Master of Science (MS), Ohio University, 2023, Biomedical Engineering (Engineering and Technology)

Abstract GUGGENBILLER, GRANT W., M.S., December 2023, Biomedical Engineering Electrospun Composite With Tunable Morphology for Burn Wound and Soft Tissue Wound Recovery Applications Director of Thesis: Dr. Andrew C. Weems Electrospinning offers a unique opportunity to produce micro- or nanoscale features using a wide array of polymers to produce 3D porous scaffolds. Here, a series of bioderived, pro-drug photopolymers, derived from salicylic acids, are photocrosslinked in the presence of polystyrene and silver sulfate to achieve a series of composite fibrous mats. The use of the three components (photopolymer, polystyrene, silver sulfate) are shown to provide an avenue towards tuning the fiber morphology. These materials display shape memory, allowing for minimally invasive medical device opportunities, as well as cytocompatibility and antimicrobial behaviors. Ultimately, these composite fibrous mats display excellent promise for both implantable tissue scaffolds as well as for medical devices including face masks or wound coverings.

Committee: Andrew Weems PhD (Advisor); Martin Kordesch PhD (Committee Member); Erin Murphy PhD (Committee Member); Douglas Goetz PhD (Committee Member) Subjects: Biomedical Engineering; Engineering; Plastics

Master of Science, The Ohio State University, 2023, Welding Engineering

High energy density welds have complex weld geometries due to the deep penetrations and low heat input associated with these processes, making it viable for many applications (aerospace, medical, defense, etc.). These complex geometries lead to difficulties in characterizing the transition between the conduction and keyhole weld mode geometries for this welding process. An ytterbium doped fiber laser with a beam diameter of 0.6 mm was used to make partial penetration autogenous weld on the nickel-based alloy, Inconel 690. Laser powers ranged from 600W – 2800W and travel speeds ranged from 5 mm/s – 150 mm/s to analyze characterization techniques of the weld's formation through conduction to keyhole mode. Six characterization techniques were attempted, with the final technique having two methods compared. First, the depth-to-width measurement were analyzed for a sudden increase as the power increased for welds made at the same travel speed. Evidence for a shift in depth-to-width ratios as the weld geometries transition were seen. A change in convexity of the weld pool measurements using ImageJ software proved a viable method for characterizing the weld mode. Uniformity was seen along the weld root's penetration was seen for longitudinal cross-sections for keyhole and conduction mode weld geometries. Weld roots within the transition of these modes showed nonuniform weld root penetrations. Inline Coherent Imaging was used to see if any notable changes of the weld's formation through the keyhole profile. Finally, analysis of the solidification rate and subsequent solidification parameters was done using a traced solid liquid interface and cell spacing measurements. These results were inconclusive as a current method of characterization, but solidification rate values were compared to those measured through cellular grain growth analysis. Cellular grain growth analysis showed that both plan and longitudinal weld cross-sections are needed when analyzing the solidifica (open full item for complete abstract)

Committee: Carolin Fink (Advisor); Boyd Panton (Advisor); Wei Zhang (Committee Member) Subjects: Engineering; Materials Science

MS, University of Cincinnati, 2022, Engineering and Applied Science: Chemical Engineering

Melt crystallized polymers display an emergent, multi-hierarchical, ordered structure made up of stacked lamellar single crystals that form fibrous or other meso structures which, in turn, form macroscopic crystallites. A dominant feature of small-angle scattering from these complex assemblies is a correlation peak associated with the stacking period. A new model-based function is proposed for small-angle scattering data from such correlated lamellar multi-hierarchical structures. Generally, routine use of scattering data has been limited to a 1-d analysis to determine the long period from Lorentz corrected data (I(q)q^2 versus q). Fourier transforms of the data are sometimes used to determine the 1-d pairwise correlation function for the electron-density distribution which has been further analyzed in terms of the structure of these materials. A simple 1-d fitting model limited to infinite width 2-d sheets was introduced by Hermans [1,2] in the 1940s with some success. A new approach is proposed that uses the Unified Function as adapted to correlated lamellar structures (UBG) and incorporates a Born-Green description of one-dimensional correlations. The UBG fit allows quantification of the average lamellar aspect ratio, the local degree of crystallinity within a stack, quantification of the stacking versus non-stacking amorphous, and two types of disorder in addition to the stacking period and lamellar thickness. UBG can account for higher levels of structure such as crystalline domains in block copolymers and convoluted lamellar structure. The UBG fit is compared to the Hermans [1,2] and a hybrid-Hermans function. Fits to data sets from a wide range of polyethylene are shown ranging from molecular weight standard samples that are isothermally crystallized, to commercial HDPE quenched from the melt and a metallocene blown film sample. Several other examples from the literature are explored. It is shown that the Unified fit allows for new understanding of the impact (open full item for complete abstract)

