Faculty Profiles - YAMAGUCHI, Tsuyoshi

Papers - YAMAGUCHI, Tsuyoshi

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Behavior of sonochemical reaction in a small pipe Reviewed

Mukai, K; Mizuno, Y; Yamaguchi, T; Asakura, Y; Yasuda, K

JAPANESE JOURNAL OF APPLIED PHYSICS Vol. 64 ( 3 ) 2025.3

Size control of Au@Pt core-shell nanoparticles for enhanced catalytic activity using ultrafine bubbles and ultrasound Open Access

Mizuno Y., Yamamoto Y., Yamaguchi T., Yasuda K.

Japanese Journal of Applied Physics, Part 1: Regular Papers and Short Notes and Review Papers Vol. 64 ( 3 ) 2025.3

Publisher：Japanese Journal of Applied Physics, Part 1: Regular Papers and Short Notes and Review Papers

Core⎯shell nanoparticles (NPs) composed of an Au core and a Pt shell (Au@Pt NPs) were synthesized. We started with the synthesis of the Au core by sonochemical reduction, followed by the Pt shell deposition by chemical reduction in the presence of a non-ionic surfactant and ultrafine bubbles (UFBs). The Pt shell thickness increased with the UFB concentration. During the shell formation, Pt NPs were thought to adsorb on the surface of UFBs by electrostatic and hydrophobic interactions, which was subsequently followed by UFBs approaching the Au NP surface and providing additional Pt NPs onto the surface. The catalytic activity of Au@Pt NPs for the reduction of 4-nitrophenol was evaluated. At Pt/Au molar ratios of 0.10, 0.20, and 0.33, the catalytic activity was enhanced as the Pt shell thickness decreased. For Pt/Au molar ratios of 0.02 and 0.05, Au@Pt NPs synthesized with UFBs exhibited better catalytic performance than those without UFBs.

DOI： 10.35848/1347-4065/ada8b5

Molecular Dynamics Simulation Study on Heterogeneous Structure, Rheology, and Dynamic Correlation of Concentrated Aqueous Solutions of a Lithium Salt Reviewed

Yamaguchi, T

JOURNAL OF PHYSICAL CHEMISTRY B Vol. 129 ( 3 ) page： 1026 - 1035 2025.1

Authorship：Lead author,　Last author,　Corresponding author Language：English Publishing type：Research paper (scientific journal) Publisher：Journal of Physical Chemistry B

Molecular dynamics simulation of an aqueous solution of lithium bis(trifluoromethanesulfonyl)amide, LiTFSA, was performed at various concentrations to relate its liquid structure with frequency-dependent shear viscosity. The structure factor exhibited a low-q peak that represents a heterogeneous structure composed of water and anion domains, and the lithium ion existed in the water domain due to its strong hydration. The frequency-dependent shear viscosity showed bimodal relaxation, and the relative contribution of the slower mode increased with an increase in the salt concentration. The cross-correlation between the shear stress and the two-body density revealed that the slower viscoelastic mode is assigned to the dynamics of the heterogeneous structure, and the assignment was also confirmed by the comparison between the viscoelastic and structural relaxations. The collective translational motions of the cation and the anion showed a strong negative correlation in a concentrated solution, reflecting the heterogeneous domain structure.

DOI： 10.1021/acs.jpcb.4c07942

Coexistence of two coacervate phases of polyglycine in water suggested by polymer reference interaction site model theory Reviewed

Yamaguchi, T; Chong, SH; Yoshida, N

JOURNAL OF CHEMICAL PHYSICS Vol. 159 ( 24 ) 2023.12

Authorship：Lead author,　Corresponding author Language：English Publishing type：Research paper (scientific journal) Publisher：Journal of Chemical Physics

Mixing Gibbs energy and phase equilibria of aqueous solutions of polyglycine were studied theoretically by means of polymer reference interaction site model integral equation theory combined with the Gibbs-Duhem method. In addition to the ordinary liquid-liquid phase separation between dilute and concentrated solutions, the theoretical calculation predicted the coexistence of two coacervate phases, namely, the lower- and higher-density coacervates. The relative thermodynamic stabilities of these two phases change with the polymerization degree of polyglycine. The higher-density coacervate phase was rapidly stabilized by increasing the polymer length, and the lower-density phase became metastable at large polymers. The hydrogen bonds between the peptide chains were strengthened, and water was thermodynamically destabilized in the higher-density coacervate. A possible relation with the formation of amyloid fibril within a liquid droplet is also discussed.

