Materials Science and Engineering Commons^™

Optimization Of The Front End Of Cdte Solar Cells, Yunfei Chen

Dissertations

The front end of CdTe solar cells consists of two layers: a transparent conducting oxide (TCO) layer and a window layer. New wider band gap materials, ZnMgO are being used to replace CdS as the window layer for the purpose of removing blue loss. For ZnMgO, three important parameters, including the atomic Mg content (x), thickness (t), and doping concentration (n) can play important roles on the performance of CdTe solar cells. In this dissertation, systematic simulation, by solar cell capacitance simulator (SCAPS), and experiments are used to investigate the influences of these …

Cellulose Reinforced Thermoplastic Composites By In-Situ Ring-Opening Polymerization, Shahab Kashani Rahimi

Dissertations

Over the past two decades, the increasing concern about the negative environmental impacts of synthetic materials has led to rising interests in utilizing renewable natural resources to develop polymer materials with comparable properties and performance to their synthetic counterparts. One of the major fields of interest is polymer composites where the replacement of synthetic fibers with bio renewable natural fibers is of great potential. However, the processing difficulties, in terms of fiber dispersion and thermal stability have limited the application of cellulosic fibers to polymers with low processing temperatures which are mostly hydrophobic polymers. As a result, the true reinforcing …

Fate Of Conductive Ink Pigments During Recycling And Landfill Deposition Of Paper-Based Printed Electronics, James Edward Atkinson

Dissertations

Printed electronics (PE) are being developed as an alternative to traditional electronics, due to the more efficient use of materials and lower cost of production. The overall goal of this study was to understand how metallic pigments in conductive inks in PE are partitioned during landfill disposal and paper recycling conditions. The purpose is to assess the potential environmental impacts of PE landfilling in terms of metal leaching and to help develop new strategies for sequestering metallic ink components while paper-based PE are subjected to conventional paper recycling methods. The objective of this research is to study the fate of …

Design And Synthesis Of Polymer Brush Surfaces With Complex Molecular Architectures And Morphologies, Wei Guo

Dissertations

The combination of surface-initiated polymerization (SIP) and postpolymerization modification (PPM) is a powerful technique for the fabrication of functional soft surfaces. Better understanding the influence of the aforementioned factors on the PPM effectiveness is valuable for fulfilling the potential of the PPM approach for the fabrication of functional soft surfaces. Specifically, by carefully balancing modification reactivity and limitation of mass transport, polymer brush with composition heterogeneity and gradient along the normal direction of the surface otherwise unattainable by methods of direct polymerization can be fabricated via the PPM approach which opens doors to new routes to polymer brush with complex …

Effect Of Chain Rigidity On Network Architecture And Deformation Behavior Of Glassy Polymer Networks, Kyler Reser Knowles

Dissertations

Processing carbon fiber composite laminates creates molecular-level strains in the thermoset matrix upon curing and cooling which can lead to failures such as geometry deformations, micro-cracking, and other issues. It is known strain creation is attributed to the significant volume and physical state changes undergone by the polymer matrix throughout the curing process, though storage and relaxation of cure-induced strains remain poorly understood. This dissertation establishes two approaches to address the issue. The first establishes testing methods to simultaneously measure key volumetric properties of a carbon fiber composite laminate and its polymer matrix. The second approach considers the rigidity of …

An Investigation Of The Use Of Cerium And Polyhedral Oligomeric Silsesquioxanes For The Protection Of Polymeric Epoxy Compounds In The Low Earth Orbit Environment, Jessica Miriam Piness

Dissertations

Low Earth orbit presents many hazards for composites including atomic oxygen, UV radiation, thermal cycling, micrometeoroids, and high energy protons. Atomic oxygen and vacuum ultraviolet radiation are of concern for space-bound polymeric materials as they degrade the polymers used as matrices for carbon fiber composites, which are used in satellites and space vehicles due to their high strength to weight ratios. Epoxy-amine thermosets comprise a common class of matrix due to processability and good thermal attributes. Polyhedral oligomeric silsesquioxanes (POSS) have shown the ability to reduce erosion in polyimides, polyurethanes, and other polymers when exposed to atomic oxygen. The POSS …

Formation Of Nanostructured Epoxy Networks Containing Polyhedral Oligomeric Silsesquioxane (Poss) And Silica Nanoparticles, Amit K. Sharma

Dissertations

This dissertation is focused on structure-property-processing relationship studies based on well-defined polyhedral oligomeric silsesquioxane (POSS) modified epoxy networks to present a comprehensive understanding of hybrid network behavior. In this research, a monoamine functional POSS molecule is incorporated into the epoxy monomer as pendant unit to mimic common epoxy structures and then crosslinked to form well-defined epoxy hybrid networks. The POSS cages behave as nanosized pendant unit in the epoxy matrices, while the mass fraction of POSS cages is varied and the effects on physical properties are examined with respect to changes in network architecture.

