Engineering Commons^™

A Computational Exploration Of The Scandate Cathode Surface, Shankar Miller-Murthy

Theses and Dissertations--Chemical and Materials Engineering

The exact surface configuration of scandate cathodes has been a point of contention for the materials community for a long time. Without proper understanding of it and the related structures and emission mechanisms, scandate cathodes remain patchy and unreliable emitters. Thus, density functional theory techniques were applied to various potential surface arrangements and found that there are several low-energy surfaces with low work functions that incorporate a scandium interlayer between tungsten and oxygen or otherwise have a scandium-on-tungsten structure. Furthermore, it was discovered that adding a monolayer of scandium directly to a tungsten surface is surprisingly favorable, thermodynamically. While none …

Interfacial Bonding Between Thermoset And Thermoplastic Polyurethane Reinforced Textile Grade Carbon Fiber: Structure Property Relationships, Surbhi Subhash Kore

Doctoral Dissertations

The research work focused on examining the interfacial adhesion of unsized, epoxy, and urethane-sized textile grade carbon fiber (TCF) reinforced in different classes of polyurethane (PU) thermoplastic (TPU) and thermoset (TSU) polyurethane (PU) through the structure-property relationship. The Carbon Fiber Technology Facility (CFTF) at Oak Ridge National Laboratory (ORNL) has produced TCF to reduce the cost of commercial-grade carbon fiber. The first part of the research examined the fundamental relationships between (a) soft segment thermoplastic polyurethane (S-TPU), (b) hard segment thermoplastic polyurethane (H-TPU), (c) thermoset polyurethane (TSU) and TCF reinforcement’s molecular behavior at the interface using the surface and thermal …

Polymeric Impulsive Actuation Mechanisms: Development, Characterization, And Modeling, Yongjin Kim

Doctoral Dissertations

Recent advances in the field of biomedical and life-sciences are increasingly demanding more life-like actuation with higher degrees of freedom in motion at small scales. Many researchers have developed various solutions to satisfy these emerging requirements. In many cases, new solutions are made possible with the development of novel polymeric actuators. Advances in polymeric actuation not only addressed problems concerning low degree of freedom in motion, large system size, and bio-incompatibility associated with conventional actuators, but also led to the discovery of novel applications, which were previously unattainable with conventional engineered systems. This dissertation focuses on developing novel actuation mechanisms …

Advanced Materials For Lithium Ion Batteries:Surface And Interface Chemistry, Yulong Liu

Electronic Thesis and Dissertation Repository

Lithium ion batteries (LIBs) are the indispensable energy storage devices in our modern society. LiFePO₄, as one of the most promising cathode, are widely used in LIBs. However, impurity phases are formed in LiFePO₄ during carbon coating process due to the intrinsic strong reducing atmosphere. Herein, as the first part of my work, interface chemistry of carbon coating on LiFePO₄ are symmetrically investigated by advanced characterization techniques. Two distinct secondary phases are formed during carbon coating process at different condition. Moreover, secondary phase formation is controllable by changing the particle size of LiFePO₄, annealing …

Synthesis, Characterization And Surface Modification Of Polydimethylsiloxane And Its Composites, Yan Wang

Doctoral Dissertations

Silicone elastomers are widely employed in composite, coatings, biomedical, sealant and electronics applications. This dissertation highlights new methodologies and formulation approaches to improve the performance of siloxane polymers, including the mechanical properties, surface properties, optical properties and transport properties. It also provides an in-depth understanding about dip-coating deposition on chemically patterned surfaces. The first chapter presents the process of transforming sand into siloxane polymers of excellent mechanical strength. History, properties and applications of siloxane polymers are systematically discussed. Another focus of this chapter is wetting, including the concepts of contact angles and capillary bridge ruptures. Five interconnected projects are discussed …

Synthesis And Characterization Of Nanoscale Polymer Films Grafted To Metal Surfaces, Yuriy Galabura

All Dissertations

Anchoring thin polymer films to metal surfaces allows us to alter, tune, and control their biocompatibility, lubrication, friction, wettability, and adhesion, while the unique properties of the underlying metallic substrates, such as magnetism and electrical conductivity, remain unaltered. This polymer/metal synergy creates significant opportunities to develop new hybrid platforms for a number of devices, actuators, and sensors. This present work focused on the synthesis and characterization of polymer layers grafted to the surface of metal objects. We report the development of a novel method for surface functionalization of arrays of high aspect ratio nickel nanowires/micronails. The polymer 'grafting to' technique …

