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Permanent URI for this collectionhttps://hdl.handle.net/20.500.14288/3
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Publication Metadata only Influence of soft segment structure, hydrogen bonding, and diisocyanate symmetry on morphology and properties of segmented thermoplastic polyurethanes and polyureas(Tubitak Scientific & Technological Research Council Turkey, 2023) Department of Chemistry; Yılgör, Emel; Yılgör, İskender; Department of Chemistry; College of SciencesA comprehensive review of the structure-morphology-property relations in segmented thermoplastic polyurethanes and polyureas (TPU) is provided. Special emphasis is given to the influence of the soft segment structure, polarity, and molecular weight, diisocyanate symmetry and the nature, extent, and strength of hydrogen bonding on the morphology and thermal and mechanical properties of TPUs. Experimental results obtained on composition-dependent TPU morphology and properties by various techniques were also compared by the morphology profiles generated by computational methods such as quantum mechanical calculations and molecular dynamics simulations.Publication Metadata only Bismuthene nanosheets as a photodynamic and photothermal antibacterial agent under NIR light illumination(Elsevier Inc., 2024) Cekceoglu, Ilknur Aksoy; Patir, Imren Hatay; Department of Chemistry; Eroğlu, Zafer; Kubanaliev, Temirlan; Metin, Önder; Department of Chemistry; Koç University Surface Science and Technology Center (KUYTAM) / Koç Üniversitesi Yüzey Teknolojileri Araştırmaları Merkezi (KUYTAM); College of Sciences; Graduate School of Sciences and EngineeringBacterial infections remain a significant public health burden due to the emergence of antibiotic resistance and their non-specific cytotoxic effects, leading to the search for novel antibacterial agents. Two-dimensional (2D) pnictogens, which stand out with their advantegeous properties such as large surface areas, compatibility with biological systems, and permeability across biological membranes, have emerged as potential materials in the fight against bacterial infections. By considering all these advantages, here for the first time, the antibacterial activity of 2D bismuth (Bismuthene, Biene) on Gram-negative Escherichia coli (E. coli) and Pseudomonas aeruginosa (P. aeruginosa), Gram-positive Staphylococcus aureus (S. aureus) and Methicillin-Resistant Staphylococcus aureus (MRSA) were examined under NIR light illumination. A growth curve analysis was conducted with a concentration of 256 mu g*mL-1 of exfoliated Biene nanosheets to assess the inhibition effect and corresponding antibacterial effect (%) against each bacterial strain. The photodynamic theraphy (PDT) and photothermal therapy (PTT)-mediated antibacterial mechanisms were explored by analyzing the generation of reactive oxygen species (ROS) via Glutathione (GSH) oxidation assay while a photothermal camera monitored temperature dynamic changes during irradiation. The high specific surface area-dependent membrane damage ability of Biene and morphological changes of the bacteria were visualized by field emission scanning electron microscope (FESEM). The exciting growth inhibition activity of Biene nanosheets for all bacterial strains was increased during irradiation, and breathtakingly the inhibition rate reached up to >= 99.1 % for P. aeruginosa, S. aureus, and MRSA. Besides, S. aureus and MRSA are more susceptible to Biene than E. coli and P. aeruginosa.Publication Metadata only In-situ surface enhanced Raman spectroscopy investigations on surface transformations of oxide derived copper electrodes during CO2RR(Academic Press Inc Elsevier Science, 2023) Department of Chemistry; Tafazoli, Saeede; Yusufoğlu, Muhammed; Balkan, Timuçin; Kaya, Sarp; Department of Chemistry; Koç University Tüpraş Energy Center (KUTEM) / Koç Üniversitesi Tüpraş Enerji Merkezi (KÜTEM); Graduate School of Sciences and Engineering; College of SciencesWe investigated the catalytic activity and C2 selectivity in electrochemical carbon dioxide reduction reac-tion (CO2RR) on two distinguished electrodeposited Cu oxides with distinct morphologies and structures. The electrode with a compact structure exhibited two times higher faradaic efficiencies of C2 products (40%). Through utilizing electrochemical surface-enhanced Raman spectroscopy (SERS), it was realized that the formation of a metastable phase (malachite) on electrode surfaces by consumption of HCO3- could cause a shift in local pH. The analysis of SERS indicated a strong correlation between the presence of the malachite phase and strongly-adsorbed CO on electrode surfaces, preventing dimerization and fur-ther reduction. This malachite phase terminating the surface can hinder the charge exchange and inter-fere with