Physical Sciences and Mathematics Commons^™

Material Formulation And Process Optimization Towards Fabricating Robust 3d Printed Structures, Austin Riggins

Doctoral Dissertations

This dissertation focuses on understanding and addressing the fundamental physicochemical phenomena that lead to weak interfaces and structural warpage in material extrusion 3D printing. Polymeric feedstocks used for this manufacturing technique were manipulated through the incorporation of additives that alter the dynamics of the matrix during and after printing. In Chapter II, adhesion between layers of structures printed from PEEK was strengthened through a combination of low-molecular weight additive incorporation and post-printing thermal annealing. Chapter III reports a method for decreasing the irreversible thermal strain of structures printed from poly(lactic acid) by introducing nanographene and photoinitiator additives into the feedstock …

Integration Of Raman Spectroscopy And Python-Based Data Analysis For Advancing Neurobiological Research, Natalie E. Dunn

Doctoral Dissertations

The field of Raman spectroscopy continues to expand into biological applications due to its usefulness as a non-invasive technique that can be utilized qualitatively and quantitatively. However, the inherent weakness of Raman scattering leads to the need for each collected spectra to undergo a preprocessing step to remove noise, background drift, and cosmic rays. Biological research in particular needs large datasets due to the increased variability in samples. As datasets grow, the need to perform preprocessing on each individual spectra becomes daunting. Often, these steps are done by hand with the help of specialized software programs. Preprocessing can be accelerated …

Synthesis Of Block Copolymer Additives For Examining Phase Morphology And Improving Mechanical Properties Of Thermoplastics Elastomers., Bishal Upadhyay

Masters Theses

Polystyrene-block-poly(1,4-butaidene)-block-polystyrene (PS-PB-PS) triblock copolymers are one of the most widely studied thermoplastic elastomers (TPEs) due to their ease of synthesis, non-polar nature, and commercial applicability. Like many block copolymers, incompatibility between PS and PB causes these TPEs to undergo microphase segregation. Many studies have examined the mechanical properties of blends of TPEs and PS homopolymer additives. However, there have been few studies focused on understanding the morphology and mechanical properties of blends of TPEs and copolymer additives with different architectures. Herein, I describe the synthesis of linear and graft copolymer additives based on the random copolymers poly(methyl methacrylate-random-cyclohexyl methacrylate) (PrC). …

The Influence Of Ion-Ion Correlations On Conductivity In Concentrated Ionic Systems, Md Dipu Ahmed

Masters Theses

This study delves into the fascinating realm of concentrated ionic systems, such as ionic liquids, superionic materials, organic ionic plastic crystals, and polyelectrolytes, which hold immense potential for energy storage applications. The focus is on understanding the intricate role of ionic correlations in shaping their ionic conductivity behavior. These correlations can either boost or impede conductivity, yet their underlying mechanisms remain elusive. Through extensive investigation of various materials, including ionic liquids with differing anionic masses, pure organic ionic plastic crystals, and doped systems, this research employs advanced techniques like dielectric spectroscopy and innovative momentum conservation models to quantify these correlations. …

Dinitrogen Functionalization Using A Molybdenum Atom: Bridging The Gap Between Small And Coordination Complexes Via Quantum Mechanical Methods, Maria Virginia White

Doctoral Dissertations

Chemistry devotes a significant amount of its research to understanding small molecule activation from an electronic structure perspective to help with the investigation of the reaction pathways of catalytically active substances that can promote biomimetic catalysis. A large portion of the energy used annually in our planet is used for the artificial nitrogen fixation (Haber-Bosch process), which renders dinitrogen activation a subject of study. Molybdenum, a fourth row transitional metal, has demonstrated its effectiveness as an essential component of the dinitrogen reduction catalytic process. To better understand the multiple dinitrogen molybdenum binding modes, the work described herein combines wave function …

Theoretical Studies Of Adsorption And Reactivity At The Gas-Solid Interface, Carson J. Mize

Doctoral Dissertations

Catalytic transformations of small molecules is of great interest for both laboratory and industrial practices. Two specific transformations are ethylene to ethylene oxide and combinations of azides and alkenes into aziridine molecules. Ethylene oxide is an epoxide used as a feed-stock for many bulk reactions and commercial products such as antifreeze and various sterilization techniques, while molecules with the aziridine functional group are used for many ring opening and closing techniques as well as in pharmaceuticals and other drug treatments. For production of ethylene oxide, the combination of oxygen adsorbed onto a silver crystal is the known catalysts for thus …

