Yasutaka Yamaguchi - Academia.edu (original) (raw)

Papers by Yasutaka Yamaguchi

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 ...

By using the molecular dynamics method, a clustering process of randomly distributed carbon atoms... more By using the molecular dynamics method, a clustering process of randomly distributed carbon atoms was simulated. A C 60 imperfect fullerene obtained in the simulation was kept at 2500 K in order to evaluate the effect of the collision-free annealing process which was almost ignored in the clustering simulation. Through successive pentagon-migration transformations, the perfect fullerene structure was achieved within a plausible time scale of 200 ns. Similar annealing simulations for smaller precursor clusters were also performed to infer the annealing effect at each stage of clustering process. Based on these simulations, a new formation model of empty fullerene was proposed. Moreover, the formation process of metal containing fullerene was also simulated using virtual L-J metal atoms.

The formation mechanism of fullerene, a new type of carbon molecule with hollow caged structure, ... more The formation mechanism of fullerene, a new type of carbon molecule with hollow caged structure, was studied by using the molecular dynamics method with the simplified classical potential function. The clustering process starting from isolated carbon atoms was simulated under controlled temperature condition. Here, translational, rotational and vibrational temperatures of each cluster were controlled to be in equilibrium. The structures of clusters which were obtained after enough calculation depended on the controlled temperature T c , yielding the graphitic sheet for T c < 2600 K, fullerene-like caged structure for 2600 K < T c < 3500 K, and chaotic 3-dimensional structure for T c > 3500 K. Through the detailed trace of precursors, it was revealed that the key feature of the formation of the caged structure was the chaotic 3-dimensional cluster of 40 to 50 atoms which had large vibrational energy. In addition, when the precursors were kept under lower vibrational energy, the successive growth of 2-dimensional graphitic structure was observed. Since the time scale of the simulation was compressed, the annealing process of each cluster was virtually omitted. In order to examine this effect, an imperfect C 60 obtained from the similar simulation was annealed at 2500 K for 50 ns without collisions. The perfect Buckminsterfullerene C 60 was finally obtained after successive Stone-Wales transformations.

The formation mechanism of fullerene, a new type of carbon molecule with a hollow caged structure... more The formation mechanism of fullerene, a new type of carbon molecule with a hollow caged structure, was studied using a molecular dynamics method. In order to simulate the basic reaction process observed in the arc-discharge or the laser vaporization fullerene generation, we have calculated the clustering process starting from randomly located isolated carbon atoms. Here, an empirical manybody carbon potential proposed by Brenner (1990) was employed. Under a certain condition of the initial density and the temperature control, the simulation yielded the hollow caged carbon network which could be regarded as an imperfect fullerene. Intermediate clusters observed in the clustering process were dimers, trimers, linear chains up to C10, mono-cyclic rings in C10-C15, poly-cyclic rings of about C20, fragments of 2 dimensional network, and the imperfect fullerene. One of the remarkable reactions was a linear chain wrapping a poly-cyclic ring to form a larger fragment of network structure.

ASME/JSME 2011 8th Thermal Engineering Joint Conference, 2011

ABSTRACT

Microscale Thermophysical Engineering, 1998

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&amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;#x27;&amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;#x27; was well correlated by the depth of the integrated potential of the surface. The layered liquid structure near the surface was also explained

JAPANESE JOURNAL OF MULTIPHASE FLOW, 2012

Surface and Interface Analysis, 2004

ABSTRACT

Physical Review B, 2007

The growth of sp and sp 2 nanostructures in a carbon plasma is simulated by tight-binding molecul... more The growth of sp and sp 2 nanostructures in a carbon plasma is simulated by tight-binding molecular dynamics. The simulations are arranged so as to mimic the cluster formation conditions typical of a pulsed microplasma cluster source which is used to grow nanostructured sp-sp 2 carbon films ͓L. Ravagnan et al., Phys. Rev. Lett. 98, 216103 ͑2007͔͒. The formation of linear, ring, and fullerenelike objects in the carbon plasma is found to proceed through a very long multistep process. Therefore, tight-binding simulations of unprecedented duration have been performed by exploiting the disconnected topology of the simulated carbon plasma which made it possible to implement a computationally efficient divide-and-diagonalize procedure. Present simulations prove that topologically different structures can be formed in experiments, depending on the plasma temperature and density. A thorough characterization of the observed structures as well as their evolution ͑caused both by thermal annealing and by cluster ripening͒ is provided.

