Mountain Scholar :: Browsing by Author "Szamel, Grzegorz, committee member"

Browsing by Author "Szamel, Grzegorz, committee member"

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Open Access
A study of structural organizations in amorphous oxide thin films for low mechanical loss mirror coatings in interferometric gravitational wave detectors
(Colorado State University. Libraries, 2021) Yang, Le, author; Menoni, Carmen S., advisor; Chung, Jean K., committee member; Szamel, Grzegorz, committee member; Bradley, Mark R., committee member
Amorphous thin films prepared from vapor deposition are nonequilibrium solids with structures dependent on their physical parameters, such as composition, and method of preparation. The macroscopic properties of an amorphous material are fundamentally connected to the atomic configuration at the microscopic level. Two-level systems, conceptualized as two adjacent potential wells in the potential energy landscape, are due to intrinsic atomic disorder in amorphous materials. When coupled with an elastic field, the configuration change between the two wells creates a dissipation of mechanical energy that manifests itself as the mechanical loss angle. The mechanical loss of the thin films composing the high reflectivity mirror coating has become the dominant noise source limiting further performance improvements for the next generation gravitational wave detectors. The study presented here comprises investigations of key structural organizations that correlate with the room temperature mechanical loss in vapor-deposited amorphous oxide thin films. In theory, manipulations of substrate temperature or use of assist ion bombardment that transfers energy to the film surface are capable of introducing structural changes during the highly dynamic transition of sputtered particles from the vapor to the solids phase. Tuning the composition by doping or nanolayering is also effective at altering the atomic structure of the amorphous materials. Herein, we discuss in detail the findings from each work. In work on Ta2O5, the effects of low energy assist ion bombardment on the mechanical loss of amorphous thin films are presented. Bombarding ions of Ar+, Xe+, and O2+ of different energy and different dose are directed to the thin films' surface during growth. Negligible influence is found from the assist ion bombardment on the atomic structure and mechanical loss of the Ta2O5 thin films. Based on an analysis of surface diffusivity, it is suggested that the dominant deposition of Ta2O2 cluster might be responsible for the unaltered mechanical loss for Ta2O5 thin films. The parameter space explored within the experimental setup is not capable of affecting the atomic arrangements. It has been proposed that modifiers such as dopants and nanolayers incorporated into the Ta2O5 matrix alter the atomic network in a beneficial way. Two systems of SiO2/Ta2O5 and TiO2/Ta2O5 in both mixture and nanolaminate forms are investigated. For the nanolaminates, it is demonstrated that thermal treatment results in a morphological change that involves layer breakup and mixture formation at the interface in the TiO2/Ta2O5 nanolaminate. Similarly, a stable mixed phase is only formed in the TiO2/Ta2O5 mixture after annealing. The formation of a mixture is suggested to be the key to the lower mechanical loss of the TiO2/Ta2O5 in contrast to the SiO2/Ta2O5 system. The two-level systems are essentially modified when the system con- figures itself in a thermodynamically more stable state. Combined with results from the atomic modeling using molecular dynamics of TiO2/Ta2O5, it is then proposed that the medium-range order in these oxides is key to lowering the room temperature mechanical loss. A direct evaluation of the modifications at the medium-range order is obtained from work on amorphous GeO2 thin films. GeO2 with a maximized degree of medium-range order is investigated with elevated temperature deposition. It is demonstrated that the medium-range or- der of amorphous GeO2, characterized by GeO4 tetrahedra connected in rings of various sizes, evolves into a more ordered configuration at elevated temperatures. A systematic decrease in mechanical loss is associated with the increase in medium-range order for the GeO2 thin films. We conclusively show that an improved packing at medium range is linked to the low mechanical loss for the amorphous oxide thin films. Furthermore, engineering of GeO2 to achieve a high refractive index is carried out by the incorporation of TiO2. We identified the optimal cation concentration Ti/(Ge+Ti) around 44%, which provides both low mechanical loss and low absorption loss for the mixture to be used in the multilayer stack. The designed high reflector multilayer is calculated to have the Brownian thermal noise near the target for next-generation Advanced LIGO. In combination, the results described in this dissertation have identified key structural organizations that affect the room temperature mechanical loss of amorphous oxide thin films. The evolution in the connecting rings of metal-centered oxygen polyhedra in these thin films is essential to altering the medium-range order in the atomic network. Such modifications could be achieved with the formation of a thermodynamically more stable phase, elevated deposition temperature, or post-deposition thermal treatment. Future work to identify the microscopic origin of low-temperature mechanical loss is envisioned for a thorough understanding of the two-level systems present in the amorphous oxides.
Open Access
Accessing molecular structure and dynamics of photoelectrochemical systems with nonlinear optical spectroscopy
(Colorado State University. Libraries, 2022) Farah, Yusef Rodney, author; Krummel, Amber T., advisor; Szamel, Grzegorz, committee member; Barisas, B. George, committee member; Bartels, Randy, committee member
Photoelectrochemical cells (PEC) are a class of solar energy device that have a variety of applications and can be used to directly generate electricity or convert the sun's energy in the form of chemical bonds through photosynthetic processes. The first PEC dates to Becquerel's discovery of the photovoltaic effect in 1839; and, after nearly 200 years of its first creation, the PEC is constantly evolving with the discovery of new fabrication techniques and materials. Sunlight harvesting materials are used in PECs to capture the sun's radiation and drive electron transfer and photocatalytic reactions. Understanding the photophysical properties of the materials used within PEC chemical systems informs on the development of high-performance, low-cost, and sustainable solar energy devices needed to address current global climate challenges and meet societal energy demands. Chemical systems in PEC architectures are nontrivial and often rely on several components working harmoniously in tandem with one another to stimulate photovoltaic or photocatalytic processes. Dye-sensitized solar cells (DSSCs) are a type of photovoltaic PEC that use molecular chromophores to absorb light, transfer electrons to a semiconductor, and accept electrons from an electrolyte. Local environmental structure of the chromophore can either promote or hinder these electron transfer events within a device. To this end, investigating the molecular structure of the chromophore, including the parameters that influence the structure, is necessary for fabricating DSSCs with optimal efficiency. The work presented in this dissertation utilizes the nonlinear optical spectroscopic technique of heterodyne-detected vibrational sum frequency generation (HD-VSFG) to investigate the interfacial structure of N3-dye, a popular chromophore used within DSSC devices. It is discovered that the interfacial structure of N3 is influenced by the substrate, pH conditions upon deposition to the substrate, and by the presence of an electrolyte. Additionally, the work presented herein investigates exciton dynamics of monolayer MoS2 photoanodes within an operational PEC. Monolayer transition metal dichalcogenides (TMDs), such MoS2, are two-dimensional semiconducting materials with fascinating photophysical properties. Only recently have monolayer TMDs been investigated for their integration within optoelectronic devices, such as PECs. By utilizing ultrafast transient absorption (TA) spectroscopy, unique exciton properties of the MoS2 photoanode are identified within operational conditions. Photocurrent generation via ultrafast hot carrier extraction is discovered, challenging the preconceived notions of the Shockley-Queisser limit; further, we explore the dynamic control of the exciton energy by tuning an external voltage bias to the PEC. PEC chemical environments are ubiquitous and the photophysical properties are dependent on many underlying parameters. Set forth in this dissertation is the foundation for applying the nonlinear optical techniques of HD-VSFG and TA across a variety of chemical systems pertaining to PECs and assessing data within an established theoretical framework to elucidate molecular structure and dynamics.
