Researcher:
Yağcı, Mustafa Barış

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Mustafa Barış

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Yağcı

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Yağcı, Mustafa Barış

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2016 - 2019222020 - 202313

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Now showing 1 - 10 of 35
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    Reversible switching of wetting properties and erasable patterning of polymer surfaces using plasma oxidation and thermal treatment
    (Elsevier Science Bv, 2018) Soydan, Seren; Jonas, Alexander; N/A; Department of Chemistry; N/A; Department of Chemistry; Department of Physics; Department of Chemistry; Rashid, Muhammed Zeeshan; Atay, İpek; Yağcı, Mustafa Barış; Yılgör, Emel; Kiraz, Alper; Yılgör, İskender; PhD Student; Post Doctorate Student; Researcher; Researcher; Faculty Member; Faculty Member; Department of Physics; Department of Chemistry; Koç University Surface Science and Technology Center (KUYTAM) / Koç Üniversitesi Yüzey Teknolojileri Araştırmaları Merkezi (KUYTAM); Graduate School of Sciences and Engineering; N/A; College of Sciences; College of Sciences; College of Sciences; College of Sciences; N/A; N/A; N/A; N/A; 40527; 22542; 24181
    Polymer surfaces reversibly switchable from superhydrophobic to superhydrophilic by exposure to oxygen plasma and subsequent thermal treatment are demonstrated. Two inherently different polymers, hydrophobic segmented polydimethylsiloxane-urea copolymer (TPSC) and hydrophilic poly(methyl methacrylate) (PMMA) are modified with fumed silica nanoparticles to prepare superhydrophobic surfaces with roughness on nanometer to micrometer scale. Smooth TPSC and PMMA surfaces are also used as control samples. Regardless of their chemical structure and surface topography, all surfaces display completely reversible wetting behavior changing from hydrophobic to hydrophilic and back for many cycles upon plasma oxidation followed by thermal annealing. Influence of plasma power, plasma exposure time, annealing temperature and annealing time on the wetting behavior of polymeric surfaces are investigated. Surface compositions, textures and topographies are characterized by X-ray photoelectron spectroscopy (XPS), scanning electron microscopy (SEM) and white light interferometry (WLI), before and after oxidation and thermal annealing. Wetting properties of the surfaces are determined by measuring their static, advancing and receding water contact angle. We conclude that the chemical structure and surface topography of the polymers play a relatively minor role in reversible wetting behavior, where the essential factors are surface oxidation and migration of polymer molecules to the surface upon thermal annealing. Reconfigurable water channels on polymer surfaces are produced by plasma treatment using a mask and thermal annealing cycles. Such patterned reconfigurable hydrophilic regions can find use in surface microfluidics and optofluidics applications. (C) 2018 Elsevier B.V. All rights reserved.
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    Machine learning-assisted design of biomedical high entropy alloys with low elastic modulus for orthopedic implants
    (Springer, 2022) Canadinc, D.; Bedir, E.; Yilmaz, R.; N/A; N/A; N/A; Department of Mechanical Engineering; Özdemir, Hüseyin Can; Yağcı, Mustafa Barış; Kılıç, Elif Bedir; Canadinç, Demircan; PhD Student; Researcher; PhD Student; Faculty Member; Department of Mechanical Engineering; Koç University Surface Science and Technology Center (KUYTAM) / Koç Üniversitesi Yüzey Teknolojileri Araştırmaları Merkezi (KUYTAM); Graduate School of Sciences and Engineering; N/A; Graduate School of Sciences and Engineering; College of Engineering; N/A; N/A; N/A; 23433
    This paper focuses on finding an optimum composition for the TiTaHfNbZr quinary high entropy alloy (HEA) system with an elastic modulus close to that of bone in order to attain a better biomechanical compatibility between the bone and the implant in orthopedic applications. To obtain the composition providing the desired structural match, machine learning (ML) tools were implemented in the current work instead of conventional trial-and-error methods. The ML algorithms utilized in this study were trained using experimental data available in the literature and then utilized to predict the optimum HEA compositions with the lowest elastic moduli. Consequently, the Ti23Ta10Hf27Nb12Zr28 and Ti28Ta10Hf30Nb14Zr18 compositions were predicted as the optimum HEA compositions with elastic moduli of 83.5 +/- 2.9 and 87.4 +/- 2.2 GPa, respectively. The materials were manufactured, and the elastic moduli were validated with nanoindentation experiments. The samples were also exposed to static immersion experiments in simulated body fluid (SBF) for 28 days to gain insight and information regarding the ion release and ensure that the new HEAs are biocompatible. The findings of the work reported herein demonstrate that the proposed ML model can successfully predict HEA compositions for an optimized biomechanical compatibility for orthopedic applications and warrant further biomedical research on the two new HEAs prior to their utility as orthopedic implant materials.
