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Razgoniaev, AntonDesign, synthesis, and characterization of photoresponsive materials using coordination bonds and other supramolecular interactions
Doctor of Philosophy (Ph.D.), Bowling Green State University, 2017, Photochemical Sciences
When designing light-responsive, healable materials and adhesives, these materials need to include controllable reversible, bonding interactions. Such dynamic interactions are difficult to control, however. In this work, we present how these interactions can be controlled by incorporating photoactive metal ions into supramolecular polymer network what allow the tuning of optical and mechanical properties of the polymers with light. Utilizing this approach, we created a series of supramolecular polymer melts and studied their mechanical and photo physical properties. We have shown that the photochemistry and photophysical properties of the metal center can be used to control the mechanical properties of the materials, and introduce new optical and mechanical properties not seen in the traditional covalent polymers. In particular, photo-induced metal-ligand bond labilization led to partial depolymerization of the supramolecular assembly, and softening of the materials. When the light stimulus was removed, the material recovered the initial stiffness back. We also investigated structure-property relationships in such systems where mechanical properties of the supramolecular polymers are controlled by coordination environment around metal cross-linking center. We also considered how polymer host matrix impacts on the photophysical and photochemical properties of chromophores that undergo molecular motion in the exited state. In particular, change in excited state dynamics of [Cu(dmp)2]+ can be used to sense viscosity of various polymers. A linear dependence of excited state lifetime and emission wavelength on viscosity was correlated with restricted photoinduced structural distortion of Cu(I) complex in more flow-resistance media.

Committee:

Alexis Ostrowski, Ph.D. (Advisor); Scott Rogers, Ph.D. (Committee Member); Alexander Tarnovsky, Ph.D. (Committee Member); R. Marshall Wilson, Ph.D. (Committee Member)

Subjects:

Chemistry; Materials Science; Polymer Chemistry; Polymers

Keywords:

Photochemistry; Chemistry; Materials Science; Polymer Chemistry; Polymers

Miranda, Michael AngeloBio Based Active Barrier Materials and Package Development
Doctor of Philosophy, University of Toledo, 2016, Chemical Engineering
The food and packaging industries are interested in approaches to reduce the permeability of oxygen in polyethylene terephthalate (PET) to extend the shelf-life of product. This has led to considerable research in barrier improvement including the use of active scavenger that permanently bind oxygen. The purpose of this work is to investigate the use of renewably sourced unsaturated fatty acids as scavengers to reduce the O¬2 permeability in PET. Specifically fatty acids were characterized and incorporated within PET using both blended and reactive extrusion to analyze the impact on thermal-mechanical and oxygen transport properties. Oleic, linoleic and linolenic acid are renewably resourced unsaturated fatty acids that are being investigated as active scavenger. Utilization of scavenger capacity and kinetics of oxidation are two key parameters that must be considered while selecting a scavenger. The O¬2 uptake capacities and the utilization of scavenger sites analysis were used to determine the most appropriate scavenger used to make a copolymer with PET. Linoleic acid was chosen due to its higher utilization capacity and relatively fast kinetics the cost was also taken into account. Thus linoleic acid was used in preparation of PET/Scavenger system. The effect of addition of unsaturated fatty acid on the thermal, mechanical properties and morphology of PET, were analyzed by preparing blends of PET/linoleic acid of loading of (0.25-2 weight %). The presence of the scavenger were analyzed using end group analysis where an increase in carboxyl end group was determined and NMR to obtain the peaks for the fatty acid. The appropriate method to determine molecular weight was also established. Effects of permeation through amorphous and biaxial oriented films with and without linoleic acid were investigated. The bottles were produced in two different ways (i) reactive extruded bottle and (ii) blended bottles (0.5% weight loading of Linoleic acid). The mechanical properties and density of the bottles were similar. The oxygen permeability of these bottles side wall was lower than that of PET. NMR on sample that has been exposed to oxygen was conducted to confirm the reactivity of linoleic acid with oxygen.

Committee:

Maria Coleman (Committee Chair); Saleh. A. Jabarin (Committee Co-Chair); Sridhar Vimajala (Committee Member); Yakov Lapitsky (Committee Member); Young- Wah Kim (Committee Member)

Subjects:

Chemical Engineering; Gases; Packaging; Polymers

Wallat, Jaqueline DianeFluorous Nanoparticle Platform for Cancer Imaging and Treatment
Doctor of Philosophy, Case Western Reserve University, 2018, Macromolecular Science and Engineering
This thesis work highlights the fabrication and use of a fluorous copolymer nanoparticle platform for drug delivery with 19F magnetic resonance imaging potential. Throughout this work, low-molecular weight random copolymers comprised of approximately equal molar concentrations of oligio(ethylene glycol methyl ether methacrylate) OEGMEMA and trifluoroethyl methacrylate TFEMA were synthesized using atom-transfer radical polymerization from an azide-functionalized initiator. In water, the copolymer self-assembles into micelles of approximately 250 nm. The azide end group provides a handle to react with an alkyne-functionalized cargo via copper catalyzed azide-alkyne cycloaddition (CuAAc), which is a robust, high-yielding, and facile reaction. The 19F NMR and MRI properties of a 5 kDa micelle were analyzed for the particle, and to enable in vitro and in vivo particle tracking, a near-infra red fluorescent dye was attached to the chain end of the copolymer via the CuAAc reaction. The biodistribution of the fluorescently labeled fluorous micelle was evaluated in vivo in breast and ovarian cancer models. This system showed exceptional uptake into tumors via passive tumor targeting with little uptake in non-tumor tissue. These promising results prompted the investigation of this micelle to serve as a drug delivery vehicle for a photodynamic therapy (PDT) reagent in two types of skin cancer. The fluorous micelle showed enhanced production of reaction oxygen species, a critical component for treatment with PDT, but often limited in the hypoxic tumor environment. The delivery of the PDT to skin cancer cells was favorable, indicating this fluorous micelle could effectively serve as a drug delivery vehicle for PDT. To extend this system toward commercially available chemotherapeutics, we sought to site-selectively deliver the chemotherapeutic Doxorubicin (DOX). The DOX was covalently modified via an acid-sensitive linkage and attached to the micelle via the CuAAC reaction. pH sensitivity enables selective delivery in acidic environments such as the tumor microenvironment or lysosomal cell compartment. The DOX-copolymer showed pH triggered release of active DOX from the carrier. In vitro, the DOX-copolymer demonstrated uptake into two in vitro models for ovarian cancer and demonstrated efficient cancer killing. Taken together, this work highlights the use of a fluorous copolymer synthesized via ATRP to enable facile fabrication of drug delivery and imaging vehicles for cancer via the CuAAc reaction.

Committee:

Jonathan Pokorski, PhD (Advisor); David Schiraldi, PhD (Committee Member); Horst von Recum, PhD (Committee Member); Gary Wnek, PhD (Committee Member)

Subjects:

Polymer Chemistry; Polymers

Keywords:

Fluorous, Nanoparticle, Cancer, ATRP, Treatment, DOX, copolymer

Seshadri, Dhruv RamakrishnaImmuno-nanotherapeutics to Inhibit Macrophage Polarization for Non-Small-Cell Lung Cancers
Master of Sciences, Case Western Reserve University, 2017, Biomedical Engineering
Lung cancer is the leading cause of cancer-related mortalities in the USA with a five-year survival rate of ~15%. For patients with Non-Small-Cell Lung Cancer (NSCLC), chemotherapy, oncogene targeted therapy, or immunotherapy are the primary modes of treatment. Response rates to immunotherapies for NSCLCs are < 20%, due to the tumor micro-environment (TME) that favors immune-evasion and pro-tumorigenic pathways such as macrophage polarization from a pro-inflammatory (M1) to a pro-tumorigenic/angiogenic (M2) phenotype. Additionally, the TME is compromised by the chronic enzymatic breakdown of the elastic matrix which catalyzes polarization. Exogenous delivery of Doxycycline (DOX) has shown to inhibit the M1-M2 phenotypic switch. We explored the utility of antibody-conjugated DOX-poly(ethylene glycol)-poly(lactic glycolic-acid) (PEG-PLGA) nanoparticles (NPs) to inhibit macrophage polarization and demonstrate that steady-state release of DOX from these NPs is possible in a low dose range to inhibit polarization and repolarize macrophages back to the M1 phenotype.