Chirality, Symmetry-Breaking, And Chemical Substitution In Multiferroics, Kiman Park

Doctoral Dissertations

Multiferroic materials attract significant attention due to their potential utility in a broad range of device applications. The inclusion of heavy metal centers in these materials enhances their magnetoelectric properties, yielding fascinating physical phenomena such as the Dzyaloshinskii–Moriya interaction, nonreciprocal directional dichroism, enhancement of spin-phonon coupling, and spin-orbit-entangled ground states. This dissertation provides a comprehensive survey of magnetoelectric multiferroics containing heavy metal centers and explores spectroscopic techniques under extreme conditions. A microscopic examination of phase transitions, symmetry-breaking, and structure-property relationships enhances the fundamental understanding of coupling mechanisms.

In A2Mo3O8 (A = Fe, Zn, Ni, and Mn), we use optical spectroscopy …

Comprehensive Studies Of Magnetic Properties Of Metal-Organic Frameworks And Molecular Compounds, Pagnareach Tin

Doctoral Dissertations

Single-ion magnets (SIMs) are at the forefront of molecular electronic spin magnets with potential applications in magnetic memory storage devices. However, the magnetic properties of the SIMs are yet to be completely understood, especially the magnetic properties of large anisotropy systems. A part of this dissertation is to utilize optical and neutron spectroscopies such as far-IR magneto-spectroscopy (FIRMS) and inelastic neutron scattering (INS) to quantify the anisotropy and study the phonon properties of the SIMs as two-dimensional (2-D) metal-organic frameworks (MOFs) or coordination polymer (CP), and a molecular magnet. In addition, ab initio calculations are used to understand the origin …

Redox-Active Polymerization Catalysts And Their Applications, Nicholas M. Shawver

Masters Theses

Traditional catalyst systems are reliable means to produce polymers with well-defined architectures and thermomechanical properties; however, they are often limited by a narrow monomer scope and their ability access few, if any, advanced polymer architectures. To address this limitation, a new class of catalysts have recently emerged that feature redox-active moieties that may access advanced architectures through catalyst electronic modulation that arises from redox events occurring on the ligand scaffold or at the active metal center itself. For example, researchers have explored the ability of redox-active catalysts to impart “on-off” kinetic control during ring-opening polymerizations and their ability to access …

Expression And Purification Of Polyketide Synthase Domains To Investigate Protein-Protein Interactions In Polyketide Biosynthetic Pathways, Mujeeb Adeyinka Wakeel

Masters Theses

Polyketide synthases (PKSs) are multienzyme proteins catalyzing the production of the polyketide class of natural products with vast structural diversity. Type II PKSs catalyze polyketide biosynthesis using discrete (standalone) enzymes (domains), while type I PKSs use covalently linked enzymes arranged in a module to catalyze polyketide production. It is hypothesized that type II PKSs are the precursors to type I PKSs, proposing that the genes encoding individual discrete enzymes in type II PKSs fused to give the multienzyme modules of type I PKSs. We reasoned that the intramolecular-like reactions occurring in type I PKS modules might be a driving force …

Synthesizing, Purifying, And Characterizing Molten Chloride Salts, Phillip W. Halstenberg

Doctoral Dissertations

Molten chloride salts have vast potential as heat transfer fluids with both nuclear and concentrated solar power applications. For application in energy systems, the characteristics that govern these systems must be well understood. This work focuses on inorganic molten chloride salts with a special emphasis on the experimental aspect of chemical research. Chapter 2 covers the synthetic approaches for the formation of molten chloride mixtures. Many salts can be purchased from industrial suppliers, but most must be purified therefore, Chapter 3 evaluates various methodology developed for removal of impurities in salt mixtures. Once the salt of proper content and purity …

Mechanochemical Synthesis Of Task-Specific Conjugated Porous Networks Towards Enhanced Energy Storage, Juntian Fan

