Engineering Commons^™

Novel Fission Track Detection For Identification And Characterization Of Special Nuclear Materials, Jonathan Allen Gill

Doctoral Dissertations

Fission track detection and analysis is used primarily in nuclear safeguards to identify special nuclear material. Identification of isotopic ratios is a crucial step in understanding the intended use of nuclear material and the nature of the materials production cycle. Unfortunately, this methodology uses etchable track detectors that require significant expertise and intensive labor to process.

This study developed a novel method using lithium fluoride (LiF) as a fluorescing nuclear track detector to conduct fission track analysis for isotopic prediction of uranium enrichment. Individual latent tracks produced by fission products were observed in LiF for the first time. These tracks …

Development Of High-Performing Polydimethylsiloxane-Based Membranes For Carbon Dioxide Separation, Tao Hong

Doctoral Dissertations

Membrane separation is highlighted as one of the most promising approaches to mitigate the excessive CO₂ [carbon dioxide] emission, due to its significant reduction of energy cost compared with many conventional separation techniques. Unfortunately, the separation performance of current membranes does not meet the practical CO₂/N₂ [nitrogen] separation requirements. And due to the huge volume of industrial flue gas, membranes with exceptionally high permeability are needed for practical reasons.

Currently, the separation mechanism of most polymeric membranes is based on size-sieving. However, this method is not sufficient for CO₂/N₂ separations due to the …

Low Energy Recoil Simulations In Mgo, Linbo3, And Litao3 Using Ab Initio Molecular Dynamics, Benjamin Aaron Petersen

Doctoral Dissertations

Ab initio molecular dynamics (AIMD) was utilized to test a series of materials, MgO, LiNbO₃ , and LiTaO₃ , to determine defect structures produced due to low energy recoil events . The kinetic energy required to displace an atom from its lattice site, the threshold displacement energy, was calculated for an array of directions in each material, based on symmetry and complexity of the structure. MgO having a simple rock salt structure provided a model material for demonstrating computational techniques used later on LiTaO₃ and LiNbO₃ . The minimum values for displacing an atom were at …

Mechanical Behavior Of Pipeline Steels And An Al0.1cocrfeni High-Entropy Alloy, Bilin Chen

Doctoral Dissertations

This dissertation is composed of two parts. The first part focuses on the mechanical behavior study on pipelines steels. More specifically, the effect of hydrogen on the deformation behavior of the crack tip of an X52 pipeline steel specimen, and the overload effects on the fatigue crack growth of an x70 pipeline weld metal are discussed. For the second part of the dissertation, fatigue behavior of an Al0.1CoCrFeNi high-entropy alloy (HEA) is studied, and the influence of heat treatment is discussed.

The objectives of the first part of this proposed work are to (1) detect the influence of hydrogen on …

Transport Of Water And Ions Through Single-Walled Armchair Carbon Nanotubes: A Molecular Dynamics Study, Michelle Patricia Aranha

Doctoral Dissertations

The narrow hydrophobic interior of a carbon nanotube (CNT) poses a barrier to the transport of water and ions, and yet, unexpectedly, numerous experimental and simulation studies have confirmed fast water transport rates comparable to those seen in biological aquaporin channels. These outstanding features of high water permeability and high solute rejection of even dissolved ions that would typically require a lot of energy for separation in commercial processes makes carbon nanotubes an exciting candidate for desalination membranes. Extending ion exclusion beyond simple mechanical sieving by the inclusion of electrostatics via added functionality to the nanotube bears promise to not …

The Rheology And Roll-To-Roll Processing Of Shear-Thickening Particle Dispersions, Sunilkumar Khandavalli

Doctoral Dissertations

Particle dispersions are ubiquitous in our daily lives ranging from food and pharmaceutical products to inks. There has been great interest in the recent years in formulation of functional inks to fabricate myriad flexible electronic devices through high-throughput roll-to-roll technologies. The formulations often contain several functional additives or rheological modifiers that can affect the microstructure, rheology and processing. Understanding the rheology of formulations is important for tuning the formulation for optimal processing. This thesis presents investigations on the rheology of particle dispersions and their impact on roll-to-roll technologies. Shear-thickening behavior is common in particle dispersions, particularly, concentrated particulate inks. We …

The Role Of Chain Configuration In Governing The Rational Design Of Polymers For Adhesion, Onyenkachi Wamuo

