İleri Malzemeler ve Nanoteknoloji Ana Bilim Dalı Tez Koleksiyonu

Permanent URI for this collectionhttps://hdl.handle.net/20.500.12573/420

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Design and control of universal test platform for lower limb assistive devices
(Abdullah Gül Üniversitesi, 2018) BİLGİ, MUHAMMET FURKAN; AGÜ, Mühendislik Fakültesi, Makine Mühendisliği Bölümü; BİLGİ, MUHAMMET FURKAN
Robotic lower limb assistive devices are highly important tools because they are being used in rehabilitation of patients who has problems with their lower limbs or enhancing the capabilty of human such as lifting or carrying high loads. Besides, testing and evaluation of these devices accurately has vital importance. Robotic testing has many advantegeous aspects such as being able to perfom long term operations and mimic dangerous conditions such as near-fall etc. Also, collecting data from test device is easier than collecting from human. First, a conceptual exoskeleton which can perform walking (weight acceptance, push-off and swing), sit to stand and stair climbing tasks is designed. To be able to perform these tasks, springs, an actuator and engage disengage mechanism are mounted on the exoskeleton and coefficient of springs, and required power of actuator are calculated. Secondly, a test platform design is proposed. After that, a controller that is meant to mimic the hip motion (center of mass motion and hip joint) is introduced by using MATLAB-Simulink.
Design of lightweight and compact knee-ankle assistive device for walking and sit to stance
(Abdullah Gül Üniversitesi, 2018) FURKAN BALTACIOĞLU, MEHMET; AGÜ, Mühendislik Fakültesi, Makine Mühendisliği Bölümü; FURKAN BALTACIOĞLU, MEHMET
In this study, design of a conceptual semi-active transfemoral prothesis which can be used for walking, sit-to-stand and stair climbing was studied. In this study, human data in literature were analyzed and according to these data, firstly conceptual design of the prosthesis was presented. The first initial concept design was also built by means of 3D printer. Thereafter according to built model, the conceptual design was modified to make it more stable for functions. Also, the theoretical spring coefficients were calculated. According to structural parameters, FEM analyses of prosthesis were made. And parts on prosthesis were optimized by using topology optimization process.
Design, synthesis, and characterization of n-type and ambipolar small molecules as air-stable and solution-processable semiconductors in ofets
(Abdullah Gül Üniversitesi, 2016) ÖZDEMİR, RESUL; AGÜ, Mühendislik Fakültesi, Malzeme Bilimi ve Nanoteknoloji Mühendisliği Bölümü; ÖZDEMİR, RESUL
The design and development of novel ambipolar and n-channel semiconductors is very crucial to advance various optoelectronic technologies including organic fieldeffect transistors (OFETs) and complementary (CMOS) integrated circuits. Although numerous ambipolar and n-channel polymers have been realized to date, small molecules have been unable to provide high device performance in combination with ambient-stability and solution-processibility. In the first part of this thesis, two novel small molecules, 2OD-TTIFDK and 2ODTTIFDM, were designed, synthesized and characterized in order to achieve ultralow band-gap (1.21-1.65 eV) semiconductors with sufficiently balanced molecular energetics for ambipolarity. Bottom-gate/top-contact OFETs fabricated via solutionshearing of 2OD-TTIFDM yield perfectly ambient stable ambipolar devices with reasonably balanced electron and hole mobilities of 0.13 cm2 /V·s and 0.01 cm2 /V·s, respectively with Ion/Ioff ratios of ~103 -104 , and 2OD-TTIFDK-based OFETs exhibit ambipolarity under vacuum with highly balanced (µe/µh ~ 2) electron and hole mobilities of 0.02 cm2 /V·s and 0.01 cm2 /V·s, respectively with Ion/Ioff ratios of ~105 -106 . Furthermore, complementary-like inverter circuits were demonstrated with the current ambipolar semiconductors resulting in high voltage gains of up to 80. Our findings clearly indicate that ambient-stability of ambipolar semiconductors is a function of molecular orbital energetics without being directly related to bulk ?-backbone structure. To the best of our knowledge, considering the processing, charge-transport and inverter ii characteristics, the current semiconductors stand out among the best performing ambipolar small molecules in the OFET and CMOS-like circuit literature. Our results provide an efficient approach in designing ultralow band-gap ambipolar small molecules with good solution-processibility and ambient-stability for various optoelectronic technologies including CMOS-like integrated circuits. In the second part of this thesis, a new solution-processable and air-stable liquidcrystalline n-channel organic semiconductor (?,?