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Publication Metadata only A mixed basis with off-center Gaussian functions for the calculation of the potential energy surfaces for pi-stacking interactions: dimers of benzene and planar C-6(Springer, 2015) Department of Chemistry; Yurtsever, İsmail Ersin; Faculty Member; Department of Chemistry; College of Sciences; 7129A practical mixed basis set was developed to facilitate accurate calculations of potential energy surfaces for pi-stacking interactions. Correlation consistent basis sets (cc-PVXZ) were augmented by p-type Gaussian functions placed above and below the planes of C-6 moieties. Moller-Plesset (MP2, SCS-MP2) and coupled cluster [CCSD(T)] calculations show that such generated basis sets provide an accurate description of p-stacking systems with favorable computation times compared to the standard augmented basis sets. The addition of these off-center functions eliminates the linear dependence of the augmented basis sets, which is one of the most encountered numerical problems during calculation of the oligomers of polyaromatic hydrocarbons (PAH). In this work, we present a comparative study of the general characteristics of the potential energy surfaces for the parallel stacked and T-shape conformations of benzene and planar C6 clusters, using a combination of cc-PVXZ and our optimized functions. We discuss properties, such as the depth and curvature of the potential functions, short and long distance behavior, and the frictional forces between two model monomers.Publication Metadata only Rattling in the cage: Ions as probes of sub-picosecond water network dynamics(American Chemical Society (ACS), 2009) Schmidt, Diedrich A.; Funkner, Stefan; Born, Benjamin P.; Gnanasekaran, Ramachandran; Schwaab, Gerhard W.; Leitner, David M.; Havenith, Martina; Department of Chemistry; Birer, Özgür; Faculty Member; Department of Chemistry; College of Sciences; N/AWe present terahertz (THz) measurements of salt solutions that shed new light on the controversy over whether salts act as kosmotropes (structure makers) or chaotropes (structure breakers), which enhance or reduce the solvent order, respectively. We have carried out precise measurements of the concentrationdependent THz absorption coefficient of 15 solvated alkali halide salts around 85 cm-1 (2.5 THz). In addition, we recorded overview spectra between 30 and 300 cm-1 using a THz Fourier transform spectrometer for six alkali halides. For all solutions we found a linear increase of THz absorption compared to pure water (THz excess) with increasing solute concentration. These results suggest that the ions may be treated as simple defects in an H-bond network. They therefore cannot be characterized as either kosmotropes or chaotropes. Below 200 cm-1, the observed THz excess of all salts can be described by a linear superposition of the water absorption and an additional absorption that is attributed to a rattling motion of the ions within the water network. By providing a comprehensive set of data for different salt solutions, we find that the solutions can all be very well described by a model that includes damped harmonic oscillations of the anions and cations within the water network. We find this model predicts the main features of THz spectra for a variety of salt solutions. The assumption of the existence of these ion rattling motions on sub-picosecond time scales is supported by THz Fourier transform spectroscopy of six alkali halides. Above 200 cm-1 the excess is interpreted in terms of a change in the wing of the water network librational mode. Accompanying molecular dynamics simulations using the TIP3P water model support our conclusion and show that the fast sub-picosecond motions of the ions and their surroundings are almost decoupled. These findings provide a complete description of the solute-induced changes in the THz solvation dynamics for the investigated salts. Our results show that THz spectroscopy is a powerful experimental tool to establish a new view on the contributions of anions and cations to the structuring of water. © 2009 American Chemical Society.Publication Metadata only Antibacterial silicone-urea/organoclay nanocomposites(Springer, 2009) Department of Chemistry; N/A; N/A; Department of Chemistry; Yılgör, Emel; Nugay, Işık Işıl; Bakan, Murat; Yılgör, İskender; Researcher; Undergraduate Student; Undergraduate Student; Faculty Member; Department of Chemistry; College of Sciences; College of