The Experts below are selected from a list of 360 Experts worldwide ranked by ideXlab platform
R Dwayne J Miller - One of the best experts on this subject based on the ideXlab platform.
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digital interference microscopy and density reconstruction of picosecond infrared laser desorption at the water Air Interface
Journal of Applied Physics, 2018Co-Authors: Frederik Busse, Sebastian Kruber, Wesley D Robertson, R Dwayne J MillerAbstract:Material ablation and evaporation using pulsed infrared lasers pose promising approaches for matrix-free laser desorption ionization and in laser surgery. For the best results, key parameters such as laser wavelength, pulse duration, and pulse energy need to be carefully adjusted to the application. We characterize the dynamics at the water-Air Interface induced by a 10 ps infrared laser tuned to the water absorption band at 3 μ m, a parameter set facilitating stress confined desorption for typical absorption depths in biological samples and tissue. By driving the ablation faster than nucleation growth, cavitation induced sample damage during the ablation process can be mitigated. The resultant explosive ablation process leads to a shock front expansion and material ejection which we capture using off-axis digital interference microscopy, an interference technique particularly useful for detecting the phase shift caused by transparent objects. It is demonstrated that the method can yield local density...
Mischa Bonn - One of the best experts on this subject based on the ideXlab platform.
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nature of excess hydrated proton at the water Air Interface
Journal of the American Chemical Society, 2020Co-Authors: Sudipta Das, Sho Imoto, Yuki Nagata, Shumei Sun, Ellen H G Backus, Mischa BonnAbstract:Understanding the interfacial molecular structure of acidic aqueous solutions is important in the context of, e.g., atmospheric chemistry, biophysics, and electrochemistry. The hydration of the interfacial proton is necessarily different from that in the bulk, given the lower effective density of water at the Interface, but has not yet been elucidated. Here, using surface-specific vibrational spectroscopy, we probe the response of interfacial protons at the water-Air Interface and reveal the interfacial proton continuum. Combined with spectral calculations based on ab initio molecular dynamics simulations, the proton at the water-Air Interface is shown to be well-hydrated, despite the limited availability of hydration water, with both Eigen and Zundel structures coexisting at the Interface. Notwithstanding the interfacial hydrated proton exhibiting bulk-like structures, a substantial interfacial stabilization by -1.3 ± 0.2 kcal/mol is observed experimentally, in good agreement with our free energy calculations. The surface propensity of the proton can be attributed to the interaction between the hydrated proton and its counterion.
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both inter and intramolecular coupling of o h groups determine the vibrational response of the water Air Interface
Journal of Physical Chemistry Letters, 2016Co-Authors: Jan Schaefer, Yuki Nagata, Ellen H G Backus, Mischa BonnAbstract:Vibrational coupling is relevant not only for dissipation of excess energy after chemical reactions but also for elucidating molecular structure and dynamics. It is particularly important for O–H stretch vibrational spectra of water, for which it is known that in bulk both intra- and intermolecular coupling alter the intensity and line shape of the spectra. In contrast with bulk, the unified picture of the inter/intra-molecular coupling of O–H groups at the water–Air Interface has been lacking. Here, combining sum-frequency generation experiments and simulation for isotopically diluted water and alcohols, we unveil effects of inter- and intramolecular coupling on the vibrational spectra of interfacial water. Our results show that both inter- and intramolecular coupling contribute to the O–H stretch vibrational response of the neat H2O surface, with intramolecular coupling generating a double-peak feature, while the intermolecular coupling induces a significant red shift in the O–H stretch response.
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molecular dynamics simulations of sfg librational modes spectra of water at the water Air Interface
Journal of Physical Chemistry C, 2016Co-Authors: Remi Khatib, Ellen H G Backus, Mischa Bonn, Taisuke Hasegawa, Marialore Sulpizi, Yuki NagataAbstract:At the water–Air Interface, the hydrogen-bond network of water molecules is interrupted, and accordingly, the structure and dynamics of the interfacial water molecules are altered considerably compared with the bulk. Such interfacial water molecules have been studied by surface-specific vibrational sum-frequency generation (SFG) spectroscopy probing high-frequency O–H stretch and H–O–H bending modes. In contrast, the low-frequency librational mode has been much less studied with SFG. Because this mode is sensitive to the hydrogen-bond connectivity, understanding the librational mode of the interfacial water is crucial for unveiling a microscopic view of the interfacial water. Here, we compute the SFG librational mode spectra at the water–Air Interface by using molecular dynamics simulation. We show that the modeling of the polarizability has a drastic effect on the simulated librational mode spectra, whereas the spectra are less sensitive to the force field models and the modeling of the dipole moment. Th...