Committee:

Anand Ramamurthi (Advisor); Eben Alsberg (Committee Member); Colin Drummond (Committee Member)

Subjects:

Biomedical Engineering; Biomedical Research; Polymer Chemistry; Polymers

Keywords:

Tumor Microenvironment, Nanomedicine, Nanoparticles, Polymers, Lung Cancer, Macrophages, Immunotherapy, Extracellular Matrix, Elastin

Wang, KaiHIGH PERFORMANCE SOLUTION-PROCESSED PEROVSKITE HYBRID SOLAR CELLS THROUGH DEVICE ENGINEERING AND NOVEL
Doctor of Philosophy, University of Akron, 2017, Polymer Engineering
ABSTRACT Efficiently and economically harnessing the solar energy via solar cell devices is one of promising solutions to address the global energy crisis. This thesis mainly focuses on a novel family of photoactive layer materials, namely organic-inorganic lead halide perovskite hybrids, and their corresponding solar cell devices, due to their potential for achieving outstanding power conversion efficiency and low-cost processibility. Specifically, the main research themes of this thesis are to achieve high performance perovskite hybrid solar cells through optimizing device structures, developing novel functional perovskite materials, and elucidating the underlying physics and mechanisms for guiding us to construct high performance solution-processed perovskite hybrid solar cells. This dissertation contains four parts and 10 chapters. In PART I, a broaden overview on both solar cell device and material is given, which specifically reviews the importance of solar energy and solar cells, comparison between previous-generation solar cells and perovskite hybrid solar cells, history of perovskite hybrid materials for solar cell application in Chapter 1 and describes the theoretical background of solar cell devices and material used for fabrication of solar cells in Chapter 2. PART II mainly includes the detailed projects on solar cell device engineering. Firstly, in Chapter 3, we employ a highly electrical conductive, polyethylene oxide (PEO)-doped poly(3,4-ethylenedioxythiophene)-poly(styrenesulfonate) (PEDOT:PSS) as the hole extraction layer (HEL) for the planar heterojunction (PHJ) perovskite hybrid solar cells (pero-HSCs). The dramatically enhanced electrical conductivity of the PEO-doped PEDOT:PSS HEL provides an efficient pathway for the hole extraction, transport, and collection from the perovskite active layer to the anode. As a result, a significantly enhanced short-circuit current (JSC) of 23.42 mA cm-2, a slightly enlarged open-circuit voltage (VOC) of 0.88 V, an enhanced FF of 80.10% and a correspondingly dramatically enhanced power conversion efficiency (PCE) of 16.52%, which is a ~45% enhancement as compared with that from the PHJ pero-HSCs incorporated with the pristine PEDOT:PSS HEL, are observed. In Chapter 4, we utilize a solution-processed ultrathin layer of an ionomer, 4-lithium styrenesulfonic acid/styrene copolymer (LiSPS), to re-engineer the interface of methylammonium lead iodide (CH3NH3PbI3) in PHJ pero-HSCs. The ionomer can sufficiently modify the rough surface of the perovskite and optimize the charge extraction efficiency between perovskite photoactive layer and the charge transport layer. As a result, PHJ pero-HSCs with an increased photocurrent density of 20.90 mA cm-2, an enlarged ¿ll factor of 77.80%, a corresponding enhanced power conversion ef¿ciency of 13.83%, high reproducibility, and low photo-current hysteresis, are achieved. In Chapter 5, because one major limitation to increasing the efficiency of pero-HSCs is the fact that the diffusion length of the electrons is shorter than that of the holes, to facilitate the electron extraction efficiency in pero-HSCs and to make this efficiency comparable with that of the holes, we fabricated BHJ pero-HSCs by mixing perovskite materials with water-/alcohol soluble fullerene derivatives. The observed enhanced JSC and enlarged FFs were a result of the balance in the charge carrier extraction efficiency and the enlarged interfacial area between the perovskite materials and the fullerene derivatives. Significantly improved power conversion efficiencies were obtained for these BHJ pero-HSCs. A greater than 22% increase in power conversion efficiency was observed for the BHJ pero-HSCs compared with planar heterojunction pero-HSCs. A remarkable 86.7% FF, the highest reported value for pero-HSCs, was observed for the BHJ pero-HSCs. Our strategy of using a BHJ structure in pero-HSCs offers an efficient and simple way to further increase the performance of these devices. PART III mainly discusses the detailed projects on novel perovskite materials development. To fabricate homogeneous and high-quality perovskite thin ¿lms via low-temperature solution processing is always a challenge to realizing high-ef¿ciency pero-HSCs, in Chapter 6, we firstly report a development of an approach to realize smooth surface morphology of CH3NH3PbI3 perovskite thin ¿lms via using strong-polar ethanol solution rather than less-polar isopropanol solution, which was previously used as the solvent for preparing perovskite thin ¿lms. In comparison with the pero-HSCs processed from isopropanol solution, more than 40% enhanced ef¿ciency is observed from pero-HSCs processed from ethanol solution. The enhanced ef¿ciency is attributed to a homogeneous high-quality perovskite thin ¿lm with dramatically low root-mean-square roughness and completely conversion of lead (II) iodide (PbI2) to CH3NH3PbI3. In Chapter 7, we report the development and investigation of novel CH3NH3PbI3: x Nd3+(where x = 0, 0.1, 0.5, 1.0, and 5.0 mol%) perovskite hybrid materials, where Pb2+ is partially substituted by an inequivalent rare-earth metal cation, neodymium (Nd3+), which was never reported in previous studies. By conducting the charge carrier mobility measurements and film morphology studies, it is found that solution-processed CH3NH3PbI3: x Nd3+ thin films exhibit significantly improved and more balanced charge carrier mobilities, and superior film quality with dramatically reduced trap-states and pin-holes, as compared with pristine CH3NH3PbI3 thin film. As a result, a descent power conversion efficiency of 20.56% for solar cells and a superior photodetectivity of ~ 1014 cm Hz1/2 W-1 from 375 nm to 800 nm at room temperature for photodetector, are observed from solution-processed perovskite photovoltaics by novel CH3NH3PbI3: x Nd3+ thin films. All these results demonstrate that our method provides a simple and facial way to boost the device performance of perovskite photovoltaics. In Chapter 8, we report the utilization of polyethylene oxide additives to anchoring the ions in the perovskite lattice to suppress the formation of point defect or the migration of ions/vacancy, for simultaneously enhancing device efficiency, minimizing photocurrent hysteresis and enhancing device stability. Consequently, efficient solar cell devices with power conversion efficiency of 19.01% with extremely low hysteresis index of 0.001 and long-term device shelf half-life time of 504 hrs (without encapsulation, stored in 50% humidity air) have been achieved. Chemical, structural and morphological analysis show that the PEO additive acts as a crosslink between neighboring perovskite crystal domains via the strong hydrogen bonding of `-OH…I-’ and `O…H-NH2CH3+’ to the perovskite. In PART IV, a brief summerization on our works in terms of both device and material engineering is presented in Chapter 9, that is, for optimizing the device configuration as well as address critical issues in previously wide-applied hybrid perovskite thin films, we mainly developed novel ideas on: (i) modifying anode buffer layer for efficient hole extraction; (ii) modifying the interfacial electrical coherence on the i-n junction; (iii) developing a bulk heterojunction concept for efficient charge extraction; for novel materials part, we also focused on three major parts: (i) optimizing the thin film quality of perovskite; (ii) tuning the crystal lattice structure by inequivalent metal doping; (iii) anchoring the ion within the perovskite lattice for reducing hysteresis and improving device stability. Finally, an outlook is given in the Chapter 10 for guiding our future work.