A novel continuous reactor method is …

Polyisobutylene Telechelic Prepolymers By In Situ End-Quenching And Post-Polymerization Modifications, Bin Yang

Dissertations

This volume focuses on the development of telechelic polyisobutylene (PIB) prepolymers by combining end-capping of living carbocationic polymerization of isobutylene (IB) with suitable reactants and post-polymerization modifications. Alkylation kinetics of PIB tert-chloride with alkoxybenzenes using either TiCl₄ or AlCl₃ were investigated. Quantitative para-position end-capped products were only achieved if the alkoxybenzene/AlCl₃ molar ratio was greater than unity; while no such molar ratio is required for TiCl₄, but the alkylation rate was slower than AlCl₃ under the same conditions. Photopolymerization kinetics analysis of PIB triphenol tri(meth)acrylates with low and high M_ns, …

Development Of Low Alloy Steel By Direct Metal Laser Sintering, Elias Jelis

Dissertations

The US Department of Defense is interested in developing, understanding, and optimizing process parameters for low alloy (4340/4140 steel) for the powder bed fusion process. Low alloy steel is used in parts where high strength and toughness are required. During parameter optimization, several aspects of the process are investigated. Powder size and morphology optimization is important for manufacturability because adequate packing is required to produce full density components. Microstructure evaluation is used in order to provide insight into parameters that lead to optimal mechanical performance and recoating performance. Influence of residual stress is evaluated with this process. Large thermal stress …

Design And Synthesis Of Dynamic Covalent Polymer Scaffolds With Controlled Architectures, Emily Annette Hoff

Dissertations

The design and synthesis of functional, controlled polymer architectures is essential to the development of new materials with precise and tailorable properties or applications. The work described in this dissertation focuses on the development of controlled polymer architectures with dynamic linkages for the design of multifunctional materials and surfaces via robust, efficient, and stimuli-responsive strategies.

In Chapter III, a post-polymerization modification strategy based on ambient temperature nucleophilic chemical deblocking of polymer scaffolds bearing N-heterocycle blocked isocyanate moieties is reported. Room temperature RAFT polymerization of three azole-N-carboxamide methacrylates, including 3,5-dimethyl pyrazole, imidazole, and 1,2,4-triazole derivatives, afforded reactive polymer scaffolds …

Nanostructured Morphologies In Glassy Polymer Networks, Brian Greenhoe

Dissertations

The body of this work describes a novel approach for the dispersion of multi-walled carbon nanotubes in a high T_g epoxy prepolymer matrix using a twin screw high-shear continuous reactor. The method demonstrated improves on previous dispersion methods in several ways. It offers increased efficiency through excellent heat transfer, while being solvent-less, scale-able, and tailorable to drive dispersion states to judiciously chosen dispersion states. Furthermore, it was shown that dispersion state and agglomerate morphology can be directed, in several ways, through processing conditions and also by controlling the matrix viscosity profile through cure. Broadband dielectric spectroscopy, optical hot-stage microscopy, …

Application Of Inkjet Printing Technology To Flexible Batteries, Yuan Gu

Dissertations

Printing technologies have been considered as alternative methods to fabricate thin films in recent years. More and more functional devices like resistors, sensors, antennas and even energy storage devices have been fabricated by printing technologies. As a typical digital printing technology, inkjet printing has much more advantages over the traditional mechanical printing technologies such as: low cost, computer controllable shape design and precise deposition. In this investigation, application of inkjet printing is used to fabricate conductive tracks and rechargeable lithium ion batteries.

Particle free silver ink is developed to solve this problem. In this research, silver complex solution is printed …

The Recent Development Of New Pigment Binders, Jae Young Shin

Dissertations

Pigment coatings are applied onto paper and paperboard to improve their appearance and printability. For pigmented coatings, pigments and binders are the most important ingredients so their selections are critical.

