Doctor of Philosophy (Ph.D.), University of Dayton, 2024, Electrical and Computer Engineering

Additive manufacturing (AM) technology is rapidly advancing across diverse fields. For instance, the use of robotic arms in various AM processes has led to significant gains in printing flexibility and manufacturing scalability. However, despite these advancements, there remains a notable research gap concerning the mechanical properties of parts 3D-printed with robotic arms. This study focuses on developing a robotic fused filament fabrication (FFF) 3D-printing process with a layer resolution of 50 μm to 300 μm. The impact of the robotic printing process on the mechanical properties of printed parts is investigated and benchmarked against a commercial FFF 3D printer. In addition, we propose a novel tool path that can vary contour layer thickness within an infill layer to improve mechanical strength by minimizing air gaps between contours. SEM images suggest that this new tool path strategy leads to a significant reduction in the fraction of the void area within the contours, confirmed by a nearly 6% increase in the ultimate tensile strength. Furthermore, a novel strategy for non-planar contours is proposed, specifically designed for thin-shell 3D models. This approach aligns tool paths parallel to the Z-axis, organized into triangular segments, and utilizes planar slicing techniques. The method involves segmenting the point cloud and systematically printing non-planar contours on top of the planar contours. Axial compression testing reveals that samples produced using this strategy exhibit mechanical properties comparable to those of conventional 3D printing. However, distinct fracture patterns are observed: in conventional 3D-printed samples, fractures occur on both inner and outer surfaces, while in non-planar printed samples, fractures are confined to the inner surfaces (planar contours) and do not propagate to the outer non-planar contours. This demonstrates the potential of non-planar printing for improved structural integrity.

Master of Sciences (Engineering), Case Western Reserve University, 2025, Macromolecular Science and Engineering

Hexagonal boron nitride is a platelet-like thermally conductive filler commonly used to increase the thermal conductivity of polymers. Good alignment of boron nitride in the in-plane direction is required to create a good network for phonon transport to achieve high thermal conductivity in composite materials. To create good alignment of platelet-like particles, extensional flow is needed, like what is experienced by a polymer melt in a layer multiplication element in forced assembly co-extrusion. As a result, films with A/B structure of hBN + polymer/unfilled polymer were made using layer multiplication co-extrusion. The high degree of alignment and confinement of boron nitride into every other layer led to a higher-than-expected thermal conductivity at relatively low loadings of boron nitride. At only 12.7vol% (25wt%) filler loading, a composite film reached a thermal conductivity of 3.41 Wm-1K-1 which is much higher than was predicted by modeling.

Doctor of Philosophy, University of Akron, 2024, Polymer Science

Global climate change has prompted a critical rethinking of plastic sourcing and waste management. Life-cycle analyses reveal that present day polymer feedstocks must be revaluated to curb adverse impacts of land-use change on greenhouse gas emissions. Carbon dioxide, as an abundantly available C1 feedstock, offers a cheap yet versatile platform for sustainable polymer synthesis. However, the commercialization of CO2-based materials is currently limited to applications in the CASE (coatings, adhesives, sealants and elastomers) domains, with traditional high environmentally impacting thermosets (due to landfilling and poor waste-management) continuing to dominate thermomechanically demanding applications such as composite resins in the automotive, aerospace and energy generation sectors. This work seeks to address these dual crises by enchaining carbon dioxide into sustainable polymer networks to enhance mechanical and chemical recyclability while delivering high thermomechanical properties that rival traditional thermosets, paving the way for sustainable, high-performance alternatives. The overarching scientific objective of this work is to investigate key aspects of polymer network dynamics with respect to chemical structure, dynamic exchange and thermomechanical performance. We seek to understand the considerations of the placement and location of network cross-links and the effects of their dynamic reactivities. Placement of network cross-links on polymer chain ends is discussed in chapters II and III in the context of polycarbonate vitrimers that selectively exchange through chain-end ester groups instead of the backbone carbonate moieties. The influence of dynamic linkages as part of a permanently cross-linked network framework is investigated in chapter V. Network properties such as cross-link density, dynamic exchange and mechanical performance are assessed for networks with varying ratio of dynamic to permanent linkages. Incorporating carbon dioxide into po (open full item for complete abstract)

