研究者詳細 - 荒井　規允

論文 - 荒井　規允

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荒井規允, 小林祐生

年次大会（一般社団法人日本機械学会） 2018 （ 0 ） J0420102 2018年

研究論文（研究会，シンポジウム資料等）, 共著, 査読有り

We have performed coarse-grained molecular simulation simulations to investigate self-assembly processes and structures of functionalized nanoparticles confined in a nanoslit. The functionalized nanoparticle is decorated with some attractive areas. On the basis of the observed temperature- and concentration-dependent morphologies, we derive semiquantitative phase diagrams of the temperature. Five distinct designs of the nanoparticles are considered. We find that various self-assembled structures depending on the number of functionalized groups. The self-assembly behavior of the functionalized nanoparticles can be qualitatively predicted when the number of groups is known. Our simulation offers a theoretical guide to control morphologies of the self-assembled nanoparticles, a novel system that may find applications in nanofluidic devices or for nanopatterning.

若手研究者より研究会に期待すること

樋口祐次, 荒井規允

アンサンブル（分子シミュレーション学会） 20 （ 2 ） 102 - 104 2018年

研究論文（研究会，シンポジウム資料等）, 共著, 査読有り, ISSN 1884-6750

分子シミュレーション研究会発足20周年を記念して，「若手研究者より研究会に期待すること」をまとめたので報告する．分子シミュレーション夏の学校，分子シミュレーションスクールでアンケートを実施し，その内容をまとめて本記事を執筆した．それぞれ28人，52人から有効なご回答をいただいた．ここでは興味深い意見を中心に取り上げさせていただく．

機械学習と粗視化シミュレーションによる高性能界面活性剤の分子構造の探索

李娜, 諸星圭, 井口拓弥, 荒井規允

年次大会（一般社団法人日本機械学会） 2018 （ 0 ） J0420101 2018年

研究論文（研究会，シンポジウム資料等）, 共著, 査読有り

The success of machine learning combined with molecular simulation has been demonstrated in predicting electronic structure of materials(1)(2). A breakthrough that can aid in the design of new molecules that can be used to enhance the performance of material science. However, the prediction of physical properties of functional materials is one of the most challenging issue because of a multiscale problem across scientific disciplines in soft matter systems(3). In this study, first we used the coarse-grained molecular simulation to solve the multiscale problem. Second, we determined whether machine learning can be used to predict dispersion and viscosity, as the representative physical properties of surfactant solution, from the chemical molecular structures of a surfactant. The results showed that relatively accurate information on these physical properties can be predicted from the molecular structure, suggesting that machine learning can be used to predict multiscale systems, such as surfactant molecules, self-assembled micelle structures, and physical properties of solutions. The results will aid in further our scientific understanding and gain new insights(4).

散逸粒子動力学法を用いた界面活性剤水溶液の管内流れと自己集合に関する研究

小林祐生, 荒井規允

年次大会（一般社団法人日本機械学会） 2018 （ 0 ） J0420103 2018年

研究論文（研究会，シンポジウム資料等）, 共著, 査読有り

A self-assembly research is currently one of the most studied branches of materials chemistry, therefore, has gained a lot of attention due to a variety of potential applications in electronics, engineering, biomedical, and optical fields. So far, many previous studies have been reported to investigate the self-assembly of surfactant for developing various functional materials. In this report, we focused on the chemical nature of the wall surface as a critical parameter which can drastically change the self-assembled structure. We have studied the rheological properties of surfactant solutions in the distinct chemical nanotubes using a computer simulation. We found that the difference in the viscosity is able to obtain depending on the chemical nature of the wall surface even if systems without the surfactant molecules. With the surfactant molecules, the characteristic viscosity behaviors were observed with rich steady-state morphologies. For example, although the concentration of surfactant is the same (c = 30%), completely different viscosity behaviors were seen in hydrophilic (shear-thinning) and hydrophobic (shear-thickening) nanotubes. Our simulation offers a guide to control the rheological properties of surfactant aqueous solutions by the chemical nature of the wall surface, the effect of confinement, concentration of surfactant aqueous solution and the self-assembled structure.

