Research Outputs
Permanent URI for this communityhttps://hdl.handle.net/20.500.14288/2
Browse
18 results
Search Results
Publication Metadata only A novel mold design for one-continuous permeability measurement of fiber preforms(Sage Publications Ltd, 2015) N/A; N/A; Department of Mechanical Engineering; Yalçınkaya, Mehmet Akif; Sarıoğlu, Ayşen; Sözer, Murat; PhD Student; Master Student; Faculty Member; Department of Mechanical Engineering; Graduate School of Sciences and Engineering; Graduate School of Sciences and Engineering; College of Engineering; N/A; N/A; 110357One-continuous permeability measurement experiments allow measuring permeability of a fiber preform within a range of fiber volume fractions by conducting a single unsaturated (a.k.a. transient) flow experiment on a dry specimen at an initial thickness, and a set of saturated flow experiments on the wetted specimen by varying the thickness of the mold cavity. This approach allows quicker database construction and reduces the effect of inherent variation of fabric structure caused by inconsistent labor on permeability. In this study, the drawbacks of previous mold designs are eliminated by using appropriate sealing, gap thickness adjustment mechanism and features that allow straightforward and reliable manual operation. Experiments for three different fabric types are conducted and the results are discussed. It is mainly observed that the unsaturated permeability is higher than the saturated permeability.Publication Metadata only Ag, Co3O4, Ag-Co3O4, and Ag/Co3O4 nanoparticles decorated mesoporous natural phosphate: effect of metal synergy and preparation method on the catalytic reduction reaction(Springer, 2022) Orfi, Hamza; Mekkaoui, Ayoub Abdelkader; Laayati, Mouhsine; Labyad, Salim Adam; El Firdoussi, Larbi; El Houssame, Soufiane; N/A; Department of Chemistry; Sündü, Buse; Metin, Önder; PhD Student; Faculty Member; Department of Chemistry; Koç University Surface Science and Technology Center (KUYTAM) / Koç Üniversitesi Yüzey Teknolojileri Araştırmaları Merkezi (KUYTAM); Graduate School of Sciences and Engineering; College of Sciences; N/A; 46962Addressed herein is a facile method for the preparation of cobalt-silver (Co-x-Ag-y) nanoparticles decorated mesoporous natural phosphate (m-NP). Various Co-x-Ag-y@NP nanocatalysts were prepared in different forms of Ag and Co3O4 including mono- and bimetallic active sites. The bimetallic nanocatalysts were prepared by two different preparation methods, namely in-situ (Ag-Co3O4) and ex-situ (Ag/Co3O4 core-shell). In the first step, colloidal Co-x-Ag-y nanoparticles were synthesized in solution and their formation was monitored by using UV-Visible spectroscopy. Furthermore, the obtained nanoparticles were characterized by XRD and IR spectroscopy. All nanoparticles were deposited on m-NP using a simple wetness impregnation method followed by a calcination at 500 degrees C. The prepared nanocatalysts were fully characterized by advanced analytical techniques including IR, XRD, XPS, SEM-EDX, FESEM, and TEM. The catalytic reduction of 4-nitrophenol was studied as a model reaction to investigate the effect of synergy created between the metals, oxidation state, catalyst structure, and preparation method on their catalytic activity. Accordingly, reaction kinetics and comparative study of various colloidal Co-x-Ag-y and m-NP supported nanocatalysts in the reduction of 4-nitrophenol was carried out. The optimized conditions were used to study the substrate scope of the catalytic reduction over various nitroarenes.Publication Metadata only Contribution of soft segment entanglement on the tensile properties of silicone–urea copolymers with low hard segment contents(Elsevier Sci Ltd, 2009) Wilkes, Garth L.; Department of Chemistry; N/A; Department of Chemistry; Yılgör, İskender; Eynur, Tuğba; Yılgör, Emel; Faculty Member; Master Student; Researcher; Department of Chemistry; College of Sciences; Graduate School of Sciences and Engineering; College of Sciences; 24181; N/A; N/ANovel, segmented thermoplastic silicone-urea (TPSU) copolymers based on rather