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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

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;

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

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

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

Zhao, WeilongMolecular Simulation Investigation on the Structure-Activity Relationships at Inorganic-Biomolecule Interfaces
Doctor of Philosophy, University of Akron, 2016, Polymer Science
In the formation of bone, the insoluble collagen matrix and soluble non-collagenous proteins (NCPs) interact with various calcium phosphate (CaP) phases to control the nucleation and growth of nanosized crystals of non-stoichiometric hydroxyapatite (HAP), producing a hierarchical, composite material bearing unique mechanical properties. The mineralization of bone illustrates an exquisite example of how the interactions between biomolecules and inorganic phases well define the nucleation, growth, and structure of composite biomaterials. Despite its critical mechanistic contributions to bone pathology, as well as its general relevance to protein-regulated biomineral formation, bone biomineralization remains poorly understood at the microscopic to atomic levels. This dissertation focuses on molecular simulation methods to understand the microscopic structure-activity relationships at the biomolecule-inorganic interface particularly relevant to bone biomineralization. The primary objectives of this dissertation are: (1) to develop reliable force field parameters for accurate outcomes from the molecular simulations; (2) to apply advanced sampling techniques to overcome the limitations of classical molecular dynamics simulation, which are widely applied in the biomineralization field, for reliably representing the specific issue of the nucleation of ionic solids (such as HAP) and capturing the conformations of biomolecules, water, and inorganic species at the interfaces; (3) to establish the structure-activity relationships of synthetic HAP-binding peptides; (4) to understand the molecular-level mechanisms in various stages of bone mineralization from the form of soluble ion complexes to amorphous and crystalline CaP phases as modulated by osteocalcin (OCN), a model NCP, and (5) to extrapolate the principles learned to general inorganic-biomolecule interfaces. The validity of force field parameters for molecular dynamics simulation of HAP-water/biomolecule interfaces is shown by benchmarking to experimental observations by calculating the structures of interfacial water, the surface energies of HAP crystal faces, and the adsorption free energies of amino acid side chains. The binding conformations and affinities of a series of synthetic peptides at the HAP (100) face are accurately obtained by employing advanced conformational sampling approaches and bioinformatics techniques. The effect of non-collagenous proteins on HAP formation is studied at the molecular and energetic levels, by performing free energy calculations using OCN as an example of NCPs. The present studies targeting the benchmarking of force fields and the applications of advanced sampling methods exemplify the appropriate implementation of simulation techniques toward molecular-level elucidation of biomolecule-inorganic interfaces. The structure-activity relationships revealed from the simulation studies using model biomolecule-CaP interfaces have profound implications toward understanding the physical mechanisms of bone mineralization and can be extended to other inorganic-organic interactions in general. These principles may also contribute to rationalizing the design of peptide-based biomaterials for applications in bone repair and regeneration.

Committee:

Nita Sahai (Advisor); Mesfin Tsige (Committee Chair); William Landis (Committee Member); Matthew Becker (Committee Member); Jie Zheng (Committee Member)

Subjects:

Biogeochemistry; Biology; Chemistry; Polymers

Keywords:

Biomineralization, Inorganic-Biomolecule Interface, Molecular Dynamics Simulation

Lee, SangjinStructure-Property Relationships in Composite Layers Polymeric Film/Foam Systems
Doctor of Philosophy, Case Western Reserve University, 2017, Macromolecular Science and Engineering
Thermoplastic foams nowadays are used in a wide variety of applications in the automotive, construction, and packaging industry because of their wide range of properties such as light weight, insulation properties, softness, excellent strength/weight ratio, material cost, energy absorption performance. However, there are still issues on the mechanical and other properties in use because of the foam structure. Recently, a new type of continuously coextruded multilayered PP film/PP foam composites was developed. The coextruded multilayered film/foam successfully mimicked the multilayer film/foam structure of natural cork with PP, which enhanced the compression properties due to multilayered film/foam structures. However, there is a lack of a clear understanding how to well optimize the structure-properties due to the insufficiency of the knowledge of rheology of materials related to branching degree of PP and molecular weights. In this thesis, therefore, the first part of thesis (Chapter 2) focuses on the understanding of the effect of strain-hardening on the BPPs film/BPPs foam morphology to optimize the multilayer structures. In Chapter 3, the mechanical properties and the dielectric properties of the multilayer BPPs film/BPPs foams (produced from Chapter 2) are characterized in terms of morphology. Mechanical properties of 16 and 32layer BPP2 film/BPP2 foams such as tensile and compression behaviors reveals the effect of the film/foam structure on the mechanical properties and gives a future idea. Dielectric properties of the biaxially oriented BPP2 foam/BPP2 films are affected by the film/foam morphology such as interfacial area. In Chapter 4 and Chapter 5, the research focuses on the morphology and mechanical properties of multilayer PPs film/PPs foam including flame retardant (FR) particles to achieve improving mechanical properties. Thus, in Chapter 4, the viscosity matched multilayer BPP2 film/BPP2 foams were investigated while in Chapter 5 the viscosity mismatched multilayer LPP film/BPP2 foams were examined. Both exhibited improved mechanical properties and the latter was further enhanced. In Chapter 6, the research emphasizes the effect of the film/foam structure of the multilayer LPP film/BPP2 foam with FR particles produced by Chapter 5 on flame retardancy via multilayer coextrusion, UL-94 test, cone-calorimeter test, and SEM/EDS analysis. The LPP film/BPP2 foam with FR particles exhibits better flame retardancy due to the efficient formation of char layer, caused by the alternating film/foam structure.