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surface tension of ab initio liquid water at the water Air Interface
Journal of Chemical Physics, 2016Co-Authors: Yuki Nagata, Tatsuhiko Ohto, Mischa Bonn, Thomas D KuhneAbstract:We report calculations on the surface tension of the water-Air Interface using ab initio molecular dynamics (AIMD) simulations. We investigate the influence of the cell size on surface tension of water from force field molecular dynamics simulations. We find that the calculated surface tension increases with increasing simulation cell size, thereby illustrating that a correction for finite size effects is essential for small systems that are customary in AIMD simulations. Moreover, AIMD simulations reveal that the use of a double-ζ basis set overestimates the experimentally measured surface tension due to the Pulay stress while more accurate triple and quadruple-ζ basis sets give converged results. We further demonstrate that van der Waals corrections critically affect the surface tension. AIMD simulations without the van der Waals correction substantially underestimate the surface tension while the van der Waals correction with the Grimme’s D2 technique results in a value for the surface tension that is too high. The Grimme’s D3 van der Waals correction provides a surface tension close to the experimental value. Whereas the specific choices for the van der Waals correction and basis sets critically affect the calculated surface tension, the surface tension is remarkably insensitive to the details of the exchange and correlation functionals, which highlights the impact of long-range interactions on the surface tension. Our simulated values provide important benchmarks, both for improving van der Waals corrections and AIMD simulations of aqueous Interfaces.
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surface tension of ab initio liquid water at the water Air Interface
arXiv: Chemical Physics, 2016Co-Authors: Yuki Nagata, Tatsuhiko Ohto, Mischa Bonn, Thomas D KuhneAbstract:We report calculations of the surface tension of the water-Air Interface using ab initio molecular dynamics (AIMD) simulations. We investigate the simulation cell size dependence of the surface tension of water from force field molecular dynamics (MD) simulations, which show that the calculated surface tension increases with increasing simulation cell size, thereby illustrating that a correction for finite size effects is required for the small system used in the AIMD simulation. The AIMD simulations reveal that the double-{\xi} basis set overestimates the experimentally measured surface tension due to the Pulay stress, while the triple and quadruple-{\xi} basis sets give similar results. We further demonstrate that the van der Waals corrections critically affect the surface tension. AIMD simulations without the van der Waals correction substantially underestimate the surface tension, while van der Waals correction with the Grimme's D2 technique results in the value for the surface tension that is too high. The Grimme's D3 van der Waals correction provides a surface tension close to the experimental value. Whereas the specific choices for the van der Waals correction and basis sets critically affect the calculated surface tension, the surface tension is remarkably insensitive to the details of the exchange and correlation functionals, which highlights the impact of long-range interactions on the surface tension. These simulated values provide important benchmarks, both for improving van der Waals corrections, and AIMD simulations of aqueous Interfaces.
Yuki Nagata - One of the best experts on this subject based on the ideXlab platform.
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nature of excess hydrated proton at the water Air Interface
Journal of the American Chemical Society, 2020Co-Authors: Sudipta Das, Sho Imoto, Yuki Nagata, Shumei Sun, Ellen H G Backus, Mischa BonnAbstract:Understanding the interfacial molecular structure of acidic aqueous solutions is important in the context of, e.g., atmospheric chemistry, biophysics, and electrochemistry. The hydration of the interfacial proton is necessarily different from that in the bulk, given the lower effective density of water at the Interface, but has not yet been elucidated. Here, using surface-specific vibrational spectroscopy, we probe the response of interfacial protons at the water-Air Interface and reveal the interfacial proton continuum. Combined with spectral calculations based on ab initio molecular dynamics simulations, the proton at the water-Air Interface is shown to be well-hydrated, despite the limited availability of hydration water, with both Eigen and Zundel structures coexisting at the Interface. Notwithstanding the interfacial hydrated proton exhibiting bulk-like structures, a substantial interfacial stabilization by -1.3 ± 0.2 kcal/mol is observed experimentally, in good agreement with our free energy calculations. The surface propensity of the proton can be attributed to the interaction between the hydrated proton and its counterion.