-2OD-TIFDMT) was designed, synthesized, and characterized. The new semiconductor exhibits a low LUMO energy level (-4.19 eV) and a narrow optical band gap (1.35 eV). Typical pseudo focal-conic fan-shaped texture of a hexagonal columnar liquid crystalline (LC) phase was observed over a wide temperature range from melting point at 139 °C to isotropic transition point at 232 °C. The semiconductor thin-films prepared by spin-coating ?,?-2OD-TIFDMT shows the formation of large (~0.5-1 µm sizes) and highly crystalline plate-like grains with good interconnectivity. The molecules were found to adopt edge-on orientation on the dielectric surface resulting in favorable charge-transporting networks of ?-? stacking along the dielectric-semiconductor interface. Top-contact/bottom-gate organic fieldeffect transistors fabricated by using the spin-coated semiconductor films, which were annealed at a low temperature (Tannealing = 50 °C), have yielded good electron mobilities as high as 0.11 cm2 /V·s and high Ion/Ioff ratios of 107 -108 with excellent ambient stability. This indicates two orders of magnitude (100×) enhancement in OFET mobility when compared with a low-temperature annealed well-known semiconductor, ß-DDTIFDMT. Side-chain engineering in the new semiconductor structure offers great advantage for the D-A-D ?-core co-planarity while maintaining a good solubility in organic solvents, and leads to favorable optoelectronic and physicochemical characteristics for better OFET performance. Thermal annealing at LC phase results in significant deterioration in charge-transport with much lower (10,000×) electron mobility. These remarkable findings demonstrate that this new small molecule is a promising semiconductor material for the development of n-channel OFETs on flexible plastic substrates and LC-state annealing in columnar liquid crystals can be deteriorating for transistor-type charge transport.
Development of novel nanomaterials for display and catalysis applications
(Abdullah Gül Üniversitesi, 2016) TAHAOĞLU, DUYGU; AGÜ, Mühendislik Fakültesi, Malzeme Bilimi ve Nanoteknoloji Mühendisliği Bölümü; TAHAOĞLU, DUYGU
Nanomaterials established a research presence due to their large variety and unique properties for many areas such as biotechnology, energy, fabrics, construction, food etc. Transparent conductors and catalysis applications are also two other important areas in which nanomaterial studies are carried out. For display applications, metal nanowires, especially silver and copper, draw too much attention as transparent conductors as an alternative to indium tin oxide (ITO), which is the most used material in this market, due to their high conductivity, low cost and availability for flexible device applications which are limitations for ITO. In catalysis applications, using nanomaterials are also important to provide two essential parameters: increasing the efficiency of reactions and lowering the cost. In this thesis, on the whole, we present the synthesis of silver and copper nanowires by optimizing some parameters for controlling the length and diameter of nanowires. For the surface passivation of nanowires, we offered some coating methods with noble metals such as gold, platinum and palladium. Also we investigated the catalytic activity of copper nanowires on dye wastewater treatment. In the first part of this study, effects of polyvinylpyrrolidone (PVP) polymer length and PVP:AgNO3 molar ratio on the efficiency of silver nanowire synthesis and nanowire size were investigated for polyol synthesis method. The results showed that reaction yield is highly depended on these parameters. Also, by using different coating methods such as direct addition or biphasic titration, and by using different noble metal precursors, galvanic exchange reactions on silver nanowire surfaces were studied. The results for coating showed that it is possible to replace silver and noble metal atoms through these methods. The next part of the thesis reports the copper nanowire synthesis ii by two different methods: hydrothermal and solution based synthesis. The copper nanowires showed different size properties for these two methods. In addition, the same coating processes were also performed for copper nanowires and the results are promising as silver nanowires. In the last part, catalytic performance of copper nanowires was studied on degradation reactions of three different organic dyes. Great differences between catalyzed and uncatalyzed reaction periods were observed for all dyes.
