Chemistry & Biochemistry Theses and Dissertations
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Item BLANKET AND PATTERNED REPROGRAMMING OF AZOPOLYMER NANORIDGES AND APPLICATIONS TO CELLULAR BIOPHYSICS(2024) Abostate, Mona Hamdy Abdelrahman; Fourkas, John J; Chemistry; Digital Repository at the University of Maryland; University of Maryland (College Park, Md.)The objective of this project is to tailor nanotopographies previously fabricated on large areas through photomodification. The original master patterns consist of nanoridges created using conventional lithography. Using an azopolymer as a photoresponsive material, replicas of the original master were prepared using soft lithography. The entire surface of the azopolymer nanoridges underwent photomodification using a 532 nm laser with varying polarizations and durations, in a process referred to as blanket reprogramming. This process resulted in controllable widening, buckling, or removal of the nanoridges due to photoisomerization and subsequent mass migration of the azopolymer. To replicate the reprogrammed surfaces, a molding procedure was employed using an acrylatic resin. The blanket reprogramming process was monitored in situ during exposure through diffraction of another reading laser beam. Cellular behaviors can be modulated in various biological contexts through interactions with their surroundings. The relationship between nanotopography and cell behavior is crucial, and has a wide range of biological consequences and medical applications. For example, nanotopography is employed to design antibacterial surfaces, preventing the adhesion of bacteria and biofilm formation, thereby reducing the risk of infections associated with medical devices. Nanostructured surfaces can inhibit the migration of cancer cells, offering insights into potential therapeutic strategies. Nanotopography is also used in nerve-regeneration scaffolds to guide neurite outgrowth, aiding in the repair of damaged neural tissue. We investigated the response of MCF10A breast epithelial cells to buckled acrylic nanoridges replicated from a master of azopolymer ridges photomodified by laser. The nanoridges became buckled after exposure to 532 nm light polarized parallel to the ridges. The impact of buckling on the dynamics and location of actin polymerization was investigated, as well as the distribution of lengths of contiguous polymerized regions. Azopolymers, known for their biocompatibility, have been employed by various research groups to create nanotopographies on which cells are plated and imaged. We conducted experiments using a spinning-disk confocal fluorescence microscope, testing exposure wavelengths ranging from 405 nm to 640 nm. Our objective was to assess the feasibility of live-cell imaging on azopolymer nanotopographies without inducing surface alterations. Our findings revealed the capability of live-cell imaging at high frame rates across a wide range of wavelengths. This result stands in contrast to prior studies, in which the selection of fluorescent dyes compatible with these materials was limited to those excited in the red spectrum and emitting in the near-infrared. I demonstrate that different patterns can be created through patterned reprogramming of the azopolymer nanoridges. A periodic arrangement of light strips was projected perpendicular to the ridges, thereby projecting an amplitude grating onto the azopolymer nanoridges. The spacing of this pattern can be adjusted by altering the mask or adjusting the magnification of the optical system. Furthermore, varying the direction of light polarization expands the potential for creating a wider variety of designs. Different types of reprogramming motifs can be implemented by projecting patterns at angles that are not perpendicular to the substrate, by tilting the incoming laser beam away from the horizontal. Various intriguing patterns, such as repeating curves, were observed, dependent on both the angle of the incident light and the direction of light polarization relative to the direction of the ridges.Item Versatile Strategies for Multifunctional Polyolefins(2023) Fischbach, Danyon Miles; Sita, Lawrence R; Chemistry; Digital Repository at the University of Maryland; University of Maryland (College Park, Md.)Polyolefins have quickly become one of the world’s most utilized products since their discovery in the 1950s. With 350 million tons produced each year, it is clear that the use of polyolefins is not subsiding in the near future. Instead, it is imperative to develop novel materials that are more efficient than their current counterparts. As the function of a plastic is derived from its properties, creating polyolefins with designable and targetable attributes is a major priority. The