Chemical and Biomolecular Engineering Theses and Dissertations

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    Battery Studies with Particular Reference to Organic Depolarizers
    (1955) Monson, William L.; Huff, W. J.; Chemical Engineering; Digital Repository at the University of Maryland; University of Maryland (College Park, MD)
    Since Volta's invention of the first primary cell, using silver and zinc, numerous other cell combinations have been studied, covering a wide variety of anode and cathode materials. The latter have included both inorganic and organic substances capable of electrochemical reduction, although, historically, organic cathode materials have received very much less attention than the inorganic. It was the purpose of this investigation to study the actual behavior of a selected number of quinones as depolarizers in primary cells. Performance of experimental cells was compared with cells of the usual dry cell composition but of the same size and construction as cells of experimental composition. The results show that certain substituted anthraquinones possess good depolarizing ability as measured by discharge voltage and coulombic capacity. Energy output in some cases was higher than that of the manganese dioxide control cells (zinc anodes in all cases) because of higher effective coulombic capacities. A qualitative study of the effect of substituents on the discharge voltages of various quinones showed that cell working voltages were much more sensitive to quinone substitution than were the calculated reversible potentials. Also, in the case of nitro-substituted anthraquinones more coulombic capacity was obtained than could be accounted for by the simple reduction to the corresponding hydroquinone. The possibility of a reduction of the nitro-group of this compound was considered. Substances investigated were benzoquinone, naphthoquinone, anthraquinone, and certain of their derivatives, using various electrolytes. The size of the experimental cells was such that about 0.2 gram of the various depolarizers could be studied conveniently.
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    (2023) Cheng, Sichao; Liu, Dongxia; Zhang, Chen; Chemical Engineering; Digital Repository at the University of Maryland; University of Maryland (College Park, Md.)
    Non-oxidative methane conversion (NMC) represents a promising pathway that directly transforms methane into higher hydrocarbons such as ethane, ethylene, acetylene, aromatics, and hydrogen in a single-step synthesis. This process holds particular appeal due to its potential for remote operation and its status as a carbon-neutral process, given that it does not produce carbon dioxide in the product effluent. As such, NMC could serve as a viable alternative to existing multi-step, energy-intensive processes like the Fischer-Tropsch synthesis and liquid petroleum gas production. Despite its potential, NMC faces significant challenges. The thermodynamic stability of methane, attributed to its strong C-H bonds, poses a considerable obstacle. Other challenges include low selectivity towards desired products, rapid catalyst deactivation, and kinetic hindrance, all of which complicate the process. As of now, these challenges have prevented the development of a commercially viable NMC process. This dissertation aims at overcoming these hurdles to unlock the full potential of NMC, paving the way for a more efficient and sustainable method of methane conversion from the perspective of both catalyst design and reaction engineering. The impact of hydrogen activation on NMC using a hydrogen-permeable SrCe0.8Zr0.2O3-δ (SCZO) perovskite oxide material over the iron/silica catalyst was explored. The SCZO oxide, with its mixed ionic and electronic conductivity, facilitates H2 activation into protons and electrons. The SCZO's ability to absorb H2 in-situ lowers its local concentration, promoted the improvement of NMC reaction thanks to the Le Chaterlie’s principle. To further improve the NMC reaction performance, an innovative autothermal catalytic wall reactor (ACWR) designed for self-sustaining NMC with high hydrocarbon product yield (>21% C2 & >27% Aromatics) and minimal coke formation. The system, potentially powered by combusting the sole co-product H2, offers a self-sustained and negative neutral operation of NMC. Further operando studies via Spatial Resolved Capillary Inlet Mass Spectrometry (SpaciMS) have demonstrated that the increased local concentration and the volcanic axial concentration profile of ethylene within the ACWR highlight its effectiveness in comparison to traditional reactor designs. With the detection of a higher ethylene concentration near the reactor wall, SpaciMS studies have also provided experimental evidence that ethylene is a surface product of the Fe/SiO2 catalyst. A novel Pulsed Heating and Quenching (PHQ) thermochemical synthesis technique was applied to methane pyrolysis to demonstrate high selectivity to valuable C2 products. The technique's salient features include rapid activation of reactants at high temperatures for increased rates and conversions, and precise control over the heating process, enhancing the selectivity of desired products.
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    Journey Through Aerosol Science: Unraveling Kidney Stone Formation, Advancing Visualization, and Particle Capture Technologies
    (2023) Rastogi, Dewansh; Asa-Awuku, Akua; Chemical Engineering; Digital Repository at the University of Maryland; University of Maryland (College Park, Md.)
    Aerosols are solid or liquid particles that are suspended in air or gas and are present throughout the Earth’s atmosphere due to a variety of anthropogenic and biogenic sources. These aerosol particles play an indispensable role in maintaining the planet's temperature, facilitating the dispersion of airborne pathogens, and enabling targeted pulmonary drug delivery. Our present comprehension of aerosol physics has been instrumental in elucidating the intricate processes of particle formation and their interactions with their immediate surroundings. Depending on their chemical composition and physical properties, these particles exhibit a range of effects on human existence. A profound understanding of the physics governing particle formation not only equips us to engineer aerosols for specific applications, such as nanoparticle synthesis, affording precise control over particle morphology and phase, but also empowers us to delve into the realm of aerosol interactions, unraveling the intricate interplay between particles and the environmental contexts they inhabit. This knowledge base in aerosol science, in turn, enables the development of advanced tools for the capture and analysis of these microscopic particles, thereby advancing our collective comprehension of the field of aerosol science. Furthermore, the physics governing aerosol interactions enables the exploration of particle-environment interactions within contexts of interest. This foundational knowledge base in aerosol science empowers the development of advanced tools for the capture and examination of these diminutive particles, furthering our collective understanding of aerosol science. Consequently, this thesis embarks on an exploration of the principles of aerosol science in multidisciplinary research and the development of new tools for the visualization and capture of aerosols.