Doctoral Dissertations

ABSTRACT THE ROLE OF CHAIN CONFIGURATION IN GOVERNING THE RATIONAL DESIGN OF POLYMERS FOR ADHESION SEPTEMBER 2017 ONYENKACHI C. WAMUO, B.Eng., FEDERAL UNIVERSITY OF TECHNOLOGY, OWERRI (FUTO), NIGERIA M.S., UNIVERSITY OF MASSACHUSETTS AMHERST Ph.D., UNIVERSITY OF MASSACHUSETTS AMHERST Directed by: Professor Shaw Ling Hsu The chain configurational control of polymers used in adhesion can be utilized as a means of tuning the cohesive properties of hot melt adhesives (HMAs). The cohesive properties control the solidification, strength, setting speed. Propylene-Ethylene copolymers (PP-co-PE) and thermoplastic polyurethanes (TPUs) were studied. In the first project, the effects of sequence distribution of the two types …

Computational Studies Of Structure–Function Relationships Of Supported And Unsupported Metal Nanoclusters, Hongbo Shi

Doctoral Dissertations

Fuel cells have been demonstrated to be promising power generation devices to address the current global energy and environmental challenges. One of the many barriers to commercialization is the cost of precious catalysts needed to achieve sufficient power output. Platinum-based materials play an important role as electrocatalysts in energy conversion technologies. In order to improve catalytic efficiency and facilitate rational design and development of new catalysts, structure–function relationships that underpin catalytic activity must be understood at a fundamental level. First, we present a systematic analysis of CO adsorption on Pt nanoclusters in the 0.2-1.5 nm size range with the aim …

Analyses Of Densely Crosslinked Phenolic Systems Using Low Field Nmr, Jigneshkumar Patel

Doctoral Dissertations

A uniform dispersion of reactants is necessary to achieve a complete reaction involving multi-components, especially for the crosslinking of rigid high-performance materials. In these reactions, miscibility is crucial for curing efficiency. This miscibility is typically enhanced by adding a third component, a plasticizer. For the reaction of the highly crystalline crosslinking agent hexamethylenetetramine (HMTA) with a strongly hydrogen-bonded phenol formaldehyde resin, furfural has been traditionally used as the plasticizer. However, the reason for its effectiveness is not clear. In this doctoral thesis work, miscibility and crosslinking efficiency of plasticizers in phenolic curing reactions are studied by thermal analysis and spectroscopic …

Fabrication Of Functional Nano-Structured Materials And Devices Using Supercritical Fluids, Shengkai Li

Doctoral Dissertations

Nano-structured materials possess unconventional properties and enable miniaturization of devices. However, fabrications of such materials and devices are challenging and in many cases cumbersome, and development of nanofabrication techniques are essential to realizing novel designs and commercializing scientific ideas. Supercritical fluids possess a unique combination of gas-like diffusion properties and liquid-like dissolution power, and are suitable reaction media for fabricating materials at the nanometer scale. This dissertation focuses on developing supercritical fluids-related techniques for fast and large-scale fabrication of novel composite materials and devices. Using supercritical fluid deposition (SFD) technique, cobalt thin films were deposited on a variety of substrates, …

Polyorganosiloxanes: Molecular Nanoparticles, Nanocomposites And Interfaces, Daniel H. Flagg

Doctoral Dissertations

Five research projects described. First, a reproducible, lab-scale synthesis of MQ silicone copolymers is presented. MQ copolymers are commercially important materials that have been ignored by the academic community. One possible reason for this is the difficulty of controlling and reproducing the preparative copolymerizations that have been reported. A reproducible method for lab-scale preparation was developed that controls molecular weight by splitting the copolymerization into the discrete steps of sol growth from silicate precursor and end-capping by trimethylsiloxy groups. Characterization of MQ products implicates that they are composed of highly condensed, polycyclic structures. The MQ copolymers prepared in the first …

Synthesis And Structure-Property Relationships Of Polymeric Membranes For Small Molecule Transport, Haomiao Yuan

Doctoral Dissertations

One key challenge for alkaline anion exchange membrane fuel cells is the lack of alkaline stable polycations. The synthesis of random, crosslinked and block copolymers based on the cobaltocenium phenylene norbornene (NPC) monomer is described. The polymers were synthesized from ring-opening metathesis polymerization (ROMP) of the NPC monomer showed excellent thermo-alkaline and thermo-oxidative stability. Random copolymers, crosslinked networks and amphiphilic diblock copolymers were prepared by copolymerizing NPC with different hydrophobic monomers: norbornene for random copolymers, dicyclopentadiene for crosslinked networks and a norbornene dibenzyl ether monomer for amphiphilic diblock copolymers. Mechanical robust membranes were prepared from all these copolymers. Polymers with …