Open Access
Asperparaline A: biosynthetic studies and synthetic efforts
(Colorado State University. Libraries, 2008) Gray, Chandele Ramsey, author; Williams, Robert M., advisor; Kennan, Alan, committee member; Szamel, Grzegorz, committee member; Parkinson, Bruce, committee member; Brennan, Patrick, committee member
Asperparaline A, a fungal metabolite isolated from Aspergillus japonicus, is of interest due to anthelmintic activity and structural similarities to the paraherquamides and brevianamides owing to the presence of bicyclo [2.2.2] diazaoctane core proposed to be derived from a biosynthetic [4+2] cycloaddition. This communication details two aspects of research regarding asperparaline A. The first goal involves the elucidation of asperparaline A as being biosynthetically composed of dimethylallylpyrophosphate and the amino acids, tryptophan and L-isoleucine, analogous to the paraherquamides. The second goal addresses the desire to develop synthetic methodology amenable to the introduction of isotopic labels for further biosynthetic studies. The proposed retrosyntheses envision the spiro-succinimide ring of asperparaline A being introduced by the photooxidation of a suitably oxidized pyrrole ring. Synthetic approaches toward asperparaline A presented include peptide coupling of β-methylproline with a prenylated pyrolylalanine, and Horner-Wadsworth-Emmons olefination of a diketopiperazine phosphonate with various aldehydes designed to allow for late stage pyrrole synthesis.
Open Access
Design and application of strongly reducing photoredox catalysts for small molecule and macromolecular synthesis
(Colorado State University. Libraries, 2019) Pearson, Ryan Michael, author; Miyake, Garret, advisor; McNally, Andy, committee member; Szamel, Grzegorz, committee member; Li, Yan Vivian, committee member
The synthesis and application of new families of strongly reducing organic photoredox catalysts are described in this dissertation. These compounds provide a platform on which catalytically relevant properties including redox potentials and absorption profiles can be tuned, as well as predicted in silico. The critical photophysical and electrochemical characteristics have been established for both dihydrophenazine and phenoxazine catalysts which enable their ability to be used as green alternatives to commonly used transition metal photocatalysts. Specifically, phenoxazines have been utilized to mediate organocatalyzed atom transfer radical polymerization (O-ATRP) for the production of well-defined polymers using visible light. To this end, a catalyst system able to synthesize acrylic polymers with predictable molecular weights and dispersities less than 1.10 has been developed. In addition, dihydrophenazines were shown to mediate trifluoromethylation and atom transfer radical addition reactions, while phenoxazines were able to mediate C-N and C-S cross coupling reactions in the presence of a nickel co-catalyst.
Open Access
Disentangle model differences and fluctuation effects in DPD simulations of diblock copolymers
(Colorado State University. Libraries, 2013) Sandhu, Paramvir, author; Wang, Qiang (David), advisor; Bailey, Travis S., committee member; Szamel, Grzegorz, committee member
In the widely used dissipative particle dynamics (DPD) simulations 1, polymers are commonly modeled as discrete Gaussian chains interacting with soft, finite-range repulsions. In the original DPD simulations of microphase separation of diblock copolymer melts by Groot and Madden 2 , the simulation results were compared and found to be consistent with the phase diagram for the "standard model" of continuous Gaussian chains with Dirac δ-function interactions obtained from self-consistent field (SCF) calculations. Since SCF theory is a mean-field theory neglecting system fluctuations/correlations while DPD simulations fully incorporate such effects, the model differences are mixed with the fluctuation/correlation effects in their comparison. Here we report the SCF phase diagram for exactly the same model system as used in DPD simulations. Comparing our phase diagram with that for the standard model highlights the effects of chain discretization and finite-range interactions, while comparing our phase diagram with DPD simulation results unambiguously (without any parameter-fitting) reveal the effects of system fluctuations/correlations neglected in the SCF theory.
