Materials Science & Engineering
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Item Magnetic nanoparticle inks for syringe printable inductors(2023) Fedderwitz, Rebecca; Kofinas, Peter; Material Science and Engineering; Digital Repository at the University of Maryland; University of Maryland (College Park, Md.)Direct Ink Writing (DIW) additive manufacturing (AM) has the transformative potential to construct complex shapes and devices with a single apparatus by exchanging the printable material at the print head. Iron cobalt (FeCo), permalloy (Ni80Fe20), and iron (II,III) oxide (Fe2O3·FeO) nanoparticles with varying magnetic properties were incorporated in resins to explore the influence of particle loading on printability and inductor device performance. It was generally found that increasing particle loading increased ink viscosity, with a loading maximum approaching 29 – 42 vol% depending on the particle type and resin mixtures due to differences in particle shape and size and resin viscosity. With more magnetic content, composites had higher magnetic permeability and inductance. Syringe printable, colloidal, aqueous magnetic inks were made using both stabilized iron oxide and MnZn doped ferrite nanoparticles with added free polymers. MnZn doped ferrite inks are printed into toroids, sintered to improve magnetic permeability and mechanical robustness, and constructed into an inductor device. Inductors with high magnetic permalloy nanoparticle content were also syringe printed into toroids and hand-wound to demonstrate their viability in fabricating three-dimensional inductors. The effect of particle size on stability and printability was observed. The research presented in this thesis investigates various methods for formulating magnetic nanoparticle inks and evaluates the contributions of particle stabilization, free polymer content, solvent composition, and particle loading on the rheological behavior required for syringe printing. Material properties and device performances were characterized using methods such as zeta potential and settling studies to observe particle functionalization and stability, rheology to study viscoelastic flow behavior, and vector network analysis to measure inductance and device efficiency to showcase the viability of this technique to manufacture passive electronic devices.Item Radiation-Induced Modification of Aramid Fibers: Optimizing Crosslinking Reactions and Indirect Grafting of Nanocellulose for Body Armor Applications(2022) Gonzalez Lopez, Lorelis; Al-Sheikhly, Mohamad; Material Science and Engineering; Digital Repository at the University of Maryland; University of Maryland (College Park, Md.)The goal of this dissertation was to design, synthesize, and analyze novel aramid fibers by covalently grafting nanocellulose through electron beam irradiation. These nanocellulose functionalized fibers showed enhanced strength and larger surface areas, which improves their performance and applicability in fiber-reinforced composites. Unmodified aramid fibers have smooth and chemically inert surfaces, which results in poor adhesion to many types of resins. Nanocellulose was chosen as the ideal filler to functionalize the fibers due to its reactive surface and high strength-to-weight ratio. Aramid fibers were further modified by radiation-induced crosslinking reactions as a means to avoid scission of the polymeric backbone and to further increase the fiber strength.An indirect radiation-induced grafting approach was used for synthesizing these novel nanocellulose-grafted aramid fibers while avoiding the irradiation of nanocellulose. The fibers were irradiated using the e-beam linear accelerator (LINAC) at the Medical Industrial Radiation Facility (MIRF) at the National Institute of Standards and Technology (NIST). After the irradiation, the fibers were kept in an inert atmosphere and then mixed with a nanocellulose solution for grafting. The grafted fibers were evaluated by gravimetric analysis, Fourier-transform infrared spectroscopy (FTIR), scanning electron microscopy (SEM), and nuclear magnetic resonance (NMR) spectroscopy. The mechanical properties of the synthesized fibers were studied by single fiber tensile tests. Aramid fibers were also irradiated at the MIRF in the presence of acetylene gas and triacrylate solution as a means to induce crosslinking reactions. These fibers were irradiated at both low doses and high dose rates at room temperature. A mechanism for the crosslinking of aramid fibers was proposed in this dissertation. Mechanical testing of the fibers after crosslinking showed an increase in the strength of the fibers of up to 15%. Ultra-high molecular weight polyethylene (UHMWPE) fibers were also studied, but due to an issue of entanglement of the fibers during the grafting process, their mechanical properties could not be analyzed. Future work will focus on using a better set up to avoid entanglement of these fibers. To complete the study of the radiation effects on polymers, this thesis explored the radiation-induced degradation of aromatic