Fujitani, Youhei

写真a

Affiliation

Faculty of Science and Technology, Department of Applied Physics and Physico-Informatics ( Yagami )

Position

Professor

Career 【 Display / hide 】

  • 1985.05
    -
    Present

    医師国家試験合格（医籍292547）

  • 1994.10
    -
    1995.12

    国立予防衛生研究所 ,主任研究官

  • 1995.01
    -
    1995.12

    東京大学医学部 ,客員研究員

  • 1995.12
    -
    1997.03

    Leiden大学化学研究所物理化学高分子化学研究部門 （オランダ政府奨学生） ,博士研究員

  • 1997.04
    -
    2002.03

    慶應義塾大学理工学部 ,専任講師

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Academic Background 【 Display / hide 】

  • 1985.03

    The University of Tokyo, Faculty of Medicine, 医学科

    University, Graduated

  • 1989.03

    The University of Tokyo, Graduate School, Division of Medicine, 第１基礎医学専攻

    Graduate School, Completed, Doctoral course

  • 1991.03

    The University of Tokyo, Faculty of Science, 物理学科

    University, Graduated

  • 1993.03

    The University of Tokyo, Graduate School, Division of Science, 物理学専攻

    Graduate School, Completed, Master's course

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Academic Degrees 【 Display / hide 】

  • Medicine　, The University of Tokyo, 1989.03

  • Science, The University of Tokyo, 1995.10

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Licenses and Qualifications 【 Display / hide 】

  • 医師免許, 1985

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Papers 【 Display / hide 】

  • Thermophoresis in a near-critical binary fluid mixture

    Fujitani Y., Kuji T.

    Physics of Fluids 37 ( 11 )  2025.11

    ISSN  10706631

    　View Summary

    We consider a rigid spherical particle immersed in a binary non-electrolyte fluid mixture which lies in the one-phase region near the demixing critical point. Mixture components differently interact with the particle surface, which generates preferential adsorption of one component onto the surface. The resultant inhomogeneity in composition, significant owing to the near criticality, causes particle motion under an imposed temperature gradient, i.e., thermophoresis. Using hydrodynamics based on a coarse-grained free-energy density, we calculate the thermophoretic mobility of the particle, far from which the critical composition is assumed. As expected from the recently predicted direction of thermoosmosis of a mixture, our numerical results show that the particle moves toward the colder side in a mixture near the upper consolute point and toward the warmer side in a mixture near the lower consolute point regardless of which mixture component is adsorbed onto the surface. This property, stemming from the requirement of the free-energy density for describing the phase separation, should hold in general and be able to be examined experimentally.

  • Fluctuation amplitudes of a trapped particle in a near-critical binary fluid mixture

    Fujitani Y.

    Physics of Fluids 37 ( 4 )  2025.04

    ISSN  10706631

    　View Summary

    We assume that a binary fluid mixture, lying in the one-phase region near the demixing critical point, contains a Brownian particle trapped by a harmonic potential. A mixture component, preferred by the particle surface via a short-range interaction, concentrates near the surface to generate a thick adsorption layer. This layer, deformed by particle motion, increases the effective mass and restoring force, thereby reducing the equal-time correlation of the fluctuations of the particle position and that of the particle velocity. We calculate these fluctuation amplitudes using the reversible part of hydrodynamics on the basis of the free-energy density of a local functional theory, which is known to describe the critical properties well. The effects of the preferential adsorption are negligible when the stiffness of the trapping potential is sufficiently large. A typical stiffness below which the effects emerge is largely determined by the strength of preferential adsorption and shifts toward larger stiffness as the adsorption is stronger. Plots of the fluctuation amplitudes against the stiffness are approximately independent of the deviation of the temperature from the critical temperature. These properties should facilitate future experimental studies on this phenomenon.

  • Force density induced by preferential adsorption in a near-critical binary fluid mixture subject to the Soret effect

    Fujitani Y.

    Journal of Chemical Physics 161 ( 20 )  2024.11

    ISSN  00219606

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    We assume that two parallel plates are immersed in a binary fluid mixture lying in the one-phase region near the demixing critical point and that the surface of each plate attracts the mixture components differently via short-range interactions. It is known that the composition inhomogeneity caused by the difference can induce a force exerted on the plate at equilibrium. In the present study, we investigate how a temperature gradient imposed vertically on the plates changes the induced force by calculating the composition profile subject to the Soret effect. Numerically solving the derived differential equation, we show that a temperature gradient within the critical regime can change the force distinctly from its equilibrium value and can make the force direction opposite to the one at equilibrium.