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structure and dynamics of water at the water Air Interface using first principles molecular dynamics simulations within generalized gradient approximation
Journal of Chemical Theory and Computation, 2019Co-Authors: Tatsuhiko Ohto, Mayank Dodia, Sho Imoto, Yuki NagataAbstract:First-principles molecular dynamics simulations within the density functional theory framework have been used to predict the surface structure of water at various aqueous Interfaces, but there is no clear consensus on the choice of appropriate simulation parameters, such as exchange–correlation functions and van der Waals corrections yet. Here, we report the systematic survey for the structure and dynamics of water at the water–Air Interface simulated with various combinations of the exchange–correlation functionals within the generalized gradient approximation and empirical dispersion corrections. Particularly, we focus on the structure and dynamics of the free O–D group of D2O, as well as the surface tension of water. Through the comparison of these quantities with the experimental and accurate force field calculations, we conclude that revPBE with van der Waals correction shows significantly better results for simulating various Air–water interfacial properties than BLYP and PBE functionals.
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both inter and intramolecular coupling of o h groups determine the vibrational response of the water Air Interface
Journal of Physical Chemistry Letters, 2016Co-Authors: Jan Schaefer, Yuki Nagata, Ellen H G Backus, Mischa BonnAbstract:Vibrational coupling is relevant not only for dissipation of excess energy after chemical reactions but also for elucidating molecular structure and dynamics. It is particularly important for O–H stretch vibrational spectra of water, for which it is known that in bulk both intra- and intermolecular coupling alter the intensity and line shape of the spectra. In contrast with bulk, the unified picture of the inter/intra-molecular coupling of O–H groups at the water–Air Interface has been lacking. Here, combining sum-frequency generation experiments and simulation for isotopically diluted water and alcohols, we unveil effects of inter- and intramolecular coupling on the vibrational spectra of interfacial water. Our results show that both inter- and intramolecular coupling contribute to the O–H stretch vibrational response of the neat H2O surface, with intramolecular coupling generating a double-peak feature, while the intermolecular coupling induces a significant red shift in the O–H stretch response.
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molecular dynamics simulations of sfg librational modes spectra of water at the water Air Interface
Journal of Physical Chemistry C, 2016Co-Authors: Remi Khatib, Ellen H G Backus, Mischa Bonn, Taisuke Hasegawa, Marialore Sulpizi, Yuki NagataAbstract:At the water–Air Interface, the hydrogen-bond network of water molecules is interrupted, and accordingly, the structure and dynamics of the interfacial water molecules are altered considerably compared with the bulk. Such interfacial water molecules have been studied by surface-specific vibrational sum-frequency generation (SFG) spectroscopy probing high-frequency O–H stretch and H–O–H bending modes. In contrast, the low-frequency librational mode has been much less studied with SFG. Because this mode is sensitive to the hydrogen-bond connectivity, understanding the librational mode of the interfacial water is crucial for unveiling a microscopic view of the interfacial water. Here, we compute the SFG librational mode spectra at the water–Air Interface by using molecular dynamics simulation. We show that the modeling of the polarizability has a drastic effect on the simulated librational mode spectra, whereas the spectra are less sensitive to the force field models and the modeling of the dipole moment. Th...
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surface tension of ab initio liquid water at the water Air Interface
Journal of Chemical Physics, 2016Co-Authors: Yuki Nagata, Tatsuhiko Ohto, Mischa Bonn, Thomas D KuhneAbstract:We report calculations on the surface tension of the water-Air Interface using ab initio molecular dynamics (AIMD) simulations. We investigate the influence of the cell size on surface tension of water from force field molecular dynamics simulations. We find that the calculated surface tension increases with increasing simulation cell size, thereby illustrating that a correction for finite size effects is essential for small systems that are customary in AIMD simulations. Moreover, AIMD simulations reveal that the use of a double-ζ basis set overestimates the experimentally measured surface tension due to the Pulay stress while more accurate triple and quadruple-ζ basis sets give converged results. We further demonstrate that van der Waals corrections critically affect the surface tension. AIMD simulations without the van der Waals correction substantially underestimate the surface tension while the van der Waals correction with the Grimme’s D2 technique results in a value for the surface tension that is too high. The Grimme’s D3 van der Waals correction provides a surface tension close to the experimental value. Whereas the specific choices for the van der Waals correction and basis sets critically affect the calculated surface tension, the surface tension is remarkably insensitive to the details of the exchange and correlation functionals, which highlights the impact of long-range interactions on the surface tension. Our simulated values provide important benchmarks, both for improving van der Waals corrections and AIMD simulations of aqueous Interfaces.