EVALUATION OF MATERIAL OPTIONS FOR ELECTRICAL POWER SUPPLYING AND PROTECTIVE WEARABLE EQUIPMENT
(Abdullah Gül Üniversitesi, Fen Bilimleri Enstitüsü, 2020) KAAN, Murat; AGÜ, Fen Bilimleri Enstitüsü, İleri Malzemeler ve Nanoteknoloji Ana Bilim Dalı
Ballistic vests used in military applications are usually made out of layers of various materials and then combined to form a solitary conservative vest. Contrasted with bygone eras, functionality and productivity of ballistic vests have improved to a critical sum. ANSYS was explicitly used to compute such finite element analysis and the initial segment of the postulation dealt with the determination of material used for the first/front layer of the vest. Since nowadays all ballistic vests almost use Kevlar and epoxy layers in the material formation of the vest, the similar material candidates were chosen for this research as well. Practically, the only choice of material that had to be decided is for the front layer of the vest since many different materials can be used in that regard. Silicon Carbide (SiC) was picked on the grounds that it demonstrated the least deformation and least stress compared to other materials that were tested in ANSYS. In total; three materials were tested and evaluated respectively were Silicon Carbide, Boron Carbide (BC) and Alumina (Al2O3). In order to prove the protection of the ballistic vest design and its reliability in the ballistic sense, 6 (six) flawless shots were fired at certain points on the vest, based on American NIJ standards. In short, the thesis examines the protection of ballistic protective vests from serious military injuries during combat and the development of a hybrid solution that will provide the vest with a new function to provide the power needs of the equipment the soldier will need during combat. In addition, a novel idea is proposed to the literature by adding the fourth layer into the FEA based examined ballistic vest.
Experimental investigation and optimization of cutting parameters to minimize the burr formation in milling of S2-glass fiber-reinforced plastics
(Abdullah Gül Üniversitesi, Fen Bilimleri Enstitüsü, 2024) Sayın, Ahmed Çağrı; AGÜ, Fen Bilimleri Enstitüsü, İleri Malzemeler ve Nanoteknoloji Ana Bilim Dalı
Composite materials have a wide range of application areas due to their high mechanical properties, low density and versatility. Milling is an important process for the composite materials to shape them according to the needs of the application area. Burrs are often created during the milling process and result in rejection of parts in the desired usage area. This study focuses on the experimental and statistical analysis of the burrs during the milling process of S2-Glass Fiber Reinforced Plastics (S2-GFRP) and Basalt Fiber Reinforced Plastics (BFRP) composites. Damages occurring during the milling process were analyzed to evaluate the mechanical performance and surface quality of composite materials. Surface quality is determined by the area and length of the burrs that were produced during the milling operations. Optimum processing parameters have been determined to ensure minimum burr area and burr length. It is determined that there are multiple optimum parameters according to the processed material and cutting direction. Burr area and burr length are measured with image analysis. The total area of burrs is calculated, and the longest burr in each sample is measured. The effect of tool material, tool coating, spindle speed and feed rate on burr area and burr length is observed. Based on the experimental results, it was determined that the tool material is the only parameter that consistently affects burr area and bur length. The data obtained aims to ensure the more reliable and efficient use of these materials in engineering applications and makes significant contributions to sustainable production processes.
