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Preparation of indium tin oxide thin films and investigation of hydrogen post-treatment effect
The development of optoelectronic devices including solar cells, liquid crystal displays, touchscreen panels and electrochromics has required a broad application of transparent conductive oxides (TCOs) as an essential component. TCOs come into prominence due to their outstanding properties such as 80% and more transmittance in the visible region of the solar spectrum and sheet resistance lower than 300 Ω/sq. Among TCOs, tin doped indium oxide (ITO) films are the most extensively preferred thin films owing to their high transmittance (~90 %) at 550 nm and low sheet resistance between 20-100 Ω/sq. Using vacuum based techniques such as magnetron sputtering can be very efficient to obtain low sheet resistance, however, this causes a dramatic increase in the production cost. Since ITO is the most extensively used transparent conductive electrode and it will have a huge market share in the near future; it is very obvious that the optical and electrical properties of the ITO films should be enhanced by means of simple and cost-effective preparation techniques. The aim of this thesis was the preparation of ITO thin films by scalable and low cost solution based methods with improved optical and electrical properties. For this purpose, thin films prepared by spin coating technique were subjected to post-treatment process to decrease sheet resistance and increase surface smoothness without causing any change in optical transmittance and crystalline structure. Effect of different parameters such as In:Sn ratio, concentration, temperature, number of deposition and post-treatment with hydrogen to sheet resistance, transparency, surface characteristics and crystalline structure were investigated. The properties of thin films were characterized by four probe measurement set-up, UV-visible spectroscopy (UV-Vis), scanning electron microscopy (SEM) and X-ray diffractometer (XRD). It has been found that 7 times deposition of 0.5 M solution including In:Sn with the ratio of 90:10 was the optimum process condition when the films were annealed at 500-600°C in air. For all samples, transmittance were measured in between 80 and 92 % at 550 nm and minimum sheet resistance was measured as 350 Ω/sq after post-treatment. Post-treatment provided a growth in crystalline size, distinct grain boundaries, and homogeneous particle distribution without influencing cubic crystalline structure due to XRD and SEM results. Subjecting the ITO films to 10 % H2 containing Ar medium at 300 °C for 3 hours was found as the most efficient process condition for post-treatment and as a result of that, approximately 70% efficiency was achieved on the reduction of sheet resistance without affecting the transmittance of the thin films.
Design, analysis, simulation and optimization of a MEMS Lorentz force magnetic field sensor for biosensing of biowarfare agents
The alarming terrorist attacks via the exploitation of bacteria and viruses in the history of mankind have set concerns globally and led the governments to identify and recognize biological warfare agents such as bacteria and viruses for taking preventative action. Hence, fast detection and precise identification of these agents have been attributed as key strategies for biodefense globally. In the interest of biological warfare agent sensing, sensitive and optimized tools/sensors are needed that are capable of quantifying the response of physical attachments of the biological agents into measurable values for their detection. For this purpose, MEMS based cantilever biosensors that are capable of prompt, real time, cost effective and label free methods of biomolecular recognition have emanated as promising early warning systems for biological defense and have been opted for studies of mass sensing and detection of biological particles. In this sense, the interdisciplinary nature of MEMS could be exploited through merging and synergizing diverse range of fields such as the Lorentz force actuated MEMS magnetic field sensors with the concept of BioMEMS microcantilever sensors by exploring the best of both worlds for achieving the ultimate objective of bioparticle sensing. In the literature, few studies were undertaken that considered the Lorentz force actuation mechanism with the microcantilever based biosensors for detecting the absorption of biological particles on the functionalized region of the sensor. The concentrations of these studies were found to be more oriented towards the simulation or the experimental demonstration of the subject with mere explorations on the optimization of the process parameters. Hence, in order to fulfill the relevant gap, an investigation has been carried out that aims at the design, simulation and optimization of a MEMS magnetic field sensor consisting of a microcantilever with a bioplate as a transducer that is actuated by exploiting the principle of Lorentz force in the static mode. In this study, the system was viewed as a whole and the design and process parameters that were potentially influential on the Lorentz force actuation mechanism of the proposed MEMS magnetic field sensor were identified and classified into categories of variables related to permanent magnet and the microcantilever biosensor. The parameters in the class of permanent magnet were identified as the type, grade, shape and dimensions of magnet and the positioning of the magnet with respect to the microcantilever biosensor in x, y, and z axes. The input parameters with regard to the microcantilever were distinguished as the sizes, materials and shapes of the microcantilever, the conductive path and the biosensor and the amount of current that could be injected into the ports of the sensor. A vacuum region encapsulating the magnetic field sensor and the permanent magnet was defined for the relative packaging of the device. A design of experiments process was modeled for simulating the Lorentz forces in Ansoft Maxwell® FEA software and an optimization procedure was developed that followed a pattern of fixating some parameters and changing only one parameter at a time to determine the relative effect of the considered parameter on the Lorentz force. The case of the varied parameter that yielded the maximum Lorentz force was opted as the ideal case and the subsequent parameter was investigated in the same manner, repeating until a full set of optimized parameters was obtained. The parameters to be optimized were selected as the shape and the ideal dimensional ratios for the magnet, the x, y and z position of the magnet with respect to the microcantilever and the variation of dc current supply. The dimensions, shapes and materials of the microcantilever, the bio-plate and the conductive path remained untouched throughout the optimization process. In addition to this, the optimization of the dimensions of the vacuum box was not conducted due to the automatic adjustment of the vacuum region with a percent ratio relative to the microcantilever and the permanent magnet. Following the series of optimizations, the resulting Lorentz force was concluded to be 2.65 times higher than that of the initial value. A joule heating analysis was conducted in COMSOL Multiphysics® to explore the volumetric distribution of the heat throughout the magnetic field sensors due to the injection of current in the interval of 0-50 mA. The relationship between the current and the average surface temperature on the sensor due to joule heating was plotted from the simulation results so as to find the potential need to define a safe current margin such that the sensor does not begin misfunctioning due to increased temperature. An exponentially increasing relationship was discovered for every incremental rise in the current and hence the 0-15 mA interval was defined to be the safe current range for the respective sensor. The analogy between the Lorentz force and the mechanical deflection of the magnetic field sensor has also been simulated in structural mechanics module of COMSOL Multiphysics® and a linearly increasing trend has been identified from the relationship. After a thorough examination and construction of relationships of the input parameters with respect to the Lorentz force, including the joule heating and the deflectional analysis, the optimized parameter values obtained from the results were employed for modeling five new designs of the microcantilever based biosensor for deriving further evaluations on the developed Lorentz force. A new optimization procedure was prepared in this respect and the effects of increasing the lengths and the widths of the middle arms of conductive paths on the Lorentz force were examined. The acts of lengthening and widening were found to be hardly affecting the Lorentz force but subsequent undertaking of a joule heating analysis for the increased width of the conductive paths presented improved average surface temperature results for the sensor. The thickness of the conductive paths for the current were also varied between 1 µm, 3 µm and 5 µm that yielded no changes on the Lorentz force in Ansoft Maxwell® while worsening the heat distributions on the microcantilever in COMSOL Multiphysics® Houle heating Analysis, thus downsizing the range of safe current. Also, the implication of increasing the surface area of the microcantilever structure with respect to the joule heating was examined and an indirect proportionality was concluded where the expansion in the surface area led to better dissemination of the heat across the volume of the sensor, maximizing the safe current intervals that would result in higher Lorentz force. A fabrication procedure for the MEMS magnetic field sensor was also described comprehensively for its practical realization. A contact has been established with a local permanent magnet manufacturer to see if the optimized dimensional sizes for the NdFe35 type block magnet was commercially available in case that the study is practically implemented. As a proof of concept, the biological warfare agents such as E. coli, variola virus, Influenza A, B and C viruses were modeled and their respective estimative weights were numerically calculated based on the data found on the literature. The translation of the weights induced by these bioparticles on the functionalized gold site of the microcantilever were simulated and the relevant characteristics of the deflections for differing numbers of the respective particles were established for the sensor. Afterwards, the methodology for mass sensing of the bioparticles by the Lorentz force based magnetic field sensor was presented and elaborated by exemplifying with an optical interferometry. The plot of the results of the simulations for the current supply corresponding to the detection of respective numbers of E. coli bacteria illustrated that the current was in the microampere range. Therefore, a requirement for an instrumentation that feeds dc current at microampere range was pointed in order to realize the detection of the respective biological agents by the sensor. Additionally, the bulkiness and the cost of the optical transduction method encouraged discussions relating to the piezoresistive method of detection through a potential modification of the developed sensor such that a compact, ready to use Lorentz force actuated microcantilever biosensor could be employed for practical field implementations in detecting biological warfare agents.
Development of graphene/bismuth nanocomposite film modified graphite electrode for voltammetric determination of heavy metals
In recent years, due to its unique chemical, physical and mechanical features, nanomaterials which are of great interest in many fields such as chemistry, physics, material science are also frequently used for the development of electrochemical nanosensors. By choosing electrodes that are modified with nanomaterials to increase their selectivity and sensitivity, successful results have been achieved in the analysis of analytes at very low concentrations. Graphene, which is a carbon-based nanomaterial and has led to the development of revolution in technology with its discovery, is at the head of the materials used for this purpose. The main difficulty with using the graphene in electrode modification is the synthesis step. According to the method used, conventional methods have drawbacks such as high cost, long synthesis time, the usage of toxic chemicals and small-scale production, so there is a need for a rapid, environmentally friendly, low-cost synthesis method for producing graphene. In the context of this thesis, development of a low-cost, green, sensitive and selective graphene-modified electrode is aimed in order to provide precise simultaneous analysis of heavy metals in water samples. As the first step of electrode development, the surface of the pencil graphite electrode was covered with graphene in one step using an electrochemical method presented in the literature. Cyclic voltammetry (CV) method has been chosen for the modification. In this method, with the application of high anodic potentials to graphite electrode, oxygen-rich graphene oxide was formed, then by applying the potential in the opposite direction oxygen groups were eliminated and graphene structures were obtained. Various modification parameters such as modification electrolyte type and concentration, number of CV cycles, CV scan rate and CV potential range are optimized in order to get the highest response for lead and cadmium. As the second step after electrode development, an electroanalytical method, square wave stripping voltammetry method, was proposed to analyze trace levels of Cd and Pb heavy metals. In this context, the electrode surface was coated with bismuth film in order to increase electrode stability and to obtain higher signals in Cd and Pb analysis. Afterward, parameters including bismuth concentration, deposition potential, deposition time, stirring speed were also optimized. In the end, a certified reference material analysis was conducted for the evaluation of the accuracy of the electrode and method. Successful results were obtained for the Cd and Pb analysis in a working range of 5-100 μg L-1 with the developed electrode. Having a low-cost, environmentally-friendly, rapid, one-step synthesis process, the developed electrode can be used for sensitive and selective trace analysis of various heavy metals in environmental and biological samples.
Elektro-üretim yöntemi ile poliakrilonitril nano liflerden iplik üretilmesi
Nanotechnology is an interdisciplinary technology that finds more application areas to itself over time. Nanoscale materials exhibit different optical, thermal and magnetic properties compared to their bulk forms, and they promise a great opportunity and possibility in technologies including medicine, information technologies, energy and environment. Nano structures are defined as materials with at least one dimension is below 100 nm. However, nanofibers are defined as fibers with diameters less than 1 µm as the current production techniques cannot produce fibers under 100 nm. There are many methods to produce nanofibers. Electrospinning is accepted as the most effective and versatile technology among those methods. Electrospinning process relies on applying electrostatic forces to produce nanofibers from various polymer solutions or melts. Basic set-up consists of three main units; feeding unit (spinneret), collector and high voltage power supply. Voltage is applied to the droplet, which is held at tip of the spinneret`s needle under influence of surface tension. When the electrostatic forces overcome the surface tension, jets eject from the droplet towards to the collector. Jets undergo stretching, elongation, solidification during their travel and nanofibers are collected on the collector. However, they are generally in randomly oriented nonwoven mat form, which limits the utilization areas. In this study it is aimed to modify the needle electrospinning technique in order to obtain three dimensional yarns from nanofibers and expand the usage areas. Polyacrylonitrile (PAN) is a polymer used in many studies due to its suitability for versatile investigations and being precursor of carbon fibers. In this study, PAN is used as the polymer and dimethylformamide (DMF) is used as solvent. Polymer solutions were prepared in three different concentrations. In the first part of the study, experiments and device modifications made based on needle electrospinning technique are explained. In the first studies, three spinnerets, which are connected to positive high voltage power supply, a grounded vertically rotating collector and yarn winding unit was used. It was observed that, although it was possible to obtain staple yarn continuously with that apparatus, all the nanofibers cannot be drawn as yarn due to tendency of the same loaded nanofibers to repel each other. Some of the nanofibers were accumulated on the collector`s walls, which would cause the yarn to break after a while. At this stage the feeding unit has been modified to use two spinnerets connected to positive and negative high voltage power supplies separately, taking advantage of the tendency of oppositely charged nanofibers to hold together. The modified apparatus was finalized using a vertically rotating unearthed collector and yarn winding unit. Ejected nanofibers were deposited towards the collector and formed a nanofibrous web by covering mouth of the collector. A conventional guide yarn, of which one end was attached to collector and the other end to the winding system, was used to pull fibrous web from the center. A cone shape was formed due to pulling of the fibrous web. Vertically rotating collector was used to give twist to the yarn at the apex of the cone. Experiments were done with different polymer concentrations, applied voltage values, polymer feed rates, spinning distances, spinnerets angles, collector types and the speeds of the collector and the winding systems. It was tried to obtain twisted PAN staple yarn, composed of nanofibers, continuously by optimizing all process parameters. It is important to ensure dried nanofibers to join yarn structure as wet nanofibers cause yarn structure to be defected. For this reason, optimization of process parameters has been studied to obtain enough stretching, elongation and solvent evaporation of nanofibers during their travel between the spinneret and the collector. The characterization of the yarns was done visually with scanning electron microscope (SEM). The effects of varying process parameters on nanofiber diameter, yarn smoothness and continuity of the process have been investigated. In the last part of the study, the experimental work held with other spinnable polymers was explained. It was observed that the developed apparatus can be used to obtain yarns from all spinnable polymers.