Committee:

Xiong Gong (Advisor); Matthew Becker (Committee Member); Alamgir Karim (Committee Member); Nicole Zacharia (Committee Chair); Jie Zheng (Committee Member)

Subjects:

Electrical Engineering; Energy; Nanoscience; Physics; Polymers

Keywords:

Energy Conversion; Photovoltaics; Lead Halide Perovskite; High Performance; Device Physics; Material Science

Das, Suma RaniInvestigation of Design and Operating Parameters in Partially-Filled Rubber Mixing Simulations
Master of Science, University of Akron, 2016, Mechanical Engineering
The modern rubber industry is always in pursuit of improvements in the properties of the final product resulting from the mixing of the rubber compounds with different fillers and additives. Depending on the functional characteristics of the final product and thus the compounding ingredients, different types of mixers can be used for the rubber mixing process. Hence, the choice of an appropriate mixer is critical in achieving the proper distribution and dispersion of fillers in rubber, and a consistent product quality, as well as is the attainment of high productivity. Besides rotor design, operational parameters such as speed ratio and the orientation of the mixing rotors with respect to each other also play significant role in the mixing performance. With the availability of high-performance computing resources and high-fidelity computational fluid dynamics tools, understanding the flow field and mixing characteristics associated with rotor orientations, speed ratios and complex rotor geometries, has become more feasible over the last two decades. As part of this effort, all the simulations here are carried out in a 75% fill chamber with two counter-rotating rotors using a CFD code. In the phase angle and rotor design studies conducted here, the rotors rotate at 20 rpm even speed, whereas for speed ratio study, only the left rotor rotates at 20 rpm and the right rotor rotates at a speed, which is a multiple of 20 rpm by the speed ratio specified. The computational models used in this research are based on a finite volume method to simulate a partially filled mixer equipped with different tangential rotor types. The model solves for transient, isothermal and incompressible set of governing fluid equations for the mixing of non-Newtonian high-viscosity rubber. The research here considers phase angles of 45°, 90° and 180°, speed ratios of 1.0, 1.125 and 1.5, and rotor designs including 2-wing, 4-wing A and the 4-wing B rotors. Investigation of each parameter type carried out separately. The flow field is analyzed via pressure and velocity contours, mass flow patterns, velocity vectors and particle trajectories. Dispersive mixing is evaluated through histograms of mixing index, joint probability density functions of mixing index and shear rate, and cumulative probability distribution functions of maximum shear stress experienced by the particles. Distributive mixing is quantified statistically using cluster distribution index, axial distribution, inter-chamber particles transfer, segregation scale and length of stretch. The results helped in understanding the mixing process and material movement, thereby generating information that could potentially improve the productivity and efficiency in tire manufacturing process.

Committee:

Abhilash Chandy, Ph.D. (Advisor); Povitsky Alex, Ph.D. (Committee Member); Choi Jae-Won, Ph.D. (Committee Member)

Subjects:

Fluid Dynamics; Industrial Engineering; Mechanical Engineering; Polymers

Keywords:

Dispersive mixing; Distributive mixing; Speed ratio; Phase angle; Rotor design; Segregation scale; Cluster distribution; Length of stretch; Partially filled; non-Newtonian; Numerical simulation; Polymer processing; Rubber Processing; Tire materials

Qian, JinQUARTZ CRYSTAL MICROBALANCE WITH DISSIPATION MEASUREMENTS OF BINDER SWELLING AND SALTS EFFECTS ON PHYSICAL CROSSLINK HYDROGEL
Master of Science, University of Akron, 2018, Polymer Engineering
Advanced active materials, such as Si, for lithium ion battery electrodes are becoming highly engineered, but their cycling performance can be significantly impacted by the mechanical, transport, and electrochemical properties of the polymeric binder in the electrode. The swelling and plasticization of most widely used binder poly(vinylidene difluoride) (PVDF), poly(acrylic acid) (PAA), branched polyethylenimine (BPEI) and potential binder sulfonated ethylene propylene rubber (SEPDM) by common carbonate-based electrolytes is probed using quartz crystal microbalance with dissipation (QCM-D). The swelling of the PVDF was significantly greater than the other polymers, while addition of Li salt only marginally deceased the swelling. The composition of ethylene and propylene carbonate in the electrolyte more significantly impacts the swelling with the 50:50 mixture exhibiting the greatest swelling. The shear modulus of the PVDF remains on the order of 10 MPa for all conditions examined. This mechanical invariance is attributed to the semi-crystalline structure of PVDF that provides a robust network. These measurements provide insight into the electrolyte-binder interactions and can be used to help select pairs for emerging high-performance electrodes from the aspect of swelling of binder by carbonate electrolyte and interaction between binder and active material. As QCM-D is a very sensitive and accurate method for in-situ real time analysis on thin film swelling and mechanical properties, it can also be used to measure salts effect on the swelling of physical crosslink hydrogel. In this study, the Hofmeister series effect on swelling of 2-(N-ethylperfluorooctane sulfonamido)ethyl acrylate (FOSA)/N,N-dimethylacrylamide (DMA) physical crosslink hydrogel which containing 9.7 mol% FOSA (DF10) is introduced. The influence of temperature and different salts species (Na2SO4 and NaClO4) are investigated. The DF10 swollen in aqueous solution dissipates significant energy to enable determine of the mechanical properties. The swelling of DF10 is reversible with temperature increases and salts concentration. Na2SO4 decreases the swelling of DF10 and increases elastic modulus. Conversely, NaClO4 increases the swelling ratio, softens the DF10 hydrogel and increases viscosity in low concentration NaClO4 solutions (from 0.003M to 0.1M). At higher NaClO4 concentration (3M), the swelling decreases slightly when compared with the swelling at 0.3M. This study demonstrated that salts have dramatic effect on swelling of DF10 in aqueous solution, resulting in the change on swelling ratio and mechanical properties of DF10 hydrogel. The efficiency of the anions in increasing swelling was found to be consistent with the Hofmeister anion sequence with the ability of destabilize the hydrophobic aggregates.

Committee:

Bryan Vogt (Advisor); Erol Sancaktar (Committee Chair); Yu Zhu (Committee Member)

Subjects:

Polymers

Zhu, HaidongSynthesis of Biodegradable Silicon Functionalized Polyester Scaffolds for Bone Tissue Engineering
Master of Science, University of Akron, 2017, Polymer Science
Tissue engineering technology uses the combination of cells, materials and engineering methods, and suitable biochemical and physicochemical factors to improve or replace biological functions. Scaffolds are frequently involved in tissue engineering. Scaffolds are biodegradable materials that have been modified to form new functional tissues for medical purposes. Many studies indicated that silicon is an essential element in bone and connective tissue formation. By functionalizing the biodegradable poly(lactic acid) with silicon, its’ application in tissue engineering is available. The silicon-functionalized copolymer used in this study was synthesized by grafting methyl methacrylate and a silicon-containing methacrylate by atom transfer radical polymerization (ATRP) from a brominated poly(lactic acid) (PLB) used as a macroinitiator. The PLB macroinitiator (GPCPSt Mn = 1.6 ×104 Da; Ð = 2.25) was prepared by incorporating 2-bromo-3-hydroxypropionic acid (BrH) as a co-monomer with lactic acid (LA). This polymerization was well controlled using CuBr as the catalyst and bipyridine as the ligand in toluene at 90 °C. The resulting graft copolymer contains PLA, PMMA and 3-(triethoxysilyl)propyl methacrylate (TESPMA). The final scaffolds prepared by compression method showed good integrity in cell culture media.