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    (2023) Liu, Lu; Zhang, Chen; Chemical Engineering; Digital Repository at the University of Maryland; University of Maryland (College Park, Md.)
    Propylene (C3H6) is a crucial petrochemical feedstock for a number of bulk chemicals and polymers. While steam cracking currently dominates C3H6 production, propane (C3H8) dehydrogenation (PDH) has been increasingly practiced addressing the gap between C3H6 demand and production. The C3H8 conversion of PDH reaction is challenged by thermodynamic limitation and catalyst deactivation at elevated reaction temperature. Membrane reactors can address both challenges and hence enhance the energy efficiency of PDH by achieving attractive and stable C3H8 conversion at low reaction temperature via selective removal of the hydrogen (H2) product to shift the reaction equilibrium. Large-scale practice of PDH membrane reactors has not occurred due to the lack of scalable membranes that can provide attractive H2/C3H8 separation performance at PDH conditions. Carbon molecular sieve (CMS) hollow fiber membranes are a class of tunable and scalable inorganic membranes that are stable under non-oxidative high-temperature conditions, and therefore are potentially promising for PDH membrane reactors.This PhD dissertation aims to investigate low-temperature propane dehydrogenation in novel membrane reactors comprising asymmetric CMS hollow fiber membranes. First, asymmetric polyimide-derived CMS hollow fiber membranes were fabricated and their high-temperature H2/C3H8 performance was assessed. The roles of membrane pyrolysis temperature, permeation temperature, and feed composition on high-temperature H2/C3H8 separation performance were systematically investigated. The effects of high-temperature H2 and C3H6 exposure on CMS pore structure and transport properties were also examined. Under a continuous permeation test (~130 hours) of H2/C3H8 feed mixture at 600 oC, the asymmetric CMS hollow fiber membranes showed stable separation performance with outstanding H2 permeance of 430 GPU and H2/C3H8 separation factor of 511 exceeding those of microporous oxide membranes. H2-permeable CMS hollow fiber membrane reactors were created using the asymmetric CMS hollow fiber membranes and platinum-based catalysts. The effects of reactor operating conditions (i.e., reaction temperature, feed space velocity, sweep flow rate, C3H8 partial pressure, number of CMS hollow fibers) on PDH performance of the CMS hollow fiber membrane reactor were studied. Due to selective removal of H2 product, the H2-permeable CMS hollow fiber membrane reactor showed up to 300% higher C3H8 conversion than equilibrium conversion. Stable performance with commercially attractive C3H8 conversion (above 30%) and high C3H6 selectivity (above 98%) were obtained in the CMS hollow fiber membrane reactor at 450 °C for over 110 hours. The CMS hollow fiber membrane reactors developed in this dissertation outperform PDH membrane reactors reported in literature by having higher conversion enhancement, lower reaction temperature, and the lowest deactivation rate. These experimental results demonstrated the attractiveness of the novel CMS hollow fiber membrane reactors for energy efficient C3H6 production. One-dimensional isothermal models were further developed by material balance to understand the cooperative reaction and separation in the CMS hollow fiber membrane reactors. The modeling results of H2-permeable CMS hollow fiber membrane reactor showed overall good agreement with experimental results. The models also demonstrated the viability of C3H6-permeable CMS hollow fiber membrane reactor and catalytic CMS hollow fiber membrane reactor, which provide valuable guidance to future development of CMS hollow fiber membrane reactors following this PhD research.
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    (2023) Dissanayake Appuhamillage, Thilini Umesha; Woehl, Taylor; Chemical Engineering; Digital Repository at the University of Maryland; University of Maryland (College Park, Md.)
    Biological nano and microstructures exist far from thermodynamic equilibrium by continuous consumption of energy that allows them to reconfigure or adapt to changes in the local environment. Utilization of these non-equilibrium structure formation processes in synthetic colloidal particle and nanoparticle (NP) systems is expected to enable unprecedented control over the dynamics of synthetic active soft materials and systems that are beyond the reach of equilibrium self – assembly. In this work we adapted two non – equilibrium structure formation processes observed in biological systems, dissipative assembly and reaction diffusion instability, to generate dynamic colloidal assemblies and self-organized patterns of nanoparticles. First, we investigated how the surface chemistry and interparticle interactions between colloids changed during chemical reaction driven dissipative assembly of polystyrene colloids. A key result was the first, time dependent measurements of the dynamic colloid surface chemistry (surface charge and hydrophobicity) during dissipative assembly. Importantly, we demonstrated that thermodynamic interparticle interaction models typically used for equilibrium self-assembly are effective in describing fuel driven colloid assembly far from equilibrium. The interparticle interaction models demonstrated that electrostatic interactions controlled the concentration of particle aggregates while the strength of hydrophobic interactions determined whether colloids underwent irreversible aggregation or dissipative assembly. Next, using a correlative fluorescence microscopy and liquid phase transmission electron microscopy (LPTEM) method, we demonstrated that aminated polymer capping ligands on metal NPs undergo crosslinking and chain scission reactions as a result of formation of hydroxyl and hydrogen radicals due to electron beam induced radiolysis of water. We demonstrated that a hydroxyl radical scavenger can minimize the electron beam induced reactions in the polymers. Based on this fundamental knowledge, we introduced an instability to an initially homogenous gold NP decorated aminopolysiloxane thin film immersed in water by scanning TEM beam. Radiolysis driven polymer radical reactions of polysiloxane coupled with diffusion of radicals, polymers, and NPs caused the polymer and NP to self-organize into repeating spatial patterns, i.e., Turing patterns, with no template or specific interparticle interactions. Spots, strings and labyrinth patterns that closely resembled Turing skin pigmentation patterns on various animals were obtained by tuning the chemistry of the system. A series of systematic experiments identified that hydroxyl radicals and NPs as critical species driving the formation of the NP patterns. We expect this work could be used as a model system in establishing design rules for nanoscale pattern formation by reaction – diffusion instability.