Pigment binders not only perform the basic required role of binding pigment particles to each other and bonding the base sheet, but also significantly influence the rheology, coater runnability, and drying behaviors of the coating formulation and the optical, viscoelastic, and printing properties of coated paper and paperboard products.

When considering the relative amount of binders to use in a coating, one may speak about main binder, co-binder and sole-binder. …

Flexographic Printing Of Conductive Silver Inks Onto Pdms: Surface Treatment And Novel Processes For Creating Printed Electronic Devices, Michael James Joyce

Dissertations

For the continued advancement of the field of printed electronic (PE), there is a need for a better understanding of the interactions between functional inks and substrates, which is required to optimize printability, mechanical, and functional properties for the creation of more robust and efficient printed devices. This body of work aims to advance the knowledge of the material properties of poly-di-methyl-siloxane, PDMS, films, their interactions with flexo inks, and their flexographic printability. As the printing of metals (i.e., Ag & Au) is a known area of interest pertaining to PE, this work focused on the characterization and optimization of …

3d Printed Bone Supplement Materials, Azem Khalifa Yahamed

Dissertations

Three-dimensional (3D) printing is an advanced rapid technology that can be used to make human bone substitutes with exact shape and designed structures, based on models created from actual individual bone medical Digital Imaging and Communications in Medicine (DICOM) images. Biocompatible polymers have been selected for 3D printing of human bone structures. The thermoplastics were 3D printed with Fused Deposition Modeling (FDM) are Acrylate Butadiene Styrene (ABS), Polylactic Acid (PLA) and ULTEM 9085 (a polyetherimide). The polyamide PA 2200 was 3D printed using Selective Laser Sintering (SLS). Digital ABS (a crosslinked acrylic polymer) was 3D printed using PolyJet Technology. These …

Experimental And Theoretical Evaluation Of In-Depth Damage Distribution In Sawn Silicon Wafers, Srinivasamurthy Devayajanam

Dissertations

As-sawn silicon wafers have surface damage that needs to be removed before any further processing into solar cells. This damage distribution can vary with cutting parameters such as wire size, slurry particle/diamond grit size, and wire usage. To date, there is no simple way to measure the degree of damage, damage depth, and damage distribution. But, this information is needed by the wafer manufacturers as well as solar cell manufacturers.

A technique based on sequential etching of silicon wafers and minority carrier lifetime (τ_eff) measurements is used to determine damage depth. In this technique, samples are sequentially etched …

Understanding Bulk Behavior Of Particulate Materials From Particle Scale Simulations, Xiaoliang Deng

Dissertations

Particulate materials play an increasingly significant role in various industries, such as pharmaceutical manufacturing, food, mining, and civil engineering. The objective of this research is to better understand bulk behaviors of particulate materials from particle scale simulations.

Packing properties of assembly of particles are investigated first, focusing on the effects of particle size, surface energy, and aspect ratio on the coordination number, porosity, and packing structures. The simulation results show that particle sizes, surface energy, and aspect ratio all influence the porosity of packing to various degrees. The heterogeneous force networks within particle assembly under external compressive loading are investigated …

Effects Of Expected Service Life Exposures On The Functional Properties And Impact Performance Of An American Football Helmet Outer Shell Material, David E. Krzeminski

Dissertations

The purpose of this dissertation is to gain a greater scientific understanding of the changes in functional material properties and impact performance of an American football helmet outer shell material under expected service life exposures. The research goals are to (i) quantify chemical, physical, thermal, and mechanical degradation of an American football outer shell material under expected environmental conditions and (ii) develop a linear drop test impact protocol to employ expected on-field impact conditions to American football helmet components and a plaque-foam (i.e., shell-liner) surrogate. Overall, a step-wise progression of analysis was demonstrated to concurrently quantify and understand changes in …

Hybrid Aryl-Ether-Ketone And Hyperbranched Epoxy Networks, John Misasi

Dissertations

In this dissertation, relationships between chemical structures, cure kinetics and network architectures are correlated to bulk mechanical properties for novel, hybrid epoxy-amine networks. The work is split into two primary sections: the first is the synthesis and characterization of multifunctional glassy networks based on aryl-ether-ketone diamine curatives, while the second is based on the synthesis and characterization of hyperbranched epoxy polymers and their resulting networks.