Committee:

Coleen Pugh (Advisor); Abraham Joy (Committee Member)

Subjects:

Polymer Chemistry; Polymers

Keywords:

Tissue engineering; scaffold; PLA; TESPMA; ATRP

Wang, HaoranPreparation of Titanium Oxide/Epoxy Hybrid Anticorrossive Coating
Master of Science, University of Akron, 2016, Polymer Engineering
ABSTRACT Using organic coating is one of the most effective methods to prevent material from the corrosion which acts as barriers to air, ions and water. The organic/inorganic hybrid material not only combines the inorganic and organic characteristic, but also may own some unique properties. Generally speaking, the organic/inorganic hybrid coating can own the specific property from inorganic part such as: thermal stability, hardness and scratch resistance, and the specific property form organic phase such as: flexibility, toughness, impact resistance and adhesion. Also, the inorganic phase can improve the anticorrosive property of organic coating. In this dissertation, six kinds of the titanium alkoxide/epoxy hybrid coating have been prepared and characterized. The standard liquid BPA epoxy resin was modified by the 3-isocyanatopropyltrietoxysilane (IPTES). The structures were confirmed by Fourier transform infrared spectroscopy (FTIR) liquid state 29Si NMR and mass spectrometry (MS).The viscoelastic properties of coating films were tested by DMTA and DSC. General coating properties including pencil hardness, cross-hatch adhesion, pull-off adhesion, reverse impact resistance and MEK resistance were tested in aluminum panel according ASTM standards. Most importantly, the anticorrosion performance was evaluated by electrical impedence spectroscopy (EIS), 240h salt spray test in steel panel and acid undercutting test.

Committee:

Mark D Soucek (Advisor)

Subjects:

Polymers

Keywords:

Tianium Oxide; Epoxy; Hybrid; Anticorrosive coating

Bo, NiDesign, Synthesis and Self-assembly of Polyhedral Oligomeric Silsesquioxane (POSS) Based Hybrid Materials
Doctor of Philosophy, University of Akron, 2018, Polymer Science
The giant molecules systems exhibit very interesting behaviors in the supramolecular assemblies over the past several years compared to other macromolecular systems. As an old Chinese saying goes “good tools are prerequisites for a successful execution of a job”. This dissertation focuses on the synthetic possibilities based on the previous work and try to explore some progress in the first part. The second part of the dissertation encapsulates the self-assembly behaviors of the synthesized giant molecular systems. A pre-functionalization method was developed to achieve giant molecular families with more abundant functionalities. Fluorinated polyhedral oligomeric silsesquioxane (FPOSS), long alkyl chain functionalized POSS (C8POSS), and protected carboxylic acid group functionalized POSS (tAPOSS) were designed and prepared. These kinds of molecules are viewed as molecular nanoparticles (MNPs). The reactivities of the modules was proved by combining them with polymer systems like polystyrene via “click” chemistry. These precisely defined functionalized POSS-containing hybrids could serve as model molecules to investigate the self-assembly behaviors of giant molecules. The solution self-assembly of a giant surfactant consisting of a polystyrene-block-poly (ethylene oxide) (PS-b-PEO) diblock copolymer tail tethered onto a fluorinated polyhedral oligomeric silsesquioxane (FPOSS) cage in 1,4-dioxane/water was investigated. Abundant unconventional micellar structures including toroids, two-dimensional hexagonally patterned colloidal nanosheets, and laterally structured vesicles were observed.2 This study not only exhibits various unique morphologies, but also promotes the fundamental understanding on the pathways of the transformations between different morphologies in the solution self-assembly behavior of giant surfactants. In the MNPs and polymer hybrid systems, the MNPs were with precise molecular weights and chemical compositions. But the polymers used still have a molecular weight distribution which originates from the nature of the polymerization methods applied. To eliminate the polydispersity effect from the system, it is crucial to have molecular systems with precise molecular weights and chemical structures from the physical point of view. Upon this anticipation, we have designed a series of dendrons which are compositionally identical, but their linkers are in different chemical connection geometries. These sets of macromolecules are composed of hydroxyl group functionalized POSS (DPOSS) and isobutyl functionalized POSS (BPOSS). The final dendron structure consists of three parts, one DPOSS at the apex, four BPOSSs at the periphery and the flexible linkers. Note that this series of dendrons is topological isomers. Self-assembled structures of four dendron topological isomers were studied using SAXS and TEM. The results help us to understand the role of linkers in a amphiphiles system and give us some guidance on how to design a molecular system in the future.

Committee:

Stephen Z. D. Cheng (Advisor); Miyoshi Toshikazu (Committee Chair); Mesfin Tsige (Committee Member); Chrys Wesdemiotis (Committee Member); Yu Zhu (Committee Member)

Subjects:

Polymer Chemistry; Polymers

Keywords:

polymer, self-assembly, POSS, FPOSS, tAPOSS, hybrid material

Yu, JiayiTunable Biodegradable Polymers for Regenerative Medicine
Doctor of Philosophy, University of Akron, 2018, Polymer Science
Since the early 1960s, synthetic biodegradable polymers have been widely used in biomedical applications due to their large chemical diversity and the reproducible properties. However, the local acidification during degradation has shown to cause significant inflammation that can lead to device or implant failure. It is necessary to design new biodegradable polymer systems that do not cause local acidosis during degradation. To facilitate this requirement, Becker group has developed the amino acid-based poly(ester urea)s. These polymers are semi-crystalline. Their hydrolysis byproducts are non-toxic and can be self-buffered by the presence of the urea linkage at each repeat unit. In addition, there is a tremendous physical and chemical landscape that is available for exploration by using different natural amino acids with different pendant groups and different diols. This dissertation outlines our efforts to develop biodegradable polymers with tunable mechanical properties, degradation rates, and bioactivity. We varied the diol chain length (Chapter 3), branch density (Chapter 4), bioceramic contents (Chapter 5) in the poly(ester urea) system; cis/trans ratio (Chapter 6) in the biodegradable elastomer system and studied how these subtle structural differences would influence the mechanical properties and water uptake ability. Based on their tunable physical properties, these materials can be selected and used for various biomedical applications (Chapter 7).