FABRICATION OF NANOCOMPOSITE MEMBRANES AND THEIR APPLICATIONS IN OILY WASTEWATER TREATMENT
(Abdullah Gül Üniversitesi, Fen Bilimleri Enstitüsü, 2017) SAKİ, Seda; AGÜ, Mühendislik Fakültesi, Malzeme Bilimi ve Nanoteknoloji Mühendisliği Bölümü
Industrial oily wastewaters are generated by various industries such as steel, food, textile, leather, petrochemical and metal milling and should be treated before discharging natural environment due to its serious environmental problems. With this view, membrane separation processes have promote a significant development of novel and green technology for oily wastewater treatment due to its clear advantages, for instance, ease in operation, efficient separation, low energy consumption and cost. Specially microfiltration (MF) and ultrafiltration (UF) membranes are playing a more prominent role in the oily wastewater treatments because of many advantages like as stable effluent quality, small area requirement, no chemicals addition, high chemical oxygen demand (COD) removal and low energy need. But the main drawback of membrane processes is the fouling problem. To overcome this problem, many researchers effort fabrication of high performance of membrane with higher hydrophilicity and antifouling properties. In this study, flat-sheet PSF/PEI nanocomposite membranes using Al2O3 and CaCO3 nanoparticles were prepared by phase inversion method. The effect of Al2O3 and CaCO3 nanoparticles were investigated on the structural properties and filtration performance of the nanocomposite membranes. Prepared membranes were characterized with scanning electron microscopy (SEM), fourier transform infrared spectroscopy (FT-IR), contact angle, porosity, water flux, thermogravimetric analysis (TGA), atomic force microscope ii (AFM), X-ray diffraction (XRD), BSA rejection, tensile strength, and viscosity measurements. Membrane permeability performance and antifouling properties towards oil water emulsion separation of these new generation nanocomposite membranes were evaluated for synthetic and real industrial oily wastewater. The results showed that there is a great potential to use these nanocomposite membranes for oily water treatment with higher permeability and antifouling capacity. All Al2O3 and CaCO3 nanocomposite membranes reached higher oil rejection ratios over 90%.
Fabrication of new generation membranes and their applications in fruit juice industry
(Abdullah Gül Üniversitesi, 2018) SEVERCAN, SOLMAZ ŞEBNEM; AGÜ, Mühendislik Fakültesi, Malzeme Bilimi ve Nanoteknoloji Mühendisliği Bölümü; SEVERCAN, SOLMAZ ŞEBNEM
When membrane processes are compared to conventional processes, they have significant advantages for instance, providing decrease in operation time and cost with saving nutritious components and sensory parameters in food production plants. Especially, in fruit juice industry, UF membranes are utilized for clarification by eliminating big molecules like suspend proteins, fat and polysaccharides, which leads turbidity. Although, UF membranes have many advantages like its affordable cost, higher film forming ability, excellent mechanical properties, and superior chemical and thermal resistance, it has a major drawback leading the fouling of the membrane. To get rid of this problem, many researchers focused on the modification of membrane surface to both increase hydrophilicity and enhance antifouling characteristics. In this study, PSF/PEI (20wt%, 2wt%) UF membranes and PSF/PEI (17wt%, 2wt%) MF membranes were prepared with the addition of different concentrations of TiO2 and Al2O3 nanoparticles (0.01, 0.03, 0.05 wt %) using phase inversion method to alter the structural and morphological properties of membranes. Turbid apple and pomegranate juice samples supplied from Döhler Inc. (Karaman, Turkey) were clarified by using cross flow membrane filtration system and dead-end filtration system at 5.4 bar transmembrane pressure, respectively. Prepared nanocomposite membranes were characterized by using scanning electron microscopy (SEM), fourier transform infrared spectroscopy (FT-IR), water-contact angle porosity and pure water flux. To investigate fouling resistance of nanocomposite membranes flux recovery ratio (FRR), flux decay ratio (DR), relative flux reduction (RFR) values were also calculated. In addition, ii clarified apple and pomegranate juice samples were characterized in terms of color, turbidity, total soluble solid, total antioxidant capacity (ABTS radical scavenging method and DPPH radical scavenging method) and total phenolic content. Total monomeric anthocyanin pigment content of pomegranate juice was also determined. The clarified juices obtained using new generation nanocomposite membranes were compared with the clarified product juice samples supplied from Döhler Inc. Membrane characterization and fruit juice characterization results demonstrated that fabricated new generation nanocomposite membranes were effective in apple and pomegranate juice clarification. Among these fabricated new generation nanocomposite membranes, the ones prepared with the addition of 0.01% of TiO2 UF membrane and prepared with the addition of 0.05% Al2O3 MF membrane exhibits superior performance in terms of clarification of apple juice and pomegranate juice, respectively.