Committee: Gregory Beaucage Ph.D. (Committee Member); Jonathan Nickels Ph.D. (Committee Member); D. Ryan Breese Ph.D. (Committee Member) Subjects: Chemical Engineering

MS, University of Cincinnati, 2021, Engineering and Applied Science: Mechanical Engineering

Monocular visual odometry has been an active area of research over the past decade owing to its variety of applications in the field of geology, autonomous driving, and mixed reality products. The fundamental challenge in working with monocular data is the absence of absolute depth information, making the odometry extraction process cumbersome. This thesis is focused on the development of a deep learning architecture to create a network for odometry estimation. The thesis particularly focuses on the transformer architecture to solve a complex vision problem. The intuition of the existing language translation network is modified to work on the comparison of images to create a novel data-driven relative state estimation methodology. This network is further modified to develop a novel architecture to create a physically consistent network that could handle images of varying aspect ratios and angles of view. This novel network addresses the pressing issue of such algorithms still being unusable for consumer-based generic purposes and develops a solution to bridge this gap by creating a data pipeline for varying camera models. The network is further tested on the KITTI dataset to ensure conformance with the real world. The results are plotted and a detailed analysis of the generalization of the network through feature representation is discussed.

Committee: Manish Kumar Ph.D. (Committee Chair); Rajnikant Sharma Ph.D. (Committee Member); David Thompson Ph.D. (Committee Member) Subjects: Mechanical Engineering

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

Shock waves are a major source of drag in supersonic flows as they affect the aero-thermodynamic performance and impose pressure and temperature loads on the structure under consideration. The aim of this work is to address such multiphysics phenomenon and mitigate the losses due to shock waves in a series of low to high aspect ratio rectangular supersonic nozzles with sharp and smooth throats. 3D steady RANS CFD is performed on a baseline converging-diverging nozzle (exit aspect ratio 2 and design Mach number 1.5) with sharp throat and the results are validated with the experimental data. Turbulence model study shows that k-omega SST compares better with the experimental data. A shock wave is present in the baseline nozzle due to the sharp throat. In order to eliminate the sharp throat, a general-purpose curve generator - Gencurve is developed and implemented using Python 3.5. Equivalent smooth nozzle geometries are created using this tool. These show improvements in various performance parameters such as discharge coefficients, thrust coefficients, etc., due to the mitigated shocks and reduced boundary layer thicknesses. The baseline and the equivalent smooth nozzle geometries are further analyzed at design (NPR 3.67) and off-design conditions using multi-physics simulations, which are, for the first time, performed on rectangular supersonic nozzles. This work highlights the significance of Fluid-Thermal-Structural-Interaction (FTSI) simulations as a diagnosis of existing designs (exit aspect ratio 2 with sharp throat) and as a means of preliminary investigation to ensure feasibility of new designs before conducting experimental and field tests. Structural deformation in the baseline design is far less than the boundary layer thickness as the impact of Shock Boundary Layer Interactions (SBLI) is not as severe. FTSI demonstrates that the discharge coefficient of the improved design is 0.99 and its structural integrity remains intact at off (open full item for complete abstract)

Committee: Shaaban Abdallah Ph.D. (Committee Chair); Milind Jog Ph.D. (Committee Member); Kiran Siddappaji Ph.D. (Committee Member) Subjects: Aerospace Materials