Nuclear Instruments and Methods in Physics Research Section B: Beam Interactions with Materials and Atoms, 2007

Using molecular-dynamics simulation, we study the impact of C 60 fullerene molecules with energie... more Using molecular-dynamics simulation, we study the impact of C 60 fullerene molecules with energies up to several tens of keV on various target materials: graphite, fullerite, Au and a condensed Ar solid. The analysis is based on single impact events. For all the target materials, fragmentation of the fullerene projectile sets in at around 1 keV impact energy; it starts the earliest in the heavy Au target. Full atomization of the projectile is observed at around 10 keV impact energy. The projectile ranges, on the other hand, depend strongly on the target material. The highest ranges are achieved in the weakly bonded Ar target. Also ranges in the fcc-C 60 solid are systematically larger than in the graphite target. Interestingly, at energies above 5 keV, the fullerene penetrates deeper into the Au target than into graphite, even though the Au has a considerably higher mass and efficiently reflects the fullerenes at lower bombarding energies; this indicates the dominant role of the cohesive energy of the target. The energy dependence of fullerene molecules is surprisingly flat and varies between E 1/3 and E 2/3 at smaller impact energies, E < 10 keV. At higher impact energies, where the projectile has been fully atomized, the energy dependence becomes more pronounced, /E.

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.

Nuclear Instruments and Methods in Physics Research Section B: Beam Interactions with Materials and Atoms, 2005

Molecular dynamics (MD) simulations of single Ar n , (CO 2) n , (C 3) n and (O 2) n cluster impac... more Molecular dynamics (MD) simulations of single Ar n , (CO 2) n , (C 3) n and (O 2) n cluster impacts (n ' 960) on a diamond (1 1 1) surface are performed in order to investigate the surface erosion process. Unlike the other three impacts which result in a remarkable emission only at higher cluster acceleration energies at E a P 75 keV, the O 2 cluster impact induces a significant effect from a lower acceleration energy E a of 30 keV on, and the erosion rate increases almost linearly with the increase of the acceleration energy. These differences are ascribed to the reactive emission pattern via the production of CO and CO 2 molecules. The erosion rate per molecule seems to be expressed as a linear function of the impact velocity minus a threshold velocity independent of the cluster size for the O 2 cluster impacts.

Molecular Physics, 2008

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.

Journal of Physics: Conference Series, 2008

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,

Journal of Non-Crystalline Solids, 2012

Using a transmission electron microscope (TEM) equipped with a manipulator, we recently demonstra... more Using a transmission electron microscope (TEM) equipped with a manipulator, we recently demonstrated the transition between the flattened state and the tubular state in rather thick carbon nanotubes (CNTs). This unique transition behavior provides a new concept of a nanosized device: a nanotorsional actuator. To realize and design the actuator, we used TEM observations and molecular dynamics simulations to examine the transition behavior and investigate how the torsion angle is determined and what the driving force is. Results indicate that a specific graphitic stacking order taken for the CNT inside determines the initial twist of a flattened CNT and thereby determines the rotational angle. Results also clarified that the transition results from thermal energy.

The Journal of Chemical Physics, 2014

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&amp;amp;#39;s relation was found to hold quantitatively well for both water-methanol and water-IPA droplets. The validity of using Bakker&amp;amp;#39;s equation on solid-liquid interfaces was also investigated, and it was shown that for tightly spaced crystal surfaces, the introduced uncertainly is small.

The Journal of Chemical Physics, 2014

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&amp;amp;amp;amp;#39;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&amp;amp;amp;amp;#39;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&amp;amp;amp;amp;#39;s equation, which is known as the description of the force balance at the three-phase interface.