Three aryl-ether-ketone (AEK) diamines of increasing molecular weights were synthesized and used to cure 4,4’-tetraglycidylether of diaminodiphenylmethane (TGDDM); the resulting networks were compared to 4,4’-diaminodiphenyl sulfone cured TGDDM. Architectural differences were created by varying cure …

Polyacrylonitrile Copolymers: Effects Of Molecular Weight, Polydispersity, Composition, And Sequencing On Thermal Ring-Closing Stabilization, Jeremy D. Moskowitz

Dissertations

Controlled polyacrylonitrile (PAN)-based carbon fiber precursors with defined molecular weights, polydispersities, compositions, and architectures have been prepared for their study on thermal ring-closing stabilization behavior. PAN and its copolymers of number average molecular weights exceeding 170,000 g/mol were successfully synthesized via low temperature reversible addition-fragmentation chain transfer (RAFT) polymerization. RAFT polymerizations of PAN-based precursors were compared to conventional free radical solution polymerizations with a focus on the effects of molecular weight and polydispersity on structural evolution and cyclization efficiency. When RAFT polymerization was extended to copolymers, it was found that RAFT copolymers achieved greater cyclization intensities and improved thermal stability …

Development Of Dual-Cure Hybrid Polybenzoxazine Thermosets, Jananee Narayanan Sivakami

Dissertations

Polybenzoxazines are potential high performance thermoset replacements for traditional phenolic resins that can undergo an autocatalytic, thermally initiated ring - opening polymerization, and possess superior processing advantages including excellent shelf-life stability, zero volatile loss and limited volumetric shrinkage. The simplistic monomer synthesis and availability of a wide variety of inexpensive starting materials allows enormous molecular design flexibility for accessing a wide range of tailorable material properties for targeted applications. Despite the fact, once fully cured, benzoxazines are difficult to handle due to their inherent brittleness, leaving a very little scope for any modifications. The motivation of this dissertation is directed …

Production And Characterization Of Composite Nano/Micro Sized Particles By Rapid Expansion Of Supercritical Solutions (Ress) Co-Precipitation, Beidi He

Dissertations

Nanoscale composites of hexahydro-1, 3, 5-trinitro-1, 3, 5-triazine (RDX) and polymer binders were produced by co-precipitation using rapid expansion of supercritical solutions (RESS). The binders used in this study are poly (vinylidene fluoride-co-hexafluoropropylene) (VDF-HFP22), polystyrene (PS) and 7-amino-4-methyl coumarin (AMC). The RDX/VDF-HFP22 and RDX/PS co-precipitated nanoparticles were characterized by Field Emission Scanning Electron Microscopy (FE-SEM) and Transmission Electron Microscopy (TEM). The average size of produced nanoparticles is ca. 100 nm. TEM analysis of RDX/PS nano-composite shows a core-shell structure with RDX as the core material and the shell consisting of the polymeric binder. X-ray Powder Diffraction (XRPD) analysis …

New Screening Methodology For Selection Of Polymeric Materials For Transdermal Drug Delivery Devices, Roberto P. Falcone

Dissertations

As medical advances extend the human lifespan, the level of chronic illnesses will increase and thus straining the needs of the health care system that, as a result, governments will need to balance expenses without upsetting national budgets.

Therefore, the selection of a precise and affordable drug delivery technology is seen as the most practical solution for governments, health care professionals, and consumers.

Transdermal drug delivery patches (TDDP) are one of the best economical technologies that are favored by pharmaceutical companies and physicians alike because it offers fewer complications when compared to other delivery technologies. TDDP provides increased efficiency, safety …

Cure Kinetics, Morphologies, And Mechanical Properties Of Thermoplastic/Mwcnt Modified Multifunctional Glassy Epoxies Prepared Via Continuous Reaction Methods, Xiaole Cheng

Dissertations

The primary goal of this dissertation is to develop a novel continuous reactor method to prepare partially cured epoxy prepolymers for aerospace prepreg applications with the aim of replacing traditional batch reactors. Compared to batch reactors, the continuous reactor is capable of solubilizing and dispersing a broad range of additives including thermoplastic tougheners, stabilizers, nanoparticles and curatives and advancing epoxy molecular weights and viscosities while reducing energy consumption.