分子シミュレーション研究会の各種データ

荒井規允, 泰岡顕治

アンサンブル（分子シミュレーション学会） 20 （ 2 ） 105 - 107 2018年

研究論文（研究会，シンポジウム資料等）, 共著, 査読有り, ISSN 1884-6750

分子シミュレーション研究会発足20周年を記念し，この20年間の研究会に関するいくつかのデータをまとめた．具体的には，研究会，討論会，夏の学校，分子シミュレーションスクール，アンサンブルに関するデータを報告する．なお各種データは，2002年までは河村雄行先生がまとめた分子シミュレーションのあゆみを参照し，その後は事務局（三上益弘先生，岡崎進先生，田中秀樹先生，泰岡）に保管されているデータを参照した．

Water Permeation and Flip-Flops Moving in Bilayer Membranes: A Dissipative Particle Dynamics Simulation

T Inokuchi, N Arai

Meeting Abstracts, 188-188 2018年

研究論文（国際会議プロシーディングス）, 共著, 査読有り

Linkage Among Molecular Simulations for Calculate Quantitative Polymeric Properties with a Minimum Amount of Calculation

R Miwatani, KZ Takahashi, N Arai

First International Conference on 4D Materials and Systems (August 26-30, 2018) 2018年

共著, 査読有り

Self-assembly and viscosity behavior of Janus nanoparticles in nanotube flow

Y Kobayashi, N Arai

Langmuir 33 (3), 736-743 （Langmuir） 33 （ 3 ） 736 - 743 2017年

研究論文（学術雑誌）, 共著, 査読有り, ISSN 0743-7463

© 2017 American Chemical Society. Janus nanoparticles (JNPs) have received considerable attention because of their characteristic physical properties that are due to more than two distinct chemical or physical surfaces. We investigated the rheological properties of a JNP solution in the nanotubes using a computer simulation. Prediction and control of the self-assembly of colloidal nanoparticles is of critical importance in materials chemistry and engineering. Herein, we show computer simulation evidence of a new type of velocity profile and a hallmark shear-thinning behavior by confining a JNP solution to a nanotube with hydrophobic and hydrophilic wall surfaces. We derived curves of the shear rate versus the viscosity for two quasi-one-dimensional nanotube systems including diluted and concentrated volume fractions of JNP solutions. For the diluted system, under relatively low shear rates, shear-thinning behavior with a moderate slope or behavior similar to a Newtonian fluid is observed because of the clustering of JNPs. Under relatively high shear rates, the slope of shear thinning changes markedly because the self-assembled structures are rearranged. Moreover, for concentrated systems, when the nanotube wall is hydrophobic, new characteristic velocity profiles that have not been reported before are observed. Our simulation offers a guide to control the rheological properties of JNP solutions by the chemical patterns on the surfaces of nanochannels, the effect of confinement, and the self-assembled structure. (Chemical Equation Presented).

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Theory of nanobubble formation and induced force in nanochannels

N Arai, T Koishi, T Ebisuzaki

Physical Review E 96 (4), 042802 （Physical Review E） 96 （ 4 ） 042802 - 10192 2017年

研究論文（学術雑誌）, 共著, 査読有り, ISSN 2470-0045

© 2017 American Physical Society. This paper presents a fundamental theory of nanobubble formation and induced force in confined nanochannels. It is shown that nanobubble formation between hydrophobic plates can be predicted from their surface tension and geometry, with estimated values for the surface free energy and the force acting on the plates in good agreement with the results of molecular dynamics simulation and experimentation. When a bubble is formed between two plates, vertical attractive force and horizontal retract force due to the shifted plates are applied to the plates. The net force exerted on the plates is not dependent on the distance between them. The short-range force between hydrophobic surfaces due to hydrophobic interaction appears to correspond to the force estimated by our theory. We compared between experimental and theoretical values for the binding energy of a molecular motor system to validate our theory. The tendency that the binding energy increases as the size of the protein increases is consistent with the theory.

