Mountain Scholar :: Browsing by Author "Prieto, Amy, committee member"

Browsing by Author "Prieto, Amy, committee member"

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Open Access
A personal thermophoretic sampler for airborne nanoparticles
(Colorado State University. Libraries, 2010) Thayer, Daniel Lee, author; Marchese, Anthony, advisor; Volckens, John, advisor; Popat, Ketul, committee member; Prieto, Amy, committee member
Engineered nanoparticles are materials with at least one dimension measuring less than 100 nm that are designed on the molecular scale to produce unique or enhanced properties that differ from the bulk material. However, the same properties that make engineered nanoparticles attractive to industry also may present potential health risks to the workers who manufacture them. Very little human exposure data exist for these particles, although they are known enter the body through a number of routes (e.g., respiration, dermal penetrations, and ingestion). Nanoparticles that enter the body can also translocate from one organ to another by virtue of their small size. A cost-effective personal sampler is necessary to evaluate levels of worker exposure to these materials to determine the relative levels of individual risk. Such a sampler must be capable of collecting nanoparticles with high efficiency for subsequent analysis of size, surface chemistry, morphology, and other properties. In addition, the sampler must be able to differentiate between incidental nanoparticles, which are nanoparticles that are naturally present in the environment, and engineered nanoparticles. As detailed in this thesis, a small thermal precipitator was designed to measure breathing-zone concentrations of airborne nanoparticles. The thermal precipitator samples aerosol by producing a 1000 °C cm ' temperature gradient between two aluminum plates (0.1 cm separation distance) using a resistive heater, a thermoelectric cooler, a temperature controller, and two thermistor sensors. The collection efficiency was evaluated for 15, 51, 100, and 240 nm particles at flow rates of 5 and 20 mL/min. Tests were also performed with a zero temperature gradient to determine losses in the device for measurement correction. The homogeneity of particle collection across the collection surface was evaluated using electron microscopy and imaging software. The results indicate that thermal precipitation is a feasible approach for personal monitoring of airborne nanoparticle concentrations in the workplace.
Open Access
Applications of inorganic nanoparticles in biological electron microscopy
(Colorado State University. Libraries, 2016) Ni, Thomas Wentung, author; Ackerson, Christopher, advisor; Prieto, Amy, committee member; Finke, Richard, committee member; Peersen, Olve, committee member
Electron microscopy is an immensely powerful for imaging at the cellular level. However, many of the macromolecules of interest are difficult to image due to low electron density. There has been an immense body of work in order to visualize these macromolecules. In the past, many of the methods of visualization revolved around staining samples with heavy metals, however these stains are non-specific. In order to develop more specific methods of tagging macromolecules, there are two different methods to consider: the first being a top-down approach, in which electron dense tags, in this case inorganic nanoparticles, are given specific ligands to take advantage of different chemistries to attach these nanoparticles to macromolecules of interest. The second method is through a bottom-up approach where biomolecules are given the specific ability to form inorganic nanoparticles. Inorganic nanoparticles have been investigated with various ligands in order to enhance binding capability to macromolecules. The chief method of functionalizing these inorganic nanoparticles comes from ligand exchange; much has been studied regarding ligand exchange, but there are still many unanswered questions. Herein, we endeavor to reveal both the mechanism of exchange and the functional unit of exchange. We also report progress towards understanding an enzyme that is capable of forming inorganic nanoparticles, which could be cloned onto proteins as well. This bottom up style has been studied in several other groups; however, none of the previously reported methods have seen much use. Herein, we report a potential NADPH-dependent enzyme that forms selenium nanoparticles.
Embargo
Charge carrier dynamics of 2-dimensional photoelectrodes probed via ultrafast spectroelectrochemistry
(Colorado State University. Libraries, 2024) Austin, Rachelle, author; Sambur, Justin, advisor; Krummel, Amber, advisor; Rappe, Anthony, committee member; Prieto, Amy, committee member; McNally, Andrew, committee member; Brewer, Samuel, committee member
The integration of hot charge carrier-based energy conversion systems with two-dimensional (2D) semiconductors holds immense promise for enhancing the efficiency of solar energy technologies and enabling novel photochemical reactions. Current approaches, however, often rely on costly multijunction architectures. In this dissertation, I present research that combines spectroelectrochemical and in-operando transient absorption spectroscopy measurements to unveil ultrafast (<50 fs) hot exciton and free charge carrier extraction in a proof-of-concept photoelectrochemical solar cell constructed from earth-abundant monolayer (ML) MoS2. Theoretical analyses of exciton states reveal enhanced electronic coupling between hot exciton states and neighboring contacts, facilitating rapid charge transfer. Additionally, I discuss insights into the physical interpretation of transient absorption (TA) spectroscopy data in 2D semiconductors, comparing historical perspectives from physical chemistry and solid-state physics literature. My perspective encompasses various physical explanations for spectral features and experimental trends, particularly focusing on the contribution of trions to TA spectra. Furthermore, I examine how different physical interpretations and data analysis procedures can yield distinct timescales and mechanisms from the same experimental results, providing a comprehensive framework for understanding charge carrier dynamics in 2D semiconductor-based optoelectronic devices.