Engineering; College of Engineering; College of Sciences; N/A; N/A; N/A; 24181Montmorillonite modified with distearyldimethyl ammonium chloride (C18-QAC) (Nanofil-15) (NF15) was incorporated into polydimethylsiloxane-urea (silicone-urea, PSU) copolymers. PSU was obtained by the reaction of equimolar amounts of aminopropyl terminated polydimethylsiloxane (PDMS) oligomer (= 3,200 g/mol) and bis(4-isocyanatohexyl) methane (HMDI). A series of PSU/NF15 nanocomposites were prepared by solution blending with organoclay loadings ranging from 0.80 to 9.60% by weight, corresponding to 0.30 to 3.60% C18-QAC. Colloidal dispersions of organophilic clay (NF15) in isopropanol were mixed with the PSU solution in isopropanol and were subjected to ultrasonic treatment. Composite films were obtained by solution casting. FTIR spectroscopy confirmed that the organoclay mainly interacted with the urea groups but not with PDMS. XRD analysis showed that nanocomposites containing up to 6.40% by weight of organoclay had fully exfoliated silicate layers in the polymer matrix, whereas 9.60% loading had an intercalated structure. Physicochemical properties of nanocomposites were determined. PSU/NF15 nanocomposites displayed excellent long-term antibacterial properties against E. coli.Publication Metadata only Motion of single terrylene molecules in confined channels of poly(butadiene)-poly(ethylene oxide) diblock copolymer(Amer Chemical Soc, 2009) N/A; Department of Physics; Department of Chemistry; Yorulmaz, Mustafa; Kiraz, Alper; Demirel, Adem Levent; Master Student; Faculty Member; Faculty Member; Department of Physics; Department of Chemistry; Graduate School of Sciences and Engineering; College of Sciences; College of Sciences; N/A; 22542; 6568The motion of terrylene probe molecules in confined PB channels of an asymmetric PB-PEO diblock copolymer has been investigated by single molecule tracking. The one-dimensional diffusion coefficients were found to be significantly smaller and had a narrower distribution compared to two-dimensional diffusion coefficients in PB. The trajectories of some single molecules showed unusual behavior of directed motion where mean square displacement had a parabolic dependence oil lag time. The likely origin of this behavior is discussed in terms of local variations in the PB channel width and the resulting change in the local density. The results show the effect of nonuniformities and heterogeneities in the channels on the motion of single molecules and demonstrate the sensitivity of single molecule tracking in characterizing self-assembled block copolymer morphologies.Publication Metadata only Effect of ambient and cryogenic milling on the microstructure and properties of tungsten matrix composites fabricated by activated sintering(Sivas Cumhuriyet Üniversitesi, 2019) Ağaoğulları, Duygu; Öveçoğlu, M. Lütfi; Department of Chemistry; Department of Chemistry; Balcı, Özge; Somer, Mehmet Suat; Researcher; Faculty Member; Department of Chemistry; College of Sciences; College of Sciences; 295531; 178882Tungsten matrix composites reinforced with TiB2 and Y2O3 particles were fabricated by milling under ambient/cryogenic conditions and Ni activated sintering. Powder blends constituting the W - 1 wt. % Ni - 2 wt. % TiB2 - 1 wt. % Y2O3 composition were mechanically milled for 12 h under ambient condition or cryomilled for 10 min or sequentially milled under ambient and cryogenic conditions. Milling was carried out in a high-energy ball mill under ambient condition whereas cryogenic milling was conducted in externally circulated liquid nitrogen. Milled powders were compacted using a hydraulic press and the pellets were sintered at 1400°C for 1 h under Ar / H2 gas flowing conditions. The effects of different milling types on the microstructural and mechanical properties of the sintered composites were investigated. After sintering, in addition to dominant W phase, small amounts of WB and NiW phases were detected in all sintered samples. The application of cryomilling after milling at ambient condition provided the disappearance of the clustered TiB2 and Y2O3 particles in the sintered sample: They were located at the grain boundaries of W1Ni matrix and homogeneously distributed through the microstructure. Sequentially milled and sintered composite had the highest relative density (95.77 %) and the highest microhardness (7.23 GPa) values among the samples. Nanoindentation tests showed that there was an improvement in the hardness and elastic modulus