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    Atomic Layer Deposition for Engineering Carbon Hollow Fiber Membrane Pore Structure
    (2023) Whitmore, Joseph; Adomaitis, Raymond; Zhang, Chen; Chemical Engineering; Digital Repository at the University of Maryland; University of Maryland (College Park, Md.)
    Alumina (Al2O3) films, fabricated using atomic layer deposition (ALD) are useful components of composite materials, providing corrosion resistance, transport barriers, or dielectric properties. The process dynamics of alumina ALD in and around pores are examined in order to support the fabrication of membranes with planar and hollow-fiber geometries. In this study carbon molecular sieve (CMS) membranes are created from pyrolysis of polymer precursors which have properties based on the geometry of and pretreatment applied to the precursor before inert-gas pyrolysis. Modeling and simulation are performed for gaseous reactant transport inside arbitrarily porous networks common to such membranes using analytic and numerical methods to identify potential mass transfer limitations. Associated experimental work used two ALD reactor systems to deposit alumina on the precursor fibers and completed membranes. When the requisite ALD parameters fell outside of the operating conditions of the commercial system, a second system was designed and constructed to support long exposures and simplify masking of undesired deposition surfaces. Characterization of the coated precursors and final CMS membranes was conducted using scanning electron microscopy (SEM), energy dispersive spectroscopy (EDS), and several performance metrics including constant-pressure permeation and pure water flux measurements. This research details study is the successful fabrication of several desirable membrane geometries using ALD, along with transport insight and a proposed reaction mechanism for coating nucleation on the polymer surface.
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    (2000) Frank, Mary Kirsten; Thirumalai, Devarajan; Institute for Physical Science and Technology; Digital Repository at the University of Maryland; University of Maryland (College Park, MD)
    The B1 domain of streptococcal protein G provides a well-characterized system for structural investigations of proteins. In this thesis, the urea-unfolded state has been characterized, the tolerance towards hydrophobic substitutions in the core has been surveyed, the hydrogen exchange behavior of the backbone amides has been elucidated, and structural information on a tetrameric mutant of this domain has been gathered. The chemical shifts of the urea-unfolded state were assigned. The secondary chemical shifts, the 3JHNa coupling constants and the short-range NOEs gave no indication of residual structure. Measurement of the backbone 15N relaxation parameters revealed a region of restricted motion in the β3- β4 turn of the native protein. Motion in the rest of the protein was uniform, with the exception of 3-4 residues at either end of the chain. A series of hydrophobic substitutions were made in the hydrophobic core. The resulting mutants were assayed for stability and overall fold . The core of the protein is particularly sensitive to substitutions at position 26. One of the mutants was unable to adopt the GB1 fold and optimized its stability by adopting a homotetrameric form. Hydrogen exchange in the backbone amides was measured at 25 °C. Rates of hydrogen exchange were inversely correlated with burial of the amide nitrogen. The slow-exchanging backbone amides did not correlate with the hydrogen bonds formed early in protein folding. Hydrogen exchange rates from NH to ND and from ND to NH were similar. The ratio between these two rates does not correlate with any obvious physical parameters of the hydrogen bonds. Chemical shifts for the tetrameric mutant (HS#124) were determined using three-dimensional heteronuclear NMR techniques. Measurement of the backbone dynamics revealed a highly flexible region between positions 8 and 22. The secondary structure and β-sheet interactions of this mutant were characterized. The β-sheet interactions were intermolecular and only one of the three β-strand pairings was similar to the β-strand pairings found in wild type GB1 . The novel pairing is between β1 of one monomer and β1 of another monomer and a shift in register is observed for the β3-β4 pairing.
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    (2023) Kim, Jung; Calabrese, Richard V.; Chemical Engineering; Digital Repository at the University of Maryland; University of Maryland (College Park, Md.)
