Doctor of Philosophy, Case Western Reserve University, 2020, Macromolecular Science and Engineering

As society evolves and technology develops further, the need for more advanced products is increasing, so polymeric materials are gaining ever more attraction because of their excellent properties such as lightweight, low cost and good resistance to corrosion. Polymer processing is one of the keys to achieve these unique materials. Various kinds of morphologies can be produced during polymer melt compounding including droplet-matrix, fibrillar, lamellar, or co-continuous structures. Co-continuous morphology, which has the coexistence of two continuous structures within the same volume, has been drawing more attention currently because of its specific superior properties including a combination of the features of both components in a favorable way, as well as additional characteristics by selectively localizing fillers in the co-continuous structures. Since processing-structure-property relationships are guiding principles in materials design, development, and tailoring, it is important to study them in co-continuous polymer blends and composites. In chapter 1 of this dissertation, the formation and properties of co-continuous blends and double-percolated co-continuous composites are introduced. In chapter 2, the formation of co-continuous poly(ethylene) oxide/ethylene-vinyl acetate blends as well as the effects of structure and processing on their surface roughness are explored. Moreover, two thermally conductive co-continuous ternary composites systems are reported in chapter 3. The role of viscosity ratio on filler distribution and electrical/thermal properties of the carbon nanofiber reinforced co-continuous polymer composites is discussed, along with the discussion of the effects of filler sizes on morphology and thermal conductivity of double-percolated polypropylene/poly(methyl methacrylate)/boron nitride polymer composites. Furthermore, two additional projects are demonstrated in chapter 4 and chapter 5. Chapter 4 compares the fiber length distributi (open full item for complete abstract)

Committee: Joao Maia (Advisor); Ica Manas-Zloczower (Committee Member); Svetlana Morozova (Committee Member); Donald Feke (Committee Member) Subjects: Polymers

Doctor of Philosophy, Case Western Reserve University, 2019, Macromolecular Science and Engineering

This work targeted to unveil the processing-structure-property relationships of four polymeric systems with diverse transport properties. The first and the second chapters concentrated on a through-pore membrane derived from polypropylene (PP) and polyamide 6 (Nylon 6) blends. The other three chapters discussed the adjustable gas barrier properties in regards to the morphologies of polymer blends and multilayer films. Among all the chapters, gas and liquid transport properties were proved as an effective identifier for the morphology. The change in transport phenomena was strongly correlated with the shift in the structure. In Chapter One and Chapter Two, porous membranes were produced from biaxial orientation of polymer blends comprising PP, Nylon 6, and polypropylene grafted maleic anhydride (PPgMA). During biaxial orientation, the continuous PP domains cavitated while the dispersed Nylon 6 domains remained rigid and spherical. The effect of blend composition on cavitation was analyzed and a ternary diagram generated to identify the composition range for through-pore formation. The membranes were found to have adjustable porosity up to 62% with nanoscale size pores. The membranes show very high filtration efficiency on separating 50 nm Latex microbeads from water suspensions. In Chapter Three, the compatibilization effect of linear low density polyethylene grafted maleic anhydride (LLDPEgMA) and high density polyethylene grafted maleic anhydride (HDPEgMA) on high density polyethylene (HDPE) /Nylon 6 blend system was investigated. HDPEgMA was identified as a better compatibilizer than LLDPEgMA for the HDPE/Nylon 6 blend system. In Chapter Four, multilayer films comprising polystyrene (PS)/polymethyl methacrylate (PMMA) and PS/polycaprolactone (PCL) alternating nanolayers with varied layer thickness were fabricated by multilayer coextrusion. The continuous layers started to break up into nanosheets and nanodroplets during the coextrusion process when the no (open full item for complete abstract)

Committee: Eric Baer (Committee Chair); Andrew Olah (Committee Member); David Schiraldi (Committee Member); Ya-Ting Liao (Committee Member) Subjects: Chemical Engineering; Materials Science; Packaging; Plastics; Polymers