Master of Science, University of Akron, 2018, Mechanical Engineering

This study numerically investigates the laterally heated vertical cylinder and the length scale associated with this reactor. For natural convection the important dimensionless characteristic is the Rayleigh number, which predicts the flow regime as laminar, transitional, or turbulent. The Rayleigh number is useful as a design tool for scaling a reactor. Up to this point the associated length scale has been assumed as various definitions of length and diameter and has not yet been thoroughly investigated. The current assumed definitions for the length scale: height, diameter, and volume to lateral surface area, are directly studied in a multi-dimensional (2D and 3D) numerical parametric study involving these length scales and aspect ratio (height/diameter). Other important characteristics such as the ratio of heating to cooling and thickness of the divider (insulator) between heating and cooling are also studied. The study begins with turbulent transient 2D axisymmetric simulations and proceeds to turbulent transient 3D simulations then compares the 3D and 2D simulations. Finally, 2D and 3D laminar simulations are investigated. Presented are the results of the fluid flow speeds, thermal environments, flow patterns, boundary layer thickness, boundary layer velocity, and normal probability density functions which provide a unique way of studying how the Rayleigh number is influenced by variables. The numerical simulations are examined for spatial step, time step, and relative convergence by a mesh study, time step study, and thermal analysis, respectively. The turbulence model used (k-ω SST) is based on recent published studies. All simulations were conducted with the commercially available software ANSYS FLUENT. Findings are discussed when they prove significant, and aid in developing a fundamental understanding of the physics occurring inside this reactor setup. The results indicate that the current the length scales assumed for this reactor are incorrec (open full item for complete abstract)

Committee: Braun Minel J (Advisor); Nicholas Garafolo G (Committee Member); Scott Sawyer (Committee Member); Abhilash Chandy J (Other) Subjects: Mechanical Engineering

Doctor of Philosophy, Case Western Reserve University, 2016, Biomedical Engineering

Each year, one million new cases of cancer are diagnosed in the United States and each case is unique, making it hard disease to prevent and treat. In the past few decades, nanoparticles have emerged as a promising platform for the development of cancer therapies. Unlike small molecule drugs, nanoparticles can be both passively and actively targeted towards tumor sites (both primary and metastatic sites). Additionally, they are able to carry large cargos for delivery of monotherapy or combination therapy, while also decreasing systemic side effects often associated with small molecule cancer therapies. Nanoparticles in the clinic, as well as in clinical and pre-clinical trials have been predominantly spherical in shape. However, recent data suggest that high aspect ratio nanoparticles may have advantages for cancer treatment, including decreased uptake by phagocytic cells, improved margination, and enhanced tumor homing and penetration. Despite this, synthesis of these materials remains challenging using chemical approaches. Therefore, I turned to towards the study of plant virus-based nanoparticles, and my dissertation focused on the study and development of high aspect ratio viral nanoparticles. Specifically, I focused on the plant viruses tobacco mosaic virus (TMV) and potato virus X (PVX). My initial studies evaluated TMV as a model high aspect ratio nanoparticle and determined that it had improved diffusion into a 3D spheroid compared to a spherical virus. Additionally, I determined that it could be stably loaded with via non-covalent interactions with a cationic photosensitizer for photodynamic therapy. In the central body of my thesis I developed the filamentous virus PVX for cancer therapy. Stealth coated PVX filaments exhibited substantially extended circulation time, while also decreasing recognition by PVX-specific antibodies, an important step towards translation of this platform. Addition of targeting ligands on the surface of the PVX filament led to se (open full item for complete abstract)

Committee: Nicole Steinmetz Ph.D. (Advisor); Horst von Recum Ph.D. (Committee Chair); Ruth Keri Ph.D. (Committee Member); David Schiraldi Ph.D. (Committee Member) Subjects: Biomedical Engineering; Nanotechnology

Doctor of Philosophy, Case Western Reserve University, 2016, Biomedical Engineering

Nanomedical approaches are of great interest due to their potential for specifically delivering packaged contrast agents and drugs to sites of disease while avoiding healthy tissue. Non-mammalian viruses, which are noninfectious to humans, can be used as unique nanoscale scaffolds with many advantages for nanotechnology and biomedicine. Compared to synthetically programmed materials, these particles can be precisely arranged into a diverse array of shapes and sizes, and there are many available avenues for easy and reproducible modification. Here, I investigated the expansion of the potential of these viruses for diverse applications in nanomedicine. First, I demonstrated the capability for interior engineering of a well-known icosahedral plant virus, cowpea mosaic virus (CPMV), for the encapsulation of a range of molecules, including fluorophores to enable optical imaging in the setting of cancer detection and diagnosis. Then, some design considerations were examined for the use of nanoparticles for fluorescence imaging, which informed our choices for subsequent studies. Dye density, dye localization, conjugation method, and cell uptake were all found to affect the resultant fluorescence intensity with the optimal design parameters being: non-aromatic linker chemistries, exterior particle conjugation, and dye spacing of around 8-10 nm. A second set of studies explored drug delivery using virus-based particles, demonstrating their utility for photodynamic therapy through solubilization of highly hydrophobic photosensitizers as well as for the treatment of chronic infections through using their native tropism. Finally, as increasing evidence suggest that shape is an important parameter for cell and tissue interactions, we explored the effect of aspect ratio and shape in mediating cell uptake and targeting the vessel wall. Nanoparticle chains were created, with clear differences seen in cell uptake due to shape-based as well as avidity effects. Additionally, in a para (open full item for complete abstract)