Open Access
Correlated electron microscopy with electro-optical imaging of hexagonal tungsten oxide nanorods
(Colorado State University. Libraries, 2019) Cashen, Christina J., author; Sambur, Justin B., advisor; Prieto, Amy, committee member; Li, Yan Vivian, committee member
Fundamental understanding of the dynamics of ion insertion into a host material are essential to accommodate the rising demand for energy storage technology. It has been established that single nanoparticle electrodes greatly improve the kinetics of the ion insertion reaction, however the heterogeneous behavior of single particles correlated to the structure of the particle has been challenging to determine. This work takes on this challenge by developing a method that implements optical microscopy to study the optical modulations of electrochromic single particle hexagonal tungsten oxide (h-WO3) nanorods with transmission electron microscopy (TEM). Heightened resolution provided by TEM reveals sub-atomic structural details which would be impossible to observe with other techniques. This work introduces a method of measuring correlated single particle optical activity of WO3 with TEM resolution images of the same particle. This study found heterogeneous optical modulations of the carbon film considerably influenced the optical activity of WO3. Bearing in mind this behavior is vital for future experiments using this method. After this is accounted, we compare the optical activity of two single particles using the common parameters: maximum optical density (max OD) and the time it takes to reach 90% of the max OD (t90). This comparison provides further evidence that the presence of nanosized step-edge gradients contribute to the ion insertion dynamics of this electrochromic host material. Further study using this method can reveal a understanding of how the presence of step-edges contributes to the local lattice dynamics upon lithiation of a nanorod.
Open Access
Design and synthesis of biologically active Largazole derivatives, including development of improved syntheses of Largazole analogs
(Colorado State University. Libraries, 2018) Dunne, Christine E., author; Williams, Robert M., advisor; Shi, Yian, committee member; Prieto, Amy, committee member; Thamm, Douglas, committee member
Natural product histone deacetylase inhibitor, Largazole, has been developed into a streamlined synthetic pathway for the development of a complex library of analogs. The library developed within the Williams laboratory encompasses an array of derivatives, including but not limited to: thiazole modification and macrocycle substitutions. The cap group of Largazole, portion of the molecule extending outside of the enzyme binding pocket, was successfully modified to install new chemical handles for biologic and dual therapeutic conjugation. Biological conjugates of Largazole, as well as its derivatives, aid in increasing selectivity and potency of the compound. Largazole has been conjugated to both biotin and folic acid for further studies. Additionally, a streamlined synthesis towards Wnt inhibitor 3289-5066 and a developed path for conjugation have been explored. Modified procedures were developed to aid in scale up and improvement of synthetic pathways. Scale up is crucial for development of sufficient material for biological testing and further development of conjugative therapeutics. One main impediment in the synthesis of Largazole peptide isostere is towards the southern fragment, specifically the Grubbs olefin metathesis. Multiple routes were explored to combat this low yielding step. Further exploration of these synthetic routes are underway.
Open Access
Discovery and properties of hybrid materials for potential applications in quantum information science
(Colorado State University. Libraries, 2022) Lundgren, Crystal J., author; Neilson, James R, advisor; Prieto, Amy, committee member; Buchanan, Kristen, committee member
Hybrid halide perovskites and their derivatives are sought after for their unique optoelectronic properties, ease of preparation, and highly tunable structure. Some conjugated π-system containing hybrid halide semiconductors derived from hybrid perovskites show a unique primary electronic transition from the inorganic layer (halide) states to the organic layer (π∗) states. This type of charge-transfer semiconductor demonstrates a quantum two-level system between these frontier orbitals, suggesting that these materials may be useful as qubits in quantum computation. For a material to be suitable for a qubit, it must contain a quantum two-level system that can be char- acterized via optically adressable emission. Here, a new family of hybrid halide semiconductors containing 4-amino-1,2,4-triazole (4AMTZ) are discovered. Chapter 2 discusses the synthesis and characterization of 4AMTZBiI4. The crystal structure of 4AMTZBiI4 is solved and con rmed with powder X-ray diffraction. Photoluminescence studies reveal that there is no optically addressable emission from this system, and the iodide congener is thus not usable as a qubit. Chapter 3 discusses the synthesis and photoluminescence emission spectra of 4AMTZBiBr4 and 4AMTZBiCl4. These studies reveal emission from both the chloride and bromide congeners at T = 77 K that is likely due to the primary charge transfer between the halide and organic states based on the blue shifting of 4AMTZBiBr4 (475 nm) relative to that of 4AMTZBiCl4 (415 nm). Another region of emission observed in both 4AMTZBiBr4 and 4AMTZBiCl4 is centered at 660 nm. This region of emission is not shifted between the halide congeners, suggesting the presence of an emissive self- trapped exciton localized on the inorganic lattice. Though these materials emit at T=77K, there is no optically addressable emission at room temperature.