Doctor of Philosophy, University of Akron, 2024, Polymer Science

The dissertation focuses on developing chemically and mechanically responsive polymers aimed at promoting sustainability in materials science. We introduce a depolymerizable graft polymer using controlled ring-opening metathesis polymerization of trans-cyclobutane fused trans-cyclooctene macromonomers, enabling high molecular weights with precise architecture control. Further studies reveal how grafting density and side-chain length influence depolymerization thermodynamics, offering insights for future polymer designs. Additionally, we examine the thermal, mechanical, and morphological properties of these graft polymers, highlighting their potential as thermoplastic materials. Extending the sustainability concepts, we design an autonomous damage-reporting coating system based on mechanochemically responsive polymers for early damage detection. To advance the understanding of bulk polymer mechanochemistry, we establish a quantitative relationship between macroscopic stress and molecular bond-breaking forces in a mechanophore-embedded double-network elastomer. Finally, our pursuit of improved mechanochemical responsiveness leads to the development of a novel anthracene–based non-scissile mechanophore.

Doctor of Philosophy, University of Akron, 2024, Polymer Science

Polyesters are extraordinarily important materials. They find use in applications as common as food packaging and textiles, and as diverse as space travel and compostable cutlery. Like other commercial plastics, polyester waste has become a substantial environmental burden. The solution best known to the public is recycling. However, recycling has its own set of drawbacks including higher cost and lower quality of the resultant material. To improve the recyclability of polyesters, we have investigated the purification of chemically depolymerized polyethylene terephthalate (PET). By studying the selective binding and extraction of terephthalate and isophthalate monomers, we have advanced the purification options for recycled PET. This provides greater opportunity for recycled materials to be used in advanced and value-added applications such as tire reinforcement. Another pathway to making polyesters acceptably sustainable is to synthesize new examples built specifically for the purpose. Doing so also gives the opportunity to sequester environmental troublemakers. The use of carbon dioxide as a feedstock for plastic manufacturing has gained momentum in recent years, and of renewed interest is the CO2 based monomer ethenylated valerolactone (EVL). Our group has previously reported its polymerization by conjugate addition/ring opening, but high molecular weight examples have not yet been discovered. Conversely, the hydrogenated monomer (FH-EVL) has been polymerized as high as 613,000 g/mol. It has also been shown to depolymerize and distill in a singular facile operation, opening pathways in chemical recycling. To combine desirable properties of the respective systems, we have synthesized and characterized their copolymers. The resulting materials show improvements in molecular weight relative to poly(EVL). NMR evidence suggests that with lower feed ratios of EVL the conjugate EVL dimer adds exclusively to the growing chain. These copolymers represent an improvement (open full item for complete abstract)

Master of Science, University of Akron, 0, Polymer Engineering

Soft Particle Glasses (SPGs) are jammed suspensions formed by packing soft and deformable particles above their random-close packing limit. These suspensions belong to a class of materials known as yield stress fluids, as they exhibit weak elastic solid-like properties at low strains and flow-like liquids at high strains above their yield stress limit. In these suspensions, the contact forces play a dominant role and are practically athermal. Due to the unique properties of these materials, they are widely used in industries as rheological modifiers in products like inks, pastes, drilling fluids, food products, and personal care products. These multifaceted practical applications make understanding the processing parameters, i.e., the rheological response and the dynamics of the system, of utmost importance. In our study, particle dynamic simulation is used to implement a 3-D simulation of SPGs, and a comprehensive analysis is made to understand the particles' motion and the changes in their microstructure under shear flow. These studies reveal that SPGs exhibit cage-like dynamics during motion, and the flow curve response for these materials is well-defined by the Herschel-Bulkley model. Our results indicate the presence of two distinct regimes, namely quasi-static and flow regimes. A constitutive equation is established between the macroscopic rheology and microscopic dynamics based on the constituent materials' intrinsic properties, like the compressibility of the particles and elastic modulus. A detailed analysis of the microscopic dynamics in the steady-state regime reveals the presence of heterogeneous flow in our suspensions. Analytical tools like the self-part of the van Hove function define the domain lengths of these heterogeneous flows. A qualitative analysis of these domains reveals that these heterogeneous flows exhibit localized dynamics at high shear rates and propagate as avalanches at low shear rates. Analysis of these mobile clusters quantifi (open full item for complete abstract)