Committee: Horst von Recum Ph.D. (Committee Chair); Nicole Steinmetz Ph.D. (Advisor); Stuart Rowan Ph.D. (Committee Member); Daniel Simon M.D. (Committee Member) Subjects: Biomedical Engineering; Nanotechnology

Doctor of Philosophy, Case Western Reserve University, 2015, EECS - Electrical Engineering

This dissertation presents an investigation into the resonant frequency behavior of large area diaphragms made from silicon carbide thin films and the development of a plate-under-tension model to determine the Young's modulus and residual stress from resonant frequency data. Test specimens consisted of single crystalline (100) 3C-SiC, polycrystalline (111) 3C-SiC and amorphous SiC thin films that were fabricated into nominally 1 x 1 mm2 diaphragms by silicon bulk micromachining. Single crystalline diaphragms ranged in thickness from ~1.5 µm to 125 nm while the polycrystalline and amorphous diaphragms were held in the 1.5 µm thickness range. A thin (~50 nm) Si3N4 diaphragm was also included in the study. Test specimens were excited into resonance using a PZT crystal and interferometry was used to detect the vibrational modes. Testing was performed in vacuum to eliminate damping. Initial testing involved measurement of resonant frequencies between 50 kHz and 2 MHz at various drive amplitudes. Each diaphragm exhibited at least 50 resonant peaks in this range, with at least one diaphragm having 250 peaks. Every diaphragm exhibited at least 5 peaks with quality factors (Q) > 10,000. The highest quality factor, as well as the largest number of high Q peaks, was observed in the diaphragm with the highest residual stress. A method to determine the Young's modulus and residual stress of a diaphragm from the resonant frequency data using a plate-under-tension model was proposed and developed. This method, which relies on the identification of numerous high order modes, was shown to be effective for the thicker films in the study (> 1 µm); however, the technique was only able to determine the residual stress for the submicron-thick films. Based on these observations, an equation that relates the Young's modulus and residual stress to diaphragm thickness, side lengths and mode number was derived to identify diaphragm parameters that are well suited for this method. As a te (open full item for complete abstract)

Committee: Christian Zorman (Committee Chair); Philip Feng (Committee Member); Francis Merat (Committee Member); Heidi Martin (Committee Member) Subjects: Electrical Engineering

Doctor of Philosophy, The Ohio State University, 2014, Mechanical Engineering

Three-passage serpentines with aspect ratios of 1:1, 1:2, and 1:6 were numerically studied using computational fluid dynamics and heat transfer. A CFD modeling methodology was systematically developed that balanced accurately resolving the flow physics with minimizing the computational cost, targeting industrial preliminary design requirements. The method was benchmarked against two published data sets consisting of turbulators on the leading and trailing walls in skewed 45 deg; to the flow offset parallel configuration with a fixed rib pitch to height ratio of 10 and a rib height to hydraulic diameter of 0.1 to 0.058, utilizing Reynolds numbers of 25,000 and 50,000 and rotation number ranging from 0 and 0.25. Predictions were completed to study the effects of changing aspect ratio between 1:1, 1:2, and 1:6 and changing rotation numbers from 0 to 0.3. The 1:6 aspect ratio predictions varied from the lower aspect ratios. Differences included flow recirculation along the leading wall of the first passage for rotation numbers greater than or equal to 0.2 and high Nusselt numbers immediately downstream of the turn for the wall opposite the Coriolis force direction. Overall enhancement values for the test section showed the aspect ratio has a greater influence on Nusselt numbers than rotation.

