Theses and Dissertations from UMD
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Item MECHANICS AND THERMAL TRANSPORT MODELING IN NANOCELLULOSE AND CELLULOSE-BASED MATERIALS(2023) RAY, UPAMANYU; Li, Teng; Mechanical Engineering; Digital Repository at the University of Maryland; University of Maryland (College Park, Md.)Cellulose, the abundantly available natural biopolymer, has the potential to be a next generation wonder material. The motivation behind this thesis stems from the efforts to obtain mechanical properties of two novel cellulose-based materials, which were fabricated using top-down (densified engineered wood) and bottoms-up (graphite-cellulose composite) approaches. It was observed that the mechanical properties of both the engineered wood (strength~596 MPa; toughness ~3.9 MJ/m3) and cellulose-graphite composite (strength~715 MPa; toughness ~27.7 MJ/m3) surpassed the equivalent features of other conventional structural materials (e.g., stainless steel, Al alloys etc.). However, these appealing properties are still considerably inferior to individual cellulose fibrils whose diameters are in the order of nanometers. A significant research effort needs to be initiated to effectively transfer the mechanical properties of the hierarchical cellulose fibers from the atomistic level to the continuum. To achieve that, a detailed understanding of the interplay of cellulose molecular chains that affects the properties of the bulk cellulosic material, is needed. Modeling investigations can shed light on such underlying mechanisms that ultimately dictate multiple properties (e.g., mechanics, thermal transport) of these cellulosic materials. To that end, this thesis (1) applies molecular dynamics simulations to decipher why microfibers made of aligned nanocellulose and carbon nanotubes possess excellent mechanical strength, along with understanding the role of water in fully recovering elastic wood under compression; (2) delineates an atomistically informed multi-scale, scalable, coarse grained (CG) modeling scheme to study the effect of cellulose fibers under different representative loads (shearing and opening), and to demonstrate a qualitative guideline for cellulose nanopaper design by understanding its failure mechanism; (3) utilizes the developed multi-scale CG scheme to illustrate the reason why a hybrid biodegradable straw, experimentally fabricated using both nano- and micro-fibers, exhibits higher mechanical strength than individual straws that were built using only nano or microfibers; (4) investigates the individual role of nanocellulose and boron nitride nanotubes in increasing the mechanical properties (tensile strength, stiffness) of the derived nanocellulose/boron-nitride nanotube hybrid material; (5) employs reverse molecular dynamics approach to explore how the boron nitride nanotube based fillers can improve thermal conductivity (k) of a nanocellulose derived material. In addition, this thesis also intends to educate the readers on two perspectives. The common link connecting them is the method of engineering intermolecular bonds. The first discussion presents a few novel mechanical design strategies to fabricate high-performance, cellulose-based functional materials. All these strategies are categorized under a few broad themes (interface engineering, topology engineering, structural engineering etc.). Another discussion has been included by branching out to other materials that, like nanocellulose, can also be tuned by intermolecular bonds engineering to achieve unique applications. Avenues for future work have been suggested which, hopefully, can act as a knowledge base for future researchers and help them formulate their own research ideas. This thesis extends the fundamental knowledge of nanocellulose-based polymer sciences and aims to facilitate the design of sustainable and programmable nanomaterials.Item DESIGN AND SYNTHESIS OF POLYOLEFIN MATERIALS FOR NANOSTRUCTURED SELF-ASSEMBLY: BUILDING BLOCKS, COPOLYMERS, AND POLYMER CONJUGATES(2022) Wentz, Charlotte Maria; Sita, Lawrence R; Chemistry; Digital Repository at the University of Maryland; University of Maryland (College Park, Md.)Polyolefin based materials are essential to today’s society in both simplistic commodity plastics to complex nanostructured materials and optoelectronic devices. In order to better understand these materials and make new impactful innovations, there is a barrier of fabrication, scalability, versatility, and programmability. The answer to the world’s plastic waste problem lies not in removing our use of polymers but relies in better understanding their properties, utilizing them as building blocks in advanced materials, and creating a long-lasting advanced material. Towards the goal of overcoming limitations in fabrication and scalability the work herein presents on utilizing a toolbox of living polymerization techniques such as living chain transfer polymerization (LCCTP) where new functionalities, stereochemical microstructures, optical properties, and physical properties of the polyolefin can be designed and systematically controlled. The polyolefins made through these techniques are scalable and versatile with end-group functionalization creating a seemingly endless choice of polymer building blocks and polymer materials. In line with creating new technologies that are programable the polyolefin building blocks made herein are utilized in multiple conjugates to create and understand methods and mechanisms of solid-state nanostructured self-assembly and access rare nonclassical phases that are highly desirable for their properties and uses in a plethora of applications. The conjugates investigated involve either a sugar-based head group covalently bond to a polymer tail to access rare and misunderstood Frank Kasper phase order-order transitions, or a perylene chromophore core covalently bond on both sides of the core in a linear fashion to polymer domains to create highly florescent or optically active materials that are useful in organic technologies such as solar cells, light emitting diodes, or nanotechnology. These perylene based conjugates can self-assemble into unique columnar phases and single gyroid phase. These results with conjugates provide methods for reliable and programmable access to rich phase behavior through the design of the polyolefin domains.