polyester-based resins. The composition of the resins studied included phenyl groups and epoxies, which complicate radiation-induced grafting and crosslinking reactions. Unlike aramid and polyethylene fibers, polyester-based resins have a C-O-C bond that is susceptible to degradation. The resins were irradiated at high doses in the presence of oxygen. The scission of the polymeric backbone of the polymers was studied using Electron Paramagnetic Resonance (EPR) analysis. EPR showed the formation of alkoxyl radicals and C-centered radicals as the primary intermediate products of the C-O-C scissions. The degradation mechanisms of the resins in the presence of different solvents were proposed. Changes in the Tg of the polymers after irradiation, as an indication of degradation, were studied by Dynamic Mechanical Analysis (DMA). The results obtained from this work show that irradiation of these resins results in continuous free radical-chain reactions that lead to the formation of recyclable oligomers.Item Processing and structural characterization toward all-cellulose nanocomposites(2021) Henderson, Doug A; Briber, Robert M; Material Science and Engineering; Digital Repository at the University of Maryland; University of Maryland (College Park, Md.)Cellulose is the most abundant biopolymer on the planet and is used in a variety of industry sectors including paper, coatings, medicine, and food. A deep understanding of cellulose is important for its development as an alternative polymer to those based on petroleum. This work focuses on two cellulose systems. The first of these, cellulose nanofibers, are the basic structural elements of naturally-occurring cellulosic materials; they exhibit excellent mechanical characteristics due to high crystallinity and a dense network of hydrogen bonding. These fibers can be separated from bulk cellulose via a TEMPO oxidation reaction followed by mechanical homogenization into a suspension in water. In this work, the production of these fibers is investigated by monitoring the change in structure of cellulose as a function of TEMPO reaction time and mechanical homogenization using small angle neutron scattering, atomic force microscopy, and optical microscopy. The second cellulose system is a molecular solution of cellulose formed using a binary solvent mixture consisting of ionic liquid and an aprotic solvent. Cellulose is difficult dissolve due to a dense hydrogen bonding network, and ionic liquids have been shown to be an effective alternative to more hazardous and energy-intensive dissolution methods for cellulose currently used in industry. The phase behavior of these solutions has been investigated using small angle neutron scattering as a function of temperature. The process of regenerating cellulose from these solutions is also investigated, as dense gels of cellulose and ionic liquid were produced with a unique multiscale ordered structure. The ultimate goal of this work is to combine cellulose nanofibers and molecular cellulose solutions in order to create all-cellulose nanocomposite films. These films are characterized using tensile testing, atomic force microscopy, and water uptake measurements in order to understand the interaction between cellulose nanofibers and molecular cellulose solutions, water resistance and tunability of mechanical properties.Item RADIATION SYNTHESIS OF IONIC LIQUID POLYMER ELECTROLYTE MEMBRANE FOR HIGH TEMPERATURE FUEL CELL APPLICATIONS(2020) Mecadon, Kevin; Al-Sheikhly, Mohamad; Material Science and Engineering; Digital Repository at the University of Maryland; University of Maryland (College Park, Md.)The purpose of this thesis was to design, synthesize and analyze innovative anhydrous fuel cell membranes that can operate at temperatures above 100°C. Operating at this higher temperature region improves performance and reliability of fuel cells: increasing proton mobility, enhancing reaction kinetics, increasing catalysis activity and reducing carbon monoxide poisoning. Traditional polymer electrolyte membrane fuel cells (PEMFCs) do not operate efficiently above 100°C because water is used as a proton conductive medium though the Grotthuss hopping mechanism. Through substituting water with protic ionic liquids and grafting onto fluorocarbon films, a new proton conductive network solid state PEM has been developed. These membranes can perform at high temperature above 100°C. Polymers were selected for grafting based on the following properties: high proton conductivity, low electrical conductivity, high mechanical properties, high chemical resistance, and high temperature and humidity stability. The method used to synthesize these anhydrous polymer electrolyte membranes (PEMs) was radiation grafting using heterocyclic protic ionic liquid monomers and fluorocarbon substrates. PEMs were prepared at the Medical Industrial Radiation Facilities (MIRF) at the National Institute of Standards and Technology (NIST). MIRF is a 10.5 MeV electron beam accelerator, which was used to radiate the fluorocarbon substrate and then indirectly graft