Phd Degree / Doktora

Permanent URI for this collectionhttps://hdl.handle.net/11147/2869

Browse

Filters

2007 - 200912010 - 20204

Settings

Author: search.filters.author.Polat, Mehmet

Search Results

Now showing 1 - 5 of 5
  • Doctoral Thesis
    Development of Chitosan Based Biofoams
    (Izmir Institute of Technology, 2020) Olcay Kurt, Aybike Nil; Polat, Mehmet; Polat, Hürriyet; Polat, Mehmet; Polat, Hürriyet
    Chitosan is a preferred bio-foam material used in many research fields such as tissue engineering and drug delivery due to its unique structural features (wide pH stability, nontoxic-biocompatible-biodegradable, anti-inflammatory, antimicrobial). However, chitosan foams are mechanically too weak to maintain the desired shape until newly formed tissue natures. A wound infection and serious tissue necrosis, endanger human's lives. So, a dressing is required to protect loss of fluids and proteins from the wound area and prevents any bacterial invasion replacing the function of skin temporarily. Therefore controlled drug release from a wound dressing is necessary with a biocompatibility and enough mechanical strength. The aim of this study was the synthesis of mechanically durable - dual porosity chitosan bio-foams to provide a controlled drug release. For this purpose, oil droplets formed in a chitosan solution were used as templates to produce micropores that also contain vancomycin (a model antibiotic-hydrophylic) and curcumin (a model anti-inflammatory-hydrophobic) in the walls of the chitosan matrix with large structural voids. An anionic surfactant, sodium dodecyl sulfate (SDS) alone, was used as a crosslinking agent which was a new approach. Then the structures were characterized by SEM, FTIR, mechanical tests and BET analysis. The chitosan foams have dual pore structures. 1) The intrinsic micro pores that the walls of chitosan matrix have with different morphology that depends on the oil phase. 2) The structural voids that the chitosan matrix have, present even in the absence of an oil phase that depends on the experimental conditions. The mechanical strength of the foams were found to be much higher (up to 250 kPa) compare to the foams produced in literature and suggested to be suitable to use for wound dressing applications. The drug release mechanism of foams were found to depend on the conditions used for foam development and the released kinetics were presented with a mathematical model.
  • Doctoral Thesis
    An In-Depth Study of Nucleation and Growth Processes During Stöber Silica Synthesis
    (Izmir Institute of Technology, 2019) Sop, Elif Suna; Polat, Mehmet
    Silica nanoparticles (SNPs) which can be synthesized with high surface area, controllable morphology and desired particle size have gained significant interests in high-end applications such as catalysis, chemical sensors, cosmetics and drug delivery applications. The sol-gel technique is the most commonly applied method for manufacturing these particles owing to its simplicity and suitability for allowing surface modifications to the final product. Though monodisperse amorphous SNPs have been studied extensively, how their formation proceeds through nucleation and growth is still a topic of debate. Over the years, a number of mathematical models have been suggested for the nucleation and growth of SNPs; some suggesting that silica growth occurred through monomer addition while some arguing that aggregation of nuclei/subparticles were the dominant mechanism. Nevertheless, a clear understanding of the nucleation and growth sub-processes is extremely important in control on the size and shape of SNPs for those industrial applications which demand specific morphology and surface properties. The need for a simple, robust and generalized model, both conceptually and mathematically, to understand formation and growth of Stöber silica particles has been the main driving force for this thesis. In this study, silica synthesis was carried out under a wide variety of experimental conditions while determining the size distributions of the formed particles kinetically during different stages of the synthesis in-situ through SEM analysis using an image analysis software. The outcome of the extensive synthesis work was to obtain a clear understanding of how the formation and growth of the silica particles proceed during synthesis. This conceptual understanding of the nucleation and growth processes was then translated into a mathematical model to predict the size of the particles as a function of synthesis time.
  • Doctoral Thesis
    Effect of Colloidal Interactions in the Forming of Lead Magnesium Niobate Ceramics
    (Izmir Institute of Technology, 2007) Deliormanlı, Aylin Müyesser; Polat, Mehmet
    Electrokinetic properties of lead magnesium niobate (PMN) powders in liquid medium are investigated in this thesis. Isoelectric point of aqueous PMN suspensions was determined as a function of solids concentration. Dissolution character of both Pb+2 and Mg+2 cations in PMN structure were examined as a function of pH. Poly(acrylic acid)-poly(ethylene) oxide PAA/PEO comb polymers were tested as the novel dispersant in this system and their effect on the stability and flow behavior of aqueous PMN suspensions was investigated. Stability and flow behavior were mainly studied by rheological measurements and sedimentation experiments as a function of pH and polyelectrolyte concentration. Adsorption of comb polymers onto PMN surface and their effect on the powder dissolution were also investigated. Results indicated that the PAA/PEO comb polymers impart stability to PMN suspensions over a wide pH range and ionic strength where pure PAA fails. In the course of this study PMN powders