Phd Degree / Doktora
Permanent URI for this collectionhttps://hdl.handle.net/11147/2869
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Doctoral Thesis Determination of Vitamin D by Sensor Technologies Based on Molecular Imprinted Polymers(Izmir Institute of Technology, 2022) Ölçer, Yekta Arya; Eroğlu, Ahmet Emin; Demir, Mustafa MuammerVitamin D is an essential nutrient in the body; it plays important roles in human health. Both its lack and excess can have health risks. As a consequence, there is a great demand for development of simple and precise detection methods for vitamin D derivatives in different samples. Molecular imprinting polymers (MIPs) are artificial receptors that can recognize target molecules in solution. In this study, two different polymerization techniques were used to obtain MIP/NIP sorbents/films for the detection of vitamin D3. Firstly, molecular imprinted solid phase extraction (MISPE) method was proposed prior to HPLC-DAD analysis. Optimized parameters were as follows; sorbent amount of 5.0 mg for 5.0 mL of 1.0 mg/L vitamin D3 in 90:10 (v/v) ratio of H2O:MeOH solution, 5 hours sorption time and MeOH:HOAc ratio of 90:10 (v/v) as desorption solution. The accuracy of the method was verified with spike recovery test for PBS:MeOH in a ratio of 90:10 (v/v) and overall recovery was found as 85.1 (±4.3, n=3). In latter case, a quartz crystal microbalance (QCM) method was proposed for determination of vitamin D3. Electrochemical polymerization of poly(4-vinylpyridine) MIP/NIP films were achieved on gold working electrode by cyclic voltammetry (CV). Mass-transfer ability of the polymer films were analyzed by electrochemical impedance spectroscopy (EIS). The electrochemical QCM (eQCM) was used to develop thin polymer films on quartz crystals and vitamin D3 determination was achieved by QCM. In a preliminary test, as small a concentration as 0.0100 mg/L vitamin D was detected with the QCM method.Doctoral Thesis Structural Engineering of Halide Perovskites and Their Association With Organics for Optoelectronic Applications(Izmir Institute of Technology, 2022) Yüce Çakır, Hürriyet; Demir, Mustafa Muammer; Yüksel Aldoğan, KıvılcımHalide perovskites show great potential for next-generation optoelectronic applications due to their unique photophysical properties with low production costs. However, their stability issues still prevent their commercialization on a large scale. The main objective of this dissertation is to understand the additive engineering strategy to improve the quality of halide perovskite films and nanocrystals for solar cells and lightemitting diodes. There are two sections to this dissertation: The first section focuses on halide perovskite films and solar cells while the second one focuses on halide perovskite nanocrystals and white light-emitting diodes. In the first section of this dissertation, in Chapter 2-3, the improvement of Sn-Pb and methylammonium-free Pb-based halide perovskite films by additives are investigated. The suppression of defects via additives is demonstrated through structural, elemental, and optical analyses. The improved performance of perovskite solar cells by decreasing defects is also shown. In Chapter 4-5, the change in stability and optical properties of the halide perovskite nanocrystals by means of additive engineering and their applications in white light-emitting diode are studied. The results in this dissertation represent a new approach to improving the structural and photophysical properties of halide perovskites and introduce a new perspective of additive engineering method in the field of halide perovskite-based optoelectronic applications.Doctoral Thesis Development of Novel Anticounterfeiting Technologies Using Heavy Metal Free Nanoparticles(Izmir Institute of Technology, 2021) Taşcıoğlu, Didem; Özçelik, Serdar; Demir, Mustafa MuammerCounterfeiting, the act of illegally copying a product, document or currency, is a growing problem and causes economic losses. Anticounterfeiting technology uses fluorescent inks that are invisible to the naked eye in daylight, but become visible under UV light. However, these inks have problems such as fading when exposed to sunlight or room light for a long time and disappear completely over time. This is due to the relevant inks are made using organic dyes that fade. The inks used in anticounterfeiting application preventing copying of secure documents such as banknotes, passports and ID cards must be health-friendly and chemically and optically stable for years. All of the existing security materials and equipments for ID cards, driver's licenses, passports, banknotes used in our country are imported. In this study, our aim is to create a new generation of security materials and codes to combat counterfeiters and to verify the generated security codes in a simple, efficient and fast way. In this study, it is aimed to produce nanoparticles, which do not contain heavy metals and show optical stability for a long time, emitting in visible region, on the basis of the security codes created. For this purpose, water and solvent-based nanoparticles synthesized which are non-toxic should have a long-term optical stability. The synthesized nanoparticles act like a pigment in security codes. The photoluminescence (emission color) of the security codes can be adjusted by size and chemical composition of nanoparticles. In this study, colloidally monodispersed and highly photoluminescent InP based nanoparticles were synthesized by the hot-injection approach under an inert atmosphere. In addition, a protective shell (ZnS, ZnSe) coating methods have been applied to provide optical stability to InP nanoparticles. Moreover, carbon-based nanoparticles with high optical stability and being dispersible in water were synthesized using the bottom-up method. Security codes that cannot be detected in daylight have been created on different subtrates (paper, polymer, glass, etc.) by using screen printing and inkjet