Sita group has played a huge role in the development of ‘precision’ polyolefins. The techniques employed allow for the scalable synthesis of a plethora of polyolefins. To do this, input variables such as the monomer, tacticity, molar mass, and molar mass distribution are controlled in an organized manner to affect output properties such as crystallinity, elasticity, and tensile strength. The ability to create diverse plastics is necessary for the functions asked of them, however, the missing element in almost all polyolefin synthesis is chemical functionality. The inert nature of polyolefins leads to limited reactivity, therefore, reducing possible chemical reactions, such as recycling. The goal of this work is to increase the scope of functional polyolefins so that new materials with improved properties can be produced. The first step in adding functionality is choosing the proper functional group. A drawback to many polyolefin functionalities currently under study is that they have a very limited scope. Functional groups are designed and used individually, requiring different compounds for each target functionality. To overcome this obstacle, aryl functional groups were targeted in this report. Phenyl functionalities are known for undergoing a range of chemical transformations leading to a wide variety of possible materials. Described in this report, aryl-functionalized polyolefins were synthesized using three different techniques. Each method has been shown to later undergo post-synthetic transformations to yield new functional groups that can either be used as contact points for macromolecular building blocks or as chromophores for optical observation. The single use or combination of these techniques has led to polyolefin-based materials that may in fact lower the barrier for the next-generation of functional polyolefins.Item A Breath of Fresh Air: Study of Reactive Porous Metal Oxides for Chemical Warfare Agent and Simulant Defeat(2022) Leonard, Matthew; Rodriguez, Efrain E; Chemistry; Digital Repository at the University of Maryland; University of Maryland (College Park, Md.)Organophosphorus molecules are a wide class of compounds that are used commerciallyas fire retardants, plasticizers, and pesticides. Organophosphorus pesticides were developed to replace environmentally persistent pesticides, such as dichlorodiphenyltrichloroethane, more commonly known as DDT. However, organophosphorus pesticides have been proven to be carcinogenic and to affect neurodevelopment negatively. A sub-class of organophosphorus molecules are highly toxic acetylcholinesterase (AChE) inhibitors, known as nerve agents. Although the Geneva convention banned the use of chemical warfare agents (CWA), the nerve agent sarin has been used as recently as 2013 on Syrian civilians. In 2018, a Novichok nerve agent was used in the attempted assassination of a former Russian spy and his daughter. Current CWA respiratory protection employs bituminous coal (BPL), carbon which is impregnated with a mixture known as ASZM-TEDA. BPL carbon impregnated with ASZM-TEDA has a wide range of reactivity, but has not changed significantly since its inception. The next-generation filtration material will need to have a large surface area to maximize reactive sites and be robust to withstand degradation. Mesoporous and nanoparticle metal oxides are highly active materials that show promise in nerve agent defeat. Within this dissertation, the goal is to develop and study reactive metal oxides to understand the factors that are important for the decomposition of CWAs and CWA simulants. In Chapter 1, I introduce the history of CWAs, the downfalls of current filtration technology, and the candidates for the next generation filter. In Chapter 2, the methods and characterization techniques used within this work are presented and discussed. In Chapter 3, to determine the effects of cation selection on methyl paraoxon decomposition, Ce4+ was isovalently doped into anatase type TiO2. Through UV/Vis spectroscopy, the degradation of methyl paraoxon was tracked and fit to pseudo-first-order kinetics, then normalized to the synthesized material’s surface area. The rate constant, normalized to the material’s surface area (kSA), reveals CeO2 is 3 to 4.6 times larger than that of TiO2 and the Ce-doped titanias. The Ce-doped titanias showed little to no change in methyl paraoxon decomposition compared to TiO2. The lack of change within the Ce-dopant titania revealed that crystal structure is a larger driving factor for methyl paraoxon decomposition than the cation identity (i.e. Ce4+ and Ti4+). Chapter 4 presents a study on the gas surface interaction between sarin and dry CuO nanoparticles (NP) through infrared (IR) spectroscopy. Sarin adsorbs to