Doctor of Philosophy, University of Akron, 2013, Chemistry

Semiflexible polymers of sufficient stiffness exhibit liquid crystalline order at low temperature and high polymer concentration. Blends of liquid crystalline and flexible polymers have interesting physical properties and important applications in organic electronics. We investigate melts and blends of flexible and semiflexible polymers with the aid of Monte Carlo simulations of an extension of Shaffer's bond-fluctuation model. To control chain stiffness we include a bending term in the Hamiltonian and investigate two models for semiflexibility that differ in the range of penalized bond angles. A study of structural, dynamic and thermodynamic properties of the first model shows that it describes melts of semiflexible chains that do not undergo a transition to a liquid crystalline state. Simulations of the second model reveal orientational order without positional order at high density and low temperature. The transition from the isotropic high-temperature phase to the nematic low-temperature phase, the IN transition, is accompanied by discontinuous changes in structural and thermodynamic properties. This agrees with mean-field theories and experimental observation that show that the IN transition is a discontinuous transition. To characterize our system fully, we determine the phase diagram and find that the IN transition temperature increases with increasing filling fraction, which agrees qualitatively with predictions by Onsager and Flory. Since pair distribution functions give insight into structure and morphology of polymers, we construct same-chain and different-chain distributions that we further differentiate by flexible and rod-like chain conformations. A study of same-chain pair distributions shows that the rod-like chains in our model align with a face diagonal in the nematic phase. Results for different-chain pair distribution functions show that a melt phase separates into a dense ordered region and a low-density disordered region when undergoing t (open full item for complete abstract)

Committee: Jutta Luettmer-Strathmann Dr. (Advisor); David Perry Dr. (Committee Member); Alper Buldum Dr. (Committee Member); David Modarelli Dr. (Committee Member); Kevin Cavicchi Dr. (Committee Member) Subjects: Chemistry; Physics; Polymers

Doctor of Philosophy, Case Western Reserve University, 2011, Macromolecular Science and Engineering

In recent years POSS (polyhedral oligomeric silsesquioxanes) has been incorporated into a number of polymers as a copolymer, graft or as a melt-blend. The advantages gained from using POSS come from its hybrid organic-inorganic nature whose inorganic core provides molecular reinforcement while its variety of functionalization schemes allow for reaction or other interactions with the host polymer. Previous work has shown the ability of POSS to reinforce polymers when incorporated through grafting or copolymerization, but there is a lack of understanding of how to obtain successful reinforcement when using POSS as a melt-blend additive. One hypothesis is that a high degree of POSS-polymer interactions are necessary which promote a pseudo-grafted structure yielding results similar to that of copolymer system. The first part of this thesis (Chapters 2 and 3) will address the role of POSS-polymer interaction in reinforcement. Specifically, Chapter 3 will discuss a new approach to predicting these interactions through the determination of Hansen solubility parameters. This approach however does not take into account the role of processing. Chapter 4 will address this by evaluating the structure-property relationships in melt-spun fiber composites. Finally, Chapter 5 will discuss a different field of polymer composites, polymer clay aerogels. In this work the use of these low-density composites as an oil absorbing media will be discussed.

Committee: David Schiraldi PhD (Committee Chair); Hatsuo Ishida PhD (Committee Member); Joao Maia PhD (Committee Member); Xiong Yu PhD (Committee Member) Subjects: Polymers

Doctor of Philosophy, Case Western Reserve University, 2007, Macromolecular Science

There has been a recent shift in the development of pharmaceutical delivery systems from systems which solubilize agents to systems that respond to external stimuli. Because of this, there is much focus on the development of systems that are responsive within the relatively narrow ranges that are expected to be seen in vivo. This work focuses on the development of drug delivery systems for the purposes of pH sensitive delivery. Initially, poly(ethylenimine) (PEI) derivatives were used as a basis for an siRNA delivery system. PEI graft copolymers were found to be efficient siRNA delivery vectors. The pH sensitivity of PEI could then subsequently be used for drug delivery via blending with poly(lactide-co-glycolide). Full miscibility was observed between these polymers via a mechanism of amide formation, with the result being a material suitable for pH sensitive drug delivery. Efforts to use this system on the nanoscale, however, were unsuccessful, leading to an alternate strategy. The alternate strategy initially quantified the factors dominating drug release from polymeric micelles, with drug solubility being found to be a major determinant. The conclusions here were used to create a system for the pH sensitive release of Β -lapachone. In this case, pH sensitive drug solubility was induced by using hydrophobic prodrugs of Β -lapachone which converted to the more soluble parent drug upon exposure to acid. These prodrugs were found to load into polymeric micelles as a function of drug solubility in core polymer. Finally, pH sensitive release of the parent drug was observed via a mechanism of intramicellar hydrolysis of prodrug into parent drug. On a larger scale, this work represents efforts leading to novel routes to pH sensitive pharmaceutical delivery systems. The buffer capacity of PEI, though observed in gene delivery, has not been previously used for drug delivery. Meanwhile, the hydrophobic prodrug strategy in a novel innovation that allows for the facile custo (open full item for complete abstract)

Committee: Jinming Gao (Advisor) Subjects:

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

Nanostructured hybrid materials can be formed using self-assembling side chains grafted to a polymer backbone. Small-angle X-ray and neutron scattering (SAXS & SANS) measurements on polyisobutylene graft copolymers with side chains containing β-alanine trimer have revealed that crystalline nanodomains form by self-assembly. Modifying the side chain chemistry allows one to tailor the β-alanine nanocrystal length from over 300nm down to approximately 10nm. The degree of crowding at the nanodomain interfaces impacts the temperature dependence of the microphase separation. Chemical variations in the side chains, such as removing C18 tails and adding C11 spacers between the backbone and β-alanine trimers have dramatic effects on nanocrystal size, domain spacings, order-disorder transition temperature and width of transition, crystal melting temperature, and bulk mechanical properties. The last chapter describes progress in defining the interface morphologies in blends modified with Interfacial Supramolecular Coupling Agents (ISCAs) containing β-alanine. Polyethylene (PE) and polypropylene (PP) constitute the majority of mixed plastic waste produced globally. In the approach studied, it is envisioned that a pair of ISCAs will populate the interfaces between PE-rich and PP-rich phases and anchor the phases together. From SAXS, SANS, Wide Angle X-ray Scattering (WAXS) and Atomic Force Microscopy (AFM) analysis it is evident that the presence of ISCAs alters the crystalline structure of the overall blend.

Committee: Mark Foster (Advisor); Mesfin Tsige (Committee Chair); Bi-min Zhang Newby (Committee Member); Toshikazu Miyoshi (Committee Member); Li Jia (Committee Member) Subjects: Engineering; Materials Science; Nanoscience; Nanotechnology; Physics

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)

Committee: Kevin Cavichhi (Advisor); Fardin Khabaz (Committee Chair); Qixin Zhou (Committee Member); Li Jia (Committee Member); Weinan Xu (Committee Member) Subjects: Chemistry; Materials Science; Plastics

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

Plastic waste is causing environmental problems due to its accumulation on land and in the oceans. Recycling plastic is both economically and environmentally beneficial; however, there are limited options available for disposing of plastic waste. The problem of plastic waste is global and requires immediate attention. One of the major obstacles to plastic recycling is the difficulty in separating different types of plastics, such as polyethylene and polypropylene, which leads to an increase in plastic waste. Although these plastics have desirable properties, they are not compatible in their solid and melt states, making it difficult to reuse them. This issue occurs not only with polyolefin mixtures but also with most plastics. There are different approaches to achieve sustainable plastics, such as using compatibilizers, chemical cycling, advanced sorting, and creating new biodegradable and petroleum-based polymers. This study aims to develop novel petroleum-based polyolefins that possess a unique structure, comparable thermal as well as potentially mechanical properties to polyethylene (PE) and isotactic-polypropylene (iPP) and are capable of forming co-crystalline phases after secondary reuse, enhancing their potential for reusability. Co-crystallizing different semicrystalline polymers is a challenge, as each polymer has its own kinetics of crystallization, chain conformation and packing structures in the crystalline region. Even low-density polyethylene cannot fully co-crystallize with high- density polyethylene. So far, only a few systems, such as stereo-complexes like poly(lactic acid)s and poly(methyl methacrylate)s, have been able to co-crystallize. However, these require specific mixing ratios that are not feasible in secondary recycling. Very recently, Hayano and Nakama synthesized a series of unique polyolefins named as hydrogenated poly(norbornene) (hPNB)s with different stereoregularity showing semicrystalline features with a wide melting tempera (open full item for complete abstract)

Committee: Toshikazu Miyoshi (Advisor); Mesfin Tsige (Committee Chair); Ali Dhinojwala (Committee Member); Chunming Liu (Committee Member); James Eagan (Committee Member) Subjects: Materials Science; Physics; Plastics

