研究テーマ / Research Activities

自己組織化単分子膜（self-assembled monolayer, SAM）をはじめとした分子スケールの表面修飾技術は，固体表面の物理化学的特性を制御する技術として，種々のプロセスやデバイスへの応用が進んでいます．特に，有機分子の自己組織化や薄膜状態での自発的構造形成を利用してボトムアップにより表面修飾を行う技術は，柔軟かつ適応性の広い方法として期待されています．これら有機分子膜の構造形成や界面親和性・濡れ性，界面を介した熱・物質輸送特性は，工学応用上極めて重要であり，ミクロな立場から輸送機構を明らかにすることを目的に研究を行っています．

Novel surface modification techniques at the molecular level such as the self-assembled monolayer (SAM) have drawn attention as techniques to control the physical and chemical properties on solid surfaces. In particular, the bottom-up processes, i.e., surface modification by utilizing the self-assembling of organic molecules or spontaneous structure formation in organic thin films have future possibilities due to their flexibility and adaptability. Structure formation, interface affinity, and heat and mass transport characteristics of organic molecular films have a critical importance in the engineering and industry. Therefore, we investigate the underlying microscopic mechanisms of these significant characteristics.

[Related publications]

• • Shih-Wei Hung, Gota Kikugawa, Junichiro Shiomi, Mechanism of temperature dependent thermal transport across the interface between self-assembled monolayer and water, Journal of Physical Chemistry C, Vol. 120 (2016), pp. 26678–26685. doi:10.1021/acs.jpcc.6b09516

• Gota Kikugawa, Taku Ohara, Tohru Kawaguchi, Ikuya Kinefuchi, and Yoichiro Matsumoto, A molecular dynamics study on heat conduction characteristics inside the alkanethiolate SAM and alkane liquid, International Journal of Heat and Mass Transfer, Vol. 78 (2014), pp. 630–635. doi:10.1016/j.ijheatmasstransfer.2014.07.040

• Gota Kikugawa, Taku Ohara, Tohru Kawaguchi, Ikuya Kinefuchi, and Yoichiro Matsumoto, A Molecular Dynamics Study on Heat Transfer Characteristics Over the Interface of Self-Assembled Monolayer and Water Solvent, ASME Journal of Heat Transfer, Vol. 136 (2014), 102401. doi:10.1115/1.4027910

• 川口 暢, 菊川 豪太, 杵淵 郁也, 八束 真一, 小原 拓, 松本 洋一郎, 非平衡分子動力学法を用いた親水性末端基を有する自己組織化膜と水の界面熱抵抗の解析, 日本機械学会論文集C編, 76巻, 768号 (2010), pp. 1936-1938, (in Japanese). weblink to CINII

• 菊川豪太, 小原拓, 川口暢, 鳥越栄一, 萩原康正, 松本洋一郎, SAM–溶媒界面の界面熱抵抗に関する分子動力学的研究, 日本機械学会論文集B, 第75巻, 第749 (2009), pp.146-154, (in Japanese). weblink to CINII

• Gota Kikugawa, Taku Ohara, Toru Kawaguchi, Eiichi Torigoe, Yasumasa Hagiwara, Yoichiro Matsumoto, A molecular dynamics study on heat transfer characteristics at the interfaces of alkanethiolate self-assembled monolayer and organic solvent, Journal of Chemical Physics, Vol.130 (2009), 074706. doi:10.1063/1.3077315

航空機や自動車など産業的にも利用が始まっているCFRP等の高分子複合材料をはじめとした高分子素材の開発には，内部の分子スケール構造や相分離構造の制御によって，機械的・化学的特性のみならず熱流動特性を設計することが必要とされています．例えば，高温等の極限状態で利用される架橋構造を有する熱硬化性樹脂は，宇宙往還機表面に使われるアブレーション材料など，分子の内部構造の変化・崩壊に伴う機械的・熱的特性の変化を予測することが極めて重要な課題となっています．また，高分子樹脂の成形過程においては樹脂の流動性や熱伝導特性が成形された製品のクオリティに大きく影響することが知られています．分子スケールからマクロスケールに至るスケール複合的な解析手法やデータ科学・機械学習の技術を活用して，有用な熱流動特性や機械特性を有する高分子材料の探索・設計を目指しています．

As for development of polymeric materials which have extensively been utilized in industry, designing thermofluid properties as well as mechanical and chemical properties by controlling the molecular-scale structure and phase separation structure inside the material is being required. For example, it is a critical issue to predict the variation in mechanical and thermal properties of polymeric resins having crosslink bonds according to the change of molecular structure when exposed to the extreme environment, e.g., ablation materials in space planes. Using integrated numerical analyses covering molecular-scale to macroscale phenomena and data-driven informatics techniques, we aim to explore and design polymeric materials which have valuable thermofluid properties and mechanical properties.