Solution-Based Assembly Of Conjugated Polymers Into Nanofibers For Organic Electronics, Daniel E. Acevedo Cartagena

Doctoral Dissertations

Solution-based crystallization of conjugated polymers offers a scalable and attractive route to develop hierarchical structures for electronic devices. The introduction of well-defined nucleation sites into metastable solutions provides a way to regulate the crystallization behavior, and therefore the morphology of the material. A crystallization method for generating metastable solutions of poly(3-hexylthiophene) (P3HT) was established. These metastable solutions allow P3HT to selectively crystallize into nanofibers (NFs) on graphene-coated surfaces. It was found that the crystallization kinetics is faster with increasing P3HT molecular weight and concentration. Through in situ atomic force microscopy, it was confirmed that NFs grow vertically in a face-on …

Guiding The Self-Assembly Of Block Copolymers In 2d And 3d With Minimal Patterning, Jaewon Choi

Doctoral Dissertations

Directed self-assembly (DSA) of block copolymers (BCPs) based on topographic patterns is one of the most promising strategies for overcoming resolution limitations in the current lithographic process and fabricating the next generation data storage devices. While the DSA of BCPs with deep topographic patterning has been extensively studied both experimentally and theoretically over the past two decades, less attention has been paid to the development of the DSA process using minimal topographic patterning. This dissertation focuses on understanding the effect of minimal topographic patterning on guiding the self-assembly of BCPs in 2D and 3D. We demonstrate that minimal trench patterns …

Correlating Long-Term Lithium Ion Battery Performance With Solid Electrolyte Interphase (Sei) Layer Properties, Seong Jin An

Doctoral Dissertations

This study was conducted to understand effects of some of key factors (i.e., anode surface properties, formation cycling conditions, and electrolyte conditions) on solid electrolyte interphase (SEI) formation in lithium ion batteries (LIBs) and the battery cycle life. The SEI layer passivates electrode surfaces and prevents electron transfer and electrolyte diffusion through it while allowing lithium ion diffusion, which is essential for stable reversible capacities. It also influences initial capacity loss, self-discharge, cycle life, rate capability and safety. Thus, SEI layer formation and electrochemical stability are primary topics in LIB development. This research involves experiments and discussions on key factors …

First-Principles Study Of Point Defect Behavior At Interfaces And In-Plane Strain Fields, Jianqi Xi

Doctoral Dissertations

Interfaces in solid materials are the so-called boundaries, separating crystals with the same structure and chemistry but different orientations, e.g. grain boundaries (GBs), different stacking sequences, e.g. stacking faults (SFs), or crystals with different structures and/or chemistries as well as orientations, e.g. the interface between substrate and thin film. In this study, first-principles calculations are used to investigate the defect behavior at different interfaces and in-plane strain fields, such as stacking fault (SF) in silicon carbide (SiC), in-plane strain field near interfaces in potassium tantalate (KTaO₃), and grain boundary in ceria (CeO₂).

Results show that the …

Advanced Purification And Direct-Write 3d Nanoprinting Via Focused Electron Beam Induced Deposition, Brett Bloxton Lewis

Doctoral Dissertations

This dissertation addresses three difficulties with focused electron beam induced deposition preventing broader application; purity, spatial control, and mechanical characterization.

Focused electron beam induced deposition (FEBID) has many advantages as a nanoscale fabrication tool. It is compatible for implementation into current lithographic techniques and has the potential to direct-write in a single step nanostructures of a high degree of complexity. FEBID is a very versatile tool capable of fabricating structures of many different compositions ranging from insulating oxides to conducting metals.

Due to the complexity of the technique and the difficulty in directly measuring many important variables, FEBID has remained …

Synthesis, Characterization And Application Of Block Copolymer And Nanoparticle Composites, Yue Gai

Doctoral Dissertations

The “bottom-up” fabrication of functional hybrid material can be achieved by using directed self-assembly of functional nanoparticles (NP) and block copolymers (BCP) as templates. The versatile nanostructures of BCP provide possibilities to precisely control NPs spatial distribution and the resulting hybrid materials exhibit enhanced electrical, mechanical and optical functionalities. Three main topics related to BCP/NP composites are discussed in this dissertation: I) the spatial distribution of large NP in linear BCP; II) the morphology control of BCP templates with new architectures; and III) the magneto-optical properties of hybrid material using magnetic NPs. For well-ordered BCP/NP composite, the ratio of NP …