Master of Science, University of Toledo, 2023, Chemical Engineering

In this work, the impact of the co-monomer, furan dicarboxylate (FDCA), on depolymerization of poly (ethylene terephthalate) (PET) was investigated. Specifically, glycolysis and alkaline hydrolysis were used to depolymerize the following polyesters: (i) PET, (ii) polyethylene furonate (PEF), (iii) a copolymer with 10 % FDCA and 90 % TPA (PETF10-I) and (iv) a melt blend of 10 % PEF and 90 % PET (PETF10-B). The alkaline hydrolysis kinetics were studied at 110 oC in 1.1 M sodium hydroxide (NaOH) solution [45, 46, 65]. Glycolysis kinetics were studied at 180 oC in ethylene glycol (EG) with a zinc acetate catalyst [31, 47, 66]. Both reactions occur at the surface of the polyester flakes so that surface wetting by the solution, surface area of flakes, and backbone structure of the polymer are important in determining reaction kinetics. In addition, this work showed that the polyester configuration played a role in depolymerization kinetics for the PET/PEF mixed systems. The PEF exhibited much faster rates of depolymerization for both hydrolysis and glycolysis than pure PET, which was attributed to the presence of five member rings that are more labile than benzene ring. The inclusion FDCA based polyesters as a co-polymer or blend resulted in increases in depolymerization rates relative to the PET. The blend exhibited faster rates of kinetics than the co-polyester indicating that the configuration or macrostructure was important in determining depolymerization kinetics. The more rapid kinetics of the blends was attributed to a combination of (i) improved surface wetting by the reaction media and (ii) high degradation rates for PEF in blends which generated small pits in surface and increased surface area. The hydrolysis product for both the blend and co-polymers of PETF10 contained FDCA and TPA. However, high purity of BHET was recovered from the reaction mixture with only traces of BHEF following glycolysis of the blends and co-polyester. While it was difficult to rec (open full item for complete abstract)

Committee: Maria Coleman (Committee Chair); Joseph Lawrence (Committee Member); Dong -Shik Kim (Committee Member) Subjects: Chemical Engineering

Doctor of Philosophy, Case Western Reserve University, 2022, Macromolecular Science and Engineering

Polymer processing is a fundamental key to achieve the desired properties to reach the needs of polymer applications. Thus, it is important to understand how the processing can contribute to material characteristics during the extrusion, while they are being processed. That is why this work propose a method able to perform analyses of the material while it is being processed during the extrusion: the on-line Fourier transform infrared (FTIR) spectroscopic system. The system consists of a device that was designed to be able to couple a commercial infrared spectrometer to an twin-screw extruder. On-line FTIR measurements can be done in different locations along the extruder barrel. Pearson VII function was used improving the linearity of mixture composition, which is proposed by Beer-Lambert's law, by around 14% when compared to the traditional methods. Polymer blends of polypropylene (PP) and polyamide 6 (PA6) at different weight composition ratio were used to validate the on-line system during extrusion. The area ratio between the IR bands at 1640 cm-1 (υC=O) and 1373 cm-1 (σC-H3) were measured on-line for all the blend compositions and shown to be in good agreement with off-line measurements. When the reactive blending of polyamide 6 (PA6) and polypropylene grafted with acrylic acid (PP-g-AA) (in blends of 80%/20% and 30/70% of PP-g-AA and PA6, respectively) was investigated along the extruder length, a increase of the IR band area ratio (1640/1373 cm-1) was achieved when the process condition aggressiveness in mixing was improved due to the generation of fresh interface between the two phases, as it is shown through scanning electron microscopy (SEM). Trough on-line FTIR measurements it was possible to visualize the development of the reactive blending reaction of PP-g-AA/PA6 blends inside the extruder. For example, different process conditions lead to the same or different amount of reaction (IR area ratio 1640/1373 cm-1) at the end of the extruder, but they fo (open full item for complete abstract)

Committee: Joao Maia (Advisor); Joao Maia (Committee Chair); Sebastiao V. Canevarolo (Committee Member); Gary E. Wnek (Committee Member); Jennifer L. W. Carter (Committee Member); Hatsuo Ishida (Committee Member); Leonardo Canto (Committee Member) Subjects: Engineering; Materials Science; Plastics; Polymers

Doctor of Philosophy, Case Western Reserve University, 2020, Macromolecular Science and Engineering

Mixing different polymers is a well-known way to obtain distinct final properties that would not be obtainable with separate components. Researching efficient and exquisite ways to blend them into morphologies and tailor interfacial microstructure is desirable to construct multiphase materials with potentially functional interfaces. Janus particles or rigid surfactants are attractive for these purposes given their distinguished interfacial activity and self-assembly prospects. In Chapter 2, from aggregate structure, kinetics, and diffusivity arguments, the way that shorter or longer Janus rods assemble interfacially is shown to impact polymer blend phase separation. In Chapter 3, their colloidal tumbling behavior under interfacial shear flow is examined to search opportunities for self-assembly and original nanotechnological applications. Conspicuously, parallel or antiparallel Janus rod alignment at the interface, as well as stacked superlattice sheets, can be tuned according to rod concentration, shear rate, aggregate shape, and interaction potential intensity. Furthermore, an inquiry into slip and momentum transfer mechanisms across polymer-polymer interfaces follows in Chapter 4. For conditions that may ultimately favor the delay of polymeric droplet coalescence and stabilize polymeric emulsions, polymer-grafted Janus rods with longer grafts should be employed among flexible or other rigid surfactants. Additionally, their corresponding grafting density may serve the purpose of controlling interfacial aggregation. In Chapter 5, the reptational diffusive behavior of very long polymer chains is reproduced to show how accounting for entanglements among polymer chains allows for slower relaxation processes in Janus-rod stabilized immiscible polymer blends. These topological constraints that are added to polymer segments make for more realistic polymer motion and predict a more pronounced viscoelastic behavior. All these investigations on the interfacial behavior of J (open full item for complete abstract)