Committee:

Joao Maia (Advisor); Alexander Jamieson (Committee Member); Lei Zhu (Committee Member); Ya-Ting Liao (Committee Member)

Subjects:

Engineering; Plastics; Polymers

Keywords:

Multilayer coextrusion, Film-Foam, Polyolefins, Flame retardancy, mechanical properties, dielectric properties,

Waweru, James KanyokoThermal Properties of Poly(arylene ether)s Prepared from N,N-Dialkyl-2,4-Difluorobenzenesulfonamides
Master of Science (MS), Wright State University, 2016, Chemistry
A series of poly(arylene ether)s were synthesized by nucleophilic aromatic substitution reaction (NAS) polycondensation of N,N-dialkyl-2,4-difluorobenzenesulfonamides. The aim of the project was to determine the thermal properties of poly(arylene ether)s by varying pendent sulfonamide activating group. The sulfonamide-activated monomers were synthesized by reacting 2,4-difluorobenzenesulfonyl chloride with a series of n-alkyl, iso-alkyl and cycloalkyl amines, ranging from n-propyl to n-octyl. Their poly(arylene ether)s were prepared with bisphenol-A as the nucleophilic reaction partner. The 4’-bromo-2,4-difluorodiphenylsulfone monomer, was utilized to synthesized copolymer with 4,4’-difluorodiphenylsulfone and bisphenol-A. The polymers were characterized by 1H and 13C NMR spectroscopy, TGA, DSC and SEC. Sulfonamide based polymers, exhibited moderate thermal stability with 5% weight loss temperature ranging from 372 oC to 405 oC. The influence of the alkyl group on glass transition temperature was examined, it was found that as the length of alkyl group length increases glass transition temperature decreased, which ranged from 34 oC to 179 oC.

Committee:

Eric Fossum, Ph.D. (Advisor); Daniel Ketcha, Ph.D. (Committee Member); William Feld, Ph.D. (Committee Member)

Subjects:

Chemistry; Polymers

Keywords:

poly arylene ethers; PAE; functionalized; sulfonamide; sulfone; pendent; glass transition temperature; ortho and para activated

Ewing, ZacharySynthesis and characterization of PEEK analogues utilizing 3,5- and 2,4-difluorobenzophenone.
Master of Science (MS), Wright State University, 2016, Chemistry
Two routes to semi-crystalline, potentially functionalizable poly(ether ether ketone), PEEK, analogues were explored using varying percentages of 4,4’-difluorobenzophenone and either 3,5-difluorobenzophenone or 2,4-difluorobenzophenone as the electrophilic component in nucleophilic aromatic substitution polycondensation reactions with hydroquinone. PEEK analogues utilizing 3,5-difluorobenzophenone were carried out in a “one-pot” fashion and their properties were compared to the same materials prepared previously by a multi-step synthetic procedure. The use of 2,4-difluorobenzophenone led to completely new PEEK analogues. The polymers were characterized via NMR spectroscopy, Size Exclusion Chromatography, Thermogravimetic Analysis, and Differential Scanning Calorimetry. Molecular weight determinations showed the synthesized polymers to be of a variety of molecular weights, with weight averaged molecular weight (Mw) values between 7,500 and 83,000 Da and dispersity (Ð) values between 2.5 and 2.9. The polycondensation reactions were also accompanied by the formation of cyclic species that could be, and were, removed via precipitation/trituration with isopropanol or mostly avoided by a judicious choice of reaction conditions. Solubility tests showed that the 3,5-homopolymers, which were semi-crystalline, and 2,4-homopolymers, which were completely amorphous, were soluble in many common organic solvents, while the solubility of the copolymers decreased as the percentage of 4,4’-difluorobenzophenone increased. Thermal analysis of the 3,5-difluorobenzophenone polymers possessed 5 % weight loss temperature values (Td 5%) that were similar to those of the previously synthesized polymers1, with values between 330 and 500°C. For both polymer systems, the glass transition temperatures (Tg) were between 86 and 129°C, which is consistently lower than those of the materials previously synthesized via the multistep protocols. The 3,5 homopolymer and 75%/25% (PEEK/PAMPPO) copolymers displayed crystallization temperatures (Tc) between 156 and 210°C with melting temperatures (Tm)¬ between 252 and 254°C. The 2,4-difluorobenzophenone polymers had Tg values ranging from 113 to 152°C with Tc and Tm values, for polymers containing 35% or less 2,4-difluorobenzophenone, ranging from 220 to 230°C, and 280 to 320°C, respectively.