DOI： 10.1063/5.0185157

Non-Newtonian Dynamics in Water-in-Salt Electrolytes Reviewed International coauthorship

Yamaguchi, T; Dukhin, A; Ryu, YJ; Zhang, DZ; Borodin, O; González, MA; Yamamuro, O; Price, DL; Saboungi, ML

JOURNAL OF PHYSICAL CHEMISTRY LETTERS Vol. 15 ( 1 ) page： 76 - 80 2023.12

Authorship：Lead author Language：English Publishing type：Research paper (scientific journal) Publisher：Journal of Physical Chemistry Letters

Water-in-salt electrolytes have attracted considerable interest in the past decade for advanced lithium-ion batteries, possessing important advantages over the non-aqueous electrolytes currently in use. A battery with a LiTFSI-water electrolyte was demonstrated in which an operating window of 3 V is made possible by a solid-electrolyte interface. Viscosity is an important property for such electrolytes, because high viscosity is normally associated with low ionic conductivity. Here, we investigate shear and longitudinal viscosities using shear stress and compressional longitudinal stress measurements as functions of frequency and concentration. We find that both viscosities are frequency-dependent and exhibit almost identical frequency and concentration dependences in the high-concentration region. A comparison to quasielastic neutron scattering experiments suggests that both are governed by structural relaxation of the TFSI- network. Thus, LiFTSI-water electrolytes appear to be an unusual case of a non-Newtonian fluid, where shear and longitudinal viscosities are determined by the same relaxation mechanism.

DOI： 10.1021/acs.jpclett.3c03145

Effects of intramolecular chain conformation on the hydration and miscibility of polyethylene glycol in water studied by means of polymer reference interaction site model theory Reviewed

Yamaguchi Tsuyoshi, Chong Song-Ho, Yoshida Norio

JOURNAL OF CHEMICAL PHYSICS Vol. 159 ( 4 ) 2023.7

Authorship：Lead author,　Corresponding author Language：English Publishing type：Research paper (scientific journal) Publisher：Journal of Chemical Physics

To examine the conventional idea that the gauche conformation of the OCCO dihedral angle promotes the dissolution of polyethylene glycol (PEG) in water through strong hydration, the thermodynamic properties of liquid mixtures of PEG and water were studied by means of polymer reference interaction site model (PRISM) theory. The intramolecular correlation functions required as input for PRISM theory were calculated by the generator matrix method, accompanied by changes in the distribution of dihedral angles. In the infinite dilution limit, the increased probability of gauche conformation of the OCCO dihedral angles stabilizes the hydration of PEG through enhanced hydrogen bonding between the ether oxygen of PEG and water. The mixing Gibbs energies of the liquid mixtures were also calculated in the whole concentration range based on the Gibbs-Duhem equation, as per our recent proposal. A liquid-liquid phase separation was observed when all the dihedral angles of PEG were in the trans conformation; for the liquid mixture to be miscible in the whole concentration range, the introduction of the OCCO gauche conformation was found to be indispensable. The above theoretical results support the conventional idea that the OCCO gauche conformation is important for the high miscibility of PEG and water.

DOI： 10.1063/5.0159130

Phase equilibrium of three-component liquid systems composed of water, alcohol, and sodium chloride studied by the reference interaction-site model integral equation theory Reviewed

Yamaguchi T., Chong S.H., Yoshida N.

Journal of Chemical Physics Vol. 158 ( 8 ) page： 084502 2023.2

Authorship：Lead author,　Corresponding author Language：English Publishing type：Research paper (scientific journal) Publisher：Journal of Chemical Physics

A theoretical method for calculating the thermodynamic properties and phase equilibria of a binary liquid mixture using the reference interaction-site model (RISM) integral equation theory, which we had proposed recently, was extended to ternary liquid systems containing salt. A novel dielectric correction of the RISM theory for a mixture of solvents was also proposed. The theory was applied to mixtures composed of water, alcohol, and NaCl, where the alcohol was either methanol or ethanol. The decrease in NaCl solubility with increasing alcohol molar fractions in the solvent was calculated. In the ethanol system, the theory yielded salt-induced liquid-liquid phase separation, which was observed experimentally in a ternary mixture of water, 1-propanol, and NaCl. The phase diagram of the ternary system was determined theoretically.