Committee: Joao Maia (Committee Chair); Veronica Calado (Advisor); Argimiro Secchi (Advisor); Shaghayegh Khani (Committee Member); Michael Hore (Committee Member); Gary Wnek (Committee Member); Daniel Lacks (Committee Member); Marcio Nele (Committee Member); Frederico Tavares (Committee Member) Subjects: Chemical Engineering; Engineering; Materials Science; Nanoscience; Nanotechnology; Polymers

Doctor of Philosophy, Case Western Reserve University, 2020, Macromolecular Science and Engineering

The most widespread types of extruder are single-screw machines (SSE), which typically are poor mixing devices but allow for large throughputs, and intermeshing co-rotating twin-screw (Co-TSE), which are good mixing devices but are not able to yield as high throughputs as SSEs. The mixing action in Co-TSEs is usually imparted via sets of kneading blocks (KBs), which impose shear-dominated flows. Shear flows are energetically inefficient for dispersive mixing by comparison with extensional flows. Our group previously developed a new Extensional Mixing Element (EME), with dispersive mixing provided by extension-dominated flow through stationary hyperbolically contracting channels. This first prototype, which was designed to impart relatively mild extension on the melt, showed tremendous improvement in dispersive mixing by comparison with aggressive KB sections. Herein, the EME design is optimized by defining the maximum contraction ratio admissible and the biaxial concept is introduced. The EME concept is also extended to SSE to enhance their dispersive mixing. Experiments are performed on immiscible polymer blends (low-viscosity ratio and high-viscosity ratio) and nanocomposites on both SSE and TSE. Morphological results showed enhancement in dispersive mixing capability of SSE when equipped with EME and mainly comparable to conventional TSE, that is, with KB as mixing sections, if not as good as TSEs equipped with EMEs. Rheological and crystallinity studies are observed to be in line with the morphological analysis. Mechanical results also showed enhanced modulus when EME is used. We also compared computationally the performance of two SSE mixing sections with significant extensional flow components, the CRD mixer and the EME. Tapered slots in the CRD and hyperbolic contractions in the EME attempt to create extensional stresses. Our studies confirm that EMEs are a better dispersive mixer than the CRD mixer, as they impose more intense and uniformly distributed ex (open full item for complete abstract)

Committee: Joao Maia Dr. (Advisor); Joao Maia Dr. (Committee Chair); Ica Manas-Zloczower Dr. (Committee Member); Hatsuo Ishida Dr. (Committee Member); Donald Feke Dr. (Committee Member) Subjects: Engineering; Fluid Dynamics; Plastics; Polymers

Doctor of Philosophy, University of Akron, 2020, Polymer Engineering

Colors are ubiquitously present in nature and are used in several day-to-day applications such as paints, textiles, cosmetics and displays. Most of these colors are pigment-based and suffer from non-environment friendliness, toxicity and non-tunability. Structural colors have received significant attention as alternatives to degradation-prone pigment-based colors. Many non-iridescent (angle-independent) structural colors in nature are produced from porous bio-polymer nanostructures with multi-functional properties such as UV-protection and hydrophobicity. However, most bioinspired synthetic non-iridescent structural colors have been attained via self-assembly of colloids and 3D printing, but they suffer from poor adhesion and robustness. Non-iridescent structural colors in nature, on the other hand, are produced from quasi-ordered porous nanostructures and are thought to form by polymeric phase separation but have not yet been achieved artificially despite their advantages including scalability. The objective of this dissertation is to develop a polymeric phase-separation process that results in non-iridescent structural coloration. Here, we report, for the first time, fabrication of non-iridescent structural colors from porous polymers via temperature-induced phase-separation of compatibilized polymer blend films. By simply tuning the molecular parameters such as composition of the polymer blend (ϕ), the color of the films can be tuned from white to blue to transparent with underlying morphological transitions from a disordered to a quasi-ordered state. Control on brightness and color saturation can be achieved by tuning optical interfaces and structural order respectively at a molecular level without using any additives by tuning molecular weight of homopolymers and block co-polymer. Gradient non-iridescent structural colors were attained from films of differential thickness via tunable coffee ring effect. We further examined the absence of green and red c (open full item for complete abstract)

