Fujitani, Youhei

写真a

Affiliation

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

Position

Professor
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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 】

  • Effects of the preferential adsorption in a near-critical binary fluid mixture on dynamics of a droplet

    Youhei Fujitani

    Physics of Fluids （American Institute of Physics)  34 （ 9 ） 092007 2022.09

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

    　View Summary

    A binary fluid mixture in the homogeneous phase near the demixing critical point can include a small spherical droplet of a third fluid-component confined by a sharp interface. Conversely, a droplet consisting of the mixture can be included in the third fluid-component. The third component is assumed to attract one mixture component more than the other via short-range interactions. The adsorption layer, enriched with the preferred component, appears on the mixture side of the interface and can thicken significantly. The preferential adsorption causes the drag coefficient to deviate. We use the hydrodynamics based on a coarse-grained free-energy functional to calculate the deviation, neglecting the weak singularity of mixture viscosity. When the mixture lies inside the droplet, the ratio of the deviation changes nonmonotonically as the ratio of the ambient viscosity to the droplet viscosity increases. When the mixture lies outside, the former ratio increases with the latter ratio and can be considerably larger for a droplet than for a rigid sphere. Then, if a composition gradient is imposed, a force-free droplet undergoes diffusiophoresis, whose mobility can be considerably larger in magnitude than that of a rigid sphere. We also discuss probable power-law dependences of the drag coefficient and the mobility on the reduced temperature. The suggested power for the mobility is connected with the universal order-parameter profile in the surface critical behavior.

  • Diffusiophoresis in a near-critical binary fluid mixture

    Youhei Fujitani

    Physics of Fluids （American Institute of Physics)  34 （ 4 ） 041701 2022.04

    Accepted,  ISSN  10706631

    　View Summary

    We consider placing a rigid spherical particle into a binary fluid mixture in the homogeneous phase near the demixing critical point. The particle surface is assumed to have a short-range interaction with each mixture component and to attract one component more than the other. Owing to large osmotic susceptibility, the adsorption layer, where the preferred component is more concentrated, can be of significant thickness. This causes a particle motion under an imposed composition gradient. Thus, diffusiophoresis emerges from a mechanism which has not been considered so far. We calculate how the mobility depends on the temperature and particle size.

  • Isothermal transport of a near-critical binary fluid mixture through a capillary tube with the preferential adsorption

    Shunsuke Yabunaka, Youhei Fujitani

    Physics of Fluids （American Institute of Physics)  34 （ 5 ） 052012 2022.03

    Research paper (scientific journal), Joint Work, Last author, Accepted,  ISSN  10706631

    　View Summary

    We study isothermal transport of a binary fluid mixture, which lies in the homogeneous phase near the demixing critical point, through a capillary tube. A short-range interaction is assumed between each mixture component and the tube's wall surface, which usually attracts one component more than the other. The resulting preferential adsorption becomes significant owing to large osmotic susceptibility. The mixture flowing out of the tube is rich in the preferred component when flow is driven by the pressure difference between the reservoirs. When flow is driven by the mass-fraction difference, the total mass flow occurs in the presence of the preferential adsorption. These phenomena can be regarded as cross-effects linked by the reciprocal relation. The latter implies that diffusioosmosis arises from the free energy of the bulk of the mixture not involving the surface potential, unlike usual diffusioosmosis far from the critical point. We also study these phenomena numerically by using the hydrodynamics based on the coarse-grained free-energy functional, which was previously obtained to reveal near-critical static properties, and using material constants that were previously obtained in some experimental studies. Influence of the critical enhancement of the transport coefficients is found to be negligible because of off-critical composition in the tube. It is also shown that the conductance, or the total mass flow rate under a given mass-fraction difference, can change non-monotonically with the temperature. The change is well expected to be large enough to be detected experimentally.