Optimization of solution blown PVDF nanofibers for air filtration applications
Air purification has become an important issue worldwide as a result of the increasing population and industrial development. Melt-blown filters, spunbond filters, and glass fiber filters are the conventional air filters. Nanofibrous filters, as another and novel alternative for air filtration, offer higher efficiency, lower resistance or pressure drop, longer filter life, and flexibility compared to traditional filters. Mainly, fiber diameter and packing density (solidity) are the dominant factors on the nanofibers for the air filtration performance. This can be explained by the fact that filter efficiency increases when the diameter of fibers decreases. In this study, PVDF based nanofibrous webs were produced for particulate air filtration application. PVDF has extremely good mechanical, thermal and physical properties to adapt to various application areas such as air filters, membranes, supercapacitors, batteries, special textile products in industrial scale application. Its hydrophobic properties make it a perfect material for protective clothes application. In literature, there are lots of publications about PVDF nanofibers and their excellent properties in different application areas. Most of these studies are used electrospinning method to produce PVDF nanofibers. Electrospinning is the well-known method to produce polymeric nanofibers with old history. Unfortunately, due to its low production rate and electric potential, electrospinning method has not been adopted by the industry completely. Centrifugal spinning and solution blown spinning methods are more suitable to produce nanofibers in the industry due to their high production rate and safer components. In non-electro nanofiber production methods, solution blowing is one of the promising technique. Pneumatic forces are used to form the fiber from a polymer solution. In this technique, compressed air forwards the polymer solution towards a collector and fibers are collected as a nonwoven structure on the collector. In this thesis study, PVDF nanofibers are produced by using a semi-industrial solution blowing machine, which has 70 cm width and infinite length. It also has a multi-nozzle system with eight needles, and a hot air system to heat the compressed air to improve the evaporation of solvents. The aim of the study is the optimization of PVDF nanofibers production and to adopt the production of nanofiber webs into the industry for air filters. Firstly to prepare the solutions, DMSO was chosen as the main solvent since it is partially a less hazardous solvent. As a result of this study, homogenous fiber production could not be performed due to the fact that the solvent could not be completely evaporated, so the second set of experiments was conducted with commonly used solvent DMF to produce PVDF nanofibers. To form the design of the experiment, Taguchi method was used and in accordance with the results, optimum conditions were determined. The effect of parameters over the fiber diameter was analyzed. Furthermore, the analysis of variance (ANOVA) was applied to observe the effects of each parameter on fiber diameter. The results were found to be statistically significant. The concentration of polymer solution was determined the most dominant parameter with making contribution approximately 66,75% over the fiber diameter increment. Under optimum conditions, nanofibrous webs were produced and subsequently the air filtration efficiency of the webs was tested. The filtration properties of the nanofibrous webs comprised of several samples that have different average fiber diameters, which involves the optimum sample, were analyzed. With the optimum sample was obtained the maximum filtration efficiency, Knudsen number, and quality factor values. The results showed that the average fiber diameter was dominant over the air filtration performance. The results also showed that the filtration efficiency of the optimum sample had approximately EPA 11 level efficiency. After the filtration results, solution blow spinning with higher fiber production efficiency can be concluded as a feasible method of producing high-performance air filters.
Design and characterization of carbon inks for perovskite solar cells
Energy demand in the world has been increasing in every day because of increasing human population and improving technology. Between the 2016 and 2040 it is estimated that energy needs of the humanity will expand 30%. Traditional energy sources couldn't meet the demand so researchers have focused on the new and renewable energy sources. Solar energy is one of the important renewable energy source can decrease the energy needs in the world. Especially in the improved countries many researches have focused on this topic to improve the efficiency and getting commercilization. According to World Energy Council datas at the end of the 2016, Germany is the leader solar installed capacity of the world. In this area, Turkey doesn't have sufficient installed solar capacity, however, installed solar capacity are growing day by day. Solar cell converts sunlight to the electricitiy with semiconductor materials and part of the solar energy sources. It can be divided into three categories and perovskite solar cell is the lastest and encouraging generation of this solar cells because of their low cost, easy to produce and high efficiency. Perovskite solar cell structure is based on with hole transport layer and without hole transport layer. For hole transport layer generally has been used spiro-Ometad which is high cost material. On the other hand, in the HTM-free perovskite solar cell, perovskite acts as a hole transport layer and conductivity is supplied from carbon electrode or gold electrode. Carbon electrode has been prefered because of its high conductivity, low cost, abundant in nature and environmentally friendly properties. Electrode can be obtained from bare carbon type or carbon ink/paste. Carbon ink generally contains carbon material, binder and solvent. Carbon material can be different type of carbon such as activated carbon, carbon black, graphtie, graphene, carbon nanotubes etc. In the ink formulation, carbon supply electrical conductivity of the ink and binder is responsible for the ink stability. According to solvent type carbon ink may be dissolved in water based or polymer based solvents. Carbon ink is preffered while the high conductivity is requested. Solar cell, supercapacitor, bioelectronic, textile, tissue engineering and sensor are main application areas of the carbon ink. In this thesis, carbon inks were designed and characterized. First carbon ink was processed at room temperature on the FTO substrate and its electrical conductivity and morphologic structures were determined. Moreover, it was applied on the perovskite solar cell and measured the photovoltaic properties. As second type, carbon inks containing carbon particles obtained by carbonization of two different type of coffee waste with different ratio of activation material were prepared and their resistivity and morphology were investigated. In the third type of carbon inks, doped polymer structures were used and processed at low temperature on FTO surface in order to measure their electrical resistivity and to determine their morphologic structures. The lowest resistivity inks obtained from all the ink types were applied by doctor blade method as electrodes on perovskite solar cell and the performance of the cells were tested.
Interaction of Poly(vinyl alcohol) and chitosan coated iron oxide nanoparticles with cell membrane models
Nanotechnology is being used at different fields from energy to food industry but its application to medical field, such as tissue engineering, bioimaging, drug design, diagnosis, is more recent. According to the World Health Organization (WHO), 8.8 million people were reported dead because of the cancer in 2015. Cancer can be treated with chemotherapy, radiotherapy and surgery but these treatment methods have serious side effects since cancer drugs are not selective so they affect both healthy and cancerous cells. One of the approaches to reduce the toxic side effects and improve patient life quality is the implementation of nanotechnology to the development of new drugs and therapies. Magnetic nanoparticles are usually made up of nickel, cobalt and iron. Because of their magnetic properties, they can be transferred to desired location with the help of external magnetic field. Generally, magnetite, hematite, maghemite and goethite are known as iron oxides types. Iron oxide nanoparticles (IOPs) are commonly preferred as MRI agent, and targeted drug design. They are, however, toxic and cause problem in physiological environment because of their negative surface charge, easy agglomeration, low stability, and free radical formation. Therefore, they should be modified to reduce their toxicity and coating their surface with polymers is an effective method proposed by different groups. In this study, iron oxide nanoparticles were coated with two different polymers and the interaction of these particles with cells were studied using artificial cell membrane models. For this purpose, chitosan and poly(vinyl alcohol) (PVA) were selected because of their biodegradable and biocompatible characteristics. Polymers were coated on IOPs surfaces by adsorption method because of its high efficiency and simplicity. In this method, polymer solutions at different concentrations were mixed with IOPs. Optimal polymer concentration was determined according to colloidal stability. Characterizations of the IOPs were done using different techniques. Zeta potential was measured to determine the surface charges, and stability, rheology to observe flow behavior, Dynamic Light Scattering (DLS) to measure particle size, and Fourier Transform Infrared Spectroscopy (FTIR) to investigate binding between IOPs and polymers. After the characterization, interaction between cell and coated and uncoated IOPs were investigated with liposome, a simple biomimetic cell membrane model. Quartz Crystal Microbalance with Dissipation (QCM-D) is used to investigate these interactions in real time and label-free. QCM-D uses piezoelectric effect of quartz crystal. When voltage is applied, quartz crystal oscillates with a defined frequency and this frequency is sensitive to the amount of material attached to the surface. Adsorption/desorption or solid/liquid interaction can be observed according to the frequency shift (Δf). QCM-D also measures viscoelastic properties of adsorbed particles on surface with changes of dissipation (ΔD) at the same time. In this thesis, the interaction of PVA and chitosan fully coated, partially coated, and uncoated IOPs were investigated with neutral, positive and negatively charged liposome layers. By using QCM-D, interactions of particles with cell were estimated in a shorter time and cheaper than cell culture experiments. Results show that, coating properties, structure and charge of lipids affect the interactions between them and electrostatic interactions are significant parameter. In the future studies, chemotherapeutic drug loaded particles can be studied both in QCM-D and cell culture to see their effect to the cells.
Investigation on the effects of mechanical forces on endothelial and monocytic cell behaviour by using microfluidic systems
In human physiology, it is known that cells can sense not only biochemical signals but also physical factors which employee in tissue functionality such as mechanical forces, geometry and matrix flexibility. Mechanobiology is the field of these physical factors function basically through mechanotransduction process. The mechanotransduction is a physiological process that is needed to sense mechanical forces and the conversion of these forces into electrical and biochemical signals. For instance, tensile strength, compression and shear stress, are the most important mechanical stimulations which have influence on cells in body. These mechanical stimulators playing major role on regulation of cellular functions like gene expression, protein synthesis, cell growth, differentiation and death which are necessary for providing the maintenance of tissue balance by triggering different electrophysiological and biochemical responses. Traction forces formed by sensing extracellular environment and responses to this environment can affect many biological processes like wound healing, angiogenesis and metastasis at cell level. Therefore, characterization of these mechanical forces in terms of magnitude and direction could be meaningful in pretending and understanding the physiological and pathological events at tissue and organ level. In tissue and organ level, shear stress which is described as the friction force per unit area in blood has tremendous importance in terms of evolution and physiology over the endothelial cells covering the inner surface of vascular network to maintain the physiological conditions. This shear stress is related to flow rate gradient on the cross section of a tube. While velocity is maximum at center, it is zero near to the inner surface. It is known that the biological responses to shear stress takes a significant part of preventing vascular diseases. Due to non-pulsatile characteristic of venous system, shear stress levels are low and between 0.076-0.76 Pa. In arterial system, flow is laminar and pulsatile with high shear stress levels that are between 1-7 Pa for large arteries and between 2-6 Pa for arterioles. Studying vascular cell biology in laboratory is difficult in terms of mimicking the dynamics in vivo environment and 3D structures. Work done by in vitro is achieved by exposing the endothelial cells into shear force in flow chambers composed of parallel plates. Besides, thanks to the devices produced by microfluidic technology which can be used instead of huge systems such as parallel plate or cone plate flow chambers, the mechanical forces, especially shear stress can be studied in in vitro environment. Because of being cheap, biocompatible and transparent, poly(dimethylsiloxane) is used in production of microfluidic devices which is used usually in cell biology studies. There are some advantages of microfluidic devices produced by poly(dimethylsiloxane) like using small amount of sample or agents, providing cell culture environment with stable liquid flow compared to traditional methods used in cell culture applications and analysis. Also, microfluidic devices are made of transparent materials, have suitability to fluorescence microscope or spectroscopy studies which enable monitoring cell behavior under long-term and high amplification conditions. In this thesis, the microchannels were designed as cavitated to mimic the environment of the atherosclerotic plaque where the shear stress and pressure difference occur depending on the diameter of the vessels and fabricated using MEMS techniques.. HUVEC is endothelial cells which is lining the inner surface of the wall seeded in the straight and cavitated microchannels were subjected to shear stress at 0.25 and 0.75 Pa, separately, for 4 hours by the syringe pump. Also, there are two subgroups as TNF--treated and untreated. The change of F-actin level in HUVEC was investigated under fluorescence microscope and fluorescence intensity of F-actin protein level was examined by Image J 1.50i programme. According to the results, there is a significant increase at 0.25 Pa in straight microchannel group with respect to control counterpart for untreated group. There is a significant decrease at 0.75 Pa groups compared to 0.25 Pa groups but MFI increased only in 0.25 Pa straight microchannel compared to control. Overall, the MFI of F-actin at 0.25 Pa is significantly higher than 0.75 Pa for TNF--untreated group. In TNF--treated group, there is not any significant difference between experimental groups. The change of ICAM-1 mRNA levels in HUVEC cells was investigated by qRT-PCR. For untreated group, there is significant increase at 0.25 Pa in cavitated group. The mRNA expression level at straight groups are lower than cavitated groups. For TNF--treated group, the mRNA expression level at 0.25 Pa is higher than 0.75 Pa for cavitated group. There is a significant difference between straight and cavitated groups at 0.25 Pa. The mRNA expression level at 0.25 Pa cavitated group is higher than control. F-actin synthesis and ICAM-1 mRNA levels have also been investigated in monocyte cells as examined in endothelial cells due to the contribution of monocytes to the process of inflammation in atherosclerotic plaque regions. In this direction, THP-1 cells were exposed to 4, 15 and 45 Pa shear stress, for 0.5 and 3 hours, separately. In addition, since TNF- is known to enhance the synthesis of F-actin polymer and ICAM-1 gene expression, experimental groups were divided into two subgroups, treated and not treated with TNF-. F-actin synthesis in Phalloidin labeled THP-1 cells was examined by fluorescence microscopy and fluorescence intensity was analyzed by Image J 1.50i program. According to the mean fluorescence intensity, F-actin synthesis was observed significantly increased at 4 Pa and 45 Pa shear stresses after 0.5 h, while the greatest increase was observed at 15 Pa. As the duration of exposure increased, a decrease in F-actin polymerization was observed at 45 Pa. Since the increase in F-actin synthesis was seen at a maximum 15 Pa shear stress, the determination of ICAM-1 mRNA level in THP-1 cells was only examined by qRT-PCR at 15 Pa. According to the results, about two-fold increase was observed in the experimental group compared to the control group. The releasing level of IL-8 chemokine molecule from THP-1 cells exposed to shear stress which secreted for leukocyte recruitment from monocyte and endothelial cells in atherosclerotic regions was examined. For this reason, the level of IL-8 in THP-1 cells were exposed 4, 15 and 45 Pa shear stress for 3 hours was examined by ELISA. According to the fluorescence intensity results, a decrease in the experimental groups was observed compared to the control group. Except the control group, the highest level was observed at 15 Pa and the lowest level at 45 Pa. Hoescht 33342 fluorescently labeled THP-1 cells were exposed to 15 Pa shear stress for 0.5 and 3 hours, respectively, were added to the HUVEC cells seeded in the wells and incubated for 1 hour, the florescence images were taken after incubation to investigate how the shear stresses affected the adhesion between the endothelial and monocyte cells. The number of cells adhered to HUVEC cells was analysed with Image J 1.50i programme. According to the results, as the duration of exposure to shear stress increases, the degree of adhesion decreases. Data obtained from these experiments will enable diagnostic, treatment and new medicine designs by revealing the targeted molecular mechanism definitely in atherosclerosis treatment within the scientific area by the future. Furthermore, examination of the changes in the molecules involved in sheared cells by microfluidic systems will greatly contribute to the work to be done in the field of nanotechnology.