Committee:

Matthew L. Becker, Ph.D. (Advisor); Bryan Vogt, Ph.D. (Committee Chair); Yu Zhu, Ph.D. (Committee Member); Amis J. Eric, Ph.D. (Committee Member); Chrys Wesdemiotis, Ph.D. (Committee Member)

Subjects:

Biomedical Engineering; Materials Science; Plastics; Polymer Chemistry; Polymers

Keywords:

biodegradable polymers; poly ester urea; diol chain length; branch density; composite; stereochemistry; mechanical property; biodegradation rate; application, processing; characterization; structure property relationship; amino acid; tunable property

Chu, YangRATIONAL CONTROLLED SELF-ASSEMBLY BEHAVIOR OF INORGANIC-ORGANIC HYBRIDS IN SOLUTION
Doctor of Philosophy, University of Akron, 2017, Polymer Science
In the past several decades, self-assembly of amphiphiles in solutions has attracted great interest of researchers due to their unique properties and applications. Besides the well-explored small-molecule surfactants and block-copolymers, giant surfactants also known as inorganic-organic amphiphilic hybrids have been regarded as a new attractive topic because they contain functional (e.g., catalytic, magnetic, oxidation-reduction redox or biologically active) inorganic nanoparticles/molecular clusters which simultaneously act as surfactant polar head groups. The self-assembly/disassembly can be triggered by different kinds of external stimuli like light, heat, magnetic field or solution polarity. Besides, the morphology and size of the assemblies are also tunable by the experimental conditions and molecular structures. In this dissertation, three representative kinds of hybrids, which include multi-headed giant surfactants based on polystyrene (PS)-polyhedral oligomeric silsesquioxane (POSS) conjugates with different number and topology of POSS heads, triangular shaped PS-POSS hybrids with different length of PS linkers and spiropyran (SP)-polyoxometalate (POM)-alkyl hybrids, are prepared to study the effect of hydrophilic head groups, hydrophobic linkers and change of hydrophobicity on the self-assembly behavior. Dynamic light scattering (DLS) and static light scattering (SLS) are used during the whole process of self-assembly to suggest the size and morphology of the assemblies and electron microscopy and atomic force microscopy confirm the results obtained by light scattering techniques. We found the rational control of the self-assembly behavior of inorganic-organic hybrids in solution can be successfully achieved due to their multiple-responsive property on light, solvent polarity, molecular structures and solution concentration.

Committee:

Tianbo Liu (Advisor); Stephen Cheng (Committee Chair); Toshikazu Miyoshi (Committee Member); Mesfin Tsige (Committee Member); Jie Zheng (Committee Member)

Subjects:

Chemistry; Polymer Chemistry; Polymers

Keywords:

Inorganic-organic hybrid; Self-assembly behavior; polyoxometalates;

Gao, YunyiSolution Behaviors of Macroions Driven by Non-covalent Interactions
Doctor of Philosophy, University of Akron, Polymer Science
Macroions demonstrate very intriguing solution behaviors that are different from colloids and simple ions due to their intermediate sizes in between. Those macroions, when carrying moderate surface charge density, can self-assemble into a spherical, hollow, singled layered "blackberry" structures in solution, with counterion-mediated attraction to be the major driving force. Other non-covalent forces such as hydrogen bonding and solvophobic interactions are also playing a significant role in directing the solution behaviors of macroions. In this dissertation, uranyl peroxide nanoclusters are investigated to further explore and expand their unique solution properties as macroions. These U60 clusters were proved to be able to distinguish different monovalent counterions and only allow certain counterions to be trapped inside their cages. The hydration shell destruction was dominantly contributing to the entropy loss during the ion binding process. Such ion selectivity properties can be accurately tuned by changing the incubating temperature of the aqueous environment. The U24Pp12 clusters, when synthesized with different counterions, showed two isomeric structures depending on the orientation of one of the polyhedral faces. The transition from a "concave ou" to a "concave in" structure was made possible by simply titrating the monovalent counterions into the U24Pp12 solutions. The non-covalently linked surfactant encapsulated nanoclusters of U60 and different cationic surfactants, were found to be able to self-assemble into vesicle-like structures, mimicking the self-assembly of those covalently linked POM-inorganic hybrids. The self-assembly and structural transition behaviors are mainly characterized by dynamic light scattering (DLS), static light scattering (SLS) and isothermal titration calorimetry (ITC).

Committee:

Tianbo Liu (Advisor); Stephen Cheng (Committee Chair); Toshikazu Miyoshi (Committee Member); Mesfin Tsige (Committee Member); Jie Zheng (Committee Member)

Subjects:

Chemistry; Physical Chemistry; Polymers

yi, fengDIFFERENT BEHAVIOR IN NONLINEAR UNIAXIAL EXTENSION BEHAVIOR OF POLYISOPRENE MELT AND SOLUTION
Master of Science, University of Akron, Polymer Science
Uniaxial extension is very fundamental experiment to research sample rheology behavior and the failure mode is valuable to focus on. My work mainly consists of two parts: extension rheology behavior of polyisoprene melt and solution. For PI melt, I used different molecular weight PI to do extension at different Rouse-Weissenberg number. The results show there are three type of failure mode: rupture, necking, tensile decohesion. The decohesion behavior disappears in the low molecular weight sample. PI also shows non-quiescent relaxation behavior.(Zhu and Wang 2013) For the solution part, I introduce extended oil add into melt to make a solution. By choosing different concentrations, we let melt and solution have the same number of entanglements per chain. After stretching at same WiR, we compare the strain-stress curves of melts and solutions.(Huang, Mednova et al. 2013)

Committee:

Wang Shi-Qing (Advisor); Tsige Mesfin (Committee Member)

Subjects:

Polymers

Bekele, SelemonStructural and Dynamical Properties of Water and Polymers at Surfaces and Interfaces: A Molecular Dynamics Investigation
Doctor of Philosophy, University of Akron, 2018, Polymer Science
All-atom molecular dynamics simulations have been carried out to study the wetting of model atactic polystyrene thin films by water droplets as a function of surface polarity, the structure and dynamics at the surface of polymer films, the properties of interfacial water molecules in contact with atactic polystyrene surfaces of varying polarity, and the spreading dynamics of water droplets of varying sizes on a completely wetting surface. The simulated contact angle of a water droplet on atactic polystyrene thin films is found to decrease monotonically with increasing degree of surface oxidation which is used as a measure of surface polarity. The number of hydrogen bonds between water molecules and the polystyrene at the interface is found to monotonically increase with polarity. The contribution of the non-dispersion interactions to the interfacial energy at the polystyrene/water interface has been determined as a function of surface polarity. The roughness of the polystyrene surface and the orientational ordering of the surface phenyl rings are found to be independent of surface polarity when the polystyrene is exposed to vacuum. Surface roughness appears to increase and orientational ordering of surface rings appears to decrease slightly with polarity when the polystyrene is in contact with water. Density profiles of polymer films as a function of distance relative to an instantaneous surface exhibit a structure indicative of a layering at the polymer/vapor interface similar to the typical layered structure observed at the polymer/substrate interface. Interfacial molecules at the polymer/vapor interface have a higher mobility compared to that in the bulk while the mobility of the molecules is lower at the polymer/substrate interface. Time correlation of the instantaneous polymer/vapor interface shows that surface fluctuations are strongly temperature dependent and are directly related to the mobility of polymer chains near the interface. Interfacial water molecules on a bare atactic polystyrene surface and those which do not make hydrogen bonds with the oxidized surfaces are found to have a faster dynamics and appear to have a universal water-water hydrogen bond relaxation time of about 5 ps. Diffusion coefficients and the relaxation times of the water molecules involved in hydrogen bonding with the surface show strong dependence on surface polarity with a hydrophobic to hydrophilic transition regime with contact angle in the range 40-50o. The spreading of water droplets on completely wetting surface is characterized by a bulk part of normal density sliding over a monolayer of high density water. The monolayer has a molecular dimension and moves ahead of the bulk part of the droplet. The monolayer motion exhibits two spreading regimes, each following a power law in time. The bulk part of the droplet initially spreads over the monolayer with increasing radius until a characteristic time t* where the monolayer changes from one power law behavior to another. For times after t* ~ 0.1- 0.5 ns, it shrinks while maintaining what appears to be a constant contact angle until it disappears altogether and only a monolayer of water remains on the substrate.

