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Permanent URI for this collectionhttps://hdl.handle.net/20.500.14288/3
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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 The first alkaline-earth azidoaurate(III), Ba[Au(N-3)(4)](2) center dot 4 H2O(Wiley, 2023) Prots, Yurii; Jach, Franziska; Afyon, Semih; Höhn, Peter; Department of Chemistry; Department of Chemistry; Department of Chemistry; Subaşı, Yaprak; Tekin, Elif Sena; Somer, Mehmet Suat; Researcher; Undergraduate Student; Faculty Member; Department of Chemistry; College of Sciences; College of Sciences; College of Sciences; N/A; N/A; 178882Transparent, dark orange Ba[Au(N-3)(4)](2) center dot 4 H2O was synthesized by reaction of Ba(N-3)(2) and AuCl3 or HAuCl4 in aqueous solution. The novel barium tetraazidoaurate(III) tetrahydrate crystallizes in the monoclinic space group Cc (no. 9) with a=1813.68(17) pm, b=1737.95(11) pm, c=682.04(8) pm and beta=108.849(4)degrees. The predominant structural features of Ba[Au(N-3)(4)](2) center dot 4 H2O are two crystallographically independent discrete anions [Au(N-3)(4)](-) with gold in a tetragonal planar coordination by nitrogen. Vibrational spectra show good agreement with those of other azidoaurates(III). Upon drying, this salt was shown to be a highly explosive material.Publication Metadata only Pi-stack dimers of small polyaromatic hydrocarbons: a path to the packing of graphenes(Amer Chemical Soc, 2009) Department of Chemistry; Yurtsever, İsmail Ersin; Faculty Member; Department of Chemistry; College of Sciences; 7129MP2 calculations of the stacking energy are reported for the dimers of a set of polycyclic aromatic hydrocarbons. The interaction strengths and their dependence on the shape-dependent measures as well as the aromatic character of the monomer are studied. For small systems involving four to six rings, the noncovalent interactions seem to be independent of the shape of the monomers. The most preferred conformations for parallel stacked dimers are not aligned exactly but off-center with small shifts; however, these shifts are on the order of 1 angstrom, and the energy necessary to keep them aligned is less than 0.5 kcal/mol per ring. Small-angle rotations within the molecular planes also do not require much energy, and in some cases they lead to stronger interactions.Publication Metadata only Structuring a quantum solvent around a weakly bound dopant: the He-Cs2((3)sigma u) complex(2009) Prosmiti, Rita; Delgado-Barrio, Gerardo; Villarreal, Pablo; Coccia, Emanuele; Gianturco, Franco A.; Department of Chemistry; Yurtsever, İsmail Ersin; Faculty Member; Department of Chemistry; College of Sciences; 7129The structure and energetics of 3,4HeCs2(3Σu) molecules are analyzed from first principles. Fixing the cesium dimer at its equilibrium distance, the electronic structure was determined through ab initio methods at the CCSD(T) level of theory using a large basis set to compute the interaction energies. At the T-shaped geometry, there is a shallow well with a depth of ∼2 cm−1 placed at R ∼6.75 Å, R being the distance from the center of mass of Cs2 to He. That depth gradually decreases to ∼0.75 cm−1, while R increases to about 11.5 Å at linear arrangements. A simple model of adding atom−atom Lennard-Jones potentials with well-depth and equilibrium distance parameters depending on the angular orientation was found to accurately reproduce the ab initio points. Using this analytical form, variational calculations at zero total angular momentum are performed, predicting a single bound level at ∼−0.106 (∼−0.042) cm−1 for the boson (fermion) species. Further calculations using Quantum Monte Carlo methods are carried out and found to be in good agreement with the variational ones. On the basis of the present results, such analytical expression could in turn be used to describe the structure and binding of larger complexes and therefore opens the possibility to further studies involving such aggregates.Publication Metadata only Electroadhesion with application to touchscreens(Royal Soc Chemistry, 2019) Ayyıldız, Mehmet; Persson, Bo N. J.; N/A; Department of Mechanical Engineering; Şirin, Ömer; Başdoğan, Çağatay; PhD Student; Faculty Member; Department of Mechanical Engineering; Graduate School of Sciences and Engineering; College of Engineering; N/A; 125489There is growing interest in touchscreens displaying tactile feedback due to their tremendous potential in consumer electronics. In these systems, the friction between the user's fingerpad and