further reductions in C2 products.Publication Metadata only Probing Pt-CeO2 interfacial interactions through adsorption characteristics of small molecules(ACADEMIC PRESS INC ELSEVIER SCIENCE, 2024) Department of Chemistry; Mohammadpour, Amin; Kaya, Sarp; Department of Chemistry; Koç University Tüpraş Energy Center (KUTEM) / Koç Üniversitesi Tüpraş Enerji Merkezi (KÜTEM); Graduate School of Sciences and Engineering; College of SciencesIn this study, we prepared a Pt/CeO2/Cu(1 2 /Cu(1 1 1) model catalyst and investigated CO and CO2 2 adsorption using infrared reflection absorption spectroscopy (IRRAS) and temperature-programmed desorption (TPD) techniques to gain insight into the interaction between Pt nanoparticles and the CeO2 2 support surface. Our observations revealed that the deposition of CeO2 2 at 700 K results in island formation on the Cu(1 1 1) surface, whereas at 520 K it leads to a more continuous film formation. Reducing the CeO2/Cu(1 2 /Cu(1 1 1) surface enhances the CO and CO2 2 uptakes on CeO2. 2 . Pt nanoparticles deposited on these surfaces remained in a metallic form, and during CO desorption, they facilitate the oxidation of CO to form CO2 2 by utilizing lattice oxygen from the interface between them and CeO2. 2 .Publication Metadata only Mesoporous graphitic carbon nitride-supported binary MPt (M: Co, Ni, Cu) nanoalloys as electrocatalysts for borohydride oxidation and hydrogen evolution reaction(Elsevier, 2020) Oliveira, Raisa C. P.; Sevim, Melike; Sljukic, Biljana; Sequeira, Cesar A. C.; Santos, Diogo M. F.; Department of Chemistry; Metin, Önder; Faculty Member; Department of Chemistry; College of Sciences; 46962In this work, binary MPt (M = Co, Ni, Cu) nanoalloys and mesoporous carbon nitride (mpg-C3N4) as support material are prepared, and then gathered together by liquid phase self-assembly in order to produce MPt/mpg-C3N4 electrocatalysts. The yielded electrocatalysts are characterized by TEM, ICP-MS and XRD techniques in order to determine their morphology, composition and textural properties. Evaluation of MPt/mpg-C3N4 (<3 wt.% of Pt) electrocatalysts performance for hydrogen evolution reaction (HER) and borohydride oxidation reaction (BOR) is carried out. Pt/mpg-C3N4 is also studied to better understand the alloying effect on the electrocatalysts' performance, being concluded that it clearly increases the catalytic activity while decreasing the necessary Pt metal amount. For HER, CoPt/mpg-C3N4 was found to be the best catalyst, presenting a Tafel slope of 109 mV dec(-1) at 65 degrees C. Regarding BOR, CuPt/mpg-C3N4 demonstrated the best catalytic activity with average activation energy and reaction order with respect to BH4- of 29.4 kJ mol(-1) and 0.87, respectively.Publication Metadata only Synthesis and photopolymerization of novel, highly reactive phosphonated-urea-methacrylates for dental materials(Elsevier Science Bv, 2013) Altin, Ayse; Akgun, Burcin; Buyukgumus, Ozlem; Bilgici, Zeynep Sarayli; Agopcan, Sesil; Avci, Duygu; N/A; Department of Chemistry; Aşık, Didar; Acar, Havva Funda Yağcı; Master Student; Faculty Member; Department of Chemistry; College of Sciences; N/A; 178902An urea methacrylate (1) and two phosphonated methacrylates (2-3) were synthesized from 2-isocyanatoethyl methacrylate (IEM) and benzyl amine (1), diethyl aminomethylphosphonate (2) and diethyl amino(phenyl)methylphosphonate (3). Their photopolymerization rates are notably higher than commercial monomers, despite the presence of only one double bond. Their polymerization rates follow the order 1 similar to 2 > 3 similar to triethylene glycol dimethacrylate (TEGDMA) > 2-hydroxyethyl methacrylate (HEMA). A tendency toward high crosslinking density during thermal bulk polymerizations, low oxygen sensitivity and high conversions with benzophenone during photopolymerization indicated the importance of hydrogen abstraction/chain transfer reactions. It was found that the addition of the monomers to HEMA significantly increased its polymerization rate, proving their utility as replacements for TEGDMA as reactive diluents for 2,2-bis[4-(2-hydroxy-3-methacryloyloxy propyloxy) phenyl] propane (Bis-GMA). Copolymer systems containing 2 and 3 showed improved T-g values compared to Bis-GMA/TEGDMA systems. (C) 2013 Elsevier Ltd. All rights reserved.Publication Metadata only A two-dimensional Monte Carlo polymerization of 5-membered rings(Scientific Technical Research Council Turkey, 1997) Esentürk, O.; Pamuk, H. A.; Department of Chemistry; Yurtsever, İsmail Ersin; Faculty Member; Department of Chemistry; College of Sciences; 7129A modification of the kinetic growth model in two dimensions for the polymerization of 5-membered rings is presented. The preliminary results reveal the validity of the modified model.Publication Metadata only Influence of severe straining and