heterocyclic protic ionic liquids to create PEMs. After synthesis, the extent and uniformity of PEM composition was analyzed using FTIR microscopy, SEM/EDS, SANS and their proton conductivity as measured by EIS. Through this research, indirect radiation grafting was shown to covalently bond ionic liquids onto fluorocarbon substrates to synthesize PEMs. The resulting ionic liquid PEMs showed proton conductivities greater than 10-3 S/cm above 100°C that behaved independent of humidity. The ionic liquid PEMs also demonstrated a positive correlation of increasing proton conductivity with increasing temperatures above 100°C even after the PEMs are dehydrated. The chemical properties and structure of the grafted ionic liquids greatly affects the proton conductive mechanisms present in the PEMs. These trends found through the course of this research will help the development of future anhydrous PEM with higher proton conductivity, performance, and reliability.Item COLD ATMOSPHERIC PRESSURE PLASMA SURFACE INTERACTIONS WITH POLYMER AND CATALYST MATERIALS(2018) Knoll, Andrew Jay; Oehrlein, Gottlieb S; Material Science and Engineering; Digital Repository at the University of Maryland; University of Maryland (College Park, Md.)Cold atmospheric pressure plasma (CAP) is an excellent source of reactive species because they are able to produce these species cheaply, in a variety of configurations, and in a way that can be distributed easily but there needs to be more understanding of how they specifically interact with surfaces. The goals of this dissertation are to understand what the critical reactive species reaching a surface are for particular applications. As a first step we find that a plasma in direct electrical contact with a polymer material shows high etching rate and non-uniform treatment whereas a remote regime treatment can lead to a relatively uniform treatment over the exposed to plasma area. The interaction of vacuum ultraviolet (VUV) light with polymer surfaces was found to be critical under conditions where local oxygen is displaced by noble gas flow. This VUV flux is also dependent on plasma source type, being highest for high voltage sources using noble gas flow. For a surface microdischarge (SMD) source we find high activation energy compared with atomic oxygen etching suggesting less reactive species reaching the surface are causing surface modification. However, for an atmospheric pressure plasma jet (APPJ) source we find that the activation energy changes over treatment distance, decreasing below the value expected for atomic oxygen as the jet gets closer to the surface. Additionally we find evidence of directional etching for the close distances which becomes less directional for further distance treatments suggesting we have a contribution from high energy species at closer distances despite there being no visible contact between the plasma plume and the polymer surface. Nickel catalyst materials interacting with plasma can be enhanced to show increased breakdown of methane and production of different product species such as CO compared to just the catalyst. This catalyst material also shows carbon deposition by CO and COO- groups by plasma treatment, though increased plasma power and temperature can then remove these groups as well.Item Synthesis of Novel Co-Polymers Using Ionizing Radiation Grafting Methods for the Extraction of Uranium from Seawater(2017) Dietz, Travis Cameron; Al-Sheikhly, Mohamad I; Material Science and Engineering; Digital Repository at the University of Maryland; University of Maryland (College Park, Md.)The world’s oceans contain a relatively uniform uranium concentration of 3 μg/L. While this is an exceedingly small concentration, the quantity of uranium throughout the oceans is about 1000 times higher than the quantity in known terrestrial deposits. To take advantage of this immense resource, radiation grafting techniques were used to attach uranium-chelating monomers to durable polymer substrates. Three novel, uranium extracting co-polymer systems have been fabricated through this process and characterized. Three different compound classes were explored for their ability to extract uranium, specifically phosphates, oxalates, and azos. These classes displayed characteristics that provide advantages to the technology over state-of-the-art systems. For the phosphates and oxalates, monomers of these classes containing allyl groups were radiation grafted onto a polymer in a single step. For the azos, a chemical precursor containing a vinyl group was initially radiation grafted to a polymer. The azo compound was then chemically attached to the functionalized polymer surface. For effective seawater deployment, a polymer substrate was chosen as an inexpensive, reusable platform for extraction. While different fabric substrates were tested, high surface area (14 m^2/g) nylon 6 fabric was chosen for its durability and its capacity for radiation grafting. Direct and indirect radiation induced graft polymerization methods were used in this work. For direct grafting, the nylon 