Physical review. E, Statistical, nonlinear, and soft matter physics, 2015
The effect of methanol mixing on a nanoscale water flow was examined by using nonequilibrium mole... more The effect of methanol mixing on a nanoscale water flow was examined by using nonequilibrium molecular dynamics simulations of a Couette-type flow between nonpolarized smooth solid surfaces. Water and methanol molecules were uniformly mixed in the bulk, whereas at the solid-liquid interface methanol molecules showed a tendency to be adsorbed on the solid surface. Similar to a macroscale Couette flow, the shear stress exerted on the solid surface was equal to the shear stress in the liquid, showing that the mechanical balance holds in nanoscale. In addition, the shear stress in the liquid bulk was equal to the viscous stress which is a product of viscosity and velocity gradient. When more methanol molecules were adsorbed on the solid surface, the friction coefficient (FC) between solid and liquid was largely reduced with a small amount of methanol and that led to a remarkable decrease of the shear stress. The cause of the FC reduction was investigated in terms of the local rotational...
Abstract The formation mechanism of empty and metal-containing fullerene was studied through MD (... more Abstract The formation mechanism of empty and metal-containing fullerene was studied through MD (molecular dynamics) simulations and FT-ICR (Fourier transform ion cyclotron resonance) mass spectroscopy of laser vaporized carbon cluster. Multi-body classical ...
A liquid droplet in contact with a solid surface was simulated by the molecular dynamics method, ... more A liquid droplet in contact with a solid surface was simulated by the molecular dynamics method, in order to study the microscopic aspects of the liquid ± solid contact phenomena and phase-change heat transfer. Measured ``contact angle'' was well correlated by the depth of the integrated potential of the surface. The layered liquid structure near the surface was also explained
Nuclear Instruments and Methods in Physics Research Section B: Beam Interactions with Materials and Atoms, 2009
ABSTRACT Single (CO2)N (N=1–20) cluster impact on three different carbon-based surfaces of fuller... more ABSTRACT Single (CO2)N (N=1–20) cluster impact on three different carbon-based surfaces of fullerite (111), graphite and diamond (100) has been investigated by MD simulations with the cluster collision energy from 5 to 14keV/cluster as a first step toward the general modeling of the reactive sputtering by cluster impact of a solid surface. A crater permanently remained on the fullerite and graphite surfaces while it was quickly replenished with fluidized carbon material on the diamond surface. In spite of the smaller crater size as well as the crater recovery resulting in the reduction of the surface area, the sputtering yields were the highest on diamond. The effective energy deposition near the surface contributes to the temperature rise and consequent sputtering seemed highly reduced due to the collision cascades especially on the fullerite target.
ABSTRACT Ejection of clusters from a solid surface by impact of size-selected clusters was invest... more ABSTRACT Ejection of clusters from a solid surface by impact of size-selected clusters was investigated by mass spectroscopy and molecular dynamics (MD) simulation. It was found experimentally that carbon cluster anions, (m = 1–12), are ejected from a graphite surface by impact of (N = 1–25) at collision energies (E col) of 0.2–14.0 keV per CO2 molecule. A yield, η, of the carbon-atom ejection in the form of C m − was measured to increase with the 4th power of E col as well as the 3.6th power of N, that is, ηN 3.6 , and levels off as E col increases further. The size distribution of the ejected remains unchanged with E col, while the average size, m, of increases in proportion to N 0.17. On the other hand, MD simulation showed that C m are produced by recombination of carbon atoms evaporated from a hot surface of a cylindrical crater-shaped defect temporarily formed on the graphite surface by the cluster impact. The E col and N dependences of η and m were explained by a thermal desorption model parameterized using the results of the MD simulation. It was concluded that the higher efficiency of the cluster ejection by the larger cluster impact is attained in terms of efficient energy localization in a larger surface area and in a shallower region due to the instantaneous energy deposition by the cluster impact and the fragile nature of graphene sheets.
