Faculty Profiles - YASUDA, Keiji

Papers - YASUDA, Keiji

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Shear and Structural Relaxation in Superconcentrated Lithium Bis(trifluoromethanesulfonyl)amide Aqueous Solutions Reviewed

Seike, Y; Yasuda, K; Yamaguchi, T; Nagai, T; Yoshida, K; Yamada, T

JOURNAL OF PHYSICAL CHEMISTRY B Vol. 129 ( 44 ) page： 11541 - 11547 2025.11

Language：English Publisher：Journal of Physical Chemistry B

Superconcentrated aqueous electrolyte solutions have been actively studied since the first report on lithium-ion batteries operating with superconcentrated aqueous solutions of lithium salt. One of the drawbacks of superconcentrated electrolytes is their high viscosity, which reduces ionic conductivity and adversely affects battery performance. In this work, we investigated the concentration- and frequency-dependent viscosity and microscopic dynamics of aqueous lithium bis(trifluoromethanesulfonyl)amide (LiTFSA) solutions using shear relaxation and quasi-elastic neutron scattering (QENS) spectroscopies. They are compared with each other to reveal the mechanism of viscosity and to provide novel insights into their fundamental physicochemical behavior. As the concentration increased from 3 to 21 molal, a strong increase in viscosity and a significant retardation of shear relaxation were observed. The comparison between the shear relaxation and QENS shows that the wavenumber of their matching shifts to lower wavenumbers as the concentration is reduced, which suggests that the spatial scale of the liquid structure is enlarged with decreasing concentration. As a result, we observed viscoelastic relaxation even in the low-viscosity region because of a characteristic heterogeneous structure absent in other normal liquids.

DOI： 10.1021/acs.jpcb.5c04968

Web of Science

Scopus

PubMed

Thermodynamic properties of water in aqueous amine solutions studied by energy-representation method Reviewed Open Access

Yokoyama, Y; Yasuda, K; Yamaguchi, T

PHYSICAL CHEMISTRY CHEMICAL PHYSICS Vol. 27 ( 41 ) page： 21970 - 21981 2025.10

Language：English Publisher：Physical Chemistry Chemical Physics

The use of aqueous amine solutions for CO<inf>2</inf> capture is considered as a promising strategy for mitigating global warming, and reducing the energy consumption of the capture process is essential for its widespread adoption. Understanding the mechanisms that govern the vapor pressure of water and enthalpy of water vaporization of CO<inf>2</inf>-loaded solutions can contribute to lowering the energy cost of CO<inf>2</inf> capture. In this study, molecular dynamics simulations of aqueous amine solutions before and after CO<inf>2</inf> absorption were performed, and the solvation free energy of water was evaluated using the energy representation method. The results revealed that vapor pressure decreases by CO<inf>2</inf> absorption, particularly due to the formation of anions that strongly interact with water through hydrogen bonding. The contributions of each solvent species to the solvation free energy and solvation energy were also quantified. It was found that the enthalpy of vaporization increases with amine concentration both before and after CO<inf>2</inf> absorption. Before CO<inf>2</inf> absorption, this increase is attributed to enhanced energetic interactions, despite the destabilization in solvation free energy due to entropic contributions. Additionally, snapshots indicated water localization in certain systems. Analysis of concentration fluctuations showed that concentration regions with greater fluctuations tended to exhibit smaller changes in vapor pressure with respect to concentration, suggesting a correlation between microscopic structure formation and macroscopic thermodynamic properties.

DOI： 10.1039/d5cp02422f

Behavior of sonochemical reaction in a small pipe Reviewed

Vol. 64 ( 3 ) 2025.3

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

Vol. 64 ( 3 ) 2025.3

放射線、低温プラズマおよび超音波によるフリーラジカル生成 Reviewed

近藤隆，熊谷純，安田啓司，井上健一，橋爪博司，田中宏昌，石川健治，堀勝

日本放射線化学会 ( 118 ) page： 3 - 11 2024.11

Synthesis of Au@Pd core-shell nanoparticles by ultrafine bubbles and ultrasound without capping and reducing agents Reviewed

Yasuda, K; Iwata, T; Mizuno, Y; Yamamoto, Y

CHEMISTRY LETTERS Vol. 53 ( 7 ) 2024.7

Dependence of reaction on vessel position, diameter, and liquid height in the sonochemical reactor with indirect irradiation Reviewed Open Access