DOI： 10.1063/5.0142256

Study of phase equilibria and thermodynamic properties of liquid mixtures using the integral equation theory: Application to water and alcohol mixtures Reviewed

Yamaguchi Tsuyoshi, Chong Song-Ho, Yoshida Norio

JOURNAL OF CHEMICAL PHYSICS Vol. 157 ( 23 ) page： 234502 2022.12

Authorship：Lead author,　Corresponding author Language：English Publishing type：Research paper (scientific journal) Publisher：Journal of Chemical Physics

A theoretical method for calculating the thermodynamic properties and phase equilibria of liquid-liquid mixtures using the integral equation theory is proposed. The solvation chemical potentials of the two components are evaluated by the integral equation theory and the isothermal-isobaric variation of the total density with composition is determined to satisfy the Gibbs-Duhem relation. Given the density of a pure component, the method can calculate the densities of the mixture at any composition. Furthermore, it can treat the phase equilibrium without thermodynamic inconsistency with respect to the Gibbs-Duhem relation. This method was combined with the reference interaction-site model integral equation theory and applied to mixtures of water + 1-alcohol by changing the alcohol from methanol to 1-butanol. The destabilization of the mixing Gibbs energy by increasing the hydrophobicity of the alcohol and demixing of the water-butanol mixture were reproduced. However, quantitative agreement with experiments is not satisfactory, and further improvements of the integral equation theory and the molecular models are required.

DOI： 10.1063/5.0131475

Effects of molecular shape and flexibility on fast sound of organic liquids Reviewed

Tsuyoshi Yamaguchi, Koji Yoshida, Shinya Hosokawa, Daisuke Ishikawa, Alfred Q. R. Baron

The Journal of Chemical Physics Vol. 157 ( 15 ) page： 154504 2022.9

Measurement of complex shear viscosity up to 3 GHz using an electrodeless AT-cut quartz transducer Reviewed

Yamaguchi Tsuyoshi, Matsuoka Tatsuro

JAPANESE JOURNAL OF APPLIED PHYSICS Vol. 61 ( SG ) 2022.7

Authorship：Lead author,　Corresponding author Language：English Publishing type：Research paper (scientific journal) Publisher：Japanese Journal of Applied Physics

An experimental method is proposed to determine the frequency-dependent complex shear viscosity of liquids based on the quartz crystal microbalance with dissipation method. An AT-cut quartz transducer without metal electrodes is immersed in a sample liquid and the transducer is electrically coupled to the circuit through the dielectric response of the sample itself. After correcting for the apparent change in the resonance properties due to the dielectric coupling of the sample, our method is able to determine the viscosity of liquids of high polarity and low viscosity at frequencies as high as 3 GHz. The method was then applied to ethylene glycol and the viscoelastic relaxation in the GHz regime was observed. Furthermore, it was also applied to room-temperature ionic liquids to show that the dielectric correction of the resonance properties is valid for conductive liquids.

DOI： 10.35848/1347-4065/ac4141

Comparison between longitudinal viscoelastic relaxation and sound dispersion of molecular liquids on the molecular scale Reviewed

Yamaguchi T.

Journal of Chemical Physics Vol. 156 ( 24 ) page： 244505 2022.6

Authorship：Lead author,　Corresponding author Language：English Publishing type：Research paper (scientific journal) Publisher：Journal of Chemical Physics

Molecular dynamics simulation on some molecular liquids was performed to study sound dispersion on the molecular scale. The sound velocity was determined from the intermediate scattering function, and the relation between the longitudinal modulus and frequency was compared with the frequency-dependent longitudinal modulus in the q = 0 limit evaluated by the Kubo-Green theory. The sound dispersion of a monoatomic liquid up to qσ ≅ 2 was almost quantitatively explained by the viscoelasticity in the q = 0 limit when the wavenumber dependence of the heat capacity ratio was taken into account. The situation was similar for a polyatomic molecular liquid for which the intramolecular degrees of freedom were fixed. For a polyatomic liquid with intramolecular degrees of freedom, the sound dispersion on the molecular scale was connected to the high-frequency limit of the ultrasonic relaxation mode assigned to the vibrational energy relaxation. After subtracting the contribution of the vibrational energy relaxation, both the longitudinal viscoelasticity and the sound dispersion depended little on the presence of intramolecular degrees of freedom.