[Related publications]

• Yutaka Oya, Gota Kikugawa, and Tomonaga Okabe, Clustering approach for multidisciplinary optimum design of cross-linked polymer, Macromolecular Theory and Simulations, Vol. 27 (2017), 1600072. doi:10.1002/mats.201600072

• Tomonaga Okabe, Yutaka Oya, Koichi Tanabe, Gota Kikugawa, and Kenichi Yoshioka, Molecular Dynamics Simulation of Closslinked Epoxy Resins: Curing and Mechanical Properties, European Polymer Journal, Vol. 80, (2016), pp. 78-88. doi:10.1016/j.eurpolymj.2016.04.019

• Gota Kikugawa, Tapan G. Desai, Pawel Keblinski, and Taku Ohara, Effect of crosslink formation on heat conduction in amorphous polymers, Journal of Applied Physics, Vol. 114 (2013), 034302. doi:10.1063/1.4813505

流体やソフトマター界面，ナノスケール構造によって形成される制限空間内の閉じ込め液体においては，界面近傍における液体中の不均質（ヘテロ）な構造発現に伴い，特異な熱・物質輸送特性が現れます．これらは，多孔質体やナノ細孔，生体高分子を介した物質移動などナノ工学・バイオ科学レベルで広く重要な要素となっています．本研究を通じて，界面近傍における閉じ込め液体の分子輸送特性が，均質なバルク液体中と大きく異なることや流体力学的効果によって分子拡散現象が強く影響を受けることが明らかになっています．分子スケールにおけるヘテロな構造や輸送現象の本質的理解と，それらに基づくマクロな熱流体解析への橋渡しとなる物理モデルの構築を目指しています．

At the fluid and soft matter interfaces or inside the confined liquid in nanoscale structures, peculiar heat and mass transfer characteristics emerges as a consequence of heterogeneous structure formation inside a liquid in the vicinity of the interfaces. These phenomena are directly relevant to the wide field of nano- and bioengineering, e.g., molecular transport through mesoporous materials and biomolecules. This study elucidates that the molecular transport in confined liquids is significantly different from that in the homogenous bulk liquids and that the molecular diffusion is highly affected by the hydrodynamic effect induced by the molecule itself. Our goal is an essential understanding of heterogeneous structure and corresponding transport phenomena at the molecular level and building of physical models which can bridge macroscopic thermal and fluid analyses based on the microscopic knowledge.

[Related publications]

• 菊川豪太, 閉じ込め液体系における自己拡散係数への有限サイズ効果, アンサンブル, Vol. 20 (2018), pp. 179-184, (in Japanese).

• Hari Krishna Chilukoti, Gota Kikugawa, and Taku Ohara, Structure and Mass Transport Characteristics at the Intrinsic Liquid-Vapor Interfaces of Alkanes, Journal of Physical Chemistry B, Vol. 120 (2016), pp 7207–7216. doi: 10.1021/acs.jpcb.6b05332

• Gota Kikugawa, Takeo Nakano, and Taku Ohara, Hydrodynamic consideration of the finite size effect on the self-diffusion coefficient in a periodic rectangular parallelepiped system, Journal of Chemical Physics, Vol. 143 (2015), 024507. doi:10.1063/1.4926841

• Gota Kikugawa, Shotaro Ando, Jo Suzuki, Yoichi Naruke, Takeo Nakano, and Taku Ohara, Effect of the computational domain size and shape on the self-diffusion coefficient in a Lennard-Jones liquid, Journal of Chemical Physics, Vol. 142 (2015), 024503. doi:10.1063/1.4905545

• Gota Kikugawa, Shu Takagi, Yoichiro Matsumoto, Taku Ohara, A molecular dynamics study on local structure of liquid-vapor interface of water and L-J fluid, Journal of Thermal Science and Technology, Vol.3 (2008), pp. 234-240. doi:10.1299/jtst.3.234

• Gota Kikugawa, Shu Takagi and Yoichiro Matsumoto, A molecular dynamics study on liquid-vapor interface absorbed by impurities, Computers and Fluids, Vol.36 (2007), pp. 69-76. doi:10.1016/j.compfluid.2005.07.007

• 菊川豪太, 高木周, 松本洋一郎, ミクロスケールにおける気液界面の局所・瞬時的定義について, 日本機械学会論文集B, 第73巻, 第725号 (2007), pp.118-125, (in Japanese). doi:10.1299/kikaib.73.118