Yasuda, K; Yamazaki, T; Asakura, Y

JAPANESE JOURNAL OF APPLIED PHYSICS Vol. 63 ( 4 ) 2024.4

Language：English Publishing type：Research paper (scientific journal) Publisher：Japanese Journal of Applied Physics

To investigate the sonochemical reaction performance caused by the indirect irradiation at 500 kHz, the glass vessel and a KI aqueous solution were used. Both the ultrasonic power and reaction rate had maximum values at every half wavelength of ultrasound. When the vessel position was adjusted to a larger absolute value of transducer impedance, the reaction rate became higher. The reaction rate and ultrasonic power increased as the vessel position moved closer to the transducer. The reaction rate first increased as the electric power applied to the transducer increased, reached a maximum value, and then decreased. This decrease phenomenon is called quenching of the sonochemical reaction. Before the quenching occurrs, the reaction rate per unit volume almost linearly increased with ultrasonic power density. The effects of the vessel diameter and liquid height on the relationship between the reaction rate per unit volume and the ultrasonic power density were small.

DOI： 10.35848/1347-4065/ad2d09

Web of Science

Scopus

Evaluation of solvent property of air-water interface based on the fluorescence spectra of 1,2′-dinaphthylamine in the aqueous solution of ultrafine bubbles Reviewed

Kodama, K; Hattori, S; Yasuda, K; Saitoh, T

ANALYTICAL SCIENCES Vol. 40 ( 2 ) page： 341 - 345 2024.2

Language：English Publishing type：Research paper (scientific journal) Publisher：Analytical Sciences

Solvent property of air–water interface was evaluated based on the fluorescence spectra of 1,2′-dinaphthylamine in water containing ultrafine bubbles (average diameter: 103 nm, standard deviation: 38 nm). Among naphthylamine derivatives whose fluorescence spectra were responsive to microscopic hydrophobicity, 1,2′-dinaphthylamine (DN) was selected because its wavelength of the maximum emission (λ<inf>max</inf>) was significantly dependent on the concentration and microenvironment of the ultrafine bubble. The λ<inf>max</inf> value of DN in water was 486 nm, while it shifted to shorter wavelength (408 nm) in the presence of 1.09 × 109 mL−1 of ultrafine bubbles. The shift of λ<inf>max</inf> value indicates that DN adsorbs on the surfaces of ultrafine bubbles and exists in hydrophobic region rather than in bulk water. By comparing with the λ<inf>max</inf> values in different solvents, the surface of ultrafine bubble was found to have similar solvent property to ethyl ether or ethyl acetate that are widely used as extracting solvents for hydrophobic organic compounds. Graphical abstract: (Figure presented.)

DOI： 10.1007/s44211-023-00454-x

Web of Science

Scopus

PubMed

Characteristics and Application of Ultrafine Bubbles Invited Reviewed Open Access

YASUDA Keiji

Vacuum and Surface Science Vol. 66 ( 11 ) page： 631 - 638 2023.11

Authorship：Lead author,　Last author,　Corresponding author Language：Japanese Publisher：The Japan Society of Vacuum and Surface Science

Ultrafine bubbles (bulk nanobubbles), small bubbles less than 1 µm in diameter, have attracted academic and industrial attention because they have numerous advantages, including chemical-free nature and extraordinarily long lifetime. Since Brownian motion velocity is much higher than buoyancy, ultrafine bubble lifetime is more than several months. But stable mechanism is still unclear, even though their inside is highly pressured. They have several characteristics, such as pH-dependent surface charge and reduction in friction. Ultrafine bubbles are generated and removed by selecting the ultrasonic frequency. This review discusses the fundamental characteristics of ultrafine bubbles and their applications. Ultrafine bubbles effectively remove proteins, dyes, and inorganic salts from solid surfaces. Ultrafine bubbles promote adsorption, desorption and extraction. Gold nanoparticles, nanocomposites of CaCO3 and pulp fiber, and follow nanoparticles are synthesized using ultrafine bubbles. Thus, ultrafine bubbles have been shown to be powerful, environmentally friendly, safe, clean, simple, and inexpensive methods.