Doctor of Philosophy, University of Akron, 2024, Polymer Engineering

Lithium-ion batteries (LIBs) are currently used in portable electronics because of their high specific capacity, voltage, cycle performance, and negligible self-discharge. However, their large-scale expansion is hindered by safety issues (thermal runaway) and insufficient energy density. To address LIB limitations, improvements are presented regarding solid polymer electrolytes (SPE), sulfur cathodes, and eutectic molten salts electrolytes (MSE). SPEs offer low flammability and high stability but suffer from low ionic conductivity. Our group developed a cross-linked PEGDA superionic conductive SPE, which exhibited a good ionic conductivity (above 1 mS/cm at 30 °C) and great electrochemical stability, but large-scale implementation remained a challenge. For this, a new aerosol jet-printed composite cathode was developed for a lithium metal battery that revealed an excellent performance, a specific capacity above 160 mAh/g at 60 °C and above 135 mAh/g at 30 °C with a high mass loading of 10 mg/cm2 containing LFP. Sulfur cathodes have a high specific capacity, theoretically, but significant drawbacks of low conductivity and volume expansion. Volume expansion was solved by melt-diffusing sulfur into porous Ketjen black. Conductivity improved by adding fluorinated graphite (CFx), which after chemical transformation remained carbon (of higher conductivity). Compared to the pure sulfur cathode, the hybrid cathode showed a higher specific capacity on the ratability test, and during long cycling, it had a stable capacity and a high specific capacity in the 200th cycle. The in-situ formation of a LiF protective layer was found to enhance cycling performance. MSE advantages are high conductivity and wide range in operating temperatures. However, MSE-based lithium batteries' operative conditions are restricted within temperatures of 100-170 °C, limiting potential salts to use. The lithium nitrate based molten salt, Li0.46K0.54NO3, on a primary half-cell battery exhibited a (open full item for complete abstract)

Doctor of Philosophy, University of Akron, 2024, Polymer Science

The field of fracture mechanics emerged well over 100 years ago and is a subject older than polymer science. Fracture mechanics provides a means to characterize material response to deformation in the presence of flaws or cracks within a specimen, based on either the critical energy release rate (Gc) or the critical stress-intensity factor (Kc) at fracture. While these fracture toughness parameters successfully allow us to rank materials, an understanding as to why they are a material constant and what determines its magnitude remains to be of great interest. Polymers have been studied extensively under this framework for quite a while; in fact, it has been ongoing since prior to the development of theories describing its chain-level physics. While fracture mechanics perfectly describes the criterion surrounding the fracture phenomenon, it cannot explain why a polymer behaves in a brittle or ductile manner in the first place. Such an understanding must come from polymer physics, which also seeks to evaluate its inherent material strength. In this dissertation, an attempt is made to juxtapose the two, showing how polymer's physics affects its fracture behavior in the case of glassy polymers, and vice versa, where we see how the presence of a notch or crack dictates the local stress and failure mechanism using photoelasticity to gain a better insight into the conditions which precede fracture. Microscopic observation of local birefringence allows us to comprehend the origin of the magnitude of fracture toughness. This dissertation also looks at the case of ductile glasses, focusing not only on the conditions surrounding tip-yielding and stability of crack propagation, but also examining the cases where tip-yielding is inhibited solely by the presence of a notch.

Doctor of Philosophy, University of Akron, 2024, Polymer Science

Polyethylene (PE) and isotactic polypropylene (iPP) are the two most abundant commodity plastics. However, these materials are incompatible in the melt blend due to the different surface energies owing to the difference in their microstructures. The transfer of stress between incompatible phases of these polymers is a challenge that contributes to mechanical recycling process losses. This prevents the mixed mechanical recycling of these polymers to yield commodity plastics for high performance applications compared to the virgin resins. As a result, there is a lack of incentive to recycle mixed plastic waste, thereby contributing to plastic pollution in the environment. Compatibilizer additives improve the performance of these blends, through non-covalent, supramolecular, and covalent interactions across PE/PP interfaces. By introducing a small amount of compatibilizer into recycled polyolefin blends, there is potential to enhance the properties, reduce waste plastic, and achieve these in economical fashions. This work investigates several methods of delivering copolymer reinforcing agents which include supramolecular coupling through diverse architectures, namely diblock structures that are proposed to form in-situ and preformed multiblock architecture. The first part of this work will highlight the synthesis of a compatibilizer system consisting of end-functionalized iPP and HDPE. These materials are referred to as Interfacial Supramolecular Coupling Agents (ISCAs) due to their proposed ability to form supramolecular H-bonds across the bulk PE/PP interfaces. The synthesis of high melting-temperature iPP with controlled molecular weight and end-group fidelity is described. Through a sequence of reactions, vinyl end-functionalized iPPs and PEs are converted to β-alanine trimer terminated polyolefins, which are being studied as potential compatibilizers for PE/PP blends. A second strategy describes the use of pre-synthesized multiblock compatibilizers which have hi (open full item for complete abstract)