6 fabric was immersed in the monomer solution and irradiated. However, for indirect grafting, only the fabric was irradiated followed by the immediate introduction of the monomer solution. All of these experiments were conducted under anaerobic conditions to prevent the reaction of oxygen with the radiolytically-produced, carbon-centered free radicals. The grafted fabrics were characterized for attachment of the monomer and their ability to extract uranium. The degree of surface grafting was determined through attenuated total reflectance Fourier transform infrared spectroscopy, scanning electron microscopy, and energy dispersive X-ray spectroscopy, among other techniques. Electron paramagnetic resonance spectroscopy was used to determine radical decay kinetics in the polymer substrate. Pulse radiolysis was used to elucidate the polymerization reaction kinetics of certain monomers. These fabrics were then exposed to uranium-doped seawater solutions and the extraction capacities of the grafted materials were determined.Item Low and Atmospheric Pressure Plasma Interactions with Biomolecules and Polymers(2015) Bartis, Elliot Andrew James; Oehrlein, Gottlieb S; Material Science and Engineering; Digital Repository at the University of Maryland; University of Maryland (College Park, Md.)Cold atmospheric plasma (CAP) sources have emerged as economical and environmentally friendly sources of reactive species with promising industrial and biomedical applications. Many different sources are studied in the literature for advanced applications including surface disinfection, wound healing, and cancer treatment, but the underlying mechanisms for these applications are not well-understood. The overall goals of this dissertation are to 1) identify how plasma treatments induce surface modifications and which plasma species are responsible for those modifications; 2) identify how changes in surface and plasma chemistry contribute to changes in biological activity of biomolecules; and 3) investigate how fluxes of reactive species produced by atmospheric pressure plasma devices can be controlled. As a first step, a well-studied low pressure plasma system was used to isolate the effects of ions, high energy photons, and radicals using Ar and H2 plasma. The finding that plasma-generated radicals can biodeactivate and modify films with negligible etching motivated further study at atmospheric pressure. Two very different CAP sources were used under mild, remote conditions to study the biological deactivation of two immune-stimulating biomolecules: lipopolysaccharide (LPS), found in bacteria such as Escherichia coli, and peptidoglycan, found in bacteria such as Staphylococcus aureus. The surface chemistry was measured to understand which plasma- generated species and surface modifications are important for biological deactivation. To simplify the complex molecular structure of the biomolecules and study specific moieties, model polymer films were studied including polystyrene, poly(methyl methacrylate), polyvinyl alcohol, and polypropylene. The interaction of the plasma plume with the environment was studied as a parameter to tune surface modifications. It was found that increasing ambient N2 concentrations in an N2/Ar ambient decreased surface modifications of LPS, similarly to how adding N2 to the O2/Ar feed gas decreased the plasma-generated O3 density and O atom optical emission. In this work, we first observed the formation of surface-bound NO3 after plasma treatment, which had not been reported in the literature. The plasma-ambient interaction was further studied using polystyrene as a model system. This detailed study demonstrated a competition between surface oxidation and nitridation, the latter of which occurs under very specific conditions. It was found that NO3 formed on all the materials studied in this dissertation after plasma treatment. This NO3 formed after treatment by both sources, but in different concentrations. The surface-bound NO3 correlated better with changes in biological activity than general oxidation, demonstrating its importance. Studying model polymers revealed that this surface moiety preferentially forms on – OH containing surfaces. Since the atmospheric pressure plasma jet (APPJ) operates with low N2/O2 admixtures to Ar and the surface microdischarge (SMD) operates with N2/O2 mixtures, the mechanisms that cause biological deactivation must be different, and are discussed.Item Radiation-Grafted Fabrics for the Extraction of Uranium from Seawater(2014) Tissot, Chanel; Briber, Robert; Nuclear Engineering; Digital Repository at the University of Maryland; University of Maryland (College Park, Md.)Much interest has been generated in extraction uranium from the ocean - the world's largest uranium reserve. This dissertation describes the development and seawater testing of a polymeric adsorbent for uranium based on radiation-induced grafting. Among all monomers and polymeric substrates tested, grafting of the monomer bis(2-methacryloxyethyl) phosphate (B2MP) onto Winged nylon fabric was determined