International Journal of Heat and Mass Transfer, 2007

ABSTRACT

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 ...

By using the molecular dynamics method, a clustering process of randomly distributed carbon atoms... more By using the molecular dynamics method, a clustering process of randomly distributed carbon atoms was simulated. A C 60 imperfect fullerene obtained in the simulation was kept at 2500 K in order to evaluate the effect of the collision-free annealing process which was almost ignored in the clustering simulation. Through successive pentagon-migration transformations, the perfect fullerene structure was achieved within a plausible time scale of 200 ns. Similar annealing simulations for smaller precursor clusters were also performed to infer the annealing effect at each stage of clustering process. Based on these simulations, a new formation model of empty fullerene was proposed. Moreover, the formation process of metal containing fullerene was also simulated using virtual L-J metal atoms.

The formation mechanism of fullerene, a new type of carbon molecule with hollow caged structure, ... more The formation mechanism of fullerene, a new type of carbon molecule with hollow caged structure, was studied by using the molecular dynamics method with the simplified classical potential function. The clustering process starting from isolated carbon atoms was simulated under controlled temperature condition. Here, translational, rotational and vibrational temperatures of each cluster were controlled to be in equilibrium. The structures of clusters which were obtained after enough calculation depended on the controlled temperature T c , yielding the graphitic sheet for T c < 2600 K, fullerene-like caged structure for 2600 K < T c < 3500 K, and chaotic 3-dimensional structure for T c > 3500 K. Through the detailed trace of precursors, it was revealed that the key feature of the formation of the caged structure was the chaotic 3-dimensional cluster of 40 to 50 atoms which had large vibrational energy. In addition, when the precursors were kept under lower vibrational energy, the successive growth of 2-dimensional graphitic structure was observed. Since the time scale of the simulation was compressed, the annealing process of each cluster was virtually omitted. In order to examine this effect, an imperfect C 60 obtained from the similar simulation was annealed at 2500 K for 50 ns without collisions. The perfect Buckminsterfullerene C 60 was finally obtained after successive Stone-Wales transformations.

The formation mechanism of fullerene, a new type of carbon molecule with a hollow caged structure... more The formation mechanism of fullerene, a new type of carbon molecule with a hollow caged structure, was studied using a molecular dynamics method. In order to simulate the basic reaction process observed in the arc-discharge or the laser vaporization fullerene generation, we have calculated the clustering process starting from randomly located isolated carbon atoms. Here, an empirical manybody carbon potential proposed by Brenner (1990) was employed. Under a certain condition of the initial density and the temperature control, the simulation yielded the hollow caged carbon network which could be regarded as an imperfect fullerene. Intermediate clusters observed in the clustering process were dimers, trimers, linear chains up to C10, mono-cyclic rings in C10-C15, poly-cyclic rings of about C20, fragments of 2 dimensional network, and the imperfect fullerene. One of the remarkable reactions was a linear chain wrapping a poly-cyclic ring to form a larger fragment of network structure.

ASME/JSME 2011 8th Thermal Engineering Joint Conference, 2011

ABSTRACT

Microscale Thermophysical Engineering, 1998

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&amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;#x27;&amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;#x27; was well correlated by the depth of the integrated potential of the surface. The layered liquid structure near the surface was also explained

JAPANESE JOURNAL OF MULTIPHASE FLOW, 2012

Surface and Interface Analysis, 2004

ABSTRACT

Physical Review B, 2007

The growth of sp and sp 2 nanostructures in a carbon plasma is simulated by tight-binding molecul... more The growth of sp and sp 2 nanostructures in a carbon plasma is simulated by tight-binding molecular dynamics. The simulations are arranged so as to mimic the cluster formation conditions typical of a pulsed microplasma cluster source which is used to grow nanostructured sp-sp 2 carbon films ͓L. Ravagnan et al., Phys. Rev. Lett. 98, 216103 ͑2007͔͒. The formation of linear, ring, and fullerenelike objects in the carbon plasma is found to proceed through a very long multistep process. Therefore, tight-binding simulations of unprecedented duration have been performed by exploiting the disconnected topology of the simulated carbon plasma which made it possible to implement a computationally efficient divide-and-diagonalize procedure. Present simulations prove that topologically different structures can be formed in experiments, depending on the plasma temperature and density. A thorough characterization of the observed structures as well as their evolution ͑caused both by thermal annealing and by cluster ripening͒ is provided.