    Pulse Jet Mixed (PJM) vessels are used to process nuclear waste due to their maintenance free operation. In this study we model the turbulent velocity field in water during normal PJM operation to gain insight into vessel operations and to evolve a modeling strategy for process design and operator training. Three transient simulation models, developed using Large Eddy Simulation (LES), unsteady Reynolds-Averaged Navier-Stokes (RANS), and Lattice Boltzmann Method (LBM) techniques, are compared to velocity measurements acquired for 3 test scenarios at 3 locations in a pilot scale vessel at the US DOE National Energy Technology Laboratory (NETL). The LES and RANS simulations are performed in ANSYS Fluent, and the LBM simulations in M-STAR.The LES model well predicts the experimental data provided that the operational pressure profile within the individual pulse tubes is considered. While the RANS model failed to predict the data and exhibited significant differences from LES with respect to turbulence quantities, it is a useful comparison tool that can quickly predict averaged flow parameters. The LBM model’s rigid grid system is deemed unsuitable, as currently configured, for the NETL PJM vessel’s wide range of length scales and curved boundaries, resulting in the longest simulation time and least accurate velocity predictions. Predicted velocity and turbulence metrics are explored to better understand the strengths and failures of the three models. Because the LES model produced the most accurate predictions, it is exploited to generate animations and still images on various 2D planes that depict extremely complex flow patterns throughout the vessel with numerous local jets and mixing layer vortices The study concludes with recommendations for future research to improve the model development and validation strategy.
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    (2023) Malek, Kotiba; Asa-Awuku, Akua; Chemical Engineering; Digital Repository at the University of Maryland; University of Maryland (College Park, Md.)
    Aerosols, tiny solid or liquid particles, are ubiquitous in the atmosphere yet their impact on climate remains poorly understood. One prominent way aerosols are able to impact the climate is through their ability to uptake water and form clouds. The chemical diversity and aerosol interactions in the atmosphere can greatly complicate the investigation of aerosol-cloud interactions. This complexity is expressed with a large uncertainty associated with aerosols’ role on climate change. This dissertation investigates the aerosol-cloud interaction by measuring the water uptake of atmospherically relevant aerosols. Our results highlight the importance of accounting for various physiochemical properties when exploring the water uptake of atmospheric aerosols. One such property is liquid-liquid phase separation (LLPS) in ternary mixtures. Our work offers new evidence, insight, and a paradigm shift to the contribution of LLPS to supersaturated droplet activation. We complemented this finding with a theoretical model, that incorporates solubility, O:C ratio, and LLPS, for predicting κ-hygroscopicity of ternary mixtures. Another physiochemical property that was shown to play a key role in droplet activation of polymeric aerosols is chemical structure. Our study shows that polycatechol is more hygroscopic than polyguaiacol and the difference in hygroscopicity is attributed to the density of hydroxyl groups in both structures. Polycatechol has a higher density of hydroxyl groups than polyguaiacol, resulting in polycatechol having stronger water uptake affinity than polyguaiacol. When maintaining the same structural makeup by investigating the water uptake of two isomeric compounds, we discovered that solubility was the driving force in water uptake. The more soluble isomer o-aminophenol was more hygroscopic than p-aminophenol. Hence, a small change in the position of functional groups can impact solubility which in turn influence hygroscopicity. Lastly, we explored the presence of gas-phase organics on the water uptake of isomers with a wide range of solubilities. Our work highlights that gas-phase organics, specifically ethanol, can influence the water uptake of aerosols. Ethanol was shown to increase water uptake efficiencies based on solubility, with the least soluble compound showing stronger affinity to water uptake. Overall, this thesis advances our knowledge and understanding of aerosol-cloud interactions and its implications on climate change.
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    Delayed Release of Hydrophilic Solutes from Capsules
    (2023) Utlu, Eylul; Raghavan, Srinivasa R.; Chemical Engineering; Digital Repository at the University of Maryland; University of Maryland (College Park, Md.)
    Hydrophilic small-molecule solutes (e.g., drugs) can be loaded into hydrogels, but the solutes leak out rapidly (in minutes) when the gels are placed in water. Solute release can be completely stopped if the gel is covered by a thin shell of paraffin wax (melting point Tm ~ 57°C); in such ‘capsules’, the wax shell is a hydrophobic solid. Here, we vary the design of our capsules to achieve ‘delayed release’ of solutes into water: i.e., no release for a delay period (6 to 72 h) followed by a slow and sustained release thereafter. The key is to include an additive in the shell that is miscible with the wax but is weakly hydrophilic and has a lower Tm. Examples are fatty acid esters, notably isopropyl palmitate (IPP, Tm ~ 11°C). For example, when a solute-loaded gel is covered by a 80/20 wax/IPP shell, we find a 3-day delay at 25°C before any release, followed by a near-constant release rate (i.e., ‘zero-order’ release) for the next 20 h. The time delay and release rate can be tuned via the concentration and type of additive in the shell. The delayed release occurs because the wax/IPP shell is an inhomogeneous crystal (as wax and IPP are only partially miscible). Our approach can be used to delay the release of dyes, drugs (e.g., diclofenac), and reactive agents (e.g., H2O2) out of the core gel. The simplicity and generality of our approach should make it useful for controlled release applications in the pharmaceutical, agrochemical, and cosmetics industries.
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    Composition-Function Analyses and Design of Plasticized Solid Polymer Electrolytes for Lithium-ion Batteries
    (2023) Ludwig, Kyle Brandyn; Kofinas, Peter; Chemical Engineering; Digital Repository at the University of Maryland; University of Maryland (College Park, Md.)
