Publications by authors named "Tomoyuki Kinjo"

Article Synopsis
  • The process of film formation from drying ionomer solutions significantly affects the structure and functionality of polymer electrolyte membranes and thin films, but the underlying mechanism is not well understood.
  • This study uses a coarse-grained model combined with all-atom molecular dynamics to clarify the microscopic details, confirming findings from small-angle X-ray scattering.
  • Results show that in dilute solutions, ionomers create small rod-like bundles (1.5-2 nm in diameter) that aggregate as water evaporates, ultimately leaving behind nanosized clusters of water near the hydrophilic areas of the bundles.
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This study aims to develop a molecular dynamics (MD) simulation procedure to investigate the wettability of primer-treated AlO surfaces by bisphenol A diglycidyl ether (BADGE) and to understand the interaction between the surface and the liquid. The MD simulation results were compared with those obtained by contact angle measurements, time-of-flight secondary ion mass spectrometry (TOF-SIMS), and atomic force microscopy (AFM) and were found to be in agreement with the experimental evaluations. The results obtained from both the MD simulations and the experiments suggest that the configuration of the primers on the surface affect its wettability.

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Article Synopsis
  • - The study uses molecular dynamics simulations to explore how organic molecules interact with the AlO (0001) surface and finds a connection between diffusion coefficients and experimental contact angles.
  • - It reveals that flexible molecules, like epoxy tridecamer, show increased wettability with rising temperatures due to enhanced interactions at the surface, while rigid molecules, such as phenylene sulfide tetramer, do not show these temperature-dependent changes.
  • - The research also examines how different molecular structures of epoxy monomers affect droplet-surface interactions, noting that hydrogen atoms in aromatic rings and methyl groups have decreased interactions with the surface as temperature increases.
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The conformation of polyelectrolyte aggregates as a function of the backbone rigidity is investigated by coarse-grained molecular dynamics simulation. The polyelectrolyte is represented by a bead-spring chain with charged side chains. The simulations start from the uniform distributions of the polyelectrolytes, and the resultant polyelectrolyte conformation after a few microseconds exhibits spherical self-aggregates, clusters, or bending bundle-like aggregates, depending on the backbone rigidity.

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Physical parameters characterizing electrokinetic transport in a confined electrolyte solution are reconstructed from the generic transport coefficients obtained within the classical nonequilibrium statistical thermodynamic framework. The electro-osmotic flow, the diffusio-osmotic flow, the osmotic current, as well as the pressure-driven Poiseuille-type flow, the electric conduction, and the ion diffusion are described by this set of transport coefficients. The reconstruction is demonstrated for an aqueous NaCl solution between two parallel charged surfaces with a nanoscale gap, by using the molecular dynamic (MD) simulations.

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Article Synopsis
  • A new boundary scheme for the lattice Boltzmann method (LBM) is introduced to effectively handle the convection-diffusion equation at the interface of two phases with differing transport properties.
  • * The scheme addresses challenges in maintaining flux continuity during transient analysis by modifying the collision operator and streaming process within LBM.
  • * Asymptotic analysis confirms that with the right parameter values, the internal boundary condition can be met with second-order accuracy, and numerical tests show that this approach aligns well with analytical solutions.
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Electrokinetic flows of an aqueous NaCl solution in nanochannels with negatively charged surfaces are studied using molecular dynamics simulations. The four transport coefficients that characterize the response to weak electric and pressure fields, namely, the coefficients for the electrical current in response to the electric field (M(jj)) and the pressure field (M(jm)), and those for the mass flow in response to the same fields (M(mj) and M(mm)), are obtained in the linear regime using a Green-Kubo approach. Nonequilibrium simulations with explicit external fields are also carried out, and the current and mass flows are directly obtained.

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We have derived an equation of motion for coarse-grained particles by using a projection operator. Because the derived coarse-grained equation is based on microscopic description, it can be the basis for models of various coarse-grained simulations. We show that by substitution of random forces into fluctuating forces in the coarse-grained equation, the equations for Brownian dynamics and dissipative particle dynamics are reproduced.

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The spermatogenic function and plasma testosterone (T) level in the sex maturation process were investigated as to 180 mixed breed cats ranging from 4 months to 2 years in age to be castrated. Testis/epididymis weights reached a peak at 10 and 8 to 9 months of age, respectively. In the testis, sperm appeared at 5 months of age.

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