Master Degree / Yüksek Lisans Tezleri
Permanent URI for this collectionhttps://hdl.handle.net/11147/3008
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Master Thesis Molecular Dynamics Studies on Heat Transfer Control Between Water and Silica Using Nanoscale Surface Patterns(01. Izmir Institute of Technology, 2020) Özen, Celal Can; Barışık, Murat; Barışık, MuratDue to recent advances in manufacturing, component sizes have tremendously decreased in computer electronics and communication devices. Miniaturization has led to a substantial increase in memory and computational power but also created heat dissipation problems. Understanding heat transfer and temperature distribution in these devices became crucial for thermal management. At nanoscale, heat transfer through dielectric materials is mostly determined by phonon transport. The phonon passage is interrupted through the interfaces which creates temperature jumps and dominates the heat transfer rates at nanoscale. Kapitza length characterizes the interfacial thermal resistance as a function of temperature jump at the solid-liquid interface. In this study, heat transfer from different nanoscale surface structures were investigated using Molecular Dynamics simulations. The systems were created by two parallel silica walls and water between them. Kapitza length values were calculated for seven different surface conditions for two different molecular surface interaction strength parameters yielding high and low wetting conditions. Measured Kapitza length values were characterized based on cavity width (w), cavity height (h), and unit crystal cavity volume (Vc). While the increase in pattern cavity width increased Kapitza length, increasing pattern cavity height decreased Kapitza value. However, a general characterization based on cavity volume could not be obtained. Instead, almost a uniform behavior was observed through the variation of Kapitza length of different size patterns as a function of Ac=Vch/w^2. Kapitza length decreased by approximately 19% and 29% for high and low wetting conditions, respectively, when Ac increased. Then, similar characterizations were done for variation of heat flux. Overall, heat flux increased by approximately 20% and 30% for high and low wetting conditions, respectively, when Ac increased. Results are important to better understand and control heat transfer between water and silica using nanoscale surface patterns.Master Thesis Molecular Dynamics Studies on Wetting Behavior of Silicon Surfaces and Heat Transfer Characteristics of Electrolyte Solution Filled Silicon Nano-Channels(Izmir Institute of Technology, 2020) Özdemir, Abdullah Cihan; Barışık, Murat; Barışık, MuratSilicon has always been of interest to researchers from various fields, especially the semiconductor industry. Silicon and silicon-based materials are frequently used in integrated circuits and micro/nano-electro-mechanical systems. Interfacial phenomena between phases is important for these applications. In this study, surface wetting and heat transfer at the solid/liquid interfacial region were investigated using the Molecular Dynamics method. The control of wetting was examined by changing silicon structure at single crystal and amorphous forms and was correlated with the surface coating thickness. Contact angles on both single crystal and amorphous surfaces were calculated. To understand the molecular regions affecting the contact angle, the near interface height parameter was defined as the distance from the surface. Then, interface densities and contact angles of single crystal and amorphous structures were calculated at each height parameter. We defined an effective range of intermolecular forces for the control of wetting. Second, heat transfer characteristics at water/silicon interfaces were examined. Solid/liquid interface is important to determine heat transfer at nanoscale. We focused on the influence of ionic conditions on heat transfer for a water-NaCl solution between two silicon walls. The surface charge density showed variation by ionic condition. We calculated surface charges naturally forming at the corresponding electrolyte concentration. With the increase in salinity, the electrolyte solution density increased and thermal conductivity decreased. Results showed good agreement with the experimental measurements. Additionally, we observed a 35% increase in heat transfer due to a decrease in interfacial thermal resistance by increasing ionic concentration to the highest salinity value of standard conditions. Heat transfer at solid/liquid interface characterized by Kapitza length was correlated with the salinity.Master