    This dissertation work examines the electrochemical properties of various solid polymer electrolytes (SPEs) through the lens of composition-function relationships. The analyses presented offer unique design perspectives for improving the performance of SPEs for use in lithium-ion batteries (LIBs). Specifically, three distinct strategies are explored to enhance the lithium ion (Li+) conductivity and reduce the electrode/electrolyte interfacial resistance, two of the major challenges of adopting SPEs as alternatives to common organic liquid electrolytes. The basis for improving ionic conductivity, in all three strategies, is the inclusion of additives in the polymer matrix to plasticize the SPE and improve ionic transport. In one strategy, an ionic liquid (IL) is used as a plasticizer to fabricate free-standing ILSPEs membranes based on a poly(ethylene oxide) (PEO) matrix with an appropriate lithium salt. Optimized ILSPE compositions were able to achieve room temperature ionic conductivity of 0.96 mS/cm, a value suitable for commercial applications, as well as long cycle life in a lithium-metal battery with a capacity of 150—175 mAh/g and >99% coulombic efficiency. In a second strategy, the IL was swapped with water as the plasticizer to fabricate PEO-based aqueous SPEs (ASPEs). The ASPEs exhibited excellent transport properties, with room temperature conductivity values of 0.68—1.75 mS/cm. Molecular dynamics simulations revealed the origin of the exceptional transport properties as the presence of highly interconnected Li+(H2O)n domains. In a final strategy, the concepts of the ILSPE and ASPE were combined through the incorporation of both IL and water into a polymer matrix. For this strategy, the polymer matrix was also changed from PEO to polyacrylonitrile (PAN) to limit the effects of crystallinity and oxidation. These “hybrid aqueous/ionic liquid” SPEs (HAILSPEs) demonstrated the exceptional transport properties of the ASPE system with the improved stability and passivation of the ILSPE system. An analysis of the composition-function relationships correlated the dramatic rise in ionic conductivity to the nearly complete decoupling of ion transport from polymer chain mobility while the unique passivating properties were shown to derive from the choice of ionic liquid, with solid electrolyte interphases comprised of LiF, Li2CO3, Li2S, and Li3N.
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    (2023) Carmona, Eric Alvaro; Albertus, Paul; Chemical Engineering; Digital Repository at the University of Maryland; University of Maryland (College Park, Md.)
    The relationship between mechanical stress states and interfacial electrochemical thermodynamics of Li metal/Li6.5La3Zr1.5Ta0.5O12 and Na metal/Na-β”-Al2O3 systems are examined in two experimental configurations with an applied uniaxial load; the solid electrolytes were pellets and the metal electrodes high-aspect-ratio electrodes. Our experimental results demonstrate that (1) the change in equilibrium potential at the metal/electrolyte interface, when stress is applied to the metal electrode, is linearly proportional to the molar volume of the metal electrode, and (2) the mechanical stress in the electrolyte has negligible effect on the equilibrium potential for an experimental setup in which the electrolyte is stressed and the electrode is left unstressed. Solid mechanics modeling of a metal electrode on a solid electrolyte pellet indicates that pressure and normal stress are within ~0.5 MPa of each other for the high aspect ratio (~1:100 thickness:diameter in our study) Li metal electrodes under loads that exceed yield conditions. To assess the effect of electrochemical-mechanical coupling on current distributions at Li/single-ion conducting solid ceramic electrolyte interfaces containing a parameterized interfacial geometric asperity, we develop a coupled electrochemical-mechanical model and carefully distinguish between the thermodynamic and kinetic effects of interfacial mechanics on the current distribution. We find that with an elastic-perfectly plastic model for Li metal, and experimentally relevant mechanical initial and boundary conditions, the stress variations along the interface for experimentally relevant stack pressures and interfacial geometries are small (e.g., <1 MPa), resulting in a small or negligible influence of the interfacial mechanical state on the interfacial current distribution for both plating and stripping. However, we find that the current distribution is sensitive to interface geometry, with sharper (i.e., smaller tip radius of curvature) asperities experiencing greater current focusing. In addition, the effect on the current distribution of an identically sized lithium peak vs. valley geometry is not the same. These interfacial geometry effects may lead to void formation on both stripping and plating and at both Li peaks and valleys. This work advances the quantitative understanding of alkali metal dendrite formation within incipient cracks and their subsequent growth, and pore formation upon stripping, both situations where properly accounting for the impact of mechanical state on the equilibrium potential can be of critical importance for calculating the current distribution. The presence of high-curvature interface geometry asperities provides an additional perspective on the superior cycling performance of flat, film-based separators (e.g., sputtered LiPON) versus particle-based separators (e.g., polycrystalline LLZO) in some conditions.
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    Machine Learning Assisted Design of MXene Aerogels for Personal Thermal Management
    (2023) Kesavan, Meera; Chen, Po-Yen; Chemical Engineering; Digital Repository at the University of Maryland; University of Maryland (College Park, Md.)
    Personal thermal management is necessary in maintaining body temperature in humans through the use of building insulation, personal garments, and heating or cooling units. Electrically conductive aerogels can be used as a multifunctional material, where the aerogel structure is intrinsically thermally insulating, and the incorporation of electrically conductive components allows for Joule heating of these materials for wearable heaters. Ti3C2Tx (MXene) has been incorporated in materials for Joule heating due to its excellent electrical conductivity. Cellulose and gelatin based aerogels have been used as bio-based materials with good structural properties in aerogels. Due to the large range of possibilities in parameters for aerogel formation, from percentage of components in each sample to sample concentration and presence or absence of glutaraldehyde, it can be tedious to test a matrix of recipes and determine the effects of each component on the electrical properties. To assist in the design of highly conductive aerogels machine learning was used as it uses a data-driven approach to analyze the effect of inputs, sample composition in this case, to predict a set of inputs that will return a desired output, which is a highly conductive aerogel.Aerogels of various compositions were fabricated and their resistances and sensitivities to applied pressure were measured to screen for highly conductive recipes and for strain insensitive samples. Of these samples, a strain insensitive sample recipe and a strain sensitive sample recipe were selected for Joule heating tests. Low voltages of 2 Volts and below, were applied to the aerogel samples and the temperature increase was measured. The stability of these samples under multiple heating and cooling cycles were tested both with and without applied compression. Through these tests we determined a strain insensitive aerogel recipe for stable temperature control regardless of pressure applied. This aerogel recipe was found to have a thermal conductivity comparable to common insulating materials at a much lower density. A machine learning model was then trained from the aerogel compositions and measured resistance values, and a prediction model with a low mean relative error of 19% was developed to assist in conductive aerogel recipe formulation.
