Materials Science and Engineering / Malzeme Bilimi ve Mühendisliği
Permanent URI for this collectionhttps://hdl.handle.net/11147/4719
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Article Citation - WoS: 14Citation - Scopus: 17Spectrophotometric Characterization of Plasticizer Migration in Poly(vinyl Chloride)-Based Artificial Leather(Elsevier Ltd., 2021) Akkuş Altındağ, İffet; Akdoğan, YaşarPlasticized polyvinyl chloride (PVC) is one of the most commonly used material in the manufacture of artificial leather because of its flexibility, high durability and low cost. While hundreds of plasticizers have been produced to obtain PVC films and artificial leathers, it is important to choose the correct plasticizer to produce the desired products. Therefore, here five non-phthalate type plasticizers with three levels (40 phr, 60 phr and 80 phr); trioctyl trimelliate (TOTM), tributyl trimelliate (TBTM), dioctyl terephthalate (DOTP), dioctyl adipate (DOA) and dioctyl succinate (BIO) were used to prepare plasticized PVC films. They were studied in terms of their compabilities with PVC polymer chains, and their effects on mechanical properties of PVC films. Although, linear plasticizers e.g. BIO and DOA have higher compabilities with PVC, a branched plasticizer e.g. TOTM showed higher mechanical properties. Moreover, a new spectrophotometric method for determination of plasticizer migration from PVC polymer matrix to the surface of artifical leather was developed. According to lightness change on the surface of PVC artifical leather before and after heat treatment at 70 °C, the migration rates of used plasticizers increase in this order: TOTM < TBTM < DOTP < BIO < DOA. © 2020 Elsevier B.V.Article Citation - WoS: 7Citation - Scopus: 7Increasing Spontaneous Wet Adhesion of Dopa With Gelation Characterized by Epr Spectroscopy(Elsevier Ltd., 2019) Göksel, Yaman; Akdoğan, YaşarThe presence of water molecules around both adhesive materials and surface results in the hydration barriers that weaken adhesion. In nature, mussels attach to various types of surfaces by using 3,4-dihydroxyphenylalanine (DOPA) containing mussel foot proteins. DOPA shows wet adhesive properties before and after contribution in the hydrogel formation. Here, the wet adhesive properties of DOPA modified four armed poly (ethylene glycol) polymer (PEG-(DOPA)(4)) and its hydrogels induced by (IO4)(-) or (Cr2O7)(2-) ions are compared by using electron paramagnetic resonance (EPR) spectroscopy in terms of their surface coverages. In water, spin labeled hydrophobic polystyrene (SL-PS) and hydrophilic silica (SL-SiO2) nanoparticles are prepared, and the percentages of their covered surface values are obtained. Without applying force, the adhesion to SL-PS increases in the order of PEG-(DOPA)(4) < PEG-(DOPA)(4) + (IO4)(-) hydrogel < PEG-(DOPA)(4) + (Cr2O7)(2-) hydrogel with the percentages of surface coverages 65%, 76% and 93%, respectively. Although, neither of PEG-(DOPA)(4) polymer and (IO4)(-) induced PEG-(DOPA)(4) hydrogel adhere to SL-SiO2 nanoparticle spontaneously, (Cr2O7)(2-) induced PEG-(DOPA)(4) hydrogel adhere to SL-SiO2 with a 59% of surface coverage. These results show that gelation mechanisms of DOPA have effect on the spontaneous adhesion of DOPA to the wet surfaces even for the hydrophilic silica surface.Article Citation - WoS: 21Citation - Scopus: 28Non-Iridescent Structural Colors From Uniform-Sized Sio2 Colloids(Elsevier Ltd., 2018) Topçu, Gökhan; Güner, Tuğrul; Demir, Mustafa MuammerStructural colors have recently attracted interest from diverse fields of research due to their ease of fabrication and eco-friendliness. These types of colors are, in principle, achieved by periodically arranged submicron-diameter colloidal particles. The interaction of light with a structure containing long-range ordered colloidal particles leads to coloration; this usually varies depending on the angle of observation (iridescence). However, the majority of the applications demand constant color that is independent of the viewing angle (non-iridescence). In this work, silica colloids were obtained using the