Browsing by Author "Krummel, Amber, committee member"
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Item Open Access Carbon-based electrodes for environmental health applications(Colorado State University. Libraries, 2019) Berg, Kathleen E., author; Henry, Charles, advisor; Ackerson, Christopher, committee member; Krummel, Amber, committee member; Lear, Kevin, committee memberEnvironmental risk factors of air pollution and unsafe water are leading contributors to human morbidity and mortality, causing millions of deaths and diseases annually worldwide. Fine particulate matter (PM2.5) air pollution is linked to millions of deaths worldwide annually along with millions of cardiovascular and respiratory diseases. Unsafe water can contain heavy metals, including manganese (Mn), which high doses are linked to a variety of neurological and developmental diseases in humans. Analytical methods for testing for environmental risk factors such as fine PM and Mn still need improving. The primary focus of the dissertation here was to use carbon-based electrodes for improvements on environmental risk factor applications. An electrochemical assay was developed and used to measure Mn(II) in aqueous samples with stencil printed carbon paste electrodes. Stencil printed carbon paste electrodes are a mixture of graphite and organic liquid; they are easy to fabricate, portable, and disposable. These electrodes also do not require modification before detecting Mn in aqueous samples, but 1,4-benzoquinone was added to the background electrolyte for improved precision. Mn was then detected in complex matrices of tea and yerba mate samples. The focus is shifted from Mn detection to air pollution applications. A commercially available stencil printed carbon electrode was used for the dithiothreitol (DTT) assay, which is an assay commonly used to estimate the health effects of air pollution samples. The presented, improved DTT assay reduces reagents and increases sample throughput, both of which will help enable larger scale air pollution studies to be executed in the future. The DTT assay was then further improved with a semi-automated system that further increases the sample throughput and reduces reagent volumes while reducing the required manual labor associated with liquid handling. The semi-automated system uses a custom carbon composite thermoplastic electrode (TPE). Changes were observed in the TPE response over time and are studied further. The dissertation shifts focus to a more fundamental electrode characterization of high performing TPEs that were previously used because TPEs have a vast array of potential analytical applications, including environmental risk factor applications. Atomic force microscopy (AFM) and scanning electrochemical microscopy (SECM) were used for a thorough investigation of the local surface topography and electrochemistry of TPEs, which is needed to assess the cause of the excellent electrochemical properties. The evidence suggests that the TPEs behave as microelectrodes, which gives rise to their high electrochemical activity. The amount of potential applications from TPEs is then increased by modifying the surface. TPEs, while being high performing and easy to pattern, have previously been limited by their solvent compatibility to aqueous solvents. Presented here is an alternative fabrication, which makes TPEs polar organic solvent compatible, that greatly increases the number of applications. The TPEs were then modified and functionalized in acetonitrile as a proof of concept that TPEs can be used in non-aqueous solvents and can have modified surfaces, which can lead to more applications. The research here uses different carbon electrodes to advance method development of environmental risk factor quantification. Advances to Mn(II) detection and fine PM health impacts were made. Fundamental understandings were developed of carbon composite TPEs and then modified to show a large potential number of future applications for continual improvement of electrochemical sensing.Item Open Access Contributions of gas-phase plasma chemistry to surface modifications and gas-surface interactions: investigations of fluorocarbon rf plasmas(Colorado State University. Libraries, 2012) Cuddy, Michael F., author; Fisher, Ellen R., advisor; Levinger, Nancy E., committee member; Rickey, Dawn, committee member; Krummel, Amber, committee member; Yalin, Azer P., committee memberThe fundamental aspects of inductively coupled fluorocarbon (FC) plasma chemistry were examined, with special emphasis on the contributions of gas-phase species to surface modifications. Characterization of the gas-phase constituents of single-source CF4-, C2F6-, C3F8-, and C3F6-based plasmas was performed using spectroscopic and mass spectrometric techniques. The effects of varying plasma parameters, including applied rf power (P) and system pressure (p) were examined. Optical emission spectroscopy (OES) and laser-induced fluorescence (LIF) spectroscopy were employed to monitor the behavior of excited and ground CFx (x = 1,2) radicals, respectively. Mass spectrometric techniques, including ion energy analyses, elucidated behaviors of nascent ions in the FC plasmas. These gas-phase data were correlated with the net effect of substrate processing for Si and ZrO2 surfaces. Surface-specific analyses were performed for post-processed substrates via x-ray photoelectron spectroscopy (XPS) and contact angle goniometry. Generally, precursors with lower F/C ratios tended to deposit robust FC films of high surface energy. Precursors of higher F/C ratio, such as CF4, were associated with etching or removal of material from surfaces. Nonetheless, a net balance between deposition of FC moieties and etching of material exists for each plasma system. The imaging of radicals interacting with surfaces (IRIS) technique provided insight into the phenomena occurring at the interface of the plasma gas-phase and substrate of interest. IRIS results demonstrate that CFx radicals scatter copiously, with surface scatter coefficients, S, generally greater than unity under most experimental conditions. Such considerable S values imply surface-mediated production of the CFx radicals at FC-passivated sites. It is inferred that the primary route to surface production of CFx arises from energetic ion bombardment and ablation of surface FC films. Other factors which may influence the observed CFx scatter coefficient include the surface with which