Biomimetic approaches for the fabrication of hollow fiber nanofiltration membranes
Membrane technologies have become pioneer technology for the water treatment. However, the operation cost of the membrane is dependent on fouling which is "the Achilles heel of the membranes" and consumed energy. The high energy requirements in commercial nanofiltration (NF), reverse osmosis (RO) and forward osmosis (FO) technologies lead researchers to develop new membrane designs having high flux values with high salt rejection values. Biomimetic approaches have gained an important place in the scientific and the technical fields. For the research and development of the membranes, the terms "learning from nature" and "innovation by imitating" become significant. In this respect, Aquaporin Z (AqpZ) protein became popular for the last eleven years. These membranes promise extremely high performance enhancements and offer a decrease in energy consumption. This thesis aims to conduct a very comprehensive study on the development of hollow fiber nanofiltration membranes with incorporated AqpZ. For this purpose, AqpZ protein was cloned from E.Coli bacteria by using many molecular methods such as PCR, ligation, chemical transformation etc. After AqpZ gene is confirmed by sequencing, purification of AqpZ is optimized. Functionality of AqpZ is obtained by reconstituting AqpZ into liposomes. Film rehydration method is used for liposome preparation. In the thesis, the effect of Aquaporin Z (AqpZ) reconstitution on liposome characteristics and behaviors was investigated by evaluating the adsorption performance of proteoliposomes onto gold, polysulfone (PS) and polyacrylonitrile (PAN) surfaces. Commercial AqpZ were used as positive control for cloned AqpZ. AqpZ incorporation into liposomes did not significantly change mean liposome diameter and surface charge, but the water permeability was increased up to almost six fold. Adsorption kinetics was monitored on gold, as the reference substrate, on PS and on PAN spin-coated sensor surfaces, as common nanofiltration membrane materials, via Quartz Crystal Microbalance with dissipation (QCM-D). The results of viscoelastic modelling showed stiffer membrane structure for the lipid bilayer of proteoliposomes compared to that of liposomes. Although liposomes and proteoliposomes were found to be successfully adsorbed on negatively charged PS and neutral charged PAN surfaces, the interaction strength and adsorption rate was found to be different for polymers having different surface properties indicating the importance of polymer for the stabilization of proteoliposomes. According to the findings of this study, PS was chosen as polymer material for membrane fabrication. Interfacial polymerization method was used to fabricate hollow fiber nanofiltration membranes. Proteoliposomes were added to the aqueous phase of interfacial polymerization. Proteoliposome concentration and interfacial polymerization conditions were optimized with flat sheet membranes. Two different proteoliposome concentrations, two different amine monomer reaction times were used and the effects of thermal treatment was investigated for the optimization of flat sheet membranes. Membrane performances were compared in terms of specific permeate flux, MgSO4 and humic rejection; flux recovery after humic acid filtration, the performance of cloned AqpZ incorporated membranes improved 1.7 times regarding TFC membranes. According to the results, increasing liposome concentration did not improved nanofiltration membrane performance. On the contrary, salt rejection performance decreased dramatically. 0.1 mg/mL proteoliposome concentration, 2 min piperazine monomer reaction time and thermal treatment at 50°C for 5 min was found to be the optimized condition. Hollow fiber ultrafiltration membranes were fabricated by phase inversion method. Ultrafiltration (UF) membrane morphology and performance was confirmed by characterization methods. UF membranes were used as support layer for nanofiltration membrane fabrication. For this purposes, in the thesis the combined effects of fabrication conditions and casting mixture composition on the properties of hollow fiber (HF) membranes were investigated. Three variables evaluated are air gap (dgap= 0 cm and 2.5 cm); coagulation bath temperature (Tc= 25°C; 35°C; 45°C) and molecular weight of polyvinylpyrrolidone (MWPVP = 10 kDa; 40 kDa; 65 kDa; 360 kDa; 1000 kDa). Prepared HF membranes were characterized in terms of specific permeate flux; surface morphology, charge and hydrophilicity; bovine serum albumin (BSA) rejection, Young modulus, and resistance to fouling by BSA. Optimal membrane morphology and performance was achieved at higher Tc and higher MWPVP. Optimized conditions were used for the preparation of hollow fiber nanofiltration membranes with Aquaporin Z (AqpZ) immobilized on the outer surface of the separation layer. Three ultrafiltration supports – polymeric, nanocomposite and reinforced were evaluated in terms of their effects on the separation properties of membranes with AqpZ. Surface characterization showed that AqpZ-reconstituted proteoliposomes were successfully integrated with the polyamide matrix leading to permeate flux enhancement of up to 2.5 times. The membranes were also evaluated in terms of salt and organic matter removal. Reinforced UF support allowed for the most effective integration between the polyamide layer and proteoliposomes giving the highest figure of merit – an aggregate metric of membrane performance that includes water permeability, selectivity and resistance to fouling.
Persea americana Mill. yapraklarından sentezlenen gümüş ve altın nanopartiküllerin biyolojik aktivitelerinin değerlendirilmesi
Nanoteknolojinin bilim ve teknoloji içerisinde multidisipliner bir alan olması sayesinde özellikle nanopartiküllerin üretimi ve kullanımı son zamanlarda yaygınlaşmaktadır. Ayrıca, dünyadaki değişimin bir sonucu olarak inovatif ve ekolojik olarak çevre dostu bilimsel yöntemlerin geliştirilmesine olan ilgi de artmaktadır. Bu tez çalışmasının amacı, Persea americana Mill. (Avokado) yaprak ekstraktları aracılığıyla gümüş ve altın nanopartikül sentezi gerçekleştirmek ve sentezlenen gümüş ve altın nanopartiküllerin biyolojik aktivitesini incelemektir. Persea americana Mill., endüstriyel tarıma ihtiyaç duymadan doğal olarak yetişebilen ve aynı zamanda Akdeniz bölgesinde de kültürü yapılabilen bir bitkidir. Ayrıca içerdiği temel besinler ile hem meyveleri hem de yaprakları ile farmakolojik, kozmetik, diyetetik açıdan önemli bir yer tutmaktadır. Bundan hareketle yapılmış olan bu tez çalışmasında Persea americana Mill. (Avokado) yapraklarından su ekstraktı hazırlanmış, daha sonra yeşil sentez yaklaşımı ile gümüş ve altın nanopartikül sentezi gerçekleştirilmiştir. Elde edilen sonuçlara göre gümüş nanopartikül sentezi sonucunda sarıdan kahverengiye dönen çözelti rengi oluşmuş, altın nanopartiküllerde de altın sarısı renginden kırmızımsı renge dönüşen çözelti rengi gözlemlenmiştir. Nanopartikülleri yapısal ve morfolojik açıdan incelemek amacıyla ultra-viyole (UV-Vis) spektroskopisi, Fourier dönüşümlü kızılötesi spektroskopisi (FT-IR), taramalı geçirimli elektron mikroskopisi (STEM), X-ray difraktometresi (XRD), nanopartikül boyut ve Zeta potansiyeli ölçümü gibi çeşitli yöntemlerden yararlanılmıştır. Karakterizasyon bulgularına bakıldığında gümüş nanopartiküller genellikle küresel şekle sahip olan ve ortalama 12.18 ± 2.18 nm aralığında görülmekte iken altın nanopartiküllerin de küresel ve üçgen şekilli morfolojiye sahip ve ortalama 14.84 ± 3.99 nm boyutlarında olduğu tespit edilmiştir. Avokado yaprak ekstraktı ve yaprak ekstraktından sentezlenen gümüş ve altın nanopartiküllerin toplam fenolik ve toplam flavonoid madde tayininin yanı sıra toplam antioksidan kapasite (fosfomolibdat), DPPH, ABTS, CUPRAC, FRAP ve metal şelatlama gibi çeşitli metotlar kullanılarak antioksidan aktivite testleri gerçekleştirilmiştir. Yapılan antioksidan testlerinde gümüş nanopartiküllerin Fosfomolibdat aktivitesi 0.29 mmol TE/g, DPPH aktivitesi 20.94 mg TE/g, ABTS aktivitesi 25.66 mg TE/g, CUPRAC aktivitesi 61.39 mg TE/g, FRAP aktivitesi 41.99 mg TE/g olarak tespit edilmişken altın nanopartiküllerin ise Fosfomolibdat aktivitesi 0.05 mmol TE/g, DPPH aktivitesi 28.14 mg TE/g, ABTS aktivitesi 1.40 mg TE/g, CUPRAC aktivitesi 35.50 mg TE/g, FRAP aktivitesi 21.48 mg TE/g olarak belirlenmiştir. Elde edilen sonuçlar avokado yaprak ekstraktının ve ekstrakttan sentezlenen gümüş ve altın nanopartiküllerin antioksidan etkiye sahip olduğunu göstermiştir.
Yumuşak jelatin kapsül ile kanabidiol içeren kenevir tohumu yağı uygulaması için polikaprolakton modifiye salım sistemi geliştirilmesi
Kanabidiol (CBD); multiple skleroz, parkinson, anoreksiya, göz tansiyonu, kanser, ağrı, bulantı ve kusma, depresyon, insomnia, stres ve kaygı bozuklukları gibi çeşitli hastalıkların tedavisinde umut vadetmektedir. Fakat CBD'nin yüksek lipofilik özellikleri, kullanım ve dozlamayı zorlaştırmakta, dolayısıyla farmasötik olarak yararlanımını kısıtlamaktadır. Bu tez çalışmasının amacı, CBD'nin gıda takviyelerinde kullanılması için elverişli bir dozaj formu geliştirilmesi ve başarılı bir şekilde kapsüllenmesinin sağlanmasıdır. Nanopartiküller (NP), farklı molekül ağırlıklarına sahip polikaprolakton (PCL) polimerleri kullanılarak, ultrasonik homojenleştirici ve ultra-turrax ile emülsifikasyon çözücü buharlaştırma yöntemi ile sentezlenmiştir. Optimizasyon çalışmalarında, farklı molekül ağırlıklarının ve farklı üretim yöntemlerinin partikül boyutuna ve zeta potansiyeline etkileri değerlendirilmiştir. En uygun polimerin 14000 g/mol molekül ağırlığına sahip PCL olduğu bulunmuş ve 5 mg, 10 mg, 15 mg ve 30 mg CBD enkapsüle edilmiş PCL NP'ler ultrasonikasyon tekniği kullanılarak hazırlanmıştır. CBD enkapsüle NP'ler morfolojik ve yüzey özellikleri açısından karakterize edilmiştir. Plasebo NP'ler ve 5mg, 10 mg, 15 mg ve 30 mg CBD enkapsüle PCL NP için sırasıyla -23,37, -10,21, -9,62, -9,93 ve -9,40 mV'lik potansiyel değerleri tayin edilmiştir. Plasebo NP'ler ve 5 mg, 10 mg, 15 mg ve 30 mg CBD enkapsüle PCL NP'lerin sırasıyla ortalama 207,5 nm 227,2 nm, 225,5 nm, 227,7 nm ve 216,9 nm boyuta sahip oldukları belirlenmiştir. İki farklı pH değerinde (1,2 ve 7,4) CBD-PCL-NP'lerin in vitro salım çalışmaları gerçekleştirilmiştir. NP'lerin DSC analizi ile etken madde-polimer uyumluluğu ortaya çıkartılmıştır. Ayrıca FT-IR analizi sonuçlarıyla, CBD'nin NP'ler içine kapsüllendiği gösterilmiştir. CBD'nin çeşitli reseptörlerle etkileşiminin incelenmesi için moleküler yerleştirme yöntemi kullanılarak in silico analizleri yapılmıştır. Bu molekülün reseptörler üzerinde yapısal davranışları, afinitesi ve toksisitesi değerlendirilmiştir. PCL-NP'nin hücre içerisine alındığı ise Nil kırmızısı enkapsüle edilmiş NPlerin hücrelerin içerisinde birikimi gösterilerek ortaya koyulmuştır. Saf CBD'nin hücrelerin çoğalmaları üzerindeki etkisi ise L929 normal fibroblast hücreleri ve MCF-7 meme kanseri hücrelerinde 24, 48, 72 saat inkübasyon sonrası hücre canlılık analizi yapılarak ve IC50 değerleri hesaplanarak belirlenmiştir. Sonuçlar, CBD-PCL-NP'lerinin kenevir tohumu yağıyla birlikte, yumuşak jelatin kapsül formunda bir gıda takviyesi olarak geliştirilebileceğini göstermiştir. Gıda takviyesi uygulaması için kullanılmak üzere elde edilen kenevir tohumu yağının yumuşak jelatin kapsül formunda prototip üretimi gerçekleştirilerek ambalajlanmıştır. Kapsülün, uzun süreli CBD salımı yaparak serbest CBD tüketimine göre farmasötik avantajlara sahip olduğu söylenebilir.
Oksijen ve sıcaklığın reaktif magnetik alan sıçratma yöntemiyle büyütülen çinko oksit ince filmlere etkisi
Çinko oksit (ZnO), yarı iletken endüstrisinde gösterdiği saydam iletken oksit (SİO) özelliği ile hızla gelişmekte olan optoelektronik teknolojisinde sıklıkla kullanılan bir malzemedir. Bu tez çalışmasında, reaktif radyo frekans magnetik alan sıçratma yöntemi ile büyütülen ZnO ince filmlerin büyütme esnasında ortamda bulunan oksijen ve alttaş sıcaklığına bağlılığı yapısal ve optik özellikleri açısından değerlendirilmiştir. Yapılan X-ışınları kırınım deseni analizleri sonucunda elde edilen bulgular incelendiğinde bütün filmlerin yüksek yönelime sahip hekzagonal wurtzite yapısında olduğu ve bunun O2 miktarına bağlı olmadığı sonucuna ulaşılmıştır. Ayrıca, Raman spektrumları da wurtzite yapısının varlığını doğrulamaktadır. Aynı zamanda tüm örneklerin yüksek geçirgenliğe sahip olduğu ve film kalınlıklarının sıcaklık artışı ile azaldığı tespit edilmiştir. Alan etkili taramalı elektron mikroskobu (FE-SEM) ve atomik kuvvet mikroskobu (AFM) sonuçları ise filmlerdeki taneciklerin oda sıcaklığında, 100 oC'de ve 200 oC'de çok değişmediği ancak 300 oC sıcaklıkta büyütülen filmlerin homojen olmayan tanecik büyümesi sergilediği tespit edilmiştir. Ancak, bu durum O2 arttıkça azalmaktadır. Bütün filmler için optik bant boşluğu ⁓3.25 eV olarak tespit edilmiştir. Yapılan bu çalışma, optoelektronikte oldukça sık kullanılan ince film çinko oksit yapılarına ilişkin kapsamlı bir optimizasyon sunmuştur.
Preparation and characterization of anti bacterial, anti scratch and easy to clean multifunctional coatings by sol gel method
Developments of science and technology help us to understand the relationship between microstructure and material properties. Materials gain new properties by decreasing their particle size from micro to nano scale. Nowadays, thin film coatings on solid surface are developing by various physical and chemical coating methods. In order to show functionality, thin coatings must have homogeneous thickness and composition throughout the coating layer. Coating methods are generally divided as physical and chemical coating methods. Among the coating methods, sol-gel method come forward as a chemical method to develop multifunctional coatings. In general, sol gel is defined as the transition from a liquid sol phase to solid gel phase. Sol-gel process does not require high process temperatures and in this process, there is a control of the material from precursor to final product at molecular level. It is a low cost process, capable to coat flat or geometric shapes and large areas as well. In addition, it allows us to produce organic-inorganic hybrid polymers, thanks to its high purity and homogenity. In hybrid compositions, organic polymers bring well adhesion and flexibility whereas inorganic molecules brings hardness. With these compositions, various functions such as thermal and chemical stability, antibacterial property, hardness, anti scratch, anti wear, wettability... etc, can be reached. In addition, hybrid coatings can easily be bonded to ceramic or glass surfaces, thanks to their covalent binding property. Organofunctional silanes are the most suitable precursors for the preparation of organic - inorganic sol gel films. Alkyl groups which contain a functional groups such as epoxy, amino or vinyl are employed as cross linking agents in polymerization reactions. Meanwhile, non reactive groups of precursors do not participate polymerization reactions and they form porous structure in the silica network. This porous structure controls optical and mechanical properties of the films such as fracture or cracking. Since, the final product may have various characteristics depending on chemical composition of precursors, hydrolysis time, the addition order of materials into solution,etc..,sol-gel method requires close monitoring of each step. In this study, various compositions containing (3-glycydyloxypropyl)trimethoxysilane (GLYMO), Titanium(IV)isopropoxide and AgNO3 were prepared by sol-gel process. It is well known from the literature, coatings having Ag+ on the surface present antibacterial properties. An experimental design of 27 different compositions were prepared by changing the amount of titanium(IV)isopropoxide, hydrolysing water and hydrolysis time. Glass substrates were coated by sol-gel dip coating method at 15 cm/min withdrawal rate. Wet coatings were cured in oven at 150°C for 30 min. For all set of coating compositions, physical tests such as, pencil hardness test, linear abrasion test,adhesion test and nanoindentation tests were employed to find the most scratch resistant coating. The effect of the amount of last hydrolysing water on gel formation was investigated by percent solid test. From the exprerimental design set, it is found that, as the amount of Titanium(IV)isopropoxide decreases, the transparency and scratch resistance of the coatings decreased as well. For all the samples, a trend of decrease in solid % according to the increase in the amount of last hydrolysing water was obtained. Coatings which have high transparency were selected. Hydrolysis and polymerisation reactions of coating solutions and thin films were investigated by FTIR and silver absorbance during redox reactions were followed by UV absorbance spectroscopy. Micro and nano structural characterization of coatings were analyzed by SEM-EDS and AFM. Viscosity measurements in specific periods were done to determine the shelf life of the coating solutions. As a result of physical tests, the hardest and the most transparent samples were chosen to improve their easy to clean property. Fluorosilane was added to the most scratch resistant coating composition in two different route and easy to clean property of the coatings was determined by contact angle measurements. The anti bacterial activity of the coatings against Gram negative Eschericia Coli (E.Coli) and Gram positive Staphylococcus Aureus (S.aureus) was examined. Consequently, antibacterial (log5), scratch resistant (8N), and easy to clean (CA = 98-108°) multi-functional sol-gel coatings were developed.