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    Optimizing mechanical properties and Ag ion release rate of silver coatings deposited on Ti-based high entropy alloys
    (Elsevier Ltd, 2023) Yilmaz R.; N/A; N/A; N/A; Department of Mechanical Engineering; Özdemir, Hüseyin Can; Yağcı, Mustafa Barış; Kılıç, Elif Bedir; Canadinç, Demircan; PhD Student; Researcher; PhD Student; Faculty Member; Department of Mechanical Engineering; Koç University Surface Science and Technology Center (KUYTAM) / Koç Üniversitesi Yüzey Teknolojileri Araştırmaları Merkezi (KUYTAM); Graduate School of Sciences and Engineering; N/A; Graduate School of Sciences and Engineering; College of Engineering; N/A; N/A; N/A; 23433
    This paper details the characterization of microstructure, texture, mechanical properties, and ion release behavior of antibacterial Ag thin films sputtered on two novel biomedical high entropy alloys (HEAs), namely the Ti23Ta10Hf27Nb12Zr28 (HEA–Ti23) and Ti28Ta10Hf30Nb14Zr18 (HEA–Ti28) alloys. Specifically, the influences of varying deposition time and Ar flow rate were investigated to reveal the mechanisms dictating the microstructure, texture, and mechanical properties of the coatings. In addition, static immersion experiments were carried out in simulated body fluid (SBF) for 28 days to establish the relationship between ion release from the coatings and the deposition parameters, microstructure, and surface texture. It was shown that texture evolution in Ag thin films depends on both film thickness and Ar flow rate, such that there exists a critical thickness at which the energy minimization mechanism is altered. A very good correlation was also observed between an increase in (111) peak intensity and a decrease in released Ag ion fraction. Overall, the findings of the work presented herein suggest that the alterations in Ag deposition parameters could be optimized to obtain the desired mechanical properties while enhancing the biocompatibility of the HEA substrates by coating them with antibacterial Ag films. 2023 Elsevier B.V.
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    Formation of mesoporous silica particles with hierarchical morphology
    (Elsevier, 2020) Ow-Yang, Cleva W.; N/A; N/A; Department of Chemistry; Department of Chemistry; Ijaz, Aatif; Yağcı, Mustafa Barış; Demirel, Adem Levent; Miko, Annamaria; Researcher; Researcher; Faculty Member; Teaching Faculty; Department of Chemistry; Koç University Surface Science and Technology Center (KUYTAM) / Koç Üniversitesi Yüzey Teknolojileri Araştırmaları Merkezi (KUYTAM); N/A; N/A; College of Sciences; College of Sciences; N/A; N/A; 6568; 163509
    The transformation of mesoporous silica morphology from monoliths to spherical particles was investigated at room temperature in Pluronic F127/TEOS system as a function of HCl acid catalyst concentration to understand and control the mechanism. It is shown that the specific surface area and the size of mesoporous spherical silica particles can simply be adjusted by the catalyst concentration without using any additives or post-treatment. Above 3 M acid concentration, novel monodisperse micron sized spherical silica with hierarchical order of two levels was obtained. These silica spheres were formed of densely packed distorted hexagonal platelets of 20-30 nm in diameter. Within these platelets mesoporous channels were oriented along a single direction, however the platelets were randomly oriented in the spherical particles. Controlling the agglomeration of mesoporous silica primary particles by the concentration of the acid catalyst to obtain micron-sized spherical particles is novel. This approach allows the synthesis of particles whose sizes can be controlled in the range of similar to 1-4 mu m and specific surface area in the range of similar to 200-500 m(2)/g. The morphology of the particles transforms from spherical shape to mesoporous monoliths at acid concentrations below 1 M due to slow hydrolysis and condensation. These results are important in understanding the role of catalyst concentration on the formation mechanism of different morphologies of mesoporous silica.