of W matrix phase, which yielded the values of 8.9 and 373.7 GPa, respectively. / Özet: Bu çalışmada, Ni ile aktive edilerek sinterlenen tungsten esaslı matrisin TiB2 ve Y2O3 partikülleri ile takviye edilmesiyle, tungsten esaslı kompozit malzeme üretimi gerçekleştirilmiştir. W - % 1 ağ. Ni - % 2 ağ. TiB2 - % 1 ağ. Y2O3 kompozisyonundan oluşan toz harmanları, normal koşullarda 12 sa mekanik olarak öğütülerek ya da 10 dk kriyojenik ortamda öğütülerek ya da normal ve kriyojenik şartlarda ardışık olarak öğütülerek hazırlanmıştır. Normal şartlarda öğütme yüksek enerjili bir değirmende uygulanırken; kriyojenik şartlarda öğütme sıvı azot ile dışarıdan çevrelenen bir sistemde yapılmıştır. Öğütülmüş tozlar hidrolik pres kullanılarak preslenmiş ve pekiştirilen bünyeler Ar/H2 gazaltı şartlarında 1400°C’de 1 sa sinterlenmiştir. Farklı öğütme koşullarının sinterlenen kompozit malzemelerin mikroyapısı ve özellikleri üzerindeki etkisi incelenmiştir. Sinterlenme sonrasında, baskın W fazına ek olarak düşük mikarda WB ve NiW fazları oluşumu gözlemlenmiştir. Normal şartlarda öğütme sonrası uygulanan kriyojenik öğütme, sinter malzemelerin mikroyapısındaki TiB2 ve Y2O3 partiküllerin topaklanmasının yok olmasına neden olmuştur: Partiküllerin W1Ni matrisinin tane sınırlarında ve homojen olarak mikroyapıda dağılması sağlanmıştır. Ardışık olarak öğütülmüş ve sinterlenmiş kompozitler, numuneler arasında en yüksek rölatif yoğunluk (% 95,77) ve mikrosertlik değerlerini (7,23 GPa) sunmuştur. Nano-indentasyon testleri sayesinde, W matris fazının sertlik ve elastisite modül değerlerinin sırasıyla 8,9 ve 373,7 GPa değerlerine kadar iyileştirildiği kanıtlanmıştır.Publication Metadata only High temperature thermoelectric properties of the type-I clathrate BA(8)NI(X)GE46(-X-Y)square(Y)(Institute of Physics (IOP) Publishing, 2014) Candolfi, Christophe; Örmeci, Alim; Baitinger, Michael; Oeschler, Niels; Steglich, Frank; Grin, Yu; Department of Chemistry; Aydemir, Umut; Faculty Member; Department of Chemistry; College of Sciences; 58403Polycrystalline samples of the type-I clathrate Ba8NixGe46-x-y square(y) were synthesized for 0.2 <= x <= 3.5 by melt quenching and for 3.5 < x <= 6.0 by melting with subsequent annealing at 700 degrees C. The maximum Ni content in the clathrate framework at this temperature was found to be x approximate to 4.2 atoms per unit cell. Thermoelectric and thermodynamic properties of the type-I clathrate were investigated from 300 to 700 K by means of electrical resistivity, thermopower, thermal conductivity and specific heat measurements. As the Ni content increases, the electronic properties gradually evolve from a metallic character (x < 3.5) towards a highly doped semiconducting state (x >= 3.5). Below x approximate to 4.0 transport is dominated by electrons, while further addition of Ni (x approximate to 4.2) switches the electrical conduction to p-type. Maximum value of the dimensionless thermoelectric figure of merit ZT approximate to 0.2 was achieved at 500K and 650K for x approximate to 2.0 and x approximate to 3.8, respectively.Publication Metadata only Nanoparticle based induction heating at low magnitudes of magnetic field strengths for breast cancer therapy(Elsevier, 2019) Zuvin, Merve; Koçak, Muhammed; Akkoç, Yunus; Kutlu, Özlem; Gözüaçık, Devrim; Koşar, Ali; N/A; Department of Chemistry; Ünal, Özlem; Acar, Havva Funda Yağcı; PhD Student; Faculty Member; Department of Chemistry; Graduate School of Sciences and Engineering; College of Sciences; N/A; 178902Magnetic hyperthermia has received much attention during the last decade due to its implementation in cancer treatment. Recently, functionalized superparamagnetic iron oxide nanoparticles (SPION) emerged as a strong alternative adjuvant treatment approach, which complements conventional methods such as chemotherapy. In this study, we demonstrate the anticancer effect of Poly(acrylic acid)-coated, anti-HER2-tagged SPIONs on breast cancer cells using a low magnetic field strength of 0.8 kAm(-1), which is significantly lower compared to the literature, with a frequency of 400 kHz. Specificity was achieved via anti-HER2 antibody attachment to nanoparticles. HER2-positive SKBR3 and MDA-MB-453 cell lines internalized the nanoparticles successfully. These nanoparticles, which were not toxic to these cell lines, led to a prominent decrease in cell proliferation and survival in MDA-MB-453 cells when subjected to hyperthermia. Therefore, the hyperthermia-targeted SPION approach could be