Committee: Michael Dunn Ph.D (Advisor); Jen-Ping Chen Ph.D (Committee Member); Randall Mathison Ph.D (Committee Member); Mohammad Samimy Ph.D (Committee Member); Jeffrey Rambo Ph.D (Committee Member) Subjects: Mechanical Engineering

Master of Science in Chemical Engineering, Cleveland State University, 2013, Fenn College of Engineering

Under this research, live cell imaging of osteoblast-like marrow stromal cells has been carried out on polished and nanotextured (NaOH-etched) medical-grade titanium alloy (Ti-6Al-4V) surfaces to examine cellular adhesion and migration. The purpose of this research was to: 1) Build and assemble suitable hardware and software to conduct live cell imaging in a micro-incubator over an extended period of time. 2) Monitor and record live osteoblast-like marrow stromal cells on polished and NaOH-etched titanium alloy surfaces from cell inoculation to about one week of culture. 3) Measure location, area and perimeter of individual cells as a function of time, and examine if, as compared / contrasted with the polished titanium surface, that the NaOH-etched titanium surface promotes adhesion and migration of cells. This was achieved by describing the mobility, morphology and overall behavior of osteoblast-like marrow stromal cells. During the cell growth cycles, data generated from image analysis included the cells' center of mass (X,Y), their area, perimeter and shape as a function of incubation time. From the change in center of mass after each 15-minute interval, the real time speed of the cells was obtained. Major observations to support comparison studies between the surfaces determined that compared with polished titanium, NaOH-etched titanium promotes cellular filopodia growth, thus, promotes attachment. Filopodia provide cellular anchoring support and when prevalent, make cells more angular in shape. The median aspect ratio (length / width) of cells was found to be 1.38 on polished and 2.36 on NaOH-etched titanium. This, in addition to lower mean circularity shape factor values of 0.26 ± 0.03 on polished and 0.11 ± 0.01 on NaOH-etched titanium imply that the nanotextured surface promotes growth of cells more anchored to the substrate. This is also confirmed by increased perimeters of cells found on the NaOH-etched surface (950.92 ± 84.88 μm) compared with perime (open full item for complete abstract)

Committee: Surendra Tewari PhD (Committee Chair); Joanne Belovich PhD (Committee Member); Ronald Midura PhD (Committee Member) Subjects: Biomedical Engineering

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

Demand for miniaturized products is ever increasing as they accomplish the task of providing the desired functionalities with high efficiency using minimalistic raw material. In order to execute functionalities like high strength and sustainability with minimal use of space, the raw materials used should possess good mechanical, chemical and physical properties. This requirement poses several challenges including high tool wear and lack of precision in the micromachining of such superlative engineering materials. Although, electrical discharge machining (EDM) and electrochemical machining (ECM) are well established nontraditional techniques to meet these challenges, they are restricted to electrically conductive materials. Several electrically non-conductive materials like ceramics and fiber-reinforced composites are increasingly being used in miniaturized pumps, reactors, accelerometers and many other biomedical devices. Micro Electrochemical Discharge Machining (micro-ECDM) has the capability to meet these challenges. However, machining high aspect ratio features on ceramics like glass still remains a formidable task due to overcut. Since electrolyte concentration plays an important role in overcut its effects on material removal needs to be studied in order to enhance the capability of this technology in machining complex and high aspect ratio features.

Committee: Sundaram Murali Meenakshi Ph.D. (Committee Chair); Anil Mital Ph.D. P.E. (Committee Member); David Thompson Ph.D. (Committee Member) Subjects: Mechanical Engineering

MS, University of Cincinnati, 0, Engineering and Applied Science: Aerospace Engineering

The integration of protrusions on aircraft, whether they are antennas or sensor turrets, can impact both aircraft safety and performance. The protrusions vary in size and shape and where they are placed on the aircraft can greatly affect the flow around the structure. This work utilizes the power and adaptability of modern computational methods to analyze finite cylinders of various aspect ratios subjected to incoming flow of varying boundary layer thickness. The geometry and flow conditions for the analysis match a wind tunnel test completed by the University of Cincinnati in 2005. This flow is challenging to model computationally because the flow is largely separated and influenced by both ends of the cylinder. The four cylinders analyzed, labeled by their diameter and height in inches, are D2H5, D4H2, D4H5, and D4H10. These four cylinders were subjected to cross-flows with two different boundary layer thicknesses for a total of eight cases. The boundary layer thicknesses were 1.5” and 6.0”. This work compared the computational results with both the wind tunnel results and with available literature. The results compared favorably with both and captured all primary flow features for this class of flows. Furthermore, the impacts of cylinder aspect ratio and boundary layer thickness were evident in the results. The lower the aspect ratio of the cylinder, the more the flow from the free-end dominates the wake. Higher aspect ratio cylinders can be divided into regions with juncture flow near the wall, Karman style shedding near the middle and free-end effects near the tip. This work also identifies a transitional cylinder aspect ratio where the flow transitions from segregated regions to being dominated by the free-end downwash. This work shows that modern computational methods are capable of modelling the complex flow about a finite cylinder and can provide valuable insight to aid in protrusion design and integration.