Doctoral Dissertations

Conjugated scaffolds with high electronic conductivity, high surface area, etc. are promising materials for diverse technological applications, especially in the electrochemical field. However, the current synthesis methods are still limited to the traditional solution-based method or the ionothermal method, which always require an inert atmosphere shield, large amounts of organic solvents, noble catalysts, long reaction time up to days, and high temperatures, etc. Therefore, there is a common goal of developing conjugated scaffolds through facile, green, straightforward pathways. Mechanochemistry, which is an efficient, sustainable, solvent-free methodology, could provide a unique reaction environment to synthesize this kind of functionalized materials, resulting …

Utilizing Ultra-Performance Chromatography High-Resolution Mass Spectrometry To Investigate Fatty Acid Mediated Antibiotic Tolerance, Brittni Woodall

Doctoral Dissertations

The lipid membrane is the first component necessary to sustain life. To maintain homeostasis, segregate cellular machinery, provide protection from the environment, and reproduce, an organism must establish a boundary in which the processes can occur. Throughout the last two decades, research has propelled our knowledge of lipid membranes much beyond original hypotheses. Once thought of to be static and uniform, the understanding of the lipid membrane has evolved to encompass a structure that is responsive, unique, and intricately constructed by the organism itself. By chance or by choice, organisms adapt the lipid membrane according to the environment for which …

The Novel Chlorination Of Zirconium Metal And Its Application To A Recycling Protocol For Zircaloy Cladding From Spent Nuclear Fuel Rods, Breanna K. Vestal

Doctoral Dissertations

A novel protocol has been developed for the chemical removal of zirconium alloy (Zircaloy) cladding from spent nuclear fuel rods and subsequent isolation and purification of nuclear-grade zirconium chloride derived therefrom. This protocol is based on the chemistry developed from two new scientific findings.

First, two new oxidative chlorination reactions have been discovered for zirconium metal. In both solvents, zirconium can be quantitatively chlorinated at temperatures less than 150°C, with the operative equations seen below. In sulfur monochloride, the reaction is completed in 2 – 4 hours via surface etching, exhibiting 0^th order kinetic behavior. The elemental sulfur byproduct …

Development And Study Of Small Database For The Activation Of Nitrous Oxide Towards Formation Of Iron(Iv)-Oxo Species, Tobias Barthalomew Robertson

Masters Theses

Nitrous oxide (N₂O) can undergo an oxygen atom transfer (OAT) reaction resulting in inert nitrogen gas (N₂O) while transferring an oxygen atom to a molecular complex or material. This process is of catalytic importance since this OAT reaction can be leveraged to form iron(IV)-oxo sites, which are known to be catalytic intermediates. Here, an investigation of the ligand field effects on primarily iron(II) complexes for the formation of iron(IV)-oxo sites with nitrous oxide as the oxidant is reported. An initial database of sixty-four molecular complexes with ligand environments varying in field strength and coordination geometry was …

Understanding The Polymerization Of Ethyl Cyanoacrylate In The Superglue Fuming Of Latent Prints To Optimize Print Retrieval, Leondra Shawntae Lawson

Masters Theses

The cyanoacrylate fuming method (CFM) is a widespread process used in forensics to make latent prints visible for detection, acquisition, and analysis. CFM is governed by the reaction of ethyl cyanoacrylate (ECA) with biological components in fingerprints, which serve as initiators for this anionic polymerization. CFM is not a well-controlled polymerization and there are different outcomes that may result from lower temperature, one of which fits the generalization of creating more ion-pair initiators. Another effect could be minimizing termination through suppressing side reactions. Alternatively, when paired with humidity, lower temperatures may cause surface condensation, decreasing the quality of the print. …

Anxiety-Like Behavior In C57bl/6j Mice Is Sexually Dimorphic And Altered By Buprenorphine, Ohm Sharma

Chancellor’s Honors Program Projects

No abstract provided.

Impact Of Cover Crop Species Diversity On Soil Nutrient Availability And Crop Productivity, Amanda Kramer

Masters Theses

Cover crops provide multiple environmental benefits that improve both soil and water quality; however, farmers only utilize them on approximately 5% of harvested U.S. cropland. Low adoption rates are attributed to yield impact concerns, seed and planting costs, and lack of advocacy. This study, which began in October 2019, assessed the effects of nitrogen rate and cover crop diversity on weed biomass, soil coverage, in-situ residue decomposition, soil nitrogen and phosphorus availability, and cash crop yield to better understand the costs and benefits of cover crop adoption at two locations in Tennessee (Milan and Spring Hill). Treatments were replicated 4 …

Elucidating The Importance Of Structure, Surfaces, And Interfaces In Polymer Nanoparticles And Nanocomposites, Jacob E. Fischer

Doctoral Dissertations

This dissertation details research conducted to elucidate the importance of structure, surfaces, and interfaces in both polymeric nanoparticles and polymer nanocomposites. The fundamental understanding that is garnered in these studies provides a foundation to rationally develop nanocomposites tailored for unique functionalities, performance and applications.