Design simualtion and analysis of piezoresistive microcantilever for biosensing applications
In the past decade, several research works demonstrated the ability of Biological Microelectromechanical System (Bio-MEMS) biosensors to detect of biomolecules such as Deoxyribonucleic Acid (DNA), proteins, Bacteria and Antigens. But due to the low concentration of the analytes that need to be detected in the samples,a minuscule signal results in the output of the sensor. In response to this, a need arisen for an optimized biosensor capable of giving high output signal in response the detection of few analytes in the sample; the ultimate goal is being able to convert the attachment of a single biomolecule into a measurable quantity. For this purpose, MEMS microcantilevers based biosensors have emerged as a promising sensing solution because it is simple, cheap, highly sensitive and more importantly does not need analytes optical labeling (Label-free). Among the different microcantilever transducing techniques, piezoresistive based microcantilever biosensors seem to be a more attractive solution being cheap, high sensitive, miniature, works well in liquid environments and having integrated readout system. Even though there are many publications in literature that concentrated on increasing the piezoresistive microcantilevers sensitivity, they only considered in optimizing few design and process parameters thus the resultant sensitivity enhancements are not good enough for practical applications. After the analyzation of the work found in literature, it was found that the parameters/approaches that be can be optimized/used to enhance the sensitivity of Piezoresistive microcantilever-based sensors are: Cantilever dimensions, Cantilever Material, Cantilever Shape, Piezoresistor's material, Piezoresistor's doping level, Piezoresistor's Dimensions, Piezoresistor's position, Stress concentration Region's (SCR) shape and position. In this study, after a systematic analyzation of the effect of each design and process parameters on the sensitivity, a step-wise optimization approach was developed in which almost all these parameters were variated one at each step while fixing the others to get the maximum possible sensitivity at the end. Throughout this work, COMSOL Multiphysics 5.0, a commercial Finite Element Analysis (FEA) tool, was used to simulate the sensor performance. At each optimization step, the goal was to optimize the parameter in such a way that it maximizes and concentrates the stress in piezoresistors region for the same applied force thus get the higher sensitivity. In total, almost 46 different simulations were done to get the final optimized sensor. Starting with a rectangular cantilever, the piezoresistor material and doping level were optimized in two steps. When the piezoresistor material was varied (single crystal silicon and Poly-silicon), it was found that the ΔR⁄R sensitivity is higher in the case of single crystal silicon. xxiv But for this sensor design, polysilicon has been chosen as the piezoresistor material because it's sensitivity does not depend on the crystal orientation, the sensor fabrication is easier, cheaper and can be realized in ITUnano laboratory. Next, by changing the doping level in the range between 1×1015 cm−3 to 1×1020 cm−3 and calculating the ∆R/R sensitivity, the doping level that will be used throughout the following simulations was determined. It was found that, 1×1018 cm−3 doping level is high enough to reduce the thermal noise effect, at the same time it does not be affected the sensitivity that much. Thus this doping level was chosen and used throughout the following simulations. Afterward, the cantilever material is varied to find the material that gives maximum stress and deflection for the same applied force. It was found that SiO2 resulted into almost 2.5x higher deflection and 1.7x higher sensitivity when compared to single crystal silicon (the starting cantilever material) case thus SiO2 has been selected as the cantilever material for this biosensor and it is used in the following optimization steps. Next, various cantilever shapes (Rectangular, Pi-shape, T-shape, Trapezoid, SteppedTrapezoid, and Triangular) were introduced, and for each shape, the dimensions were varied bearing in mind the process and device limits. The results from all these simulations were compared to find the optimized shape which gives the maximum sensitivity. During the rectangular shape microcantilever optimization step, it was found that the cantilever thickness has the highest effect on the sensor sensitivity when compared to the change in cantilever length and width. In addition to that, after the different rectangular microcantilever dimensions were optimized (length, width and thickness), the sensitivity increased 18.3x folds. Also, adding two side holes to the rectangular cantilever structure (T-shape) increased the sensitivity by 1.6 factor. Overall, for the same applied force, the trapezoid-shaped microcantilever design gave higher sensitivity (more than 46x times greater than the starting sensor sensitivity) whereas the stepped-trapezoid shaped gave the highest maximum deflection. Afterward, Stress Concentration Region (SCR) was introduced in the optimized trapezoid structure in different locations and orientations seeking for further sensitivity enhancement. From the simulations, it was found that adding a 30µ×10µm SCR rectangular hole to the optimized trapezoid structure 15µm away from the clamped cantilever edge, resulted in almost 1.6x times sensitivity enhancement which gave the best sensitivity value compared to the other positions. Regarding the normalized change in resistance to the applied force the final sensor's sensitivity equals to -1.5×10-8 Ω/Ω ⁄pN; this means that for each 1pN (10-10 g) biomolecules attach to this biosensor; the piezoresistor resistivity will decrease by 1.5×10-8 Ω. When compared to the starting sensor, the final sensor design gave 73.5x times better ΔR⁄R sensitivity and it is more sensitive than the other sensor designs previously reported in the literature. The fabrication sequence for this sensor was prepared, but due to technical problems in some of the devices found in ITUnano laboratory, the sensor has not been fabricated.
Aerosol filtration performance of nanofibrous webs produced via centrifugal spinning technique
Nanofibers are one of the important nano scale products. Owing to their large specific surface area and high porosity, they are widely investigated for filtration, energy and biomedical applications [1]. So far, electrospinning is by far the most common method for nanofiber production, but this method has some difficulties such as low production rate (~1 ml/h/nozzle) and high voltage necessity (up to 60 kV) [2]. However, the wide-spread commercial use of electrospinning is limited mainly due to its low production rate. Most other nanofiber production methods, such as melt-blowing, bicomponent fiber spinning, phase separation, template synthesis, and self-assembly, are complex and can only be used to make nanofibers from limited types of polymers. Centrifugal spinning is an alternative method for producing nanofibers from various materials at high speed and low cost. In this thesis, the centrifugal spinning method was reviewed thoroughly. An overview on the centrifugal spinning process was given, and it was compared with the conventional nanofiber production methods. In addition, the nanofiber filter media were produced via custom made lab scale centrifugal spinning machine. There are three experimental chapters presented in the thesis. At the beginning a custom made centrifugal spinning device was designed and manufactured. The system were introduced. After the manufacture, several experimental studies were performed using various polymer solutions. Especially, the studies were concentrated on thermoplastic polyurethane (TPU) nanofibers. After the morphology characterization, an optimization study on fiber diameter of TPU nanofibers was performed. The optimal process parameter levels were determined, and also the effects of these parameters on fiber diameter were demonstrated statistically. Then, the filtration performance of the produced webs were analyzed. A correlation between the fiber diameter and filtration quality has been established. It is expected that this study will leave a positive impression onto the forthcoming studies on nanofibers especially for the nanofibrous filter production.
Copper zinc tin sulfite CZT(S,Se) for solar cell applications
Over the last years, the need for renewable energy has grown day by day. Solar energy is one of the most important assets of renewable energy. The earth has proved itself as a non-infinite energy source. Climate change and global warming are warning the humanity for sustainable solutions. Renewable energy is one of those solutions that needs an urgent attention. Solar energy is one of the early corners of this subject. But the technology has to change as soon as possible. Silicon solar cells have been dominating the solar energy market since the day one. Their reliable performance makes silicon solar cells a viable asset but the availability of the raw materials is a matter of concern. They are physically fragile and heavy form makes it ungainly technology. Thin film solar cell technologies are the biggest rival on the subject to silicon, they have important advantages like being lightweight, flexible, cheap and easily manufactured. However, they cannot achieve the same performance as silicon solar cells yet. CZTS is a quaternary absorber layer material for solar cell technologies. It has several advantages like consisting of earth abundant, cheap, and non-toxic materials. Also one of the most important competitive edges for CZTS is that its structure is quite similar with CIGS and CIS. They have high-efficiency numbers to compete with silicon cells. However, they have two disadvantages. One of them is having toxic materials inside and the other one is that they are getting more expensive day by day (their cost is increasing over the last years). The screening technologies are using the same raw materials (elements) with them so the market price for those elements are getting more expensive. That makes element prices higher and higher every second. So, CZTS already has a place on market for itself. The advantages mentioned before makes CZTS attractive for scientists. In this study, CZTS ink was produced by hot injection method. Metal precursors were used in the reaction. Precursors can be listed as; Copper (II) acetylacetonate, Zinc acetylacetonate hydrate and tin (IV) bis(acetylacetonate) dibromide as cation precursors and elemental sulfur as a sulfur source were used. Oleylamine was used to dissolve the precursors and also as a surfactant for the reaction. The reaction occurred in a closed chamber under an inert atmosphere. Reactants were washed from oleylamine after the reaction. The product has been kept dispersed in toluene. Cadmium Sulfide layer was coated on samples by chemical bath deposition technique. Cadmium acetate and thiourea were used as source materials. Zinc oxide powder was produced by using zinc acetate and potassium hydroxide. The final product was kept in methanol solution to be used later as an n-type layer. Spray coating technique was utilized to coat samples with CZTS and ZnO. The molybdenum coated glass was used as the substrate. CZTS layer was coated first, followed by annealing of the film at 330 oC for an hour. After the annealing step, spin coating was utilized to coat CZTS one more time. This step is applied to reduce the roughness of the film. Annealing was then applied one more time on samples after the spin coating. CdS layer was coated onto the CZTS layer via chemical bath deposition as mentioned above. Finally, ZnO layer is deposited via spray coating. Molybdenum is used as an electrode and for the counter electrode aluminum was thermally evaporated onto the samples. Masks were used to protect the samples to be coated fully. Mo / CZTS / CdS / ZnO / Al configuration was obtained. Samples were characterized at each step to see if the films were what they are expected. Diodic plots were identified by current-voltage characterization. The final formation was showing the effects of the solar cell, producing current. To sum up, quaternary CZTS compound was produced and made into a film form successfully. Coating a CdS layer on top of the CZTS layer was achieved. ZnO particles were produced and used as an n-type layer. Solar cell layers were prepared in that order, and then it's tested against light until a working solar cell was achieved. In the study, CZTS solar cell production conditions were optimized.
Synthesize and characterization of ZnSe based type I and type II heterostructure nanostructures
Nanostructured materials are of interest because they can bridge the gap between the bulk and molecular levels and leads to entirely new avenues for applications, especially in electronics, optoelectronics and biology. When a solid exhibits a distinct variation of optical and electronic properties with a variation of particle size <100 nm, it can be called a nanostructure, and is categorized as (1) two dimensional, e.g., thin films or quantum wells, (2) one dimensional, e.g., quantum wires, or(3) zero dimensional e.g., quantum dots. QDs can be sytnhesized in core or core/shell forms due to interest and generally are made from III-V and II-VI family or semiconductors in the periodic table. The small size of quantum dots (QDs) result in an observable quantum confinement effect, defined by an increasing bandgap accompanied by the quantization of the energy levels to discrete values. This effect is accompanied by an exaltation of the coulomb interaction between the charge carriers. Once an electron-hole pair is created by the absorption of a photon, they interact with each other by means of their opposite charges, forming a quasi-particle called "exciton". The total energy of an exciton indicates the color (wavelength) of the light emitted by the quantum systems. If these excitons are confined in the core, they are called Type I and if they seperetly move around core and shell they are called Type II semiconductors. The intermediate case, in which one charge carrier is localized to the core and the other is delocalized over the whole structure, is known as type-I1/2 or quasi type-II. ZnSe based core/shell QDs exhibit novel properties, making them attractive from both experimental and practical point of view. Semiconductor QDs, typically prepared as core/shell NCs, are a class of strained materials with novel properties. In core/shell NCs, lattice mismatch induced stress between core and shell affects the structural, electronic and optical properties such as core diameter, band offsets and exciton energy. In this thesis, the synthesis of ZnSe core and ZnSe/Cd(Zn)S core/shellZnSe/CdxZn1-xS core/ternary shell and ZnSe/Cd(Zn)S/Zn(Cd)S core/multishell NCs was aimed and the NCs characterized by UV-Vis, PL, HRTEM and XRD along with obtaining strain amount in interfacial layer and calculating capped core diameter theoretically after the compressive and tensile shell deposition. The ZnSe core and the other core/shell heterostructurs were synthezed in our nanosemlab with our equipments according to the latest techniques referenced in articles. The XRD analysis used for determining the atomic and molecular structure of the produced QDs and for characterization of optical properties UV-Vis, PL analysis were done. The induced interface strain from lattice mismatch between core and shell was calculated from continuum elastic theory and applied in effective mass approximation method to obtain the corresponding capped core diameter. The calculated results were compared with diameter of bare core TEM images to obtain the amount the core stretched or squeezed after deposition of tensile or compressive shells. The stretched and squeezed amount of the capped core found to be in proportion with lattice mismatch amount in the core/shell structure.
Production and characterization of CdSe based binary/binary and ternary/binary heterostructure multi shell quantum dots
Colloidal semiconductor NCs (also known as quantum dots (QDs)) with their diameters range between 2-10 nm have gained a huge interest for both optical and electronical applications such as solar cells, light emitting diodes, lasers, fluorescence imaging and for fundamental studies over the last few decades due to their sizedependent optical, physical and chemical properties. QDs can be synthesized in core (bare) and core/shell forms in accordance to their application interest and are made from III-V and II-VI group semiconductors family in the periodic Table. Their optical, physical and chemical properties can be altered with deposition of shell on core. The introduced shell material's composition or spacer layer in multishell cause changes in charactristics of semiconductors. CdSe semiconductor is a subject of many studies due to their bright luminescence in the visible range of optical spectrum with different particle size. In this thesis, like most of investigations, the optical, physical and structural properties of CdSe based QDs is evaluated. The synthesis of CdSe bare core, CdSe/Cd(Zn)S core/shell, CdSe/Cd1-xZnxS core/ternary shell and CdSe/Cd(Zn)S/Zn(Cd)S core-multishell NCs are done at relatively low temperature. Then, the produced hetero structures are optically and structural characterized using UV-Vis, PL, HRTEM, XRD analysis. On the other hand, interfacial strain amount was obtained theoretically in order to calculate the capped core diameter changes after shell deposition. Interfacial strain effect cause the Bragg's 2Ɵ diffraction degree to slide in XRD analysis. In this phenomenon, this shift noticed toward higher degrees after capping the core with compressive shell while introducing lower compressive shell led in less shift in Bragg's 2Ɵ degrees. Another effect of capping CdSe core with shell of different composition observed in absorption and photoluminescence spectra. The red shift of absorption and photoluminescence peak is recorded in UV-vis and PL spectrum after shell deposition. Depending on the diameter of CdSe NCs, the red shift amount differs in absorption spectra. Using the exciton energy from absorption spectrum, the capped core size of the core was calculated. The conventional Brus equation used to calculate capped core diameter with the obtained exciton energy. For the first time, we substituted interfacial strain amount in Brus equation to observe capped core size changes after deposition of compressive shell. Interfacial strain amount is calculated from continuum elastic theory and core squeeze or stretch was observed after capping process. Result of the obtained theoretically capped core size were compared with the bare CdSe core size from TEM image to evaluate the accuracy of our proposed theoretic method. Logic and good overlap of the theoretical and experimental results showed the accuracy of the proposed theoric method.
