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Öğe Dodesiltrimetilamonyum bromid ile hazırlanan ikili sistemlerin faz davranışı(Ege Üniversitesi, 2010) Alihanoğlu, Hatice Şengül; Cebe, EmineDodecyltrimethylammonium bromide (DTAB)/etil alkol ikili sisteminin faz davranısı incelenmistir. Anizotropik tekstürleri karakterize etmek ve ısısal geçisleri teshis etmek için optik polarize mikroskop kullanılmıstır. DTAB+etanol sistemindeki arafazlar, artan DTAB konsantrasyonu ile izleyen sırada belirlenmistir: isotropik-hexagonal-lamellar. Bu sıvı kristallerin yapısal dönüsümü, diferansiyel tarama kalorimetresi ile dogrulanmıstır. Kırma indisinin sıcaklık ve kompozisyona baglılıgı için deneysel sonuçlar verilmis ve tartısılmıstır.;Liyotropik sıvı kristal, faz diyagramı, DTAB, kırmaindisi, diferansiyel tarama kalorimetresi (DSC).;Lyotropic liquid crystal, phase diagram, DTAB, refractive index, differential scanning calorimetry (DSC).Öğe Dynamic phenomena and viscous properties in a liquid crystal: A theoretical treatment and molecular dynamic simulations (vol 514, pg 124, 2011)(Elsevier Science Bv, 2012) Capar, M. Ilk; Cebe, Emine; Zakharov, A. V.Öğe Molecular dynamic study of the odd-even effect in some 4-n-alkyl-4 '-cyanobiphenyls(Amer Physical Soc, 2006) Capar, Mine Ilk; Cebe, EmineUsing a united atom model, we performed molecular dynamics (MD) simulations on the 4-n-alkyl-4 '-cyanobiphenyl (nCB) liquid crystal homologous series for n=5-9 at a constant reduced temperature in the nematic phase. To evaluate the rotational diffusion coefficient (RDC), the second- and fourth-rank order parameters (OP's) and correlation time were calculated from MD trajectories. We analyzed the rotational viscosity coefficient (RVC) by using the Nemtsov-Zakharov and Fialkowski methods based on statistical-mechanical approaches. The simulated RDC, RVC, and OP's were found to be reasonable when compared with previous theoretical and experimental data. These quantities were also calculated for the rigid core and alkyl chain segments separately for each mesogen, to take a closer look at the molecule tail-chain flexibility. The properties calculated for a rigid core were compared with those for an alkyl chain, and satisfactory results were obtained. Odd-even effects for RDF, RVC, and molecular ordering parameters were calculated for five mesogens.Öğe Molecular Dynamics Simulation of 4-N-Hexyl-4 '-Cyanobiphenyl Adsorbed at the Air-Water Interface(Iop Publishing Ltd, 2018) Gurbulak, Oguz; Cebe, EmineThe interfacial behavior of 4-n-hexyl-4'-cyanobiphenyl (6CB) molecules at the air-water interface is investigated by full atomistic molecular dynamics simulations. To understand the morphology and the structure of adsorbed 6CB molecules in detail, the snapshots and mass density profiles of the simulation system are generated. The average tilt angles between the interface normal and various vectors defined in the rigid and alkyl parts of 6CB are in good agreement with the experimental data available. The interfacial thickness and monolayer width are obtained from the mass density profiles of water and 6CB phase, respectively. The second and fourth rank orientational order parameters of cyanobiphenyl core are found to be larger than those of an elastic alkyl chain. Bond order parameters for 6CB are also calculated. The calculated oxygen-oxygen radial distribution function and hydrogen bonding statistics for bulk water are compared with those for the interfacial region. The surface tensions of the systems are calculated. All simulation results are compared with the available literature data.