Thesis Increasing Doxorubicin (dox) Release From Liposomes(Izmir Institute of Technology, 2019) Hanoğlu, Berçem Dilan; Özdemir, Ekrem; Altun, Zekiye SultanCancer is the second most common cause of death in the world and its incidence is increasing day by day. Doxorubicin (DOX) is an anthracycline group drug frequently used in many cancer treatments including breast cancer. However, free DOX has many harmful side effects and need to be encapsulated into nanocarrier such as liposomes. Although liposomal DOX has many advantages over its free form, liposomal DOX has undesirable side effects such as hand and foot syndrome. In this thesis, it was aimed to develop a more effective liposomal DOX delivery and release systems. Liposomes were prepared with alkaline solutions containing tris, sodium carbonate, ammonium chloride, and ammonium sulfate. DOX loading into liposomes and the percentage of release from liposomes were examined. A loading efficiency of about 80% was achieved, while the release was found to be below 13% at room temperature. The release of DOX was found to be enhanced from liposomes in the presence of ammonia (NH3), whose content was dependent on pH. Temperature was also found an important parameter and enhances DOX release at higher temperatures than the phase transition temperature of the lipid. A two-component liposomal system was proposed where ammonia (NH3) would be released from one liposome and enhance the DOX release from other liposomes. It was found that temperature, pH, and ammonia (NH3) concentration affected DOX release from liposomes. As a result, DOX was successfully loaded into liposomes and ready to study their effect on breast cancer cells.Master Thesis Properties of Thin Film Lixlaytio3 Electrolyte for All-Solid State Li-On Batteries(Izmir Institute of Technology, 2016) Gülen, Sena; Aygün, Gülnur; Aygün Özyüzer, GülnurOne of the requirements of daily life, the most preferred rechargeable batteries are Li-ion batteries because of high energy, long life cycle and eco-friendly properties. Having high energy density, no memory effect and slow energy losses, these batteries have applications in portable electronic devices, power source for space vehicles, electric cars etc. Furthermore, there is a strong interest in all solid-state rechargeable lithium-ion battery research, because these batteries will replace the conventional liquid electrolyte Li-ion batteries due to use of non-combustible inorganic solid electrolyte, which has high safety and reliability. While the bulk ionic conductivity of La0.5Li0.5TiO3 (LLTO) produced by solid-state reaction is 10-3 S/cm, the total ionic conductivity of LLTO is 10-5 S/cm. Another way to increase ionic property is to dope the solid electrolyte with transition metals. The substitution of transition metal leads to decrease of the lattice parameter because of reduced average ionic radius. This causes increase of Li-ion content and also ionic conductivity. In this study, initially pure and Al doped targets were fabricated by using solid-state reaction after that the available targets are placed to the sputtering gun. When the all optimizations of the system were completed, pure and Al doped LLTO thin films were deposited by RF (radio frequency) magnetron sputtering technique on ITO coated soda lime glass substrates. While the thin film was been deposited, the substrate was heated at approximately 220 oC. For ionic conductivity measurement of the Al doped LLTO electrolyte, small circular Al contact regions were created on Al doped LLTO thin films by thermal evaporation system. Afterword the impedance spectra of the sandwich structure in a frequency range of 1 Hz - 200 MHz was recorded by using probe station. Thickness, the crystal structure, optical transmission, chemical compositions, surfaces and porosity of the thin films are investigated by surface profilometer, XRD, UV-Visible Spectroscopy, XPS, and Raman Spectroscopy respectively.Master Thesis Hydrothermal Preparation of Single Crystalline Ceo2 Nanoparticles and the Influence of Alkali Hydroxides on Their Structure and Optical Behavior(Izmir Institute of Technology, 2009) Kepenekci, Özlem; Eanes, Mehtap; Eanes, MehtapSingle crystalline cerium oxide nanoparticles were synthesized via hydrothermal method by mixing aqueous solution of cerium nitrate [Ce(NO3)3.6H2O] with an alkali base. Several characterization methods were used to identify morphology and crystalline nature such as X-ray Diffraction, Scanning and Transmission Electron Microscopes. This study is divided into three parts. In the first part, some controlling parameters like, that were affecting size and shape of CeO2 