Committee:

Eric Fossum, Ph.D. (Advisor); William Feld, Ph.D. (Committee Member); Daniel Ketcha, Ph.D. (Committee Member)

Subjects:

Chemistry; Plastics; Polymer Chemistry; Polymers

Keywords:

Polymer; PEEK; 2,4-difluorobenzophenone; 3,5-difluorobenzophenone

Wheeler, Nicholas RobertLifetime and Degradation Science of Polymeric Encapsulant in Photovoltaic Systems: Investigating the Role of Ethylene Vinyl Acetate in Photovoltaic Module Performance Loss with Semi-gSEM Analytics
Doctor of Philosophy, Case Western Reserve University, 2017, Macromolecular Science and Engineering
The lifetime performance and degradation behavior of photovoltaic (PV) modules is of the utmost importance for the success and growth of solar energy as a major resource for fulfilling growing worldwide energy needs. While PV reliability has been a concern for some time, existing qualification testing methods do not reflect a cohesive picture of the science behind module degradation, and are not capable of accurately predicting module lifetime performance. Towards these goals, a statistical methodology, semi-gSEM, was developed and applied to investigate the response of full sized PV modules to accelerated stress conditions. The results of this initial study indicated that a correlation exists between system level power loss and the buildup of acetic acid resulting from the hydrolytic degradation of ethylene-vinyl acetate (EVA) polymer encapsulant. To further explore this proposed mechanistic pathway, a study was designed and conducted to characterize the degradation of mini-module samples under damp heat accelerated stress conditions. Mini-module samples featured two construction geometries that differed in the thicknesses of screen-printed silver conductive lines (SP-Ag) to assess the impact of gridline size on damp heat induced degradation. Samples were measured non-destructively at many points along their degradation pathway, using techniques that gathered both chemical and electrical information. The semi-gSEM analytical method was applied to this dataset to highlight degradation pathways and mechanisms observed in the experimental results. An EVA encapsulant spectroscopic degradation feature was found to be statistically related to quantified degradation features of simultaneously measured EL images. In turn, the EL image degradation was found to be statistically related to I-V curve parameters describing system level power loss. The degradation pathway observed was attributed to EVA encapsulant degradation leading to metallization corrosion and ultimately system level power loss in the PV mini-module samples. Mini-module samples with thinner SP-Ag conductive lines were observed to be more severely damaged by the metallization corrosion process. This represents a valuable step in exploring the often misunderstood role of EVA degradation in PV module performance loss under damp heat conditions, and demonstrates novel methodologies for building a more integrated picture of PV module degradation as a whole.

Committee:

Roger French (Advisor); Michael Hore (Committee Member); Timothy Peshek (Committee Member); Laura Bruckman (Committee Member); Ozan Akkus (Committee Member)

Subjects:

Materials Science; Plastics; Polymers

Keywords:

Photovoltaics, PV, Lifetime and Degradation Science, EVA, semi-gSEM, Statistics, Data Science, Polymer Degradation, Polymer Science, Polymer Engineering, Materials Science

Giammanco, Giuseppe E.Photochemistry of Fe(III)-carboxylates in polysaccharide-based materials with tunable mechanical properties
Doctor of Philosophy (Ph.D.), Bowling Green State University, 2016, Photochemical Sciences
We present the formulation and study of light-responsive materials based on carboxylate-containing polysaccharides. The functional groups in these natural polymers allow for strong interactions with transition metal ions such as Fe(III). The known photochemistry of hydroxycarboxylic acids in natural waters inspired us in exploring the visible light induced photochemistry of the carboxylates in these polysaccharides when coordinated to Fe(III) ions. Described in this dissertation are the design and characterization of the Fe(III)-polysaccharide materials, specifically the mechanistic aspects of the photochemistry and the effects that these reactions have on the structure of the polymer materials. We present a study of the quantitative photochemistry of different polysaccharide systems, where the presence of uronic acids was important for the photoreaction to take place. Alginate (Alg), pectate (Pec), hyaluronic acid (Hya), xanthan gum (Xan), and a polysaccharide extracted from the Noni fruit (NoniPs), were among the natural uronic acid-containing polysaccharide (UCPS) systems we analyzed. Potato starch, lacking of uronate groups, did not present any photochemistry in the presence of Fe(III); however, we were able to induce a photochemical response in this polysaccharide upon chemical manipulation of its functional groups. Important structure-function relationships were drawn from this study. The uronate moiety present in these polysaccharides is then envisioned as a tool to induce response to light in a variety of materials. Following this approach, we report the formulation of materials for controlled drug release, able to encapsulate and release different drug models only upon illumination with visible light. Furthermore, hybrid hydrogels were prepared from UPCS and non-responsive polymers. Different properties of these materials could be tuned by controlling the irradiation time, intensity and location. These hybrid gels were evaluated as scaffolds for tissue engineering showing great promise, as changes in the behavior of the growing cells were observed as a result of the photochemical treatment of the material. We present these natural and readily available, polysaccharide-based, metal-coordination materials as convenient building blocks in the formulation of new stimuli responsive materials. The photochemical methods developed here can be used as convenient tools for creating advanced materials with tailored patterns and gradients of mechanical properties.