Structure And Catalytic Properties Of Ultra-Small Ceria Nanoparticles, Xing Huang

Theses and Dissertations--Chemical and Materials Engineering

Cerium dioxide (ceria) is an excellent catalytic material due to its ability to both facilitate oxidation/reduction reactions as well as store/release oxygen as an oxygen buffer. The traditional approach to assess and improve ceria's catalytic behavior focuses on how efficiently O-vacancies can be generated and/or annihilated within the material, and how to extend established understandings of "bulk" ceria to further explain the greatly enhanced catalytic behavior of ultra-small ceria nanoparticles (uCNPs) with sizes less than 10 nm. Here, using density functional theory (DFT) calculations, we reexamine the atomic and electronic structures of uCNPs, especially their surface configurations. A unique picture …

Surface Instabilities For Adhesion Control, Chelsea Simone Davis

Open Access Dissertations

Controlling the specific adhesive properties of surfaces is a technologically complex challenge that has piqued the interest of many research groups around the world. While many scientists have used complex topographic and chemically altered surfaces to tune adhesion, others have shown that naturally occurring phenomena, such as elastic instabilities, can impact adhesion. We provide a thorough investigation into the effects of periodic surface buckling instabilities, or wrinkles, on adhesion. Wrinkles are an attractive surface patterning alternative as they form spontaneously over large areas and their dimensions, namely wavelength and amplitude, can be controlled on length scales relevant for adhesion control. …

Surface Characterization Of Nephila Clavipes Dragline Silk, Benoit Faugas

All Theses

To design synthetic fibers for extreme applications, many research groups are trying to identify how the structure of natural fibers (such as spider silk) leads to desirable properties such as high tensile strength.
Spider silk is a biological fiber having mechanical properties that exceed those of the best man made fibers in terms of high tensile strength and large extensibility, this combination providing the silk with a large work of rupture. While the bulk structure, composition and properties have been intensively studied elsewhere, this study focuses on elucidating the Nephila clavipes spider dragline silk surface structure and composition, as well …

Interface Engineered Diamond Coatings For Dry Machining Applications, Humberto Arturo Gomez Vega

USF Tampa Graduate Theses and Dissertations

Several studies have been propose to improve the adhesion of diamond films on cemented carbide tool materials, however a systematic study in identifying the role of the factors that affect the final diamond adhesion and the resulting machining performance of the tool under real manufacturing conditions is still unexplored. CVD diamond film's extraordinary qualities bring little benefit if the film fails to adhere sufficiently to the substrate. Inadequate adhesion undermines tool performance and longevity, causing unpredictable behavior under load and possibly leading to unexpected failure of the tool in the production line. This dissertation investigates the effects of different surface …

Synthesis And Characterization Of Macromolecular Layers Grafted To Polymer Surfaces, Oleksandr Burtovyy

All Dissertations

The composition and behavior of surfaces and interfaces play a pivotal role in dictating the overall efficiency of the majority of polymeric materials and devices. Surface properties of the materials can be altered using surface modification techniques. It is necessary to highlight that successful methods of surface modification should affect only the upper layer of the polymer material without changing bulk properties. The processes must introduce new functionalities to the surface, optimize surface roughness, lubrication, hydrophobicity, hydrophilicity, adhesion, conductivity, and/or biocompatibility.
Research presented in this dissertation is dedicated to the synthesis, characterization, and application of thin macromolecular layers anchored to …

Preparation And Surface Studies Of Negative Electron Affinity Semiconductors Photocathodes, Khaled A. Elamrawi

Electrical & Computer Engineering Theses & Dissertations

Fabrication of high quantum efficiency, long lifetime negative electron affinity photocathodes is important for applications such as photomultipliers, image intensifiers, electron beam lithography, electron microscopy, and polarized electron sources. The surface cleanliness of the III-V semiconductor photocathode is crucial in obtaining high photosensitivity.

GaAs(100) and InP(100) photocathodes are prepared by atomic hydrogen cleaning. The cleaning effect on the photocathode performance is discussed. The surface degradation mechanisms which reduce the photocathode lifetime are presented. The photocathode surface cleanliness, structure, and morphology are studied using reflection high-energy electron diffraction (RHEED).

Quantum efficiencies of ∼14% and 8% are obtained for GaAs and InP, …