Soft polymeric nanoparticles, have shown to imbue non-traditional diffusive properties, the strength of which decreases with crosslinking density of the nanoparticle. The crosslinking dependent morphology of these nanoparticles is first characterized in a dilute solution of good solvent (Chapter 2). The scattering results revealed that the structure ranges from a swollen polymer in good solvent (0% …

Controlling Polymer Molecular Structure And Morphology: From Illumination Of Conjugated Polymers To Polymer Chain Depolymerization, Josh Moncada

Doctoral Dissertations

Polymers remain a prominent component of our lives, and finding methods to control their structure or morphology are needed to tune material properties. This dissertation reports methods to alter the conformation, morphology, or structure of polymeric materials. Chapter two describes the impact of exposure to white light during annealing of conjugated polymer blends on their morphology and optoelectronic performance. The observed changes in the morphology correlate strongly to the variation in photoluminescence (PL) with illumination, including that the PL varies less with illumination at higher Poly[2-methoxy-5-(2-ethylhexyloxy)-1,4-phenylenevinylene] loadings, offering foundational understanding to guide the structure and optoelectronic performance of conjugated polymer …

Intra-Skeletal Variation In Stable Isotopes Through Non-Destructive Approaches: Applications Of The Patterns Of Skeletal Remodeling To Biological Anthropology, Armando Anzellini

Doctoral Dissertations

Stable isotope analysis is a well-established method in biological anthropology used to deliver data on residence, diet, and life history. Samples for these analyses are often collected from the diaphyses of long bones with an assumption of an expected rate of turnover between five and ten years, depending on the skeletal element. However, the biological foundations of this assumption are still uncertain, especially concerning the intra-skeletal and intra-element variation of isotopic signatures that may relate to patterns of remodeling. Exploring these gaps in intra-element isotopic variation requires fine-grained work using multiple bones from multiple individuals, but such work is limited …

Light Matter Interactions: A Study Of Soft Materials Using Linear And Nonlinear Spectroscopy, Muhammad Redwan Hassan

Doctoral Dissertations

The adoption of complex fluids for various industrial applications is becoming normal. Complex fluids offer tunability, wide range solubility, and chemical and thermal stability which are the factors that conventional polar and non-polar solvents often lack. However, fundamental studies of these fluid systems are still lacking which is limiting the appropriate use of these complex fluids in many applications. The goal of this dissertation was to study and characterize complex fluids for application in electrolytes for redox flow batteries. Chapter 3 and chapter 4 feature the study of microemulsions and deep eutectic solvents (DES) by fluorescence techniques. Fluorescence studies of …

Analytical Techniques For The Analysis Of Uranium Bearing Materials, Nathaniel D. Fletcher

Doctoral Dissertations

The interest in the use of nuclear power has increased drastically in recent years. This is due to significantly increased efficiency at producing energy when compared to fossil fuels. With the increased use of nuclear power comes an increased need to for monitor for uranium bearing materials outside of regulatory control. This dissertation covers four projects aimed at improving the analysis of these materials. The first projects aims to develop a method that allows for the analysis of elements that exist in nature as anions by triple quadrupole ICP – MS. This would allow for the ability to measure more …

Transition Metal Computational Catalysis: Mechanistic Approaches And Development Of Novel Performance Metrics, Brett Anthony Smith

Doctoral Dissertations

Computational catalysis is an ever-growing field, thanks in part to the incredible progression of computational power and the efficiency offered by our current methodologies. Additionally, the accuracy of computation and the emergence of new methods that can decompose energetics and sterics into quantitative descriptors has allowed for researchers to begin to identify important structure-function relationships that predict the properties of unexplored subspaces within the overall chemical space. Catalytic descriptors have been used frequently in data driven high-throughput computational screenings. With the use of machine learning, a large portion of the chemical space an be predicted in matter of minutes or …