the radical interacts, the vibrational temperature (ΘV) of the radical in its gas phase, and radical interactions in the gas phase. The analyses of ΘV in particular were extended to diatomic radicals from other plasma sources, including nitric oxide and fluorosilane systems, to gauge the contributions of vibrational energy to surface reactivity. In general, a monotonic increase in S is observed for CF, NO, and SiF radicals with increasing ΘV. Preliminary results for mixed plasma precursor systems (i.e. FC/H2, FC/O2) indicate that the choice of feed gas additives has a profound effect on surface modification. Hydrogen additions tend to promote FC film deposition through scavenging of fluorine atoms, whereas oxygen consumes polymerizing species, thus favoring etching regimes. Time-resolved optical emission spectroscopy (TR-OES) studies of gas-phase species elucidate the mechanisms by which these processes occur. Ultimately, the work presented herein expands the fundamental chemical and physical understanding of fluorocarbon plasma systems.Item Open Access Developing and investigating copper and iron chalcogenide nanoparticle syntheses to elucidate the underlying processes of formation(Colorado State University. Libraries, 2021) Moloney, Lily June, author; Prieto, Amy L., advisor; Sambur, Justin, committee member; Krummel, Amber, committee member; Buchanan, Kristen, committee memberNanoparticle technology is rapidly growing field due to the unique, tunable properties of nanoparticles (NPs) as compared to their bulk counterparts, enabling a wide range of new applications. The key step, however, to applying NP systems to new areas is developing high quality syntheses. Specifically, solution-based methods for synthesizing NPs offer many synthetic handles for tuning structure/property relationships by controlling composition, size, morphology and capping agents. To effectively design syntheses to control the resulting properties, in depth investigation of the underlying fundamental processes are required. Elucidation of these processes would allow trends to be illuminated and a toolkit of synthesis methods could be built. However, a myriad of interactions (organic, inorganic, solid-state) occur during these reactions, and often these interactions are intertwined with each other. Therefore, careful examination of nanoparticle synthesis for various systems are necessary to advance the NP field. In Chapter 1, we review literature reports that exemplify the careful examination of underlying mechanisms and pathways required for developing synthesis methods that allow for control over composition, size, morphology. This chapter is split into two major sections; 1) balancing precursor reactivities and elucidating mechanisms and 2) understanding reaction pathways. The first section is split into anion and cation speciation/reactivity. The anion section focuses on the development of chalcogenide reactivity trends and how these trends have led to advanced nanoparticle control. The cation section considers the use of metal-amide complexes to increase and balance reactivities of cations to produce small, phase pure NPs. In depth mechanism studies of these metal-amide reactions in model unary and binary system led to the utilization of this reagent in more complex ternary systems. The second section focuses on investigation of reaction pathways, discussing how exploration of the reaction phase space as well as determination of intermediates is important for achieving a full picture. We end with a brief discussion on the importance of thorough characterization for describing these reaction mechanisms and pathways accurately. The importance of investigating the reaction pathway was inspiration for the research described in Chapter 2. Few solution-based techniques to synthesize Cu3Si, a material with applications in electronics, batteries, and photovoltaics, exist. This could stem from the limited number of Si precursors viable in solution-based techniques. This led us to explore the reaction between Mg2Si and CuCl2 in oleylamine, as a solution-based metathesis route to form Cu3Si particles. The reaction pathway and the role of the solvent were characterized and elucidated. It was found that the reaction proceeds through a two-step pathway, where a Si matrix, Cu particles, and MgCl2 initially form. Then, the Cu particles diffuse into the Si matrix to form Cu3Si particles encased in a Si matrix (Cu3Si@Si matrix). Additionally, various solvents are tested to understand the importance of the solvent for the reaction to proceed successfully. The coordinating ability of the solvent was important, where an overly non-coordinating or coordinating solvent limited the production of Cu3Si@Si matrix particles. Oleylamine was found to be a “goldy-locks” solvent as the coordination supported both steps of the reaction. In Chapter 3, the mechanistic metal-silylamide studies described in Chapter 1 offered inspiration. Specifically, Rebecca C. Miller in our group was recently able to synthesize Fe2GeS4 by utilizing lithium bis(trimethylsilyl)amide (LiHMDS). The increased understanding of the Fe-Ge-S phase space and the role of the LiHMDS gained from this previous study led to the research presented in Chapter 3. In this chapter, we report the first nanoparticle synthesis of Fe2GeSe4 and Fe2GeS4-xSex (x = 0.8 and 1) via a LiHMDS-assisted hot-injection method. This system allowed the role of LiHMDS in balancing not only the cationic but also anionic species to be investigated. This was done by exploring the synthesis parameters, the pre-injection chalcogen speciation, and the reaction pathways. Finally, in Chapter 4, synthesis methods attempted toward Cu2SiSe3 formation are described and a future direction for this project is proposed. Copper-based chalcogenides have gained much attention due to their exemplary intrinsic and structural properties. Cu2SiSe3 has been theorized to be a potential photovoltaic material, yet a NP synthesis of this material has not been realized. Exploration of hot injection, metathesis, and solvothermal solution phase methods are reported. However, all efforts resulted in binary Cu/Se phases over the formation of the desired ternary. A future direction for this project could be instead focusing on investigating reactivity trends of the group IV elements, Si, Ge, and Sn, using an amide-assisted synthesis of the Cu2IVSe3 materials.Item Open Access Development and implementation of near-infrared