Committee:

Alexis Ostrowski, Ph.D. (Advisor); Michael Geusz, Ph.D. (Committee Member); George Bullerjahn, Ph.D. (Committee Member); R. Marshall Wilson, Ph.D. (Committee Member)

Subjects:

Chemical Engineering; Chemistry; Materials Science; Polymer Chemistry; Polymers

Keywords:

photochemistry; polymers; polysaccharides; hydrogels; stimuli-responsive materials; iron; coordination chemistry; biomimetic materials; drug delivery; tissue engineering; cartilage; biomaterials; nanotechnology; photopatterning; green chemistry

Jang, Keon-SooExploring mechanics via structural interplay in supramolecular networks, melt-extruded fibers, and liquid crystal/polymer blends
Doctor of Philosophy, Case Western Reserve University, Macromolecular Science and Engineering
Particular polymeric materials often require enhanced mechanics with thermal stability. Our goal is to investigate mechanical and thermal responses for stretchable coextruded fibers and supramolecular elastomers, and phase diagrams of thermally stable liquid crystal (LC) blends. This thesis is organized into three parts. Part I (Chapter 2) investigates the mechanical and thermal properties of drawn, melt-extruded polyolefin fibers. The mechanics, fiber dimensions and specific surface area of fibers were tuned as a function of draw ratio. Part II (Chapter 3) details the enhancement of mechanical and thermal properties of supramolecular elastomers containing both dynamic and covalent crosslinks. Via the precise control of UV exposure, the cure and the degradation of the UV-curable groups within the main elastomeric chains were investigated to achieve optimum mechanical properties, yielding robust supramolecular elastomers. Understanding of this structural interplay exhibits synergistic benefits derived from combination of dynamic and covalent crosslinks and provides new insight into the design and architecture of mechanically-tunable supramolecular elastomers. Part III (Chapters 4 and 5) explores thermally stable LC/polymer blends fabricated using thermally-induced phase separation (TIPS) for applications in extrusion and injection molding. Due to the limited thermal stability of current commercially available LCs, the usage of TIPS has been restricted. To overcome this issue, two different smectic liquid crystal series based on the biphenyl moiety were designed and examined for their thermal stability, liquid crystalline properties, and phase behavior (miscibility, phase separation, and phase diagrams) for polymer-dispersed liquid crystals (PDLCs). The chain length and structural impact on the polymer thermal properties and constructed phase diagrams for PDLC were investigated.

Committee:

LaShanda Korley (Advisor)

Subjects:

Polymers

Ge, SiruiThe Entanglement-Disentanglement Transition (EDT) During Creep With Either Constant Or Oscillatory Stress In Highly-Entangled Polybutadiene Solution
Master of Science, University of Akron, Polymer Science
Nonlinear rheological behavior of entangled polymer systems has been investigated for decades, most of which were carried out in strain-controlled mode. In 2004, the yield-like Entanglement-Disentanglement Transition (EDT) was observed in entangled polymer solutions during creep at constant stress. The 2004 study attracted further investigations that attributed the EDT to edge instability. In this work, it is shown that the EDT can take place in absence of any edge instability in the highly entangled 1,4-polybutadiene solutions. In addition, the behavior of EDT was also studied using oscillatory stress-controlled mode (LAOStress) to minimize edge effect. In the LAOStress, EDT takes place when the responding strain grows in amplitude over time. The distortion of the strain response was observed upon the EDT. In order to reflect the nonlinear viscoelasticity, the harmonic analysis and strain decomposition was conducted. Apparent higher harmonics was found in the strain response. In addition, different disentanglement mechanisms are founded in two samples.