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Programmed self-assembly of branched nanocrystals with an amphiphilic surface pattern

Y Taniguchi, MAB Sazali, Y Kobayashi, N Arai, T Kawai, T Nakashima

ACS nano 11 (9), 9312-9320 （ACS Nano） 11 （ 9 ） 9312 - 9320 2017年

研究論文（学術雑誌）, 共著, 査読有り, ISSN 19360851

© 2017 American Chemical Society. Site-selective surface modification on the shape-controlled nanocrystals is a key approach in the programmed self-assembly of inorganic colloidal materials. This study demonstrates a simple methodology to gain self-assemblies of semiconductor nanocrystals with branched shapes through tip-to-tip attachment. Short-chained water-soluble cationic thiols are employed as a surface ligand for CdSe tetrapods and CdSe/CdS core/shell octapods. Because of the less affinity of arm-tip to the surface ligands compared to the arm-side wall, the tip-surface becomes uncapped to give a hydrophobic nature, affording an amphiphilic surface pattern. The amphiphilic tetrapods aggregated into porous agglomerates through tip-to-tip connection in water, while they afforded a hexagonally arranged Kagome-like two-dimensional (2D) assembly by the simple casting of aqueous dispersion with the aid of a convective self-assembly mechanism. A 2D net-like assembly was similarly obtained from amphiphilic octapods. A dissipative particle dynamics simulation using a planar tripod model with an amphiphilic surface pattern reproduced the formation of the Kagome-like assembly in a 2D confined space, demonstrating that the lateral diffusion of nanoparticles and the firm contacts between the hydrophobic tips play crucial roles in the self-assembly.

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Liquid-crystal ordering mediated by self-assembly of surfactant solution confined in nanodroplet: a dissipative particle dynamics study

T Inokuchi, N Arai

Molecular Simulation 43 (13-16), 1218-1226 （Molecular Simulation） 43 （ 13-16 ） 1218 - 1226 2017年

研究論文（学術雑誌）, 共著, 査読有り, ISSN 0892-7022

© 2017 Informa UK Limited, trading as Taylor & Francis Group. In recent years, photonic crystal technology has received much attention. In this study, we focus on liquid crystal droplets considered as one of photonic crystals. It was reported that the orientation of liquid crystal molecules can be controlled by covering the droplet surface with surfactant solutions (Moreno-Razo et al. Nature. 2012;485:86). We investigated a system in which surfactant solutions are added to liquid crystal droplets with based on their study. The effect of surfactant concentration on the orientation behaviour of the liquid crystal molecules was observed. Phase transition of liquid crystal was also observed with changes to the temperature of the liquid crystal droplets. Various self-assembled structures and changes in liquid crystal droplet properties were discussed. We believe that the results of our work will help in further pursuing the research on photonic crystal devices.

Amphiphilic self-assembly of semiconductor nanocrystals with heterogeneous compositions

Y Taniguchi, T Takishita, Y Kobayashi, N Arai, T Kawai, T Nakashima

EPL (Europhysics Letters) 118 (6), 68001 （EPL） 118 （ 6 ） 2017年

研究論文（学術雑誌）, 共著, 査読有り, ISSN 0295-5075

© Copyright EPLA, 2017. We describe herein that amphiphilic semiconductor nanocrystals (NCs) self-assembled into network structures with heterogeneous compositions. The semiconductor nanorods and tetrapods were subjected to ligand exchange with short-chained water-soluble thiolates, giving an amphiphilic surface pattern with a hydrophilic wall and hydrophobic tips. The amphiphilic NCs self-assembled through hydrophobic effects between tip-surfaces in water. The hydrophobic effect-facilitated self-assembly of NCs was well reproduced by a dissipative particle dynamics simulation. The amphiphilic self-assembly of NCs was demonstrated regardless of NC-shapes and compositions to give semiconductor NC-network structures with heterogeneous compositions. The tandem connection of luminescent core/shell nanorods demonstrated energy transfer between the nanorods in the self-assembly.