Committee: Alamgir Karim (Advisor); Matthew Shawkey (Advisor); Sadhan Jana (Committee Member); Xiong Gong (Committee Chair); Erol Sancaktar (Committee Member); Tianbo Liu (Committee Member) Subjects: Polymer Chemistry

Doctor of Philosophy, University of Akron, 2019, Polymer Engineering

Shape memory polymers (SMPs) are a type of material capable of indefinitely holding a deformed shape and recovering their original shape upon the application of an external stimulus, such as temperature. SMPs contain at least two networks consisting of a permanent crosslinked polymer matrix and a second reversible, shape fixing network. These networks could be chemically bonded in single chemistry systems such as block copolymers containing elastic and glassy or crystalline phases or be blended together through elastomer and crystalline small molecule mixtures. This dissertation primarily focuses on SMP blends derived from fatty acid-elastomer blends with the aim being to further simplify the fabrication of these materials. The mechanical, thermal, and morphological properties of a series of different blends, along with several styrenic block copolymers, were studied to understand the structure-property relationships between their permanent and reversible networks. In Chapter II, fatty acid swollen natural rubber shape memory polymers were investigated as a function of swelling extent, acid polarity, and applied deformation. The fatty acid-rubber systems demonstrate a 40-50 wt% effective fatty acid solid phase loading range where the fixity of a programmed shape remained > 95% while maintaining structural integrity. The strength of the crystalline fatty acid networks were determined through dynamic mechanical analysis (DMA) moduli measurements where, under large uniaxial deformations, the modulus of the fatty acid was found to increase compared to the unstrained material. This was consistent with preferential alignment of crystal platelets along the strain direction as determined by small angle X-ray scattering (SAXS) measurements. In Chapter III, SMP foams were fabricated by immersing a polyurethane foam inside stearic acid-isopropyl alcohol solutions of varying concentration. Samples were programmed using DMA or a compression press. It was determined that f (open full item for complete abstract)

Committee: Kevin Cavicchi (Advisor); Mukerrem Cakmak (Advisor); Li Jia (Committee Member); Jiang Zhe (Committee Member); Sadhan Jana (Committee Chair) Subjects: Polymers

PhD, University of Cincinnati, 2018, Engineering and Applied Science: Biomedical Engineering

Myelomeningocele (MMC) is a neurologic defect characterized by failure of neural tube closure in the spinal column. This leads to cerebrospinal fluid leakage or contact with amniotic fluid, which can translate into sexual dysfunctions and paralysis after birth. The recently developed minimally-invasive technique for MMC repair is called fetoscopy, which involves a surgical patch, expanded for defect coverage on the fetus' back. Currently used inert patches do not degrade after implantation, necessitating a post-natal removal surgery, while collagen-based patches employed in are associated with poor mechanical integrity. Also, these patches are not tailored for fetoscopic MMC repair, and their response in fetal environment is unexplored. Deployment and expansion of coiled patch using surgical tools at defect site is time-consuming and cumbersome. Some of these existing patches have mesh-like structure for tissue in-growth, which makes their barrier properties debatable. Upon implantation at defect site, the patch encounters amniotic fluid and body fluids, as well as fluid forces due to fetal movement in the womb. This necessitates analysis of biodegradability and mechanical response of the patch for its adaptability in fetoscopic MMC repair. Taking the above requirements into consideration, we designed a patch comprising a blend of poly (L-lactic acid) (PLA) and poly (ε-caprolactone) (PCL), both polymers approved by the U.S. Food and Drug Administration for hard and soft tissue repair in spine. Different PLA-PCL formulations were characterized for surface and thermal properties, and the ideal formulation was chosen as our designed patch based on aptitude for thermal expansion at in-vivo temperature (37°C). This will enable self-expansion of the coiled patch at defect site, saving time and reducing difficulty level of surgery. The designed patch was characterized for barrier properties to ensure its watertight nature, and for biocompatibility after exposure to huma (open full item for complete abstract)

Committee: Chia-Ying Lin Ph.D. (Committee Chair); Yoonjee Park Ph.D. (Committee Member); Jose Peiro (Committee Member); Marepalli Rao Ph.D. (Committee Member) Subjects: Biomedical Research

Doctor of Philosophy, Case Western Reserve University, 2011, Macromolecular Science and Engineering