Open Access
Enhanced surface functionality via plasma modification and plasma deposition techniques to create more biologically relevant materials
(Colorado State University. Libraries, 2013) Shearer, Jeffrey C., author; Fisher, Ellen R., advisor; Henry, Charles, committee member; Szamel, Grzegorz, committee member; Bailey, Travis, committee member; Buchanan, Kristen, committee member
Functionalizing nanoparticles and other unusually shaped substrates to create more biologically relevant materials has become central to a wide range of research programs. One of the primary challenges in this field is creating highly functionalized surfaces without modifying the underlying bulk material. Traditional wet chemistry techniques utilize thin film depositions to functionalize nanomaterials with oxygen and nitrogen containing functional groups, such as -OH and -NHx. These functional groups can serve to create surfaces that are amenable to cell adhesion or can act as reactive groups for further attachment of larger structures, such as macromolecules or antiviral agents. Additional layers, such as SiO2, are often added between the nanomaterial and the functionalized coating to act as a barrier films, adhesion layers, and to increase overall hydrophilicity. However, some wet chemistry techniques can damage the bulk material during processing. This dissertation examines the use of plasma processing as an alternative method for producing these highly functionalized surfaces on nanoparticles and polymeric scaffolds through the use of plasma modification and plasma enhanced chemical vapor deposition techniques. Specifically, this dissertation will focus on (1) plasma deposition of SiO2 barrier films on nanoparticle substrates; (2) surface functionalization of amine and alcohol groups through (a) plasma co-polymerization and (b) plasma modification; and (3) the design and construction of plasma hardware to facilitate plasma processing of nanoparticles and polymeric scaffolds. The body of work presented herein first examines the fabrication of composite nanoparticles by plasma processing. SiOxCy and hexylamine films were coated onto TiO2 nanoparticles to demonstrate enhanced water dispersion properties. Continuous wave and pulsed allyl alcohol plasmas were used to produce highly functionalized Fe2O3 supported nanoparticles. Specifically, film composition was correlated to gas-phase excited state species and the pulsing duty cycle to better understand the mechanisms of allyl alcohol deposition in our plasma systems. While these studies specifically examined supported nanoparticle substrates, some applications might require the complete functionalization of the entire nanoparticle surface. To overcome this challenge, a rotating drum plasma reactor was designed as a method for functionalizing the surface of individual Fe2O3 nanoparticles. Specifically, data show how the rotating motion of the reactor is beneficial for increasing the alcohol surface functionality of the nanoparticles when treated with pulsed allyl alcohol plasmas. Plasma copolymerization was used to deposit films rich in both oxygen and nitrogen containing functional groups using allyl alcohol and allyl amine plasma systems. Functional group retention and surface wettability was maximized under pulsed plasma conditions, and films produced under pulsed plasma conditions did not exhibit hydrophobic recovery or experience loss of nitrogen as the films aged. Plasma surface modification with N2/H2O and NH3/H2O, and plasma deposition with allyl alcohol and allyl amine, were used to increase the wettability of poly(caprolactone) scaffolds while simultaneously implanting functional groups onto the scaffold surface and into the scaffold core. While plasma deposition methods did not modify the internal core of the scaffold as much as modification methods, it afforded the ability to have higher water absorption rates after a three week aging period. Additionally, cell viability studies were conducted with N2/H2O plasma treated scaffolds and showed enhanced cell growth on plasma treated scaffolds over non plasma-treated scaffolds.
Open Access
Fast off-lattice Monte Carlo simulations of phase transitions in block copolymers and liquid crystals
(Colorado State University. Libraries, 2015) Zong, Jing, author; Wang, Qiang, advisor; Bailey, Travis S., committee member; Szamel, Grzegorz, committee member; Watson, A. Ted, committee member
The basic idea of the so-called fast off-lattice Monte Carlo (FOMC) simulations is to perform particle-based Monte Carlo (MC) simulations in continuum with the excluded-volume interactions modeled by soft repulsive potentials that allow particle complete overlapping, where using soft potentials naturally arises from the application of coarse-grained models. This method is particularly suitable for the study of equilibrium properties of soft matter. One apparent advantage of FOMC is that using soft potentials can greatly improve the sampling efficiency in the simulations. Another advantage is that FOMC simulations can be performed in any statistical ensemble, and all the advanced off-lattice MC techniques proposed to date can be readily applied to further improve the sampling efficiency. Moreover, it provides a powerful methodology to directly compare theoretical results with simulation results without any parameter fitting. Last but not least, using FOMC is the only way to study experimentally accessible fluctuation/correlation effects in many-chain systems. This work makes use of FOMC simulations to study phase transitions in block copolymers and liquid crystals. To compare with the simulations results, various theoretical methods are also applied in the research. Chapter 2 is devoted to study the classic yet unsolved problem of fluctuation/correlation effects on the order-disorder transition (ODT) of symmetric diblock copolymer (DBC). In Chapter 3, we highlight the importance of quantitative and parameter-fitting-free comparisons among different models/methods. In Chapter 4, we investigate the effect of system compressibility on the ODT of DBC melts. In Chapter 5, we extend FOMC simulations to study the isotropic-nematic transition of liquid crystals. Finally, in Chapter 6, we briefly summarize all the studies in this dissertation and give some directions to future work.
Open Access
Fluorine-containing fullerenes and endometallofullerenes: synthesis, structure, and spectroscopic characterization
(Colorado State University. Libraries, 2010) Shustova, Natalia Borisovna, author; Strauss, Steven H., advisor; Anderson, Oren P., committee member; Szamel, Grzegorz, committee member; Elliott, Cecil Michael, committee member; Roess, Deborah A., committee member
Many new members of a relatively new class of exohedral fullerene derivatives with fluorine-containing electron-withdrawing groups have been prepared and studied by spectroscopic methods and X-ray crystallography. The fluorination and/or perfluoroalkylation reactions were performed with C60, C70, the higher hollow fullerenes C60+m (m = 14, 16, 18, 20, and 22), the endohedral metallofullerene Sc3N@C80-Ih(7), and the azafullerene dimer (C59N)2. Several efficient synthetic methods have been developed for perfluoroalkylation, which involved high-temperature reactions with AgCF3CO2 and with thermally or photochemically activated reactions with RFI reagents (RF = CF3, C2F5, n-C3F7, i-C3F7, n-C4F9, and n-C6F13). Structural studies of the C60(RF)n and C70(RF)n products demonstrated that variation of the size and structure of the RF radical led to the formation of derivatives with unprecedented addition patterns and hence unprecedented properties. Many of these derivatives were shown to have superior electron-accepting properties. Trifluoromethylation of a sample of insoluble hollow higher fullerenes resulted in the structural characterization of several new dodecakis(trifluoromethyl) fullerene compounds, and this led to the first experimental observation of fullerenes C74-D3h and C78-D3h(5). In the case of trifluoromethylation of (C59N)2, a strong effect of the heteroatom on the addition patterns of the products was discovered. The first X-ray crystal structure of a single regioisomer of C59N(CF3)5, as well as spectroscopic studies of C59N(CF3)7,9,11, revealed unexpected addition patterns which resemble that of Cs-C60X6 derivatives. The isolation and characterization of seventeen Sc3N@(C80-Ih)(CF3)n (even n = 2-16) compounds, including the X-ray structures of Sc3N@(C80-Ih(7))(CF3)10, Sc3N@(C80-Ih(7))(CF3)12, Sc3N@(C80-Ih(7))(CF3)14, and Sc3N@(C80-Ih(7))(CF3)16, have demonstrated for the first time a strong mutual effect of (i) the presence of the Sc3N cluster on the addition pattern and (ii) the addition pattern on the position of and structure of the Sc3N cluster.
