小林 祐生 (コバヤシ ユウセイ)

Kobayashi, Yusei

写真a

所属(所属キャンパス)

理工学部 機械工学科 (矢上)

職名

助教(有期)

外部リンク

 

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  • Self-assembly of polymer-tethered nanoparticles with uniform and Janus surfaces in nanotubes

    Sato T., Kobayashi Y., Michioka T., Arai N.

    Soft Matter (Soft Matter)  17 ( 15 ) 4047 - 4058 2021年04月

    ISSN  1744683X

     概要を見る

    In this study, a coarse-grained molecular simulation was performed to investigate the morphologies and phase diagrams of self-assembled polymer-tethered nanoparticles (NPs) confined in nanotubes (NTs). Unlike ordinary NPs, polymer-tethered NPs have two distinct characteristic lengths, which are key factors that determine their self-assembly. Herein, two distinct types of NT walls and three types of polymer-tethered NPs were considered: hydrophilic and hydrophobic walls, and hydrophilic, hydrophobic, and Janus surfaces. First, the qualitative phase diagrams of the axial pressure,Pz,versusthe ratio of the NT radius to the NP radius,L, were derived. The results revealed that diverse self-assembled morphologies, which are not formed in non-tethered NPs, were observed in the polymer-tethered NPs. For example, three types of ordered structures with different structural characteristic lengths, depending onPz, were obtained. In addition, the effect of the chemical nature of the polymer-tethered NP surface on the self-assembled morphology confined in NTs was investigated. Clusters of water molecules were formed, particularly in the hydrophobic polymer-tethered NPs, and these clusters caused the structural distortion of the NP. Moreover, in the polymer-tethered NPs with the Janus amphiphilic surface, the hydrophobic and hydrophilic polymer tethered NPs assembled in the axial direction to form an ordered structure, and a double-helix structure was formed atL= 3.0 in the hydrophobic NT. The results of these simulations indicate that the self-assembly behaviours of polymer-tethered NPs can be qualitatively predicted based on the chemical nature of the NT walls and the surface design of the polymer-tethered NP.

  • Structure and Shear Response of Janus Colloid-Polymer Mixtures in Solution

    Kobayashi Y., Arai N., Nikoubashman A.

    Langmuir (Langmuir)  36 ( 47 ) 14214 - 14223 2020年12月

    ISSN  07437463

     概要を見る

    We investigate the structure and rheological properties of dilute colloid-polymer mixtures at rest and under shear via molecular simulations that take into account hydrodynamic interactions. Mixtures of amphiphilic Janus colloids (JCs) and hydrophobic/amphiphilic polymers are considered for various solvent qualities and polymer concentrations. Free polymers, small polymer droplets, and hybrid aggregates coexist in mixtures with slightly hydrophobic homopolymers. As the solvent quality worsens, all polymers aggregate into small droplets, covered and stabilized by the JCs. In mixtures with amphiphilic polymers, we observe the coexistence of free polymers, purely polymeric micelles, and hybrid aggregates. At low shear rates, all mixtures exhibit a Newtonian-like response with intrinsic shear viscosities that are up to 2 times as large as of pure suspensions of nonadsorbing colloids at the same concentration. Furthermore, the mean aggregation number increases slightly due to the flow-enhanced collision of aggregates. At larger shear rates, however, the aggregates break up, the polymers align in the flow direction, and the mixtures exhibit shear-thinning. This shear-induced breakup occurs at stronger shear compared to pure JC suspensions, indicating that the adsorbed polymers reinforce the hybrid aggregates.

  • Effect of the Janus Amphiphilic Wall on the Viscosity Behavior of Aqueous Surfactant Solutions

    Tsujinoue H., Kobayashi Y., Arai N.

    Langmuir (Langmuir)  36 ( 36 ) 10690 - 10698 2020年09月

    ISSN  07437463

     概要を見る

    The effects of the chemical nature of an interface are one of the key parameters which can affect self-assembly and rheological behavior. To date, several studies have reported self-assembled structures and rheological behaviors in the development of various functional materials. In this study, we investigated the self-assembly and viscosity behavior of aqueous surfactant solutions confined in three types of Janus amphiphilic nanotubes (JANTs), which have two, four, and eight sequential domains, respectively, using molecular simulation. We found that the viscosity behavior depends on the surfactant concentration and the chemical nature of the wall surface. For instance, although the concentration levels of the surfactants are the same (c = 10%), completely different viscosity behaviors were observed in the two sequential domains (Newtonian-like) and the four and eight sequential domains (strong shear-thinning) of the JANTs. Our simulations demonstrated how the rheological properties of aqueous surfactant solutions, including viscosity and velocity profiles, can be controlled by the chemical nature of the JANT wall surface, effect of confinement, and their self-assembly structures. Considering the foregoing, we hope that our study offers new knowledge on nanofluid systems.

  • A biointerface effect on the self-assembly of ribonucleic acids: A possible mechanism of RNA polymerisation in the self-replication cycle

    Arai N., Kobayashi Y., Yasuoka K.

    Nanoscale (Nanoscale)  12 ( 12 ) 6691 - 6698 2020年03月

    ISSN  20403364

     概要を見る

    Despite decades of intensive research, many questions remain on the formation and growth of the first cells on Earth. Here, we used computer simulation to compare the self-assembly process of ribonucleic acids in two environments: Enclosed in a vesicle-cell membrane and in the bulk. The self-assembly was found to be more favoured in the former environment, and the origin of such a biointerface effect was identified. These results will contribute to a better understanding of the origin of life on the primitive Earth.

  • Replica exchange dissipative particle dynamics method on threadlike micellar aqueous solutions

    Kobayashi Y., Nomura K., Kaneko T., Arai N.

    Journal of Physics Condensed Matter (Journal of Physics Condensed Matter)  32 ( 11 )  2020年

    ISSN  09538984

     概要を見る

    The self-assembly of surfactant molecules can spontaneously result in a variety of micelle morphologies, such as spherical micelles, threadlike micelles, and vesicles, and it is therefore crucial to predict and control the self-assembly to achieve a helpful process in the fields of materials chemistry and engineering. A dissipative particle dynamics (DPD) method used in a coarse-grained molecular simulation is applied to simulate various self-assembling soft matter systems because it can handle greater length and time scales than a typical molecular dynamics simulation (MD). It should be noted that the thorough sampling of a system is not assured at low temperatures because of large complex systems with coarse-grained representations. In this article, we demonstrate that the replica exchange method (REM) is very effective for even a DPD in which the energy barrier is comparatively lower than that of a MD. A replica exchange on DPD (REDPD) simulation for threadlike micellar aqueous solutions was conducted, and the values of the potential energy and the mean aggregation number were compared. As a result, the correct values and a self-assembled structure within a low-temperature range can only be obtained through the REDPD.

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競争的資金等の研究課題 【 表示 / 非表示

  • ポリマーナノコンポジットの構造制御と機械特性発現メカニズムの解明

    2021年08月
    -
    2023年03月

    文部科学省・日本学術振興会, 科学研究費助成事業, 小林 祐生, 研究活動スタート支援, 補助金,  代表

 

担当授業科目 【 表示 / 非表示

  • 機械工学ものづくりプロジェクト

    2021年度

  • 自然科学実験

    2021年度

  • 理工学基礎実験

    2021年度

  • 形状情報の表現

    2021年度