Open Access
Enabling and understanding low-temperature kinetic pathways in solid-state metathesis reactions
(Colorado State University. Libraries, 2020) Todd, Paul Kendrick, author; Neilson, James, advisor; Finke, Richard, committee member; Prieto, Amy, committee member; Henry, Chuck, committee member; Ma, Kaka, committee member
For the kinetic pathway to influence the outcome of a solid-state reaction, diffusion barriers must be lowered or circumvented through low-temperature chemistry. Traditional ceramic synthesis use high temperatures to overcome diffusion, yet they result in the thermodynamically stable product. If the desired product lies higher in energy, they are unattainable at such temperatures. Extrinsic parameters, like pressure, can be used to change the stability of products (kinetic trapping), yet require extreme conditions. Another strategy involves kinetically controlling the energy barriers of the reaction to select for a given product. Here, we use solid-state metathesis reactions to understand and control kinetic pathways in the formation of complex oxides and binary metal sulfides. Through simple changes to precursor composition, three unique polymorphs of yttrium manganese oxide are synthesized, two of which are metastable phases. Using in situ diagnostics, the reaction pathways are characterized to identity intermediates and the temperature regimes at which they react. Using this information we identify why different polymorphs form using different precursors. Additionally, small functional organosilicon molecules are shown to catalyze the formation of iron(II) sulfide using metathesis reactions. Here we show that the Si-O functional group stabilizes intermediate species along the pathway to avoid forming more stable intermediates. The result is higher yields of FeS2 at lower temperatures and times. The included chapters will hopefully better inform future solid-state chemists when exploring new composition spaces and reaction pathways.
Open Access
Engineering phthalocyanines and carbon composites for use in sensing, microfluidics and dye sensitized solar cells
(Colorado State University. Libraries, 2018) Klunder, Kevin Jay, author; Henry, Charles, advisor; Prieto, Amy, committee member; Reynolds, Melissa, committee member; Barisas, George, committee member; Jathar, Shantanu, committee member
The focus of this thesis is on fundamental and applied electrochemistry in the areas of photovoltaics, sensors, and microfluidics. Photovoltaics are important as they are needed to reduce the amount of greenhouse gases, pollution, and reliance on finite energy sources that are currently associated with energy production. A thin film photovoltaic device known as a dye sensitized solar cell (DSSC) is studied in his work. Specifically the cathode of the DSSC is studied in detail. A new method to create a highly transparent and catalytic DSSC cathode coating is proposed. The phthalocyanine based coatings have ~97% transmittance at 550 nm and low charge transfer resistance of ~1.3 Ω cm2, representing one of the best cathode coatings in terms of transparency and charge transfer resistance to date. Electrochemical sensors and electrochemical microfluidics can be used to monitor air, water and soil pollution, both of which can occur from anthropogenic and/or natural sources. Quantifying this pollution is vital for human and animal safety. Electrochemical sensors are also used for health diagnostics and are commonly applied in blood glucose monitoring. It is projected that wearable forms of electrochemical sensors will emerge as a vital class of real-time point-of-care sensors to monitor health indicators in the near future. To advance the field of electrochemical sensors and electrochemical microfluidics low cost, easily miniaturized, patterned, and shaped electrodes are needed. The work here introduces a new fabrication method for carbon composites which enables electrodes to be patterned and made into micron features in a facile manor through solvent or melt processing. The composites are also shown to be easily integrated into microfluidic devices, demonstrated with the assembly of electrochemical droplet microfluidics. The ease of fabrication of the new composites represents a milestone for the widespread use of low cost carbon composites in complex electrochemical systems. Within this thesis, Raman, SEM, XRF, and a wide range of electrochemical redox species and techniques are used to determine what factors affect the electrochemical activity, capacitance, and conductivity of the carbon composites. Finally, phthalocyanines for uses in electrochemical catalysis are a recurring theme throughout the thesis. Chapter 4 is dedicated to creating new types of electropolymerizable phthalocyanines. Cobalt phthalocyanine is integrated into the carbon composites from Chapter 2 for uses in thiol oxidation and the sensing of thiols. The thiol of interest was dithiothreitol (DTT) which is used in the "DTT assay". The DTT assay is a chemical measure of oxidative potential of particulate matter, and is commonly used to try and understand health effects relating to air pollution. Here, low volume disposable cells, as well as flow based sensors are developed for the detection of DTT.