IMPROVING THE FLAME RETARDANCY USING NANOPARTICLES IN CABLE INSULATION
(Abdullah Gül Üniversitesi, Fen Bilimleri Enstitüsü, 2021) YILDIZ, Uğur; AGÜ, Fen Bilimleri Enstitüsü, İleri Malzemeler ve Nanoteknoloji Ana Bilim Dalı
Al(OH)3 (ATH) and Mg(OH)2 (MDH) like materials are frequently used as flame retardants due to their ability to form water and oxide-based substances under the influence of heat. In this study, it is aimed to produce cable insulations with improved flame retardant properties by synthesizing nano-sized Mg(OH)2 and using this material together with EVA (ethylene-vinyl-acetate) copolymer and micro-sized Al(OH)3 and Mg(OH)2 . The study can be divided into four parts. In the first part, the flame retardant properties of ATH and MDH were compared. In the second part, different raw materials were used for the synthesis of Mg(OH)2 nanoparticles; in the third part, the synthesis was carried out at factory scale and compared with the commercial product. The samples were characterized by scanning electron microscopy (SEM), Fourier transform infrared spectrometer (FT-IR), X-Ray diffraction analysis (XRD), X-Ray fluorescence analysis (XRF) and Thermogravimetric analysis (TGA). In the last part, different amounts of nano-sized Mg(OH)2 particles were added to the formulas using both ATH and MDH; the effects on flame retardant performances were investigated by the Limiting Oxygen Index (LOI) test and the vertical burning test. Mechanical properties such as elongation and tensile strength were also studied. It has been observed that the synthesized Mg(OH)2 particles with a thickness of 5- 10 nm and lengths reaching 900 nm, mixed in ATH based samples at a maximum rate of 9% and in MDH based samples at a maximum rate of 10%; LOI values increased by 26% for ATH based samples and 38% for MDH based samples. However, considering the losses in mechanical properties with the increase of nanoparticle additive, it has been seen that a maximum rate of 5% nano-sized Mg(OH)2 can be added. Even in this case, the LOI values increased by 8.6% in ATH based samples and 26% in MDH based samples.
INVESTIGATION OF HYDROGEN EMBRITTLEMENT BY A MULTI-SCALE MODELLING APPROACH
(Abdullah Gül Üniversitesi, Fen Bilimleri Enstitüsü, 2021) KAPÇI, Mehmet Fazıl; AGÜ, Fen Bilimleri Enstitüsü, İleri Malzemeler ve Nanoteknoloji Ana Bilim Dalı
Hydrogen exposure of metallic materials during their service times or during the application of processes e.g. machining, welding, electroplating leads to degradation of the mechanical properties which is a phenomenon known as hydrogen embrittlement. Diffused hydrogen into metal can accumulate in crystal defects and alter the mechanical behavior under loading. In this thesis, diffusion of the hydrogen as well as the atomistic mechanisms of dislocation mobility depending on the presence of hydrogen were investigated for two edge dislocation systems that are active in the plasticity of α-Fe, specifically ½<111>{110} and ½<111>{112}. In particular, the glide of the dislocation pile-ups through a single crystal, as well as transmission of the pile-ups across the grain boundary were evaluated in bcc iron crystals that contain hydrogen concentrations in different amounts. Additionally, the uniaxial tensile response under a constant strain rate was analyzed for the aforementioned structures. Lastly, diffusion and backdiffusion of the hydrogen into bcc, fcc, and hcp crystal structures were investigated with numerical models. The results reveal that the presence of hydrogen decreases the velocity of the dislocations – in contrast to the commonly invoked HELP (Hydrogenenhanced localized plasticity) mechanism -, although some localization was observed near the grain boundary where dislocations were pinned by elastic stress fields. In the presence of pre-exisiting dislocations, hydrogen-induced hardening was observed as a consequence of the restriction of the dislocation mobility under uniaxial tension. Furthermore, it was observed that hydrogen accumulation in the grain boundary suppresses the formation of new grains that leads to a hardening response in the stressstrain behaviour which can initiate brittle fracture points
Investigation of interaction between nanocrystal quantum dot films and escherichia coli
(Abdullah Gül Üniversitesi, Fen Bilimleri Enstitüsü, 2017) Ünlü, Miray; 0000-0001-8165-6164; AGÜ, Fen Bilimleri Enstitüsü, İleri Malzemeler ve Nanoteknoloji Ana Bilim Dalı