Hot injection synthesis and structural and optical characterization of CdSe/ZnSe and CdSe/ZnS quantum dots
In this thesis, first of all CdSe QDs were synthesis with hot injection chemically methods, after that it coated with ZnSe, ZnS, to create type-I core/shell respectively. Then they characterized by PL, UV-Vis, XRD, and strain amount in interfacial layer was obtained and capped core diameter after tensile shell deposition and the compressive theoretically calculated. The CdSe core and relative core/shell heterostructures synthesized in nanosemlab with our equipments according to the latest techniques referenced in articles. First, the optical properties were analyzed with UV-Vis, PL, then molecular and atomic structur of the synthesized QDs were analyzed by XRD. Molarity of core QDs were challenged us due to the difficulty of counting the number of QDs in our solution. To overcome this issue the molarity of QDs were calculated theoritically from litratures and different shell molarity were tested. The interface strain from lattice mismatch between core and shell was analyzed from applied in effective mass approximation and continuum elastic theory method to obtain the corresponding capped core diameter.
Nano boyutta malzeme katkılarının betonun elektriksel direnç birim şekil değiştirme ilişkisine etkisi
Ülkemizde son yirmi yılda, depremlerin, malzeme bozulmalarının ve çevresel faktörlerin sebep olduğu hasarlar yüzünden yıkılan betonarme yapılar, binlerce insanın yaralanmasına veya hayatını kaybetmesine sebep olmuştur. Yapı sağlığının izlenmesi, can ve mal kaybının oluşmasını önlemek için hayati öneme sahiptir. Yapı sağlığını izlemek için kullanılan gerinim pulları noktasal ölçüm yaparlar, duyarlılıkları düşüktür, ömürleri kısadır, yüksek maliyetlidir. Bu çalışmada, kendi birim şekil değiştirmesini ve hasarını ölçen akıllı beton üretilmiştir. Akıllı betonu belirlemek için, farklı iletken malzemeleri farklı hacimsel oranlarda içeren karışımlar tasarlandı. Her karışımdan üretilen örneklere basınç testi uygulandı. Elektriksel direnç değişimi ile basınç birim şekil değiştirmesi arasındaki ilişki belirlendi. Basınç birim şekil değiştirmesine en duyarlı makro boyutta malzeme katkılı karışımlar ve nano boyutta malzeme katkılı karışımlar belirlendi. Bu karışımlara yarmada çekme testi ve eğilme testi uygulandı. Birim şekil değiştirmeye ve çatlak uzunluğuna en duyarlı karışım akıllı beton olarak seçildi. Akıllı beton farklı yükleme hızlarında test edildi. Sıcaklık ve nemin akıllı betona etkileri araştırıldı. Çevresel elektrot metodu ve alternatif akım etkileri araştırıldı. Elektrik akımının birim şekil değiştirmeye dik olduğu çapraz yüklemenin etkileri araştırıldı. Akıllı beton, elektriksel direnç değişimi ile birim şekil değiştirme arasında güçlü bir doğrusal ilişki verdi. Elektriksel direnç değişimi ile birim şekil değiştirme mekanizması, basınç, yarmada çekme ve çapraz yükleme testleri için tanımlandı. Gömülü elektrot metodunun çevresel elektrot metodundan daha iyi olduğu gözlemlendi. Akıllı beton doğru akım uygulamaları, alternatif akıma daha yüksek duyarlılık verdi. Uzun dönemde, birim şekil değiştirme duyarlılığı azaldı; uzun süre bekleyen ve nemi arttırmak için suya batırılmış akıllı beton, aynı yaş numunelerine göre daha yüksek bir birim şekil değiştirme duyarlılığına sahiptir. Büyük ölçekte akıllı beton numuneleri birim şekil değiştirme ile elektriksel direnç değişimi arasında güçlü doğrusal ilişki gösterdi. Akıllı beton yapı sağlığını izlemek için prefabrik ve önemli yapılarda kullanılabilir.
Development of nano-material based optical chemical sensors indicating oxygen levels in petrochemistry related workplaces
In workplaces, especially in refineries, volatile petroleum solvents are usually in the form of mixtures of alkanes, cyclic alkanes, alkenes and the aromatics. Such atmospheres which are deficient in oxygen may not provide adequate sensory warning of danger. Therefore correct and continuous monitoring of oxygen levels in such environments is quite important. On the other hand, ruthenium (II) derivatives are known as oxygen sensitive dyes and have intensively been used in the design of optical chemical sensors. Most of the ruthenium dyes suffer from leaching from host matrices due to the water solubilities. In order to provide the best host/dye compatibility we used the amphiphilic ruthenium derivatives in silicon based matrices. In this work, emission-based oxygen sensing properties of highly luminescent ruthenium (II) derivatives were tested in the presence and absence of some volatile organics. Newly synthesized two orange-red emitting alkyl branched ruthenium complexes were used along with silver nanoparticles (AgNPs) in two different silicon based matrices for oxygen sensing purposes. The sensing materials were fabricated in form of thin films and electrospun nanofibers. Ionic liquid and perfluorinated compounds were exploited as additives to enhance the response to oxygen. Oxygen induced spectral changes at 630 nm were followed for both gas phase and dissolved oxygen as the analytical signal. The oxygen sensitivities of the probes were also tested by lifetime based and kinetic mode measurements. Utilization of the amphiphilic Ru dyes in silicon along with AgNPs in the form of electrospun fibers resulted in many advantages such as enhanced long term stability, increased surface area, sensitivity and improvement in all sensor dynamics. Sensing characteristics of the offered design were tested and calibrated in the presence of vapors of benzene, toluene, ethylbenzene, hexane and xylene, which simulate refinery related work places.
Antifungal hibrit kaplamaların hazırlanması ve karakterizasyonu
Bu çalışmada, polikarbonat (PC) ve polimetil metakrilat (PMMA) yüzeylere kekik yağı, karabiber yağı, kimyon yağı ve çay ağacı yağı katkılı 3-(Trimethoxsilyl)propyl methacrylate (TMSPM) ve tetraethyl orthosilicate (TEOS) bağlayıcı madde bazlı hibrit kaplamalar yapılmıştır. Hibrit kaplama yüzeyleri termal ve UV ile kürlenmiştir. Kaplanan PC ve PMMA polimer yüzeyleri Fourirer Dönüşümlü Kızılötesi (FTIR) Spektroskopisi analizi, dijital mikroskop görüntülemesi, temas açısı analizi ve antifungal duyarlılık ile karakterize edilmiştir. Kaplamasız PC için 87.84°, PMMA için 95.89° temas açısı verilmiştir. FTIR analizlerinde TEOS, kekik yağı, kimyon yağı, çay ağacı yağı ve karabiber yağı için karakteristik pikler elde edilmiştir. Dijital mikroskop görüntüleri için 2.059-49.322 µm aralığında kalınlık elde edilmiştir. Anrifungal duyarlılık testinde Aspergillus flavus küfü için ek etkili olanlar sırasıyla kekik yağı, çay ağacı yağı, kimyon yağı, TEOS ve karabiber yağı sırasını takip etmiştir. Anahtar Kelimeler: Antifungal, Silan, Esansiyel yağlar, Kaplama, Polimer
Investigation of corrosion properties of Ni matrix nanocomposite coatings produced by electrodeposition technique
This research aimed to investigate electrochemical corrosion behavior of Nickel matrix nanocomposite coatings produced by electrodeposition technique in a Watts bath containing titanium dioxide and Zinc doped titanium dioxide nanoparticles. In this study, titanium dioxide and Zinc doped titanium dioxide nanoparticles were prepared using a sol-gel method. Obtained results indicate that all synthesized nanoparticles and particle sizes were below 100 nm. Nickel matrix nanocomposite coatings were produced by using electrochemical deposition tecnique on stainless steel substrates. The Watts bath for production of nanocomposite coatings were prepared using the different amounts of titanium dioxide and Zinc doped titanium dioxide nanoparticles. Besides, applied current density on the coating performance were investigated in order to optimize the coating properties. Pure Nickel coatings were also deposited under the same experimental conditions for comparison. The structural, morphological, mechanical and corrosion properties of the Nickel matrix nanocomposite coatings were investigated. The surface morphology, elemental composition and phase structure of the nanocomposite coatings were examined by Scanning Electron Microscopy, Energy Dispersive Spectrometer and X-ray Diffraction, respectively. Obtained results show that Nickel-Titanium dioxide and Nickel- Zinc/Titanium dioxide nanocomposite coatings improved corrosion properties.
Theoretical investigation of CU based intermetallic compounds at nanoscale
Intermetallic compounds (IMCs), including transition metals and p-block metals, exhibit high resistance to oxidation and corrosion, low density, high conductivity, and magnetic polarizability. There is growing interest in intermetallic compounds (IMCs) consisting of transition metals and p-block elements, particularly aluminum (TM-Al IMCs). These alloys exhibit a unique combination of properties that make them well-suited for extreme thermal environments. Notably, they possess a favorable balance of low density and high melting temperatures, which contributes to their structural integrity and thermal stability. This thesis employs the first-principles computational approach grounded in Theory of Density Functional (DFT) to analyze the structural and electronic characteristics, charge density distribution, spin polarizability, and magnetic properties of Cu(3-x)MnxAl (x = 0, 1) intermetallic compounds. The study implemented the Perdew, Burke, Ernzerhof (PBE) exchange-correlation functional as part of the Approximation of Generalized Gradient (GGA) framework. The calculation of metallic and conductive nature and structural properties was performed simultaneously for all crystal lattices of Cu(3-x)MnxAl (L12, D03, and Heusler L21) with 221-Pm3m, 225-Fm3m space groups. Notably, the study clarifies the stoichiometric similarity and difference between L12 and D03 type structures by presenting a detailed discussion of the D03 structure and its targeted properties for the first time. The lattice constant values obtained by performing various optimizations shows remarkable consistency with previously reported theoretical and experimental measurements. Density Functional Theory-DFT calculations were utilized to analyze the electronic structurethe electronic structure, including band structure, total density and partial density of states, Major and minor spin state densities, map of charge density distribution, and Mulliken bond population. Additionally, the study investigated the chemical bonding characteristics and mechanical properties of intermetallic compounds (IMCs), such as elastic constants, elastic moduli, Pugh's ratio, elastic anisotropy, Poisson's ratio, and Cauchy pressure. The directional dependence of each mechanical property (young, bulk, shear modulus) and the corresponding mechanical properties were calculated. The electron density distribution and population analysis are consistent and reveal the dominant bonding type in each IMC. Furthermore, a Spin Polarizability analysis has been carried out to demonstrate the magnetic nature of the Cu2MnAl (L21) Full Heusler alloy upon the addition of the Mn atom.
Development of high temperature tribological features of electroless nib and NiB/Al2O3 nanocomposite coatings
This study examines the microstructural, mechanical, and tribological performance of electroless NiB and NiB-Al2O3 coatings applied to mild steel (St-37) substrates. In this dissertation, the electroless NiB and NiB-Al2O3 coatings were deposited onto the steel substrates to produce homogeneous microstructures using the electroless deposition method. The effects of electroless deposition parameters on the microstructure and the friction behaviours of the coatings were investigated in detail. A temperature-controlled wear testing setup was employed to evaluate their high-temperature tribological behavior. The investigation specifically explored the influence of Al2O3 nanoparticle concentration, the configuration of the wear test, and the testing temperature on the dominant wear mechanisms of the coatings. Tribological testing was carried out to assess the performance of the coatings under varying thermal conditions. The tests were conducted at four distinct temperatures: 25 °C (room temperature), 200 °C, 400 °C, and 600 °C to evaluate the influence of elevated temperatures on the friction and wear characteristics of the coatings. A ball-on-disk configuration was utilized for providing controlled and consistent test conditions. During the experiments, a constant applied load of 3 N was applied to simulate realistic contact pressures typically encountered in practical applications. By systematically increasing the temperature, the study aimed to observe and analyze how thermal effects, and changes in material properties, impacted the tribological behavior of the coatings. The results provided valuable insights into the coatings' ability to maintain wear resistance and frictional performance across a wide range of operating temperatures. The experimental findings revealed that the electroless NiB-Al2O3 nanocomposite coatings consistently demonstrated a lower wear rate across all tested temperatures compared to the electroless NiB coatings without Al2O3 reinforcement. This enhanced wear resistance was attributed to the incorporation of Al2O3 nanoparticles, which significantly improved the coatings' ability to withstand wear under varying tribological conditions. Detailed characterization of the microstructures of the coatings, worn surfaces, and wear mechanisms was carried out using advanced analytical techniques, including Scanning Electron Microscopy (SEM) for observing surface morphology, Energy Dispersive X-ray Spectroscopy (EDS) for elemental analysis, X-ray Diffraction (XRD) and Raman Spectroscopy for chemical and structural identification. These techniques provided a comprehensive understanding of the tribological behavior of the coatings and the role of Al2O3 in improving their performance under high-temperature conditions.
Preparation of polybenzoxazine-EPDM rubber based hydrophobic nanocomposite materials
The aim of this thesis is to prepare a hydrophobic nanocomposite with Polybenzoxazine (PBZ) and ethylene-propylene-diene-monomer rubber (EPDM) filled by nano titanium dioxide (TiO₂) and polytetrafluoroethylene (PTFE/Teflon). In this work, the first step in the process is to synthesize fluorine-containing PBZ. Fluorine is intended to contribute to hydrophobicity of the PBZ. PBZ was synthesized by ring-opening polymerization, catalyzed by dimethyl amino ethanol (DMAE) base catalyst using benzoxazine monomer obtained from 4-hydroxy benzaldehyde, 2-(trifluoromethyl)aniline and paraformaldehyde. In order for the PBZ polymer to be ring-opening polymerization to take place, the reactants were magnetically mixed in an oil bath at 100 °C for 24 hours. As a result of polymerization, a hard brittle, light-yellow color solid polymer was obtained. Since the synthesized PBZ is a hard and brittle polymer on its own, it is necessary to get help from another polymer to improve the elasticity for polymer nanocomposite samples. Thus, it was prepared a blend with PBZ and EPDM rubber. Polymer nanocomposite samples with weigh ratios of 40% EPDM and 40% PBZ blend matrix, 10% nano TiO2 and 10% PTFE additives were prepared. Since at least one of the fillers must be nano-sized in order to meet the condition of being a nanocomposite, 0-20 nanometer TiO2 additive is used. Both nano TiO2 and PTFE additives helped to prepare a hydrophobic polymer nanocomposite. Since one of the matrix components is EPDM rubber, some of the samples were cross-linked with 0.1% sulfur by weight to perform the vulcanization step, which is an important step in the use of rubber material. Polymer nanocomposite samples prepared with and without sulfur were heated and cured with temperatures of 25 °C, 100 °C, 150 °C and 180 °C, respectively. The effect of sulfur and curing temperature on the hydrophobicity of polymer nanocomposite samples was studied. The EPDM-PBZ nanocomposites were also characterized by UV-vis., TGA-DTA, SEM, SEM-EDX, FTIR, contact angle measurement characterizations. The contact angle was noted as 101.1° for PBZE1-EPDM-PTFE-Nano TiO2 nanocomposite sample. According to the UV results, the samples showed wide range abroad absorption peaks. According to all test results, the preparation of a hydrophobic polymer nanocomposite was successful. It was observed that the additives were homogeneously distributed in the matrix, there was no agglomeration. When the prepared polymer nanocomposites were compared to whether they were hydrophobic or not, it was clearly seen that the temperature and the curing process by cross-linking with sulfur increased the hydrophobicity in the samples. In particular, the EPDM-PBZ polymer nanocomposite sample with sulfur, vulcanized at 150 °C presented better hydrophobic features with a contact angle of 110°.