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    (2023) Davoudi, Omid; Klauda, Jeffery B; Sukharev, Sergei; Chemical Engineering; Digital Repository at the University of Maryland; University of Maryland (College Park, Md.)
    Divalent cations bound to anionic lipids are necessary co-factors for many signaling mechanisms taking place at both the inner and outer surfaces of the cytoplasmic membrane. Coordination of divalent ions jointly by phospholipid headgroups and specific protein domains mediates recognition and triggers secondary messenger cascades or membrane fusion events. Phosphoryl oxygens of phospholipids are common contributors to divalent ion coordination. With the aims of elucidating the affinities of the calcium ion Ca(2+) and its toxic competitor beryllium Be(2+) to different types of phosphate groups taking place in many ‘building blocks’ of the cell, improving simulation force fields and better understanding the nature of beryllium toxicity, here we use isothermal titration calorimetry (ITC) to study the thermodynamic parameters and coordination of these ions by phosphates. Particularly, we focus on the differences between phosphates in the phosphodiester configuration that connect the glycerol backbone with a headgroup (as in phosphatidylglycerol, PG) and terminal monoester phosphates such as in phosphatidic acid (PA) and most phosphorylated proteins. The comparison of small model compounds, dimethyl phosphate (DMP, mimicking phosphate in phosphatidyl glycerol) with glycerol-3-phosphate (Gly3P, emulating phosphate in phosphatidic acid) shows that the affinity of Be(2+) for Gly3P is about one order of magnitude higher than for DMP and may exhibit at least two binding configurations. The Be(2+) -DMP thermograms in most cases are well fitted with a one-site model. Upon completing the survey of small (model) compounds, we performed experiments to compare the binding parameters of Be(2+) to POPA and to POPG-containing liposomes with the parameters obtained on respective model compounds. We also present several pilot binding experiments performed with POPS liposomes; however, the fit is poor.
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    Assessing the Thermal Safety and Thermochemistry of Lithium Metal All-Solid-State Batteries Through Differential Scanning Calorimetry and Modeling
    (2023) Johnson, Nathan Brenner; Albertus, Paul; Chemical Engineering; Digital Repository at the University of Maryland; University of Maryland (College Park, Md.)
    Solid-state batteries are often considered to have superior safety compared to their liquid electrolyte counterparts, but further analysis is needed, especially because the desired higher specific energy of a solid-state lithium metal battery results in a higher potential temperature rise from the electrical energy in the cell. Safety is a multi-faceted issue that should be carefully assessed. We build "all-inclusive microcell" Differential Scanning Calorimetry samples that include all cell stack layers for a Li0.43CoO2 | Li7La3Zr2O12 | Li cell in commercially relevant material ratios (e.g. capacity matched electrodes) and gather heat flow data. From this data, we use thermodynamically calculated enthalpies of reactions for this cell chemistry to predict key points in cell thermal runaway (e.g., onset temperature, maximum temperature) and assess battery safety at the materials stage of cell development. We construct a model of the temperature rise during a thermal ramp test and short circuit in a large-format solid-state Li0.43CoO2 | Li7La3Zr2O12 | Li battery based on microcell heat flow measurements. Our model shows self-heating onset temperatures at ∼200-250°C, due to O2 released from the metal oxide cathode. Cascading exothermic reactions may drive the cell temperature during thermal runaway to ∼1000 °C in our model, comparable to temperature rise from high-energy Li-ion cells, but subject to key assumptions such as O2 reacting with Li. Higher energy density cathode materials such as LiNi0.8Co0.15Al0.05O2 in our model show peak temperatures >1300°C. Transport of O2 or Li through the solid-state separator (e.g., through cracks), and the passivation of Li metal by solid products such as Li2O, are key determinants of the peak temperature. Our work demonstrates the critical importance of the management of molten Li and O2 gas within the cell, and the importance of future modeling and experimental work to quantify the rate of the 2Li+1/2O2→Li2O reaction, and others, within a large format Li metal solid-state battery.
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    (2023) Mao, Chun-Ning; Asa-Awuku, Akua; Chemical Engineering; Digital Repository at the University of Maryland; University of Maryland (College Park, Md.)