Open Access
Exploration based design methodology using the theory of constraints in extending plastics manufacturing for novel high performing fabrics
(Colorado State University. Libraries, 2022) Shekoni, Aderemi, author; Troxell, Wade, advisor; Simske, Steve, committee member; Young, Peter, committee member; Prieto, Amy, committee member
The world of textiles is comprised of several materials. From the conventional, such as cotton and silk, to the contemporary, such as polyester and nylon, textiles have changed over time. Nonwovens, a category of material frequently referred to as the "third-generation" of textiles, have emerged as one of the most exciting breakthroughs in the textile industry during the past few years. Nonwovens, which are frequently confused with fibers, yarns, and fabrics, have evolved as a new category of versatile material with medicinal and industrial applications. An issue associated with the use of lightweight nonwovens is their single-use, in which a fabric weight category can be employed for only one product. The number of products per weight class that can be utilized in businesses that utilize the materials is limited. Therefore, companies utilizing these textiles in their operations must engage with plastic producers to plan, implement, and develop a single weight class for a single product. This procedure is time-consuming and generates plastic waste because of unfinished fabrics. By creating a multipurpose nonwoven fabric, organizations will be able to improve their operations by saving time and energy, improving profits, decreasing plastic waste, and enabling process innovation. To use a fabric with the same weight and similar physical properties in a different product, a different fabric is manufactured for that process, despite the similarity in weight and physical properties between the fabric used in the previous process and the fabric needed for the new process. Due to this limitation, the concept of redesigning nonwoven materials for different applications was conceived. Air Permeability, a barrier to airflow, is a significant component in the inability to support numerous uses. When a fabric's desired attribute is not satisfied, the fabric's air permeability can be optimized by utilizing a variety of process approaches to attain the appropriate performance qualities. This permits the use of a single fabric in a variety of items. Due to the fabric's weight and volume, the usage of nonwoven in aviation and public works has expanded drastically. Thermal insulation is one of the most prevalent applications of nonwoven materials in the aviation industry. Nonwoven fabrics are also utilized as dynamic biofilters for filtration in public works, with an aerobic layer that aids in the recovery of alkalinity in the filtration systems used in these facilities. The two significant outcomes of this research are (1) Improvement of the airflow barrier, also known as air permeability (AP), which enables the use of a single weight class to make several goods as opposed to a single weight class for a single product, and the addition of a thermal barrier to the fabric. Permeability enhancements in nonwovens enhance the fabric's sound absorption, filtration, and heat absorption. (2) The capacity to recycle undesired nonwoven fabrics following production, as opposed to disposing of the plastic components in landfills. Nonwovens are semi-crystalline polypropylene plastics that are not easily biodegradable due to the strong chemical bond between the polypropylene polymers. Because polypropylenes, which are plastics, are not biodegradable, unused nonwoven fabrics are landfilled. It was through the process of prototyping that a subsystem alteration was made that enabled the development of nonwoven fabric with better air permeability. Design as Exploration concepts are used to accomplish this. Reicofil I, II, III, and IV are the four nonwoven production systems used in this research to develop the novel fabric. In addition, this study has handled another issue by reusing and recycling unwanted fabrics to reduce the amount of plastic waste in landfills. An extrusion method that recycles rejected and waste fabrics were the result of these approaches. The innovative method used in developing the new nonwoven fabric is being explored for use in the production of plastic films to improve the quality of goods made with polyethylene plastic polymers.
Open Access
Fabrication and analysis of vanadium oxides and vanadium oxide based magnetic hybrid structures
(Colorado State University. Libraries, 2021) Sutton, Logan, author; Wu, Mingzhong, advisor; de la Venta, Jose, committee member; Ross, Kathryn, committee member; Prieto, Amy, committee member
Vanadium oxide films and vanadium oxide-based magnetic hybrid structures are fabricated using various techniques and studied optically, electrically, structurally, and magnetically for their potential applications into magnetic recording, room temperature refrigeration, and optical switches. The different types of behavior seen in the transitions of the vanadium oxide class of compounds can be altered and optimized according to desirable qualities for these applications. Several different techniques were used for the fabrication of vanadium oxide-ferromagnetic (FM) composites with the goal of causing magnetic coupling and the optimization of coupling between the vanadium oxide compound and the FM compound. The ball milling process was used as the primary step in formation of the composites, but was shown to be ineffective at causing coupling between the compounds if used alone. The addition of a sintering process was shown to successfully couple V2O3 and Ni, with an optimization of the process determined to be primarily dependent on temperature. Optimized composites showed up to 56% changes in coercivity at the transition temperature of the V2O3. VO2 based composites were unable to be coupled due to problems with the reduction and oxidation of the compounds involved, and a lack of diffusion. A sol-gel technique for the fabrication of VO2 layers was optimized for large transitional properties and refined for reproducibility. Magnetic hybrid structures formed from the sol-gel fabricated films were shown to have comparable properties to their sputtered counterparts. W doped films fabricated using the sol-gel technique, when compared to doping using a sputtering technique, were demonstrated to allow for larger control over the ideal doping range. Doping was shown to have negligible effect on the morphology of the films, but produced several W based impurities. Although doping produced expected shifts and decreases in the transitional electrical transport properties, there were also unexplained shifts in the absolute resistance for higher doping. Magnetic hybrid structures based on doped films still produced large changes in the magnetic properties of the FM layer, but these changes were shifted to lower temperatures and reduced. Transmission and reflection of VO2 films fabricated using different techniques were shown to have different qualitative and quantitative behaviors at different optical wavelengths of incidence. Most films were shown to have downward switching in both the transmission and reflection at the transition, however thinner films sometimes showed upward switching in the transmission. Downward bumps caused by interference were seen in the reflection at 980 nm, as well as at 635 nm for two other films. The model that was developed to try to reproduce this behavior is successful for 60% of the films, and able to reproduce all of the qualitative behaviors described. However the trends in the fitted refractive index do not help elucidate what physical mechanism is responsible for the differences seen between samples.
