Phd Degree / Doktora

Permanent URI for this collectionhttps://hdl.handle.net/11147/2869

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Publisher: search.filters.publisher.Izmir Institute of TechnologySubject: search.filters.subject.Polymers

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Now showing 1 - 4 of 4
  • Doctoral Thesis
    Preparation of Nanostructured Interface by Polymer Grafting on Various Solid Substrates for Biosensor Applications
    (Izmir Institute of Technology, 2021) Özenler, Sezer; Yıldız, Ümit Hakan
    This thesis presents the utilization, various applications, and characterization of the soft material-based coating formed on the gold surface with varying thickness and chemical properties resulting from the isocyanate-gold interaction. Theoretical calculations regarding the interaction of isocyanate with the gold surface revealed the character of the bond formed and the orientation of the functional groups on the surface. Results by X-ray photoelectron spectroscopy showed the tendency to shift to the high energy at N 1s and C 1s binding energies in the gold-interacting isocyanate group. In the next steps, the isocyanate-activated gold substrate was subjected to sequential incubation of 1,4-butanediol/hexamethylene diisocyanate, and thin-film formation was achieved by surface assisted (SurfAst) urethane polymerization. It was revealed with three different applications that a nano-porous polyurethane (PU) structure was formed on the gold substrate and could be postmodified by using SurfAst polymerization method. In the first application, modification with polyethylene glycol (PEG) was provided to obtain antifouling properties. The PEG-terminated PU structure on the gold surface was shown to reduce protein adhesion by approximately ten-fold. In the second application, SurfAst was applied on the 11-mercaptodecanoic acid incubated surface and grafting onto the poly (N-allyl-N-methyl-N-(3-((4-methylthiophen-3-yl)oxy)propyl) prop-2-en-1-aminium surface was characterized. As a result of PT grafting, PT nanowires with an average height of 100 nm, a width of 250 nm, and a length of 7 μm were obtained on the gold surface. In the last application, a soft nanogel was obtained by a reactive layer-layer (rLBL) coating method using the aza-Michael addition reaction of branched polyethyleneimine and polyester on the isocyanate functional surface. The mechanical and electrical permeability and coating properties of the nanogel layer were assessed. In conclusion, the high potential of isocyanate in surface activation has been demonstrated theoretically and experimentally. Effective modification of gold surfaces by polymer grafting with the SurfAst method and rLBL coating techniques has been achieved.
  • Doctoral Thesis
    Macromolecular Design of Hydroxyl Functional Linear and Star-Shaped L-Lactide and ?-Caprolactone Biodegradable Polyesters Utilizing Biosafe Catalysts for Biomedical Applications
    (Izmir Institute of Technology, 2017) Başalp, Dildare; Tıhmınlıoğlu, Funda
    In the present study, macromolecular design of homo and copolymers of lactide (LA) and ε-caprolactone (CL) in different structures by the use of biocompatible catalysts and co-initiators were performed to satisfy a need of tailor-made bioassimilable polymeric structures without any hazardous metal contaminants for various medical applications. Linear and star shaped (di, tetra and hexa functional) poly(L-lactide) (PLLA) and poly(ε-caprolactone) (PCL) homo/copolymers were synthesized by using bismuth(III)acetate (Bi(III)Ac) and creatinine as biosafe catalysts and ethylene glycol, pentaerythritol and myo-inositol as co-initiators. The effect of catalyst type on polymer properties was observed by differences in crystalline structure. Crystalline and amorphous linear and star shaped PLLAs were obtained by using Bi(III)Ac and creatinine as catalysts, respectively. The activity of creatinine was very low comparing to Bi(III)Ac and SnOct2 catalysts. The reactivity of LA monomer was found to be higher than that of CL monomer. The high molecular weight polymers having low PDI values were obtained by using Bi(III)Ac catalyst contary to creatinine catalyst. The decrease in glass transition temperatures and molecular weights of synthesized PLLA and PCL homo/copolymers were observed with the increase in amount of co-initiators due to the decrease in chain length and disruption of crystal formation. The cytotoxicity properties of the catalysts and synthesized linear and functional homo/co PLLAs and PCLs were carried out according to MTT assay. Cytotoxicity of Bi(III)Ac was found as lower than that of SnOct2. Creatinine and the synthesized polymers did not show any cytotoxic properties. The observation of no cytotoxic effect of creatinine catalyst results in the biosafe usage of creatinine catalyst instead of toxic SnOct2 for the synthesis of moderate or low molecular weight homo/co PLLAs and PCLs in bioapplications.
  • Doctoral Thesis
    Enhancement of Thermal, Electrical and Optical Properties of Zinc Oxide Filled Polymer Matrix Nano Composites
    (Izmir Institute of Technology, 2009) Özmıhçı, Filiz; Balköse, Devrim
    The purpose of this study is to enhance the electrical, thermal and optical properties of polyethylene and polypropylene by the addition of zinc oxide (ZnO) filler.Embedding ZnO in a polymeric matrix could make an economic, weight saving, chemically resistive, optical, flexible and conductive materials which possesses the properties of zinc oxide.Composites with higher electrical and thermal conductivity having luminescence properties were prepared using commercial and hydrothermally synthesized ZnO powders with different particle size and conductivity. Effect of ZnO loading and surface treatment on composite properties was investigated. Luminescence effects in green and blue regions were detected in all powders due to the defects on the structure of ZnO.The powders were found to be moderately conductive materials, as well. Un-homogenously dispersed composites were prepared using rheomixer since especially nano powders tended to be agglomerated in the composite. On the other hand, different surface properties of powder and polymer caused adhesion and wetting problems. Microvoids were detected in the interphase, as well.Composites can be used as an electrostatic dissipation and moderate electrical conductive applications in the field of electrical conductivity, as a heat sink in the field of thermal conductivity and as a solid state lamp due to luminescence properties. Stiffness of the composites was very high compared to neat polymer and can be properly used as an engineering material.
  • Doctoral Thesis
    The Effects of Diatom Frustule Filling on the Quasi-Static and High Strain Rate Mechanical Behavior of Polymer Matrices
    (Izmir Institute of Technology, 2010) Gültürk, Elif; Güden, Mustafa
    In this study quasi-static tension and quasi-static (1x10-3 and 1x10-1 s-1) and high strain rate (300-600 s-1) compression and quasi-static tensile behavior of diatom frustules-filled, Diatomaceous earth (CD) and Kieslguhr (ND), epoxy matrices were investigated experimentally and microscopically. For comparison, the compression and tensile behavior of the neat epoxy was also determined. Compression results showed that diatom frustules filling increased both modulus and yield strength of the epoxy matrix at quasi-static and high strain rates. ND frustules filled epoxy samples showed a higher strain rate sensitivity compare with CD filled samples. Tensile test results showed that the modulus of filled epoxy increased with increasing frustule content. The frustule filling, however, decreases the tensile failure strains of the epoxy and increased the tensile strength slightly. Microscopic observations on the fracture surfaces and the mounted cross-sections of deformed samples showed that the failure mechanisms were debonding of the frustules-epoxy interface and the fracture of the frustules at quasistatic strain rates while the failure of the filled composite at high strain rate was dominated by the fracture of the matrices. These results confirmed that significant benefits might anticipated from the use of diatom frustules as reinforcements and fillers in polymeric materials. Various methods; acid leaching, thermal shock and ball milling were further applied to process nano size silica powder from frustules. Projectile impact tests indicated that frustule addition increased the ballistic resistance of epoxy matrices. Finally, the strength and modulus of the filled epoxy matrices were predicted using analytical models developed for short fiber composites.