M13 virus template as a new approach to electrochemical energy storage in Li-O2 breathing battery cathodes
Due to high potential energy densities of lithium-oxygen (Li-O2) batteries (11,140 Wh kg-1) have been explored as one of the most promising energy storage systems for the future generation of state-of-the-art batteries. During discharge, oxygen (from the atmosphere) is reduced at the cathode (Oxygen reduction reaction, ORR), where it reacts with lithium ions released from the lithium metal anode to generate Li2O2, and the discharge residue decomposes during charging (Oxygen evolution reaction, OER). Cathode catalysts significantly improve ORR/OER and the electrochemical stability of Li-O2 systems. To accelerate ORR and OER in Li-O2 cells, a suitable air cathode architecture must possess sufficiently porous distribution to allow oxygen diffusion, high conductivity to transfer lithium ions, chemically stable, and highly catalytic activity. Therefore, we first report metal nanoparticles (e.g., Pd and Ru) and α-manganese oxide nanowire supported by reduced graphene oxide. In the Li-O2 cathode, noble metals are used as oxygen evolution reaction (OER) electrocatalysts to minimise charge overpotential and provide stable cycling performance. MnO2 is an appealing, useful transition metal oxide catalyst in Li-O2 batteries due to its cost effective, high catalytic activity, and good oxygen reduction characteristics. In the first experiment, Ruthenium nanoparticles were incorporated on MnO2 surfaces, and then the mixture was applied to 50% graphene via ball milling. This electrode demonstrates the charge overpotential and stability up to 40 cycles at a limited capacity of 800 mAh g-1. The produced rGO@Pd@α-MnO2 hybrid nanocomposite cathode delivered a full discharge capacity of 7500 mAh g-1 and maintain cycle life upto 50 cycles with a low discharge/charge potential gap of 0.4 V. Our result shows higher stability of Pd despite Ru. Furthermore, graphene-based electrodes with different graphene content (e.g. 100%, 75%, 50%) were prepared, and by reducing graphene, the higher performance of Li-O2 cell was obtained due to preventing side reactions. On the other hand, plant extract and M13 virus were utilized for the reduction of graphene oxide and preparation of MnO2 nanowires, respectively. Using these biomaterials assist in designing advanced nanomaterials through a green and biocompatible process. Overall, the synergistically effects of α-MnO2 nanowires and metal nanoparticles are combined in this study by decorating graphene sheets to boost cyclability and capacity, resulting in highly efficient Li-O2 cell performance.
Lityum iyon piller için yüksek kapasiteli LiFePO4/C/rGO nanokompozit pozitif elektrot
The development of new electrode materials with superior electrochemical capabilities, primarily dictated by the cathode materials, is required for widespread and extended applications of Li-ion secondary batteries. Because of its excellent stability, availability, and environmental friendliness, LiFePO4 (LFP) is widely recognized as a viable cathode material. This study used a low-cost iron (III) as the base material to manufacture single-phase LFP material with submicron particles using a simple solution combustion process based on the glycine–nitrate technique. The optimal Glycine to LiFePO4 ratio was found to be as 1:4 to produce high purity LiFePO4 and produced LiFePO4 showed 102 mAh/g discharge capacity at the constant rate of C/20. Sucrose was utilized as a carbon source to obtain carbon-coated LiFePO4 powders. The discharge capacity of the as-prepared LiFePO4/C sample with 12% carbon content is around 157 mAh/g at a 0.1 C rate and 88 mAh/g at a 5 C rate. Furthermore, throughout the 50-cycle at varying current rates, the electrodes showed excellent cycling performance. To enhance the capacity of carbon-coated LiFePO4, different amount of Graphene was reinforced to the cathode material. The carbon-coated lithium iron phosphate with 4 wt.% graphene showed a specific capacity of 197 mAh/g. The highly conductive graphene flakes wrapped around carbon-coated lithium iron phosphate enhance electron migration during charge and discharge operations, decreasing irreversible capacity during the first cycle and resulting in a coulombic efficiency of 99% at varied C-rates.
Nano silicon reinforced carbon anodes for high-capacity lithium ion battery: State of charge (SOC) and battery life time testing
The importance of active materials for anodes has gained significant attention in recent times. Carbonaceous materials are typically used as anode candidates in lithium-ion batteries (LIBs), but their low theoretical capacity of 372mAh/g restricts their applications in advanced LIBs. Therefore, Silicon (Si) is considered a prominent alternative anode material for LIBs to replace graphite. Since the theoretical capacity of Si is ten times higher than graphite; however, it suffers from massive mechanical deformations induced during cycling. For this purpose, composites of Si-graphite are proposed for better cycling performance and increased specific capacity. Herein, nano Si powder (<100nm) containing mesocarbon microbeads (MCMB) composites are prepared, and their rate capabilities as anode material for LIBs have been investigated at different current densities. Diverse compositions of the active anode materials (Si and MCMB), carbon black (CB), a binder sodium carboxymethylcellulose (CMC-Na), and distilled water as a solvent have been utilized for the fabrication of anodes, and the fabricated anodes have been morphologically and electrochemically characterized. Moreover, the state-of-charge (SOC) analysis has been evaluated by setting three different upper and lower cut-off voltages. Our analysis revealed that a composite comprising the lowest Si content (5wt%) exhibited better rate performance and retained a capacity of 455mAh/g after 60 cycles. 15wt% Si showed the worst rate capability performance. Similarly, in theSOCanalysis,a moderate voltage window between 1-0.05V was found optimalon the basis of rate capability results. Voltage window between 1-0.07V lead to quick capacity loss and large surface cracks confirmed in FESEM images. Additionally, in the SOC analysis, 5wt% Si showed the best cycling performance and lost only 10% of its capacity at 1C and 13% at C/2 after 200 cycles between 1-0.05V.
Nanoyapılı Pt ve Pt-Ag alaşımlarının üretimi, karakterizasyonu ve hidrojen gaz algılama özelliklerinin incelenmesi
This thesis presented hydrogen (H2) sensing properties of platinum (Pt) and platinum-silver (Pt-Ag) thin films. Pt and PtAg films were deposited on glass substrate by magnetron sputter technique. The Pt thin films with different thickness (2-50 nm) were prepared using RF sputtering method. The thicknesses of the films were controlled by a piezoelectric sensor placed in sputter system at the same time of coating process. On the other hand in this study, 3 nm PtxAg1-x (x: 0.95, 0.90, 0.80 and 0.50) thin films were coated by co-sputtering technique. The structural properties of Pt and PtAg alloy films were characterized by X-ray diffraction (XRD), scanning electron microscopy (SEM), X-ray photoelectron spectroscopy (XPS) and energy dispersive X-ray spectroscopy (EDX) techniques. Hydrogen sensing properties of the Pt and PtAg films were investigated depending on film thickness, temperature and concentration. Temperature dependent resistances and the gas measurements of the Pt and PtAg thin films were studied under a dry air flow and hydrogen ambient at a temperature range from 30 °C to 200 °C. Thus the best working performances of Pt and PtAg sensors were detected. The results showed that the resistance is directly proportional with temperature, and inversely proportional with the thickness of Pt thin film sensors. The H2 sensing properties of Pt thin film sensors were examined in the concentration range of 0.1 % - 1 % H2. Among the results for Pt thin films, it was revealed that the Pt thin film with 2 nm thickness exhibited the best sensing performance to H2 at 30 °C under dry air flow. The best response time was obtained at high temperatures for Pt thin film sensors. H2 sensitivity of PtAg sensors were also investigated in the concentration of 25 ppm - 1000 ppm H2. The resistances and the sensitivities of PtAg thin film sensors were increased with enhancing the temperature. Among the results for PtAg sensors, 3 nm Pt0.80Ag0.20 sensor showed the best sensitivity properties at 150 oC.
Optoelekrtonik uygulamalara yönelik nano malzeme destekli florofor, fosfor veya fosfor karışımlarının polimerik matriksler içerisinde incelenmesi
In this thesis we investigated the interactions between the commercially available LED phosphorus and nano-scale materials or dyes in terms of their emission abilities in polymers. In the first part of the thesis, photoluminescence of the Eu2+ doped Ca-α-Sialon (Ca-α-SiAlON:Eu2+), Ce3+ doped lutetium aluminum garnet (LuAG:Ce3+) and their binary blends with the quinine sulphate (QS) were investigated by steady-state and decay time measurements. The Ca-α-SiAlON:Eu2+ exhibited 44% increase in the intensity when blended with the QS. Similarly, the binary blend of QS-LuAG:Ce3+ exhibited 98% enhancement in the intensity. Excited state lifetimes of the phosphors were also studied in nanosecond and microsecond time scales, respectively. Spectral data presented some evidence for the donor-acceptor relationship of the QS/ Ca-α-SiAlON:Eu2+ and QS/LuAG:Ce3+ counterparts where the QS was the donor. The offered phosphor blends, exhibited enhancement in the optical brightness without any spectral shift. In the second part of the thesis, CO2 sensitive HPTS dye was used along with the bioactive glasses and ionic liquid. The bioactive glasses equipped with the rare earths of Er3+, Tb3+ and Er3+and Tb3+, were chosen due to their porous structure, optical transparency and intrinsic fluorescence. After spectral characterization steps we exposed the composites towards varying concentrations of the CO2 and recorded the intensity based response both in steady-state and kinetic mode. We also determined the decay times in the absence and presence of the CO2. We obtained promising results from the studies performed by using the bio-compatible bioactive glasses in terms of enhanced optical brightness and CO2 sensitivity.
Organik-inorganik hibrit nanokompozit malzemenin hazırlanması, karakterizasyonu, optimizasyonu ve uygulaması
Kurkumin, zerdeçal (Curcuma longa) köklerinde bulunan ve antioksidan, antienflamatuar, antimikrobiyal ve antikanserojenik aktiviteler sergileyen doğal bir polifenoldur. Kurkumin sahip olduğu olağanüstü biyolojik özellikleri nedeniyle farmasötik açıdan ilgi çekici bir terapötik ajandır. Bu umut verici biyomedikal özelliklere rağmen, serbest kurkumin moleküllerinin sudaki çözünürlüğünün az olması nedeniyle klinik etki ve biyoyararlanımı düşüktür. Bu nedenle, çözünürlüğünü ve biyouyumluluğunu arttırmak için ilaca uygun bir dağıtım sistemi sağlamak esastır. Bu çalışmada, nanokompozit malzemelerin sahip oldukları üstün özellikler ile moleküler baskılanmış polimerlerin kompozitlere kattığı yüksek seçicilik, mekanik kararlılık, tekrar kullanılabilirlik gibi üstün özelliklerinden yararlanılarak kurkuminin spesifik bağlanması ve kontrollü salımı için karbon bazlı moleküler baskılanmış nanokompozit ilaç dağıtım sistemi geliştirilmesi hedeflenmektedir. Bu amaçla, fonksiyonel monomer olarak kitosan ve derin ötektik çözücü ve fulleren kullanılarak hazırlanan CTS-DES-FUL@MIP nanokompoziti, deneysel tasarım ile dizayn edilmiş ve miniemülsiyon polimerizasyonuna göre sentezlenmiştir. Sentez parametrelerini etkileyen sekiz değişkenin (kitosan miktarı, fulleren miktarı, SDS hacmi, karıştırma hızı, sıcaklık, çapraz bağlayıcı miktarı, hegzadekan miktarı ve DES miktarı) taranması Plackett-Burman tasarımı ile yapılarak kurkuminin adsorpsiyonu için önemli olan parametreler belirlenmiştir. Daha sonra bu parametreler, tepki yüzeyi metodolojisi ile optimize edilmiştir. Ayrıca, optimize koşullar altında sentezlenen CTS-DES-FUL@MIP nanokompozitinin spesifik bağlanmasının belirlenmesi amacıyla adsorpsiyon parametrelerinin optimizasyonu ve adsorpsiyon performansı incelenmiştir. CTS-DES-FUL@MIP nanokompozitinden kurkuminin kontrollü salımı, simüle edilmiş gastrointestinal sıvılarında inkübasyon yöntemiyle araştırılmıştır. CTS-DES-FUL@MIP nanokompozitinden 120 saatlik sürenin sonunda salım %96,90 oranında gerçekleşmiştir. Buna dayanarak, baskılama işlemine bağlı olarak kurkumin ile CTS-DES-FUL@MIP nanokompozitin fonksiyonel monomerleri arasındaki yüksek spesifik etkileşimler nedeniyle uzun sürede salımın gerçekleştiği söylenebilir. Sonuç olarak, sentezlenen kurkumin baskılanmış polimerin kurkumin için etkili bir taşıyıcı olabileceği söylenebilmektedir.
Epoksi termoset polimer sistemlerin mekanik karakteristiklerinin nanoyapılar kullanılarak geliştirilmesi
Epoxy thermoset polymer composites are extensively utilized in a variety of industries, including the automotive, aviation, space, marine and electrical-electronic industries due to their outstanding mechanical, chemical, thermal, and electrical properties. However, since the neat epoxy intrinsically has a brittle structure, it should be incorporated with various particles to improve the fracture resistance and toughness. In this study, silica particles varying with different particle sizes and filler contents were used to prepare diglycidyl ether of bisphenol-A (DGEBPA) epoxy composite cured with methyl tetra hydro phthalic anhydride (MTHPA) to examine the impact of filler content and particle size on the composite's fracture behaviour. In accordance with ASTM-D5045 standard, linear elastic fracture mechanics were used to describe the fracture behaviour of composite materials. It was concluded that the fracture toughness increases with increasing particle size at the micro dimension but decreases inversely when shifted towards the nano dimension. The fracture surfaces were examined by SEM imaging technique, and toughening mechanisms were defined depending on the silica particle size and content. Before the fracture mechanics test studies, a time temperature transformation (TTT) diagram was constructed for the existing epoxy composite system, which can be used as a tool for the optimization of the process parameters.
ZnO nanoyapıların üretilmesi, karakterizasyonu ve uygulama alanlarının araştırılması
It is common knowledge that zinc oxide (ZnO) as a substantial semiconductor material because of its broad band gap (3.37eV) and good seperation energy (60 meV). Anodic oxidation of ZnO molecules have drawn interest because of their cost-effective synthesis, high efficiency and simplicity of the process. Anodization parameters (voltage, time, ph, electrolyte) can influence the morphology of ZnO. Also, ZnO is widely used in several implementations such as photovoltaic cell, chemical sensor, antibacterial agent and photocatalysts. Structures and different morphologies of ZnO can exert influence on its photocatalytic activity. In this thesis, ZnO nanostructures were produced succesfully through anodic oxidation method. Before anodization, a large portion of bulk Zn was cut off into nine pieces with dimensions 3x3 cm2. These samples were sanded up to acquire the appropriate material surface. After that, samples sonicated in ethanol, acetone and deionized water in an ultrasonic bath for ten minutes separately. Produced ZnO samples were heat treated at 300 °C for one hour with the heating rate of 5 °C/minute. The synthesized ZnO nanostructures were characterized to investigate their structure, elemental composition, photocatalytic activity and morphology with aid of X-ray diffraction, X-ray photoelectron spectroscopy, scanning electron microscopy and UV-Vis spectrophotometer. Concludes from this produced ZnO specimens can make use of as photocatalyst.
