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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 Chaos in rotating triatomic clusters(Editions Physique, 1997) Department of Chemistry; Yurtsever, İsmail Ersin; Faculty Member; Department of Chemistry; College of Sciences; 7129Lyapunov exponent distributions of rotating triatomic Lennard-Jones clusters are calculated to analyze the effects of the vibrational and rotational motion on the extent of chaotic behavior. Initial momentum components are assigned to atoms either to rotate the clusters around symmetry axes or to generate random angular momenta. In both cases, it is seen that the initial kinetic energy assigned to vibrational modes is the dominant factor which determines the degree of chaos.Publication Metadata only Crystal structure of sodium tetrastrontium tris (dinitridoborate), NaSr4[BN2]3(R Oldenbourg Verlag, 2000) Carrillo-Cabrera, Wilder; Peters, K. von Schnering, Hans Georg; Department of Chemistry; Somer, Mehmet Suat; Faculty Member; Department of Chemistry; College of Sciences; 178882B3N6NaSr4, cubic, Im (3) over bar m (NO. 229), a = 7.568(1) Angstrom, V = 433.5 Angstrom(3), Z = 2, R-gt(F) = 0.053, wR(F) = 0.043, T = 293 K.Publication Metadata only Structures and properties of NbOF3 and TaOF3 - with a remark to the O/F ordering in the SnF4 type structure(Wiley-V C H Verlag Gmbh, 2002) Köhler, J; Simon, A; van Wullen, L; Cordier, S; Roisnel, T; Poulain, M; Department of Chemistry; Somer, Mehmet Suat; Faculty Member; Department of Chemistry; College of Sciences; 178882Powder samples of NbOF3 und TaOF3 were prepared by heating mixtures of NbO2F and NbF5 or TaO2F and TaF5, respectively, in the corresponding stoichiometric ratio in platinum crucibles under argon atmosphere (180-220degreesC). Both oxide fluorides are coulourless with a slight greyish tinge. They are sensitive to moisture and decompose in air at room temperature within hours. Both, NbOF3 and TaOF3 crystallize as a variant of the SnF4 type structure, space group 14/mmm. The structures have been refined from X-ray powder diffraction data using the Rietveld method (a = 3.9675(1) Angstrom, c = 8.4033(1) Angstrom, R-B = 3.60%, R-p = 4.58% for NbOF3 and a = 3.9448(1) Angstrom, c = 8.4860(1) Angstrom, R-a = 2.07%, R-p = 2.44% for TaOF3). Characteristic building units are sheets of corner sharing MX6 octahedra which are stacked via van der Waals interactions to a three dimensional framework. The occupancy of the two crystallographic sites for the anions by O and F is discussed on the basis of structure refinements, bond order summations, IR and NMR data and calculations of the Madelung parts of the lattice energy.Publication Metadata only Nanoparticle silicalite-1 crystallization from clear solutions: nucleation(Elsevier Science Bv, 2009) Tokay, Begüm; Erdem-Şenatalar, Ayşe; Schueth, Ferdi; Thompson, Robert W.; Department of Chemistry; Somer, Mehmet Suat; Faculty Member; Department of Chemistry; College of Sciences; 178882Despite much effort spent by various research groups, there remain many aspects of nanoparticle silicalite-1 crystallization from clear solutions which require further investigation. In order to shed light, especially on the nucleation of silicalite-1, particle growth at 100 degrees C from several starting compositions known to yield colloidal silicalite-1, which have been studied previously by other researchers using various techniques, was followed in this study by laser light scattering using scattering angles of 90 degrees and 173 degrees, and zeta potential and pH measurements. Crystallinity was monitored by X-ray diffraction, Fourier transform infrared analysis and transmission electron microscopy. Thermogravimetric analyses and density measurements were also used to characterize the products obtained at various times during the syntheses. The results demonstrate that the distinct time of sudden jump in the effective diameter of the nanoparticles in solution, as observed more clearly by using the back-scattering device, and which marks the beginning of the constant linear growth rate of the particles, corresponds to the nucleation of the silicalite-1 crystal structure. This time was also shown to coincide with the exo-endo thermal switch time of the reaction mechanism, which has been observed previously by another research group. Nucleation was accompanied by an aggregation of a population of smaller particles, as indicated by the broadening of the particle size distribution, and the variation of the pH and zeta potential values during synthesis.Publication Metadata only Synthesis, characterization and properties of naphthoxazine-functional poly(propyleneoxide)s(PERGAMON-ELSEVIER SCIENCE LTD, 2006) Yıldırım, Ayfer; Kıskan, Barış; Yağcı, Yusuf; Department of Chemistry; Demirel, Adem Levent; Faculty Member; Department of Chemistry; College of Sciences; 6568Thermally curable naphthoxazine-functionalized polymers were synthesized by the reaction of linear (diamines) and branched (triamines) poly(propyleneoxide)s (Jeffamine series) having various molecular weights, with p-formaldehyde, and 2-naphthol. The structures of the resulting polymers were characterized by using FT-IR and H-1-NMR. In addition, curing behavior of these polymers was studied using differential scanning calorimeter (DSC). Hydrophilicity of these polymers, both in cured and non-cured states, was investigated by water contact angle measurements. The surface topographies of the polymers were also examined by atomic force microscope (AFM).Publication Metadata only A coarse graining approach in molecular simulations: fuzzy potentials(Istanbul Technical University, 2003) Department of Chemistry; Department of Chemistry; Yurtsever, İsmail Ersin; Eşsiz, Şebnem; Faculty Member; Undergraduated Student; Department of Chemistry; College of Sciences; College of Sciences; 7129; 191615A new representation for interaction potential functions is presented. Unlike the orthodox approaches, the potential function is not a fixed function in terms of internuclear coordinates but a probabilistic one which contains information over a wide range of angular degrees of freedom. It is shown that such approaches can provide practical solutions for bulk systems of high density.Publication Metadata only Crystallization of poly(ethylene oxide) in thin films(Taylor & Francis Inc, 2003) N/A; Department of Chemistry; Department of Chemistry; Ok, Salim; Demirel, Adem Levent; Undergraduate Student; Faculty Member; Department of Chemistry; College of Sciences; College of Sciences; N/A; 6568Crystallization of poly(ethylene oxide) (PEO) in thin films was studied using hot-stage polarized optical microscopy. Isothermal linear crystal growth rates were measured for various film thicknesses at various degrees of undercooling. At a given crystallization temperature, the linear crystal growth rate decreased exponentially with decreasing film thickness below a film thickness of 80 nm. Films showed similar spherulitic morphology down to a film thickness of 30 nm. Control experiments on hydrophilic and hydrophobic surfaces showed that surface chemistry affects stability of the polymer films and causes a competition between crystallization and dewetting.