In order to prove this concept, polyethersulfone (PES) modified 4, 4’-diaminodiphenylsulfone (44DDS)/tetraglycidyl-4, 4’-diaminodiphenylmethane (TGDDM) epoxy prepolymers were firstly prepared using both continuous reactor and batch reactor methods. Kinetic studies confirmed the chain …

Electronic, Optical, Mechanical And Thermoelectric Properties Of Graphene, Sarang Vilas Muley

Dissertations

Graphene, a two-dimensional allotrope of graphite with sp² bonded carbon atoms, is arranged in honeycomb structure. Its quasi one-dimensional form is graphene nanoribbon (GNR). Graphene related materials have been found to display excellent electronic, chemical, mechanical properties along with uniquely high thermal conductivity, electrical conductivity and high optical transparency. With excellent electrical characteristics such as high carrier transport properties, quantum Hall effect at room temperature and unusual magnetic properties, graphene has applications in optoelectronic devices.

Electronically, graphene is a zero bandgap semiconductor making it essential to tailor its structure for obtaining specific band structure. Narrow GNRs are known to …

Inkjet Printing Multifunctional Chromatic Sensors And Chromism Study, Aide Wu

Dissertations

The thermochromism and chemochromism of polydiacetylene (PDAs) and PDA/ZnO nano composites have been systematically studied by attentuated total reflection (ATR)- Fourier transform infrared (FTIR), temperature-dependent Raman, colorimetric (using optical densitometry) and differential scanning calorimetry (DSC). Reversibility of PDAs has been enhanced by the formation of chelation between the carboxylic groups on side chain of diacetylene and Zn ion. The thermochromatic transition temperature increases with the concentration of ZnO.

Thin films of polydiacetylene (PDAs) and PDA/ZnO nanocomposites have been successfully fabricated by inkjet printing both solution type and suspension type ink. Results suggest that PDA monomers are well-aligned and closely packed …

Continuous Polymer Coating Of Host Particles By Hollow Fiber-Based Crystallizers, Dengyue Chen

Dissertations

Currently, no technique is available to continuously film coat nano-sized drug particles with a polymer to produce large amounts of free-flowing coated particles. In this work, Eudragit RL 100 and Poly (D, L-lactide-co-glycolide) (PLGA) are chosen as the coating polymers; Cosmo 55 (550 nm silica particles), Aerosi l 200 (hydrophilic 12 nm silica), Aerosil R974 (hydrophobic 12 nm silica) and Griseofulvin (10 lam drug particles) are chosen as the host particles. Two novel crystal l izers are designed and fabricated to continuously coat the host particles with different polymers: solid hollow fiber cooling crystallizer (SH FCC) and porous hollow fiber …

Polymeric Nitrogen By Plasma Enhanced Chemical Vapor Deposition, El Mostafa Benchafia

Dissertations

With the urgent need for new environmentally-friendly energetic materials, the field of polymeric nitrogen, predicted to be a high energy density energetic, is now at a critical stage in its development. In spite of extensive first principles calculations regarding the existence and stability of different polymeric nitrogen structures, their successful syntheses have been rare. This dissertation describes the first detailed study of a plasma-enhanced chemical vapor deposition (PECVD) approach to the synthesis of polymeric nitrogen. PECVD provides non-equilibrium conditions known to produce high pressure-temperature phases. Molecular nitrogen mixed with hydrogen and argon is used as the gas phase precursor to …

Printing Functional Electronic Circuits And Components, Ahmed Tausif Aijazi

Dissertations

The purpose of this study was to investigate the challenges in printing reliable multilayer flexible circuits, devices and components. Gravure was used as the primary printing process for this work, but due to some limitations of gravure, other printing methods were also investigated. At first a systematic study was done to determine the optimum parameters for the gravure printing of sub 50 micron lines. Commercially available silver nanoparticle inks were printed on a lab scale gravure printer, Accupress®. The highest resolution line that was electrically conductive was 36μm wide. The 9μm, 18μm and 27μm lines were printed but were not …

Utilization Of Aqueous Raft Prepared Copolymers To Improve Anticancer Drug Efficacy, Andrew Christopher Holley

Dissertations

The advent of controlled radical polymerization (CRP) techniques, along with advancements in facile conjugation chemistry, now allow synthetic tailoring of precise, polymeric architectures necessary for drug/gene delivery. Reversible addition- fragmentation chain transfer (RAFT) polymerization and its aqueous counterpart (aRAFT) afford quantitative control over key synthetic parameters including block length, microstructure, and placement of structo-pendent and structo-terminal functionality for conjugation of active agents and targeting moieties. The relevance of water-soluble and amphiphilic (co)polymers synthesized by RAFT for in vitro delivery of therapeutics in biological fluids is an especially attractive feature. In many cases, polymerization, binding, conjugation, …