Committee: Ephraim Gutmark Ph.D. D.Sc. (Committee Chair); David Munday Ph.D. (Committee Member); Mark Turner Sc.D. (Committee Member) Subjects: Aerospace Materials

MS, University of Cincinnati, 2012, Engineering and Applied Science: Mechanical Engineering

Measurements in experimental studies of adiabatic single bubble growth dynamics bear the combined effects of both the testing parameters and the test system features. The present study investigates the impact of specific experimental methods and system features, namely gas flow path, system volume, orifice construction, and visualization surface, on the measurement of adiabatic single-bubble growth dynamics at the tip of submerged capillary orifices. The present work jointly focuses on characterization of bubble volume and shape during nucleation and growth. Photos of bubble growth from a 1.75 mm capillary tube orifice were taken for glycerin, water, and 75 wt% aqueous glycerin for system volumes from 0.2 – 301.5 mL over a range of flow rates from 0.01 – 1.6 mL/s, photographed through both planar and curved surfaces. Interfacial aspect ratio and included volume from each system modification were analyzed to determine the effect of system volume and to understand the impact of flow metering on the constant gas flow boundary values in water and aqueous glycerin as well as the influence of curvature in the visualization surface and the effects of liquid viscosity in the presence of these system features. It was found that interfacial aspect ratio decreases with increasing system volume and with decreasing viscosity over the full range of flow rates considered. Additionally, interfacial aspect ratio decreases when a cylindrical visualization surface is used, owing in part to horizontal magnification. Furthermore, it is observed that bubble shape must be treated distinctly from bubble volume when surface curvature is present or system volume is minimized.

Committee: Raj Manglik PhD (Committee Chair); Jude Iroh PhD (Committee Member); Milind Jog PhD (Committee Member) Subjects: Mechanical Engineering

MS, University of Cincinnati, 2011, Engineering and Applied Science: Mechanical Engineering

High aspect ratio metallic cylindrical rods having diameters in the sub millimeter range are increasingly being used as micro tools to machine complex micro features including deep hole micro drilling in a wide variety of engineering materials including metals and ceramics. They are also being used in applications such as ultrafine micro needles for intracellular sensing probes and micro robotic manipulators. Accurate and precise micro tools are essential for the micromachining of these highly complex features. Micro tools produced by the well known wire electro-discharge grinding suffer deformation due to the thermal stresses. Therefore, electrochemical machining has been explored as an alternate micro tool manufacturing technique. In this thesis, a micro electrochemical machining system has been designed and built in-house and a mathematical model has been developed to predict the final diameter of the anode based on the velocity of the cathode movement. Experimental verification of the model reveals good correlation with theoretical predictions. Large pulse on-times have successfully been used to fabricate micro tools having diameters of 10 micrometers with aspect ratios as high as 450. Pulse on-time between 5 to 10 ms was found to be an optimum range for successful micromachining using the in-house built micro electrochemical system. Pulse on-times lower than this optimum range result in a conical shape while pulse on-times higher than the optimum range result in a reverse conical shape.

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

Doctor of Philosophy in Engineering, University of Toledo, 2010, Electrical Engineering

