藤谷 洋平 (フジタニ ヨウヘイ)

Fujitani, Youhei

写真a

所属(所属キャンパス)

理工学部 物理情報工学科 (矢上)

職名

教授

経歴 【 表示 / 非表示

  • 1985年05月
    -
    継続中

    医師国家試験合格(医籍292547)

  • 1994年10月
    -
    1995年12月

    国立予防衛生研究所 ,主任研究官

  • 1995年01月
    -
    1995年12月

    東京大学医学部 ,客員研究員

  • 1995年12月
    -
    1997年03月

    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年04月
    -
    2002年03月

    慶應義塾大学理工学部 ,専任講師

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学歴 【 表示 / 非表示

  • 1985年03月

    東京大学, 医学部, 医学科

    大学, 卒業

  • 1989年03月

    東京大学, 医学研究科, 第1基礎医学専攻

    大学院, 修了, 博士

  • 1991年03月

    東京大学, 理学部, 物理学科

    大学, 卒業

  • 1993年03月

    東京大学, 理学系研究科, 物理学専攻

    大学院, 修了, 修士

学位 【 表示 / 非表示

  • 医学 , 東京大学, 1989年03月

  • 理学 , 東京大学, 1995年10月

免許・資格 【 表示 / 非表示

  • 医師免許, 1985年

 

論文 【 表示 / 非表示

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

    Fujitani Y.

    Physics of Fluids 37 ( 4 )  2025年04月

    ISSN  10706631

     概要を見る

    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年11月

    ISSN  00219606

     概要を見る

    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

    Yabunaka S., Fujitani Y.

    Physical Review E (American Physical Society)  109 ( 6 ) 064610 2024年06月

    研究論文(学術雑誌), 最終著者, 責任著者, 査読有り,  ISSN  24700045

     概要を見る

    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年05月

    研究論文(学術雑誌), 単著, 筆頭著者, 査読有り,  ISSN  03783812

     概要を見る

    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.

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

    Fujitani Y.

    Physics of Fluids (American Institute of Physics)  34 ( 9 ) 092007 2022年09月

    研究論文(学術雑誌), 単著, 筆頭著者, 査読有り,  ISSN  10706631

     概要を見る

    A large amount of 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 immersed in the third fluid-component. In either of the situations, we assume that the third component attracts 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 because of large susceptibility. The preferential adsorption affects flows, causing the drag coefficient to deviate. We use the hydrodynamics based on a coarse-grained free-energy functional to calculate the deviation, while 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 deviation ratio increases with the viscosity 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. These results can be utilized in future applications in the droplet microfluidics. 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.

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KOARA(リポジトリ)収録論文等 【 表示 / 非表示

研究発表 【 表示 / 非表示

  • Diffusiophoresis of a colloidal particle in a near-critical binary fluid mixture

    Youhei Fujitani

    7th International Soft Matter Conference (Osaka) , 

    2023年09月

    ポスター発表

  • Diffusiophoresis near a critical point of a binary fluid mixture

    Youhei Fujitani and Shunsuke Yabunaka

    28th International Conference on Statistical Physics (Tokyo) , 

    2023年08月

    口頭発表(一般)

  • 相分離臨界点近くの一様相にある二成分流体中のコロイド粒子の拡散泳動

    藤谷洋平、藪中俊介

    日本物理学会年秋季大会 (東京) , 

    2022年09月

    口頭発表(一般), 日本物理学会

  • 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年03月

    ポスター発表, 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年03月

    ポスター発表

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Works 【 表示 / 非表示

  • 物理数学の手引き

    藤谷 洋平

    2004年04月
    -
    継続中

    その他, 単独

     発表内容を見る

    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.

 

担当授業科目 【 表示 / 非表示

  • 統計物理

    2025年度

  • プレゼンテーション技法

    2025年度

  • 分布系の数理

    2025年度

  • 自然科学実験

    2025年度

  • 基礎理工学課題研究

    2025年度

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所属学協会 【 表示 / 非表示

  • 日本物理学会, 

    1990年03月
    -
    継続中

委員歴 【 表示 / 非表示

  • 2016年04月
    -
    継続中

    Associate Editor, Journal of the Physical Society of Japan

  • 2011年09月
    -
    2013年03月

    会誌編集委員, 日本物理学会

  • 2006年05月
    -
    2007年04月

    領域12世話人, 日本物理学会