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    Enhancing biocompatibility of NiTi shape memory alloys by simple NH3 treatments
    (Elsevier, 2020) N/A; N/A; N/A; Department of Chemical and Biological Engineering; Department of Chemistry; Department of Mechanical Engineering; Öztulum, Samira Fatma Kurtoğlu; Yağcı, Mustafa Barış; Uzun, Alper; Ünal, Uğur; Canadinç, Demircan; PhD Student; Researcher; Faculty Member; Faculty Member; Faculty Member; Department of Chemical and Biological Engineering; Department of Chemistry; Department of Mechanical Engineering; Koç University Tüpraş Energy Center (KUTEM) / Koç Üniversitesi Tüpraş Enerji Merkezi (KÜTEM); Koç University Surface Science and Technology Center (KUYTAM) / Koç Üniversitesi Yüzey Teknolojileri Araştırmaları Merkezi (KUYTAM); Graduate School of Sciences and Engineering; N/A; College of Engineering; College of Sciences; College of Engineering; 384798; N/A; 59917; 42079; 23433
    This paper presents the treatment of NiTi shape memory alloys (SMAs) in flowing ammonia at 700 degrees C as a simple and cost-effective nitriding process to provide a protective surface layer hindering Ni ion release in biological environments. Experimental results demonstrated that a smooth protective TiN layer on the NiTi SMAs along with TiOxNy and TiO2 formed on the surface upon treating the as-received NiTi SMA in ammonia at 700 degrees C. The protective TiN layer and the smooth surface hinder the amount of Ni ion release to artificial saliva (AS) after 28 days of immersion, while the dry air treatment at similar conditions results in a significantly rough surface, leading to about 20 times higher Ni ion release. Overall, the findings presented herein demonstrate that NH3 nitriding is an effective method to eliminate the Ni presence from the surface and to obtain a smooth final surface, which, in turn, restricts the Ni ion release from the NiTi SMA into AS. Consequently, nitriding the surface of NiTi under NH3 at 700 degrees C turned out as a promising method to lower Ni ion release and thereby contribute to the biocompatibility of NiTi SMAs, which, however; needs to be further validated through further experimentation.
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    Tribological behavior of tialn, altin, and alcrn coatings at boundary lubricating condition
    (Springer/Plenum Publishers, 2018) Ozkan, Dogus; Erarslan, Yaman; Sulukan, Egemen; Kara, Levent; Yilmaz, M. Alper; Yagci, M. Baris; N/A; Yağcı, Mustafa Barış; Researcher;  Koç University Surface Science and Technology Center (KUYTAM) / Koç Üniversitesi Yüzey Teknolojileri Araştırmaları Merkezi (KUYTAM); N/A; N/A
    In this study, similar to 3.5 mu m thick multilayer titanium alumina nitride (TiAlN), alumina titanium nitride (AlTiN), and alumina chromium nitride (AlCrN) coatings were deposited on the H13 steel surface by cathodic arc physical vapor deposition(CAPVD) method. The tribological performance of the coatings was evaluated by a tribometer at boundary lubrication condition. Then, coating surfaces were observed by optical microscope, optical profilometer, and atomic force microscope to evaluate the morphological changes, wear volumes, and tribofilm thickness. Also, scanning electron microscopy (energy dispersive X-ray) and X-ray photoelectron spectrometry analyses were applied to coating surfaces for the tribochemical evolution of the tribofilm. Results showed that AlCrN coating performed the best tribological behavior at boundary lubricated condition, when compared to TiAlN and AlTiN coatings and it can be used as a wear resistant cam tappet coating in internal combustion engines.
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    COx-free hydrogen production from ammonia decomposition over sepiolite-supported nickel catalysts
    (Pergamon-Elsevier Science Ltd, 2018) Soyer-Uzun, Sezen; N/A; N/A; N/A; N/A; Department of Chemical and Biological Engineering; Öztulum, Samira Fatma Kurtoğlu; Sarp, Seda; Akkaya, Ceren Yılmaz; Yağcı, Mustafa Barış; Uzun, Alper; PhD Student; Undergraduate Student; Researcher; Researcher; Faculty Member; Department of Chemical and Biological Engineering; Koç University Tüpraş Energy Center (KUTEM) / Koç Üniversitesi Tüpraş Enerji Merkezi (KÜTEM); Koç University Surface Science and Technology Center (KUYTAM) / Koç Üniversitesi Yüzey Teknolojileri Araştırmaları Merkezi (KUYTAM); Graduate School of Sciences and Engineering; College of Engineering; College of Engineering; N/A; College of Engineering; 384798; N/A; N/A; N/A; 59917
    Sepiolite, a clay mineral, was utilized as a support for nickel-based catalysts for COx-free hydrogen production from ammonia decomposition. First, the physical and chemical properties of sepiolite were changed by calcining it at temperatures varying from 500 to 1000 degrees C, then nickel was impregnated on these calcined supports and tested for ammonia decomposition at various temperatures following reduction at 650 degrees C. Results indicated that even though the catalysts contained almost the same amount of nickel, they showed different hydrogen production performance. Detailed characterization of the catalysts before and after reaction illustrated that the support obtained by calcining sepiolite at 700 degrees C shows good basic properties with a high surface area offering a high degree of nickel dispersion. These properties lead to promising hydrogen production rates which are on par, if not higher, than most of the nickel-based catalysts prepared on supports, which are either not cheap or require tedious preparation procedures.