    Polymeric nanoparticles affect many aspects of human life. They directly absorb or scatter sunlight, or indirectly act as cloud condensation nuclei (CCN) to change the Earth’s climate. Additionally, micro-plastics released into the environment have the potential to degrade into nano-size particles. Plastic nanoparticles' sizes, number concentration, and hygroscopicity are important properties to understanding nano-plastics’ fates. In this work, I explored aerosol measurement techniques, aerosol hygroscopicity, and polymer nanoparticles to understand subsequent effects in the environment and on human health. The project was divided into three objectives:For the first objective, I developed the single-parameter hygroscopicity model for polymeric aerosols with Flory-Huggins Köhler theory. Traditional hygroscopicity, derived from Raoult’s law, depends on the molecular volume of the solute. For polymers with a high molecular volume, the predicted hygroscopicity from traditional Köhler theory is zero. However, the experimental results showed that polymers could take up water and readily act as CCN. I developed the expression of the hygroscopicity for polymers and showed the relation between the polymer-water interaction parameter and the water-uptake ability. I also considered water-insoluble polymers and the water-adsorption model combined with Köhler theory to define water-uptake. Thus the CCN activity of polystyrene and surface modified polystyrene particles were also measured. For the second objective, I predicted the fraction of the multiply charged particles, showing that the extinction cross section measured by Cavity Ring Down Spectroscopy (CRD) was influenced by a small amount of multiply charged particles using a Differential Mobility Analyzer (DMA). The initial results indicated that ~4% to ~6% of the total number concentration are triply and quadruply charged particles at 200 nm electrical mobility. This small percentage if neglected could induce errors greater than 5% in subsequent extinction cross section measurements. Thus, the errors induced with commercially available DMAs in the extinction cross section measurement were evaluated. For the third objective, I studied the fate of the nano-plastics in the environment. Results showed that low density polyethylene (LDPE) powders generated particles less than 100 nm at temperatures above 40 oC. I quantified the number concentration of 5 materials in water via traditional atmospheric aerosol measurement techniques. The five materials are cellulose, SiO2, LDPE, polyethylene terephthalate (PET), and polyvinyl chloride (PVC). They were all common materials used for food packaging. Furthermore, the hygroscopicities of the nano-plastics were measured. I demonstrated that the nano-plastics could act as CCN under a supersaturated environment and hence affect the climate. The results showed that the plastic materials (LDPE, PVC, PET) were more hygroscopic than cellulose. The nano-plastics could travel further and be found in remote and cold areas like Antarctica, the Arctic, and high mountains. The work in this objective provided evidence of wet deposition being a possible route for nano-plastics to come to the ground. Plastics are relatively new materials compared to papers, clays, and glasses, but have already been massively produced. The work in this thesis contributed to our understanding of the impact on nano-plastics to the environment. The interaction of the water and nano-plastics in the environment was studied. The measurements of size distribution and hygroscopicity of nano-plastics can be applied in the climate model to reduce the uncertainties in the indirect effect of the aerosols in future studies.
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    (2022) Gohil, Kanishk; Asa-Awuku, Akua A; Chemical Engineering; Digital Repository at the University of Maryland; University of Maryland (College Park, Md.)
    Aerosols can affect the net radiation budget and global climate of the Earth either “directly” – through their radiative properties, or “indirectly” – through their cloud-forming abilities by acting as Cloud Condensation Nuclei (CCN). The interactions between aerosols and clouds are the most significant sources of uncertainty in the overall radiative forcing from due to a lack of understanding related to the droplet formation mechanism of aerosols. These uncertainties are majorly associated with the carbonaceous aerosols present in the atmosphere, notably due to their compositional diversity, vastly variable physicochemical properties, and unique water uptake characteristics. In this dissertation, new lab-based measurement techniques and computational methods have been developed to resolve the CCN activity and water uptake behavior of pure and mixed carbonaceous aerosol particles.The first part of this dissertation accomplishes two goals: 1. The development and application of a new CCN measurement method, and 2. The formulation of a new computational framework for CCN activity analysis of aerosols. The results in this dissertation demonstrate the significance of size-resolved morphology and dissolution properties of aerosol particles in improving their CCN activity analysis under varying ambient conditions. Furthermore, these results suggest that in the future, more comprehensive CCN analysis frameworks can be developed by explicitly treating other physical and chemical properties of the aerosols to further improve their CCN activity analysis. The second part of this dissertation focuses on large-scale analysis. The CCN analysis framework is implemented into a climate model to quantify the water uptake behavior of carbonaceous aerosols, and then study the subsequent variabilities associated with the physical and radiative properties of ambient aerosols and clouds. Statistical techniques are also developed in this work for chemical characterization of ambient aerosols. The characterization results show large regional compositional variations in ambient aerosol populations. These results also suggest that the knowledge of chemical species is necessary to quantify the water uptake properties of the aerosol population.
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    (2022) He, Xinzi; Wang, Chunsheng; Chemical Engineering; Digital Repository at the University of Maryland; University of Maryland (College Park, Md.)