Master of Science, The Ohio State University, 2024, Food Science and Technology

Two polymer coatings derived from spent coffee grounds were explored as a bio-sourced biodegradable alternative to traditional petroleum-based non-biodegradable plastic coatings used commonly in food packaging. The aim of this research is to formulate a bioplastic coating derived from spent coffee grounds that can serve as a viable alternative to current petroleum-based wax films used in the food packaging industry. Water vapor transmission rate (WVTR) and oxygen transmission rate (OTR) tests were conducted to assess the coatings' barrier properties. Results indicated inferior water vapor resistance compared to the control, yet an enhanced water barrier of the cardboard alone. The coffee oil coating demonstrated superior OTR performance compared to the other samples. Biodegradability experiments conducted over 73 days revealed partial degradation of the coffee oil coated cardboard, showing potential as a bio-sourced biodegradable alternative. However, challenges encountered in biodegradability testing methodology require further investigation. Crystallization and thermal analysis revealed differences between cured and uncured samples, indicating structural changes during curing. Rheological analysis demonstrated Newtonian behavior in uncured samples and shear thinning in cured samples, providing insights into material behavior under increased deformation rates. Adhesion tests confirmed polymer adhesion to cardboard, with no observed odor or microbial growth. Overall, the coffee oil coating presents a promising option for sustainable food packaging, but further research is necessary to optimize properties.

Doctor of Philosophy, University of Akron, 2024, Polymer Engineering

Two-dimensional (2D) nanomaterials, such as graphene and transition metal dichalcogenides have been at the forefront of materials science due to their excellent and tunable mechanical, electrical, thermal, and optical properties. But they also have limitations including processability, scalability, and high cost, which constrain their applications in many fields. One strategy to overcome such limitations is to integrate 2D nanomaterials with other functional components including polymers and metallic nanostructures. The synergistic interactions between those components can lead to unprecedented properties. In this research, we focus on how to design functional nanocomposites based on the integration of 2D nanomaterials and other components, with targeted applications in solid lubrication and filtration/molecular separation. In the first study, we demonstrated that by integrating graphene oxide and polydopamine into sprayable nanocoatings, they can substantially enhance the filtration performance of filters based on polymer fiber network. In the second study, we showed that by in situ synthesis of graphene/titanium oxide hybrid nanosheets and transforming them into nanoscrolls, they can act as high-performance solid lubricants due to the high stability and significantly reduced contact area. In the third study, we demonstrated that the integration of 2D Fe2O3 nanosheets and graphene by a scalable microwave-assisted method, high-performance solid lubricants can be created, which substantially reduced the friction between steel-to-steel or steel-to-silicon. This research provides insight into the rational design and synthesis of functional 2D nanocomposites and can be further explored in areas including energy conversion/storage, catalysis, and advanced manufacturing.

Doctor of Philosophy, Case Western Reserve University, 2024, Macromolecular Science and Engineering

New processes and development of advanced technologies are essential for society to progress. The polymer field is vast and further expanding with the creation of new techniques and products. An advanced extrusion processing technique that has been beneficial in creating new products with very interesting properties takes the form of multi-layer co-extrusion. Initially multi-layer co-extrusion was and, in some cases, still is limited by the number of layers that can be achieved, the properties of different polymers can be combined to form products that are superior in different aspects due to the material selection. Layer multiplying co-extrusion was developed to achieve high layer numbers with the use of typically only two to three extruders. This work examines the layer multiplication technique capabilities for highly filled polymer layered systems and annular structures for pipe and blow molding applications. Limited work has been performed with filled polymer systems with using the layer multiplication technique. This work examines a model system to investigate effects of fillers at high loading levels on the stability of the layer structures created. The interface between filled and unfilled layers was examined xix to see the effect of particles at the interface. Along with this, particles with different rigidities were examined to investigate the effect of changing the rigidity of particles in confinement on the mechanical properties of the overall films. Previous work examined the creation of a tubing die for the layer multiplication technique to achieve high layer number annular structures. This work utilizes this tubing die to examine how angular rotation of the outer wall of the die land effects the weld line presence and pressure properties of the resultant tubes. The development of annular structures also allows for creation of blow molded structures. This work examines blow molding of high layer number bottles using a simple tabletop set-up and the (open full item for complete abstract)