Committee:

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

Subjects:

Materials Science; Physics; Polymers

Chen, WeiLocal Structure and Molecular Dynamics of Supramolecules And Semicrystalline Polymers As Investigated By Solid State NMR
Doctor of Philosophy, University of Akron, 2016, Polymer Science
In this dissertation, we have focused on the study of the interplay of structure and molecular dynamics of soft materials including supramolecules and semicrystalline polymers at the molecular scale through various state-of-the-art solid state NMR techniques. The dissertation is consisting of three parts. In Chapter IV, we focus on the atomic scale dynamics for a Janus bisamide supramolecule. Relationship between unique structure and dynamics will be demonstrated. On the basis of the determined conformations and packing structures of the alkyl chains in ordered and disordered crystalline phases, along with the geometry and kinetic parameters of the structural elements’ dynamics, the self-assembly, the phase-transition mechanisms, and the relationship between the structure and dynamics of the asymmetric Janus bisamide supramolecules were addressed. In Chapter V, we investigate molecular dynamics of semicrystalline polymers including poly-lactic acid-PLA, polyethylene oxide PEO, and polyoxymethylene POM in well controlled morphologies. Based on dynamic frequency and geometry of molecular motions, we’ve discussed possible structural factors that influence chain dynamics in the crystalline regions. In Chapter VI, we investigate the chain-trajectory of PLA stereocomplex by 13C Double-Quantum -DQ NMR in combination with spin-dynamics simulation. Poly-L-lactide PLLA and poly-D-lactide -PDLA alternatively pack with each other and form stereocomplex crystals -SCs. The habits of SCs formed in the dilute solution depend highly on the molecular weight Mw. It was demonstrated that the ensemble average of the successive adjacent re-entry number n for the l-PLLA chains drastically changes depending on Mws of the counter PDLA chains in the SCs. It was concluded that the limited space for two kinds of PLA chains at the fold surface significantly influence the chain-folding patterns inside the SCs and as a result led to the unique Mw dependence of the crystal morphology.

Committee:

Toshikazu Miyoshi (Advisor); Stephen Z.D. Cheng (Committee Chair); Ali Dhinojwala (Committee Member); Mesfin Tsige (Committee Member); Thein Kyu (Committee Member)

Subjects:

Polymers

Keywords:

Supramolecule; Semicrystalline Polymer; Solid state NMR; polyethylene oxide ;PEO; polyoxymethylene ;POM; polylactide; PLA

Li, YifanHigh Performance Perovskite Hybrid Solar Cell Via Interfacial Engineering
Master of Science, University of Akron, 2016, Polymer Engineering
Perovskite (CH3NH3PbI3 based materials) hybrid solar cell has been one of the most promising photovoltaic device due its plenty of advantages such as low price of raw materials, easy fabricating procedure and relative high power converted efficiency (PCE) (compared to polymer solar cells) and so on. However, the still not very high efficiency of perovskite hybrid solar cells makes it at a disadvantage position in the competition with traditional silicon solar cells. Thus, to make it more competitive, efficiency enhancement comes to a vital issued need to be addressed. There are three chapters in this thesis. In chapter 1, a general introduction of perovskite hybrid solar cells including working mechanism and development is giving. In chapter 2, we use the electrochemical material PSBEDOT to function as the hole transfer layer to observe the high performance of perovskite devices. In chapter 3, to improve the efficiency of perovskite hybrid solar cells, we have blended commercial available Fe3O4 nanoparticles in to the active layer of perovskite hybrid solar cells to see any performance improvement. To further enhance the device performance, some magnetic treatments have been done in the perovskite layer of the device including the involving of magnetic nanoparticles and external magnetic field. Finally, we have got a result with PCE reaching 14.40% with a dramatically enhanced short current density.

Committee:

Xiong Gong (Advisor)

Subjects:

