). Through surface GBE (SGBE) by UNSM and subsequent annealing, the fraction of low Σ CSLs was increased from 34% in the baseline condition to 54%. Cold rolling and subsequent annealing were also used to modify the microstructure of entire sample by increasing the fraction of low Σ CSLs from 41.1% at baseline to 71.5%. The effect of optimization of GBCD on sensitization and IGC was evaluated by double loop electrochemical potentiokinetic reactivation (DLEPR) testing. Electron Back Scattered Diffraction (EBSD) scanning of the sample after DLEPR test showed that the precipitation of carbides arrested at triple junction types J1 and J2 during sensitization treatment. The degree of sensitization (DOS) in the GBEed condition was lower than that in the solution annealed (SA) condition. Iterative cycles of UNSM and single cycle of cold rolling followed by strain annealing can be very effective in improving the resistance to IGC of SS316.

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

MS, University of Cincinnati, 2016, Engineering and Applied Science: Materials Science

In this study, the effects of Ultrasonic Nanocrystal Surface Modification (UNSM) on residual stress, near surface microstructure, hardness, high cycle fatigue, biocompatibility and corrosion behaviour of a low-modulus beta Ti-35Nb-7Zr-5Ta-0.3O (wt %) was studied. The UNSM is novel mechanical surface treatment which effectively improves mechanical properties, fatigue life and wear of engineering components. UNSM causes severe plastic deformation on the surface, thus inducing deep compressive stresses and a surface nano-crystalline layer in the component which improves hardness, yield strength and fatigue life. At first, the as-received specimens were solution treated at 850º C for 1 hour and water quenched to obtain a single phase ß structure. The solution treated specimens were then subjected to UNSM treatment with two different static (20N and 50N) and dynamic loads (20% and 50%). The microstructure after UNSM was characterized by optical, scanning electron microscope (SEM), Electron Backscattered Diffraction (EBSD) and transmission electron Microscopy (TEM). Nanoindentation test was also performed to determine local properties like hardness with distance from the treated surface. The UNSM treated specimen induces compressive residual stresses as high as -1600 MPa and shows significant increase in surface hardness from 4.5 GPa to 6 GPa. The residual compressive stresses and hardness increases with increase in static load. The severe plastic deformation caused by UNSM produces nanocrystalline layer of about 1 µm from the treated surface and a gradient microstructure of deformation bands and high dislocation density which was confirmed by transmission electron microscopy. The deformation mechanism after UNSM was also studied. The deformation mechanism in this alloy is dominated by dislocation movement and occurrence of deformation bands with high dislocation density. Three-point bending fatigue tests were also performed to study improvement in fatigue life (open full item for complete abstract)

Committee: Vijay Vasudevan Ph.D. (Committee Chair); Ashley Paz y Puente Ph.D. (Committee Member); Rodney Roseman Ph.D. (Committee Member) Subjects: Materials Science

Doctor of Philosophy, Case Western Reserve University, 2017, Macromolecular Science and Engineering

The goal of this thesis was to develop surface modified melt coextruded polymeric fibers for biomedical applications. Materials derived from polymeric fibers are critically important in tissue engineering and regenerative medicine. The applications of materials reported within range from simple cell-seeding scaffolds to complex chemical gradients and finally wound healing patches. Chapter I introduces common fiber processing techniques and compare them to melt coextrusion. Furthermore, the need for diverse surface modification methods to incorporate bioactive cues is reviewed for inducing cell responses. Chapter II describes surface modification of coextruded PCL fibers by covalent grafting with biomolecules using a two-step chemistry and the impact of the chemical reaction after fiber drawing. First, a clickable benzophenone was introduced using photochemistry. After modifying fibers with alkyne groups, both fluorescent dyes and azido-RGD peptides were covalently incorporated using the copper-catalyzed azide-alkyne cycloaddition reaction. The RGD modified fibers showed dramatically improved cell adhesion when compared to neat PCL fibers. Furthermore, tuning mechanical properties and surface area are critical for biomaterial scaffolds, which is often done through post-process drawing. Uniaxial orientation of fibers was studied to correlate three significant parameters; surface area, mechanical properties and modification density. Chapter III describes the incorporation of multiple functional biomolecules, using several types of bioconjugation chemistries, including CuAAC, thiol-ene and oxime chemistries. Utilizing multiple chemistries allowed for deposition of several different molecules onto a single fiber, which promoted cellular differentiation and cell adhesion. A single peptide could not sufficiently provide both phenotypes. Chapter IV details surface modification of non-woven mats to create anti-fouling fibrous patches. Fiber mats were fabricated using a (open full item for complete abstract)

Committee: Jonathan Pokorski Ph.D. (Committee Chair); LaShanda Korley Ph.D. (Committee Member); Gary Wnek Ph.D. (Committee Member); Horst von Recum Ph.D. (Committee Member) Subjects: Polymer Chemistry

Master of Science, University of Akron, 2016, Polymer Science

Carbon nanotubes (CNTs) are considered to be one of the most promising materials to be used in thermally conductive polymer composites, since CNTs couple extremely high thermal conductivity with high aspect ratios, thus enduing CNTs with the ability to form percolated networks at very low loadings. [1] The addition of a small amount of CNTs is expected to increase thermal conductivity dramatically, however, thermal conductivity measurements of CNT-polymer nanocomposites present unclear results. This is primarily attributed to: (1) CNTs are easy to aggregate into bundles when blended with polymers due to the strong Van der Waals interactions, causing poor dispersion in the matrix. [1] (2) CNT-polymer interfacial resistance that comes from the large interfacial resistance between CNT and polymer matrix, hindering the phonon conducting heat in polymers and CNTs, [1] which is found to be the dominant reason. [2] While it is very important to study CNT-polymer interfacial resistance in order to produce CNT-polymer composites with higher thermal conductivity, controlling the dispersion of CNTs is extremely challenging. In this work, 3-D CNT foams have been synthesized and used as the templates to fabricate CNT- polyvinyl alcohol (PVA) composites, because in foams the dispersion of CNTs is perfectly controlled. CNT foams have been modified using water plasma modification and metal coating in the hope of forming hydrogen bonding and metal complexation between CNTs and PVA matrix.