CuO through the P=O bond, and proceeds to decompose on the surface. Distinct red shifts in the delta(P-CH3) and rho(P-CH3) modes indicate the cleavage of the P-F bond, producing isopropyl methyl phosphonic acid (IMPA). Concurrently, a mode attributed to (O-P-O) begins to grow in, demonstrating that sarin forms a bridging species on the surface. Sarin continues to degrade on the dry CuO surface once the sarin feed is removed. Upon heating above 423 K, all modes associated with IMPA simultaneously decrease, indicating that IMPA desorbs from the surface. These observations were further corroborated through computational methods. Finally, in Chapter 5, I seek to enhance the reactivity of CuO by placing the cation Cu2+ within a Jahn-Teller active geometry. Mesoporous NiO and Cu-doped NiO were synthesized and exposed to diisopropyl fluorophosphate (DFP) in different environments and studied through diffuse reflectance IR Fourier transform spectroscopy (DRIFTS). Ordered mesoporous Cu-doped NiO was successfully synthesized through a hard templating method. Through X-ray diffraction (XRD), Cu2+ was incorporated into the NiO rock-salt lattice without phase separation for < 20%. The mesoporous metal oxides (MMO) maintained high surface areas (67.89-94.38 m2/g), with a main pore size of ~2.4 nm. Shifts in the Raman spectra indicate the dopant, Cu2+, reduces nickel vacancies resulting in a decrease in Ni3+ defect states. Upon DFP exposure, NiO was highly oxidative producing CO, CO2, carbonyls, and carbonates due to the active oxygen species formed by the Ni2+ vacancies. The mesoporous Cu-doped NiO samples were less reactive to DFP oxidation, due to the Cu2+ occupying the nickel vacancies, resulting in a reduction of active oxygen species.Item Correlating Chemical Activity and Structure in Mesoporous Metal Oxides for Nerve Agent Decomposition(2022) Li, Tianyu; Rodriguez,, Efrain E; Chemistry; Digital Repository at the University of Maryland; University of Maryland (College Park, Md.)GB (sarin), a chemical ware fare agent (CWA), due to its extreme fatal toxicity and its involvement in a few terrorist and battle attacks, has become an increasing concern for the national public and military safety. Developing filter materials that can strongly adsorb and effectively decompose GB thus attracts growing research interest. The great diversity of metaloxides and their abundant surface chemistry suggest an opportunity to realize their potential as filter materials. This dissertation outlines our effort to gain a fundamental understanding of the interaction between GB (also its simulant DMMP) and metal oxides. We aim to determine the structural factors that influence the performance of metal oxides on adsorbing and decomposing GB and to ultimately predict the behavior of a given metal oxide. We used two mesoporous metal oxides (TiO2 and CeO2) as two model systems and performed systematic studies on their interaction with GB and its simulant DMMP. We utilized multiple techniques to fully characterize the crystal and surface characters of the mesoporous metal oxides. The interactions between GB/DMMP and metal oxides were explored by different spectroscopic techniques (majorly infrared techniques). Combining the experimental observations and DFT calculations on two different metal oxides, we propose several governing parameters of the metal oxides to impact their reactivity for decomposing GB. We also derive a simplified and qualitative model to predict the reaction behavior and activity of metal oxides when interacting with GB.Item Tuning Crystallographic and Magnetic Symmetry in Lithium Transition Metal Phosphates and Thiophosphates(2022) Diethrich, Timothy; Rodriguez, Efrain E.; Chemistry; Digital Repository at the University of Maryland; University of Maryland (College Park, Md.)Ferroic ordering needs no introduction; ferromagnetic, ferroelectric, and ferroelastic materials have had a significant impact on the materials science community for many years. While these three main types of ferroic ordering are well known, there is a fourth and final, lesser known ferroic ordering known as ferrotoroidicity. A ferrotoroidic material undergoes a spontaneous, physical alignment of toroidal moments under a critical temperature. This study is focused on broadening our current understanding of ferrotoroidics by studying two families of materials: LiMPO4, and Li2MP2S6, where M = Fe, Mn, and Co. While these two materials initially appear to be similar in some regards, many differences can be observed as a deeper dive is taken into their crystallography and magnetic structures. For a toroidal moment to exist, a specific orientation of magnetic moments is required, because of this, only certain magnetic point groups are allowed. For