Electrical Engineering; Polymers

Ji, ShanzuoBIO-INSPIRED POLYMER LENS SYSTEMS FROM MULTILAYERED FILMS
Doctor of Philosophy, Case Western Reserve University, 2016, Macromolecular Science and Engineering
CHAPTER1: A synthetic polymeric lens was designed and fabricated based on a bio-inspired, “Age=5” human eye lens design by utilizing a nanolayered polymer film-based technique. The internal refractive index distribution of an anterior and posterior GRIN lens were characterized and confirmed against design by µATR-FTIR. 3D surface topography of the fabricated aspheric anterior and posterior lenses was measured by placido-cone topography and exhibited confirmation of the desired aspheric surface shape. Furthermore, the wavefronts of aspheric posterior GRIN and PMMA lenses were measured and simulated by interferometry and Zemax software, respectively. Their results show that the gradient index distribution reduces the overall wavefront error as compared a homogenous PMMA lens of an identical geometry. Finally, the anterior and posterior GRIN lenses were assembled into a bio-inspired GRIN human eye lens through which a clear imaging was possible. CHAPTER 2: A nanolayered polymer films approach to designing and fabricating gradient refractive index lens (GRIN) lenses with designer refractive index distribution profiles and an independently prescribed lens surface geometry has been demonstrated to produce a new class of gradient index optics. This approach utilized nanolayered polymer composite materials from polymethylmethacrylate (PMMA) and a styrene-co-acrylonitrile copolymer (SAN) with a tailorable refractive index intermediate to bulk materials to fabricate discrete gradient refractive index profile materials. A process to fabricate nanolayered polymer GRIN optics from these materials through thermoforming and finishing steps is also described. A review of a collection of technology-demonstrating nanolayered GRIN case studies is which include: optical performance of an f/# 2.25 spherical GRIN plano-convex singlet 1/10 the weight of a similar BK7 lens and a bio-inspired aspheric human eye lens. Original research on the fabrication and characterization of a Luneburg inspired GRIN ball lens is presented as a developing application of the nanolayered polymer technology. CHAPTER 3: Compact and adaptive-focus tunable lenses have drawn increasing attention in the field of imaging applications including cellphone cameras, video endoscopes, and optical fiber components. This study demonstrated an all-solid-state thermoplastic elastomer tunable lens where the focal length was altered by the lens radius variation under a compressive pressure. The elastic behavior of the lens material was also investigated in the hysteresis study, which indicated that the conditioned lens material possessed a better elastomeric properties after the first cycle of loading and unloading. The radius of curvature of the tunable lens was simultaneously measured by a corneal topographer during compression. The results showed at a 0.4 mm compression, the lens curvature decreased from 12.86 mm down to 10.41 mm, which resulted in 19% of focal length change in the tunable lens. An ANSYS finite element analysis (FEA) model was used to predict shape deformation of the tunable lens during compression, which correlated well with the experimental results. CHAPTER 4: Triple shape memory polymers are capable of memorizing two temporary shapes and sequentially recovering from the first temporary shape to the second temporary shape, and eventually to the permanent shape upon exposure to heat. In this paper, unique three component multilayered films with ATBTATBTA configuration were produced by using a forced assembly multilayer film coextrusion process for a novel triple shape memory system. The films consisted of 65 polyurethane (PU) layers and 64 ethylene vinyl acetate (EVA) layers and separated by 128 poly(vinyl acetate) (PVAc) layers. The resulting films have two well separated thermal transition temperatures, one from the melting temperature of EVA and the other from the glass transition temperature of PVAc, which were used to subsequently fix two temporary shapes. The cyclic thermo-mechanical testing results showed that 257-layered PU/EVA/PVAc films possessed outstanding triple shape memory performance in term of shape fixity and shape recovery ratios. This approach allows greater design flexibility to some specific applications that are in need of simultaneous adjustment of the mechanical and shape memory properties.

Committee:

Eric Baer, Prof. (Committee Chair); Alexander Jamieson , Prof. (Committee Member); Andrew Olah, Dr. (Committee Member); Donald Schuele, Prof. (Committee Member)

Subjects:

Polymers

Keywords:

Bi-oinspired Gradient Refractive Index Lens; Triple Shape Memory Polymer Films; Multilayer Film Co-extrusion; and Structure-Properties-Relationships

Cao, PengfeiPOLY(CAPROLACTONE) WITH UNCONVENTIONAL ARCHITECTURES: DESIGN, SYNTHESIS, CHARACTERIZATION AND POTENTIAL APPLICATIONS
Doctor of Philosophy, Case Western Reserve University, 2016, Macromolecular Science and Engineering
The poly(caprolactone) (PCL) with unconventional architectures are of high interest for their unique chemical and physical properties. The PCL with star-shaped architectures can be obtained in large quantity in high yielding, while their application investigation is still limited. The property study and application investigation on the topologically interesting PCLs, such as catenated PCL and trefoil knotted PCL, were rarely investigated due to the synthesis challenges. Chapter 1 reviews the synthesis and application of poly(caprolactone). In addition, recent advances in the synthesis of poly(caprolatone)s with unconventional architectures, such as hyperbranched PCL, star-like PCL and especially cyclic PCL, are also discussed. Chapter 2 demonstrates an efficient functionalization method of hyperbranched PEI with high molecular weight by the ring-opening polymerization of CL to extend the terminal groups. The conformation freedom was also tuned by the modification of arm lengths and core sizes. Chapter 3 reports a highly stable polymer protected noble-metal nanoparticle in powder form. The star-like copolymer can transfer and stabilize the pre-synthesized citrate-capped noble metal nanoparticle (NMNPs) from the aqueous layer to the organic layer. The hybrid powder obtained after evaporation of the organic solvent exhibited excellent thermal and long-term stability. Chapter 4 demonstrated a facile approach for the synthesis of catenated polymers via a ring-expansion strategy. Insertion of caprolactone monomers into the catenated initiator, which was obtained from the ring closure reaction between the phenanthroline copper (I) complex and dibutyldimethoxytin, affords a catenated polymer. Chapter 5 reported the catenated poly(caprolactone)s with different DPns by modifying the feed ratio of monomer to catenane initiator. Catenated poly(lactide) was also synthesized in a similar manner. The comparative crystallinity of the catenated PCL with their linear analogue was also studied. Chapter 6 demonstrates for the first time the reasonable synthesis of a knotted polymer from a bis-copper(I) templated phenanthroline initiator. The comparative property study with linear analogue and an AFM image demonstrate the structure of the trefoil knotted polymer. Finally in Chapter 7, conclusions, perspectives, and future work on these topics are discussed.