Nuclear Instruments and Methods in Physics Research Section B: Beam Interactions with Materials and Atoms, 2007

Using molecular-dynamics simulation, we study the impact of C 60 fullerene molecules with energie... more Using molecular-dynamics simulation, we study the impact of C 60 fullerene molecules with energies up to several tens of keV on various target materials: graphite, fullerite, Au and a condensed Ar solid. The analysis is based on single impact events. For all the target materials, fragmentation of the fullerene projectile sets in at around 1 keV impact energy; it starts the earliest in the heavy Au target. Full atomization of the projectile is observed at around 10 keV impact energy. The projectile ranges, on the other hand, depend strongly on the target material. The highest ranges are achieved in the weakly bonded Ar target. Also ranges in the fcc-C 60 solid are systematically larger than in the graphite target. Interestingly, at energies above 5 keV, the fullerene penetrates deeper into the Au target than into graphite, even though the Au has a considerably higher mass and efficiently reflects the fullerenes at lower bombarding energies; this indicates the dominant role of the cohesive energy of the target. The energy dependence of fullerene molecules is surprisingly flat and varies between E 1/3 and E 2/3 at smaller impact energies, E < 10 keV. At higher impact energies, where the projectile has been fully atomized, the energy dependence becomes more pronounced, /E.

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.

Nuclear Instruments and Methods in Physics Research Section B: Beam Interactions with Materials and Atoms, 2005

Molecular dynamics (MD) simulations of single Ar n , (CO 2) n , (C 3) n and (O 2) n cluster impac... more Molecular dynamics (MD) simulations of single Ar n , (CO 2) n , (C 3) n and (O 2) n cluster impacts (n ' 960) on a diamond (1 1 1) surface are performed in order to investigate the surface erosion process. Unlike the other three impacts which result in a remarkable emission only at higher cluster acceleration energies at E a P 75 keV, the O 2 cluster impact induces a significant effect from a lower acceleration energy E a of 30 keV on, and the erosion rate increases almost linearly with the increase of the acceleration energy. These differences are ascribed to the reactive emission pattern via the production of CO and CO 2 molecules. The erosion rate per molecule seems to be expressed as a linear function of the impact velocity minus a threshold velocity independent of the cluster size for the O 2 cluster impacts.

Molecular Physics, 2008

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.

Journal of Physics: Conference Series, 2008

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,

Journal of Non-Crystalline Solids, 2012

Using a transmission electron microscope (TEM) equipped with a manipulator, we recently demonstra... more Using a transmission electron microscope (TEM) equipped with a manipulator, we recently demonstrated the transition between the flattened state and the tubular state in rather thick carbon nanotubes (CNTs). This unique transition behavior provides a new concept of a nanosized device: a nanotorsional actuator. To realize and design the actuator, we used TEM observations and molecular dynamics simulations to examine the transition behavior and investigate how the torsion angle is determined and what the driving force is. Results indicate that a specific graphitic stacking order taken for the CNT inside determines the initial twist of a flattened CNT and thereby determines the rotational angle. Results also clarified that the transition results from thermal energy.

The Journal of Chemical Physics, 2014

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&amp;amp;#39;s relation was found to hold quantitatively well for both water-methanol and water-IPA droplets. The validity of using Bakker&amp;amp;#39;s equation on solid-liquid interfaces was also investigated, and it was shown that for tightly spaced crystal surfaces, the introduced uncertainly is small.

The Journal of Chemical Physics, 2014

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&amp;amp;amp;amp;#39;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&amp;amp;amp;amp;#39;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&amp;amp;amp;amp;#39;s equation, which is known as the description of the force balance at the three-phase interface.

International Journal of Heat and Mass Transfer, 2007

ABSTRACT