example, LiFePO4 has an “allowed” magnetic point group of m’mm, while it’s delithiated counterpart FePO4 has a “forbidden” magnetic point group of 222. This work has found that by using a new selective oxidation technique, lithium concentration can be controlled in the Li1−xFexMn1−xPO4 solid solution series. Neutron powder diffraction and representational analysis were used to find the magnetic point groups of each member of this series. In the end, each structure was solved and the largest transition temperature to date was reported for a potential ferrotoroidic material. The magnetic exchange interactions can be used to describe the magnetic phase changes that occuracross the Li1−xFexMn1−xPO4 series. The second group of materials in this study is the lithium transition metal thiophosphates of the formula Li2MP2S6, where M = Fe, Co. The structure of Li2FeP2S6 has been previously studied but no magnetic properties of this material have been reported. In addition, neither the structural nor magnetic properties have been reported for the cobalt analog. Single crystalXRD was used to confirm the previously reported crystal structure of Li2FeP2S6 and to find the novel crystal structure of Li2CoP2S6; both crystallize in a trigonal P31m space group. While isostructural in some regard, there are some crucial differences between these materials. The site occupancies are different, resulting in non-trivial charge balances and a unique thiophosphate distortion. Originally, these materials were chosen because their nuclear structure was predicted to host long-range antiferromagnetic order and potentially ferrotoroidic order. Contrary to expectations, magnetic susceptibility and field dependent measurements demonstrated paramagnetic behavior for both the iron and the cobalt sample down to 2 K. This result was further confirmed by a lack of magnetic reflections in the time-of-flight neutron powder diffraction data. While the phosphates and the thiophosphates demonstrated very different structural andmagnetic results, they both remain relevant materials for not only ferrotoroidics, but also magnetoelectrics, spintronics, quantum materials, and much more.Item DESIGN AND SYNTHESIS OF POLYOLEFIN MATERIALS FOR NANOSTRUCTURED SELF-ASSEMBLY: BUILDING BLOCKS, COPOLYMERS, AND POLYMER CONJUGATES(2022) Wentz, Charlotte Maria; Sita, Lawrence R; Chemistry; Digital Repository at the University of Maryland; University of Maryland (College Park, Md.)Polyolefin based materials are essential to today’s society in both simplistic commodity plastics to complex nanostructured materials and optoelectronic devices. In order to better understand these materials and make new impactful innovations, there is a barrier of fabrication, scalability, versatility, and programmability. The answer to the world’s plastic waste problem lies not in removing our use of polymers but relies in better understanding their properties, utilizing them as building blocks in advanced materials, and creating a long-lasting advanced material. Towards the goal of overcoming limitations in fabrication and scalability the work herein presents on utilizing a toolbox of living polymerization techniques such as living chain transfer polymerization (LCCTP) where new functionalities, stereochemical microstructures, optical properties, and physical properties of the polyolefin can be designed and systematically controlled. The polyolefins made through these techniques are scalable and versatile with end-group functionalization creating a seemingly endless choice of polymer building blocks and polymer materials. In line with creating new technologies that are programable the polyolefin building blocks made herein are utilized in multiple conjugates to create and understand methods and mechanisms of solid-state nanostructured self-assembly and access rare nonclassical phases that are highly desirable for their properties and uses in a plethora of applications. The conjugates investigated involve either a sugar-based head group covalently bond to a polymer tail to access rare and misunderstood Frank Kasper phase order-order transitions, or a perylene chromophore core covalently bond on both sides of the core in a linear fashion to polymer domains to create highly florescent or optically active materials that are useful in organic technologies such as solar cells, light emitting diodes, or nanotechnology. These perylene based conjugates can self-assemble into unique columnar phases and single gyroid phase. These results with conjugates provide methods for reliable and programmable access to rich phase behavior through the design of the polyolefin domains.Item UNDERSTANDING AND TAILORING THE REACTIVE CHARACTERISTICS OF NANOENERGETIC COMPOSITES VIA STRUCTURAL AND