Doctor of Philosophy, University of Akron, 2024, Polymer Engineering

This doctoral research delves into the fabrication and development of thermoplastic bilayer actuators, representing a class of materials designed for responsive and controlled movement triggered by environmental stimuli. Unlike traditional bilayer actuators where two different materials with distinct thermal expansion coefficients are used for the individual layers, this study incorporates a phase change material (PCM) into the thermal plastic elastomer (TPE) system and utilizes material anisotropy to generate differential strain between the layers. Through Fused Filament Fabrication (FFF) 3D printing, two layers of the same material are printed, demonstrating reversible bending and deformation in response to temperature changes. Leveraging the inherent properties of thermoplastics, these bilayer actuators can find applications in soft robotics and offer precise and programmable mechanical motion. The dissertation is composed of three projects. The first project investigated the relationships between structure and processing during fiber extrusion and FFF 3D printing. The study focused on nanostructured thermoplastic elastomer-based materials, particularly SEBS Kraton G1652. Printing parameters, such as printing temperature, printing speed, and bed temperature, are systematically studied, emphasizing Small Angle X-ray Scattering (SAXS) for characterizing sample orientation. The study revealed insights into how printing parameters influence material orientation and internal stress. The second project explored the phase behavior of SEBS/wax blends, utilizing paraffin wax, octacosane, as a phase change material. Thin films of SEBS/wax were fabricated through solvent casting, and SAXS was employed to characterize micromorphology. The goal was to achieve a cylindrical morphology, which could introduce anisotropy for subsequent 3D printing steps. Challenges arose with the addition of wax, which would shift the morphology to isotropic spheres. Shape actuation tests w (open full item for complete abstract)

Doctor of Philosophy, University of Akron, 2024, Polymer Engineering

In this work, High Density Polyethylene (HDPE) composites were made using Torrefied Soybean Hulls (TSBH) and Carbon Black (CB) to study the interactions affiliated with the TSBH content for as-received as well as size-reduced particles. The Milled TSBH (MTSBH) was shown to integrate well at low loadings, but showed signs of favoring filler-filler interactions over filler-matrix interactions, reducing the overall effectiveness as the loadings increased. Rheological testing showed that the higher-loaded MTSBH composites behaved similar to composites with larger particles as the loading increased, indicating that clusters had formed. Unmilled TSBH (UTSBH) showed good mechanical strength, but the particle size was shown to limit its ability to integrate into the material, even at low loadings. The addition of CB was shown to have the most impact on the low loading MTSBH composites, where the MTSBH-CB interactions were shown to influence the filler network in electrical resistance testing where a nonlinear trend was observed in the composite resistivity with the addition of MTSBH. In UTSBH composites, there were less signs of CB-UTSBH interactions due to the relatively large particle size. To contrast the hydrophilic matrix behavior of HDPE, Nylon-6 (PA6) was used as a matrix for the TSBH composites. In cases where either TSBH filler was used, the composite performance was shown to improve to a greater degree than in the case of HDPE due to the hydrophilic groups contained in the PA6 backbone. Similar to the HDPE composites, the TSBH particles showed a lack of effectiveness at higher filler loadings, though MTSBH showed more effective integration which indicates that this is a result of particle size. The CB and MTSBH showed synergistic effects with high CB and low MTSBH loading during cyclic tension testing, where the increase in strain energy density required for a test was less when the CB was present that when it was not. This effect was seen throughout the mono (open full item for complete abstract)

Doctor of Philosophy, Case Western Reserve University, 2024, Macromolecular Science and Engineering