Open Access
Force field models in halogen bonding
(Colorado State University. Libraries, 2019) Billman, Mardi Marie, author; Rappé, Anthony, advisor; Prieto, Amy, committee member; Strauss, Stephen, committee member; Ho, Pui Shing, committee member
Halogen bonding schemes have been proposed to replace those of hydrogen bonding in biomolecules, such as proteins and DNA, because halogens can counter-intuitively attract a Lewis base. Unlike hydrogen bonding, halogen bonding strength is dependent on a number of factors, such as electrostatics, exchange repulsion, dispersion, and charge transfer. Understanding the underlying energetic components of halogen bonding at a fundamental level, defined herein to mean the subatomic level, is necessary to utilize halogen bonding in a biomolecular context. Our aspiration throughout this research has not been to quantify the strength of the underlying interactions. Instead, it has been to identify and explain the interactions as dependent on the uneven distribution of valence electrons inherent to the halogens, and apply our findings to developing force field models. Chapter 2: The Cambridge Structural Database was used to show that crystals of halogen bonding structures exhibit a distance-angle correlation. The correlation is similar to that present in crystals of hydrogen bonding structures, though with a diminished angular dependence beyond the sum of the van der Waals radii. Halogen bonding strength, approximated by bonding frequency, was found to be inversely proportional to non-bonding distance. The shape of the distance-angle correlation would continue to be studied in Chapters 3–4. Chapter 3: An angular dependence was illustrated in Chapter 2 at short non-bonding distances; the interaction energy must have been dependent on anisotropic, short-range components such as electrostatics and exchange repulsion. The electronic structure of halogen-containing compounds was studied independently as a function of distance and then as a function of angle. Electron-withdrawing and -donating moieties were used to observe the dependence of electrostatics, exchange repulsion, and dispersion on the polarizability of the halogen. Both substituent and periodic trends were observed, where halogen bonding strength increased with -hole and aspherical shape of the halogen atom. Chapter 4: Atomic halogens were used to study the anisotropic electrostatic potential and exchange repulsion directly, without influence of the substituent groups present in Chapter 3. Our hypothesis was that theoretical models of the electrostatic potential and exchange repulsion would display an angular dependence because of the inherent s2px2py2pz1 valence electron configuration. The halogen atoms were defined as a linear combination of core and valence s and p wavefunctions, fitted simultaneously to Hartree-Fock calculations of the orbital shapes, electrostatic potential, and exchange repulsion. The shape of the exchange repulsion model as a function of distance and angle, in conjunction with dispersion, could explain the distance-angle correlation of experimental and theoretical halogen bonding. The electrostatic potential, associated with the -hole model of halogen bonding, did not vanish at long distance. Instead, it was found that the presence of a dipole-dipole interaction was necessary to recreate experimental results. Chapter 5: The purpose of this study was to begin development on a multimolecular system to model solvent interactions with halogen bonding structures. We found that halogen bonding trimer systems have a cooperative non-bonding energy due to the electrostatics, dispersion, and partial charge transfer from Lewis base to halogen. The polarization of the model hydrogen-bond enhanced halogen bonds increased the electrostatic attraction within the trimer systems. The charge transfer stabilized the structure and lead to decrease in bond distances relative to the corresponding dimers. Because attractive dispersion interactions are inversely dependent on interaction distance, the overall dispersive attraction increased in the trimer system as well. Chapter 6: A novel model was created to examine the process of charge transfer as a function of distance in halogen bonding dimers. Two molecular models of borane with ammonia and diatomic bromine with ammonia were developed and fitted to computational calculations. The results of the models showed that the cross-term of the charge transfer interaction between reactant and product components contributes to the attraction between Lewis acids and bases.