ultrafast laser sources generated by nonlinear fiber propagation(Colorado State University. Libraries, 2015) Domingue, Scott R., author; Bartels, Randy, advisor; Krummel, Amber, committee member; Krapf, Diego, committee member; Marconi, Mario, committee memberThis dissertation is broken up into three parts: (I) generating high-quality ultrafast pulses around 1060 nm, (II) using the pulses from part (I) to generate pulses around 1300 nm, and (III) analyzing newly developed experimental theories and methods utilizing these pulses for linear and nonlinear microscopy. The majority of the work in this dissertation is choreographing the dance between nonlinear spectral broadening in optical fiber and the associated complexity in accumulated spectral phase. We have developed and employed several systems which manage to accomplish this task quite elegantly due to our technological contributions, producing high-quality pulses with high oscillator-type pulse energies both at 1060 and 1250 nm. In addition to developing some theory and techniques extending current types of nonlinear microscopy, we have as a capstone an experimental microscope cascading several of our primary source and application technologies to conduct an entirely new form of spectroscopic absorption imaging.Item Open Access Development of N-aryl phenoxazines as strongly reducing organic photoredox catalysts(Colorado State University. Libraries, 2020) McCarthy, Blaine Gould, author; Miyake, Garret, advisor; Bandar, Jeffrey, committee member; Krummel, Amber, committee member; James, Susan, committee memberN-aryl phenoxazines were identified as a new family of organic photoredox catalysts capable of effecting single electron transfer reductions from the photoexcited state. A number of phenoxazines bearing different N-aryl and core substituents were synthesized, characterized, and employed as catalysts. Spectroscopic and electrochemical characterization of these phenoxazines was used to establish structure-property relationships for the design of visible-light absorbing, strongly reducing organic photoredox catalysts. The application of phenoxazines as catalysts for organocatalyzed atom transfer radical polymerization (O-ATRP), a light-driven method for the synthesis of well-defined polymers, revealed the importance of several catalyst properties for achieving control over the polymerization. Investigation of the properties and catalytic performance of N-aryl phenoxazines has provided fundamental insight into the reactivity of organic excited state reductants and photophysical properties of organic molecules. The catalysts developed through this work provide sustainable alternatives to more commonly used precious-metal containing photoredox catalysts.Item Open Access Exploring phase selectivity and morphological control in Cu-Sb-Se nanoparticle synthesis(Colorado State University. Libraries, 2023) Kale, Amanda R., author; Prieto, Amy L., advisor; Sambur, Justin, committee member; Krummel, Amber, committee member; Ma, Kaka, committee memberNanoparticles are used in a variety of applications, such as optoelectronics, medicine, and energy generation and storage. Different applications necessitate different nanoparticle compositions and morphologies. Thus, developing fine synthetic control over composition, phase, and morphology is of interest to the field. Solution-phase nanoparticle synthesis allows control over particle shape and size, though phase purity is often an issue in ternary syntheses. Often precursor reactivity must be balanced to avoid binary sinks; however, in the Cu-Sb-Se system, the ternaries compete with one another. In this dissertation we explore the knobs of a hot-injection synthesis in oleylamine that can be tuned to favor different Cu-Sb-Se ternary phases and control particle morphologies. In Chapter I we begin with a discussion of the term precursor reactivity and how we define it here. We also address the common frameworks used to explain reactivity, and the specific challenges of balancing reactivity in multinary chalcogenide syntheses. We also discuss how these challenges manifest in the Cu-Sb-Se system, and why the structures and phase space of this material are interesting to study. In Chapter II we discuss a guide for fitting X-ray diffraction data for complex nanomaterial systems, outlining important considerations when working on the nanoscale as well as our sequential approach to refinements and recommended best practices. We also discuss a case study on the refinements of anisotropic, multiphase systems, which we use for the following chapter. The main synthetic work follows in the next two chapters, focusing first in Chapter III on the decomposition of metastable Cu3SbSe3 to thermodynamic CuSbSe2. We investigate how this can be manipulated through the addition of an amide base. In Chapter IV, we explore tuning morphology and specifically nanosheet branching in CuSbSe2, in which we show that we can induce twinning in CuSbSe2 and initial characterization suggests that this occurs in a different manner than in the very similar sulfide system. Finally, in Chapter V we reflect on the considerations and next steps for this work, including preliminary results on the use of soft base ligands to complex Cu, as well as on promising directions of field of nanoparticle synthesis as a whole.Item Open Access Exploring the impacts of nanoconfinement using nuclear magnetic resonance (NMR) spectroscopy(Colorado State University. Libraries, 2022) Miller, Samantha L., author; Levinger, Nancy, advisor; Krummel, Amber, committee member; Crans, Debbie, committee member; Graham, James, committee memberThe chemical reactivity of molecules is typically studied under bulk aqueous conditions in the research laboratory. Although this standard may be appropriate for processes destined to be scaled up for industrial purposes, it ignores the fact that a great deal of the chemistry underlying physiological reactions occur in confined environments, like cellular organelles, protein pockets, or porous interfaces. The dissertation begins by describing the methodology for synthesizing size tunable reverse micelles, or surfactant enveloped nanodroplets. After physical perturbation, the ternary mixture of polar (usually aqueous), nonpolar, and amphiphilic surfactant self-assemble. Two small molecules, glucose and urea, were studied in these nano environments using a combination of analytical techniques including dynamic light scattering, differential