Open Access
Hyperpolarized and thermally polarized quadrupolar noble gas nuclei studied by nuclear magnetic resonance spectroscopy and magnetic resonance imaging
(Colorado State University. Libraries, 2010) Stupic, Karl Francis, author; Meersmann, Thomas, advisor; Fisher, Ellen R., committee member; Szamel, Grzegorz, committee member; Prieto, Amy L. (Amy Lucia), committee member; Roberts, Jacob Lyman, committee member
This dissertation consists of several studies of two quadrupolar nuclei, 83Kr and 131Xe, with nuclear spin states of I = 9/2 and I = 3/2, respectively. These nuclei possess a nuclear electric quadrupole moment that strongly interacts with the surrounding electric field gradient (EFG). The quadrupolar interactions in these noble gas atoms dominate the longitudinal (T1) spin relaxation. To fully study these nuclei, high non-equilibrium nuclear spin polarization, referred to as hyperpolarization (hp), is generated using spin exchange optical pumping (SEOP). By employing this technique, enhanced nuclear magnetic resonance (NMR) signals many orders of magnitude above that of a thermally polarized (Boltzmann distribution of spin states) sample are possible and allow for experiments where signal averaging over long periods of time is prohibited (i.e. in vivo). The gas phase 83Kr T1 is shown to be sensitive to the surface composition/chemistry and the surface-to-volume ratio in an ideal system of closest packed glass beads. Understanding the behavior of 83Kr in these conditions allows for its development as a surface sensitive probe that could provide information in opaque porous media environments. Similar relaxation behavior can be observed in 131Xe; however, the quadrupolar interactions experienced by 131Xe also induce an observable splitting in the NMR spectrum. This quadrupolar splitting is extremely sensitive to surfaces during periods of adsorption as well as to the magnetic field strength when a 131Xe atom is present in the bulk gas phase. As the influence on the quadrupolar splitting can be more readily observed than the relaxation of either 83Kr or 131Xe, the observed splitting in 131Xe NMR can provide helpful insights into quadrupolar behavior experienced by both nuclei. To develop a better understanding of the quadrupolar behavior, both 131Xe quadrupolar splitting and 83Kr relaxation are explored as functions of magnetic field strength, gas phase composition and co-adsorbing species. In closing, improvements in polarization of 83Kr from line-narrowed diode array lasers as well as new delivery techniques have provided improvements that allow for the implementation of variable flip angle FLASH imaging sequence in an excised, intact rat lung. Additionally, initial evidence suggests the T1 of 83Kr can differentiate between the regions of the lung (the trachea, the bronchi and bronchioles, and the alveoli), which has potential as a diagnostic tool for the biomedical community. Improvements in signal intensity are needed to achieve in vivo studies, additional enhancements are possible through improved SEOP and by using isotopically enriched gases.
Open Access
I. Cognitive and instructional factors relating to students' development of personal models of chemical systems in the general chemistry laboratory. II. Solvation in supercritical carbon dioxide/ethanol mixtures studied by molecular dynamics simulation
(Colorado State University. Libraries, 2014) Anthony, Seth, author; Rickey, Dawn, advisor; Ladanyi, Branka M., advisor; Szamel, Grzegorz, committee member; Prieto, Amy L., committee member; DeLosh, Edward L., committee member
Part I. Students' participation in inquiry-based chemistry laboratory curricula, and, in particular, engagement with key thinking processes in conjunction with these experiences, is linked with success at the difficult task of "transfer" - applying their knowledge in new contexts to solve unfamiliar types of problems. We investigate factors related to classroom experiences, student metacognition, and instructor feedback that may affect students' engagement in key aspects of the Model-Observe-Reflect-Explain (MORE) laboratory curriculum - production of written molecular-level models of chemical systems, describing changes to those models, and supporting those changes with reference to experimental evidence - and related behaviors. Participation in introductory activities that emphasize reviewing and critiquing of sample models and peers' models are associated with improvement in several of these key aspects. When students' self-assessments of the quality of aspects of their models are solicited, students are generally overconfident in the quality of their models, but these self-ratings are also sensitive to the strictness of grades assigned by their instructor. Furthermore, students who produce higher-quality models are also more accurate in their self-assessments, suggesting the importance of self-evaluation as part of the model-writing process. While the written feedback delivered by instructors did not have significant impacts on student model quality or self-assessments, students' resubmissions of models were significantly improved when students received "reflective" feedback prompting them to self-evaluate the quality of their models. Analysis of several case studies indicates that the content and extent of molecular-level ideas expressed in students' models are linked with the depth of discussion and content of discussion that occurred during the laboratory period, with ideas developed or personally committed to by students during the laboratory period being likely to appear in students' post-laboratory refined models. These discussions during the laboratory period are primarily prompted by factors external to the students or their laboratory groups such as questions posed by the instructor or laboratory materials. Part II. Solvation of polar molecules within non-polar supercritical carbon dioxide is often facilitated by the introduction of polar cosolvents as entrainers, which are believed to preferentially surround solute molecules. Molecular dynamics simulations of supercritical carbon dioxide/ethanol mixtures reveal that ethanol molecules form hydrogen-bonded aggregates of varying sizes and structures, with cyclic tetramers and pentamers being unusually prevalent. The dynamics of ethanol molecules within these mixtures at a range of thermodynamic conditions can largely be explained by differences in size and structure in these aggregates. Simulations that include solute molecules reveal enhancement of the polar cosolvent around hydrogen-bonding sites on the solute molecules, corroborating and helping to explain previously reported experimental trends in solute mobility.