Committee: Ali Dhinojwala (Advisor); Yu Zhu (Committee Member) Subjects: Nanoscience; Physical Chemistry; Polymers

Master of Science (MS), Ohio University, 2014, Chemical Engineering (Engineering and Technology)

Graphite is currently the state-of-the-art anode material for most of the commercial lithium ion batteries. Current status and future demand of flake graphite in the market suggests that flake graphite could become a critical material in near future for countries such as United States. As one of the potential solutions to meet the future demand of graphite, recycling flake graphite from its different waste resources was proposed. The limitation of current technologies and a new perspective towards the future concept of "battery recycling" were also pointed out. Several aging mechanisms affecting used graphite anodes as challenges in recycling battery-grade flake graphite from spent lithium ion batteries were introduced. In an attempt to solve the mentioned concerns, surface modification of graphite anodes using carbon-coated Fe3O4 nanospindles (C-Fe3O4 NSs) was studied to increase the quality of aged graphite anodes. A thin layer of synthesized C-Fe3O4 NSs was coated on the surface of graphite anodes to prevent direct contact of graphite's surface and electrolyte. The effect of C-Fe3O4 NSs on the dischargecharge performance and cycling behavior of graphite was investigated. Moreover, the electrochemical performance was studied by electrochemical impedance spectroscopy. The results indicate that C-Fe3O4 coating decreased growth of solid electrolyte interface (SEI) film on the surface of graphite and prevented intercalation of solvated lithium ions. Additionally, the C-Fe3O4 film increased the capacity of graphite, and improved the long term cycle-ability. However, the impedance analysis indicated more resistance in case of C-Fe3O4 coated graphite which is due to low ionic conductivity of Fe3O4 compared to graphite.

Committee: Gerardine Botte (Advisor) Subjects: Chemical Engineering

MS, University of Cincinnati, 2014, Engineering and Applied Science: Mechanical Engineering

Additive Manufacturing (AM) is a process of manufacturing parts by combining layers of materials which are deposited on top of each other. AM processes have become very popular among different industries particularly in the automotive, medical and aerospace sectors due to the ability of the AM processes to manufacture complex parts rapidly without the need for specialized tooling. In the AM process, the CAD file is converted into a stereolithography (STL) file, which is the industry standard used as an input to AM processes. This STL file is then sliced by the AM machine into successive layers for depositing material. Since the STL file is a planar approximation of the CAD surface, the contours of the slices are also piecewise linear approximation of the CAD contour. This linear approximation leads to errors in the boundaries of the contours which lead to errors in the surfaces of the manufactured part.

Committee: Sundararaman Anand Ph.D. (Committee Chair); Sundaram Murali Meenakshi Ph.D. (Committee Member); David Thompson Ph.D. (Committee Member) Subjects: Mechanical Engineering

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

Polyisobutylene (PIB) has a unique combination of properties including chemical/oxidative resistance, low Tg (~70 °C) and hydrophobicity.1 PIB-based materials have also been found to have excellent biocompatibility and biostability: a PIB-based triblock copolymer thermoplastic elastomer (TPE) [poly(styrene-b-isobutylene-b-styrene)] (SIBS) is FDA-approved as a drug eluting coating for coronary stents.2 A new generation of PIB-based TPEs, with an arborescent or tree-like core (arbPIB) and plastic phases composed of blocks of polystyrene or poly(p-methyl styrene) (MS) has been developed in Professor Puskas group. These materials display unique TPE properties to make them very attractive for biomedical applications.3 The biocompatibility of these novel block copolymers has already been demonstrated in vitro and in vivo in rabbits.4 The Puskas group proposed to modify the surface properties of PIB-based TPEs using a modular approach. Using this approach it is possible to modify the surface chemistry and topology independently. The surface chemistry can be modified by “gluing” low molecular weight functionalized PIBs (PIB-X) to the surface of the TPEs. This “modular” approach will give unprecedented control over surface chemistry and topology and will contribute to new fundamental understanding of the effects of surface properties on the biocompatibility of polymeric materials. In this work PIB with a primary hydroxy head group (HO-PIB) was made in situ by living carbocationic polymerization using propylene oxide as initiator and titanium tetrachloride (TiCl4) as coinitiator. PIB functionalized with non-fouling moieties (PIB-X) was then synthesized from HO-PIB using Candida antarctica Lipase B (CALB) as enzymatic catalyst and spin coated onto the surface of the TPE. Protein adsorption studies using Surface Plasmon Resonance (SPR) demonstrated decreased fibrinogen (Fg) adsorption to the modified surface. XPS analyses provided clear evidence of the effectiveness of the mo (open full item for complete abstract)

Committee: Judit E. Puskas Dr. (Advisor); William Landis Dr. (Committee Chair); Gary R. Hamed Dr. (Committee Member); Chrys Wesdemiotis Dr. (Committee Member); Nic D. Leipzig Dr. (Committee Member) Subjects: Biomedical Research; Materials Science; Polymer Chemistry