scanning calorimetry, and molecular dynamics simulations that complemented the myriad nuclear magnetic resonance (NMR) spectroscopy studies. Quantification of single hydrogen exchange between glucose and water using exchange spectroscopy NMR in conjunction with custom MatLab code revealed that confinement of glucose and water within 8-10 nanometer reverse micelles slows the process of exchange by introducing a quantifiable energy barrier of ~75 kJ/mol. Deuterium NMR spectroscopy provided evidence for hydrogen tunneling below 283 K, a surprisingly high temperature for this phenomenon. The same robust methods of kinetic and structural analysis were used to characterize urea in water reverse micelles. Results showed that in addition to its well-known ability to denature proteins, urea can disrupt amphiphilic membranes and cause a ten-fold increase in the membrane surface area at low temperatures ~273 K as a result of this destabilization. Finally, the use of fluorine NMR spectroscopy demonstrated that the reverse micelle nanodroplet environments could achieve higher ionic strengths (~9.0 M) with simple divalent salts than possible in standard bulk solutions (~5.0 M). Together, these results presented compelling evidence that utilization of reverse micelle nanodroplets could provide alternative environments to facilitate previously inaccessible, novel conditions.Item Open Access Investigation into catalyst interactions in a dye-sensitized photoelectrochemical cell for water oxidation catalysis(Colorado State University. Libraries, 2022) Jewell, Carly Francis, author; Finke, Richard, advisor; Shores, Matthew, committee member; Krummel, Amber, committee member; Sampath, Walajabad, committee memberSolar energy has the potential to contribute significantly to solving the global energy crisis. However, solar energy is both diffuse and intermittent, meaning the capture and storage of this energy is critical. One method of storing this energy is the generation of storable hydrogen fuel via photoelectrochemical water-splitting, that is, storing energy in chemical bonds, specifically the H-H bond. However, the efficiency of the water-splitting process is limited by the water oxidation reaction, a four-electron process occurring at the anode. As such, water splitting devices, and more specifically water-oxidation devices, have been the focus of research for several decades. One such strategy, employed herein, uses molecular light-harvesting dyes and associated materials to capture and convert energy from the sun into chemical bonds. The work presented in this dissertation examines one such water-oxidation dye-sensitized photoelectrochemical cell (DS-PEC) with the goal of better understanding how charge-carrier interactions in the system are impacted by varying the system's catalyst, architecture and device composition. Throughout this dissertation a photoanode consisting of nanostructured SnO2 coated in perylene diimide dye N,N'-bis(phosphonomethyl)-3,4,9,10-perylenediimide plus photoelectrochemically deposited cobalt oxide (CoOx) is examined. Chapter I provides an in-depth overview to water-oxidation catalysis with a focus on the state of DS-PECs in the literature. Chapter II looks to understand the impact of an alumina overlayer on this DS-PEC system, with the specific goal of better understanding why the addition of the CoOx catalyst decreases photocurrent and increases recombination, a so-called "anti-catalyst" effect. The studies presented in Chapter II demonstrate that the presence of an ultrathin alumina overlayer by atomic layer deposition (ALD) increases photocurrents and decreases recombination in the device, although the addition of CoOx catalyst still decreases photocurrent. Chapter III examines the same system with the continued goal of identifying the source of increased recombination and decreased photocurrents with CoOx catalyst addition. Through a series of controls, residual carbon attributable to organic stabilizer used in the nanostructured SnO2 synthesis is discovered to be the culprit of this "anti-catalysis" effect. Anodes made using more carbon-free SnO2 deposited by ALD, rather than the nanostructured SnO2 with residual carbon, show an increase in photocurrents with CoOx addition. Subsequently, Chapter IV looks at two methods of overcoming and outcompeting the recombination attributable to residual carbon in the device. The effect of the residual carbon is shown to be mitigated through both the use of a more active iridium-based catalyst, amorphous Li-IrOx, rather than CoOx, and then through the use of a more carbon-free ALD-SnO2, without organic stabilizer, rather than nanostructured SnO2. The planar ALD-SnO2 is compared to the nanostructured SnO2 both on a per dye basis and on an electrochemically active surface area basis. The results presented in this dissertation offer fundamental insights into achieving both a better understanding, and an improved performance, of DS-PECs for water-oxidation catalysis that is a critical component of solar energy capture and storage.Item Open Access Kinetic control of solid state metathesis reactions(Colorado State University. Libraries, 2017) Martinolich, Andrew J., author; Neilson, James, advisor; Prieto, Amy, committee member; Krummel, Amber, committee member; Shores, Matthew, committee member; de la Venta, Jose, committee memberThe control of solid state reaction pathways will enable the design and discovery of new functional inorganic materials. A range of synthetic approaches have been used to shift solid state chemistry away from thermodynamic control, in which the most energetically favorable product forms, towards a regime of kinetic control, so that metastable materials can be controllably produced. This work focuses on the use of solid state metathesis in the preparation of transition metal sulfides and selenides, and understanding the reaction pathways through which these reactions proceed. Through a range of structural probes combined with thermal analysis techniques, the reaction pathways are identified. The challenge of changing the pathway is then tackled, aiming to maximize mixing in the reaction mixtures to overcome the classical diffusion limitations in solids at low temperatures. Changing the reaction pathway promotes the formation of metastable intermediates and products, highlighted by the formation of the superconducting cubic polymorph of CuSe2. Future work is suggested, surrounding the idea of