Hitoshi Washizu

Self-assembled ionic liquid crystals can transport water and ions via the periodic nanochannels, and these materials are promising candidates as water treatment membranes. Molecular insights on the water transport process are, however, less investigated because of computational difficulties of ionic soft matters and the self-assembly. Here we report specific behavior of water molecules in the nanochannels by using the self-consistent modeling combining density functional theory and molecular dyn

Abstract This paper reviews recent research in molecular dynamics studies of the traction properties of hydrocarbon fluids under elastohydrodynamic lubrication, focusing on the technical problems that arise on making predictions of the traction properties of an oil film with a submicron thickness at the actual sliding contacts of the machine elements by at a nanoscale molecular simulation. The effect of the oil film thickness and shear rate are examined including the result of a submicron thickn

This study focuses on designing solid lubricant particles by combining graphene and iron nanoparticles (namely, graphene-iron (GI) particles) and carrying out studies for behaviors of their lubrication for the iron contact by molecular dynamics simulations. By the annealing process of melting and cooling iron, we can create the lubricant particle, where the iron nanoparticle tightly holds the graphene sheet. In the sliding friction investigations, it is found that the influences of orientation o

Monte Carlo simulations are performed to determine the anisotropy of the electric polarizability of a model DNA fragment in aqueous salt solution. By taking into consideration the participation of coions in the electroneutrality condition, at every simulation step, we obtain a list of counterions constituting the net charge arranged in increasing order of their distance from the DNA and calculate the contribution to the dipole moment from the first n counterions in the list. We define a partial

Coarse-grained Metropolis Monte Carlo Brownian Dynamics simulations are used to clarify the ultralow friction mechanism of a transfer film of multilayered graphene sheets. Each circular graphene sheet consists of 400 to 1,000,000 atoms confined between the upper and lower sliders and are allowed to move in 3 translational and 1 rotational directions due to thermal motion at 300 K. The sheet-sheet interaction energy is calculated by the sum of the pair potential of the sp2 carbons. The sliding si

Anisotropy of the electrical polarizability Δα of model DNA fragments in salt-free aqueous solutions is determined by Monte Carlo simulation. According to the fluctuation−dissipation theorem, the electrical polarizability of polyelectrolytes is related to the fluctuations of the dipole moment generated in the counterion atmosphere around the polyion in the absence of an applied electric field. At every simulation step we numerically sort counterions in increasing order of the sum of their distan

Friction control of machine elements on a molecular level is a challenging subject in vehicle technology. We describe the molecular dynamics studies of friction in two significant lubrication regimes. As a case of elastohydrodynamic lubrication, we introduce the mechanism of momentum transfer related to the molecular structure of the hydrocarbon fluids, phase transition of the fluids under high pressure, and a submicron thickness simulation of the oil film using a tera-flops computer. For bounda

The optimal method of the polymer Materials Informatics (MI) has not been developed because the amorphous nature of the higher-order structure affects these properties. We have now tried to develop the polymer MI's descriptor of the higher-order structure using persistent homology as the topological method. We have experimentally studied the influence of the MD simulation cell size as the higher-order structure of the polymer on its electrical properties important for a soft material sensor or a

The no-slip boundary condition widely used in the macroscopic fluid mechanics has not been explained from the molecular level. This letter describes all atom molecular dynamics simulation to study boundary slip of hydrocarbon oil film under shear of a submicron thickness confined between solid walls. The large time-space scale simulation under the realistic interactions of fluid atoms, solid-fluid interaction and sliding speed has shown the no-slip of the oil film. The difference between the nan

A key to achieve the accuracy of molecular dynamics (MD) simulation is the set of force fields used to express the atomistic interactions. In particular, the electrostatic interaction remains the main issue for the precise simulation of various ionic soft materials from ionic liquids to their supramolecular compounds. In this study, we test the nonpolarizable force fields of ionic liquids (ILs) and self-assembled ionic liquid crystals (ILCs) for which the intermolecular charge transfer and intra

Abstract As an example of a very low friction system, Monte Carlo Brownian dynamics simulations have been used to calculate equilibrium structures of a polyelectrolyte brush grafted onto planes. The polymers were calculated in a semi-flexible coarse-grain model that is appropriate to treat the charge density of the polyion. The effect of linear charge density on the polyion ξ , the surface negative charge, and added salts were studied. In salt-free solution, scaling theories predicted the struct