the surface of the touchscreen is modulated to display tactile effects. One of the promising techniques used in this regard is electrostatic actuation. If, for example, an alternating voltage is applied to the conductive layer of a surface capacitive touchscreen, an attractive electrostatic force is generated between the finger and the surface, which results in an increase in frictional forces acting on the finger moving on the surface. By altering the amplitude, frequency, and waveform of this signal, a rich set of tactile effects can be generated on the touchscreen. Despite the ease of implementation and its powerful effect on our tactile sensation, the contact mechanics leading to an increase in friction due to electroadhesion has not been fully understood yet. In this paper, we present experimental results for how the friction between a finger and a touchscreen depends on the electrostatic attraction and the applied normal pressure. The dependency of the finger-touchscreen interaction on the applied voltage and on several other parameters is also investigated using a mean field theory based on multiscale contact mechanics. We present detailed theoretical analysis of how the area of real contact and the friction force depend on contact parameters, and show that it is possible to further augment the friction force, and hence the tactile feedback displayed to the user by carefully choosing those parameters.Publication Metadata only The CH-3 Sigma+ anion: inelastic rate coefficients from collisions with he at interstellar conditions(American Chemical Society (ACS), 2023) de la Fuente, Jorge Alonso; Sanz-Sanz, Cristina; Gonzalez-Sanchez, Lola; Wester, Roland; Gianturco, Francesco A.; Department of Chemistry; Yurtsever, İsmail Ersin; Faculty Member; Department of Chemistry; College of Sciences; 7129We present accurate ab initio calculations on several properties of a gas-phase system of interest in the interstellar medium (ISM), where the title molecular anion has been often surmised but not yet confirmed by observations. The CH-3 sigma+ constitutes the smallest term in the series of longer anionic polyynes which have been observed in the ISM (e.g., C4H-and several others). Hence, its dynamical behavior in collision with He atoms, one of the most abundant atoms in that environment, can provide quantitative indicators on the changes which can occur in the rotational state population of the title anion when driven by this collision dynamics. We therefore report an accurate evaluation of the full potential energy surface (PES) which acts between the molecular anion in its ground vibrational state and the He atom. The relevant inelastic scattering cross sections and the corresponding inelastic rate coefficients are then computed within a quantum treatment of the collisions. We find that the fairly small values of the final inelastic rate coefficients indicate state-changing processes by collisions to be inefficient paths for modifying the rotational state populations of this anion and therefore to aid its possible observation from direct radiative emission in the microwave region.Publication Metadata only Influence of kosmotrope and chaotrope salts on water structural relaxation(American Chemical Society (ACS), 2020) Luo, Peng; Zhai, Yanqin; Mamontov, Eugene; Xu, Guangyong; Faraone, Antonio; Department of Chemical and Biological Engineering; Şenses, Erkan; Faculty Member; Department of Chemical and Biological Engineering; College of Engineering; 280298The structural relaxation in water solutions of kosmotrope (structure maker) and chaotrope (structure breaker) salts, namely sodium chloride, potassium chloride, and cesium chloride, were studied through quasielastic neutron scattering measurements. We found that the collective dynamics relaxation time at the structure factor peak obtained using heavy water solutions shows a distinctively different behavior in the kosmotrope as opposed to the chaotrope solutions, increasing with the salt concentration in the former and decreasing in the latter. In both cases the trends are proportional to the concentration dependence of the relative viscosity of the solutions. These results indicate that kosmotropes and chaotropes influence the solutions viscosity by impacting in opposite ways the hydrogen bond network of water, strengthening it in one case and softening it in the other.Publication Metadata only Energy landscapes in photochemical dissociation of small peroxides(Amer Chemical Soc, 2019) N/A; N/A; N/A; Department of Chemistry; Tabriz, Meisam Farzalipour; Çizmeciyan, Melisa