Semiconductor nanocrytals also known as quantum dots (QD) with high photoluminesce quantum yield (PLQY), size tunability and favorable optical characteristics occupy a significant area in display technology, solar energy conversion and biotechnology. Size tuning feature of QDs allows peak emission wavelength ranging from ultraviolet to infrared spectral region. In literature, QD based studies have been performed in visible spectral range by employing mostly cadmium, being a toxic heavy metal. Recently, the search for less toxic alternatives revealed the cadmium free compounds, particularly InP. Cadmium free semiconductor nanocrytals' potential to be used as fluorescent probes in biodetection and biolabeling area has been proved over the past decades. Pathogens threaten life particularly via water sources like rivers, reservoirs and groundwater. Increasing demand for managing the 'contamination of drinkable water by pathogenic bacteria' problem needs a broad perspective about pathogens and their membrane characteristics which are integral part of microorganism detection platforms. Bacteria are categorized mainly upon their membrane properties which are gram negative and gram positive. Extra wall called as peptidoglycan layer in gram positive bacteria makes them more resistant to external forces. Gram negative bacteria with wavy wall is relatively more prone to their environment. One of the most known pathogenic bacteria, E. Coli, have damaged and destroyed many lives throughout the world. High growth rate enables this microorganism to spread around large areas in short time. Therefore, accurate and definite detection of this bacteria in water is crucial. The main frame of this research depends on QD based biodetection of bacteria. First of all, organic based QDs (50% PLQY) containing triocytlyphosphine-sulfur ligand were synthesized and via successful phase transfer, QDs in aqueous solvent with 20% PLQY were achieved. Although surface is damaged during ligand exchange procedure, QDs in aqueous solvent with high PLQY were obtained. SiO2 was covered with QDs thanks to the attraction between their NH2 group and carboxylic ends, respectively. In the final step, this hybrid structure was encapsulated with SiO2 and silica coated QDs (SCQD) were formed. In order to utilize SCQDs in bacteria detection, fluorescent agents were embeded in polymeric films which were formed by spin coating. As a result, SCQD facilitates the attachment of negatively charged bacteria onto the surface of the films. Appropriately grown DH5 alpha (E. Coli strain) expressing green fluorescent protein (GFP) was used as pathogen in the detection part. SCQD thin films were treated with water containing E.Coli DH5 alpha. Positively charged SCQD attracted negatively charged bacteria and the conjugation between them was analysed with time resolved spectroscopy and monitored with fluorescence microscope. Thus, usage of QDs as biosensor in pathogen detection could provide an insight in the future studies. Keywords: biodetection, E.coli, quantum dots, semiconductors, silica coated quantum dots, indium phosphate, InP QD
Nanoparticle reinforced hybrid composite material production process optimization / Nano-parçacık takviyeli hibrit kompozit üretimi için reçine geçişli kalıplama prosesi optimizasyonu
(Abdullah Gül Üniversitesi, 2017) DOĞUŞ KAÇMAZ, AZER; AGÜ, Fen Bilimleri Enstitüsü, İleri Malzemeler ve Nanoteknoloji Ana Bilim Dalı; DOĞUŞ KAÇMAZ, AZER
Composite materials have increasing application areas in today's industry and daily life due to their low density structure and high mechanical properties. Also, thermalstability and electrical conductivity can be improved by particle inclusion. Composite materials consist of preform, matrix and particles in matrix. Various production methods have been developed to bring these components together. Among these production methods, liquid composite molding methods are the most widely used methods for producing parts having advanced properties. A different method logic has been tried to obtain more homogeneous product than traditional resin Transfer Molding method in order to produce composite parts with superior mechanical properties. Since the Resin Transfer Molding (RTM) method is expensive and time-consuming, simulation is the fastest and economical method for optimization of the process. In this study, COMSOL software was used for numeric analysis. As a result, when production of hybrid composite materials with highly different permeable components performed with Resin Transfer Molding Method, Compression Resin Transfer Molding (CRTM) logic works much more precisely in terms of avoiding voids and providing homogeneity through preform when filling is performed from the top.