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
Investigating the biosynthetic mechanisms of the brevianamides & penicimutamides through the total synthesis of secondary metabolites
(Colorado State University. Libraries, 2020) McCauley, Morgan Taylor, author; Bandar, Jeff, advisor; Kennan, Alan, committee member; Szamel, Grzegorz, committee member; Slayden, Richard, committee member
The class of prenylated indole alkaloids containing a bicyclo[2.2.2]diazaoctane ring system consists of secondary metabolites isolated from fungal genera that possess diverse biological activities. Recent findings have established three ways in which the bicyclic core in this class can be constructed: (1) Generation of the monoxopiperazines (malbrancheamides and related families) by an NADPH-dependent bi-functional reductase/Diels-Alderase; (2) An enantiodivergent generation of the dioxopiperazines by some cytochrome P450 creation of achiral azadienes and successive enzyme-mediated stereoselective intramolecular hetero-Diels-Alder (IMDA) reaction in the notoamide/stephacidin families; and (3): non-Diels-Alderase generation of the bicycle of the brevianamides directed by a novel cofactor-independent pinacolase, culminating in a spontaneous IMDA reaction. The goal of the current work was to employ total synthesis to assist with the full characterization of unknown metabolites and decipher biochemical mechanisms employed in fungal organisms. Through this, the first total synthesis of brevianamide X and penicimutamide E, along with the synthesis of brevianamide A, and an improved, enantioselective synthesis of brevianamide Y were completed. The details of the novel synthetic work carried out by the author can be found in Chapters 3 and 5. Further synthetic efforts to better understand and access a variety of natural products are in progress to decipher the intrinsic transformations organism found in nature harness.
Open Access
Low-temperature oxidizing plasma surface modification and composite polymer thin-film fabrication techniques for tailoring the composition and behavior of polymer surfaces
(Colorado State University. Libraries, 2014) Tompkins, Brendan D., author; Fisher, Ellen R., advisor; Henry, Charles S., committee member; Bailey, Travis S., committee member; Szamel, Grzegorz, committee member; James, Susan P., committee member
This dissertation examines methods for modifying the composition and behavior of polymer material surfaces. This is accomplished using (1) low-temperature low-density oxidizing plasmas to etch and implant new functionality on polymers, and (2) plasma enhanced chemical vapor deposition (PECVD) techniques to fabricate composite polymer materials. Emphases are placed on the structure of modified polymer surfaces, the evolution of polymer surfaces after treatment, and the species responsible for modifying polymers during plasma processing. H2O vapor plasma modification of high-density polyethylene (HDPE), low-density polyethylene (LDPE), polypropylene (PP), polystyrene (PS), polycarbonate (PC), and 75A polyurethane (PU) was examined to further our understanding of polymer surface reorganization leading to hydrophobic recovery. Water contact angles (wCA) measurements showed that PP and PS were the most susceptible to hydrophobic recovery, while PC and HDPE were the most stable. X-ray photoelectron spectroscopy (XPS) revealed a significant quantity of polar functional groups on the surface of all treated polymer samples. Shifts in the C1s binding energies (BE) with sample age were measured on PP and PS, revealing that surface reorganization was responsible for hydrophobic recovery on these materials. Differential scanning calorimetry (DSC) was used to rule out the intrinsic thermal properties as the cause of reorganization and hydrophobic recovery on HDPE, LDPE, and PP. The different contributions that polymer cross-linking and chain scission mechanisms make to polymer aging effects are considered. The H2O plasma treatment technique was extended to the modification of 0.2 µm and 3.0 µm track-etched polycarbonate (PC-TE) and track-etched polyethylene terephthalate (PET-TE) membranes with the goal of permanently increasing the hydrophilicity of the membrane surfaces. Contact angle measurements on freshly treated and aged samples confirmed the wettability of the membrane surfaces was significantly improved by plasma treatment. XPS and SEM analyses revealed increased oxygen incorporation onto the surface of the membranes, without any damage to the surface or pore structure. Contact angle measurements on a membrane treated in a stacked assembly suggest the plasma effectively modified the entire pore cross section. Plasma treatment also increased water flux through the membranes, with results from plasma modified membranes matching those from commercially available hydrophilic membranes (treated with wetting agent). Mechanisms for the observed modification are discussed in terms of OH and O radicals implanting oxygen functionality into the polymers. Oxidizing plasma systems (O2, CO2, H2O vapor, and formic acid vapor) were used to modify track-etched polycarbonate membranes and explore the mechanisms and species responsible for etching polycarbonate during plasma processing. Etch rates were measured using scanning electron microscopy; modified polycarbonate surfaces were further characterized using x-ray photoelectron spectroscopy and water contact angles. Etch rates and surface characterization results were combined with optical emission spectroscopy data used to identify gas-phase species and their relative densities. Although the oxide functionalities implanted by each plasma system were similar, the H2O vapor and formic acid vapor plasmas yielded the lowest contact angles after treatment. The CO2, H2O vapor, and formic acid vapor plasma-modified surfaces were, however, found to be similarly stable one month after treatment. Overall, etch rate correlated directly to the relative gas-phase density of atomic oxygen and, to a lesser extent, hydroxyl radicals. PECVD of acetic acid vapor (CH3COOH) was used to deposit films on PC-TE and silicon wafer substrates. The CH3COOH films were characterized using XPS, wCA, and SEM. This modification technique resulted in continuous deposition and self-limiting deposition of a-CxOyHz films on Si wafers and PC-TE, respectively. The self-limiting deposition on PC-TE revealed that resulting films have minimal impact on 3D PC structures. This technique would allow for more precise fabrication of patterned or nano-textured PC. PECVD is used to synthesize hydrocarbon/fluorocarbon thin films with compositional gradients by continuously changing the ratio of gases in a C3F8/H2 plasma. The films are characterized using variable angle spectroscopic ellipsometry (VASE), Fourier transform infrared spectroscopy (FTIR), XPS, wCA, and SEM. These methods revealed that shifting spectroscopic signals can be used to characterize organization in the deposited film. Using these methods, along with gas-phase diagnostics, film chemistry and the underlying deposition mechanisms are elucidated, leading to a model that accurately predicts film thickness.