high molecular weight aminopropyl terminated polydimethylsiloxane (PDMS) soft segments ( 10,800 and 31,500 g/mol), a cycloaliphatic diisocyanate (HMDI) and various diamine chain extenders were synthesized. Copolymers with very low urea hard segment contents of 1.43-14.4% by weight were prepared. In spite of very low hard segment contents, solution cast films showed very good microphase separation and displayed reasonable mechanical properties. Tensile strengths of TPSU copolymers showed a linear dependence on their urea hard segment contents, regardless of the structure of the diamine chain extender used. The modulus of silicone-urea copolymers is dependent on the urea concentration, but not on the extender type or PDMS molecular weight. When silicone-urea copolymers with identical urea hard segment contents were compared, copolymers based on PDMS-31,500 showed higher elongation at break values and ultimate tensile strengths than those based on PDMS-10,800. Since the critical entanglement molecular weight (M(e)) of PDMS is about 24,500 g/mol, these results suggest there is a significant contribution from soft segment chain entanglement effects in the PDMS-31,500 system regarding the tensile properties and failure mechanisms of the silicone-urea copolymers.Publication Metadata only Discovery of an exceptionally strong luminescence of polyethyleneimine-superparamagnetic iron oxide nanoparticles(Wiley-V C H Verlag Gmbh, 2018) Erdem, Emre; Ow-Yang, Cleva W.; N/A; Department of Chemistry; Department of Chemistry; N/A; N/A; Department of Chemistry; Ünal, Özlem; Yurtsever, İsmail Ersin; Khodadust, Rouhollah; Yağcı, Mustafa Barış; Durmuşoğlu, Emek Göksu; Acar, Havva Funda Yağcı; PhD Student; Faculty Member; Other; Researcher; N/A; Faculty Member; Department of Chemistry; Koç University Surface Science and Technology Center (KUYTAM) / Koç Üniversitesi Yüzey Teknolojileri Araştırmaları Merkezi (KUYTAM); Graduate School of Sciences and Engineering; College of Sciences; College of Sciences; N/A; N/A; College of Sciences; N/A; 7129; N/A; N/A; N/A; 178902Polyethyleneimine (PEI) is rarely recognized as a luminescent polymer but is frequently used for the production of cationic nanoparticles and tagged with an organic fluorophore to be tracked optically. Herein, a strongly luminescent, branched PEI-superparamagnetic iron oxide nanoparticle (bPEI-SPION) without a traditional fluorophore is reported. A tremendous enhancement (1200 times) in the weak blue luminescence of bPEI is achieved only if it is adsorbed on a SPION during the synthesis of nanoparticles, which is improved further upon protonation, irreversibly. This is quite unexpected since SPIONs are strong absorbers in the visible region. All reaction parameters, different synthetic methods, as well as protonation are studied as independent factors to understand the origin of such enhancement. Detailed spectroscopic analysis and density functional theory calculations indicate that partial amine oxidation and Fe3+ reduction takes place during the synthesis, which significantly contributes to the luminescence enhancement. In addition, PEI-SPION exhibits excitation wavelength dependent emission and maintains its magnetic properties.Publication Metadata only Effect of part thickness variation on the mold filling time in vacuum infusion process(Sage Publications Ltd, 2014) N/A; Department of Mechanical Engineering; Yalçınkaya, Mehmet Akif; Sözer, Murat; PhD Student; Faculty Member; Department of Mechanical Engineering; Graduate School of Sciences and Engineering; College of Engineering; N/A; 110357An experimental setup was used to fairly compare mold filling times in vacuum infusion and resin transfer molding, and a 9.5% shorter mold filling time in vacuum infusion was observed than in resin transfer molding. The setup was also used to conduct compaction and permeability characterization experiments, and the results were used in a simplified vacuum infusion model, which is more straightforward to solve than the conventional full and coupled models in the literature. Simulated filling time in vacuum infusion