to produce adsorbents of the highest degrees of grafting. Degree of grafting was optimized by irradiating at a range of dose rates and total absorbed doses and by varying monomer concentration, solvent, purging gas and radiation source. Both the University of Maryland's Co-60 gamma irradiator and 1-9 MeV pulsed LINAC were utilized. The grafted adsorbents were tested for uranium extraction capacity using a Uranium-233 radiotracer in synthetic seawater at natural (3.3 ppb) uranium concentrations. It was determined that adsorbents of degrees of grafting between 75 and 100% obtained the highest distribution coefficients for uranium. Kinetic studies revealed an increase in Uranium-233 concentration on the adsorbent over the course of 4 hours after which time a steady-state was reached. Correlation of this data with kinetic models indicated pseudo-second order kinetics, suggesting the rate-limiting adsorption mechanism as chemical complexation between Uranium-233 and the phosphate-containing adsorbent. Overall, the highest performing adsorbents obtained distribution coefficients of 1.2 × 104 mL/g and Uranium-233 loadings of 1.0 × 10-2 mg-U/g-adsorbent. These values were a result of performing the extractions at 3.3 Uranium-233, a concentration several orders of magnitude lower than those reported in similar studies. The chemical changes that occurred upon grafting were investigated with FTIR and Raman analysis of virgin, irradiated and B2MP-grafted Winged nylon. Characterization of the grafted adsorbents with SEM revealed a unique morphology for the grafted fabrics that has been attributed to the precipitation of homopolymer from the solvent during irradiation. SEM/EDS analysis of a grafted adsorbent contacted with Uranium-233-spiked synthetic seawater revealed the presence of several elements abundant in seawater, indicating that competition between uranium and other seawater ions is likely to limit the uranium uptake capacity of the adsorbent.Item THERMODYNMICS AND STRUCTURE OF POLY(ETHYLENE OXIDE) IN MIXTURES OF WATER AND ETHANOL(2011) SHIN, SANG HAK; Briber, Robert M; Material Science and Engineering; Digital Repository at the University of Maryland; University of Maryland (College Park, Md.)Poly(ethylene oxide) (PEO) is one of the most researched synthetic polymers due to the complex behavior which arises from the interplay of the hydrophilic and hydrophobic sites on the polymer chain. PEO in ethanol forms an opaque gel-like mixture with a partially crystalline structure. Addition of a small amount of water disrupts the gel: 5 wt % PEO in ethanol becomes a transparent solution with the addition of 4 vol % water. The phase behavior of PEO in mixed solvents have been studied using small-angle neutron scattering (SANS). PEO solutions (5 wt % PEO) which contain 4 vol % - 10 vol % (and higher) water behave as an athermal polymer solution and the phase behavior changes from UCST to LCST rapidly as the fraction of water is increased. 2 wt % PEO in water and 10 wt % PEO in ethanol/ water mixtures are examined to assess the role of hydration. The observed phase behavior is consistent with a hydration layer forming upon the addition of water as the system shifts from UCST to LCST behavior. At the molecular level, two or three water molecules can hydrate one PEO monomer (water molecules form a sheath around the PEO macromolecule) which is consistent with the suppression of crystallization and change in the mentioned phase behavior as observed by SANS. The clustering effect of aqueous PEO solution (M.W of PEO = 90,000 g/mol) is monitored as an excess scattering intensity at low-Q. Clustering intensity at Q = 0.004 Å^-1 is used for evaluating the clustering effect. The clustering intensity is proportional to the inverse temperature and levels off when the temperature is less than 50 ˚C. When the temperature is increased over 50 ˚C, the clustering intensity starts decreasing. The clustering of PEO is monitored in ethanol/ water mixtures. The clustering intensity increases as the fraction of water is increased. Based on the solvation intensity behavior, we confirmed that the ethanol/ water mixtures obey a random solvent mixing rule, whereby solvent mixtures are better at solvating the polymer that any of the two solvents. The solution behavior of PEO in ethanol was investigated in the presence of salt (CaCl2) using SANS. Binding of Ca2+ ions to the PEO oxygens transforms the neutral polymer to a weakly charged polyelectrolyte. We observed that the PEO/ethanol solution is better solvated at higher salt concentration due to the electrostatic repulsion of weakly charged monomers. The association of the Ca2+ ions with the PEO oxygen atoms transforms the neutral polymer to a weakly charged polyelectrolyte and gives rise to repulsive interactions between the PEO/Ca2+ complexes. Addition of salt disrupts the gel, which is consistent with better solvation as the salt concentration is increased. Moreover, SANS shows that the phase behavior of PEO/ethanol changes from UCST to LCST as the salt concentration is increased.