Stöber method at different sizes from 150 to 300 nm in an alcoholic dispersion. The casting of the dispersion on a substrate leaves behind a photonic crystal showing a colorful iridescent film. However, centrifugation and redispersion of the SiO2 particles into fresh solvent may cause the formation of small, aggregated silica domains in the new dispersion. The casting of this dispersion allows for the development of photonic glass, presumably due to the accumulation of aggregates showing stable colloidal film independent of viewing angle. Moreover, depending on the size of the silica colloids, non-iridescent photonic glasses with various colors (violet, blue, green, and orange) are obtained.Article Citation - WoS: 50Citation - Scopus: 49Validation of Inter-Atomic Potential for Ws2 and Wse2 Crystals Through Assessment of Thermal Transport Properties(Elsevier Ltd., 2018) Mobaraki, Arash; Kandemir, Ali; Yapıcıoğlu, Haluk; Gülseren, Oğuz; Sevik, CemIn recent years, transition metal dichalcogenides (TMDs) displaying astonishing properties are emerged as a new class of two-dimensional layered materials. The understanding and characterization of thermal transport in these materials are crucial for efficient engineering of 2D TMD materials for applications such as thermoelectric devices or overcoming general overheating issues. In this work, we obtain accurate Stillinger-Weber type empirical potential parameter sets for single-layer WS2 and WSe2 crystals by utilizing particle swarm optimization, a stochastic search algorithm. For both systems, our results are quite consistent with first-principles calculations in terms of bond distances, lattice parameters, elastic constants and vibrational properties. Using the generated potentials, we investigate the effect of temperature on phonon energies and phonon linewidth by employing spectral energy density analysis. We compare the calculated frequency shift with respect to temperature with corresponding experimental data, clearly demonstrating the accuracy of the generated inter-atomic potentials in this study. Also, we evaluate the lattice thermal conductivities of these materials by means of classical molecular dynamics simulations. The predicted thermal properties are in very good agreement with the ones calculated from first-principles.Article Citation - WoS: 46Citation - Scopus: 50Investigation of Europium Concentration Dependence on the Luminescent Properties of Borogermanate Glasses(Elsevier Ltd., 2017) Gökçe, Melis; Şentürk, Ufuk; Uslu, Deniz K.; Burgaz, Gözde; Şahin, Yüksel; Gökçe, Aytaç GürhanIn order to elucidate the effect of europium content on the optical and luminescent properties of borogermanate glasses, a series of Eu3+ doped 30B2O3-40GeO2-(30-x)Gd2O3 glasses with various doping levels (x=1–9 mol%) have been synthesized and studied with transmission, absorption, photoluminescence and decay time measurements. The transmission spectra proved that the title glasses maintained a high transparency about 80% in the 440 to 900 nm region. Based on the absorption spectra, the optical band gaps obtained from Tauc's plot can be narrowed by increasing content of Eu3+. From the photoluminescence spectra, the strongest red emission has been observed from the 5D0→7F2 level of Eu3+ ions in borogermanate glasses. The strongest emission and excitation intensities of Eu3+ ions are at the doping level of x=7 mol% and then these intensities decrease due to concentration quenching. The red to orange ratio (R/O) of 5D0→7F2 to 5D0→7F1 transitions has been investigated to predict the local environment of Eu3+ ions. Judd-Ofelt (J-O) analyses have been performed from the emission spectra. The values of R/O and Ω2 present an increase with increasing doping level, indicating the lower symmetric environment for Eu3+ ions and higher covalency for Eu-O bond. The emission efficiency calculated from J-O theory is 75% at x=2 mol%. The decay time curves of 6P7/2→8S7/2 transition of Gd3+ ions and 5D0–7F2 transition of Eu3+ ions confirm the energy transfer from Gd3+ to Eu3+ ions.Article Citation - Scopus: 2Enthalpy-Driven Selective Loading of