Frederik Busse - One of the best experts on this subject based on the ideXlab platform.
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digital interference microscopy and density reconstruction of picosecond infrared laser desorption at the water Air Interface
Journal of Applied Physics, 2018Co-Authors: Frederik Busse, Sebastian Kruber, Wesley D Robertson, R Dwayne J MillerAbstract:Material ablation and evaporation using pulsed infrared lasers pose promising approaches for matrix-free laser desorption ionization and in laser surgery. For the best results, key parameters such as laser wavelength, pulse duration, and pulse energy need to be carefully adjusted to the application. We characterize the dynamics at the water-Air Interface induced by a 10 ps infrared laser tuned to the water absorption band at 3 μ m, a parameter set facilitating stress confined desorption for typical absorption depths in biological samples and tissue. By driving the ablation faster than nucleation growth, cavitation induced sample damage during the ablation process can be mitigated. The resultant explosive ablation process leads to a shock front expansion and material ejection which we capture using off-axis digital interference microscopy, an interference technique particularly useful for detecting the phase shift caused by transparent objects. It is demonstrated that the method can yield local density...
George M Whitesides - One of the best experts on this subject based on the ideXlab platform.
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self assembly of gears at a fluid Air Interface
Journal of the American Chemical Society, 2003Co-Authors: Michael J Fuerstman, Bartosz A Grzybowski, Howard A Stone, George M WhitesidesAbstract:This paper describes a dynamic systema system that develops order only when dissipating energycomprising millimeter to centimeter scale gears that self-assemble into a simple machine at a fluid/Air Interface. The gears are driven externally and indirectly by magnetic interactions; they are made of poly(dimethylsiloxane) (PDMS) or magnetically doped PDMS, and fabricated by soft lithography. Transfer of torque between gears can take place through three different mechanisms: mechanical interaction, hydrodynamic shear, and capillarity/overlap of menisci. Interplay between these forces allows interactions and motions that are not possible with conventional systems of gears.
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dynamics of self assembly of magnetized disks rotating at the liquid Air Interface
Proceedings of the National Academy of Sciences of the United States of America, 2002Co-Authors: Bartosz A Grzybowski, Howard A Stone, George M WhitesidesAbstract:This paper is a theoretical study of dynamic self assembly in a system of millimeter-sized magnetized disks floating at a liquid–Air Interface and spinning under the influence of a rotating magnetic field. Equations of motions are derived that account for the hydrodynamic and magnetic forces acting in the system. Numerical integration of these equations predicts formation of ordered structures of spinning disks; the simulated structures reproduce the patterns observed experimentally.
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dynamic self assembly of magnetized millimetre sized objects rotating at a liquid Air Interface
Nature, 2000Co-Authors: Bartosz A Grzybowski, Howard A Stone, George M WhitesidesAbstract:Spontaneous pattern formation by self-assembly is of long-standing and continuing interest not only for its aesthetic appeal, but also for its fundamental and technological relevance. So far, the study of self-organization processes has mainly focused on static structures, but dynamic systems--those that develop order only when dissipating energy--are of particular interest for studying complex behaviour. Here we describe the formation of dynamic patterns of millimetre-sized magnetic disks at a liquid-Air Interface, subject to a magnetic field produced by a rotating permanent magnet. The disks spin around their axes with angular frequency equal to that of the magnet, and are attracted towards its axis of rotation while repelling each other. This repulsive hydrodynamic interaction is due to fluid motion associated with spinning; the interplay between attractive and repulsive interactions leads to the formation of patterns exhibiting various types of ordering, some of which are entirely new. This versatile system should lead to a better understanding of dynamic self-assembly, while providing a test-bed for stability theories of interacting point vortices and vortex patches.