This dissertation covers a wide array of polymer science, from investigating the barrier properties of polymer blends for commercial products and their specifications to using novel approaches to incorporate glassy inorganic materials within a polymer matrix for high density data storage materials to using common materials in new ways to increase the use range of low density clay aerogels to using bioinspired chemistry to develop reinforcement of current materials and bone replacement materials. Chapter 2 discusses the advances in oxygen barrier materials through innovative approaches to modifying the refractive index change induced by biaxial orientation by simple melt blending procedures. Chapter 3 discusses an approach to developing 3D data storage devices by the blending of common optical polymers with inorganic chalcogenide glasses. Chapter 4 discusses the vast mechanical improvement of a polymer/clay aerogel composite material by a simple dip coating procedure. Chapters 5-7 involve the use of biomineralization for various purposes. In Chapter 5 a polyethylene imine/clay aerogel is coated by a silica layer to impart vastly superior mechanical properties, while a layering approach modestly improves mechanical performance. In Chapter 6 a polyacrylic acid/clay aerogel is subjected to CaCO3 deposition, showing the ability to grow large amounts of CaCO3 in relatively short times. Chapter 7 discusses an electrophoretic mineralization approach to collagen hydrogels.

Committee: David Schiraldi (Committee Chair); LaShonda Korley (Committee Member); Gary Wnek (Committee Member); Horst von Recum (Committee Member) Subjects: Polymers

Doctor of Philosophy, Case Western Reserve University, 1993, Macromolecular Science

Changes in mechanical properties during isothermal physical aging were investigated for three miscible blends: polystyrene(PS)/poly(2,4-dimethyl 1,6-phenylene oxide)(PPO), PS/poly(vinyl methyl ether)(PVME), and poly(methyl methacrylate)(PMMA)/poly(ethylene oxide)(PEO). The aim was to compare the kinetics of the physical aging process between blends and pure components, using tensile stress relaxation and dynamic mechanical measurements. Positron annihilation lifetime (PAL) spectroscopy was used as a probe for structural disorder (free volume) to aid interpretation of the physical aging studies. Analysis of the aging stress relaxation data by generation of a stretched exponential master function, as proposed by Struik, was possible for both blends and homopolymers. Discrepancies in the scaling of the characteristic stress relaxation time τ with respect to the temperature distance Tg-T between PS/PPO, PS/PVME and the PS homopolymer were resolved by invoking the presence of concentration fluctuations in the blends. By selecting the onset glass transition temperature (Tgi) as a reference point, the relaxation times for PS/PPO and PS/PVME glasses can be scaling to those of pure PS. This indicates that the initial stress decay is determined by the more mobile regions in the b lends. However, this temperature scaling does not apply to the PMMA/PEO blend for which the τ values at fixed Tgi-T are larger than for pure PMMA, suggesting that, in this system, the interaction between the blend components produces a more dense matrix. Using the coupling theory of Ngai as a guide, we infer that the width of the spectrum of stress relaxation times in the blend may be increased by the presence of concentration fluctuations, or by an increase in matrix density (lower free volume). Thus, the increase observed in the spectral widths for both blends and homopolymers at lower temperatures indicates that the relaxing elements become more strongly coupled to the surrounding matrix. For th (open full item for complete abstract)

Committee: Alexander Jamieson (Advisor) Subjects:

Doctor of Philosophy, University of Akron, 2012, Polymer Engineering

Polymeric biomaterials have been widely used in many biomedical applications including sutures, tissue scaffolds, drug delivery devices, and wound dressing. Among biopolymers, biodegradable polymers are of utmost interest because they can be absorbed and excreted without surgical revision. Moreover, physical and mechanical properties can be simply diversified by physical blending to meet the needs of biomedical applications. However, novel materials capable of delivering naturally bioactive molecules represent a new generation of biomaterials. This study focuses on modification of biopolymer blends by a naturally bioactive substance named genistein for biomedical applications and highlights the establishment of phase diagrams which are effective tools to predict the final morphology and to determine the processing windows of the mixtures. Phase diagrams of various blends of poly(D,L-lactic acid) (PDLLA), poly(ε-caprolactone) (PCL), poly(ethylene oxide) (PEO), poly(ethylene glycol) (PEG), poly(ethylene glycol) diacrylate (PEGDA), and genistein were constructed experimentally and theoretically based on the combined Flory-Huggins free energy of liquid-liquid phase separation and the phase field free energy pertaining to crystal solidification. It has been found that phase behaviors of each binary blend strongly depend on chemical nature, crystallinity, and molar mass of each constituent. Novel biomaterials, i.e., PEGDA-based hydrogels and PEO/PDLLA electrospun mats containing genistein were fabricated based on guidance afforded by the ternary and binary phase diagrams. During photopolymerization with visible blue light, polymerization of genistein/PEGDA mixtures induced phase separation and crystallization. The evolution of phase diagrams with conversion suggested that the conversion (α) was about 0.65 ± 0.1. In vitro biocompatibility assessments showed that genistein has improved antioxidant and anti-inflammatory activities of the PEGDA-based hydrogels. For geni (open full item for complete abstract)