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 Electrically Induced Gelation, Rupture, and Adhesion of Polymeric Materials(2017) Gargava, Ankit; Raghavan, Srinivasa R; Chemical Engineering; Digital Repository at the University of Maryland; University of Maryland (College Park, Md.)There has been considerable interest in developing stimuli-responsive soft materials for applications in drug delivery, biosensing, and tissue engineering. A variety of stimuli have been studied so far, including temperature, pH, light, and magnetic fields. In this dissertation, we explore the use of electric fields as a stimulus for either creating new soft materials or for rupturing existing ones. Our materials are based typically on biocompatible polymers such as the polysaccharides alginate, chitosan, and agarose. We also discuss the advantages and disadvantages of electric fields over other stimuli. First, we describe the use of electric fields to form transparent and robust alginate gels around an initial mold made of agarose. Moreover, we can melt away the agarose by heat, leaving us with hollow alginate tubes. In our technique, a tubular agarose mold with dissolved calcium chloride (CaCl2) is placed in a solution of sodium alginate. A voltage of ~ 10 V is then applied, with the mold as the anode and the container as the cathode. As the Ca2+ ions migrate from the mold towards the cathode, they contact the alginate chains at the mold surface. In turn, the Ca2+ crosslinks the alginate chains into a gel, and the gel grows outward with time. The technique can be used to grow multiple layers of alginate, each with a different content, and it is also safe for encapsulation of biological species. Complex tubular structures with multiple branches and specific patterns can be created. Next, we report that electric fields can be used to rupture particles formed by ionic complexation. The particles under study are typically in the microscale (~ 200 µm radius) and are either uniformly crosslinked microbeads (e.g., alginate/Cu2+) or microcapsules formed by complexation of oppositely charged polymers (alginate and chitosan). When these particles are placed in aqueous solution and subjected to an electric field of about 10 V/cm (applied remotely, i.e., electrodes not in contact), the particles rupture within about 5 min. A possible mechanism for the electric-field-induced disruption is discussed. We also use the above particles to create electrically actuatable valves, where the flow of a liquid occurs only when the particle blocking the flow is disrupted by the field. In our final study, we show that polyelectrolyte gels and beads can be rapidly induced to adhere by an electric field. We typically work with crosslinked acrylate hydrogels made with cationic co-monomers, and anionic beads made by contacting alginate with Ca2+. When the cationic gel (connected to an anode) is contacted for just a few seconds with the anionic bead (connected to a cathode) under a voltage of ~ 10 V, the two form a strong adhesive bond. When the polarity of the electrodes is reversed, the phenomenon is reversed, i.e., the gel and bead can be easily detached. We suggest that the adhesion is due to electrophoretic migration of polyelectrolyte chains, resulting in the formation of polyion complexes. Applications of this reversible adhesion are discussed for the pick-up and drop-off of soft cargo, and for the sorting of beads.Item Prediction of Upward Flame Spread over Polymers(2016) Leventon, Isaac Tibor; Stoliarov, Stanislav I; Mechanical Engineering; Digital Repository at the University of Maryland; University of Maryland (College Park, Md.)In this work, the existing understanding of flame spread dynamics is enhanced through an extensive study of the heat transfer from flames spreading vertically upwards across 5 cm wide, 20 cm tall samples of extruded Poly (Methyl Methacrylate) (PMMA). These experiments have provided highly spatially resolved measurements of flame to surface heat flux and material burning rate at the critical length scale of interest, with a level of accuracy and detail unmatched by previous empirical or computational studies. Using these measurements, a wall flame model was developed that describes a flame’s heat feedback profile (both in the continuous flame region and the thermal plume above) solely as a function of material burning rate. Additional experiments were conducted to measure flame heat flux and sample mass loss rate as flames spread vertically upwards over the surface of seven other commonly used polymers, two of which are glass reinforced composite materials. Using these measurements, our wall flame model has been generalized such that it can predict heat feedback from flames supported by a wide range of