Natali; Birer, Özgür; Yurtsever, İsmail Ersin; Master Student; 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; Graduate School of Sciences and Engineering; N/A; College of Sciences; N/A; N/A; N/A; 7129Organic peroxides are known to have important roles in many chemical and biochemical processes such as intermediates in the oxidation of various hydrocarbons, as initiators of free-radical polymerization and cross-linking agents, etc. Consequently, the study of the organic peroxides and their radicals are of fundamental interest and importance. Although several reaction pathways after dissociation of organic peroxides have been successfully identified using time-resolved optical absorption spectroscopy, interpretation of the data can be complicated due to spectral overlap of parent molecules, intermediates, and products. Therefore, a reliable theoretical framework is necessary in case of complex or less studied systems. In this study, we investigated the plausible thermal dissociation pathways of diethyl peroxide, ditert butyl peroxide, and dicumyl peroxide by density functional theory with M06-2X hybrid functional and compared its results to coupled cluster single double and perturbative triple, CCSD(T), level energies. Our results indicate that methyl radical elimination is the main dissociation mechanism for all of the studied peroxides after O-O bond cleavage which has been also observed in experiments. The resulting relative energies of the M06-2X functional were found to have reasonable accuracy in comparison with the CCSD(T) method. We also show that time-dependent density functional theory (TD-DFT) with the M06-2X functional provides a suitable guide for interpretation of time-resolved optical absorption spectra of peroxides. The experimental transient absorption spectra of dicumyl peroxide are interpreted using the theoretically predicted pathways and transient radical species. Both results agree within experimental resolution and accuracy. We propose that the traditionally assigned visible absorption is not due to the cumuloxyl radical and the photodissociation of dicumyl peroxide involves other pathways with extremely short-lived radicals.Publication Metadata only Low-cost optical assays for point-of-care diagnosis in resource-limited settings(Amer Chemical Soc, 2021) Jiang, Nan; Tansukawat, Natha Dean; Gonzalez-Macia, Laura; Ateş, H. Ceren; Dinçer, Can; Güder, Fırat; Yetişen, Ali K.; Department of Mechanical Engineering; Taşoğlu, Savaş; Faculty Member; Department of Mechanical Engineering; College of Engineering; 291971Readily deployable, low-cost point-of-care medical devices such as lateral flow assays (LFAs), microfluidic paper-based analytical devices (mu PADs), and microfluidic thread-based analytical devices (mu TADs) are urgently needed in resource-poor settings. Governed by the ASSURED criteria (affordable, sensitive, specific, user-friendly, rapid and robust, equipment-free, and deliverability) set by the World Health Organization, these reliable platforms can screen a myriad of chemical and biological analytes including viruses, bacteria, proteins, electrolytes, and narcotics. The Ebola epidemic in 2014 and the ongoing pandemic of SARS-CoV-2 have exemplified the ever-increasing importance of timely diagnostics to limit the spread of diseases. This review provides a comprehensive survey of LFAs, mu PADs, and mu TADs that can be deployed in resource-limited settings. The subsequent commercialization of these technologies will benefit the public health, especially in areas where access to healthcare is limited.Publication Metadata only HCHO in a cold, quantum solvent: size and shape of its "bubbles" in (4)He droplets from stochastic simulations(Amer Chemical Soc, 2010) Marinetti, Fabio; Gianturco, Francesco A.; Department of Chemistry; Yurtsever, İsmail Ersin; Faculty Member; Department of Chemistry; College of Sciences; 7129The full interaction between formaldehyde and He-4 atoms has been obtained from a first-principle calculation of the forces at play. In order to describe the nanoscopic features of HCHO being solvated in a quantum liquid, further Monte Carlo calculations for the system HCHO@He-N with N up to 20 have been carried out. The energetics and structure of the systems, as N changes, are extensively analyzed, and the excluded volume ("bubble") created by the inner cage that surrounds the solvated molecule is described and discussed to provide molecular microsolvation details for the title system.
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