    Lithium-ion batteries (LIBs) have expanded their application from electronics to electric vehicles (EVs). To ease the safety concerns and the “range anxiety”, solid-state lithium batteries (SSLBs) become a more attractive choice. The replacement of flammable and toxic liquid electrolytes with solid-state electrolytes (SSEs) makes it a safer option. The utilization and compatibility of high specific capacity materials such as sulfur cathode and lithium-metal anode increase the cell energy density. However, SSLBs still face challenges towards practical application, which mainly from the solid-solid contact nature on the interfaces. On the anode side, lithium dendrite growth and high interface resistance both hindered the longevity of the cells. On the cathode side, low initial Coulombic efficiency (CE) and low capacity utilization of sulfur obstructed the realization of high loading cathodes.In this dissertation, I addressed both challenges of dendrite and contact on the anode side by adding strontium into lithium anodes. Different from all previous metal/metal oxide coating on garnet or Li alloy anodes that form lithiophilic interlayer, a lithiophilic/lithiophobic bifunctional layer is formed to reduce the interfacial resistance and to suppress the growth of lithium dendrite, which is confirmed by comprehensive material characterizations, electrochemical evaluations, and simulations. The optimum Li-Sr | garnet | Li-Sr symmetric cells achieve a high critical current density (CCD) of 1.3 mA/cm2 and can be cycled for 1,000 cycles under 0.5 mA/cm2 at room temperature, providing a new strategy for high-performance garnet SSLB. Furthermore, I (1) verified the importance of lithiophobic on dendrite suppression by discovering and successfully constructing the highest interface energy (γ, against lithium) material ever reported among all lithium compounds that can be formed on the electrolyte | anode interface; (2) revealed the impact of anode properties on the interface by enhancing the Li self-diffusivity by a co-doping method, achieved an outperformed critical loading of 4.1 mAh/cm2 at 1.0 mA∙cm-2 at room temperature. On the cathode side, I tackled both low CE and low capacity utilization issues by promoting both Li+ and e- transportation across the cathode | SSE interface, resulting in high capacity utilization of 96.5% and high capacity retention of 88.8% after 145 cycles at a high loading of 4.0 mAh cm-2 under room temperature in Li6PS5Cl based SSLB.
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    Interface Broadening and Radiation Enhanced Diffusion During Sputter Depth Profiling
    (1988) Chambers, George Paul; Rousch, Marvin; Chemical and Nuclear Engineering; Digital Repository at the University of Maryland; University of Maryland (College Park, Md)
    The process of ion bombardment of solids has been investigated using Monte Carlo Computer Code simulation in conjunction with ultra-high vacuum experimental techniques. The computer code EVOLVE has been used to study the shape of the resultant collision cascade as well as the origins of sputtered particles while experimental studies of interface regions have been performed to elucidate the physical processes occurring during sputtering. The EVOLVE code models the target as an amorphous multicomponent semi-infinite solid. The target composition during ion bombardment is simulated. The study concludes that recoil activity grows in size and tends to move away from the target surface with increasing time. It is further concluded that the majority of sputtered atoms originate from early generations and are produced from sites near the entry point of the bombarding ion. Low energy noble gas ion bombardment of thin-film Cr/Ni multilayered structures has been performed in conjunction with Auger electron spectroscopy under UHV conditions. An accurate, reliable, and systematic parameterization of the interface region between metallic layers is presented. It is concluded from this study that the extent of the distortion of the interface region due to ion induced broadening is dependent not only on the material system used but on the experimental conditions employed as well. Lastly, radiation enhanced diffusion (RED) has been studied using Ag/Ni thin-film multilayered structures. A physical mathematical model of the radiation broadened Ag layer, capable of successfully deconvoluting the contributions to interface broadening due to RED from those due to cascade mixing and microstructure development, is presented and shown to be an accurate characterization of the interface region. It is concluded from the application of this model that RED can contribute substantially to interface broadening in multicomponent systems with low activation energies of diffusion. It is further concluded from this study that elevated temperatures, sustained during the depth profiling process, can cause the effects of RED to subside dramatically. This phenomenon is most probably due to the dispersion of complex defects responsible for the RED process.
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    Effect of Protein Folding State and Conformational Fluctuations on Hydrogel Formation and Protein Aggregation
    (2022) Nikfarjam, Shakiba; Woehl, Taylor J; Anisimov, Mikhail; Chemical Engineering; Digital Repository at the University of Maryland; University of Maryland (College Park, Md.)
    In this thesis we investigate the role of protein unfolding on protein aggregation and hydrogel formation in two different systems. In the context of designing protein-based hydrogels as biomaterials, we investigate how protein unfolding affects the formation dynamics of hydrogels in response to temperature changes, denaturation, and chemical reactions. In a second context we establish how microsecond to millisecond fluctuations in an amyloid forming protein, beta-2-microglobulin, correlate to the amyloid forming propensity of the protein, with an emphasis on understanding how conformational changes in the native folded state provide thermodynamic driving forces for amyloid nucleation.The work on protein hydrogel yielded two key results. First, we observed that the lifetime of dissipative hydrogels decreased and their mechanical stiffness increased with increasing denaturant concentration and constant fuel concentration. At a higher denaturant concentration, the concentration of solvent-accessible cysteines increases the stiffness of the hydrogel at the cost of a faster consumption of H_2 O_2, which is the cause of the shorter gel lifetime. This work utilizing biological macromolecules in kinetically controlled dissipative structures opens the door to future applications of such systems in which the biomolecules' structures can control the reaction kinetics. Another substantial outcome of our work is to uncover mechanisms underlying the initiation of nucleation in the initial stages of amyloid aggregate formation. The study of conformational fluctuations in the structure of the amyloid-forming protein beta 2-microglobulin (β_2 M) yielded three key results. First, β_2 M variants' aggregation propensity correlates with their conformational fluctuations rate. A longer-lived misfolded subpopulation increases the chance of aggregation initiation by increasing the collision chance of the protein's sticky regions. Second, the observed millisecond interconversions agree with the timescales required for the interconversion of a protein's structure between its subpopulations. Third, the fluctuations themselves could be a driving force for the nucleation of aggregates by decreasing the lag-time of nucleus formation by a sudden large fluctuation.