Open Access
Molecular dynamics simulations of peptide and protein systems
(Colorado State University. Libraries, 2021) Weber, Ryan Nicholas, author; McCullagh, Martin, advisor; Szamel, Grzegorz, committee member; Finke, Richard, committee member; Wang, Qiang, committee member
Molecular systems composed of amino acids play an important role in biological systems and have numerous functions and applications due to their enormous chemical versatility. These systems are usually divided into peptides and proteins based on the number of amino acids that compose each molecule. Molecular dynamics simulations can provide molecular-level insights into the self-assembly of peptide systems and the function of protein systems where experimental methods fail. Peptides are utilized for their switchable and self-assembling properties for the engineering of novel biomaterials which are responsive to external stimuli. Often, peptides are paired with aromatic molecules to incorporate interesting optoelectronic properties into the material. Chapter 2 discusses a molecular dynamics simulation study on the self-assembling properties of the self-complimentary (RXDX)4 sequence paired with an unnatural coumarin amino acid for the design of a pH-switchable, optoelectronic, self-assembling biomaterial. Specifically, it is found that the hydrophobicity of the peptide sequence plays a significant role in the stability and pH-switchability of (RXDX)4 and coumarin-(RXDX)4 β-sheet fibers. Proteins are essential to all known life and participate in nearly every cellular process. There are many varieties of proteins with important diverse functions. Helicase proteins hydrolyze NTP to catalyze the translocation and unwinding of double-stranded nucleic acids such as RNA and DNA and play a critical and extensive role in viral replication. Nsp13 is a helicase protein that is an important component of the viral replication machinery of the severe acute respiratory syndrome coronavirus-2 and remains a promising target for antiviral drugs. Chapter 3 presents a molecular dynamics simulation study on the ATP-dependent translocation mechanism of the SARS-CoV-2 nsp13 helicase. Specifically, the results from the study suggest that nsp13 may translocate using an inchworm stepping mechanism and that the binding of ATP may cause the first step in the translocation cycle. Motifs Ia, IV, and V are identified as key motifs in the translocation mechanism of nsp13 and as potential targets for the development of antiviral drugs against SARS-CoV-2. Although molecular dynamics simulation is a powerful approach to investigate condensed phase molecular phenomenon such as protein folding, allostery, and self-assembly, molecular dynamics is limited in the size and length of simulations that can be performed. Implicit solvent simulation methods, such as Implicit Solvation using the Superposition Approximation (IS-SPA), were developed to address these issues in solvated systems. The goal of IS-SPA is to improve the efficiency of molecular dynamics simulations by removing the solvent from the system, but still include the effect of the solvent on the solute. Chapter 4 presents the development and optimization of an IS-SPA molecular dynamics code on a GPU using CUDA. Specifically, the performance of three different IS-SPA CUDA algorithms are compared. The future studies of the self-assembly of peptide systems for the design of biomaterials, the ATP-dependent translocation mechanism of the SARS-CoV-2 nsp13, and the optimization of the GPU-capable IS-SPA molecular dynamics code in CUDA are discussed in the final chapter.
Embargo
Navigating the thermodynamic landscape in search of synthetic routes to ternary nitrides
(Colorado State University. Libraries, 2022) Rom, Christopher Linfield, author; Neilson, James R., advisor; Prieto, Amy L., advisor; Sambur, Justin, committee member; Szamel, Grzegorz, committee member; Buchanan, Kristen, committee member
Ternary nitride materials—a class of ceramics composed of two different metals bound with anionic nitrogen (N3-) as a solid—are underexplored because they are difficult to make. Nitrides rarely occur in nature, as the oxygen in the air (O2) is more reactive towards metals than the nitrogen (N2). Consequently, oxide minerals dominate the earth's crust while nitride minerals are extremely rare. Almost all ternary nitrides that have been discovered have synthesized, usually with rigorously air-free conditions. Despite much effort in the past century, the number of known ternary nitrides (approximately 450) pales in comparison to that of ternary oxides (over 4,000). Yet there are world-changing materials within this small number of compounds, like the (In,Ga)N alloys that underpin efficient blue light emitting diodes. Fortunately, recent computational work has predicted a number of theoretically stable ternary nitrides, providing targets for synthesis. This dissertation focuses on the synthesis of new ternary nitrides. Guided by increasingly user-friendly computational tools, these chapters describe syntheses overcome the thermodynamic barriers that often inhibit the formation of new ternary nitrides. Along the way, several new materials are discovered and characterized for promising magnetic and semiconducting properties: MnSnN2, MgWN2 in two structure types, Mg3WN4, MgZrN2, CaZrN2, and CaHfN2. These adventures in synthesis not only report new compounds, but also highlight promising strategies for future explorations of uncharted nitride phase space.
Open Access
Organopolymerization of multifunctional γ-butyrolactones
(Colorado State University. Libraries, 2018) Tang, Jing, author; Chen, Eugene Y.-X., advisor; Szamel, Grzegorz, committee member; Miyake, Garret M., committee member; Bailey, Travis S., committee member; Belfiore, Laurence A., committee member
The complexity of polymerizations increases drastically as the functionality of monomers increases, which brings about challenges for elucidation of polymerization mechanisms, establishing control of the polymerization, and characterization of the resulting polymer structures. On the other hand, the increased multifunctionality in monomers and polymers offers new opportunities to create polymers with unique structures and interesting properties. The research described in this dissertation demonstrates both challenges and advantages that multifunctionality brings into the polymerization and polymer structures. The first successful polymerization of the naturally occurring, OH-containing, tri-functional monomer Tulipalin B (βHMBL) was achieved by utilizing N-heterocyclic carbene and phosphazene superbase catalysts. Owing to its presence of both the reactive exocyclic double bond and hydroxyl group, the resulting P βHMBL is a branched vinyl–ether lactone copolymer structure with six different types of substructural units. The results reveal multiple types of reaction pathways and their mechanistic crossovers involved in the polymerization, including conjugate Michael and oxa-Michael additions, proton transfer processes, as well as ene-type dehydration reactions, enabled by proton transfer. The reactions of other less complicated multifunctional γ-butyrolactone-based monomers under same conditions was also studied to help uncover the polymerization mechanism, including the polymerization of bifunctional (endocyclic double bond, lactone ring) dihydrofuran-2(3H)-one (FO), 3-methylfuran-2(5H)-one (3-MFO), and 5-methylfuran-2(5H)-one (5-MFO), as well as trifunctional (endocyclic or exocyclic double bond, lactone ring, hydroxyl group) 3-(hydroxymethyl) furan-2(5H) one (3-HMFO). The polymerization of the parent FO leads to a vinyl-addition polymer, while the predominant trimerization and dimerization are observed in the reaction involving the two methyl substituted derivatives, 3-MFO and 5-MFO. The polymerization of trifunctional 3-HMFO gives a poly(vinyl–ether lactone) copolymer structure, via two different types of base activation mechanisms and a combination of Michael and ox-Michael additions and proton transfer processes. This thesis work also investigates how different initiation and termination chain ends of poly(γ butyrolactone) (PγBL) affect the materials properties, including thermal stability, thermal transitions, thermal recyclability, hydrolytic degradation, and dynamic mechanical behavior. Four different chain end-capped polymers with similar molecular weights have been synthesized. The termination chain end showed a large effect on polymer decomposition temperature and hydrolytic degradation. Overall, by chain-end capping, linear PγBL behaves much like cyclic PγBL in those properties sensitive to the chain ends.