Open Access
Glyme-synthesized nanomaterials
(Colorado State University. Libraries, 2021) Armstrong, James, author; Ackerson, Christopher J., advisor; Prieto, Amy, committee member; Kennan, Alan, committee member; Basaraba, Randall, committee member
Nanomaterials include materials with at least one dimension in the nanometer range. These materials include nanoparticles, quantum dots, thin films, self-assembled materials, supramolecular materials and more. Nanoscience is an intriguing field for cutting edge research for energy, biology, medicine, optical and other applications. Coinage-metal (Au, Ag, Cu) nanomaterials are particularly of interest for the stability of nanoparticles synthesized with these metals. These metals can also be utilized to produce supramolecular assemblies, e.g. Hydrogels. In particular, this dissertation will cover four projects involving coinage metal nanomaterials. Chapter 2 discusses the ligand-exchange of a gold-thiolate nanocluster synthesized in diglyme, while chapters 3-5 investigate a unique supramolecular assembly of coinage-metal thiolates using glymes as antisolvent. Chapter 3 explores the underlying makeup of these amorphous assemblies, while chapters 4 and 5 investigate the application of this supramolecular assembly for additive manufacturing applications and antimicrobial applications, respectively. All of these products are linked through the synthesis and characterization of nanomaterials, which require the use of glymes (1,2-dme, diglyme, triglyme, etc.) as a necessary synthetic solvent or antisolvent. Nanoclusters are small, atomically precise nanoparticles with a metal core and a passivating layer of organic ligands. Coinage metal nanoclusters are studied for their stability, especially gold nanoclusters, allowing for long-term studies of properties and applications, as well as post-synthetic modifications. Precise control over ligand shell composition, particularly of mixed ligand layers is desired for control over nanocluster functionality. Supramolecular materials build bulk properties through noncovalent interactions. Self-assembled supramolecular materials utilize small molecules which assemble into larger secondary and tertiary structures. These materials are of interest for a broad range of applications like additive manufacturing and biological applications. The motivation behind this work was to explore nanomaterials which results from a glyme based synthesis. Gold nanocluster synthesis in diglyme is found to produce a stable gold-thiolate nanocluster with a single glyme ligand. The precision of a single-unique ligand could lead to further enhancements in nanocluster functionality in the future. Addition of glyme to a coinage-metal thiolate solution results in the rapid precipitation of a rigid supramolecular assembly. The resultant metallogel exhibits properties unique from similar materials without the use of glyme in synthesis. The metallogel is composed of oligomers reminiscent of nanoparticle precursors; as such, metallogel-nanoparticle composites are readily synthesized.
Open Access
Implicit solvation using the superposition approximation applied to many-atom solvents with static geometry and electrostatic dipole
(Colorado State University. Libraries, 2020) Mattson, Max Atticus, author; Krummel, Amber T., advisor; McCullagh, Martin, advisor; Szamel, Grzegorz, committee member; Prieto, Amy, committee member; Krueger, David, committee member
Large-scale molecular aggregation of organic molecules, such as perylene diimides, is a phenomenon that continues to generate interest in the ﬁeld of solar light-harvesting. Functionalization of the molecules can lead to diﬀerent aggregate structures which in turn alter the spectroscopic properties of the molecules. To improve the next generation of perylene diimide solar cells a detailed understanding of their aggregation is necessary. A critical aid in understanding the spectroscopic properties of large-scale aggregating systems is molecular simulation. Thus development of an eﬃcient and accurate method for simulating large-scale aggregating systems at dilute concentrations is imperative. The Implicit Solvation Using the Superposition Approximation model (IS-SPA) was originally developed to eﬃciently model nonpolar solvent–solute interactions for chargeless solutes in TIP3P water, improving the eﬃciency of dilute molecular simulations by two orders of magnitude. In the work presented here, IS-SPA is developed for charged solutes in chloroform solvent. Chloroform is the ﬁrst solvent model developed for IS-SPA that is composed of more than one Lennard-Jones potential. Solvent distribution and force histograms were measured from all-atom explicit-solvent molecular dynamics simulations, instead of using analytic functions, and tested for Lennard-Jones sphere solutes of various sizes. The level of detail employed in describing the 3-dimensional structure of chloroform is tested by approximating chloroform as an ellipsoid, spheroid, and sphere by using 3-, 2-, and 1-dimensional distribution and force histograms respectively. A perylene diimide derivative, lumogen orange, was studied for its unfamiliar aggregation mechanism in chloroform and tetrahydrofuran solvents via Fourier-transform infrared and 2dimensional infrared spectroscopies as well as all-atom explicit-solvent molecular dynamics simulations and quantum mechanical frequency calculations. Molecular simulations identiﬁed two categories of likely aggregate dimer structures: the expected -stack structure, and a less familiar edge-sharing structure where the most highly charged atoms of the perylene diimide core are strongly interacting. Quantum mechanical vibrational frequency calculations were performed for various likely dimer aggregate structures identiﬁed in molecular simulation and compared to experimental spectroscopic results. The experimental spectra of the aggregating system share qualities with the edge-sharing dimer frequency calculations however larger aggregate structures should be tested. A violanthrone derivative, violanthrone-79 (V-79), was studied for its diﬀering aggregation mechanisms in chloroform and tetrahydrofuran solvents via Fourier-transform infrared and 2dimensional infrared spectroscopies as well as all-atom explicit-solvent molecular dynamics simulations and quantum mechanical frequency calculations. The -stacking aggregate structure of V-79 is supported by all methods used, however, the type of -stacking orientations are diﬀerent between the two solvents. Chloroform supports parallel -stacked aggregates while tetrahydrofuran supports anti-parallel -stacked aggregates which show diﬀering vibrational energy delocalization between the aggregated molecules. The publications in chapters 3 and 4 demonstrate the power of combining experimental spectroscopy and computational methods like molecular dynamics simulations and quantum mechanical frequency calculations, however, they also show how having larger simulations with multiple solute molecules are needed. This is why developing IS-SPA to be used for these simulations is necessary. Further developments to IS-SPA are discussed regarding the importance of various symmetries of chloroform and the subsequent dimensionalities of the histograms used to describe its distribution and Lennard-Jones force. Two methods for describing the Coulombic forces of chloroform solvation are discussed and tested on oppositely charged Lennard-Jones sphere solutes. The radially symmetric treatment fails to capture the Coulombic forces of the spherical solute system from all-atom explicit-solvent molecular dynamics simulations. A dipole polarization treatment is presented and tested for the charged spherical solute system which better captures the Coulombic forces measured from all-atom explicit-solvent molecular dynamics simulations. Additional considerations for the improvement of IS-SPA and the developments in this work are presented. The dipole polarization approximation outlined in chapter 5 assumes that each chloroform is a static dipole, allowing the dipole magnitude to ﬂuctuate as well as polarize is a more physically rigorous approximation that will likely improve the accuracy of Coulombic forces in IS-SPA. A novel method, drawn from the knowledge gained studying chloroform, for the eﬃcient modeling of new solvent types including ﬂexible solvent molecules in IS-SPA is discussed.