maximizing diffusion and mixing at low temperatures. Understanding the properties of reactants, intermediates, and products to direct the reaction pathway is paramount in controlling the pathways through which reactions occur. This will progress the field of synthetic solid state chemistry towards the ability to design materials and reactions that are not limited by thermodynamics, in turn yielding the discovery of a range of new, functional compounds.Item Open Access Mesoscopic revelations: studying the shape of AOT reverse micelles(Colorado State University. Libraries, 2024) Gale, Christopher D., author; Levinger, Nancy E., advisor; Krummel, Amber, committee member; Prieto, Amy, committee member; Buchanan, Kristen, committee memberAerosol-OT (AOT) reverse micelles are a quintessential model system for studying nanoconfinement, creating consistent reverse micelles with a repeatable and very small size (~1-10 nm) using just 3 components. These reverse micelles have been used for studying the behavior of water and solutes in nanoconfinement, modeling the behavior of key solutes and proteins in a system more analogous to in vivo work, synthesizing nanoparticles, and even as a vehicle for suspending proteins in a low-viscosity solvent for high quality NMR experiments. Despite their usefulness, AOT reverse micelle's shape is poorly understood, but important to understanding behavior within a reverse micelle. Interfacial properties have been found to be key to many aspects of behavior within AOT reverse micelles and distance from the interface as well as the actual amount of interface present are highly dependent on shape. Therefore, the study of shape is key to a better understanding of AOT reverse micelles and behavior in nanonconfinement. In this work, I develop a series of metrics for shape--- coordinate-pair eccentricity (CPE), convexity, and the curvature distribution--- and apply them to several simulations of AOT reverse micelles. The simulations were designed to test the impact of the force field on the shape and behavior of the reverse micelles, including the first parameterization of AOT into the OPLS force field. The system was extensively checked to ensure equilibration was achieved and the system was not biased by the starting configuration. To aid in the shape analysis, I have developed a model and a formal proof to predict how the CPE changes for an arbitrary shape as it grows to model the shape behavior of general core-shell structures. Additionally, I measured the dipole moment of AOT, the rotational anisotropy decay of water, and several radial distribution functions to provide experimental verification where possible and further explore the behavior of the AOT reverse micelle system. Several key findings emerge from this work. Most notably, I find that AOT reverse micelles are significantly aspherical and non-convex over every force field tested, providing robust evidence that AOT reverse micelles are aspherical at any given moment in time. This provides strong evidence in support of the idea that experimental observations of spherical particles are the result of ensemble averaging. I also observe that the shape at the AOT/oil interface is comparatively more spherical with a "Goldilock's" value of convexity, neither too high nor too low, compared to the water/AOT interface. My model predicts that the CPE should fall with the addition of a shell, here provided by the AOT surfactant layer, suggesting this is largely the result of geometry. There is great variation between simulations and metrics in their dynamics, but in general, the shape appears to change on the order of 10 ns. This provides a useful method of deducing which values may or may not be impacted by shape, based on the time scale. For instance, it can reasonably be said that shape likely has no impact on water dynamics based on the roughly four orders of magnitude difference in the time scales of each process, which is supported by my own findings. Across all metrics studied, there are noticeable differences between simulations, but none of the differences are consistent. I believe this observation has important implications for both the behavior and simulation of AOT reverse micelles. First, this implies that the forces and interactions giving rise to different aspects of the reverse micelle are complex and largely independent, and that there is a disconnect between molecular-level measurements like radial distribution functions and and mesoscopic-level measurements like shape. Second, this implies that any simulation parameterized on one measure has no guarantee that it reproduces any other aspect of the reverse micelle accurately.Item Open Access Microchip capillary electrophoresis: improvements using detection geometry, on-line preconcentration and surface modification(Colorado State University. Libraries, 2012) Guan, Qian, author; Henry, Charles S., advisor; Strauss, Steven H., committee member; Van Orden, Alan K., committee member; Krummel, Amber, committee member; Hanneman, William H., committee memberCapillary electrophoresis and related microfluidic technologies have been utilized with great success for a variety of bioanalytical applications. Microchip capillary electrophoresis (MCE) has the advantages of decreased analysis time, integrated sample processing, high portability, high throughput, minimal reagent consumption, and low analysis cost. This thesis will focus on the optimization of our previous microchip capillary electrophoresis coupled electrochemical detection (MCE-ECD) design for improved separation and detection performance using detection geometry, on-line preconcentration and surface modification. The first effort to improve detection sensitivity and limits of detection (LODs) of our previous MCE-ECD system is established by an implementation of a capillary expansion (bubble cell) at the detection zone. Bubble cell widths were varied from 1× to 10× the separation channel width (50 μm) to investigate the effects of electrode surface area on detection sensitivity, LOD, and separation efficiency. Improved detection sensitivity and decreased LODs were obtained with increased bubble cell width, and LODs of dopamine and catechol detected in a 5× bubble cell were 25 nM and 50 nM respectively. In addition, fluorescent imaging results demonstrate ~8% to ~12% loss in separation efficiency in 4× and 5× bubble cell, respectively. Another effort for enhancing detection sensitivity and reducing LODs