CHEMICAL MODIFICATIONS(2022) XU, FEIYU; Zachariah, Michael R; Chemistry; Digital Repository at the University of Maryland; University of Maryland (College Park, Md.)Nanoenergetic composites are nanostructured fuel and oxidizer mixtures that store a large amount of chemical energy and release it, typically in the form of heat, upon ignition. They are promising candidates for energy intensive applications such as propellants and pyrotechnics, due to their high energy density. The overall reaction kinetics of the heterogenous nanoenergetic system is controlled by mass transfer. The use of nanoparticles is to reduce diffusion length and thus increase energy release rate. The objective of the proposed research is to understand how intrinsic properties of fuel and oxidizer affect the reaction of nanoenergetic composites, and to develop novel, multifunctional nanoenergetic materials with tunable ignition threshold and energy release rate. Experiments were conducted utilizing primarily a time resolved Temperature-Jump time-of-flight mass spectrometer (T-Jump TOFMS) to analyze gas phase reaction intermediatespecies and products at a high heating rate (~105 K/s), along with a combustion cell for reactivity evaluation. New fuels including hydrogenated amorphous silicon, and oxidizers including oxygen deficient Co3O4-x and ferroelectric Bi2WO6 were investigated. The role of surface chemistry in the energetic characteristics of silicon nanoparticles was investigated, leading to the uncovering of a new reaction mechanism. Modulating the initiation temperature of aluminothermic reaction via defect engineered metal oxide was demonstrated. A study of piezoelectric oxidizers reveals the superior reactivity of a complex metal oxide. Moreover, tuning the energy release rate of I2O5 based biocidal nanoenergetic composites via a ternary system was studied. These results indicate that by modifying the chemistry or structure of fuels and oxidizers, the combustion characteristics of nanoenergetic composites can be tailored.Item Controlled synthesis of carbon nanotubes: from mechanisms to applications(2021) Cheng, Xiyuan; Wang, YuHuang; Chemistry; Digital Repository at the University of Maryland; University of Maryland (College Park, Md.)Carbon nanotubes exhibit exceptional properties in many different aspects. However, harnessing those properties in real applications is challenging mainly due to the structural heterogeneity, high impurity contents, and architectural defects that originate in the synthesis. In this dissertation, I aim to understand the nucleation and growth mechanisms of both the catalyst and carbon nanotubes in chemical vapor deposition processes and establish a relationship between the structure and properties of the synthesized carbon nanotubes. I will also discuss applications enabled by some of the nanotubes that I synthesized. First, I will discuss the structure control of vertically aligned carbon nanotube arrays to show that the nanotube diameter, density, and growth pattern are correlated with the migration and aggregation behavior of the catalyst across the substrate. Then, I will present experimental studies revealing new insights into the nucleation of the catalyst particles in the gas phase. Based on the new fundamental understanding of the nucleation and growth of both metal catalysts and carbon nanotubes, we have developed a new method to produce semi-aligned high-quality nanotube films, with a tunable number of walls, continuously at an ambient atmosphere with a record high production rate of 1400 m h-1. With this technique, we have reduced the catalyst impurity content and increased the production rate of the carbon nanotubes while simultaneously maintaining a high Raman G/D ratio of >70. The carbon-catalyst interaction during carbon nanotube growth is also studied by planting and etching the carbon nanotubes on a metal melt. We found that the carbon was readily removed by H2 from the growing front of the carbon nanotubes. Finally, we exploited the applications of these synthesized carbon nanotubes in achieving high power thin-film thermoacoustics, high power battery, and dynamic mechanical interface.Item RAPID HEATING AND CHEMICAL SPECIATION CHARACTERIZATION FOR COMBUSTION PERFORMANCE ANALYSIS OF METALLIZED, NANOSCALE THERMITES AND PVDF BOUND SOLID PROPELLANT COMPOSITIONS(2021) Rehwoldt, Miles Christian; Rodriguez, Efrain; Zachariah, Michael R; Chemical Physics; Digital Repository at the University of Maryland; University of Maryland (College Park, Md.)Energetic materials research focuses on performance analysis of cost-effective solid materials which safely, precisely, and efficiently transitions stored chemical potential energy to kinetic energy at a rate throttled through chemical or