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 member
The 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.
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 member
Aerosol-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.
Open Access
Metal organic frameworks as heterogenous nitric oxide catalysts for use in the development of therapeutic polymer materials
(Colorado State University. Libraries, 2014) Harding, Jacqueline L., author; Reynolds, Melissa, advisor; Prieto, Amy, committee member; Crans, Debbie, committee member; Bailey, Travis, committee member; Worley, Deanna, committee member
Implantable polymeric medical devices are subject to surface biofouling due to the deposition of microbial agents and the accumulation of proteins at the material interface. Consequently, medical devices which are intended for beneficial functions can become a potentially fatal threat. As a result biofouling resistant materials are vigorously sought through the manipulation of material surface properties and by eluting therapeutics on the material surface. Nitric oxide (NO) is a bioactive agent generated by most nucleated cells in the human body and is known to mediate antimicrobial and antithrombus effects while maintain the capacity to promote the proliferation of healthy tissues. As such, the development of NO releasing biomaterials is known to reduce incidences of surface biofouling. However, current NO releasing materials are limited to short lifetimes of used based on limited capacity of exogenous NO which can be incorporated into the material. In order to circumvent this problem the goal of this research is to develop a biomaterial which generates NO from an endogenously supplied source. Metal organic frameworks (MOFs) were selected for investigation as heterogeneous catalysts for the generation of NO from bioavailable NO donors, S-nitrosothiols (RSNOS). MOFs were evaluated as NO catalysts based on their capacity to react with various RSNO substrates and their maintained structural integrity under reaction conditions. Presented herein is the successful demonstration of a Cu-MOF for the catalytic generation of NO from bioavailable RSNOs donors. However, the limited stability of this proof of principle MOF in aqueous solution prompted the development of a MOF-NO catalyst that is suitable for physiological applications through tuning the organic ligands used in the construction of the framework. Finally a two-fold demonstration of the feasibility towards designing composite MOF based biomaterials is presented as blended materials prepared via commercial manufacturing processes and via surface growth of MOFs on flexible polymeric substrates.
Open Access
Optically detected ion insertion dynamics in hexagonal tungsten oxide
(Colorado State University. Libraries, 2021) Evans, R. Colby, author; Sambur, Justin Barret, advisor; Prieto, Amy, committee member; Levinger, Nancy, committee member; Weinberger, Christopher R., committee member
Nanoparticle electrodes are attractive for electrochemical energy storage applications because their nanoscale dimensions decrease ion transport distances and generally increase ion insertion/extraction efficiency. However, nanoparticles vary in size, shape, defect density, and surface composition, which impacts charge storage dynamics and warrants their investigation at the single-nanoparticle level. This dissertation demonstrates a non-destructive, high-throughput electro-optical imaging approach to quantitatively measure electrochemical ion insertion reactions at the single-nanoparticle level. Electro-optical measurements relate the optical density change of a nanoparticle to redox changes of its redox-active elements under working electrochemical conditions. The technique was benchmarked by studying Li-ion insertion in hexagonal tungsten oxide (h-WO3) nanorods. Interestingly, the optically detected response revealed underlying processes that are hidden in conventional electrochemical measurements. This imaging technique may be applied to h-WO3 particles as small as 13 nm in diameter and a wide range of electrochemical materials such as electrochromic smart windows, batteries, solid oxide fuel cells, and sensors. This dissertation will focus on the impact of single particle h-WO3 on smart windows and batteries. Smart windows are devices used to modulate solar radiation into buildings and rely on the same ion insertion reaction as batteries. Electro-optical imaging showed that single nanorods exhibit a particle-dependent waiting time for optical changes (from 100 ms to 10 s) due to Li-ion insertion at optically inactive surface sites. Additionally, longer nanorods have larger optical modulation at equivalent electrochemical conditions than shorter nanorods and exhibit a Li-ion gradient that increases from the nanorod ends to the middle. The particle-dependent ion-insertion kinetics contribute to variable rate for optical density change and magnitudes across large-area smart windows. Single particles modulate optical density (undergo ion insertion reactions) 4 times faster and 20 times more reversibly than thin films made of the same particles. A smart window device architecture is proposed to maximize lifetime based on these findings. More information can be found in CHAPTER 4. Further, the role of crystalline surface facets on the role of ion insertion were investigated. Two samples of h-WO3 were synthesized with different ratios of surface facets exposed to a Li-ion containing electrolyte. The sample with unique {120} facets exhibited reversible optical switching after 500 cycles and negligible variation in interfacial charge transfer resistance. The (120) surface