Committee:

Mesfin Tsige (Advisor); Ali Dhinojwala (Committee Chair); Toshikazu Miyoshi (Committee Member); Hunter King (Committee Member); Jie Zheng (Committee Member)

Subjects:

Condensed Matter Physics; Materials Science; Nanoscience; Polymers

Keywords:

MD simulation;molecular dynamics;oxidized surfaces; water contact angle; interfacial water;surfaces and interfaces;droplet spreading;

Ammar, Ali M.REDUCTION OF GRAPHENE OXIDE USING MICROWAVE AND ITS EFFECT ON POLYMER NANOCOMPOSITES PROPERTIES
Doctor of Philosophy, University of Akron, 2018, Polymer Engineering
Graphene and graphene oxide GO as Nano-fillers have been used in numerous applications. Reduced graphene oxide, for example, is one of the most attractive additives that have been targeted to use in polymer nanocomposites due to its strong mechanical properties, electric conductivity, and gas barrier properties. However, there are many of obstacles make it difficult to be produced in large quantity at low cost and safe processes. There are many methods to reduce graphene oxide rGO and one of the interesting one that used in this research project is solution reduction of graphene oxide using Microwave. In this project, we have investigated the time effect on reduction of graphene oxide in Microwave and its polymer application properties. We have three sub projects that have been studied for the comparison of adding graphene oxide to different time reduced graphene oxide at the same weight contents and conditions. The first project, the effect of GO and rGO on polymer thin films blend phase separation. We observed that the domain size of the polymer blend phase separation changed with adding graphene oxide comparing to reduced graphene oxide due to the interaction with polymer chain. The second project, we have investigated the addition of GO and rGO on polymer gas barrier properties. Two gases have been tested: Oxygen (O2) and Carbon dioxide (CO2) at two different pressures. The remarkable result of this project is that the addition of rGOs worked as a barrier for these gases comparing to GO and Pure films. The last- project, we have studied the effect of adding GO and rGO on polymer fibers for its oil sorption capacity application and the structure morphology of these fibers.

Committee:

Karim Alamgir, Dr. (Advisor); Kevin Cavicchi, Dr. (Committee Chair); Joy Abraham, Dr. (Committee Member); George Chase, Dr. (Committee Member); Nicole Zacharia, Dr. (Committee Member)

Subjects:

Polymers

Keywords:

Graphene oxide reduced graphene oxide polymer nanocomposites properties

Jain, DharamdeepHumidity Driven Performance of Biological Adhesives
Doctor of Philosophy, University of Akron, 2018, Polymer Science
Biological adhesives are sticky secretions or structures produced by several organisms in nature to serve roles such as locomotion, prey capture and defense. These adhesives stick in a variety of environmental conditions and can maintain their adhesion exceptionally well. The present work focuses on understanding one such environmental factor, `humidity’ and presents its correlation with the material composition in influencing the adhesion mechanism in two diverse biological attachment systems: Capture silk and Gecko setae. Understanding adhesion in these natural systems is essential with respect to humidity since many synthetic materials including glues fail in presence of water. The first and second studies focus on the glue laden capture silk produced by web building spiders. In the first study, we explored the capture silk of cobweb weaver `black widow spider’ known as `gumfoot glue’. We first investigated the chemical composition of the glue and for the first time reported that it is majorly a combination of hygroscopic organic salts (low molecular mass compounds, LMMCs) and novel glycoproteins, apart from previously known peptides. Next, we correlated the glue composition with humidity based macro and molecular level studies and showed the synergistic role of LMMCs and glycoproteins in adhesion across the range of humidity conditions. Based on the first study which showed the presence and importance of diverse LMMCs in capture silk adhesion, we designed our second study in understanding the role of LMMCs in the capture silk. Based on hypothesis that LMMC’s compositions control the maximum adhesion and viscosity trends across species, we designed the study in which by using Solution-State NMR, we first analyzed the water-soluble extract of glues for four different spider species from diverse habitats and found extract belonging to each species is a distinct combination of organic LMMCs present in varied proportions. Next, we studied the water uptake of glues and their isolated LMMCs compositions. The results showed that hygroscopic strength of LMMCs alone can’t explain the adhesion response of glues. We believe it is the chemical interactions of diverse LMMCs with glycoproteins that controls the adhesion mechanism of capture silks in presence of humidity. In the third, fourth and fifth studies, we switch to a different adhesive system and present investigations based on the hairs present on gecko feet, known as `setae’. In the third study, we first time established the chemical composition of hairs by characterizing molts from gecko feet and showed the presence of ß-keratin and unbound lipids. Also, we showed lipids in hairs were more mobile as compared to lipids in epidermal skin based on which we proposed structural arrangement of lipids and keratin in the setal hairs. The fourth study focused on understanding the role of surface lipids detected in the third study. By means of shear adhesion and contact angle experiments, we found those lipids do not affect adhesive and anti-adhesive properties respectively. The existing hypothesis of ß-keratin softening and leading to higher adhesion in presence of humidity was tested in our fifth study. By series of water uptake and NMR measurements, we found ß-keratin absorbs water and gets soft at a macro and molecular level. Friction cell based shear adhesion measurements on setae supported the hypothesis and showed an increase in adhesion with increase in humidity. The research studies presented provides a detailed account of correlation of environmentally relevant parameter, `humidity’ with the building blocks of capture silk and gecko setae and their adhesion performance. The results provide design insights in developing synthetic materials such as adhesives that can work in different humidity environments.

Committee:

Ali Dhinojwala, Dr. (Advisor); Mesfin Tsige, Dr. (Committee Chair); Todd A. Blackledge, Dr. (Committee Member); Miyoshi Toshikazu, Dr. (Committee Member); Joy Abraham, Dr. (Committee Member)

Subjects:

Biology; Biophysics; Materials Science; Polymers

Keywords:

Biomimicry, Adhesion, Spider Silk, Capture Silk, Geckos, Setae, Water, Lipids, Keratin, Glycoproteins, Hygroscopic Compounds

Stapleton, Jacob DSYNTHESIS OF UPPER CRITICAL SOLUTION TEMPERATURE POLYMER FOR APPLICATIONS IN BIOTECHNOLOGY
Master of Science, Miami University, 2017, Chemical, Paper & Biomedical Engineering
There has been significant interest in the conjugation of proteins with lower critical solution temperature (LCTS) polymers such as poly(N-isopropylacrylamide). These protein-polymer conjugates, which become insoluble with an increase of temperature, have been studied as a means to increase protein stability, modify enzyme activity, and for applications such as biocatalysis, bioseparations, and drug delivery. There are very few examples of protein-polymer conjugates with upper critical solution temperature (UCST) polymers. In this case, proteins conjugated with UCST polymers would become insoluble by lowering the temperature below the UCST temperature. This type of protein-polymer conjugate could be especially useful for recovery and recycling of temperature sensitive proteins. In this study, RAFT polymerization was used to create a family of UCST polymers composed of a random copolymer of acrylamide and acrylonitrile (p(AAm-co-AN) and of the zwitterionic polymer poly(N,N’-dimethyl(methacryloylethyl)ammonium propane sulfonate) (pDMAPS). The resulting polymers were studied to determine the impact of polymer chain length, polymer composition, solution pH and salt concentration on the cloud point temperature. Different approaches to synthesize protein-polymer conjugates with UCST polymer were explored.