printing methods, which are well known printing methods using the synthesized nanoparticles. In addition, the authenticity of the security codes was checked using a commercial fiber optic based spectrometer (Ocean Optics spectrometer) and a handy hand-held optical device called the Quantag sensor developed by Quantag Nanotechnologies. Thus, a verification method that can be distinguished by a simple detection device is proposed. The synthesized nanoparticles were furthermore dispersed in a polymer solution to create random droplet and droplet/fiber patterns by electrospinning method. Thus, unique and inimitable security codes detectable under UV light were created which may be used in the fight against counterfeiting. To check the authenticity of the original security codes created; images collected with a simple smartphone microscope and a database was created in which the original patterns were recorded. The originality of the random patterns obtained was checked by comparing it with the patterns recorded in the database. In addition, the spectral information of the particle from the droplet/fiber pattern obtained was determined with a simple hand-held device (Ocean Optics optical spectrometer). Thus, by reading spectral information from the pattern, the spectral signature of the nanoparticles was determined and thus a second-step security was created. In this way, a two-stage anticounterfeiting technology that is impossible to imitate has been developed. As a conclusion, it is believed that the security codes developed in this study will pave the way for the commercialization of quantum labeling technology.Doctoral Thesis Magnetic Effect in the Biological Functioning of Hemoglobin: Dft+qmc Approach Within an Effective Multi-Orbital Anderson Impurity Model(Izmir Institute of Technology, 2019) Mayda, Selma; Bulut, Nejat; Demir, Mustafa MuammerHemoglobin corresponds to O2 transportation from lungs to the tissues and exhibits high-spin to low-spin transition by binding of O2 to Fe. In this thesis, we study the electronic and magnetic properties of the deoxy and the oxy forms of the human adult hemoglobin (HbA) to investigate the mechanism of the spin transition. We use an effective multi-orbital Anderson model and the parameters of this model are determined by the density functional theory (DFT) calculations. Then, this model is solved by using a quantum Monte Carlo (QMC) algorithm. The DFT+QMC results show that new electronic states named as the impurity bound states (IBS) exist in both deoxy-HbA and oxy-HbA.We also observe that as the temperature decreases, a magnetic gap is opened at the Fermi level for oxy-HbA. This gap arises from the Fe-O2 charge transfer. We find that both the IBS and the opening of the magnetic gap are responsible for the spin transition in hemoglobin. In addition, the DFT+QMC calculations show that antiferromagnetic (AF) correlations between the Fe(3d) and the surrounding orbitals exist in both deoxy-HbA and oxy-HbA. For deoxy-HbA, the anomalous magnetic circular dichrosim signal in the UV region is experimental evidence for these AF correlations. In the light of these magnetic measurements, we propose some explanations for the Bohr effect and the cooperativity which are the fundemental functional properties of the hemoglobin. The results presented in this thesis show that the magnetic effects play a crucial role in the funtioning of the hemoglobin.Doctoral Thesis The Fabrication of Plasmonic/Photonic Nanostructures in Polymers: Mechanical Sensor Applications(Izmir Institute of Technology, 2019) Topçu, Gökhan; Demir, Mustafa Muammer; Eanes, MehtapFunctional polymer nanocomposites offer futuristic properties by the association of inorganic additive micro-/nanostructures into the polymers. With the growing knowledge of the physical fundamentals, stimuli-responsive polymeric composites enable detection of chemical, thermal, and mechanical changes by optical sensors and probes. Since the accurate real-time detection of the change in mechanical loading is vital for construction and industrial fields, the use of colorimetric pressure elements in a static body is important for the prediction of catastrophic failures. In this thesis, strain/pressure responsive colorimetric films were produced. A number of polymer nanocomposite-based mechanical sensors are presented. By transferring the optical activity (coherent reflection and plasmonic coupling) of the additives into various polymeric matrices having different mechanical features, the strain and pressure sensors are developed for practical applications. There are two approaches used for the fabrication of polymeric mechanical sensors: i) PDMS/SiO2 composites, ii) PAAm/Au NP composites. The coherent reflectivity of SiO2 colloidal particle arrays was used to develop strain sensors while controllable localized surface plasmon resonance of Au NPs was employed for pressure sensors. These optical systems were separately associated with viscoelastic and elastic polymeric systems, and sensor properties were discussed.Doctoral Thesis Separation of Macromolecules From Aqueous Systems Using Electrospun Fibers(Izmir Institute of Technology, 2018) Işık, Tuğba; Demir, Mustafa MuammerElectrospinning has been recognised as a versatile method for the fabrication of continuous polymeric fibers with various type of morphology. Since it allows changing the fiber diameter, surface morphology and porosity by adjusting the solution and instrumental parameters, electrospun fibers present a wide range of properties that cannot be found in bulk materials. Through this thesis, removal of several types of pollutants from the aqueous systems was studied by using the electrospun fibers fabricated from both virgin and waste polymers. The first part of the dissertation deals with the removal of macromolecular pollutants from aqueous systems by using waste-based electrospun fibers. Electrospun fibers fabricated from CD cover and expanded polystyrene wastes were