features an open network of square window channels that may enable reversible ion transport and reduced ion trapping, enhancing the optical switching stability. However, the {120}-dominant sample exhibited lower coloration efficiency (CE) than the {100}-dominant sample. The reduced optical density changes in the {120}-dominant sample could be due to a greater fraction of optically inactive trigonal cavity sites on the {001} endcaps. The results indicate surface facet and particle morphology engineering are viable strategies to enhance the CE and long-term stability/lifetime in electrochromic thin films for smart window applications. More information can be found in CHAPTER 5. On average, these h-WO3 particles exhibit a hybrid charge storage mechanism: both diffusion-limited (battery-like, slower) and pseudocapacitive (capacitor-like, faster) mechanisms contribute to the total charge stored. Individual particles exhibit different charge storage mechanisms at the same applied potential. Longer nanorods store more pseudocapacitive charge than shorter nanorods, presumably due to 1) a surface step edge gradient that exposes large hexagonal window Li-ion binding sites along the nanorod length and/or 2) higher structural water content that influences the Li-ion binding energetics and diffusion behavior. Importantly, penetration depth of Li-ion insertion was quantified which showed that Li ions insert as deep as two-unit cells below the surface. The methodology presented herein can be applied to a wide range of solid-state ion-insertion materials and its implications for future discoveries are discussed. More information can be found in CHAPTER 6.
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 member
To view the abstract, please see the full text of the document.
Open Access
Polymerization catalysis for the precision synthesis of chiral and sustainable polymers
(Colorado State University. Libraries, 2011) Miyake, Garret M., author; Chen, Eugene, advisor; Bailey, Travis, committee member; Prieto, Amy, committee member; Strauss, Steven, committee member; Wang, David, committee member
Polymerization catalysis for the precision synthesis of chiral and sustainable polymers is described in this dissertation. The central theme of chiral polymers has revolved around the employment of newly synthesized enantiomeric zirconocenium ester enolate catalysts. These catalysts have been utilized in the asymmetric coordination polymerization of prochiral functionalized vinyl monomers towards optically-active, solution stable, one-handed helical polymers. These enantiomeric catalysts have also been used in the successful kinetic resolution polymerization of a racemic methacrylamide monomer. The stereospecific polymerization of chiral oxazolidinone functionalized alkenes has been performed, producing highly isotactic polymers that assume helical or random-coil secondary conformations, dictated by the proximity of the chiral oxazolidinone to the main-chain of the polymer. Investigating applications of helical polymers, two pseudo-enantiomeric helical poly(phenyl acetylene)s bearing chiral organocatalyst side-groups have been synthesized and the effects of the helix-sense and helicity on the enantioselectivity of these catalysts was subsequently examined. Towards sustainable polymers, renewable butyrolactone-based vinylidene monomers are of particular interest in exploring the prospects of substituting the petroleum-based methacrylate monomers for specialty chemicals production. The polymerization of such monomers by group III and IV transition metal catalysts has been investigated resulting in the synthesis of sustainable polymers with controlled molecular weights. These butyrolactone-based monomers have also been successfully polymerized in a rapid and living fashion, using ambiphilic silicon propagating species.
Open Access
Probing buried defects in zinc oxide nanoparticles using defect-mediated energy transfer
(Colorado State University. Libraries, 2019) Beck, Lacey, author; Sambur, Justin, advisor; Prieto, Amy, committee member; Bartels, Randy, committee member
Semiconductor nanocrystals are actively explored as light harvesting materials for solar energy conversion and optoelectronic applications such as solar cells and light emitting diodes. The underlying processes in such systems include charge carrier generation, recombination, and transport. Defects influence these underlying processes by introducing energy levels inside the semiconductor bandgap that trap charge carriers. Despite their critical importance, the real space distribution of defect sites in semiconductor nanocrystals is often unknown. Here we demonstrate an ensemble-level energy transfer measurement approach to study the radiative defect states in a size series of ZnO nanocrystals. In this approach, ZnO defects that have energy levels inside the band gap engage in energy transfer with surface adsorbed AlexaFluor dye molecule acceptors. By quantifying the defect-mediated energy transfer efficiency as a function of nanocrystal size and reaction time, we determined that the radiative defect sites in ZnO are located between the nanocrystal core and surface (i.e., near surface sites) and the distance between the defect sites and the surface increases as the nanocrystals grow larger. The all-optical energy transfer approach represents a non-destructive characterization method to determine the spatial distribution of defects in semiconductor nanocrystals. The defect distributions can be correlated with optoelectronic or photocatalytic properties to elucidate structure/function relationships in a wide range of applications that involve light-matter interactions.