were consolidated using two different wet shaping methods. First, PMN films were produced using aqueous tape casting method which is widely used in the manufacture of multilayer ceramic capacitors. Secondly, three-dimensional PMN lattices were produced using robocasting method. In the former case, the goal was to provide alternative recipes for the aqueous tape casting process to be utilized in industrial applications since the current technology is based on the organic solvent based techniques. Results showed that it was possible to produce high quality PMN films with thicknesses in the range of 10 to 250 .m using aqueous based tape casting process. In the latter case, the results showed that robocasting is a suitable technique for the preparation of three dimensional PMN ceramics. Based on these results overall conclusion and the contribution of this study can be summarized as follows: The work carried out gives new insights into the manufacturing of PMN based ceramics using aqueous based techniques. Such improvements may bring benefits in the manufacturing of smaller electronic components employed in the personal computers and mobile phones and other consumer products in the near future.
  • Doctoral Thesis
    Estimation of the Surface Charge Distribution of Solids in Liquids by Using Atomic Force Microscopy
    (Izmir Institute of Technology, 2011) Yelken Özek, Gülnihal; Polat, Mehmet
    Colloidal systems are widely encountered in minerals, ceramics, environment, biology, pharmaceuticals and cosmetics industries. These systems consist of micronsized particulates dispersed in a solvent. Homogeneity, dispersibility, stability of colloidal systems determines the economy and success of the final product in these applications. Control and manipulation of these properties depend on detailed analysis of the interactions among the particles. Electrophoretic potential measurements or colloidal titration methods are widely employed to characterize the charging of colloidal systems. However these methods only yield average charging information, not the charge distribution on the surface. Atomic Force Microscope (AFM) allows topographic surface analysis at nanometer level resolutions. Though it is widely used to obtain derived information AFM directly measures the forces between the tip and the surface atoms. The objective of the present work is to assess the applicability of AFM to surface charge mapping, i.e., the detection of positive or negative charged regions on metal oxide surfaces. Hence, well defined tips were prepared and allowed to interact with well defined oxide surfaces under different pH conditions. The influence of solution ion concentration and pH on the forces measured was also investigated. These measured force-distance curves were analyzed using a new solution of the one dimensional Poisson-Boltzmann equation to isolate the electrical double layer force, hence the surface charge on each measurement point. The new solution in question provides analytical expressions for all charging conditions which are amenable to such analysis.Repetitive force measurements on a predefined grid on the solid surface ultimately yield the charge distribution of the surface. Such an analysis procedure is new and advances the charge measurements on solids in solution to a new level.
  • Doctoral Thesis
    Fixation and Stabilization of Heavy Metals in a Product Composed of Fly Ash and Industrial Acidic Wastes
    (Izmir Institute of Technology, 2010) Üzelyalçın Ülkü, Berna; Polat, Mehmet
    Large quantities of fly ash are produced in the world while only a very small portion of it finds utilization as a product. Since even larger quantities of fly ash should be expected to be generated in an increasingly energy-hungry world, finding new, smart pathways towards fly ash utilization carries its own weight in achieving sustainable development. Manufacturing light-weight fly ash aggregates which could also be used as sinks for other wastes with acceptable environmental foot-print and possible added value is exactly one such pathway. This thesis comprises of the studies where a fly ash sample from a large Thermal Power Plant (Soma fly ash) is used to stabilize an extremely acidic industrial waste in an aggregate structure with the aim that the aggregates produced had acceptable environmental impact and possible product value. The study is divided into several parts. Initial chapters contain the characterization studies of both the fly ash from Soma, Manisa Thermal Power Plant and the highly acidic industrial waste from a metal stripping factory in Cigli-Izmir. Later chapters contain the methodology and the experimental parts of the work. The acidity of the aggregates was also optimized keeping in mind the present environmental regulations. Solid/liquid ratio, effect of aging of the aggregates, effect of leaching from the aggregates and their mechanical strengths were the main experimental parameters investigated. Mineralogical composition of the aggregates was compared with the raw fly ash to shed light on the fixation mechanism. The fly ash was rich in especially Si, Al and Ca and some heavy metals in trace amounts whereas the acidic waste contained huge amounts of Zn, Fe and other heavy metals. This study demonstrated conclusively that the acidic waste was not only neutralized by the fly ash to disposable levels, but also that the leaching of both the major and minor elements from the aggregate body into the water was below the environmental limits in force both in Europe and Turkey today. The produced aggregates were also observed to possess the low-strength-material properties which open the possibility for their utilization in construction applications.