was 31% shorter than in resin transfer molding. The faster resin flow in vacuum infusion is explained by the fact that the thickness in the wetted upstream region increases with time, and thus the effective permeability in that region increases.Publication Metadata only Effect of permeability characterization at different boundary and flow conditions on vacuum infusion process modeling(Sage Publications Ltd, 2017) N/A; N/A; Department of Mechanical Engineering; Yalçınkaya, Mehmet Akif; Çağlar, Barış; Sözer, Murat; PhD Student; PhD Student; Faculty Member; Department of Mechanical Engineering; Graduate School of Sciences and Engineering; Graduate School of Sciences and Engineering; College of Engineering; N/A; N/A; 110357Permeability characterization of a fabric preform is a key factor that affects the accuracy of process modeling of vacuum infusion. There are various flow types and boundary conditions (such as one-dimensional or radial flow under constant injection pressure or constant injection flow rate during unsaturated or saturated flow regimes) used in permeability measurement experiments in the literature. This study investigates the effect of using different flow and injection boundary conditions in permeability characterization on the results of coupled one-dimensional mold-filling and compaction model. The results of the model are compared with vacuum infusion mold-filling experiments. It is shown that using the permeability measured at constant injection pressure and unsaturated flow results in the closest fill time compared to the experiments for all three types of fabrics investigated in this study.Publication Metadata only Effect of surface modification of colloidal silica nanoparticles on the rigid amorphous fraction and mechanical properties of amorphous polyurethane-urea-silica nanocomposites(Wiley, 2019) Oguz, Oğuzhan; Candau, Nicolas; Bernhard, Stephane H. F.; Heinz, Ozge; Stochlet, Gregory; Plummer, Christopher J. G.; Menceloğlu, Yusuf Z.; N/A; Department of Chemistry; Department of Chemistry; Söz, Çağla Koşak; Yılgör, Emel; Yılgör, İskender; PhD Student; Researcher; Faculty Member; Department of Chemistry; Koç University Surface Science and Technology Center (KUYTAM) / Koç Üniversitesi Yüzey Teknolojileri Araştırmaları Merkezi (KUYTAM); Graduate School of Sciences and Engineering; College of Sciences; College of Sciences; N/A; N/A; 24181Colloidal silica nanoparticles (NPs) modified with eight different silane coupling agents were incorporated into an amorphous poly(tetramethylene oxide)-based polyurethane-urea copolymer matrix at a concentration of 10 wt % (4.4 vol %) in order to investigate the effect of their surface chemistry on the structure-property behavior of the resulting nanocomposites. The rigid amorphous fraction (RAF) of the nanocomposite matrix as determined by differential scanning calorimetry and dynamic mechanical analysis was confirmed to vary significantly with the surface chemistry of the NPs and to be strongly correlated with the bulk mechanical properties in simple tension. Hence, nanocomposites with an RAF of about 30 wt % showed a 120% increase in Young's modulus, a 25% increase in tensile strength, a 15% decrease in elongation at break with respect to the neat matrix, which had no detectable RAF, whereas nanocomposites with an RAF of less than 5% showed a 60% increase in Young's modulus, a 10% increase in tensile strength and a 5% decrease in the elongation at break.Publication Metadata only Electro-conductive silica nanoparticles-incorporated hydrogel based on alginate as a biomimetic scaffold for bone tissue engineering application(Taylor and Francis Ltd., 2023) Derakhshankhah, Hossein; Eskandani, Morteza; Vandghanooni, Somayeh; Jaymand, Mehdi; Department of Mechanical Engineering; N/A; Taşoğlu, Savaş; Nakhjavani, Sattar Akbar; Faculty Member; Researcher; Department of Mechanical Engineering; Koç University Research Center for Translational Medicine (KUTTAM) / Koç Üniversitesi Translasyonel Tıp Araştırma Merkezi (KUTTAM); College of Engineering; N/A; 291971; N/AAn innovative electrically conductive