Öğe Molecular dynamics simulations on the adsorption of 4-n-octyl-4-cyanobiphenyl (8CB) at the air/water interface(Taylor & Francis Inc, 2018) Gurbulak, Oguz; Cebe, EmineThe influence of surface coverage to the structural properties of 4-n-octyl-4 '-cyanobiphenyl (8CB) monolayer at the air/water interface was studied by full atomistic molecular dynamics simulations. These properties include density profiles, interface thickness, monolayer width, orientational order parameters, and atom-pair radial distribution functions. The calculated tilt angles of the cyanobiphenyl and alkyl parts are in fairly good agreement with the experiments. The simulation results exhibit the general trends in the previous experimental and simulation data. [GRAPHICS] .Öğe Molecular dynamics study of 5CB at the air-water interface: From gas to beyond the monolayer collapse(Elsevier Science Bv, 2018) Gurbulak, Oguz; Cebe, EmineWe extend our earlier fully atomistic molecular dynamics (MD) study [Gurbulak, 0., and Cebe, E. (2017)] to the analysis of the interfacial behaviour of 4-n-pentyl-4'-cyanobiphenyl (5CB) at the air/water interface with surface coverages ranging from 0.07 to 5.01 molecules/nm(2). The density profiles of interfacial species and simulated tilt angles lead to the alignment variation of molecules from planar to tilted with increasing surface density of 5CB that is in good accord with experiments. Order parameters of various ranks and C-H bond order parameters relevant for deuterium nuclear magnetic resonance spectra were computed. The orientational order of mesogen molecules is considerably enhanced with respect to that for pure nematic 5CB, and increases also with surface density. The calculated interfacial thickness, monolayer width, and radial distribution functions were compared with previously reported results. (C) 2018 Elsevier B.V. All rights reserved.Öğe Odd-even effects in the homologous series of alkyl-cyanobiphenyl liquid crystals: A molecular dynamic study(Wiley, 2007) Capar, Mine Ilk; Cebe, EmineFor the first five members of the homologous series of 4-n-alkyl-4'-cyanobiphenyls in the nematic and isotropic phases, molecular dynamics (MD) simulations were performed by using a united atom model. An odd-even effect was seen to be found in the molecular length, width, biaxiality, and inertia tensor anisotropy with the length of alkyl chain. The distributions of the molecular length, width, and inertia tensor anisotropy were presented. The orientational distributions of the last C-C bonds in the alkyl chain were also evaluated for nematic and isotropic phases. (c) 2007 Wiley Periodicals, Inc.Öğe Polar bileşenli organik çözeltilerde viskozite ölçümleri ve bazı fiziksel yöntemlerle karşılaştırılması1980(Ege Üniversitesi, Fen Bilimleri Enstitüsü, 1980) Cebe, Emine; Ertaş, İsmetSalisilik asit ve fenolün birkaç alkol ve formik asitte hazırlanmış ikili çözeltilerinde, 200C-450C sıcaklık aralığında ve çözünenin 0.3'den küçük mol kesirleri için viskozite ölçümleri yapılmıştır. Ln ç = f(1/T) grafiklerinin doğrusal olduğu, konsantrasyonla viskozite değişiminin maksimum ve minimumlar içerdiği görülmüştür. Moleküller arası kuvvetler ve özellikle hidrojen bağlarının bu anormalliklere yol açtığı söylenebilir. Eyring eşitliği ile aktivasyon enerjileri, aktivasyon serbest enerjileri ve aktivasyon entropileri hesaplanmıştır.(1) Aktivasyon enerjilerinin nonassosiye maddelerinkinden daha büyük olduğu,(2)Aktivasyon serbest enerjileri ve aktivasyon entropilerinin sıcaklıkla azaldığı bulunmuştur. Viskozite ölçülerinden elde edilen sonuçları doğrulamak için aritmetik ortalamalı mol kütlesi (MS ) ve 200C deki kırma indisleri de ölçülmüştür. MS ve nD2'nin konsantrasyonla değişimleri, ç = f(N1) grafiklerindeki konsantrasyon bölgesinde kalan anormallikler göstermektedir. Ayrıca çözeltinin UV spektrumları alınmış ve maksimum absorbsiyon dalgaboyu, normal hekzanlı çözeltininkiyle karşılaştırılmıştır. Sonuçlar n ï* geçişlerinin kısa dalgaboylarına kaydığını, hidrojen bağı etkisiyle spektrumun ince yapısının kaybolduğunu göstermektedir. Çözgenlerin absorbansı yüksek olduğundan maksimum dalgaboylarına konsantrasyonun etkisi incelenememiştir.