Committee:

Rigoberto Advincula (Advisor); David Schiraldi (Committee Member); Clemens Burda (Committee Member); Jon Pokorski (Committee Member)

Subjects:

Nanotechnology; Organic Chemistry; Polymer Chemistry; Polymers

Babak, LotfizadehDehkordiRHEOLOGY AND TRIBOLOGY OF LUBRICANTS WITH POLYMERIC VISCOSITY MODIFIERS
Doctor of Philosophy, University of Akron, Mechanical Engineering
Elastohydrodynamic lubrication (EHL) theory has been used to model the lubrication state of antifriction machine elements, where initial viscosity and pressure viscosity coefficients are essential parameters in film thickness modeling. Since the pressures of lubricants in the contact zone can be very high, it is important to know the rheological properties of lubricants in these pressure and temperature regimes. The characteristics of viscosity behavior as a function of pressure are also essential for a universal definition of the pressure viscosity coefficient in order to estimate film thickness in an EHL regime. In this study, viscosities and pressure-viscosity coefficients of ten commercial engine and gear oils and seventeen laboratory-produced oil/polymer viscosity modifiers (VM) additives are measured up to 1.3 GPa at 40, 75 and 100 °C. For the first time, a sharp increase in the viscosity and piezoviscous factor is observed in both mineral-based and synthetic-based oils with different VMs. Analysis of the experimental results indicates that sharp increase in viscosity observed in these experiments are believed to arise from physical changes in the VMs, that is liquid-solid phase transition. Evidence is offered that polymer properties such as molecular weight, concentration and structure influence the onset of the phase transitions. A modified Yasutomi model, which normally describes the pressure dependence of the viscosity of lubricants very well, fails to predict the viscosity of the specimens above the onset of sharp increase in viscosity. A design of experiment (DOE) analysis using Design-Expert software indicates that pressure and temperature are the most critical parameters in the viscosity variation. Tribological tests demonstrate that wear in the contact, zone occurs at temperatures and stresses that coincides with the VM phase transitions in both commercial and laboratory synthesized oil/VMs. Tribological results also indicate that the onset of the sharp increase in viscosity can have significant and unanticipated consequences on the elastohydrodynamic contact and can adversely affect EHL theory. The onset of the steep rise in viscosity may also affect the torque and power losses in a mechanical system. Hence, this previously unknown behavior of the lubricant with VMs should be seriously considered in the application of lubricant in mechanical system.

Committee:

Gary Doll (Advisor); Paul Shiller (Committee Member); Greg Morscher (Committee Member); Matthew Becker (Committee Member); Ryan Evans (Committee Member)

Subjects:

Energy; Engineering; Mechanical Engineering; Physics; Polymer Chemistry; Polymers

Keywords:

Lubricants, Engine oils, Rheology, Tribology, Polymer additive, Viscosity Modifier, High pressure, Viscosity, Friction, Wear

Wang, YiwenSYNTHESIS OF NANOPARTICLES BY SINGLE-CHAIN COLLAPSE OF HYPERBRANCHED POLYMERS USING SOL-GEL CHEMISTRY
Master of Science, University of Akron, Polymer Science
Recently nanoparticles made from linear polymers has achieved great success because of its significant potential in science, pharmaceutical and drug delivery fields, but seldom are nanoparticles made by hyperbranched polymers reported. In our project, we aimed to synthesize nanoparticles from hyperbranched polymers. In the synthesis of nanoparticles, there is a limitation in getting well-defined particles; that is, the particle structure is often uncontrollable. To solve this problem, single-chain collapse is applied here to provide an easy path to obtain particles with small diameters. In this project, we synthesized nanoparticles based on a hyperbranched copolymer poly[(methyl acrylate)-co-(3-(triethoxysilyl)propyl methacrylate)], which was prepared by the copolymerization of (2-bromo-2-methoxycarbonyl)ethyl acrylate, with 3-(triethoxysilyl)propyl methacrylate (TESPMA). With (2-bromo-2-methoxycarbonyl)ethyl acrylate, as an inimer, and 3-(trimethoxysilyl)propyl methacrylate (TMSPMA) as a silicon-containing monomer, the trialkoxysilyl groups provide crosslink sites for intarmolecular single-chain collapse by gelation. These highly branched polymers were snythesized by atom transfer radical polymerization (ATRP). The nanoparticles were produced later by gelation of the triethoxysilyl groups in dilute solution to guarantee intramolecular crosslink.