materials. For the seven materials tested here – which present a varied range of burning behaviors including dripping, polymer melt flow, sample burnout, and heavy soot formation – model-predicted flame heat flux has been shown to match experimental measurements (taken across the full length of the flame) with an average accuracy of 3.9 kW m-2 (approximately 10 – 15 % of peak measured flame heat flux). This flame model has since been coupled with a powerful solid phase pyrolysis solver, ThermaKin2D, which computes the transient rate of gaseous fuel production of constituents of a pyrolyzing solid in response to an external heat flux, based on fundamental physical and chemical properties. Together, this unified model captures the two fundamental controlling mechanisms of upward flame spread – gas phase flame heat transfer and solid phase material degradation. This has enabled simulations of flame spread dynamics with a reasonable computational cost and accuracy beyond that of current models. This unified model of material degradation provides the framework to quantitatively study material burning behavior in response to a wide range of common fire scenarios.Item A New Scale-Up Approach Through the Evaluation of Stress History Within a Twin-Screw Extruder(2014) Fukuda, Graeme Masuhiro; Bigio, David I.; Mechanical Engineering; Digital Repository at the University of Maryland; University of Maryland (College Park, Md.)The development of any new product manufactured by extrusion requires initial testing at the laboratory level. Once the behaviors of the product and process are understood, the operation is scaled-up to an industrial grade procedure. Scale-up/down is used in a wide variety of markets such as food processing, food packaging, tubing, and pharmaceutical industries. Product quality is critical to the success of all these applications, but is often made difficult when compounding with additives, fillers, pigments, plasticizers, and other supplemental ingredients. Product quality is achieved when the constituents are well mixed. Stress is a critical parameter in accomplishing good mixing. Through the use of polymeric stress beads, a methodology has been developed to measure residence stress distributions in real time. The methodology has enabled the analysis of both model and industrial grade extruders. Evaluation of both processes has led to the creation of a new scale-up approach for dispersive mixing. The new scale-up rule based on percent drag flow was shown to be a more accurate dispersive mixing scale-up approach for a range of operating conditions compared to the current industry standard.Item Discrete and Polymeric Complexes Comprising Bis-nor-seco-CB[10] and Oligoammonium Ions(2009) Nally, Regan; Isaacs, Lyle; Chemistry; Digital Repository at the University of Maryland; University of Maryland (College Park, Md.)ABSTRACT Title of Document: DISCRETE AND POLYMERIC COMPLEXES COMPRISING BIS-NOR-SECO-CB[10] AND OLIGOAMMONIUM IONS Regan C. Nally, Ph.D., 2009 Directed By: Professor Lyle D. Isaacs Department of Chemistry and Biochemistry Supramolecular architectures composed of multiple components are challenging to produce, as the enthalpic gain must be greater than the entropic penalty of strict geometrical arrangements. Therefore, it is the goal of supramolecular chemists to strategically design and synthesize molecules that will exhibit selectivity toward formation of a particular complex. This dissertation describes the formation of supramolecular architectures of increasing size and is organized in the following way. Chapter 1 introduces the reader to the field of supramolecular polymer chemistry. Chapter 2 describes the synthesis of a series of monovalent ditopic guests (II-1 - II-6) and their complexation properties toward double cavity cucurbituril host bis-ns-CB[10]. We observed the preferential formation of 1:1, 2:2, and oligomeric complexes rather than the desired n:n supramolecular polymers. Guest II-7 which contains a longer biphenyl spacer successfully precludes the formation of the 1:1 complex but results in the formation of the 2:2 complex (bis-ns-CB[10]2*II-72) rather than supramolecular polymer. Guest II-8 is heterovalent and ditopic and is shown to reversibly form 2:2 and 1:2 complexes (bis-ns-CB[10]2*II-82 and bis-ns-CB[10]*II-82) in response to changes in host:guest stoichiometry. Lastly, this equilibrium can be manipulated by the addition of exogenous CB[6] which selectively targets the hexanediammonium ion binding region of II-8 and delivers the penta-molecular complex bis-ns-CB[10]*II-82*CB[6]2. Chapter 3 describes the formation of a main chain supramolecular polymer from a mixture of poly(diallyldimethylammonium chloride) (III-1) and bis-ns-CB[10]. The bis-ns-CB[10] molecular container behaves as a molecular handcuff, bringing together two ends of individual polymers to form III-1n* bis-ns-CB[10]m, resulting in an extension of the length of polymer. The effect of bis-ns-CB[10] on the physical properties of the polymer was investigated using viscometry in aqueous solution. A decrease in the ηrel was observed upon increasing concentrations of bis-ns-CB[10] to a solution of III-1. Atomic force microscopy (AFM), and diffusion-ordered spectroscopy (DOSY) were performed to probe the mode of interaction between polymer III-1 and bis-ns-CB[10]. Collectively, the data supports the two roles for bis-ns-CB[10]: 1) as a deaggregation agent, and 2) as a molecular handcuff that non-covalently links individual polymer strands resulting in overall extension of the polymer.