nanoparticles, were studied. It was found that size of CeO2 nanoparticles increased when increasing both reaction time and temperature. Alkali base concentration promoted the particle growth. Also, particle morphology was more uniform rather than aggregated in presence of higher concentrated alkali base. When the alkali base type was changed, the use of NaOH produced larger cubic nanocrystals of CeO2 than KOH and LiOH.Second part is related to determine the optical properties of CeO2 nanoparticles. Based on the UV-Vis and Fluorescence Spectroscopy results, size, bandgap and defect level of CeO2 nanoparticles can be easily determined. Nanoparticles in presence of NaOH alkali base were found to produce less defective CeO2 nanoparticles as compared to KOH and LiOH. The last part of this work is to evaluate the shape effect on morphology, size and optical properties of CeO2 nanoparticles. Rod crystals of CeO2 were produced when the hydrothermal synthesis temperature was low (120°C) or when the reaction time was short (1 hour). When the synthesis temperature was higher than 160°C well defined cubic crystals of CeO2 started to form.Master Thesis Production and Characterization of Water Soluble Cdsete Based Core/Shell Nanocrystals and Their Applications in Bioimaging(İzmir Institute of Technology, 2009) Özdemir, Seda; Özçelik, SerdarIn recent years, nanotechnology has become one of the most intensively studied fields. At the nanometer scale, materials have unique electrical, optical, magnetic and chemical properties. They can be used for a wide variety of applications such as electrooptical devices, tagging and medical applications. The goal of this study was to produce water-dispersible alloyed CdSexTe1-x semiconductor nanocrystals, which are suitable to interact with biomolecules. CdSexTe1-x nanocrystals were synthesized by a single step aqueous synthesis method. Monodisperse, CdSexTe1-x nanocrystals with zinc blende structure were obtained in water. Synthesized nanocrystals emit in the range from 528 nm to 620 nm. CdSexTe1-x nanocrystals have 17% photoluminescence quantum yield, after the CdS shell coating the photoluminescence quantum yield increased up to 22%. MTT test and Trypan Blue tests were used to evaluate the toxicity of CdSexTe1-x nanocrystals. MTT measurements reveal that the MCF7 cancer cells are not affected by the nanocrystals at any dosage and exposure condition, but lethal effects are determined at the concentration of 1.0ug/ml for the PC3 cells. The BEAS 2B cells are very sensitive to the nanocrystals and do not proliferate at concentration of 0.5ug/ml. Confocal microscopy studies show that the nanocrystals has ability to penetrate to the cytoplasm of cells.Master Thesis Production of Nano Calcite in Large Scale(Izmir Institute of Technology, 2013) Alıcı, Sezen Duygu; Özdemir, EkremCalcium carbonate (CaCO3) has been used extensively as filling material in various industries in order to improve some mechanical properties of the composite materials and to reduce the product costs. There are mainly two methods for synthesizing CaCO3 crystals: chemical method and carbonization method. The carbonization method is the most appropriate method for nano calcite production. A systematic study was conducted on the synthesis of calcite in nano sizes, homogeneous size distribution, and different morphologies by employing the newly developed small penetration method. The effects of various parameters on the particle size and morphologies such as flow rates of raw materials, concentration, pipe diameter, volumes of stabilization tank and reaction chamber, length in the reaction chamber, stirring rate, and temperature were investigated. Calcite particles of about 100-150 nm were achieved to produce in homogeneous size distributions for the developed method at large scale.Master Thesis Production of Nano Caco3 in Bench Scale by Small Penetration Theory(Izmir Institute of Technology, 2013) Toprak, Görkem; Özdemir, EkremCalcium carbonate (CaCO3) has been used as filling material in various industries such as paint, paper, and polymeric materials. Using filling materials will enhance some of the physical properties of the composite material and decrease the product costs. Especially, the physical properties of the composite materials were enhanced significantly when the CaCO3 is used in nano sizes. CaCO3 can be produced from natural sources by crushing, grinding, and sieving processes, however, calcite obtained from the natural sources are usually in micron sizes and they are not in the desired quality and purity. Here, it was proposed that the dissolution rate of CO2 is the limiting step in CaCO3 