Committee:

Jason Berberich (Advisor); Justin Saul (Committee Member); Jessica Sparks (Committee Member)

Subjects:

Chemical Engineering; Chemistry; Polymer Chemistry; Polymers

Yixiao, FengZINC ALUMINUM PHOSPHATE PIGMENTED POLYURETHANE/POLYSILOXANE COATINGS FOR ANTICORROSION
Master of Science in Polymer Engineering, University of Akron, 2018, Polymer Engineering
In this project, the effect of TEOS on the zinc aluminum phosphate pigmented polyurethane coatings was studied. Also, the optimum pigment volume concentration at which the coating showed the best protection was determined by EIS and salt spray test. FT-IR, mass spectrometry, NMR and optical microscope were used to characterize the intermediates, coating films and pigment dispersion. Anti-corrosion, viscoelastic, mechanical and other general coating properties of modified PU coatings were investigated for comparison. EIS and salt spray data proved that the incorporation of TEOS to ZPA pigmented polyurethane coatings offered more durable and improved anti-corrosion protection, because the encapsulated inhibitive pigment was released slowly with time. The optimum ZPA loading for the PU coating with 5wt% TEOS was at lambda 0.65. ZPA, as an inhibitive pigment, could form a protection precipitation layer on the surface of steel, thus enhancing the adhesion to the steel. While the incorporation of TEOS to ZPA pigmented PU coatings decreased the pull-off adhesion, because of the interaction between TEOS and ZPA, leading to less crosslinking between TEOS and steel and thinner protection precipitation layer on the steel surface.

Committee:

Mark Soucek (Advisor)

Subjects:

Polymer Chemistry; Polymers

Keywords:

anti-corrosion, zinc aluminum phosphate, hybrid coating

Yang, MoSynthesis and Characterization of Halatopolymers by Reversible Addition Fragmentation Chain Transfer (RAFT) Polymerization
Master of Science, University of Akron, 2016, Polymer Engineering
A halatopolymer is a class of ionically-bonded materials that display both salt-like and polymer-like properties. Due to the presence of the ionic-bond in the main polymer chain, halatopolymers show some unique thermal and mechanical properties. Reversible Addition Fragmentation chain Transfer (RAFT) polymerization is a kind of controlled free radical polymerization which has been widely used in the synthesis of homopolymers or block copolymers. Trithiocarbonates (TTC) compounds have played an essential role in RAFT polymerization as chain transfer agents. In this work, the concepts of halatopolymers and RAFT polymerization have been combined by using carboxylic acid-terminated trithiocarbonate RAFT agent to synthesis trithiocarbonate-containing halatopolymers. The 1H NMR spectra and FTIR spectra confirmed the successful synthesis of trithiocarbonate-containing halatopolymers. Then these trithiocarbonate-containing halatopolymer were used as RAFT agents to synthesize halato carboxy-telechelic polystyrene homopolymers by solution polymerization. TGA, GPC and viscosity tests were used to characterize the structure and properties of the halato carboxy-telechelic polystyrenes. The calcium carboxy-telechelic polystyrene-b-poly(n-butyl acrylate)-b-polystyrene triblock copolymers were synthesized by using calcium carboxy-telechelic polystyrenes as RAFT agents. Thermal and rheological properties of these polymers were characterized, where the intermolecular ionic interactions strongly influence the mechanical properties compared to the non-ionic ABA triblock copolymers.

Committee:

Kevin Cavicchi (Advisor); Nicole Zacharia (Committee Member); David Simmons (Committee Chair)

Subjects:

Polymer Chemistry; Polymers

Keywords:

Halatopolymer, RAFT polymerization, Homopolymer, Block copolymer

venoor, varun Investigation of Poly(3-hydroxybutyrate-co-3-hydroxyvalerate)/Natural Rubber blends and Polystyrene/Polybutadiene Silica Nano-Composites
Master of Science, The Ohio State University, 2017, Chemical Engineering
Increased use of bio-based polymers and rubbers could help decrease our dependency on fossil fuel feedstocks. Poly(3-hydroxybutyrate-co-3-hydroxyvalerate) (PHBV) is a semicrystalline polymer. PHBV gets its importace from being biocompatible and biodegradable. Virgin PHBV is a brittle thermoplastic with high water and oxygen transmission rates. Also, PHBV has poor thermal properties above 160ºC, thus limiting its packaging application. It has been previously demonstrated that improved bioplastic properties (increased softness and flexibility) can be achieved by blending natural high viscosity rubber (gel) extracted from natural rubber, with PHBV. These blended materials proved suitable for making TV trays and blown films. However, commercial sources of high viscosity natural rubber were found to no longer exist. The preliminary objective of this work was to manufacture peroxide cured high viscosity natural rubber matched to that of natural rubber gel so that the bioplastic-rubber blend could be scaled up to commercially meaningful volumes. A new organic peroxide cure system was sourced, which is completely consumed during an initial heating step and so can be used to induce controlled and complete crosslinking. Hence, organic peroxide cured matched viscosity natural rubber (MVNR) was developed to achieve properties comparable to that of high viscosity rubber (Hevea gel). Different lodgings of peroxide such as 0.5, 1, 1.5, 2 phr (parts per hundred rubber) were considered. Rheological and mechanical testing’s were conducted on each of the peroxide cured natural rubber samples. 2phr peroxide (Luperox101XL45) cured natural rubber (SMR-L) at 180oC was found to have higher complex viscosity than Hevea gel. This matched viscosity natural rubber is referred as MVNR. Our next step was to incorporate this MVNR into a PHBV matrix. Dynamic vulcanization effectively dispersed and vulcanized the elastomeric (MVNR) phase within the thermoplastic (PHBV) matrix. Such systems are called thermoplastic vulcanizates (TPV) or thermoplastic elastomers (TPE). A two-stage process was employed to produce these TPVs. Firstly, 2, 5, 10, 15, 20 and 25 percent weight loadings of natural rubber (SMR-L) were melt blended with PHBV in a twin-screw extruder. These blends were then dynamically vulcanized with required the quantity of peroxide (2phr on weight loading of rubber) to produce TPVs. These TPVs were characterized for thermal properties and rheological properties. FTIR spectroscopic analysis was conducted to investigate the interfacial interaction between the cross-linked elastomer and PHBV matrix. In the recent years, the need for reduction in rolling resistance (low hysteresis tire tread) and increased traction of tires has taken center stage. Fillers such as silica (silane modified and unmodified) and carbon black have been extensively used in the tire industry improve properties of virgin polymers. The presence of nanoparticle fillers within the polymer matrix is known to alter molecular mobility, relaxation behavior, free volume, crystallization and glass transition temperature (Tg) of the resulting composites. Desorption and re-adsorption of polymer chains near nanoparticles is an important mechanism determining hysteresis. In-depth understanding of polymer-filler interaction is still needed. To understand the physics of polymer-filler interaction, simple filled polymeric systems were investigated. Virgin polybutadiene (PBD) and polystyrene (PS) was reinforced with unfunctionalized and silane functionalized silica. Reinforcement of filler was carried out using melt blending in a DACA micro-compounder and solvent casting. The rheological analysis was carried on pure and silica filled PBD and PS systems. Viscoelastic properties of unfunctionalized silica/polymer (PBD and PS) and functionalized silica/polymer (PBD and PS) were measured: the loss and storage modulus of both the system increased with loading. The increase in storage modulus is attributed to increased polymer-filler interaction, rendering it to be elastic sold in nature. In future, the dielectric spectroscopic analysis will be carried out to understand polymer relaxation behavior within the unfunctionalized silica/polymer and silane functionalized silica/polymer system.