DOI： 10.1063/5.0098098

Implementation of solvent polarization in three-dimensional reference interaction-site model self-consistent field theory Reviewed

Yoshida N., Yamaguchi T., Nakano H.

Chemical Physics Letters Vol. 797 2022.6

Language：English Publishing type：Research paper (scientific journal) Publisher：Chemical Physics Letters

The three-dimensional reference interaction-site model self-consistent field (3D-RISM-SCF) theory is an electronic structure theory of solvated molecules, which can handle the electronic polarization of the solute molecule induced by the interaction with the solvent, whereas the electronic polarization of solvent molecules is ignored. Here, the solvent-polarizable model is implemented to take into account the electronic polarization of solvent molecules. It is applied to the water molecule in an aqueous solution and the p-nitroaniline molecule in an aqueous solution, and the effects of the solvent polarization on the properties of these solutes are demonstrated.

DOI： 10.1016/j.cplett.2022.139579

Volume viscosity and ultrasonic relaxation of ethanol-water mixtures studied by molecular dynamics simulations Reviewed

Yamaguchi Tsuyoshi

PHYSICAL CHEMISTRY CHEMICAL PHYSICS Vol. 24 ( 20 ) page： 12311 - 12318 2022.5

Authorship：Lead author,　Last author,　Corresponding author Language：English Publishing type：Research paper (scientific journal) Publisher：Physical Chemistry Chemical Physics

The volume viscosity of ethanol-water mixtures at various compositions was calculated by means of equilibrium molecular dynamics simulations, and the results were compared with acoustic experiments. The volume viscosity exhibited a strong maximum around the ethanol mole fraction of 0.27, which is in agreement with experiments. The relaxation in the 100 ps regime, which had been revealed by ultrasonic spectroscopy, was also reproduced. Analysis of the two-body density and the adiabatic pressure fluctuation demonstrated that the large volume viscosity of the mixture originates from the long-range concentration fluctuation.

DOI： 10.1039/d2cp00856d

Coupling between Translational Diffusion of a Solute and Dynamicsof the Heterogeneous Structure: Higher Alcohols and Ionic Liquids Reviewed

Yamaguchi Tsuyoshi

JOURNAL OF PHYSICAL CHEMISTRY B Vol. 126 ( 16 ) page： 3125 - 3134 2022.4

Authorship：Lead author,　Last author,　Corresponding author Language：English Publishing type：Research paper (scientific journal) Publisher：Journal of Physical Chemistry B

Translational diffusion of nonpolar monoatomic solutes in a room-temperature ionic liquid and 1-octanol was studied by molecular dynamics simulation. The diffusion coefficient was evaluated in two different ways: (1) from the mean-square displacement of a freely diffusing solute and (2) from the time correlation function of force acting on a fixed solute. The diffusion of the free solute is much greater than the prediction of the Stokes-Einstein (SE) relation when the size of the solute is small, as has been reported by many experimental works. In contrast, the friction on fixed small solutes follows the SE relation. The mechanism of the solute diffusion in both solvents was then analyzed based on the coupling between the translational motion of the solute and the collective dynamics of the heterogeneous intermediate-range structure characteristic to these solvents. Analysis revealed that the coupling is present in all systems, but the relaxation is fast in the cases of free and small solutes. This suggests that the coupling can relax through the motion of the solute when the solute is free and small, while the relaxation of the heterogeneous structure itself is required for large or fixed solutes. The difference in the relaxation dynamics of the friction on the solute and the shear viscosity is explained as the coupling with different dynamic modes of the solvent. Therefore, the validity of the SE relation may not be a good criterion to judge whether the mechanisms of the diffusion and the viscosity are the same or not.