architectural means. Heterogenous compositions of metal fuels and solid materials with a high storage capacity of condensed oxidizing elements, such as oxygen and/or fluorine, is a class of energetic material of interest given its relatively high reaction enthalpies and adiabatic flame temperatures. In the wake of the earliest instances of metal fuels being used as a high energy additive during World War II, characterizing the reaction mechanisms of micron and nanoparticle aluminum fuels with various oxidizer sources has been a primary subject of research within the solid energetics community. The advent of nanotechnologies within the past two decades brought with it the promise of a prospective revolution within the energetics community to expand the utility and characterization of metallized energetic materials in solid propellants and pyrotechnics. Significant prior research has mapped reactivity advantages, as well as the many short comings of aluminum-based nanoscale energetic formulations. Examples of short comings include difficulties of materials processing, relative increase in native oxide shell thickness, and particle aggregate sintering before primary reaction. The less than flaw-less promises of nanoscale aluminum fuels have thus become the impetus for the development of novel architectural solutions and material formulations to eliminate drawbacks of nanomaterial energetics while maintaining and improving the benefits. This dissertation focuses on further understanding reaction mechanisms and overall combustion behavior of nanoscale solid energetic composite materials and their potential future applications. My research branches out from the heavy research involved in binary, aluminum centric systems by developing generalized intuition of reaction and combustion behaviors through modeling efforts and coupling time-of-flight mass spectrometry to rapid heating techniques and novel modes of product sampling. The studies emphasize reaction mechanisms and microwave sensitivities of under-utilized compositions using metal fuels such as titanium, generalize the understanding of the interaction of fluoropolymer binders with metal fuels and oxidizer particles, and characterize how multi-scale architectural structure-function relations of materials effect ignition properties and energy release rates.Item INVESTIGATION OF SOLID-STATE SELF-ASSEMBLY OF ONE- AND MULTI- COMPONENT SUGAR POLYOLEFIN CONJUGATES AND MECHANISMS FOR FRANK-KASPER MESOPHASE TRANSITIONS(2020) Lachmayr, Katchen K.; Sita., Lawrence R.; Chemistry; Digital Repository at the University of Maryland; University of Maryland (College Park, Md.)The self-assembly of molecules provides the basis of life and has become ubiquitous for the development of nanostructured materials. Nanostructured materials have long reaching impacts for the furtherment of science, as the next revolution in technology requires the ability to fabricate nanostructured materials with sub-10-nm feature sizes. To this end, the work herein, presents on methods and mechanisms of solid-state nanostructured mesophase formation, through the isolation of complex phases and understanding of thermotropic order-order transition pathways. This extends to both solid-state classical and nonclassical phases, including the highly desirable, bicontinuous double gyroid, and uncommon Frank-Kasper (FK) phases resulting from self-assembly of the sugar polyolefin conjugates. The sugar polyolefin conjugates are produced through practical and scalable bulk quantities that demonstrate the dynamic self-assembly on the nanometer-scale, which results from rapid thermally induced order-order phase transitions. Production of different derivatives of the sugar polyolefin conjugates and blended systems, can significantly lower the barriers to access uncommon and complex mesophases through the elucidation of transition mechanisms for FK mesophases. To better understand the basic principles and mechanisms of formation that result in the complex packing motifs of FK phases, single- and multi-component systems were devised. These mechanisms avoid the need for large structural reconfigurations of spheres, and dynamic mass transfer, as previous solid-state thermotropic mechanisms have required. Additionally, a general strategy for design, modulation, and utilization of functionally competent soft matter solid-state FK phases is provided from developments with a two-component system utilizing a small molecule additive. These results demonstrate the sugar polyolefin conjugates as an exceptional class of self-assembling amphiphilic materials, which provide methods for reliably producing Frank-Kasper phases from single- and multi-component systems, in addition to remarkable classical phase behavior.