  • Thermo-osmosis of a near-critical binary fluid mixture: A general formulation and universal flow direction

    Shunsuke Yabunaka and Youhei Fujitani

    Physical Review E (American Physical Society)  109 ( 6 ) 064610 2024.06

    Research paper (scientific journal), Last author, Corresponding author, Accepted,  ISSN  24700045

    　View Summary

    We consider a binary fluid mixture, which lies in the one-phase region near the demixing critical point, and study its transport through a capillary tube linking two large reservoirs. We assume that short-range interactions cause preferential adsorption of one component onto the tube's wall. The adsorption layer can become much thicker than the molecular size, which enables us to apply hydrodynamics based on a coarse-grained free-energy functional. For transport processes induced by gradients of the pressure, composition, and temperature along a cylindrical tube, we obtain the formulas of the Onsager coefficients to extend our previous results on isothermal transport, assuming the critical composition in the middle of each reservoir in the reference equilibrium state. Among the processes, we focus on thermo-osmosis - mass flow due to a temperature gradient. We explicitly derive a formula for the thermal force density, which is nonvanishing in the adsorption layer and causes thermo-osmosis. This formula for a near-critical binary fluid mixture is an extension of the conventional formula for a one-component fluid, expressed in terms of local excess enthalpy. We predict that the direction of thermo-osmotic flow of a mixture near the upper (lower) consolute point is the same as (opposite to) that of the temperature gradient, irrespective of which component is adsorbed on the wall. Our procedure would also be applied to dynamics of a soft material, whose mesoscopic inhomogeneity can be described by a coarse-grained free-energy functional.

  • Preferential adsorption in a near-critical binary fluid mixture as analyzed in the framework of the non-random two-liquid model

    Youhei Fujitani

    Fluid Phase Equilibria (Elsevier)  580   114050 2024.05

    Research paper (scientific journal), Single Work, Lead author, Accepted,  ISSN  03783812

    　View Summary

    We consider a binary fluid mixture, which lies in the one-phase region near the demixing critical point. Short-range interactions between the mixture components and a solid surface in contact with the mixture can make the mixture composition inhomogeneous significantly near the surface. This inhomogeneity has been shown to cause various phenomena by using the renormalized local functional theory. In its free-energy density, the order-parameter field is coarse-grained without rescaled and only the most singular part is specified. In the present study, on the basis of the crossover theory, we introduce a square-gradient term to the free-energy density of the extended non-random two-liquid model, which includes more than the most singular part. Thanks to similarity between the renormalized local functional theory and the crossover theory, the relationship between the two free-energy densities can be clarified. Supposing a mixture of nitroethane and 3-methylpentane and a mixture of 2,6-lutidine and water, we use the proposed free-energy density to calculate the inhomogeneous composition profile numerically. The free-energy density also enables us to calculate excess densities of entropy and enthalpy, unlike that of the renormalized local functional theory. We also find that the magnitude of the thermal force density, which is induced by a temperature gradient to cause flow in thermoosmosis, can depend on the calculation procedures significantly.

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Papers, etc., Registered in KOARA 【 Display / hide 】

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Presentations 【 Display / hide 】

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Works 【 Display / hide 】

  • 物理数学の手引き

    FUJITANI YOUHEI

    2004.04
    -
    Present
    , 

    Other, Single

    　View Details

    学部講義「数理物理」・大学院講義「応用数理解析」の講義ノートを拡張して，180ページあまりの冊子としTex製本して，講義に活用した．ただし，出版社を介してはおらず非売品である．

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Courses Taught 【 Display / hide 】

  • STATISTICALMECHANICS

    2025

  • PRESENTATION TECHNIQUE

    2025

  • MATHEMATICS OF DISTRIBUTED SYSTEMS

    2025

  • LABORATORY IN SCIENCE

    2025

  • INDEPENDENT STUDY ON FUNDAMENTAL SCIENCE AND TECHNOLOGY

    2025

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Memberships in Academic Societies 【 Display / hide 】

  • 日本物理学会, 

    1990.03
    -
    Present
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Committee Experiences 【 Display / hide 】

  • 2016.04
    -
    Present

    Associate Editor, Journal of the Physical Society of Japan

  • 2011.09
    -
    2013.03

    会誌編集委員, 日本物理学会

  • 2006.05
    -
    2007.04

    領域12世話人, 日本物理学会

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