Termal analizler için mikro ve nano yapılı aygıtlar
The recent advent of micro and nano devices increased the interest in small scale material properties, such as elasticity, conductivity or heat capacity, which are considerably different from their bulk counterparts due to, primarily, increasing surface to volume ratios. These novel properties must be analyzed by using ultra-sensitive devices since characterization of these properties is not possible with conventional probing instrumentation due to their large mass or volume which decreases signal to noise ratio. Microelectromechanical systems (MEMS) with short response time and high sensitivity are suitable for such measurements, such as very small mass detection (zeptograms) and calorimetry of small volume materials (yoctocalories).In this thesis a MEMS cantilever was used for thermomechanical characterization of thin film amorphous semiconductors. 100 nm thick As2S3 and Ge-As-Se-Te glasses were thermally evaporated onto a bilayer microcantilever. The microcantilever was deflected and vibrated by electrothermal actuation. By monitoring deflection, amplitude and phase of the cantilever oscillation, multiple glass transition and melting points were identified; the effects of the variation of thermal expansion coefficients (CTE), reversible and irreversible heat capacities and Young?s modulus of the thin film samples were observed simultaneously. Hence the possibility of the integration of calorimetry, thermomechanical analysis (TMA) and dynamical mechanical thermal analysis (DMTA) in a single MEMS device was demonstrate
Nanomalzemelerin sentezi ve [Ru(bpy)3]2+ kompleksi ile birlikte sensör özelliklerinin araştırılması
In this study, optical properties of tris(2,2-bipyridyl)ruthenium (II) chloride ([Ru(bpy)3]2+), a ruthenium complex, together with various nanoparticles (TiO2 and core-shell TiO2@Ag nanoparticles) were investigated in the oxygen-permeable polymeric material. Plasticizer containing polymethylmethacrylate (PMMA) was shaped in form of thin film by applying the spin coating process and its optical properties and sensitivity towards oxygen were observed. It is known from previous studies that the [Ru(bpy)3]2+ complex exhibits extraordinary optical properties and high oxygen sensitivity when embedded in the above-mentioned matrix and used in combination with silver nanoparticles. In our thesis, the presented design is totally different from the earlier published literature. The porous and straight thin composite films were fabricated via the spin coating technique. Unlike the previous studies, the semiconductor TiO2 and core-shell TiO2@Ag nanoparticles were doped into these composite materials and the spectral properties of the prepared thin films were examined. Luminescence signal variations resulting from the application of oxygen sensor at 626 nm were recorded.
Çeşitli yöntemlerle magnetit nanotaneciklerin hazırlanması ve karakterizasyonu
Magnetite nanoparticles are used in various fields including iron-containing fluid, catalyst, pigments, magnetic recording media, medical diagnosis and treatment. Size of the particles and their morphology, electrical, optical and magnetic properties and limit their use. Synthesis methods determine the morphological homogeneity and size distribution of nanoparticles. Currently there are printing materials called toners that are imported for use in many printers of various brands and models. Iron-based inorganic minerals with different magnetic properties are used in these materials. The aim of this study is to prepare and characterize magnetite nanoparticles for use in printers and photocopiers. In this context, co-precipitation, thermal synthesis, sol-gel synthesis, reverse micelle synthesis, hydro-/solvo-thermal, sonochemical, microwave, and biosynthesis have been proposed. Magnetite nanoparticles were synthesized by co-precipitation and solvothermal/ hydrothermal methods. Stability of the nanoparticles stability is achieved by coating with oleic acid (OA), stearic acid (SA), sodium dodecyl sulfate (SDS), hexadecyltrimethylammonium bromide (CTAB), (3-aminopropyl)triethoxysilane (APTES), oleyl amine (OAm) and hexadecyltrimethoxysilane (HDTMS). Characterization of the prepared samples was performed by techniques such as XRD, FTIR, TGA, SEM, XPS and VSM.
Elektrokromik cihaz uygulamaları için metal oksit ince film katmanlarının mıknatıssal saçtırma tekniğiyle kaplanması
Electrochromism is the property of certain materials which involves a change from a bleaching state to a colored state as effect either by the action of an electrical voltage or current. Electrochromic devices (ECD) are formed by materials that are capable of continuously and reversibly modulating their color, usually from a bleaching state to a colored one, with the application of a small electric current. Among this electrochromic materials, WO3 and NiOx metal oxides are the dominant among the electrochromic metal oxides. The applied electric current induces in them a reaction of reduction (gain of electrons) or oxidation (loss of electrons) that modifies the range of energies in which the compound interacts with visible light. In this work WO3 and NiOx were deposited onto ITO coated glass by reactive DC magnetron sputtering in Ar/O2 mixing gas at room temperature. For the deposition process was employed off-axis sputtering method in which the substrate is positioned out of the high-energy particles. The electrochemical properties of the WO3 and NiOx series were measured by using conventional three-electrode configuration in 1 M LiClO4-PC electrolyte.Then with the aim to test the performance of the electrochromic metal oxide films, a five-layer battery-like structure ECD (ITO/WO3/electrolyte/NiOx/ITO) was assembled with an Li+ based liquid electrolyte.The results confirm that off-axis magnetron sputtering provides good feasibility to deposit metal oxide thin films with a good electrochromic performance.
Dijital radyografi sisteminin tasarımı, geliştirilmesi ve üretimi
The development of scintillation materials are important because of the ever-increasing need for materials in high-energy physics and digital radiography. The present composition of the scintillators consists of organic or inorganic materials, each of which is suitable for different applications. Inorganic crystal scintillators are widely used because of their superior energy solubility and stiffness for high energy radiation. In the scope of the thesis, inorganic Gd2O2SO4 phosphorescent nanoparticles which are doped with pure and rare earth elements (Dy3+, Ce3+, Eu3+, Ho3+, Pr3+, Tb3+) are optimized according to the density of the dopants. In line with this optimization, scintillator materials were produced by the sol-gel method and characterized. The characterization process was carried out separately in three different production stages, namely solution, gel, and final product. In this process, the pH and turbidity values of the solutions were determined. Slightly acidic (pH: 6.1) and fully dissolved solutions were obtained. FTIR analysis was performed to determine organic bonds to the sol-gel material, and DTA-TG thermal analyzes were performed to determine exothermic-endothermic reactions. The heat treatment temperature required to find the correct phase was determined at this stage. The final product was then obtained and characterization was completed using FTIR, XRD, XPS, SEM and PL devices, respectively. When the characterizations are evaluated in detail, it is seen that the produced Gd2O2SO4: RE3+ nanoparticles are successfully produced in the desired phase structure and nanostructure. In addition, the specific emission spectra and decay times of each of the nanoparticles activated with different rare earth elements have been determined. This clearly shows that the produced scintillators can also be used in different detectors for the intended purpose in digital imaging.
Savunma sanayiinde aşırı koşullara maruz kalan hafif alaşımların yüzey modifikasyonu
Bu çalışmada, alüminyum oksit, silisyum oksit, wolfram-titanyum karbür ve titanyum karbür parçacıklar ilave edilerek hazırlanan çözeltilerde, plazma elektrolitik oksidasyon (PEO) yöntemiyle AA7075 alaşımı üzerine seramik kaplamalar geliştirilmiştir. Parçacıkların ilave edildiği ana çözeltinin kimyasal bileşimi, en düşük gözenekliliğe ve en yüksek sertliğe sahip kaplamayı elde etmek için yapılan optimizasyon çalışması sonucunda belirlenmiştir. Kaplamaların faz bileşimi x-ışını kırınımı (XRD) yöntemiyle incelenmiştir. Taramalı elektron mikroskobu (SEM) ile kaplamaların yüzey morfolojisi ve kesitin mikroyapısı incelenmiştir. Enerji dağılımlı x-ışını spektrometresi (EDX) sayesinde kaplamaların kimyasal analizi yapılmıştır. Kaplamaların sertlik değerleri mikroVickers sertlik test cihazıyla ölçülmüştür. Kaplama yapılan altlık alaşımların sürtünme ve aşınma davranışını incelemek amacıyla 100Cr6 çelik ve alüminyum oksit bilyelere karşı kuru kaymalı aşınma testleri yapılmıştır. Aşınma testi sonrası yüzey profilometresiyle aşınma profili çıkarılarak aşınan malzeme hacmi hesaplanmıştır. Yapılan testler sonucunda AA7075 alaşımın yüzey sertliği ve aşınma dayanımının üretilen PEO kaplamalarla önemli ölçüde arttığı gözlenmiştir. Kaplamalar yoğun iç tabaka ve gözenekli üst tabakadan oluşmaktadır. Kaplama sertliğinin altlık/kaplama arayüzeyine yakın bölgede yüksek, yüzeye doğru ilerledikçe gözenekliliğin artışından dolayı düştüğü belirlenmiştir. Silisyum oksit parçacık içeren çözeltilerde üretilen kaplamaların diğer kaplamalara göre daha kalın ve pürüzlü olduğu tespit edilmiştir. En düşük aşınma kaybı titanyum karbür içeren çözeltilerde üretilen kaplamada elde edilmiştir.
Doğrudan alkollü yakıt pilleri için yenilikçi katalizör sentezi
In this thesis work, non-precious nitrogen-doped iron-nickel and iron nanoparticles, supported on three-dimensional reduced graphene oxide, are prepared via a combination of sacrificial support method and wet impregnation method as alternative anode catalysts to precious metal catalysts of the direct methanol fuel cells for electro-oxidation of methanol. Graphene oxide was synthesized via an improved Hummers method. Nitrogen doping was carried out by the pyrolysis of urea, which also provided the reduction of graphene oxide support simultaneously. Electrocatalytic activities of the catalysts for methanol electro-oxidation in acidic media were obtained by cyclic voltammetry (CV). Morphologies of the synthesized materials were obtained using scanning electron microscopy (SEM). The presence and distribution properties of the nanosized iron and nickel particles were detected via scanning electron microscopy-energy dispersive X-ray spectroscopy (SEM-EDS). Quantitative analyses of iron and nickel were conducted by inductively coupled plasma-optical emission spectrometry (ICP-OES). X-ray photoelectron spectroscopy (XPS) analyses were executed to obtain the surface chemical composition and bonding of the synthesized materials and to prove the formation of the alloy. Crystal structures of the materials produced were determined by examining their X-ray diffraction (XRD) patterns. Thermogravimetric analyses (TGA) of the samples were done under a nitrogen atmosphere to obtain their thermal behaviors.
Memristans malzemelerin FPGA sistemlerde simülasyonu ve performansının incelenmesi
Günümüz teknolojisinde tümleşik devreler üzerindeki bileşen sayısı Moore yasası sınırlarına ulaşmış olup halihazırda kullanılmakta olan Complementary Metal Oxide Semiconductor (Cmos) teknolojisinin getirilerini arttıracak geleceğin teknolojileri araştırılmaktadır. Bu teknolojiler arasında memristör teknolojisinin düşük güç tüketimi, düşük alan işgali ve en önemlisi sistem gücü kesilse dahi veriyi tutabilmesi rakipleri arasında yıldızının parlamasına sebep olmuştur. Bu tezde, memristörler ile mantık tasarımları, memristörlerin Complementary Metal Oxide Semiconductor (Cmos) sistemlere melez yapılarda entegrasyonu, Complementary Metal Oxide Semiconductor (Cmos) uyumluluğu Virtuoso Cadence Design Envoriment programında simule edilmiş, Field Programmable Gate Array (FPGA) ve veri depolama sistemlerinde kullanılan çapraz çubuk (Crossbar) mimarilerinde memristör teknolojisinin getirdiği sinsi akım (sneakpath current) problemleri gibi sorunlar ve çözüm yöntemleri araştırılarak farklı çözüm yolları önerilmiştir. Bu tezde memristör teknolojisinin araştırılması, milli teknoloji atılımımızda yeni teknolojilere entegrasyonun daha kolay sağlanmasına ve bu konuda söz sahibi olunmasına yardımcı olacağı düşünülmektedir.
Katkılı nanopartikül içeren kaplamaların yapısal özelliklerinin incelenmesi
Main purpose of this thesis is to synthesize doped nanoparticles with sol-gel method in order to use them for deposition of Ni based nanocomposite coatings by electrodeposition technique and to investigate its effect on structural properties of the nanocomposite coatings. At first, undoped, Mn doped and Mn-N codoped titanium dioxide nanoparticles were synthesized by sol-gel method. Titanium tetraisopropoxide were used as the precursor. Structural analysis and particle size measurements of the nanoparticles were conducted by using X-Ray Diffraction (XRD) and particle size analyzer, respectively. Subsequently, Ni and Ni based nanocomposite coatings were fabricated on steel substrate by electrodeposition method. XRD and Scanning Electron Microscope (SEM) analysis were done to investigate crystalline structure and surface morphology, respectively. Electrochemical measurements of Ni and Ni based nanocomposite coatings were performed using a Gamry potentiostat/galvanostat system controlled by Gamry Framework Software. It was observed that nanocomposite coatings with doped nanoparticles has shown enhanced surface properties, compared to the undoped nanoparticle coatings.
ZnO, CuO ve γ-Fe3O4 nanopartiküllerin yeşil sentezi ve buğday genotipleri üzerindeki etkilerinin doku kültüründe araştırılması
Yapılan bu tez çalışmasında; ZnO, CuO ve γ-Fe3O4 nanopartikül yapılarının yeşil sentez yoluyla sentezlenmesi, karakterize edilmesi, iki farklı buğday genotipi üzerine olgun embriyo kültür tekniği kullanılarak etkilerinin araştırılması amaç edinilmiştir. Nanopartikül yapılarını sentezlemek için Euphorbia (Euphorbia amygdaloides) bitkisi ekstraktından elde edilen peroksidaz enziminden faydalanılmıştır. Kısmi olarak saflaştırılan peroksidaz enziminin %60-80 amonyum sülfat çöktürme yöntemiyle Euphorbia (Euphorbia amygdaloides) bitkisinden 149.5 kat saflaştırıldığı belirlenmiştir. Peroksidaz enzimi kullanılarak ZnO, CuO ve γ-Fe3O4 nanopartikül (NP)'lerin yeşil sentezi gerçekleştirilmiştir. Bu amaçla; NP'lerin sentezi için pH, sıcaklık, zaman, metal iyonu konsantrasyonu gibi çeşitli biyokimyasal verilerin optimizasyon işlemleri yapılmıştır. Elde edilen bulgulara göre ZnO, CuO ve γ-Fe3O4 nanopartiküllerin sentezlenme süreleri sırasıyla 30 dk, 30 dk ve 15 dk olmuştur. Optimum sentezlenme pH'larının 7.5, 8.0 ve 11.0 olduğu saptanırken, 30°C, 25°C ve 20°C'ler optimum sentez sıcaklıkları olarak belirlenmiştir. Elde edilen nanopartikül yapılarının karakterizasyonu için FT-IR, XRD ve SEM spektrum analizleri yapılmıştır. ZnO NP yapıları 60-80 nm arasında boyutlara sahipken, CuO NP yapıları 50-120 nm arasında, γ-Fe3O4 NP yapılarının ise 30-80 nm arasında boyutları arasında olduğu belirlenmiştir. Çalışmanın devamında ZnO, CuO ve γ-Fe3O4 nanopartiküllerinin, Kırik ve ES-26 olmak üzere iki ayrı buğday (Triticum aestivum L.) genotipinin olgun embriyo kültüründe, mikro element olarak etkileri araştırılmıştır. Bu kapsamda NP yapılarının hem Murashige and Skoog besi ortamında var olan normal miktarıyla(1x), hem de bu miktarın iki(2x) ve üç(3x) katları şeklinde test edilmiştir. Çalışma negatif ve pozitif kontrollerle desteklenmiştir. Elde edilen bulgularda, nanopartikül içeren uygulamalarda gelişmeye bırakılan buğday embriyolarının nanopartikül yapılarından aktif bir biçimde yararlanamadığı düşünülmektedir. Sonuç olarak kontrole kıyasla nanopartikül içeren uygulamaların gelişimleri daha az olmuştur. Tüm uygulamalar arasında kallus oluşum oranı bakımından 3x CuO NP içeren ortamlar ile 3x ZnO NP içeren ortamların kontrollere kıyasla daha başarılı sonuç verdiği belirlenmiştir. Bitki oluşturma kabiliyeti bakımından en başarılı grup kontrol grubu olmuştur. Bu doğrultuda kontrole kıyasla bitki rejenerasyonunun nanopartikül uygulamalarıyla artış göstermediği görülmektedir. Ancak bu durumun temelde nanopartiküllerin bitki tarafından yararlanım süreciyle ilgili olduğu düşünülmektedir. Toksik bir etki oluşturup oluşturmadığı ise gelecek çalışmaların konusu olmaya adaydır. Bu çalışma, olgun embriyo kültüründe yeşil sentez yoluyla elde edilen NP yapılarının test edilmesi noktasında bir ilk olma özelliği taşımaktadır. Bu durum embriyoların doku kültürü gelişim aşamalarına NP'lerin oluşturacağı etkilerin belirlenmesi noktasında literatürde bir eksikliği giderecektir.