This dissertation is a study on the formation of conical tips with nanoscale sharpness on silicon films, as well as various microbumps or nano-sharp structures on metal films, as a result of localized single-pulse laser irradiation. Such conical tips with nanoscale structures are referred to as nanotips in this work. A Q-switched nanosecond-pulse Nd:YAG laser, emitting at its fourth harmonic of 266 nm, was employed. Irradiation of silicon-on-insulator, gold, platinum and other metal films, with thicknesses of several hundred nanometers, was studied in ambient air, low-vacuum or argon atmospheres. Individual circular laser spots, several micrometers in diameter, were used together with spot patterns generated through the use of a mask projection technique. The laser based formation method studied and developed during this research allows for the fabrication of nano-tips, and microbumps, in a single step, at far less expense when compared to traditional lithography based techniques. It also offers precise control over the location of these structures unlike other laser based techniques. In addition, it eliminates the use of expensive and complex femtosecond or excimer lasers as well as their respective optical systems, which in principle, can be used to fabricate similar structures. This laser based technique has proven capable of fabricating conical silicon tips in silicon-on-insulator films; where each of these tips is situated in the center of a circular depression with a depth, tens of nanometers below the original surface. The height of the tip apex is several hundred nanometers above the original surface with an estimated radius of curvature of 35-40 nm. Laser irradiation of gold films has produced microbumps with high-aspect-ratio protrusions with have heights of more than 3 µm above the original film surface, while the apex is estimated to have a radius of curvature of 5-10 nm. Irradiation of other metal films has produced various sized microbumps with and w (open full item for complete abstract)

Committee: Daniel Georgiev PhD (Advisor); Junghwan Kim PhD (Committee Member); Roger King PhD (Committee Member); Sylvain Marsillac PhD (Committee Member); Thomas Stuart PhD (Committee Member) Subjects: Electrical Engineering; Engineering; Physics

Doctor of Philosophy, Case Western Reserve University, 1990, Mechanical Engineering

Steady thermocapillary flows in a two-dimensional rectangular enclosure of unit order aspect ratio are studied for fluids of small, unit order, and large Prandtl numbers. Scaling analysis is applied to obtain velocity and length scales for different flow regimes along with the dimensionless parameters that define these regimes. The scaling analysis in this work is for the entire range of the Reynolds number and the influence of the flow on the driving force, which leads to a change in the thermal signature, is also incorporated. Numerical simulations are performed and agreements are found between the results from the scaling analysis and the results from the numerical simulations. The analysis also predicts the behavior of the thermocapillary flow in the range of Marangoni number at which present numerical schema are incapable of simulating.

Committee: Simon Ostrach (Advisor) Subjects:

Doctor of Philosophy, University of Akron, 2012, Mechanical Engineering

The ability of geckos to adhere to vertical solid surfaces comes from their remarkable feet with millions of projections terminating in nanometer spatulae. We present a simple yet robust method for fabricating directionally sensitive dry adhesives. By using electrospun nylon 6 nanofiber arrays, we create gecko-inspired dry adhesives, that are electrically insulating, and that show shear adhesion strength of 27 N/cm2 on a glass slide. This measured value is 270% that reported of gecko feet and 97-fold above normal adhesion strength of the same arrays. The data indicate a strong shear binding-on and easy normal lifting-off. This anisotropic strength distribution is attributed to an enhanced shear adhesion strength with decreasing fiber diameter (d) and an optimum performance of nanofiber arrays in the shear direction over a specific range of thicknesses. With use of electrospinning, we report the fabrication of nylon 6 nanofiber arrays that show a friction coefficient (µ) of ~11.5. These arrays possess significant shear adhesion strength and low normal adhesion strength. Increasing the applied normal load considerably enhances the shear adhesion strength and µ, irrespective of d and fiber arrays thickness (T). Fiber bending stiffness and fiber surface roughness are considerably decreased with diminishing d while fiber packing density is noticeably increased. These enhancements are proposed to considerably upsurge the shear adhesion strength between nanofiber arrays and a glass slide. The latter upsurge is mainly attributed to a sizeable proliferation in van der Waals (vdW) forces. These nanofiber arrays can be alternatively bound-on and lifted-off over a glass slide with a trivial decrease in the initial µ and adhesion strength. By using selective coating technique, we have also created hierarchical structures having closely packed nanofibers with d of 50 nm. We determine the effects of applied normal load, fiber surface roughness, loading angle, d, T, and repea (open full item for complete abstract)

Committee: Shing-Chung Wong Dr. (Advisor); Gregory Morscher Dr. (Committee Member); Peter Niewiarowski Dr. (Committee Member); Darrell Reneker Dr. (Committee Member); Erol Sancaktar Dr. (Committee Member); Tirumalai Srivatsan Dr. (Committee Member) Subjects: Materials Science; Mechanical Engineering; Nanotechnology; Polymers; Robotics; Technology