Committee:

Koelling Kurt , PhD (Advisor); Cornish Katrina, PhD (Committee Member); Vodovotz Yael, PhD (Committee Member)

Subjects:

Chemical Engineering; Packaging; Plastics; Polymer Chemistry; Polymers

Keywords:

PHBV, Natural Rubber, Peroxide, Dynamic Vulcanization, Polystyrene, Polybutadiene, Silica

Chai, QinyuanSynthesis and Characterization of Shape Memory Polyurethane/ureas Containing Sulfated Sugar Units
PhD, University of Cincinnati, 2018, Arts and Sciences: Chemistry
Shape memory polymers are stimuli responsive materials with their shape can be temporarily changed and fixed into certain shape. Once applying some stimuli such as heat, light, chemicals, pH change etc., they can quickly recover back to the original shape without any external force needed. Due to this excellent flexibility of shape, shape memory polymers are widely investigated as promising novel materials in various fields. This dissertation is mainly based on the work of synthesis, characterization and modification of shape memory polyurethane/ureas with sulfated sugar units for potential blood contacting applications. First, covalently crosslinked polyurethane/urea polymers were synthesized using diamine monomers modified with pendant glucose groups and 2,4-toluene diisocyanate (TDI), poly(ethylene glycol) (PEG) and 1,1,1-tris(hydroxymethyl)ethane (triol) comonomers. The polymers displayed shape memory behavior with a switching temperature dependent on the glass transition temperature. The glass transition temperature is tuned by varying the mole ratio between the glucose-diamine and PEG used in the polymerization. The polymer recovered to the permanent shape when heated to 50 °C. Finally, the surface of a film of the polymer can be sulfated without sacrificing the shape memory properties. Then, this type of shape memory material with anticoagulant surfaces was processed into highly interconnected foam structure by solvent casting/particulate leaching technology. The synthesized foams good shape memory behavior as evidenced by fixity and recovery values. The materials properties of the foams can easily be tuned by varying the template used to prepare the foam. The heparin-inspired polymers impart excellent resistance to platelet adhesion indicating excellent blood compatibility of the material surface. At last, the synthesized shape memory polymer foams were composited with hydrogels based on HEAA, AA, NIPAM, and combination of AA and gelatin. The hydrogel was well dispersed in the foam cells characterized by SEM. The hydrogel incorporated SMP foams gave significantly enhanced fluid up take while remaining the shape memory effects. Moreover, ascorbic acid as example drug can be loaded into the composite material and gradually released out over 48 h.

Committee:

Neil Ayres, Ph.D. (Committee Chair); Allan Pinhas, Ph.D. (Committee Member); David Smithrud, Ph.D. (Committee Member)

Subjects:

Polymers

Keywords:

shape memory polymers;anticoagulant;hydrogels;foams;sulfated glycopolymer

Towslee, Jenna HarrisDNA as a Natural Flame Retardant Additive for Commercial Polymers
Master of Sciences (Engineering), Case Western Reserve University, 2017, Macromolecular Science and Engineering
The flame retardant properties of deoxyribonucleic acid (DNA) were investigated in melt-processed low-density polyethylene (LDPE) and polystyrene (PS). DNA showed increased compatibility with the LDPE polymer matrix relative to industrially used intumescent melamine polyphosphate (MPP). Addition of DNA to polymer substrates resulted in a significantly smaller compounding torque relative to MPP samples. Furthermore, DNA in both substrates reduced burn distance during horizontal burn testing at loading levels above 5% w/w and 10% w/w for LDPE and PS respectively. PS samples subjected to larger scale mixing with repeated heat processing had comparable flame retardant properties to single step compounded samples. This research both broadens the field of green flame retardant additives and highlights the capacity of DNA to act as an all-in-one intumescent flame retardant additive in large-scale commodity polymer applications.

Committee:

Jonathan Pokorski, Ph.D. (Advisor); David Schiraldi, Ph.D (Committee Member); Gary Wnek, Ph.D. (Committee Member)

Subjects:

Polymers

Keywords:

commercial polymers; flame retardant additives

Elmushyakhi, AbrahamIn-Plane Fatigue Characterization of Core Joints in Sandwich Composite Structures
Doctor of Philosophy (Ph.D.), University of Dayton, 2017, Materials Engineering
In practice, adjacent preform sandwich cores are joined with a simple butt joint without special precautions. When molded, this gap is filled with resin and creates a resin rich area. Stress risers will be amplified under cyclic load, and consequently, the serviceability of the structure will be affected. Designers and researchers are aware of this problem; however, quantifying this effect and its intensity and consequence on the service life of the structures has not yet been developed. Despite pervious findings, limited experimental data backed by a comprehensive root cause failure analysis is available for sandwich under axial static, fatigue and post-fatigue. If such a comprehensive experimental characterization is conducted, specifically understanding the nature of the damage, intensity, and residual strength, then a valid multi-scale damage model could be generated to predict the material state and fatigue life of similar composite structures with/without core joints under in-plane static and fatigue load. This research study characterized the effect of scarf and butt core joints in foam core sandwich structures under in-plane static and fatigue loads (R=0.1 and R= -1). Post-Fatigue tensile tests were also performed to predict the residual strength of such structures. Nondestructive Evaluation Techniques were used to locate the stress concentrations and damage creation. A logical blend of experimental and analytical prediction of the service life of composite sandwich structures is carried out. The testing protocol and the S-N curves provided in this work could be reproducible and extrapolated to any kind of core material. This research study will benefit composite engineers and joint designers in both academia and industry to better apprehend the influence of core joints and its consequence on the functionality of sandwich structures.

Committee:

Elias Toubia (Advisor); Paul Murray (Committee Member); Thomas Whitney (Committee Member); Youssef Raffoul (Committee Member)

Subjects:

Aerospace Engineering; Aerospace Materials; Civil Engineering; Composition; Design; Engineering; Materials Science; Mechanical Engineering; Polymers

Keywords:

Sandwich Composite Structures; Design; Fatigue; Damage; Joints; Lightweight Materials; E-glass-vinyl ester; GFRP Laminate; Modeling; Prediction; Nondestructive Testing

Xing, LiwenUV-Triggered and Thermo-Induced Crosslinking of Polymers Containing 1-Functionalized Benzocyclobutenes
Master of Science, University of Akron, 2017, Polymer Science
Benzocyclobutenes (BCBs) and their derivatives have attracted increasing interest due to their stability at room temperature and ability to thermally ring-open to form o-quinodimethanes (o-QDMs) upon heating. o-QDMs are reactive dienes that rapidly react with dienophiles such as maleimides to generate Diels-Alder [4+2] cycloaddition products.1 1-Hydroxy-o-QDM formed upon heating from 1-hydroxyBCB can undergo not only Diels-Alder cycloaddition reactions in the presence of dienophiles, but also rearrange to form o-tolualdehydes in the absence of a dienophile.2 o-Tolualdehydes, however, can isomerize back to 1-hydroxy-o-QDMs when irradiated with UV light.1 UV-triggered Diels-Alder reaction between o-tolualdehyde and a dienophile can be carried out at ambient temperature without an external catalyst, and has been extensively applied to polymer synthesis. 3-6 Nevertheless, previous work focused only on performing this kind of reaction at the polymer chain ends to accomplish either cyclization4 or modular conjugation.6 In addition, thermo-crosslinking of polymers using 1-hydroxyBCBs as crosslinkers have not been reported. This project established appropriate reaction conditions for both thermo-induced Diels-Alder reaction between 1-hydroxyBCB and bismaleimide and UV-triggered Diels-Alder reaction between o-tolualdehyde and bismaleimide. Copolymers of styrene and vinyl-1-acetoxyBCB were prepared via Activator ReGenerated by Electron Transfer Atom Transfer Radical Polymerization (ARGET ATRP). These copolymers underwent transesterification to generate pendant 1-hydroxyBCB moieties. Subsequently, thermo- and photo-induced crosslinking reactions can be conducted on these copolymers.

Committee:

Coleen Pugh (Advisor); Li Jia (Committee Member)

Subjects:

Chemistry; Organic Chemistry; Polymer Chemistry; Polymers

Keywords:

Benzocyclobutene; crosslinking; o-tolualdehyde; UV-triggered crosslinking

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