Proton conductive polymer/metal organic framework composi·te membranes / Proton iletken polimer/metal organik kafes yapılar içeren
(Abdullah Gül Üniversitesi, 2015) MUSTAFA ERKARTAL; AGÜ, Fen Bilimleri Enstitüsü, Malzeme Bilimi ve Makine Mühendisliği Ana Bilim Dalı; MUSTAFA ERKARTAL
Proton exchange membrane fuel cells (PEMFCs) are one of the most innovative research areas in search of novel power sources, especially because of their no to low greenhouse gas emissions, high efficiency, diverse fuel options and low maintenance costs. Hence, PEMFCs are regarded as one of the potential alternatives for the conventional power generators. Proton exchange membrane (PEM) is the core component of the PEMFC. Still, Nafion® and PBI are the commonly used membrane materials in fuel cell technology. The development of novel PEMs with high proton conductivity, good mechanical and chemical stability and cost-effective manufacturing remain as obstacles for the commercialization of PEMFCs. In this thesis for the first time, we present preparation and characterization of two types of novel composite proton exchange membranes which consist of zeolitic imidazolat framework-8 (ZIF-8). In the first part of this study, consisting of poly(vinyl alcohol) (PVA), poly(2- acrylamido-2-methyl-1-propanesulfonic acid) (PAMPS) and zeolitic imidazolat framework-8 (ZIF-8) ternary Nafion-like composite membranes were prepared with different composition to use in the PEMFCs which of their operation temperatures below 100 0C. All of the membranes were structurally characterized and their proton conductivities were measured by electrochemical impedance spectroscopy. The fully hydrated membrane with 55 PVA/40 PAMPS/5 ZIF-8 composition shows the highest proton conductivity with about 0.13 S cm-1 at 80 0C and the result thus obtained is comparable to the proton conductivity value of the Nafion in the literature. The aim of second part of this study is the preparing of membranes for high temperature proton exchange fuel cells (HTPEMFCs), which operate between 100-200 0C, the binary mixed membrane were manufactured incorporation of PBI and ZIF-8. In the membrane PBI ii was used as host polymer whereas ZIF-8 is used as filler material. Among the structurally well-characterized membranes, the membrane with 12.5 ZIF-8/PBI membrane has the highest proton conductivity with about 0.0045 S cm-1 at 160 0C under anhydrous condition.
QUANTUM DOT BASED BIOSENSING
(Abdullah Gül Üniversitesi, Fen Bilimleri Enstitüsü, 2017) ÜNLÜ, Miray; AGÜ, Fen Bilimleri Enstitüsü, İleri Malzemeler ve Nanoteknoloji Ana Bilim Dalı
Semiconductor nanocrytals also known as quantum dots (QD) with high photoluminesce quantum yield (PLQY), size tunability and favorable optical characteristics occupy a significant area in display technology, solar energy conversion and bioapplications. Size tuning feature of QDs allows emission wavelength ranging from ultraviolet to infrared spectral region. In literature, QD based studies have been performed in visible spectral range by employing mostly cadmium, being a toxic heavy metal. Recently, the search for less toxic alternatives revealed the cadmium free compounds, particularly InP. Cadmium free semiconductor nanocrytals’ potential to be used as fluorescent probes in biodetection and biolabeling area has been proved over the past decades. Pathogens threaten life particularly via water sources like rivers, reservoirs and groundwater. Increasing demand for managing the ‘contamination of drinkable water by pathogenic bacteria’ problem needs a broad perspective about pathogens and their membrane characteristics which are integral part of microorganism detection platforms. Bacteria are categorized mainly upon their membrane properties which are gram negative and gram positive. Extra wall called as peptidoglycan layer in gram positive bacteria makes them more resistant to external forces. Gram negative bacteria with wavy wall is relatively more prone to their environment. One of the most known pathogenic bacteria, E. Coli, have damaged and destroyed many lives throughout the world. High growth rate enables this microorganism to spread around large areas in short time. Therefore, accurate and definite detection of this bacteria in water is crucial. The main frame of this research depends on QD based biodetection of bacteria. First of all, organic based QDs (50% PLQY) containing triocytlyphosphine-sulfur ligand were synthesized and via successful phase transfer, aqueous QDs with 20% PLQY were achieved. Although surface is damaged during ligand exchange procedure, aqueous QDs with high PLQY were obtained. SiO2 was covered with QDs thanks to the attraction between their NH2 group and carboxylic ends, respectively. In the final step, this hybrid structure was covered with SiO2 and silica coated QDs (SCQD) were formed. In order to utilize SCQDs in bacteria detection, fluorescent agents were embeded in polymeric films which were formed by spin coating. As a result, SCQD facilitates the attachment of negatively charged bacteria onto the surface of the films. Appropriately grown DH5 alpha (E. Coli strain) expressing green fluorescent protein (GFP) was used as pathogen in the detection part. SCQD thin films were treated with water containing E.Coli DH5 alpha. Positively charged SCQD attracted negatively charged bacteria and the conjugation between them was analysed with time resolved spectroscopy and monitored with fluorescence microscope. Thus, usage of QDs as biosensor in pathogen detection could provide an insight in the future studies.