involves using field amplified sample injection and field amplified sample stacking. Stacking effects were shown for both methods using DC amperometric and pulsed amperometric detections. Decreased LODs of dopamine were achieved using both on-line sample preconcentration methods. The use of mixed surfactants to affect electroosmotic flow (EOF) and alter separation selectivity for electrophoretic separations in poly(dimethylsiloxane) (PDMS) is also presented in this thesis. First the effect of surfactant concentration on EOF was studied using the current monitoring method for a single anionic surfactant (sodium dodecyl sulfate, SDS), a single zwitterionic surfactant (N-tetradecylammonium-N,N-dimethyl-3-ammonio-1-propane sulfonate, TDAPS), and a mixed ionic/zwitterionic surfactant system (SDS/TDAPS). SDS increases the EOF as reported previously while TDAPS shows an initial increase in EOF followed by a reduction in EOF at higher concentrations. The addition of TDAPS to a solution containing SDS makes the EOF decrease in a concentration dependent manner. The mixed SDS/TDAPS surfactant system allows tuning of the EOF across a range of pH and concentration conditions. After establishing EOF behavior, the adsorption/desorption rates were measured and show a slower adsorption/desorption rate for TDAPS than SDS. Next, capacitively coupled contactless conductivity detection (C4D) is introduced for EOF measurements on PDMS microchips as an alternative to the current monitoring method to improve measurement reproducibility. EOF measurements as a function of the surfactant concentration were performed simultaneously using both methods for three nonionic surfactants, (polyoxyethylene (20) sorbitan monolaurate (Tween 20), polyoxyethylene octyl phenyl ether (Triton X-100), polyethylene glycol, (PEG 400)), mixed ionic/nonionic surfactant systems (SDS/Tween 20, SDS/Triton X-100, and SDS/PEG 400) and mixed zwitterionic/nonionic surfactant systems (TDAPS/Tween 20, TDAPS/Triton X-100, and TDAPS/PEG 400). EOF for the nonionic surfactants decreases with increasing surfactant concentration. The addition of SDS or TDAPS to a nonionic surfactant increases EOF relative to the pure nonionic surfactant. Next, separation and electrochemical detection of two groups of model analytes were explored using mixed surfactant systems. Similar analyte resolution with greater peak heights was achieved with mixed surfactant systems relative to the single surfactant system. Finally, the utility of mixed surfactant systems to achieve improved separation chemistry of biologically relevant compounds in complex sample matrixes was demonstrated in two applications, which include the detection of catecholamine release from rat pheochromocytoma (PC12) cells by stimulation with 80 mM K+ and the detection of reduced glutathione (GSH) in red blood cells (RBCs) exposed to fly ash suspension as a model environmental oxidant.Item Open Access Microfluidics for environmental analysis(Colorado State University. Libraries, 2018) Gerold, Chase T., author; Henry, Charles S., advisor; Krummel, Amber, committee member; Levinger, Nancy, committee member; Finke, Richard, committee member; Dandy, David, committee memberDuring my graduate dissertation work I designed and utilized microfluidic devices to study, model, and assess environmental systems. Investigation of environmental systems is important for areas of industry, agriculture, and human health. While effective and well-established, traditional methods to perform environmental assessment typically involve instrumentation that is expensive and has limited portability. Because of this, analysis of environmental systems can have considerable financial burden and be limited to laboratory settings. To overcome the limitations of traditional methods researchers have turned to microfluidic devices to perform environmental analyses. Microfluidics function as a versatile, inexpensive, and rapidly prototyped analytical tool that can achieve analysis in field setting with limited infrastructure; furthermore, microfluidic devices can also be used to study fundamental chemistry or model complex environmental systems. Given the advantages of microfluidic devices, the research presented herein was accomplished using this alternative to traditional instrumentation. The research projects described in this dissertation involve: 1) the study of fundamental chemistry associated with surfactant surface fouling facilitated by divalent metal cations; 2) the creation of a microfluidic device to study fluid interactions within an oil reservoir; and 3) the fabrication of a paper-based microfluidic to selectively quantify K+ in complex samples. The first research topic discussed involves observation of dynamic evidence that supports the hypothesized cation bridging phenomenon. Experimental results were acquired by pairing traditional microfluidics with the current monitoring method to observe relative changes to a charged surface's zeta potential. Divalent metal cations were found to increase surfactant adsorption, and cations of increasing charge density were found to have a greater effect on surface charge. Analysis of the experimental data further supports theoretical cation bridging models and expands on knowledge relating to the mechanism by which surfactant adsorption occurs. This work was published in the ACS journal Langmuir (2018, 34 (4), pp 1550–1556). The second project discussed herein focuses on the development of the microfluidic Flow On Rock Device (FORD) that was designed to study fluid interactions within complex media. The FORD was designed to be an alternative to existing fluid modeling methods and microfluidic devices that test oil recovery strategies. Fabrication of the FORD was accomplished by incorporating real reservoir rock core samples into the device. The novelty of this device is due to the simplicity and accuracy by which the physical and chemical characteristics are represented. This project has been accepted for publication pending minor revisions in Microfluidics and Nanofluidics. The final project discussed the creation of the first non-electrochemical microfluidic paper-based analytical device (µPAD) capable of quantitatively measuring alkali or alkaline earth metals using K+ as a model analyte. This device was fabricated by combining distance-based analytical quantification in µPADs with optode nanosensors. Experimental results were obtained using the naked eye without the requirement