Chemical and Biomolecular Engineering Theses and Dissertations

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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.
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.
FABRICATION OF ASYMMETRIC CERAMIC MEMBRANES VIA INDIRECT ADDITIVE MANUFACTURING
(2022) richard, patrick; Liu, Dongxia; Lazarus, Nathan; Chemical Engineering; Digital Repository at the University of Maryland; University of Maryland (College Park, Md.)
A dearth of literature regarding the fabrication of separation membranes via indirect additive manufacturing undermines the significant progress made by 3D technologies to improve resolution, printing time, and ease of operation. That is to say, the benefits of 3D printing may be realized even with an indirect route. This thesis aims to employ bench-scale stereolithography (SLA) to print a mold design that may be combined with a conventional technique to consistently yield viable alumina membrane supports for separation application. An iterative approach was applied to mitigate potential sources of variability, including poor mold design, mold casting, and ceramic substrate coating. Once the procedure was established, multiple alumina supports were fabricated, characterized, and coated with zeolite A(LTA) separation layers for pervaporation separations. The alumina supports demonstrated highly-ordered macroscopic structures, asymmetric microstructures, acceptable dimensional shrinkage (15.4%-18.5%), moderate density (2.89g/cm3), and good porosity (35.5%). The LTA-coated asymmetric membrane exhibited excellent separation performance with a flux of 0.800 kg/(m2•h) and a separation factor of 5190 for the pervaporation separation of an ethanol-water mixture. Although the generalizability is limited to other high-resolution bench-scale SLA printers, it is clear that high-quality ceramic separation membranes or substrates may be fabricated with an indirect additive manufacturing approach. Thus, the findings of this thesis provide a highly repeatable and reproducible fabrication pathway for challenging materials and geometries while still exploiting the unparalleled precision and control of 3D printing.
TISSUE ADHESIVE, SPRAYABLE POLYMER BLENDS AS ADJUVANT SURGICAL TOOLS
(2022) Erdi, Metecan; Kofinas, Peter; Chemical Engineering; Digital Repository at the University of Maryland; University of Maryland (College Park, Md.)
Commercial materials deployed in surgery for treatment of high-impact clinical pathologies suffer from shortcomings stemming from a combination of poor mechanical properties, difficulty in precise application, and non-specific prevention mechanisms. Work in this dissertation seeks to counteract these concerns through a multitude of blending approaches with biodegradable polymers and therapeutic agents for improved outcomes following traumatic tissue injury. The polymer blends were spray deposited using solution blow spinning, a method of fiber production where material rapidly accumulates onto target tissue substrate and forms a stable interface. The first thrust of this dissertation hones on deposition of a biocompatible, wet tissue adhesive. These tissue adhesives were fabricated through molecular weight ratio blends of poly(lactide-co-caprolactone) (PLCL), a synthetic, biodegradable copolymer with viscoelastic properties fostering pressure-dependent adhesion. High molecular weight PLCL endowed the composite material with rigidity and inherent cohesive strength, while low molecular weight PLCL induced spreadability and adhesive strength. Such optimized material behavior presented an ability to not only adhere to hydrophilic surfaces, but also demonstrated an ability to act as a media for biocompatible and complete wound healing. Efficacy as an adhesive in wound dressings was exhibited through spray deposition of blend adhesives to bandage substrates in a porcine partial thickness burn wound model and comparison with a poly(urethane)-based clinical control material. The second thrust of this dissertation focuses on development of an effectively applied barrier material for prevention of post-operative fibrotic scar tissue termed as adhesions. Rapid generation of tissue-conformal polymer fibers through solution blow spinning yields a material that is inherently flexible, thereby counteracting the brittle architecture of a sheet-like film currently deployed in surgery. Prevention of asymmetric fibrosis was accomplished through tuned surface biodegradation via high and low molecular weight PLCL blends. This strategy seeks to physically prevent prolonged retention of adhesion-generating molecules at the site of injury, as well as biologically counteract underlying inflammatory processes through controlled release of a therapeutic, apolipoprotein mimetic peptide from composite PLCL fiber mat. Adhesion prevention efficacy was qualified in high impact pre-clinical mouse models of cecal ligation and cecal anastomosis, and compared to pre-fabricated, dried hydrogel barrier and aqueous therapeutic suspension controls. Both adhesion severity and resultant wound healing response were significantly improved versus no treatment and clinically adopted controls.
NOVEL AQUEOUS-BASED ELECTROLYTES AND ELECTRODE SYSTEMS FOR THE NEXT GENERATION OF AQUEOUS LITHIUM-ION BATTERIES
(2022) Eidson, Nicolas Thierry; Wang, Chunsheng; Chemical Engineering; Digital Repository at the University of Maryland; University of Maryland (College Park, Md.)
Aqueous Li-ion batteries are a vital component for the future electrification of society. Their extreme safety and reduced manufacturing costs could enable them to fit into many niche markets. Current aqueous Li-ion battery systems suffer from many of the same form factor restrictions as organic Li-ion batteries and rely heavily on maximizing the amount of LiTFSI in the system at the cost of important properties such as electrolyte cost, viscosity, and ionic conductivity in order to maintain the highly concentrated electrolyte classification. They are also limited by the lack of suitable anodes to replace the dominant choice of LTO. Much of the advancement in recent years has been due to the focus on improving the SEI with less attention paid to other important concerns. The goal of this research is not only to continue advancing the limits of aqueous Li-ion batteries, but to shed light on some of the other areas that are often overlooked but of equal importance. Reported here are three key advancements in the development of a novel aqueous cell chemistry for form factor, electrolyte, and anode. First is the development of a gel polymer electrolyte and gel protection layer for the fabrication of a flexible 4V aqueous Li-ion battery employing a Graphite/LCO electrode pair, with focus given to the system’s feasibility to be transitioned to industry. Second, the development of a safer hybrid electrolyte and subsequent transition from the highly concentrated electrolyte regime to the first reported localized highly concentrated hybrid aqueous/non-aqueous electrolyte. Finally, the first incorporation of TNO as an anode replacement for LTO. With the combination of this novel electrolyte and aqueous anode chemistry, a TNO/LMO full cell using a 1,4-dioxane diluted water/TEP co-solvent electrolyte provided an initial discharge capacity of 187 mAh/g reaching a Coulombic efficiency of >99.5% and a capacity retention of 92% after 90 cycles at a cycling cutoff potential of 2.8V.

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