Cdse0.75s0.25 Nanoalloys in Triblock Copolymer Polystyrene-B(Elsevier Ltd., 2016) Aşkın, Görkem; Çeçen, Volkan; Ünlütürk, Seçil Sevim; Özçelik, Serdar; Demir, Mustafa MuammerCdSe0.75S0.25 nanoalloys were blended with asymmetric triblock copolymer of polystyrene-b-polyisoprene-b-polystyrene(PS-SIS) in tetrahydrofuran. The fraction of styrene block varies from 14 to 22% with respect to isoprene by mass. The morphology of the copolymer cast film experiences a phase change from cylinder to lamella. CdSe0.75S0.25 nanoalloys were prepared by two-phase method. The surface of the nanoalloys was capped by either oleic acid (OA) or n-tri-octylphosphonic acid (TOPO) in situ. The mean diameter of the alloyed particles is around 12 nm in both systems. The chemical nature of the nanoalloy surface was found to influence the dispersion of the particles over polymer volume. The size of the nanoalloy domains in PS is 50 nm, on average, consisting of approximately 0.7 wt% nanoalloys. However, the size of the nanoalloy domains is smaller when they are loaded into PS-SIS. The structure formation is predominantly determined by enthalpic compatibilization. Atomic force microscopy results suggest that the nanoalloys capped with TOPO sequester into PS-rich domains and enlarge the domain. On the other hand, the ones capped with OA prefer to locate in polyisoprene domains. The increase of particles over 1.0 wt% distorts the lamella structure.Article Citation - WoS: 36Citation - Scopus: 36Surfactant-Assisted Formation of Organophilic Ceo2 Nanoparticles(Elsevier Ltd., 2012) Tunusoğlu, Özge; Muñoz-Espí, Rafael; Akbey, Ümit; Demir, Mustafa MuammerWe report a simple one-pot method to prepare organically functionalized CeO 2 nanoparticles by controlled chemical precipitation. The particles were nucleated by mixing aqueous solutions of Ce(NO 3) 3·6H 2O and ammonia at room temperature. Different small organic molecules were chosen as capping agents and injected into the reaction medium at the beginning of the synthesis: 3-(mercaptopropyl) trimethoxy silane (MPS), hexadecyltrimethyl ammonium bromide (CTAB), 3-mercapto propionic acid (3-MPA), and thioglycolic acid (TGA). The resulting nanocrystals were quasi-spherical and had a narrow mean size distribution with an average size smaller than 10nm. Dynamic nuclear polarization enhanced NMR (DNP-NMR) and FTIR measurements suggested a chemical grafting of the surfactant and a homogeneous surface modification. The colloidal stabilities were characterized by dynamic light scattering and zeta potential measurements. The stabilization by aliphatic groups was tested with a frequently used hydrophobic monomer, methyl methacrylate. According to the results, CTAB is the most effective of the used stabilizing surfactant. The mechanism of formation of the organophilic CeO 2 nanoparticles is discussed.Article Citation - WoS: 12Citation - Scopus: 12Dispersion of Organophilic Ag Nanoparticles in Ps-Pmma Blends(Elsevier Ltd., 2015) Tüzüner, Şeyda; Demir, Mustafa Muammer.Abstract The preparation of stable composites with well-controlled particle location is one of the challenges in formulating new polymer/nanoparticle mixtures. In this study, cetyltriammonium bromide (CTAB)-capped monodisperse Ag nanoparticles were prepared and mixed with an equimass blend of polystyrene (PS) and poly(methyl methacrylate) (PMMA) in solution. The surface of the blend film without nanoparticles showed spherical pits with a size of 4.5 μm in diameter. The integration of CTAB-capped nanoparticles into the blend film developed surface bumps with a size of 0.4 μm in diameter. The organophilic Ag nanoparticles were distributed heterogeneously in the immiscible PS-PMMA blend. When the diameter of particle domains reached approximately 20 nm, particles were preferentially located at the interface of the PS and PMMA domains. Larger particle domains with a diameter of 90 nm were found to be in the PMMA-rich phase. Isothermal post-treatment of the PS-PMMA/Ag composite films directs the particle domains into PS domains. Thermodynamic factors that contribute to the observed morphologies are discussed.