Solution-processable rodshaped molecular semiconductors and fieldeffect transistor applications
(Abdullah Gül Üniversitesi, 2018) DENEME, İBRAHİM; AGÜ, Fen Bilimleri Enstitüsü, Malzeme Bilimi ve Makine Mühendisliği Ana Bilim Dalı; DENEME, İBRAHİM
The structural design and synthetic development of novel n-channel organic semiconductors have attracted considerable scientific and technological attention in order to understand the fundamentals of charge-transport mechanisms in organic (opto)electronics. Although large number of n-channel semiconductors have been reported in the literature over the past few decades, solution-processable and air-stable n-channel semiconductors are still scarce. Herein, we report the design, synthesis, single crystal structures, optoelectronic properties, solution-processed thin-film morphologies/microstructures, and organic field effect characteristics of two molecular indeno[1,2-b]fluorenes containing (triisopropylsilyl)ethynyl groups in the 2,8-positions functionalized with carbonyl and dicyanovinylene moieties in the 6,12-positions. Inclusion of electron-withdrawing carbonyl, dicyanovinylene, and (triisopropylsilyl)ethynyl groups to indeno[1,2-b]fluorene cores create fully acceptor type ?-conjugated structures, 2,8-(triisopropylsilyl)ethynyl-indeno[1,2-b]fluorine-6,12- diones (TIPS-IFDK) and 2,8-(triisopropylsilyl)ethynyl-indeno [1,2-b]fluorine-6,12- bis(dicyanoviynlene) (TIPS-IFDM). HOMO/LUMO energies of the new compounds are -5.77/-3.65 eV and -5.84/-4.18 eV for TIPS-IFDK and TIPS-IFDM, respectively. Slightly increased optical band gaps of 2.12 eV (for TIPS-IFDK) and 1.66 eV (for TIPS-IFDM) compared to previously developed donor-acceptor type indenofluorenes could be attributable to their acceptor type ?-conjugated structures. Solid-state ii arrangements and intermolecular ?-? interactions of TIPS-IFDK and TIPS-IFDM were examined via single single-crystal X-ray diffraction (XRD) analysis. The new semiconductors exhibited 1-D columns in the solid-state. OFETs in top-contact/bottomgate transistor geometry utilizing TIPS-IFDM semiconductor layer fabricated via solution-shearing possessed n-channel charge transporting characteristics with an airstable electron mobility 0.02 cm2 (V s)-1 and Ion/Ioff ratios of 107 . However, TIPS-IFDK exhibited three orders of magnitude lower electron mobility in OFETs because of less effective ?-? interactions and the poor crystallinity in thin-film phase, and TIPS-IFDK based OFETs did not exhibit ambient stability. Electronic effects of (trialkylsilyl)ethynyl grops substitutions on frontier molecular orbitals were reavealed by DFT calculations. To the best of our knowledge, TIPS-IFDM is the first example of a solution-processable, air-stable n-type molecular semiconductor functionalized with (trialkylsilyl)ethynyl groups along the long molecular axis. Our results clearly provide a novel molecular design approach for the development of easily synthesizable, solution-processable semiconductors for ambientstable n-channel organic field-effect transistors and potentially various organic (opto)electronic technologies.

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