We have carried out atomistic simulations of grain-grain collisions for spherical grains of 1.4 a... more We have carried out atomistic simulations of grain-grain collisions for spherical grains of 1.4 and 4 nm radii, with relative velocities of 3.6-6.1 km/s and a number of impact parameters. Since the initial grains are crystallites without any pre-existing defects, grain shattering due to nucleation of cracks was not observed in our simulations. We find grain fusion in some events,
Molecular dynamics simulations of single water, water-methanol, or water-IPA (isopropyl-alcohol) ... more Molecular dynamics simulations of single water, water-methanol, or water-IPA (isopropyl-alcohol) mixture droplets on a solid surface were performed with various mixture ratios. An increase in alcohol fraction generally gave an increase in droplet wettability. Both methanol and IPA molecules showed a strong preference to gather at various interfaces, with methanol molecules also showing a tendency to diffuse into the droplet bulk. Specific interfacial tensions were investigated using quasi-one-dimensional simulation systems, and liquid-vapor and solid-liquid interfacial tensions were found to decrease greatly due to the presence of interfacial alcohol, while solid-vapor interfacial tensions were proved to have little influence on wettability. Young's relation was found to hold quantitatively well for both water-methanol and water-IPA droplets. The validity of using Bakker's equation on solid-liquid interfaces was also investigated, and it was shown that for tightly spaced crystal surfaces, the introduced uncertainly is small.
Molecular dynamics simulations of a nanoscale liquid droplet on a solid surface are carried out i... more Molecular dynamics simulations of a nanoscale liquid droplet on a solid surface are carried out in order to examine the pressure tensor field around the multiphase interfaces, and to explore the validity of Young's equation. By applying the virial theorem to a hemicylindrical droplet consisting of argon molecules on a solid surface, two-dimensional distribution of the pressure tensor is obtained. Tensile principal pressure tangential to the interface is observed around the liquid-vapor transition layer, while both tensile and compressive principal pressure tangential to the interface exists around the solid-liquid transition layer due to the inhomogeneous density distribution. The two features intermix inside the overlap region between the transition layers at the contact line. The contact angle is evaluated by using a contour line of the maximum principal pressure difference. The interfacial tensions are calculated by using Bakker's equation and Young-Laplace equation to the pressure tensor distribution. The relation between measured contact angle and calculated interfacial tensions turns out to be consistent with Young's equation, which is known as the description of the force balance at the three-phase interface.
Physical review. E, Statistical, nonlinear, and soft matter physics, 2015
The effect of methanol mixing on a nanoscale water flow was examined by using nonequilibrium mole... more The effect of methanol mixing on a nanoscale water flow was examined by using nonequilibrium molecular dynamics simulations of a Couette-type flow between nonpolarized smooth solid surfaces. Water and methanol molecules were uniformly mixed in the bulk, whereas at the solid-liquid interface methanol molecules showed a tendency to be adsorbed on the solid surface. Similar to a macroscale Couette flow, the shear stress exerted on the solid surface was equal to the shear stress in the liquid, showing that the mechanical balance holds in nanoscale. In addition, the shear stress in the liquid bulk was equal to the viscous stress which is a product of viscosity and velocity gradient. When more methanol molecules were adsorbed on the solid surface, the friction coefficient (FC) between solid and liquid was largely reduced with a small amount of methanol and that led to a remarkable decrease of the shear stress. The cause of the FC reduction was investigated in terms of the local rotational...
Abstract The formation mechanism of empty and metal-containing fullerene was studied through MD (... more Abstract The formation mechanism of empty and metal-containing fullerene was studied through MD (molecular dynamics) simulations and FT-ICR (Fourier transform ion cyclotron resonance) mass spectroscopy of laser vaporized carbon cluster. Multi-body classical ...
A liquid droplet in contact with a solid surface was simulated by the molecular dynamics method, ... more A liquid droplet in contact with a solid surface was simulated by the molecular dynamics method, in order to study the microscopic aspects of the liquid ± solid contact phenomena and phase-change heat transfer. Measured ``contact angle'' was well correlated by the depth of the integrated potential of the surface. The layered liquid structure near the surface was also explained
Nuclear Instruments and Methods in Physics Research Section B: Beam Interactions with Materials and Atoms, 2009
ABSTRACT Single (CO2)N (N=1–20) cluster impact on three different carbon-based surfaces of fuller... more ABSTRACT Single (CO2)N (N=1–20) cluster impact on three different carbon-based surfaces of fullerite (111), graphite and diamond (100) has been investigated by MD simulations with the cluster collision energy from 5 to 14keV/cluster as a first step toward the general modeling of the reactive sputtering by cluster impact of a solid surface. A crater permanently remained on the fullerite and graphite surfaces while it was quickly replenished with fluidized carbon material on the diamond surface. In spite of the smaller crater size as well as the crater recovery resulting in the reduction of the surface area, the sputtering yields were the highest on diamond. The effective energy deposition near the surface contributes to the temperature rise and consequent sputtering seemed highly reduced due to the collision cascades especially on the fullerite target.