  • Suppression of viscosity enhancement around a Brownian particle in a near-critical binary fluid mixture

    Youhei Fujitani

    Journal of Fluid Mechanics （Cambridge University Press)  907   A21 2021.01

    Research paper (scientific journal), Single Work, Lead author, Last author, Corresponding author, Accepted,  ISSN  00221120

    　View Summary

    We consider the Brownian motion of a rigid spherical particle in a binary fluid mixture, which lies in the homogeneous phase near the demixing critical point, assuming that neither component is more attracted by the particle surface. In a recent study, it was experimentally shown that the self-diffusion coefficient first decreases and then reaches a plateau as the critical point is approached. The decrease should reflect the critical enhancement of the viscosity, while the plateau was interpreted as representing the suppression of the enhancement due to the shear around the particle. To examine this interpretation, we take into account the local shear rate to calculate the dependence of the drag coefficient on the particle speed, and then utilize a Langevin equation to calculate the self-diffusion coefficient.

  • Drag coefficient of a rigid spherical particle in a near-critical binary fluid mixture, beyond the regime of the Gaussian model

    Shunsuke Yabunaka, Youhei Fujitani

    Journal of Fluid Mechanics （Cambridge University Press)  886   A2 2020.03

    Research paper (scientific journal), Joint Work, Last author, Accepted,  ISSN  00221120

    　View Summary

    The drag coefficient of a rigid spherical particle deviates from Stokes law when it is put into a near-critical fluid mixture in the homogeneous phase with the critical composition. The deviation is experimentally shown to depend approximately linearly on the correlation length of the composition fluctuation far from the particle , and is suggested to be caused by the preferential adsorption between one component and the particle surface. In contrast, the dependence was shown to be much steeper in the previous theoretical studies based on the Gaussian free-energy density. In the vicinity of the particle, especially when the adsorption of the preferred component makes the composition strongly off-critical, the correlation length becomes very small as compared with. This spatial inhomogeneity, not considered in the previous theoretical studies, can influence the dependence of on. To examine this possibility, we here apply a renormalized local functional theory, describing the preferential adsorption in terms of the surface field. This theory was previously proposed to explain the interaction of walls immersed in a (near-)critical binary fluid mixture. The free-energy density in this theory, coarse-grained up to the local correlation length, has a very complicated dependence on the order parameter, as compared with the Gaussian free-energy density. Still, a concise expression of the drag coefficient, which was derived in one of the previous theoretical studies, turns out to be valid in the present formulation. We show that, as becomes larger, the dependence of on becomes distinctly gradual and close to the linear dependence.

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

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Presentations 【 Display / hide 】

  • 相分離臨界点近くの二成分流体において選択的親和性のないコロイド剛体球の自己拡散係数

    藤谷洋平

    日本物理学会年次大会 (福岡) , 

    2020.03
    , 

    Poster presentation, 日本物理学会

  • 相分離臨界点近くの二成分流体膜にあって膜粘性の異なる円形液体領域の抵抗係数

    谷文之、藤谷洋平

    日本物理学会第74回年次大会 (九州大学伊都キャンパス) , 

    2019.03
    , 

    Poster presentation

  • 臨界点近くの2成分混合系中のコロイドの抵抗係数

    薮中俊介、藤谷洋平

    日本物理学会第74回年次大会 (九州大学伊都キャンパス) , 

    2019.03
    , 

    Oral presentation (general)

  • Drag coefficient of a Circular Liquid Domain in a Near-Critical Binary Fluid Membrane

    Youhei Fujitani

    Soft matter physics; from the perspective of the essential heterogeneity (Nishijin Plaza, Kyushuu University) , 

    2018.12
    , 

    Oral presentation (general)

  • 相分離臨界点近くの一様相にある二成分流体におけるコロイド粒子の動力学への浸透圧の影響

    FUJITANI YOUHEI

    日本物理学会年次大会 (東京理科大（野田）) , 

    2018.03
    , 

    Poster presentation

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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

    2022

  • RELAXATION PROCESS OF CLASSICAL FLUIDS

    2022

  • PRESENTATION TECHNIQUE

    2022

  • MATHEMATICS OF DISTRIBUTED SYSTEMS

    2022

  • MATHEMATICAL METHODS IN THE PHYSICAL SCIENCES

    2022

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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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