hydrogel was fabricated through the incorporation of silica nanoparticles (SiO2 NPs) and poly(aniline-co-dopamine) (PANI-co-PDA) into oxidized alginate (OAlg) as a biomimetic scaffold for bone tissue engineering application. The developed self-healing chemical hydrogel was characterized by FTIR, SEM, TEM, XRD, and TGA. The electrical conductivity and swelling ratio of the hydrogel were obtained as 1.7 × 10−3 S cm−1 and 130%, respectively. Cytocompatibility and cell proliferation potential of the developed scaffold were approved by MTT assay using MG-63 cells. FE-SEM imaging approved the potential of the fabricated scaffold for hydroxyapatite (HA) formation and bioactivity induction through immersing in SBF solution.Publication Metadata only Entangled polymer dynamics in attractive nanocomposite melts(American Chemical Society (ACS), 2020) Şenses, Erkan; Tyagi, Madhu Sudan; Faraone, Antonio; Department of Chemical and Biological Engineering; N/A; Şenses, Erkan; Darvishi, Saeid; Faculty Member; PhD Student; Department of Chemical and Biological Engineering; College of Engineering; Graduate School of Sciences and Engineering; 280298; N/AWe investigate single chain dynamics of an entangled linear poly(ethylene oxide) melt in the presence of well-dispersed attractive nanoparticles using high-resolution neutron spectroscopy at particle volume fractions as high as 0.53. The short-time dynamics shows a decrease of the Rouse rates with particle loading, yet the change remains within a factor of 2, with no evidence of segment immobilization as often hypothesized. The apparent reptation tube diameter shrinks by approximate to 10% from the bulk at a 0.28 particle volume fraction when the face-to-face interparticle distance approaches the single chain size. The tube diameter is remarkably concentration-independent at higher loadings where all chains are essentially bound to particle surfaces. These direct experimental observations on the microscopic chain dynamics in attractive nanocomposites are distinct from their nonattractive counterparts and account for some of the unusual dynamic behaviors of the nanoparticles as well as rheology in the composites.Publication Metadata only Facile preparation of superhydrophobic polymer surfaces(Elsevier Sci Ltd, 2012) Department of Chemistry; N/A; N/A; Department of Chemistry; Yılgör, İskender; Bilgin, Sevilay; Işık, Mehmet; Yılgör, Emel; Faculty Member; PhD Student; Researcher; Researcher; Department of Chemistry; College of Sciences; Graduate School of Sciences and Engineering; Graduate School of Sciences and Engineering; College of Sciences; 24181; N/A; N/A; N/AA simple and general method has been developed for the preparation of polymeric materials with superhydrophobic surfaces. The process is applicable to a large number of polymers, thermoplastic or thermoset. In this manuscript preparation and characteristics of superhydrophobic surfaces prepared from a segmented polydimethylsiloxane-urea copolymer (TPSU), a polyether based polyurethaneurea (TPU), poly(methyl methacrylate) (PMMA), polystyrene (PS), polycarbonate (PC) and a crosslinked epoxy resin (EPOXY) are discussed. All samples were prepared onto glass surfaces by using a simple, multi-step spin-coating procedure. In the first step a thin film of the desired polymer was coated onto the glass slide. This was followed by spin-coating of two layers of hydrophobic fumed silica using a dispersion in tetrahydrofuran. Finally to obtain a durable surface, a very thin film of the parent polymer was spincoated from a very dilute solution containing 2.5% by weight hydrophobic silica and 0.25% by weight matrix polymer in tetrahydrofuran. Surfaces were characterized by scanning electron microscopy (SEM), which clearly showed the formation of rough surfaces with homogeneously distributed silica particles in 1-10 mu m range. Static water contact angle and contact angle hysteresis measurements proved the formation of superhydrophobic surfaces. Samples displayed static water contact angles larger than 170 degrees and very low contact angle hysteresis of less than 3 degrees.