Characterization Of Electronic And Ionic Transport In Soft And Hard Functional Materials, Lawrence A. Renna

Doctoral Dissertations

Control over concurrent transport of multiple carrier types is desired in both soft and hard materials. For both types of materials, I demonstrate ways to characterize and execute governance over both electronic and ionic transport, and apply these concepts in the fabrication of devices with applications in conducting composites, photovoltaics, electrochemical energy storage, and memristors. In soft materials, such as polymers, the topology of the binary polymer mesoscale morphology has major implications on the charge/ion transport. Traditional approaches to co-continuous structures involve either using blends of polymers or diblock copolymers. In polymer blends, the structures are kinetically trapped and …

Dynamic Range Limitations Of Low-Noise Microwave Transistors At Cryogenic Temperatures, Ahmet Hakan Coskun

Doctoral Dissertations

Dynamic range is an important metric that specifies the limits of input signal amplitude for the ideal operation of a given receiver. The low end of dynamic range is defined by the noise floor whereas the upper limit is determined by large-signal distortion. While dynamic range can be predicted in the temperature range where compact transistor models are valid, the lack of large-signal models at temperatures below -55 C prevents the prediction and optimization of dynamic range for applications that require cryogenic cooling. For decades, the main goal concerning the performance of these applications was lowering the noise floor of …

Modulation Of Cell Behaviors On Photo-Crosslinked Polymer Networks And Polymer Spherulites, Jinbo Dou

Doctoral Dissertations

This dissertation presents novel biodegradable and photo-crosslinkable poly(-caprolactone) acrylates (PCLAs) to achieve polymer networks with controllable surface chemistry, stiffness, and topographical features, as well as crystallization-induced PCL, poly(3-hydroxybutyrate) (PHB) and poly(L-lactic acid) (PLLA) surfaces for investigating cell-material interactions. Chapter I reviews the recent progress of injectable polymeric biomaterials in the last decade for various tissue engineering applications. Chapter II investigates the variation of thermal and mechanical properties of PCL triacrylate (PCLTA) networks with different crosslinking time, and further studies the smooth muscle cell (SMC) responses to these networks. Chapter III studies the SMC responses to hydrolyzed PCLTA/methoxyl polyethylene glycol monoacrylate …

Effect Of Crosslinking On Carbon Nanotube Materials Through Chemical Treatment And Irradiation, Xinyi Lu

Doctoral Dissertations

Carbon nanotubes (CNTs) exhibit a variety of exceptional properties, especially their ultrahigh tensile strength on the order of 100GPa show promise for constituting the next-generation carbon fiber. However, challenges remain to translate these properties into useful technology, primarily due to the sliding of the tubes past one another under tensile loading. The work presented in this dissertation is focused on enhancing the interaction between the CNTs and their bundles in a macro-assembly, in order to improve the tensile properties of the material.

Applying inter-tube crosslinks has been predicted to significantly enhance the stress transfer between the CNT components. We developed …

Experimental And Computational Investigation Of High Entropy Alloys For Elevated-Temperature Applications, Haoyan Diao

Doctoral Dissertations

To create and design novel structural materials with enhanced creep-resistance, fundamental studies have been conducted on high-entropy alloys (HEAs), using (1) thermodynamic calculations, (2) mechanical tests, (3) neutron diffraction, (4) characterization techniques, and (5) crystal-plasticity finite-element modeling (CPFEM), to explore future candidates for next-generation power plants.

All the constituent binary and ternary systems of the Al-Cr-Cu-Fe-Mn-Ni and Al-Co-Cr- Fe-Ni systems were thermodynamically modeled within the whole composition range. Comparisons between the calculated phase diagrams and literature data are in good agreement. The Al_xCrCuFeMnNi HEAs have disordered [face-centered-cubic (FCC) + body-centered-cubic (BCC)] crystal structures. Excessive alloying of the Al …

Excitations Of Quasi-Particles In Nanostructured Systems, Jingxuan Ge

Doctoral Dissertations

The excitation of quasiparticles, like the investigated excitons and plasmons here, are the optically most prominent responses of materials. In nanostructured system, the sample quality is crucial for quantitative investigations of these optical excitations. We used electron beam evaporation, nano-second laser dewetting, and electron metalorganic chemical vapor deposition techniques to prepare well-defined and “clean” transmission electron microscopy (TEM) samples. Electron energy-loss microscopy (EELS) performed in STEM mode was employed to investigate the structural and electro-optical properties. Quantifit software was used to analyze the EELS spectra quantitatively in terms of inelastic scattering probability, energy and lifetime.