utilized for the protein-rich medical waste treatment by using Bovine Serum Albumin, Myoglobin and Trypsin as protein models. Electrospun fibers from expanded polystyrene wastes were utilized for the remediation of oily wastewaters. The second part of the dissertation deals with the polyatomic nuclear waste removal using uranyl ions as analyte and amidoxime functionalized PIM-1 electrospun fibers. The last part of this dissertation describes an approach for the fabrication of fluorine-free hydrophobic surfaces by electrospraying of methacrylate based linear and hyperbranched copolymers.Doctoral Thesis Down-Converting Polymer Composites and Their White Light Applications(Izmir Institute of Technology, 2018) Güner, Tuğrul; Demir, Mustafa MuammerDown-converting materials, which are luminescent materials that can emit at lower energies than their excitation energies, have been employed in a broad range of application area including phosphor-converted white LEDs, display technologies, solar cells, etc. In general, they can be obtained in the form powder or in dispersion. Therefore, to use them in an application, various methods such as spin coating can be applied or they can be prepared in the form of ceramic plate or polymer composite. In this thesis, we fabricate polymeric composite of some of these down-converting materials to use them in white light applications. In this sense, we have prepared these down-converting materials together with suitable polymers to form polymer/down-converting material composite in order to obtain free-standing film. Among those, polydimethylsiloxane was used in most of our applications especially the ones that involve inorganic downconverting materials. Second, polystyrene was employed to produce electrospun fibers in the case of when organic down-converting materials were used. After obtaining these composites in the form of free-standing film, we have focused specifically their use as color conversion layers over blue or UV LED chip to produce white light. The last part of the thesis describes our future prospects. We think that halide perovskites, which have high quantum yield, low cost, ease of synthesis, and wavelength tunability, can be promising materials in order to be employed as color conversion layer in white light applications. The details of these material systems, and their recent use in phosphorconverted white LED applications were summarized.Doctoral Thesis Synthesis and Chracterization of Polyimide Derivative Adhesives(Izmir Institute of Technology, 2018) Acar, Oktay; Demir, Mustafa Muammer; Tirkeş, SehaWhile the rapid advancement of technology is pushing the limits, today need for special advanced materials has been increased in order to obtain high-tech products with desired performance. Lightweight materials that can operate at high temperatures have critical importance in aerospace field. Between those materials, polyimides come front with their unique mechanical properties and high thermo-oxidative stabilities. They are commonly used in defense and aerospace industries as adhesives, coatings and resins in composites operating at high temperatures. PMR-15 (Polymerization of Monomeric Reactants) is considered as a state-ofthe-art high temperature resistant structural adhesive, due to its low cost, exceptional thermo-mechanical strength and thermo-oxidative resistance, up to 300 °C. However, PMR-15 has both limited processing and flexibility properties. LARC-RP46 (Langley Research Center) was developed as an alternative to PMR-15 resin. It has a higher melt flow rate to some extent. In this thesis, MDA-BTDA-ODA copolyimide adhesives with nadic end caps were synthesized. The chemical structures of the synthesized resins were verified by FTIR and 1H NMR analysis. The copolymers have thermal stabilities as high as 500 °C and Tg at around 400 °C. They showed superior adhesion performance up to 16.3 MPa. Compared to both commercial PMR-15 and LARC RP-46 polyimides, copolyimide resins showed significant processability. Kinetics of curing process of the resins was investigated by using the autocatalytic kinetic model of Kamal – Sourour. The experimental data are well-fitted with the model. The activation energies were calculated by kinetic constants derived from the model.Doctoral Thesis Preparation of Nanosized Ceo2 Particles and Their Incorporation Into Transparent Acrylate Polymers(Izmir Institute of Technology, 2014) Tunusoğlu, Özge; Demir, Mustafa Muammer; Tanoğlu, MetinNanoparticles having a size smaller than 100 nm are important building blocks of nanomaterials. Organically functionalized CeO2 nanoparticles were prepared by colloidal synthesis in this work. The particles were nucleated by mixing aqueous solutions of Ce(NO3)3·6H2O and ammonia at room temperature. Different small organic molecules were chosen as capping agents and injected into the reaction medium at the beginning of the synthesis: 3- (mercaptopropyl) trimethoxy silane (MPS), hexadecyltrimethyl ammonium bromide (CTAB), 3-mercapto propionic acid (3-MPA), and thioglycolic acid (TGA). The resulting nanocrystals were quasi-spherical and has a narrow mean size distribution with an average size smaller than 10 nm. Polymerization of monomer/nanoparticle dispersion, namely in situ polymerization, has been frequently used for the fabrication of polymer nanocomposites. Both in situ and ex situ approaches were applied for surface functionalization. The particles were dispersed into methyl methacrylate and free radical polymerization was carried out. The process of nanocomposite formation was examined in terms of conversion, molecular weight, and molecular weight distribution. The polymerization responds merely to the in situ functionalized particles. Regardless of the capping agents used, the particles function as a retarder and inhibitor. Their interaction with polymerization medium shows many complexities such that molecular weight is found to be strongly dependent on the capping agent employed.