Stronsiyum florür-germanıum içeren ince film cam üretimi ve karektrizasyonu
Bu araştırmada RF kopartma yöntemi kullanılarak, özelbir tür camın ince filmleri üretilmiştir. Bu çalışmada, ilk başlangıçta belirli miktarlarda: SrF2, SiO2, SrO, Al2O3, Na2CO3 ve K2CO3 malzemelerin karışımları kullanlarak ince film camlar elde edilmiştir. Daha sonra bu karışıma %3, %5 ve %10 oranlarında Ge katksı yapılarak camların soğuruculuk özelliklerideğiştirlmiştir. İlk olarak kaplamalar 6, 8, 10, 12, 14 ve 16 saat'de adi cam alttaşın üzerine yapılmıştır. Numunelerin XRD ve görünür ışık bölgesindeki soğurmaları analiz edilmiş ve 16 saat süre ile yapılan numunenin soğurma analizinde pik değerlerini net bir şekilde gözlemlenmiştir. Bu çalışma boyunca Ge un %3, %5 ve %10 yüzdesinde katkısı olan targetlerinin ince filmi, birde kuvartz alttaş üzerindede 16 saatde yapıldı ve numunelerinin XRD analizlerinde düzenli kristal pikleri oluşumu gözlemlendi. Farklı oranlarda kuvartz üzerinde yapılan numuneler, faz ayırma prensibi için, 570C 580C, 590C, 600C ve 610C sıcaklıkta, 3 saat süre boyunca fırın içerisine bırakıldı ve XRD sonuçları düzenli bir kristal oluşumunu gösterdi. Bu numunelerden XRD, SEM, soğurma analizi, geçirgenlik ve elektrik iletkenliği analizleri alındı.
ZnO, Fe3O4 ve ZnO/Fe3O4 nanopartikülleri immobilize luffa sponge lifleri kullanılarak atık sulardan direkt mavi 15 azo boyar maddelerin giderilmesi; kinetik ve denge modellemesi
Bu çalışmada Luffa sponge ve ZnO, Fe3O4 ve ZnO/Fe3O4 nanopartiküllerinin kullanımı ile oluşturulan membran formlarıyla (saf Luffa sponge, Luffa s.+ZnO, Luffa s.+Fe3O4, Luffa s.+ZnO/Fe3O4) Direkt Mavi 15 azo boyalarının sulardan uzaklaştırılması çalışılmıştır. Bu amaçla ilk olarak ZnO ve Fe3O4 nanopartikülleri yeşil sentez yöntemi ile Euphorbia amygdaloides'den kısmi olarak 149,5 kat ve 29,5 verimle saflaştırılan peroksidaz enzimi katalizörlüğünde elde edilmiştir. Sentezlenen nanopartiküllere yönelik karakterizasyon çalışmaları yapılmıştır. ZnO için 304 nm, Fe3O4 için 481 nm'de ölçüm alınmıştır. 30°C'de ZnO için pH 6,0 ortamı Fe3O4 için pH 8,0 ortamı optimum pH ortamları olarak belirlenmiştir. 5 mM ZnCl2 ve 1mM FeCl2-Fe2Cl3 konsantrasyonları ile maksimum nanopartikül sentezi sağlanmıştır. Nanopartiküllere ait SEM, FT-IR ve XRD ölçümleri alınmıştır. Acinetobacter calcoaceticus strain ve Pediococcus acidilactici bakterilerine karşı disk difüzyon metodu ile nanopartiküllerin antimikrobiyal aktivitesi bulunmuştur. Bu nanopartiküller kullanılarak saf Luffa sponge, Luffa s.+ZnO, Luffa s.+Fe3O4, Luffa s.+ZnO/Fe3O4 membran formları oluşturulmuştur ve SEM, FT-IR ve XRD karakterizasyonu yapılmıştır. Membran formları ile Direkt Mavi 15 azo boyasının adsorpsiyonu çalışılmıştır. Yapılan optimizasyon çalışmaları doğrultusunda optimum temas süresi 45 dk, optimum pH 8,0, optimum sıcaklık 20°C, optimum boya konsantrasyonu 200 mg/L, optimum Luffa sponge miktarı 0,025 gr olarak belirlenmiştir. Membran formları ile boyanın adsorpsiyonuna yönelik SEM, FT-IR ve XRD karakterizasyonu yapılmıştır. Her bir membran formu yapılan analizlerde farklı değerler sergilemekle birlikte birbirine yakın değerlerde sergilemişlerdir. Nanopartikül yüklü membran formları saf Luffa sponge membran formuna kıyasla avantaj sağlamıştır. Langmiur ve Freundlich adsorpsiyon izoterm, birinci ve ikinci dereceden reaksiyon kinetiği, termodinamik sabitlerin hesaplanması çalışmaları yapılmıştır. Anahtar Kelimeler: Remediasyon, Nanopartikül, Direkt Mavi 15, Luffa Sponge
GOx ve AOX enzimleri ile pirinç, bakır, alüminyum ve paslanmaz çelik iş parçalarının enzimatik nanobiyo-işlemesi
Çalışmada pirinç, bakır, alüminyum ve paslanmaz çelik iş parçalarının enzimatik nanobiyo-işlemesi yapıldı. Bu işleme yönteminde iki farklı enzim; glukoz oksidaz (GOx) ve alkol oksidaz (AOX) işleme aracı olarak kullanıldı. Enzimatik işlemenin temeli oksijen ortamında enzim ve substrat arasında gerçekleşen kimyasal tepkime esnasında hidrojen peroksitin (H2O2) yerinde üretimi ve ardından reaksiyon ortamında bulunan Fe2+ iyonlarının H2O2 ile Fe3+'e yükseltgenmesine dayalıdır ve biyo-Fenton reaksiyonu olarak tanımlanmaktadır. Bioreaksiyon ortamında bulunan metal iş parçalarının oksidasyonu üretilen Fe3+ iyonları tarafından sağlanmaktadır. Böylece bir işleme çevrimi gerçekleşmektedir. Bu çalışmada; enzimatik işlemeyi etkileyen parametrelerin (pH, sıcaklık, zaman, enzim miktarı vb.) biyo-işleme üzerine etkisi araştırıldı ve en uygun koşullar belirlendi. Yapılan enzimatik işlemenin metal iş parçaları üzerine etkisini gözlemlemek için SMRR miktarı, ayrıca yüzey morfolojileri ve yüzeyde oluşan pürüzlülük miktarları SEM ve AFM analizleri yapılarak belirlendi. Elde edilen sonuçlar metal parçalarının geleneksel yöntemlerle (HCl, H2SO4 ve H2O2) yapılan biyo-işleme sonuçlarıyla karşılaştırıldı. Paslanmaz çelik iş parçalarının enzimatik işlemeye bütün koşullar altında direnç gösterdi ve yüzeylerinde her hangi bir biyo-işlemenin gerçekleşmediği belirlendi. Tüm metal iş parçalarının enzimatik işlenmesinde; GOx enzimi AOX enzimine göre daha etkili işleme gerçekleştirdiği ve işleme koşullarında daha dayanıklı olduğu tespit edildi. Sonuçlara göre; GOx ve AOX enzimleriyle yapılan biyo-işlemeler, metallerin yüzeyinde herhangi bir tahribata neden olmadan üniform bir şekilde metal kaldırmayı gerçekleştirdiği, geleneksel yöntemlerle yapılan işlemede metal yüzeylerinin büyük ölçüde tahrip olduğu belirlendi. Ayrıca, enzimatik işleme sonucunda iş parçalarının yüzey morfolojisinin kontrol numuneye daha fazla benzerlik gösterdiği belirlendi.
Aspergillus sp. TK4 kullanılarak titanyum dioksit (TiO2) nanopartikülünün biyosentezi ve karakterizasyonu
Titanyum dioksit (TiO2) nanopartikülleri, boya, kozmetik, ilaç ve kağıt gibi birçok endüstriyel ve tıbbi alanda yaygın bir şekilde kullanılmaktadır. Bu çalışmada, Aspergillus sp. TK4 izolatı tarafından TiO2 nanopartiküllerinin daha güvenli, yeşil, ucuz ve kontrollü üretimine olanak sağlayan biyosentez yöntemi ile üretilmesi hedeflenmiştir. TiO2 nanopartikülleri Taramalı Elektron Mikroskobu (SEM) ve Enerji Dağınımlı X-Işınları Spektroskopisi (EDAX) analitik teknikleriyle karakterize edilmiştir. Nanopartiküllerin karakterizasyon verileri, TiO2 nanoparçacıklarının küresel bir yapıda olduğunu ve boyutlarının 50-200 nm arasında değiştiğini ortaya koymuştur.
RF saçtırma yöntemi ile InXGa1-XN üçlü bileşiğinin ince film olarak büyütülmesi ve karakterisitik özelliklerinin deneysel olarak incelenmesi
Bu tez çalışmasında radyo frekanslı magnetron saçtırma (sputtering) tekniği kullanılarak indiyum galyum nitrür üçlü bileşiği farklı büyütme parametreleri altında büyütülmüştür. InGaN bileşiğinin yapısal, optik ve morfolojik özellikleri ayrıntılı bir şekilde incelenmiştir. Yapısal analiz için XRD, XPS, Raman; optik özellikleri için soğurma ölçüm tekniği; morfolojik özellikleri için SEM ve AFM ölçüm teknikleri kullanılmıştır. Saçtırma tekniğiyle yapılan büyütmelerde optimum şartlar sağlamak için altlık, altlık sıcaklığı, RF güç değişimi, çalışma basıncı ve azot gazı akış oranı gibi birçok parametre dikkate alınmıştır. Büyütülen filmlerin XRD analizinde birçok film hekzagonal kristal yapı sergilemiştir. Farklı çalışma parametreleri altında büyütülen filmlerin XRD piklerinin yönelimi ve şiddeti değişmiştir. Bazı parametreler altında ise film yapısının dentritik yapıda olduğu gözlemlenmiştir. XPS sonuçlarında spektrumdan Ga, N, In ve O da dâhil olmak üzere dört çeşit element, hem yüzeyde hem de InGaN filmi içerisinde gözlemlenmektedir. Ayrıca büyütülen InGaN filmlerin kimyasal durumları da XPS ile incelenmiştir. Bu analiz için O (1s), In (3d5/2), Ga (2p3/2) ve N (1s) fotoelektron pikleri seçilmiştir. Göreceli olarak yüksek yoğunluklu O-ilişkili XPS O (1s) özelliği ile belirtildiği gibi, büyütülen InGaN filmlerin yüzeyi önemli derecede oksitlenmiştir. Raman analizinde InGaN bileşiğine ait optik fonon modları A1(LO) ve E2(high) olmaktadır. Raman analizi sonucunda InGaN filmine ait Raman değişimlerini gösteren piklerden silisyum altlığa ait olan pik 520 cm-1 değerinde çok güçlü olduğundan E2(high) moduna ait pik (430 cm-1 – 490 cm-1) çok zayıf olmaktadır. Diğer taraftan A1(LO) moduna ait pik ise çok yayvan bir şekilde görülmekte olup (616 cm-1 - 720 cm-1) aralığında oluşmuştur. Filmlere ait karakteristik Raman değişimi pikleri strenching modunda bulunmaktadır. SEM analizinde filme ait kristal yapısı ve tanecik sınırları belirgin bir şekilde görülmekte olup hem kristal oluşumu hem de dentritik yapı oluşumu desteklenmektedir. AFM sonuçlarında yapılarda yer yer tepeler ve çukurlar mevcut olup kısmen homojendirler ve topaklanmaya benzer daire şeklinde yumrular dağınık bir şekilde yerleşmiştirler. Ayrıca farklı parametreler altında büyütülen tüm filmler 0.48 nm-85.48 nm arasında çizgisel pürüzlülüğe sahiptirler. Optik özelliklere bakıldığında soğurma ölçümlerinde elde edilen yasak enerji aralığı değerlerinin tüm büyütme parametreleri dikkate alındığında en düşük 2.34 eV ve en yüksek 3.26 eV olduğu tespit edilmiştir. Elde edilen geniş yasak enerji aralığı, InGaN filmlerini çok sayıda bilinen PV aygıtı konfigürasyonunu ve tandem yapılarını mümkün kılan çok yönlü bir potansiyel PV malzemesi yapmaktadır. Morfolojik özelikleri nedeniyle optoelektronik ve mühendislikte sürtünme uygulamaları için uygun birer yapı olduklarını söyleyebiliriz. Ayrıca hekzagonal kristal yapıya sahip filmlerin de LED, lazer diyot ve güç elektroniği gibi aygıt uygulamalarında kullanılabileceğini söyleyebiliriz.
Deneysel meme kanseri modelinde disülfiram yüklü nanoparçacıkların antikanser etkisinin incelenmesi
Bu çalışmada toksik olmayan, biyouyumlu ve gözenekli yapıya sahip manyetik silika nano materyallerin (Fe3O4@mSiO2) kullanıldığı ilaç taşıyıcı sistemin hazırlanması amaçlanmıştır. İlaç taşıma sisteminin suda çözünürlüğünü artırmak ve kanser hücrelerine spesifikliğini sağlamak amacıyla ilaç yüklenmiş yapı, folik asit bağlı polietilenimin (PEI-FA) ile kaplanmıştır. Böylece ~160 nm boyutlarına sahip manyetik çekirdekli mezogözenekli folik asit takılı nano taşıyıcı sistem (mMDPF) hazırlanmıştır. mMDPF'lerin ilaç yükleme oranı %4,35 olarak belirlenmiştir. Partiküllerin ilaç salım kinetiği araştırılmış ve en iyi ilaç salımı pH 6,0'da 37°C'de elde edilmiştir. mMDPF, bakır ve/veya sodyum nitroprusit ile birlikte MCF-7 ve MCF-10A hücrelerine uygulanarak ilaç sisteminin meme kanseri tedavisinde etkinliği artırılmıştır. mMDPF'nin MCF-7 hücreleri tarafından daha fazla alındığı ve MCF-7'ye karşı toksik etkisinin MCF-10A'ya göre çok daha yüksek olduğu gözlenmiştir.