Tethered Axial Coordination As A Control Modality In Rhodium(Ii)-Catalyzed Carbene Transfer Reactions, Anthony Dean Abshire

Doctoral Dissertations

Rhodium(II) paddlewheels are versatile carbene transfer catalyst that are broadly applied in insertion reactions, cycloadditions, and ylide transformations. The effects of axial coordination in rhodium(II)-catalyzed carbene transfer reactions are still little understood due to compounding factors that are difficult to isolate. Traditionally, researchers study axial coordination by addition of Lewis base additives. To ensure interaction between the Lewis base and catalyst, high molar equivalents are used. This can also have the undesired effect of hampering the activity of the catalyst and suppressing the yield of the reaction. We have developed ligands with a tethered Lewis base to overcome these issues. …

Development Of Raman Spectroscopic Methods For Detection Of Molecules Indicating Life In Extraterrestrial Environments, Grace Sarabia

Doctoral Dissertations

Mineral analysis is of great importance to the understanding of the world around us and worlds beyond. Geology, chemistry, and environmental studies all benefit from characterization of the structure and properties of minerals. While various techniques have been applied towards the study of minerals, we propose that Raman spectroscopy is specifically suited for the detection and study of minerals under various conditions, including for terrestrial and space applications.

In our terrestrial studies, we explored the polymorphs of calcium carbonate within freshwater mollusk shell matrices with Raman spectroscopy. We found that aragonite was the main calcium carbonate polymorph present in the …

Synthesis And Characterization Of 2,6-Diisopropylphenoxy Tetrapyrazinoporphyrazines As Potential Molecular Qubits, Benjamin Marx

Masters Theses

This thesis reports the synthesis of metal-free and metal-containing phthalocyanine derivatives using methods typical for that class of functional dyes. A mixture of the target compounds prepared here, one paramagnetic and one diamagnetic tetrapyrazinoporphyrazine, will be tested for their potential use in spintronics – the application of spin-active species in molecular electronics. Phthalocyanines and their derivatives are well-known for their ease of preparation and tunability; they have been utilized as sensitizers for photodynamic therapy of cancer and solar cells, as well as in catalysis and chemical sensing. Tetrapyrazinoporphyrazine complexes are compared with the parent phthalocyanine as their chemistry is similar …

Driving Piezochromism And Metallicity In Van Der Waals Materials Under Compression, Nathan Harms

Doctoral Dissertations

Complex chalcogenides provide an important platform to explore the interplay between structure, charge, and spin across pressure-induced phase transitions. Where much of the previous research has been focused on tuning these materials towards the single-layer limit, we instead explore the modification of bond lengths and bond angles under compression. In the first project we revealed piezochromism in MnPS₃. We combined high pressure optical spectroscopy and first-principles calculations to analyze the dramatic color change (green → yellow → red → black) that takes place as the charge gap shifts across the visible and into the near infrared region, moving …

Functional Bottlebrush Polymer Additives For Thin Films And Coatings, Travis S. Laws

Doctoral Dissertations

Bottlebrush polymers are a class of highly branched polymers consisting of polymeric side chains that are densely grafted to a linear backbone. Their highly branched architecture results in surface enrichment across a broad range of materials. The goal of my research has been centered around the design of functional bottlebrush polymers and their use as surface active additives in blend films and coatings.

In the first chapter, we examine the segregation behavior of polystyrene bottlebrushes that are blended with linear polystyrene. We systematically vary the lengths of the bottlebrush backbone (Nb), side-chain (Nsc), and the linear matrix (Nm) in order …

How Dynamic Bond Results In The Unique Viscoelastic Behavior Of The Associating Polymers, Sirui Ge

Doctoral Dissertations

Associating polymer is a special kind of polymer possessing transient reversible bonds in addition to the conventional covalent bonds. The reversible bonds provide unique dynamics and fascinating viscoelastic properties, resulting in attractive applications for these polymers, such as self-healing and shape memory materials. Despite many years of studies, the understanding of dynamics of polymers with reversible bonds, especially on molecular level, is still in the rudimentary stage, preventing the rational design of the potential novel functional materials based on associating polymers. In this dissertation, we provide a detailed and quantitative understanding of the dynamics and viscoelastic properties of associating polymers. …