strain rate on the evolution of dislocation structures during micro-/nanoindentation in high entropy lamellar eutectics(Elsevier, 2018) Maity, T.; Prashanth, K. G.; Kim, J. T.; Schoberl, T.; Wang, Z.; Eckert, J.; Department of Chemistry; Balcı, Özge; Researcher; Department of Chemistry; College of Sciences; 295531Eutectic high entropy composites (EHECs) can exhibit an excellent combination of high strength and high ductility; however, the mechanisms responsible for the strength-ductility trade-off remain unpredicted. The influence of strain rate (epsilon) over dot on the severe deformation imposed by high-pressure torsion (HPT) was used to evaluate the deformation mechanisms for a series of CoCrFeNiNbx (x molar ratio, 0 <= x <= 0.80) EHECs. Systematic and detailed micro-/nanoindentation investigations were performed and the results suggest that strain hardening (Taylor hardening) and grain-boundary strengthening (H-P strengthening) are the predominant strengthening mechanisms. Nanoindentation at different loading conditions (varying (epsilon) over dot) revealed that the measured hardness in the eutectic regime increases gradually because of dislocation-lamellae-interface interactions. Based on the deformation mechanisms operating at different strain rates (epsilon) over dot, the density of geometrically necessary dislocations (GNDs) and statistically stored dislocations (SSDs), determined by the Nix-Gao approach, are used to explain the strain hardening phenomena. The results reveal that a large volume fraction of lamellae-interfaces accommodate more dislocations upon straining these EHECs. Lamellae-interface GNDs (rho(GG)) are activated at higher strain rates and can be effectively stored, thereby improving the global strain and strain hardening.Publication Metadata only Residual stress gradients in electroplated nickel thin films(Elsevier Science Bv, 2015) N/A; N/A; Department of Chemistry; Department of Mechanical Engineering; Kılınç, Yasin; Ünal, Uğur; Alaca, Burhanettin Erdem; PhD Student; Faculty Member; Faculty Member; Department of Chemistry; 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; College of Sciences; College of Engineering; N/A; 42079; 115108Residual stress gradients in electroplated nickel films of 1 mu m thickness are characterized for a wide range of current densities (1-20 mA/cm(2)) and electroplating temperatures (30-60 degrees C) in a nickel sulfamate bath. Although a variety of stress measurements is available, exploration of stress gradients remain unstudied at the scale of 1 mu m. Stress gradients - unlike uniform stresses - can cause significant bending even in monolayered released structures. Moreover, examples of misinterpretation of wafer curvature data as a measure of stress gradients exist in the literature. Based on these motivations, monolayered Ni microcantilevers are employed in this work as mechanical transducers for the characterization of stress gradients within the nickel film. Experiments are supported with finite element simulations. Residual stress gradient is found to vary in the range of about 130 to 70 MP/mu m with the sign change indicating a transition from downward to upward deflection of the microcantilever. Thus, a window of electroplating parameters is established yielding zero residual stress gradients, i.e. straight cantilevers, without the use of any additive agents.Publication Metadata only Optical sensors based on palladium and polymer-coated optical fiber resonators(Spie-Int Soc Optical Engineering, 2019) Eryürek, Mustafa; N/A; Department of Physics; Department of Chemistry; Department of Chemistry; Department of Physics; Bavili, Nima; Morova, Berna; Yılgör, İskender; Yılgör, Emel; Kiraz, Alper; PhD Student; Researcher; Faculty Member; Researcher; Faculty Member; Department of Chemistry; Department of Physics; Koç University Research Center for Translational Medicine (KUTTAM) / Koç Üniversitesi Translasyonel Tıp Araştırma Merkezi (KUTTAM); N/A; College of Science; College of Sciences; College of Sciences; College of Sciences; N/A; 152935; 24181; N/A; 22542In this work, we present robust and easy-to-fabricate optical gas and vapor sensors based on optical fiber resonators (OFR) coated with palladium (Pd) thin films, Pd micro-particles and polymer brushes (PB). Pd based sensors are used for hydrogen (H-2) gas detection in concentration range of 0% to 1% and polymer brush-coated OFR are used for detection of vapor in concentration range of 0 to 25%. Sensing mechanism of these sensors is based on spectral shift of resonance wavelength which are called whispering gallery modes (WGMs). This spectral shift is due to volume expansion of the sensing material. Tapered fiber is used in order to excite WGMs in coated OFRs. Good sensitivity and repeatability results are obtained for all three types of sensors.