crystallization and a small penetration method was developed for the limited dissolution of CO2 in the Ca(OH)2 solution. When Ca(OH)2 was added into the 10 mM CaCO3, zeta potential values of CaCO3 particles were increased from negative to positive value indicating that CaCO3 particles were stabilized in the presence of Ca(OH)2 solution. Rice-like CaCO3 particles were synthesized at the very early stage of crystallization. When crystallization progresses, the high energetic end sites started to dissolve, and the dissolution was progressed through the inside of the particles resulting in hollow calcite particles. BET surface area of hollow calcite particles was found to be 14.75 m2/g. Different parameters such as Ca(OH)2 flow rate, CO2 flow rate, Ca(OH)2 concentration, pipe diameter etc. were studied. Calcite particles in nano sizes, homogeneous size distribution, hollow shapes, and different morphologies were achieved to be produced.Master Thesis Investigation of Shell Microstructure of Microbubbles for Diagnostic Ultrasound(Izmir Institute of Technology, 2013) Köse, Derya; Kılıç Özdemir, Sevgi; Kılıç Özdemir, SevgiIn this study we reported the effect of shear stress, protein adhesion, temperature, secondary interactions and gas core on microbubble stability which are the main reasons of microbubble dissolution in body. Air filled DSPC/PEG40St microbubbles were examined under shear stress. Increasing PEG40St molar ratio increased the resistivity microbubbles against shear stress. To investigate effect of emulsifier type, microbubbles were produced by mixing DSPC with DSPE-PEG1000, DSPE-PEG2000 and PEG40St at 5:5 molar ratio and PEG40St microbubbles were more stable since it provide better curvature to microbubble shell due to its shape. Shear stress experiments were also performed at different temperatures. With increasing temperature microbubbles became less stable since van der Waals interactions between shell components decreased. When microbubbles were filled with perfluorocarbon, since its solubility is lower and more hydrophobic than air, the stability of microbubbles against shear stress increased. Protein adhesion to microbubble shell was investigated by Langmuir Blodgett (LB) and Surface Plasmon Resonance techniques. Both techniques showed that, as the PEG40St molar ratio and packing density increased, protein adhesion decreased. Secondary interactions between shell components were examined via LB technique and visualized via Brewster Angle Microscopy. As third component to DSPC/PEG40St mixture, StGly, StNH2, DSPS, DSTAP was added and ternary mixtures were generally miscible. Since StGly and StNH2 has single tail, they cannot provide curvature in bubble surface. DSPS and DSTAP mixtures may be recommended drug delivery.Master Thesis Development of a Novel Electrocardiography Sensor Based on a Composite Silver Chloride Nanoparticles and Polyaniline(Izmir Institute of Technology, 2013) Taşcıoğlu, Didem; Özçelik, SerdarThe electrical activity of the heart is detected by electrodes attached to the surface of the skin. These electrodes detect bioelectrical signals in the human body. Physilogical status of heart condition especially cardiovascular diseases and disturbances in the cardiac rthym are recorded by electrocardiography (ECG). Despite the fact that the usage of disposable ECG electrodes in our country is substantial nearly as 70 million in 2010, these electrodes are not fabricated in Turkey. In the scope of this study, it was aimed to develop a novel sensor based on synthesized AgCl/Polyaniline nanocomposites for ECG electrodes. In this study, the production of silver chloride (AgCl) nanoparticles was achieved by the polyol method. ABS (Acrylonitrile butadiene styrene) was used as a supporting material of the ECG electrode. Synthesized AgCl nanoparticles were not easily adsorbed on the surface of ABS. We develop a synthetic chemistry to perform simultaneous synthesis of AgCl nanoparticle and polymerization of aniline on surface of ABS. Polyaniline acts as a chemical linker between the nanoparticle and ABS surface in the same batch reactor. The synthesized composite based on polyaniline and AgCl nanoparticles completely covers the surface of ABS. To evaluate electrodes, we fabricated a disposable ECG electrode and compared it with the disposable electrodes that are commercially available. The electrocardiography data indicated that the fabricated electrodes were demonstrated a performance which is comparable with the commercial electrodes. The results demonstrate that a novel ECG electrodes can be manufactured based on this new composite material and method develop in our laboratory.