Open Access
Part 1, executed electronic state decomposition of energetic molecules. Part 2, conformation specific reactivity of radical cation intermediates of bioactive molecules
(Colorado State University. Libraries, 2010) Bhattacharya, Atanu, author; Bernstein, Elliot R., advisor; Levinger, Nancy E., committee member; Van Orden, Alan K., committee member; Szamel, Grzegorz, committee member; Bartels, Randy A., committee member
Energetic materials have a wide variety of industrial, civil, and military applications. They include a number of organic compounds such as RDX (1,3,5- trinitroheahydro-s-triazine), HMX (octahydro-1,3,5,7-tetranitro-l ,3,5,7-tetrazocine), DAAF (3,3'-diamino-4,4'-azoxyfurazan), DAATO35 (3,3'-azobis(6-amino-l,2,4,5- tetrazine)-mixed N-oxides), etc. These materials release huge chemical energy during their decomposition. The decomposition of energetic materials is initiated with a shock or compression wave or a spark. Such events in solids generate molecules in the excited electronic states. Hence, in order to maximize release of the stored chemical energy in the most efficient and useful manner and to design new energetic materials, the unimolecular decomposition mechanisms and dynamics from excited electronic states should be understood for these systems. This thesis describes understanding about unimolecular decomposition of energetic materials from their excited electronic states. A few fundamental questions at molecular level dealing with electronic excitation of energetic materials are addressed here: (a) what happens immediately after electronic excitation of energetic molecules?; (b) how is excess energy partitioned among product molecules following electronic excitation?; (b) what are the mechanism and dynamics of molecular decomposition?; (d) does nonadiabatic chemistry (a process that span multiple electronic potential energy surfaces) through conical intersection (crossing of different potential energy surfaces) dominate system behavior? Both energy and time resolved spectroscopic techniques are used in this effort. The product internal state (rotational and vibrational) distributions are probed using mass and energy resolved spectroscopic techniques using time-of-flight mass spectrometry (TOFMS) and laser induced fluorescence (LIF) spectroscopy. Analyzing the product internal state distributions, the mechanisms of unimolecular decomposition of energetic molecules from excited electronic states are determined. The femtosecond pump-probe spectroscopic technique is utilized to determine ultrafast decomposition dynamics of these molecules. From a theoretical point of view, multiconfigurational methodologies such as, CASSCF and CASMP2 are used to model the processes involving excited electronic states of energetic molecules. Influence of nonadiabatic chemistry in the overall decomposition of energetic molecules is also theoretically judged. The primary energetic systems whose nonadiabatic chemistry discussed here are the nitramine (e.g., RDX, HMX), furazan (e.g., DAAF), and tetrazine-N-oxide (e.g., DAATO3.5) based energetic species. A number of model systems, which are simple analogue molecules of the large and more complex energetic materials, are studied in detail to understand nonadiabatic energetic behavior of a single energetic moiety of particular class. Subsequently, the decomposition mechanism for more complex energetic systems are studied and compared with that of their model systems. Nitramine energetic materials and model systems undergo nitro-nitrite isomerization followed by IV NO elimination. Nitramine energetic materials dissociates in the ground state generating rotationally cold (20 K) distribution of the NO product. Nitramine model systems dissociates in the excited state surface producing rotationally hot (-120 K) distribution of the NO product. The nitro-nitrite isomerization happens through conical intersection. Furazan based model molecules (e.g., furazan) possess two different pathways of decomposition: ring contraction and ring opening. These two pathways are electronically nonadiabatic. The ring contraction mechanism generates rotationally cold (20 K) product NO and the ring opening mechanism generates rotationally hot (100 K) product NO. Furazan based energetic material (DAAF), however, dissociates only through a ring contraction mechanism. Thus nonadiabatic pathways control the decomposition of furazan based molecules. Decomposition of tetrazine-2,4-dioxide based molecules involves a ring contraction mechanism through (Si/So)ci, producing only rotationally cold (20 K) but vibrationally hot (1200 K) distributions of the NO product. Tetrazine-l,4-dioxde undergoes similar decomposition pathway through (Si/So)ci; however, it produces rotationally hotter (50 K) but vibrationally colder distribution of the NO product. Thus the relative position of the oxygen atoms attached to the tetrazine ring is important parameter along with their nonadiabatic chemistry controlling their final energetic reactivity. Decomposition dynamics of all energetic materials is faster than 180 fs. Considering the influence of conical intersections in the excited electronic state decomposition of energetic materials, rotationally cold N2 product is predicted to be the major decomposition product of high nitrogen content energetic species. The present work infers that generation of internally cold product is an important characteristics of a true energetic molecule. Presence of low lying chemically relevant conical intersections provides a direct pathway of ultrafast decomposition chemistry of energetic molecules. The energy barrier to the low lying chemically relevant conical intersection, in principle, would be a point of interest to make a system more or less energetic.
Open Access
Quantum dot studies with time-resolved super-resolution microscopy
(Colorado State University. Libraries, 2021) Dunlap, Megan Kathryn, author; Van Orden, Alan, advisor; Gelfand, Martin, advisor; Krapf, Diego, committee member; Prieto, Amy, committee member; Szamel, Grzegorz, committee member
Quantum dots (QDs) are semiconductor nanoparticles whose optical properties make them ideal candidates for a myriad of applications including fluorescence imaging and light harvesting technologies. They are highly emissive and their stochastic switching between states of low and high intensity, called blinking, lends them particularly well to super-resolution (SR) microscopy studies. This thesis is devoted to the development and application of a SR microscope with exceptionally high temporal resolution, so that the fluorescence lifetime, intensity, and emitter location can be simultaneously monitored. This time-resolved SR microscope is used to characterize CdSe/CdS core/shell QDs and clusters of QDs. Small clusters of ~2-5 QDs exhibited fluorescence intensities and lifetimes indicative of directed energy transfer, and regions were resolved within the clusters that were responsible for donating and accepting energy. Correlated images of the same clusters with scanning electron microscopy were used to verify the true distances between QDs in an attempt to confirm the distance-dependence of the Foerster energy transfer rate. A new analysis method was developed for resolving non-blinking emitters based on the lifetime information accessible with the time-resolved SR microscope.