Committee:

Coleen Pugh (Advisor)

Subjects:

Polymers

Keywords:

hyperbranched polymer, nanoparticles

HE, ZHOUYINGORGANIC/INORGANIC HYBRID COATINGS FOR ANTICORROSION
Doctor of Philosophy, University of Akron, 2015, Polymer Engineering
Compared to organic coatings, organic-inorganic hybrid coatings can potentially improve the anticorrosion performance. The organic phase provides the excellent mechaincal and barrier properties while the inorganic phase acts as an adhesion promoter and corrosion inhibitor. Despite that many studies on alkoxylsilane-based hybrid coatings have been developed and studied, their weatherability and anticorrosion performance has been rarely evaluated. On the other hand, organic-inorganic hybrid coatings based on mixed sol-gel precursors have received much less attention compared to alkoxylsilane-based hybrid coatings. In the first part, polyurethane hybrid coatings with a unique hybrid crosslinked structure as an improved unicoat were successfully prepared. The effect of polyesters on physical properties of the hybrid coatings was studied. Polyurethane coatings derived from cycloaliphatic polyester show comparable properties than those derived from the commercially viable aromatic polyester. Introducing the polysiloxane part into the polyurethane coatings enhanced the crosslinking density, Tg, mechanical properties, and general coating properties. The increased adhesion between the hybrid coating and the substrate make the hybrid coating a good candidate for anticorrosion application, which is shown by electrochemical impedance spectroscopy (EIS). The degradation mechanism of the polyurethane/polysiloxane hybrid coatings under various weathering conditions was shown to be the scission of the urethane and ester groups in the organic phase along with reorganizing and rearranging of the inorganic phase. The anticorrosion performance of the cycloaliphatic hybrid was much better than that of aromatic based hybrid under outdoor weathering based on visual observation and EIS analysis. Acid undercutting is an issue for TEOS based hybrid coating. In the second part, design of experiments (DOEs) was used to statistically investigate on the effect of sol-gel precursors. The synergistic effect of the mixed sol-gel precursors was shown to enhance the overall properties and was also observed structurally by SAXS and SEM. The improved resistance to the acid undercutting was observed for mixed sol-gel precursors based hybrids. The application of hybrids provides excellent anticorrosive properties as observed in salt spray and EIS study. The formation of Al2O3 protective layer as well as M-O-Al covalent bond provided the basis for excellent corrosion protection on Al substrate. However, the generation of Fe ions as corrosion product caused the accumulation of electrolyte, which resulted in the delamination of the coating on steel substrate. In this way, the corrosion of steel substrate is much faster than that of Al substrate. The maintenance of high impedance and corresponding resistance and capacitance based on EIS results further confirmed the great anticorrosion performance of hybrids on both Al and steel substrate.

Committee:

Mark Soucek (Advisor); Alamgir Karim (Committee Member); Kevin Cavicchi (Committee Member); Chrys Wesdemiotis (Committee Member); Wiley Youngs (Committee Member)

Subjects:

Polymer Chemistry; Polymers

Park, ChangKyooDevelopment of Precise Femtosecond Laser Micromachining Processes for Metals and Electrospun Nanofibers
Doctor of Philosophy, The Ohio State University, 2015, Materials Science and Engineering
Femtosecond pulse lasers have proven to be versatile for micro-scale ablation of a variety of materials with high quality machining due to minimal residual stress, heat affected zone, and melting. In addition, femtosecond laser is one of the non-cleanroom techniques that does not require masking, chemical reagents, and multiple steps. This simple and convenient micromachining technique enables machining of various materials in 3-dimensional geometry. However, some factors such as optical scattering, beam shape, and debris accumulation hinder the high quality of ablation. In this dissertation, femtosecond laser was employed for the micromachining of electrospun nanofibers and metals. Optimization of a process for the high quality femtosecond laser machining was investigated. Femtosecond laser and electrospun poly(e-caprolactone) (PCL) nanofibers mesh interaction was analyzed by optical property measurements and the optical absorption and scattering coefficients were estimated. The specific energy required for ablating a unit volume of pure PCL nanofibers and polydimethylsiloxane-poly(e-caprolactone) (PDMS-PCL) core-shell nanofibers was measured. Material inherent optical properties including the ablation threshold fluence and the incubation coefficient of PDMS and PCL were estimated. Circular grooves were fabricated on aluminum, stainless steel 316, and Stellite 6 and circular disks were successfully machined from a thick section of Stellite. The tapered cross-section was detected from the Stellite disk and the tapering was minimized by varying pulse energy during ablation process. Moreover, a novel debris removal technique based on DC-dielectrophoresis (DEP) force was used to machine the linear and circular grooves on aluminum and the ablation depth and precision were compared with the gas jet debris removal technique.

Committee:

Dave Farson (Advisor); John Lannutti (Committee Member); Antonio Ramirez (Committee Member)

Subjects:

Materials Science; Metallurgy; Optics; Polymers

Keywords:

Femtosecond laser, Ablation, Metal, Polymer, Electrospun nanofiber, Scattering, Tapering, Debris removal, DC-dielectrophoresis

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