ABSTRACT Ejection of clusters from a solid surface by impact of size-selected clusters was invest... more ABSTRACT Ejection of clusters from a solid surface by impact of size-selected clusters was investigated by mass spectroscopy and molecular dynamics (MD) simulation. It was found experimentally that carbon cluster anions, (m = 1–12), are ejected from a graphite surface by impact of (N = 1–25) at collision energies (E col) of 0.2–14.0 keV per CO2 molecule. A yield, η, of the carbon-atom ejection in the form of C m − was measured to increase with the 4th power of E col as well as the 3.6th power of N, that is, ηN 3.6 , and levels off as E col increases further. The size distribution of the ejected remains unchanged with E col, while the average size, m, of increases in proportion to N 0.17. On the other hand, MD simulation showed that C m are produced by recombination of carbon atoms evaporated from a hot surface of a cylindrical crater-shaped defect temporarily formed on the graphite surface by the cluster impact. The E col and N dependences of η and m were explained by a thermal desorption model parameterized using the results of the MD simulation. It was concluded that the higher efficiency of the cluster ejection by the larger cluster impact is attained in terms of efficient energy localization in a larger surface area and in a shallower region due to the instantaneous energy deposition by the cluster impact and the fragile nature of graphene sheets.
We have carried out atomistic simulations of grain-grain collisions for spherical grains of 1.4 a... more We have carried out atomistic simulations of grain-grain collisions for spherical grains of 1.4 and 4 nm radii, with relative velocities of 3.6-6.1 km/s and a number of impact parameters. Since the initial grains are crystallites without any pre-existing defects, grain shattering due to nucleation of cracks was not observed in our simulations. We find grain fusion in some events,
Molecular dynamics simulations of single water, water-methanol, or water-IPA (isopropyl-alcohol) ... more Molecular dynamics simulations of single water, water-methanol, or water-IPA (isopropyl-alcohol) mixture droplets on a solid surface were performed with various mixture ratios. An increase in alcohol fraction generally gave an increase in droplet wettability. Both methanol and IPA molecules showed a strong preference to gather at various interfaces, with methanol molecules also showing a tendency to diffuse into the droplet bulk. Specific interfacial tensions were investigated using quasi-one-dimensional simulation systems, and liquid-vapor and solid-liquid interfacial tensions were found to decrease greatly due to the presence of interfacial alcohol, while solid-vapor interfacial tensions were proved to have little influence on wettability. Young's relation was found to hold quantitatively well for both water-methanol and water-IPA droplets. The validity of using Bakker's equation on solid-liquid interfaces was also investigated, and it was shown that for tightly spaced crystal surfaces, the introduced uncertainly is small.
Molecular dynamics simulations of a nanoscale liquid droplet on a solid surface are carried out i... more Molecular dynamics simulations of a nanoscale liquid droplet on a solid surface are carried out in order to examine the pressure tensor field around the multiphase interfaces, and to explore the validity of Young's equation. By applying the virial theorem to a hemicylindrical droplet consisting of argon molecules on a solid surface, two-dimensional distribution of the pressure tensor is obtained. Tensile principal pressure tangential to the interface is observed around the liquid-vapor transition layer, while both tensile and compressive principal pressure tangential to the interface exists around the solid-liquid transition layer due to the inhomogeneous density distribution. The two features intermix inside the overlap region between the transition layers at the contact line. The contact angle is evaluated by using a contour line of the maximum principal pressure difference. The interfacial tensions are calculated by using Bakker's equation and Young-Laplace equation to the pressure tensor distribution. The relation between measured contact angle and calculated interfacial tensions turns out to be consistent with Young's equation, which is known as the description of the force balance at the three-phase interface.
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Papers by Yasutaka Yamaguchi