of a power source or external hardware. The resulting distance-based µPAD showed high selectivity and the capacity to quantify K+ in real undiluted human serum samples. This work has been published in the ACS journal Analytical Chemistry (2018, 90 (7), pp 4894–4900). The research projects briefly described above and thoroughly discussed later within this dissertation were made possible by the utilization of microfluidic devices. These projects investigated various aspects of environmental chemistry without the use of traditional instrumentation or methods. The experimental results that were obtained further the fundamental understanding of surfactant adsorption, provide an inexpensive and accurate model to observe fluid interactions within reservoir rock material, and allow for the selective quantification of K+ in a paper-based device without the use of a power source. The funding for each of these projects was supplied by BP plc and Global Good, as is mentioned accordingly within this dissertation.Item Open Access Organic-inorganic dipolar and quadrupolar coupling underlies the structure and properties of hybrid perovskites(Colorado State University. Libraries, 2020) Mozur, Eve M., author; Neilson, James R., advisor; Prieto, Amy, committee member; Krummel, Amber, committee member; Sites, James, committee memberTo view the abstract, please see the full text of the document.Item Open Access Photoelectrochemical microscopy studies of transition metal dichalcogenides nanoflakes: addressing open questions of structure-function relationships(Colorado State University. Libraries, 2022) Van Erdewyk, Michael, author; Sambur, Justin, advisor; Krummel, Amber, committee member; Henry, Charles, committee member; Stasevich, Tim, committee memberTransition metal dichalcogenides (TMDs) are exciting materials for applications in solar energy conversion. However, to advance technologies that leverage these materials, a strong understanding of fundamental photoelectrochemistry and related processes is necessary. Photoelectrochemical microscopy methods are well poised in this aspect. Methods like scanning photoelectrochemical microscopy allow for the excitation of small, localized region of a material with a focused laser and the subsequent measurement of the photocurrent. The measured photocurrent can be related to the position of the laser and the physical attributes of the material surface at the location, and variations in the photocurrent across the surface can be tracked. In this way, the technique offers insight into how different surface motifs affect the photoelectrochemical behavior of the material. This method can be combined with other spectroscopies, such as photoluminescence or Raman, to can further understanding about the studied material. The following work details the use of photoelectrochemical microscopy methods to answer questions relating to both the structure and underlying properties of mechanically exfoliated TMD nanoflakes.Item Open Access The flavivirus NS3 helicase Motif V controls unwinding function and alters viral pathogenesis in mosquitoes(Colorado State University. Libraries, 2020) Du Pont, Kelly Elizabeth, author; McCullagh, Martin, advisor; Geiss, Brian J., advisor; Szamel, Grzegorz, committee member; Snow, Christopher, committee member; Krummel, Amber, committee member; Ho, Shing, committee memberOver half of the world's population is at risk of flavivirus (e.g. dengue virus, West Nile virus, Japanese Encephalitis virus, and Zika virus) infection making it a global health concern. These specific mosquito-borne flaviviruses are responsible for causing a variety of symptoms and outcomes including flu-like fevers, encephalitis, hemorrhagic fevers, microcephaly, Guillain-Barré syndrome, and death. Unfortunately, vaccines and anti-viral therapeutics are not always effective in protecting against and treating viral infections. Sometimes these therapies cause more severe symptoms through an antibody dependent enhancement. Therefore, there is a pressing need for the development of effective anti-viral therapies against each flavivirus. For the advancement of these interventional strategies, a fundamental understanding of how flaviviruses replicate within hosts, including the mosquito vector, is required. This dissertation investigates how flaviviruses regulate viral replication, pathogenesis and mosquito transmission through the nonstructural protein 3 (NS3) helicase structure and function. A combination of virology, biochemistry, and computational simulations will be utilized to address how NS3 plays a role in viral infection, viral replication, and viral protein structure. An essential aspect of flaviviral genome replication is the unwinding of the double-stranded RNA intermediate via the C-terminal helicase domain of NS3. NS3 helicase translocates along and unwinds the double-stranded nucleic acids in an ATP-dependent manner. However, the mechanism of energy transduction between the ATP- and RNA-binding pockets is not well understood. Previous simulations in the group led us to hypothesize that Motif V is a critical component of the transduction mechanism. Here, we tested Motif V mutations in both sub-genomic replicon and recombinant protein systems to examine viral genome replication, helicase unwinding activity, ATP hydrolysis activity, and RNA binding affinity activity. NS3 helicase mutants, T407A and S411A, indicated reduced viral genome replication and increased turnover rates of helicase unwinding activity by a factor of 1.7 and 3.5 respectively. Additionally, we simulated Motif V mutants to probe the structural changes within NS3 helicase caused by the mutations. These simulations indicate that Motif V controls communication between the ATP-binding pocket and the helical gate. Motif V mutations T407A and S411A exhibit a hyperactive helicase phenotype leading to the regulation of translocation and unwinding during viral genome replication. Next, we utilized T407A and S411A West Nile virus (Kunjin subtype) mutants in cell culture and in vivo to probe the how these mutations play a role in pathogenesis and transmission of flaviviruses. Of the two Kunjin virus mutants, only S411A Kunjin virus was recovered. In cell culture, S411A Kunjin decreased viral infection and increased cytopathogenicity as compared to WT Kunjin. Similarly, in surviving Culex quinquefasciatus mosquitoes, S411A Kunjin decreased infection rates as compared to WT Kunjin, but S411A Kunjin infection