We found that the ferroplasmon …

All Acrylic Based Thermoplastic Elastomers: Design And Synthesis For Improved Mechanical Performance, Wei Lu

Doctoral Dissertations

Thermoplastic elastomers (TPEs) have been widely studied because of their recyclability, good processability, low production cost and distinct performance. Compared to the widely-used styrenic TPEs, acrylate based TPEs have potential advantages including exceptional chemical, heat, oxygen and UV resistance, optical transparence, and oil resistance. However, their high entanglement molecular weight lead to “disappointing” mechanical performance as compared to styrenic TPEs. The work described in this dissertation is aimed at employing various approaches to develop the all acrylic based thermoplastic elastomers with improved mechanical performance.

The first part of this work focuses on the introduction of acrylic polymers with high glass …

Surface Energy In Bond-Counting Models On Bravais And Non-Bravais Lattices, Tim Ryan Krumwiede

Doctoral Dissertations

Continuum models in computational material science require the choice of a surface energy function, based on properties of the material of interest. This work shows how to use atomistic bond-counting models and crystal geometry to inform this choice. We will examine some of the difficulties that arise in the comparison between these models due to differing types of truncation. New crystal geometry methods are required when considering materials with non-Bravais lattice structure, resulting in a multi-valued surface energy. These methods will then be presented in the context of the two-dimensional material graphene in a way that correctly predicts its equilibrium …

Thiol-Ene Chemistry As An Enabler Of New Polymer Structures And Architectures, Joel M. Sarapas

Doctoral Dissertations

This dissertation focuses on two distinct projects: the synthesis and design of novel cell penetrating peptides mimics (CPPMs), and the implementation of the thiol-ene click reaction to generate new polymer architectures and chemistries. Guanidinium-rich CPPMs were generated through both ROMP and RAFT polymerizations, allowing for a comparison to be made across polymer backbone chemistries with respect to both siRNA and protein cellular internalization. A particularly effective methacrylate derived block copolymer was able to deliver siRNA to nearly an entire Jurkat T cell population. The thiol-ene reaction was implemented initially within the context of improving material design for solid polymer electrolytes …

Deformation And Adhesion Of Soft Composite Systems For Bio-Inspired Adhesives And Wrinkled Surface Fabrication, Michael Imburgia

Doctoral Dissertations

The study of soft material deformation and adhesion has broad applicability to industries ranging from automobile tires to medical prosthetics and implants. When a mechanical load is imposed on a soft material system, a variety of issues can arise, including non-linear deformations at interfaces between soft and rigid components. The work presented in this dissertation embraces the occurrence of these non-linear deformations, leading to the design of functional systems that incorporate a soft elastomer layer with application to bio-inspired adhesives and wrinkled surface fabrication. Understanding the deformation of a soft elastomer layer and how the system loading and geometry influence …

New Synthetic Platforms For Functional Polymer Zwitterions And Degradable Materials, Chiachih Chang

Doctoral Dissertations

This thesis describes new synthetic platforms for a series of functional polymeric materials containing hydrophilic and/or zwitterionic moieties as pendent groups. The hydrophilicity, biocompatibility, and degradability of these polymers hinged on innovative monomer designs and adaption of appropriate polymerization strategies including controlled radical polymerization, metathesis polymerization, and ring-opening polymerization. Novel, functional sulfobetaine polymers having functional groups (i.e, alkenes and alkynes) directly attached to the zwitterionic moieties were prepared and shown to stabilize oil-water interfaces, allowing for interfacial crosslinking to afford robust polymer capsules. This represents the first example of inserting functionality directly into the zwitterionic moieties of polymer zwitterions, allowing …

Processing, Microstructure, And Mechanical Properties Of Zirconium Diboride-Molybdenum Disilicide Ceramics And Dual Composite Architectures, Ryan Joseph Grohsmeyer

Doctoral Dissertations

"This research had two objectives: characterization of processing-microstructure-mechanical property relationships of conventional ZrB₂-MoSi₂ ceramics at room temperature (RT) and 1500⁰C in air, and fabrication of ZrB₂-MoSi₂ dual composite architectures (DCAs) for use near 1500⁰C. Elastic moduli, fracture toughness, and flexure strength were measured at RT and 1500⁰C for 15 ZrB₂-MoSi₂ ceramics hot pressed using fine, medium, or coarse ZrB₂ starting powder with 5-70 vol.% MoSi₂, referred to as FX, MX, and CX respectively where X is the nominal MoSi₂ content. MoSi₂ decomposed during sintering, resulting in …