Traditionally, extrinsic approaches (e.g. blending and using additives) have been used to enhance the mechanical properties (e.g. toughness) of commercially available semicrystalline thermoplastics. In a continual search for economically scalable, scrapless, simple, and versatile manufacturing approaches, novel solid-state processes have a unique advantage over melt-processing methods alone. Cold-roll milling, or plastically deforming a workpiece by passing it through two counter-rotating rollers below its primary softening temperature, is well-established in the production of ductile metals. Roll-milling not only reduces thickness, but also cold-works the material improving its strength through microstructural refinement. In polymers, a crystalline network structure develops. The focus of this work is on biaxial cold-rolling (cross-rolling) which involves cross-passes alternately 90 ° apart, resulting in a sheet with planar isotropy. In the first part of this dissertation (chapter 2), the deformation of HDPE by cross-rolling is studied. Enhanced barrier properties (measured by oxygen permeability analyzer), increased visible light transmission (measured by spectrophotometer), and increased tensile fracture strength were observed after cross-rolling. A connection to discontinuous change in crystalline structure with thickness reduction (i.e. lamellar fragmentation) detected by density measurement, thermal analysis, and small-angle x-ray scattering (SAXS) is discussed. The second portion (chapters 3-5) focuses on the cross-roll pre-deformation of semicrystalline polymers below both the Tm and Tg at room temperature, and subsequently annealing at temperatures both below and above the Tg. In chapter 3, the Izod impact toughness of poly(p-phenylene sulfide), a notoriously low toughness high-temperature engineering thermoplastic, is found to increase by a factor of 10 after cross-rolling. The elongation to failure is enhanced by a factor of nearly 6 by cross- (open full item for complete abstract)

Master of Science (MS), Ohio University, 2023, Biomedical Engineering (Engineering and Technology)

Abstract GUGGENBILLER, GRANT W., M.S., December 2023, Biomedical Engineering Electrospun Composite With Tunable Morphology for Burn Wound and Soft Tissue Wound Recovery Applications Director of Thesis: Dr. Andrew C. Weems Electrospinning offers a unique opportunity to produce micro- or nanoscale features using a wide array of polymers to produce 3D porous scaffolds. Here, a series of bioderived, pro-drug photopolymers, derived from salicylic acids, are photocrosslinked in the presence of polystyrene and silver sulfate to achieve a series of composite fibrous mats. The use of the three components (photopolymer, polystyrene, silver sulfate) are shown to provide an avenue towards tuning the fiber morphology. These materials display shape memory, allowing for minimally invasive medical device opportunities, as well as cytocompatibility and antimicrobial behaviors. Ultimately, these composite fibrous mats display excellent promise for both implantable tissue scaffolds as well as for medical devices including face masks or wound coverings.

Doctor of Philosophy, University of Akron, 2023, Polymer Science

This thesis outlines our efforts towards designing new materials to tackle interesting challenges in the areas of chemically recyclable polymers and polymer mechanochemistry in bulk polymer networks. Part I outlines some key results in the first area. Here, we sought to develop a new platform for chemically recyclable polymers that allows access to polymers with tunable functionalities and properties, yields high molecular weight polymer and can undergo depolymerization under ambient conditions. Chapter I introduces the reader to the relevant background for chemical recycling to monomer, ring olefin metathesis polymerization and advances in chemically recyclable polymer based on olefin metathesis chemistry. Chapter II outlines the design of trans-cyclobutane fused cyclooctenes (tCBCO) as monomers for chemically recyclable polymers, their polymerization thermodynamics, and the depolymerization behavior and thermomechanical properties of the corresponding polymers. Chapter III extends this platform to the area of semi-fluorinated polymers. Chapter IV seeks to study the effects of substituents on the cyclobutane core and their stereochemistry on the polymerizability of tCBCO monomers and the depolymerizability and thermal properties of the resulting polymers. Part II deals with computational and experimental studies relevant to polymer mechanochemistry with an emphasis on bulk mechanochemical activation. Chapter V outlines the relevant conceptual background for polymer mechanochemistry and some key advances and challenges facing mechanochemistry in bulk materials. Chapter VI discusses our design for mechanophore containing vitrimers with the aim of enhancing mechanochemical activation. We envision that the dynamic exchange can be used to fix a stretched network topology in vitrimers under strain, thereby increasing the number of load-bearing strands and thus, the mechanochemical activation. To this end, the synthesis and characterization of mechanophore containing vi (open full item for complete abstract)