DOI： 10.1021/acs.jpcb.2c01053

Decoupling between Solvent Viscosity and Diffusion of a Small Solute Induced by Self-Motion Reviewed

Yamaguchi Tsuyoshi

JOURNAL OF PHYSICAL CHEMISTRY LETTERS Vol. 12 ( 32 ) page： 7696 - 7700 2021.8

Authorship：Lead author,　Last author,　Corresponding author Language：English Publishing type：Research paper (scientific journal) Publisher：Journal of Physical Chemistry Letters

The self-diffusion of a monatomic solute in liquid 1-octanol and n-tetradecane was investigated by means of a molecular dynamics simulation. The diffusion coefficient of a solute as small as argon is much greater than that obtained from the hydrodynamic-based Stokes-Einstein (SE) relation, as was reported experimentally. A relaxation of the memory function of a freely diffusing solute is much faster than that of the autocorrelation function of a shear stress. However, the SE behavior is recovered when the solute is spatially fixed, and the diffusion coefficient is calculated from the force-force autocorrelation function. A relaxation of the autocorrelation function of the force also follows that of shear stress. The fast diffusion of a small solute is thus ascribed to the decoupling between the structural relaxation of solvent and the solute diffusion induced by the self-motion of the solute.

DOI： 10.1021/acs.jpclett.1c02219

Molecular dynamics simulation study on the isomerization reaction in a solvent with slow structural relaxation Reviewed

CHEMICAL PHYSICS Vol. 542 page： 111056 2021.2

Solvation dynamics in electronically polarizable solvents: Theoretical treatment using solvent-polarizable three-dimensional reference interaction-site model theory combined with time-dependent density functional theory Reviewed

Yamaguchi Tsuyoshi, Yoshida Norio

JOURNAL OF CHEMICAL PHYSICS Vol. 154 ( 4 ) page： 044504 2021.1

Energy analysis of CO<inf>2</inf> separation process with low energy consumption using phase separation solvent

Maeda N., Nakanishi K., Kishimoto A., Machida H., Yamaguchi T., Norinaga K.

15th Greenhouse Gas Control Technologies Conference 2021, GHGT 2021 2021

Publisher：15th Greenhouse Gas Control Technologies Conference 2021, GHGT 2021

We calculated the energy required for regeneration when the phase separation solvent solvent is applied to the treatment of exhaust gas from coal-fired power plants. This solvent is characterized by regeneration at a low temperature of less than 100°C. As a result, it was clarified that under ideal conditions with no pressure drop and no heat loss, the required energy could be suppressed to 1.5 GJ/ton-CO2 by satisfying the following conditions; i) pinch point of the heat exchanger between rich-amine and lean-amine: 1 °C, ii) water concentration of the solvent: kept at 10 wt%, iii) COP of the heat pump: 5.5. However, increase of the pinch point, increase of the water concentration, and decrease of the COP will all result in a significant increase in the required energy. Therefore, in order to realize a process with low energy consumption, it is essential to meet these design constraints.

Durability and fire-hazardous-risk evaluation of unique phase separation solvent using high-boiling amine and ether

Maeda N., Kishimoto A., Machida H., Yamaguchi T., Yanase K., Norinaga K.

15th Greenhouse Gas Control Technologies Conference 2021, GHGT 2021 2021

Publisher：15th Greenhouse Gas Control Technologies Conference 2021, GHGT 2021

Durability and fire hazard risk evaluation were conducted to determine the process feasibility on the unique phase separation solvent with low regeneration temperature (90 °C), consisting of amine, ether, and small amount of water. The results we obtained are as follows; I) The amine degradation rate of the phase separation solvent would be less than 1/10 of that of monoethanolamine (MEA), which was contributed by its high oxidative resistant nature and low regeneration temperature. II) The gas composition formed in the absorber was completely out of combustible range and almost no accumulations of explosive compounds such as peroxides were observed when in contact with 6 % oxygen containing gas (dry base). Therefore, we believe that the phase separation solvent is applicable to the treatment of exhaust gas from coal-fired thermal power plants.

Coupling between Structural and Dielectric Relaxations of Methanol and Ethanol Studied by Molecular Dynamics Simulation Reviewed

JOURNAL OF PHYSICAL CHEMISTRY B Vol. 124 ( 32 ) page： 7027 - 7036 2020.8

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