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粗視化分子シミュレーションを用いたナノチューブ内における界面活性剤水溶液の自己集合と粘性挙動

小林祐生, 荒井規允

年次大会（一般社団法人日本機械学会） 2017 （ 0 ） J0470102 2017年

研究論文（研究会，シンポジウム資料等）, 共著, 査読有り

In recent years, Janus amphiphilic nanotubes with complex surfaces have been synthesized. However, the self-assembly behavior of surfactant solutions confined in a Janus amphiphilic nanotube has not been investigated so far. We performed molecular simulations to investigate the morphologies and phase diagrams of a surfactant confined in Janus amphiphilic nanotube consisting of both hydrophobic and hydrophilic surfaces. We derived a phase diagram of the representative snapshots of equilibrium morphologies. Morphologies that were not observed in the bulk eventuated in confined systems. Moreover, the self-assembled structures were found to be dependent on the spatial confinement. Furthermore, the self-assembled structures confined in hydroneutral and Janus amphiphilic nanotubes were compared. The results suggested that the self-assembled structures confined in the Janus amphiphilic nanotube resembled that confined in the hydroneutral nanotube owing to a strong confinement effect. Our simulation offers a guide to control the rheological properties of surfactant solutions by the chemical patterns on the surfaces of nanochannels, the effect of confinement, and the self-assembled structure.

散逸粒子動力学法を用いたテレケリックポリマー水溶液のせん断流れ下の振る舞い

荒井規允

年次大会（一般社団法人日本機械学会） 2017 （ 0 ） J0470101 2017年

研究論文（研究会，シンポジウム資料等）, 単著, 査読有り

A telechelic polymer is an amphiphilic polymer which can form micellar structures when dissolved in water. A telechelic polymer solution shows viscoelastic behavior due to the formation of a characteristic network, i.e. loop, bridge, and dangling chain. For industrial purposes, it has been utilized for paint, cosmetics, etc. as a thickening agent. It is thus strongly demanding to predict or control its rheological properties. However, detailed studies in the molecular level have not been clarified out yet. In this study, we adopted a dissipative particle dynamics simulation method to investigate the relation between the characteristic rheological properties and the molecular structure in telechelic polymer solutions.

Size dependence of static polymer droplet behavior from many-body dissipative particle dynamics simulation

N Kadoya, N Arai

Physical Review E 95 (4), 043109 （Physical Review E） 95 （ 4 ） 043109 2017年

研究論文（学術雑誌）, 共著, 査読有り, ISSN 2470-0045

© 2017 American Physical Society. This is an open access article distributed under the terms of the Creative Commons Attribution License, which permits unrestricted use, distribution, and reproduction in any medium, provided the original author and source are credited. We used molecular simulation to study the static behavior of polymer droplets in vacuum and on solid surfaces, namely the size of the droplet and the contact angle, respectively. The effects of the polymer chain length and the total number of particles were calculated by the many-body dissipative particle dynamics method. For the spherical droplet containing the same number of particles, we show that its radius depends on the polymer chain length. The radius of the droplet is also proportional to one-third power of the total number of particles for all given chain lengths. For the hemispherical droplet, the contact angle increases with the number of particles in the droplet, and this effect is relatively strong, especially for longer polymer chains. The effect of wettability of the solid surface was also investigated by using polymerphobic (low-affinity) and polymerphilic (high-affinity) surfaces. As the chain length increases, the contact angle on the low-affinity surface decreases, while that on the hydrophilic surface increases. The simulation reveals that there is a critical affinity for the monomer on the solid surface; above and below which the wettability increases and decreases as the molecular length increases, respectively.

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Self-assembly of surfactant aqueous solution confined in a Janus amphiphilic nanotube

Y Kobayashi, N Arai

Molecular Simulation 43 (13-16), 1153-1159 （Molecular Simulation） 43 （ 13-16 ） 1153 - 1159 2017年