Doctor of Philosophy, University of Akron, 2023, Polymer Engineering

One-way shape memory polymers (SMPs) possess the unique ability to remember a programmed 'temporary shape' and revert to its original shape when exposed to an external stimulus. Typically, SMPs contain two structure-spanning, solid networks; a permanent elastic network that is strained during programming to drive shape recovery; and a temporary network that fixes the programmed shape. The shape-shifting features of SMPs make them useful for a wide range of potential applications, including 4D printing, soft robotics, flexible electronics, soft aeronautical engineering, and biomedical devices. An interesting pathway to develop SMPs is by blending an elastomer and a crystalline small molecule, where the elastomer forms the permanent network (that promotes shape recovery), and the small molecule crystal forms the temporary networks (that promotes shape fixity). Typical examples of these systems include crosslinked elastomers (natural rubber) swelled in fatty acids (lauric acid, stearic acid, and palmitic acid), straight-chain alkanes (eicosane, tetracosane) or synthetic waxes (paraffin wax). However, a drawback of this approach is the blooming and expulsion of the small molecule during shape programming and recovery. This dissertation attempts to focus on semi-crystalline shape memory elastomers developed from blends of high cis 1,4 polybutadiene and reactive monomers (octadecyl acrylate and benzyl methacrylate) or molecular crystals (n-eicosane and n-tetracosane) with the aim being reducing the effect of blooming while keeping a simple fabrication route to develop these SMPs. The synthetic, network, mechanical, thermal, and morphological properties of a series of polybutadiene-based semicrystalline or glassy blends were studied to understand the structureproperty relationships between their permanent and reversible networks. Furthermore, it will be shown that thermally annealed high cis 1,4 polybutadiene also demonstrates thermoresponsive actuatio (open full item for complete abstract)

Master of Science, University of Akron, 2023, Mechanical Engineering

Recent advancements in polymer science and manufacturing have made market interest for Gradient Refractive Index (GRIN) lens technology grow exponentially. At the forefront of this field, Peak Nano is developing a process to engineer lenses for a variety of applications from medical to defense [1]. In the compression molding process step of manufacturing a GRIN lens, it is required to heat the polymer laminate above Glass Transition Temperature (Tg). This is currently achieved by conduction and convection heating of a charge inside the molding tool. Due to the poor thermal properties of polymers, a long transient is required for the charge to reach steady state. Additional difficulty is involved with GRIN laminates as the material properties are different for each layer. As stakeholder, Peak Nano would benefit from a shorter transient and improved thermal uniformity at steady state. Optical transmission data collected for the GRIN material blends indicated potential in heating via infrared (IR) radiation. A novel IR heating method was then developed for comparison to the conventional strategy. Results of this model gave improved heating time and uniformity over the current process. From there, a simulation matrix was generated, and the most successful setup was presented as a viable replacement to the conventional process.

Doctor of Philosophy, University of Akron, 2023, Polymer Science

Polyurethanes are a versatile class of polymers that have been used in various applications ranging from coatings to medical devices. The chemical structure of polyurethane can be modified to obtain desired properties. Herein, we demonstrated the ability to modulate functional groups of polyurethanes to tailor their properties in two platforms, segmented polyurethane for degradable biomaterials and random polyurethane copolymers for enhancing the antimicrobial action of antibiotics. Medical devices made from segmented polyurethanes are generally bio-inert and have very low surface wettability. Although there are multiple approaches being employed for surface functionalization, each approach has significant deficiencies such as low surface functionalization or the need for complicated processes. Through this work, I was seeking to improve our fundamental understanding of how bulk functionalization will affect the presence of functional groups at the surface. The work sought to correlate the positional variation of the cationic amine group in either the soft or hard segment to the mechanical and surface properties of modified segmented polyurethanes. Furthermore, the degradation profile of cationic segmented polyurethanes in oxidative and hydrolytic environments was examined and correlations between the degradation profile and the the polyurethane compositions were developed. Antibiotic-resistant bacterial infections are one of the most pressing problems costing billions of dollars to the healthcare system. In particular, gram-negative bacterial infections are challenging to cure since gram-negative bacteria have an outer membrane acting as a selective membrane barrier. This work demonstrates how cationic polyurethanes can act as an outer membrane destabilizer. This work shows that the combination of a cationic polyurethane along with an antibiotic that is not able to traverse an intact outer membrane, is an effective treatment for multi-drug resistant bac (open full item for complete abstract)