Phd Degree / Doktora

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Access Right: Embargoed AccessDepartment: search.filters.department.Thesis (Doctoral)--İzmir Institute of Technology, Chemical Engineering

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  • Doctoral Thesis
    Electrochemical and Oxygen/Water Permeation Behavior of Fluorinated Siloxane Copolymers Synthesized Via Initiated Chemical Vapor Deposition
    (Izmir Institute of Technology, 2021) Cihanoğlu, Gizem; Ebil, Özgenç
    Metal-air batteries are considered as one of the best alternatives to current Li-ion batteries with their high energy densities (1000-13000 Wh/kg) also, they are lightweight, cheap, and safe. However, secondary alkaline metal-air batteries suffer from catalyst corrosion, anode passivation and corrosion, electrolyte loss, and pore-clogging leading to performance loss and reduced cycle life. This thesis aims to evaluate the feasibility of highly cross-linked, hydrophobic, and oxygen selective thin homopolymers and copolymers films as potential candidates for Gas Diffusion Layer (GDL) materials in Gas Diffusion Electrodes (GDEs) for alkaline metal-air batteries. Homopolymers of 2,4,6,8-tetramethyl-2,4,6,8-tetravinylcyclotetrasiloxane (V4D4), 2-(perfluorohexyl)ethyl acrylate (PFHEA) and 2-(perfluoroalkyl)ethylmethacrylate (PFEMA) and their copolymers were synthesized via initiated chemical vapor deposition (iCVD). iCVD deposited fluoropolymer thin films exhibited low water transmission rates and excellent oxygen diffusion with a high oxygen/water selectivity up to 13.6. GDEs with iCVD GDLs exhibited higher oxygen reduction current density (228.2 mA cm-2) when compared to commercial counterparts (132.7 mA cm-2). In addition, the chemical stability, durability and corrosion protection aspects of these films were investigated by substrate adhesion and immersion tests in organic solvents and NaCl solution. The results of the corrosion test together with chemical stability and durability evaluation indicate that iCVD deposited copolymers exhibit excellent adhesion, good solvent resistance and offer effective physical and chemical protection without the need for surface pretreatment. iCVD copolymer films provide better anti-corrosion barriers with lower corrosion efficiency (85-99 %) for metal surfaces compared to homopolymer counterparts. By combining siloxane and fluorinated matrix, the copolymer films provide enhanced oxygen transport and reduce moisture entrance significantly as a GDLs and also improve physical, chemical, corrosion protection.
  • Doctoral Thesis
    Dna Adsorption on Silica, Alumina and Hydroxyapatite and Imaging of Dna by Atomic Force Microscopy
    (Izmir Institute of Technology, 2013) Yetgin, Senem; Balköse, Devrim; Balköse, Devrim
    The scope of the study is to investigate calf thymus DNA adsorption process on solid powders such as silica, alumina and hydroxyapatite (HAP) to improve DNA solid phase extraction efficiency and to visiulize DNA adsorption by atomic force microscopy (AFM). The equilibrium and kinetics of the DNA adsorption were investigated in batch adsorption on a commercial silica gel and a synthesized silica aerogel, commercial alumina and HAP powders from aqueous DNA solution. Commercial DNA extraction kit adsorbents were also characterized and used for adsorption. Adsorbed DNA was imaged in ambient air on flat surfaces of mica, silica and alumina wafers and HAP particles coated glass surfaces and a HAP pellet surface by AFM. Effects of ambient air, nitrogen flow and freeze drying methods on DNA morphology on the releted surfaces were also investigated. Adsorption of DNA on silica, alumina and HAP increased with the decrease of pH from 9.0 to 2.0. Enhancements of the adsorption capacities of adsorbents were obtained with the addition of MgCl2. It was found that the Van der Waals and the hydrogen bonds rather than the surface charge were the cause of the adsorption. The adsorption isotherms of DNA on silica, alumina and HAP were fitted to Langmuir model in pH range 2-9. The adsorption kinetics obeyed pseudo second order model. The sharpest image of DNA by AFM was obtained by freeze drying method on alumina surface. Dispersed DNA in water was adsorbed on the surfaces not as single molecules but as supercoils consisting of many molecules.