increased mortality compared with that of WT Kunjin infection. Additionally, S411A Kunjin increased viral dissemination and saliva positivity rates in surviving mosquitoes compared to WT Kunjin. These data suggest that S411A Kunjin increases pathogenesis in mosquitoes. Overall, these computational simulation, biochemical assay, and virology data indicate that flavivirus NS3 helicase Motif V may play a role in the pathogenesis, dissemination, and transmission efficiency of Kunjin virus, not just regulation of translocation and unwinding during viral genome replication. The molecular level insights presented in this dissertation provide the fundamental research for understanding how to target specific regions of NS3 helicase for the advancement of anti-viral therapeutics.Item Open Access Topological techniques for characterization of patterns in differential equations(Colorado State University. Libraries, 2017) Neville, Rachel A., author; Shipman, Patrick, advisor; Adams, Henry, committee member; Krummel, Amber, committee member; Shonkwiler, Clayton, committee memberComplex data can be challenging to untangle. Recent advances in computing capabilities has allowed for practical application of tools from algebraic topology, which have proven to be useful for qualitative and quantitative analysis of complex data. The primary tool in computational topology is persistent homology. It provides a valuable lens through which to study and characterize complex data arising as orbits of dynamical systems and solutions of PDEs. In some cases, this includes leveraging tools from machine learning to classify data based on topological characteristics. We see a unique pattern arising in the persistence diagram of a class of one-dimensional discrete dynamical systems--even in chaotic parameter regimes, and connect this to the dynamics of the system in Chapter 2. Geometric pattern structure tell us something about the parameters driving the dynamics in the system as is the case for anisotropic Kuramoto-Sivashinsky equation which displays chaotic bubbling. We will see this in Chapters 3 and 4. Defects in pattern-forming systems be detected and tracked and studied to characterize the degree of order in near-hexagonal nanodot structures formed by ion bombardment, which will be developed in Chapter 5.Item Embargo Tuning antimony anodes through electrodeposition to inform on the reaction and degradation mechanisms in sodium-ion batteries(Colorado State University. Libraries, 2023) Nieto, Kelly, author; Prieto, Amy L., advisor; Sambur, Justin, committee member; Krummel, Amber, committee member; Bandhauer, Todd, committee memberElectrification of portable devices, transportation, and large grid-level storage necessitate a portfolio of energy storage devices tailored to specific applications. Sodium-ion batteries are a naturally abundant alternative to lithium, but high performing anodes must be developed in order to reach widespread commercialization. Alloy-based anodes such as antimony (Sb) are attractive targets for their high theoretical capacities. However, the electrochemical performance of Sb is poor, and the reaction mechanism is poorly understood. Herein, antimony-based anodes for sodium-ion batteries are explored to elucidate sodiation pathways and investigate the role of electrode fabrication, electrolyte composition, and architecture on the reaction and degradation mechanism. Chapter I describes our research methodology and consists of our synthetic method of electrodeposition, materials characterization, battery assembly, and electrochemical characterization. Through this process, we can develop a better understanding of the electrochemical performance of alloy-based anode materials. The tunability of electrodeposition as a synthetic technique for the fabrication of Sb-based anodes is exploited in Chapter II. The effects of solution additives in the electrodeposition of Sb anodes are investigated and provide insight into how the morphology and crystallinity of the deposited anodes can be tuned. It was revealed that CTAB and SPS could significantly tune the electrodeposition of Sb films by altering the deposition by causing structural changes that either improved cycle life or rate capabilities. In Chapter III, electrodeposited and slurry cast Sb anodes were compared through differential capacity analysis, and it was demonstrated that electrode fabrication can significantly impact the sodiation/desodiation reaction pathway. Additionally, electrodeposited Sb anodes provided valuable insight into the mechanism without having to deconvolute the influences of binders and additives necessary in slurry casting. Chapter IV describes preliminary studies on how electrolyte composition can influence sodiation/desodiation reactions during Sb anode cycling. Traditional battery electrolytes are composed of carbonate species and salts, which are reduced onto the anode surface to form the solid electrolyte interphase (SEI). Due to the inherent volume expansion of Sb anodes when sodiated/desodiated, the SEI is hypothesized to continuously form and affect the cyclability of these anodes. In this investigation, we have found that electrolyte composition can influence the cycle life and sodiation/desodiation pathway, and we describe additional studies to probe how the SEI could hinder sodium ion transport. Chapter V builds upon Chapter II and explores how electrodeposition can be employed to develop three-dimensional (3D) electrodes to enhance the energy and power density of Sb-based anodes. Although we show that experimental parameters can be tuned to obtain uniform coverage, significant challenges in achieving conformal coverage of the current collector while maintaining high active material loading remain. The final chapter, Chapter VI, concludes the dissertation by describing further directions required to deepen the understanding of the degradation mechanism for Sb. We have begun to develop a 3D-printed optical, electrochemical cell that can couple operando optical studies with electrochemical studies to understand how electrode composition, structure, and electrolyte composition affect mechanical stability and ionic/electronic diffusivity in these electrodes. Understanding these fundamental processes and developing tools and characterization techniques to study alloy-based anode materials will lay the foundation for creating earth-abundant energy storage systems with high energy densities and long cycle life.