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    Mechanical properties of titahfnbzr high-entropy alloy coatings deposited on niti shape memory alloy substrates
    (Springer, 2018) N/A; N/A; N/A; N/A; N/A; Department of Mechanical Engineering; Motallebzadeh, Amir; Yağcı, Mustafa Barış; Kılıç, Elif Bedir; Aksoy, Cem Bahadır; Canadinç, Demircan; Researcher; Researcher; PhD Student; PhD Student; Faculty Member; Department of Mechanical Engineering; Koç University Surface Science and Technology Center (KUYTAM) / Koç Üniversitesi Yüzey Teknolojileri Araştırmaları Merkezi (KUYTAM); N/A; N/A; Graduate School of Sciences and Engineering; Graduate School of Sciences and Engineering; College of Engineering; N/A; N/A; N/A; N/A; 23433
    TiTaHfNbZr high-entropy alloy (HEa) thin films with thicknesses of about 750 and 1500 nm were deposited on NiTi substrates by RF magnetron sputtering using TiTaHfNbZr equimolar targets. the thorough experimental analysis on microstructure and mechanical properties of deposited films revealed that the TiTaHfNbZr films exhibited amorphous and cauliflower-like structure, where grain size and surface roughness increased concomitant with film thickness. More importantly, the current findings demonstrate that the TiTaHfNbZr HEa films with mechanical properties of the same order as those of the NiTi substrate constitute promising biomedical coatings effective in preventing Ni release.
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    From corrosion behavior to radiation response: a comprehensive biocompatibility assessment of a cocrmo medium entropy alloy for utility in orthopedic and dental implants
    (Elsevier Sci Ltd, 2022) Gerstein, G.; Maier, H. J.; Cabuk, H.; Bukulmez, T.; Cananoglu, M.; Toker, S. M.; Gunes, S.; Soykan, M. N.; N/A; N/A; Department of Mechanical Engineering; N/A; Gürel, Şeyma; Nazarahari, Alireza; Canadinç, Demircan; Yağcı, Mustafa Barış; Master Student; PhD Student; Faculty Member; Researcher; Department of Mechanical Engineering; Koç University Surface Science and Technology Center (KUYTAM) / Koç Üniversitesi Yüzey Teknolojileri Araştırmaları Merkezi (KUYTAM); Graduate School of Sciences and Engineering; Graduate School of Sciences and Engineering; College of Engineering; N/A; N/A; N/A; 23433; N/A
    This paper presents a thorough biocompatibility evaluation of a CoCrMo medium entropy alloy to assess its potential to be utilized in orthopedic and dental implants. For this purpose, a wide range of systematic exper-iments were carried out, including static immersion, cell culture and radiation experiments. In particular, chemical biocompatibility and ion release behavior of the CoCrMo alloy were studied by carrying out static immersion experiments in artificial saliva (AS), simulated body fluid (SBF) and fetal bovine serum (FBS). Detailed analysis of the surfaces of the tested samples demonstrated that both passive oxide layer and hy-droxyapatite formation occur on the CoCrMo sample surfaces immersed in AS, SBF and FBS for 28 days. The response of living cells to the CoCrMo alloy was tested utilizing cell culture experiments, and the evidence of Saos-2 cell viability and proliferation supported the static biocompatibility experiment results, indicating the potential of the CoCrMo alloy to be utilized as an orthopedic implant material. Finally, the effect of a CoCrMo implant on the actual radiation dose induced upon malignant tissue in the vicinity of the implant during a radiotherapy was evaluated by applying medical grade radiation to water phantoms circumventing CoCrMo samples. The results showed that the radiation accumulation in the tissue within the immediate vicinity of a CoCrMo implant would be a minimum, eliminating some of the undesired side effects. Overall, the results of the three different types of experiments reported in this paper have clearly demonstrated that the CoCrMo medium entropy alloy investigated in this study has significant potential to be utilized as a safe implant material in dental and orthopedic implants.
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    Friction and wear behaviors of tin coatings under dry and vacuum conditions
    (Taylor & Francis Inc, 2019) Kara, Levent; Özkan, Doğuş; Sulukan, Egemen; Sert, Yaşar; Sert, Tugay Sonsuz; N/A; Yağcı, Mustafa Barış; Researcher;  Koç University Surface Science and Technology Center (KUYTAM) / Koç Üniversitesi Yüzey Teknolojileri Araştırmaları Merkezi (KUYTAM); N/A; N/A
    In this study, pure TiN coatings were applied on AISI 52100 steel surfaces with a magnetron sputterer at different direct current (DC) powers and N-2 flows to develop a wear-resistant coating for sliding tribopairs working in atmospheric and vacuum conditions. Wear and friction characteristics of these coatings were investigated with a tribometer under both vacuum and atmospheric conditions. DC power and N-2 flow affected the coating thickness and structure. TiN coatings showed different wear and friction characteristics under ambient and vacuum conditions due to the oxidation level of the surface.