Open Access
Stable and unstable tiling patterns of ABC miktoarm triblock terpolymers studied via GPU-accelerated self-consistent field calculations
(Colorado State University. Libraries, 2022) Hawthorne, Cody, author; Wang, David, advisor; Bailey, Travis, committee member; Miyake, Garrett M., committee member; Szamel, Grzegorz, committee member
Block copolymers are macromolecules formed from linking together two or more chemically distinct types of polymers. Provided the different monomers that make up each polymer are immiscible enough, melts of these molecules will self-assemble into highly ordered, periodic structures at length scales typically on the order of nanometers. The exemplary and simplest material in this respect is the AB diblock copolymer, a linear macromolecule formed by bonding together two immiscible polymers (or 'blocks') A and B. This material is capable of assembling into lamellar, cylindrical, spherical, and networked morphologies depending on the length of the A block and degree of immiscibility between A and B. The ability to control bulk properties of block copolymers via tuning these molecular properties, as well as the length scales that these ordered structures form at, makes them intriguing candidates for next generation technological applications in lithography, photonics, and transport. In order to realize these applications it is imperative to have an intimate understanding of the phase behavior of the materials such that the morphology that will form at a given combination of parameters can be predicted reliably. Self-consistent field theory, or SCFT, has emerged as a useful theory for investigating block copolymer phase behavior. This statistical-mechanical theory has been successfully used to construct phase diagrams of the self-assembled morphologies of various block copolymer systems. These phase diagrams provide the connection between molecular properties (such as block lengths, block incompatibility, and chain architecture) and bulk properties necessary in order to control the behavior of the material. The theory must, in general, be solved numerically – an open-source software termed 'PSCFPP' has recently been made available for this purpose, capable of implementing high-performance SCFT calculations for arbitrarily complex acyclic block copolymers by taking advantage of the massive parallelization of GPUs. In this work, PSCFPP is used to apply SCFT to a neat melt of complex ABC miktoarm triblock terpolymers, which are an interesting class of block copolymer formed by linking three distinct polymers A, B, and C at a single junction point. The resulting star-shaped macromolecule is referred to as a 'miktoarm' and exhibits unique morphologies such as the Archimedean tiling patterns that cannot be found in other block copolymer materials. To focus on the effect of composition, which has not yet been fully elucidated, we restrict the interaction parameters between monomers ABC to the symmetric case where all are equivalent. The central region of the phase diagram, where the effect of the miktoarm architecture is most significant, is mapped out in detail and a 3D morphology previously thought to be metastable is shown to be a stable phase. Further, discrepancies in the literature concerning the stability of multiple 2D tiling patterns are resolved such that the phase diagram presented is the most accurate for the system to date. Finally, a 2D morphology of some interest owing to the possibility of exhibiting photonic band gaps is definitively shown to be stable in this system and its thermodynamic properties analyzed to ascertain what drives its formation. These results provide a solid foundation for further refinement of our understanding of ABC miktoarm phase behavior and demonstrate the utility of a software such as PSCFPP for obtaining high-accuracy SCF results.
Open Access
Strong fullerene and polycyclic aromatic hydrocarbon electron acceptors with perfluorinated substituents
(Colorado State University. Libraries, 2015) San, Long K., author; Strauss, Steven H., advisor; Henry, Charles, committee member; Borch, Thomas, committee member; Szamel, Grzegorz, committee member; Wang, Qiang, committee member
The world energy consumption is increasing at an alarming rate and only 10% comes from renewable energy resources. Harnessing the potential energy provided by the sun would provide enough energy to meet the world energy demands and more. One method to improve the collection of solar power is to provide materials that are lightweight, flexible, robust, and low manufacturing costs. The focus of this dissertation include the molecular design of novel materials to be used as organic semiconductors in a variety of applications such as organic photovoltaic and organic light emitting diodes. One very important aspect of these organic electronics is the electron acceptors employed in such devices. The need for strong electron acceptors and higher stabilities under thermal and oxidative stress were investigated by the perfluoroalkylation and perfluorobenzylation of fullerenes and polycyclic aromatic hydrocarbons. The first chapter of this dissertation demonstrates the novel fullerene derivative (nicknamed faux hawk) that possesses physicochemical properties suitable for use in organic photovoltaics. In fact, an organic photovoltaic figure of merit (ϕΣμ, yield of free charge carriers x sum of the charge carrier mobilities) determined from time resolved microwave conductivity measurements showed that faux hawk is comparable to that of the most studied fullerene electron acceptor, PCBM. Other properties are compared between faux hawk and PCBM. Mechanistic insight revealed, for the first time in fullerene chemistry, the formation of a carbon–carbon bond via a carbanion from the fullerene cage. The second chapter of this dissertation investigates novel polycyclic aromatic hydrocarbons containing fluorine withdrawing functional groups via perfluoroalkylation and, for the first time, perfluorobenzylation. These fluoromodifications have profound influences on the physicochemical and electronic properties that are all important for designing new electron acceptors. For example, the perfluorobenzylation greatly affects the π‐π intermolecular interactions and is more electron withdrawing than the trifluoromethyl group. Often times a bulky functional group is desired to promote certain properties (i.e., fluorescence). Several analytical methodologies including ¹⁹F and ¹H NMR spectroscopy, absorption and emission spectroscopy, mass spectrometry, cyclic voltammetry, gas-phase electron affinity, low-temperature photoelectron spectroscopy, X-ray diffraction, and DFT calculations are used to characterize the compounds discussed. These fundamental studies allow for future molecular engineering and design of even stronger electron acceptors. At the same time, the organic semiconductor library is expanding for use in optoelectronics.