研究論文（学術雑誌）, 共著, 査読有り, ISSN 0892-7022

© 2017 Informa UK Limited, trading as Taylor & Francis Group. In recent years, Janus amphiphilic nanotubes with complex surfaces have been synthesized. However, the self-assembly behaviour of surfactant solutions confined in a Janus amphiphilic nanotube has not been investigated so far. We performed molecular simulations to investigate the morphologies and phase diagrams of a surfactant confined in Janus amphiphilic nanotube consisting of both hydrophobic and hydrophilic surfaces. We derived a phase diagram of the representative snapshots of equilibrium morphologies. Morphologies that were not observed in the bulk eventuated in confined systems. Moreover, the self-assembled structures were found to be dependent on the spatial confinement. Furthermore, the self-assembled structures confined in hydroneutral and Janus amphiphilic nanotubes were compared. The results suggested that the self-assembled structures confined in the Janus amphiphilic nanotube resembled that confined in the hydroneutral nanotube owing to a strong confinement effect. Further developments in controlling the morphologies and self-assemblies will greatly advance their applications of these materials in nanofluidic devices, or for nanopatterning.

Amphiphilic self-assembly of semiconductor nanocrystals with heterogeneous compositions (a)

Y Taniguchi, T Takishita, Y Kobayashi, N Arai, T Kawai, T Nakashima

EPL (Europhysics Letters) 118 (6), 68001 2017年

査読有り

Self-assembly behaviours of primitive and modern lipid membrane solutions: a coarse-grained molecular simulation study

N Arai, Y Yoshimoto, K Yasuoka, T Ebisuzaki

Physical Chemistry Chemical Physics 18 (28), 19426-19432 （Physical Chemistry Chemical Physics） 18 （ 28 ） 19426 - 19432 2016年

研究論文（学術雑誌）, 共著, 査読有り, ISSN 1463-9076

© the Owner Societies 2016. Researchers have studied the origin of life and the process of evolution on early Earth for decades. However, we lack a comprehensive understanding of biogenesis, because there are many stages in the formation and growth of the first cell. We investigate the self-replication processes of coacervate protocells using computer simulations of single-chain lipid and phospholipid aqueous mixtures. Based on a morphological phase diagram, we develop a model of prebiotic self-replication driven by only environmental factors (i.e. temperature and lipid concentrations) without any external force. Moreover, we investigate high concentration structures during the process of self-replication. These structures have an advantage in fusion and repair of cell membranes. Therefore, lipid hot spots may have existed in primordial soup.

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Correction: Self-assembly of Janus nanoparticles with a hydrophobic hemisphere in nanotubes

Y Kobayashi, N Arai

Soft matter 12 (6), 1924-1924 （Royal Society of Chemistry ({RSC})） 12 （ 6 ） 1924 - 1924 2016年

研究論文（学術雑誌）, 共著, 査読有り, ISSN 1744-683X

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Self-assembly of Janus oligomers into onion-like vesicles with layer-by-layer water discharging capability: A minimalist model

N Arai, K Yasuoka, XC Zeng

ACS nano 10 (8), 8026-8037 （ACS Nano） 10 （ 8 ） 8026 - 8037 2016年

研究論文（学術雑誌）, 共著, 査読有り, ISSN 1936-0851

© 2016 American Chemical Society. A vesicle in a cell is an enclosed structure in which the interior fluid is encompassed by a lipid bilayer. Synthetic vesicles are known as the liposomes. Liposomes with a single phospholipid bilayer are called unilamellar liposomes; otherwise, they are called multilamellar liposomes or onion-like liposomes (vesicles). One prototype synthetic onion-like vesicle, namely, onion-like dendrimersomes, have been recently produced via the self-assembly of amphiphilic Janus dendrimers (Proc. Natl. Acad. Sci. U.S.A. 2016, 113, 1162). Herein, we show computer simulation evidence of another type of onion-like vesicle, namely, onion-like oligomersomes, via the self-assembly of amphiphilic Janus oligomers in water. Specifically, we investigate the minimum-sized oligomers (or minimalist model) that can give rise to the onion-like oligomersomes as well as the composition-dependent phase diagrams. Insights into the formation condition and formation process of the onion-like oligomersomes are obtained. We demonstrate that the discharge of the in-vesicle water is through the remarkable "peeling-one-onion-layer-at-a-time" fashion, a feature that can be utilized for a clinical dosing regimen. The ability to control the formation of onion-like oligomersomes by design can be exploited for applications in drug and gene delivery.

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