developed as a potential cancer treatment approach against breast cancer and possible other cancer types.Publication Metadata only Melt-centrifuged (BI,SB)(2)TE-3: engineering microstructure toward high thermoelectric efficiency(Wiley-V C H Verlag Gmbh, 2018) Pan, Yu; Grovogui, Jann A.; Witting, Ian T.; Hanus, Riley; Xu, Yaobin; Wu, Jinsong; Wu, Chao-Feng; Sun, Fu-Hua; Zhuang, Hua-Lu; Dong, Jin-Feng; Li, Jing-Feng; Dravid, Vinayak P.; Snyder, G. Jeffrey; Department of Chemistry; Aydemir, Umut; Faculty Member; Department of Chemistry; College of Sciences; 58403Microstructure engineering is an effective strategy to reduce lattice thermal conductivity (kappa(l)) and enhance the thermoelectric figure of merit (zT). Through a new process based on melt-centrifugation to squeeze out excess eutectic liquid, microstructure modulation is realized to manipulate the formation of dislocations and clean grain boundaries, resulting in a porous network with a platelet structure. In this way, phonon transport is strongly disrupted by a combination of porosity, pore surfaces/junctions, grain boundaries, and lattice dislocations. These collectively result in a approximate to 60% reduction of kappa(l) compared to zone melted ingot, while the charge carriers remain relatively mobile across the liquid-fused grains. This porous material displays a zT value of 1.2, which is higher than fully dense conventional zone melted ingots and hot pressed (Bi,Sb)(2)Te-3 alloys. A segmented leg of melt-centrifuged Bi0.5Sb1.5Te3 and Bi0.3Sb1.7Te3 could produce a high device ZT exceeding 1.0 over the whole temperature range of 323-523 K and an efficiency up to 9%. The present work demonstrates a method for synthesizing high-efficiency porous thermoelectric materials through an unconventional melt-centrifugation technique.Publication Metadata only Investigation of the factors affecting the photothermal therapy potential of small iron oxide nanoparticles over the 730-840 nm spectral region(Royal Soc Chemistry, 2018) N/A; N/A; N/A; Department of Physics; Department of Chemistry; Bilici, Kübra; Muti, Abdullah; Duman, Fatma Demir; Sennaroğlu, Alphan; Acar, Havva Funda Yağcı; PhD Student; PhD Student; PhD Student; Faculty Member; Faculty Member; Department of Physics; Department of Chemistry; Graduate School of Sciences and Engineering; Graduate School of Sciences and Engineering; Graduate School of Sciences and Engineering; College of Sciences; College of Sciences; N/A; N/A; N/A; 23851; 178902The use of superparamagnetic iron oxide nanoparticles (SPIONs) as a sensitizer in photothermal therapy (PTT) is relatively new and the origin of such a phenomenon is not known. Usually, large crystals and aggregated particles are preferred in the literature, suggesting that these increase the absorbance of particles at the irradiation wavelength, and hence, provide a larger temperature increase. This study has two major goals: identification of the key factors that affect the photo-induced temperature increase in well-controlled experiments and the influence of laser irradiation on nanoparticle properties. Small, biocompatible poly(acrylic acid) coated SPIONs (PAA/SPIONs) were used since they are more practical for future medical use than large aggregates. We studied the impact of three major laser-dependent variables, namely the wavelength (between 728 and 838 nm), intensity (1.85-9.76 W cm(-2)) and power (105-800 mW) as well as attenuation at the irradiation wavelength, on photothermal heating achieved with PAA/SPIONs. Within the studied range of these variables, only the laser power plays a critical role on the magnitude of photothermal heating in solutions. There is no strong correlation between the attenuation at the excitation wavelength and the temperature increase. In addition, extensive characterization of SPIONs before and after irradiation revealed no significant difference, which supports the re-usability of SPIONs. Lastly, the PTT potential of these small PAA/SPIONs was demonstrated in vitro on HeLa cells. At these low laser powers no temperature increase in SPION-free water or cell death in SPION-free cells was detected. Hence, this study provides a new insight into the photothermal effect of SPIONs, provides a clear and repeatable experimental procedure and demonstrates great potential for small SPIONs to be exploited in PTT.Publication Metadata only 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; 24181Polymer 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.