DOI： 10.1380/vss.66.631

Open Access

CiNii Research

Development of high efficiency sonochemical reactors Invited Reviewed

Yasuda Keiji, Asakura Yoshiyuki

THE JOURNAL OF THE ACOUSTICAL SOCIETY OF JAPAN Vol. 79 ( 11 ) page： 569 - 575 2023.11

超音波霧化とウルトラファインバブルによるアミノ酸の濃縮 Invited

安田啓司

超音波TECHNO Vol. 35 ( 5 ) page： 50 - 53 2023.9

Characteristics of Ultrafine Bubbles (Bulk Nanobubbles) and Their Application to Particle-Related Technology Invited Open Access

Yasuda Keiji

KONA Powder and Particle Journal Vol. 41 ( 0 ) page： 183 - 196 2023.3

Language：English Publishing type：Research paper (scientific journal) Publisher：Hosokawa Powder Technology Foundation

Ultrafine bubbles (bulk nanobubbles), small bubbles with a diameter of less than 1 μm, have attracted academic and industrial attention because of their numerous advantages, including their chemical-free nature and extraordinarily long lifetime. The long lifetime is related to the much higher Brownian motion velocity compared to buoyancy. The reason why ultrafine bubbles can endure under stable conditions is still unclear, even though their inside is highly pressured. They have several characteristics, such as pH-dependent surface charge and reduced friction. They are also closely related to ultrasound. Ultrafine bubbles are generated and removed by selecting the ultrasonic frequency. Reaction and separation using ultrasonic cavitation and atomization, respectively, are enhanced by ultrafine bubbles. They can produce hollow nanoparticles, enhance adsorption on activated carbon, and clean solid surfaces. This review discusses the fundamental and ultrasonic characteristics of ultrafine bubbles and their application in particle-related technology, encompassing fine particle synthesis, adsorption, desorption, extraction, cleaning, and prevention of fouling.

DOI： 10.14356/kona.2024004

液中プラズマ法によるナノグラフェン合成に及ぼす超音波の影響 Invited

安田啓司, 長谷川健太, 近藤博基, 堀勝

超音波TECHNO Vol. 34 ( 5 ) page： 42 - 46 2022.10

ウルトラファインバブルのソノケミストリーへの応用 Invited

安田啓司

Bulletin of the Japan Society of Sonochemistry Vol. 16 ( 2 ) page： 26 - 34 2022.9

ファインバブルの特徴 Invited

安田啓司

粉体技術 Vol. 14 ( 8 ) page： 597 - 601 2022.8

Enrichment of amino acids from its aqueous solution by ultrasonic atomization and ultrafine bubbles Reviewed Open Access

Vol. 61 ( SG ) page： SG10321 - SG10325 2022.7

ウルトラファインバブルによる超音波合成した金ナノ粒子の粒子径制御 Invited

安田啓司

超音波TECHNO Vol. 34 ( 3 ) page： 83 - 87 2022.6

Study on the efficiency of a transducer for sonochemistry by calorimetry Reviewed Open Access

Y. Asakura and K. Yasuda

Japanese Journal of Applied Physics Vol. 61 page： GS1032 2022.5

Curcumin-loaded liposome preparation in ultrasound environment under pressurized carbon dioxide Reviewed Open Access

Wahyudiono, J. He, X. Hu, S. Machmudah, K. Yasuda, S. Takami, H. Kanda, M. Goto

FOODS Vol. 11 ( 10 ) page： 1469 2022.5

Generation and Reduction of Ultrafine Bubbles by Ultrasonic Irradiation Invited

YASUDA Keiji, ASAKURA Yoshiyuki

JAPANESE JOURNAL OF MULTIPHASE FLOW Vol. 36 ( 1 ) page： 12 - 19 2022.3

Language：Japanese Publishing type：Research paper (scientific journal) Publisher：THE JAPANESE SOCIETY FOR MULTIPHASE FLOW

Ultrasound was irradiated to ultrapure water. Ultrafine bubbles with a diameter of 90 - 100 nm were generated. Number concentration of ultrafine bubbles increased with time and approached asymptotically to an equilibrium value. Ultrafine bubble concentration increased with increasing ultrasonic power and decreasing frequency. For comparison, highly concentrated ultrafine bubble water was prepared by pressurized dissolution method, and ultrasound was also irradiated to the ultrafine bubble water. Reduction of ultrafine bubbles was observed and ultrafine bubble concentration decreased to the equilibrium value. Ultrafine bubble concentration decreased with increasing ultrasonic power and frequency. Generation and reduction of ultrafine bubbles by ultrasound was modeled to analyze experimental data. The results calculated by our model were in good agreement with the experimental data.

DOI： 10.3811/jjmf.2022.t002

CiNii Research

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Papers - YASUDA, Keiji