Committee: Thein Kyu Dr. (Advisor); Avraam Isayev Dr. (Committee Member); Kevin Cavicchi Dr. (Committee Member); Li Jia Dr. (Committee Member); Rebecca Willits Dr. (Committee Member) Subjects: Polymers

Doctor of Philosophy, University of Akron, 2012, Polymer Science

Important contributions to our understanding of polymer surfaces rely very heavily on the development of new techniques for the study of those surfaces. The unifying aspect of the research described in this dissertation is the exploitation of advances in polymer surface characterization for purposes of elucidating surface behavior and properties. The results have implications for an interesting diversity of polymer science applications ranging from the design of superior latex films, to detection of trace components on surfaces, to the engineering of blend surface properties by varying chain molecular architecture. To design superior latex films it is important to connect mesoscale morphological features as well as adhesion properties of dried latex films to their macroscopic properties observable by eye. Using conventional scanning probe microscopy (SPM) probes, but exploiting in particular highly resolved adhesion mapping, dried latex films containing various fluorosurfactants, polymers, and cross-linking agents were studied. It was found that a complex that forms between the fluorosurfactant and a zinc cross-linking agent leads to mesoscale lateral phase separation. The presence of these lateral inhomogeneities correlates well with the poor performance on the macroscopic level. While conventional SPM techniques can analyze surface properties of samples, there is still a need for a non-invasive, robust imaging technology capable of simultaneously collecting topographic and chemical information with nanoscale resolution. This has been realized with tip enhanced Raman spectroscopy (TERS). Metallized probes are a key enabling component for this technique, which has the potential for high sensitivity detection and surface chemical imaging with very high (nm) resolution. However, the robustness of the metallized probes has been a hindrance to the application and commercialization of the technique. An ultrathin protective coating of aluminum oxide for the metallized pr (open full item for complete abstract)

Committee: Mark D. Foster Dr. (Advisor); Mesfin Tsige Dr. (Committee Member); Darrell Reneker Dr. (Committee Member); Matthew Becker Dr. (Committee Member); Edward Evans Dr. (Committee Member) Subjects: Polymers

Doctor of Philosophy, University of Akron, 2011, Polymer Science

Interfaces are important in many areas including adhesion, friction, coatings, nanocomposites, heat transfer, biomedical implants and cell biology. Most interfacial experiments involve force measurements and, consequently, molecular models to explain the force results. To make progress in this field, it is necessary to understand the structure of interfacial molecules in direct contact. Here, we have used the interface sensitivity of infrared-visible sum frequency generation spectroscopy (SFG) to probe the molecular structure of contact and sliding interfaces in-situ along with force measurements. SFG is a second order nonlinear optical technique that provides information on the chemical structure, orientation and concentration of molecules at interfaces. Two types of interfaces are probed in the current study. The initial two studies focus on static interfaces and the remaining three on dynamic interfaces. In the first investigation, we have studied polar interactions at solid-liquid and solid-solid interfaces using SFG spectroscopy. The shift of the sapphire surface hydroxyl peak in contact with several polar and non-polar liquids and polymers is used to determine the interaction energy. The trend in the interaction energies cannot be explained by only measuring water contact angles. Molecular rearrangements at the sapphire interface, to maximize the acid-base interactions, play a dominant role and these effects are not accounted for in the current theoretical models. The second investigation probes the interactions of polystyrene (PS)-poly(methyl methacrylate) (PMMA) blends with a sapphire surface. The acid-base interaction of carboxyl groups with surface hydroxyl groups is a strong driving force for segregation of PMMA next to the sapphire surface. Even with 0.005 weight fraction of PMMA in the blend, the concentration at the sapphire-blend interface is similar to that of bulk PMMA. This result is significant for understanding and controlling the interfaces res (open full item for complete abstract)

Committee: Ali Dhinojwala Dr. (Advisor); Mark Foster Dr. (Committee Chair); Gary Hamed Dr. (Committee Member); Alamgir Karim Dr. (Committee Member); Jutta Strathmann Dr. (Committee Member) Subjects: Materials Science; Physical Chemistry; Polymer Chemistry; Polymers