論文 - 荒井　規允

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

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<p>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.</p>

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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

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<p>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.</p>

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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

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© 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

　概要を見る

© 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.

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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

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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

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© 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

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© 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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Self-assembly of Janus nanoparticles with a hydrophobic hemisphere in nanotubes (vol 12, pg 378, 2016)

Yusei Kobayashi, Noriyoshi Arai

SOFT MATTER （ROYAL SOC CHEMISTRY）  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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Molecular dynamics simulation of the melting processes of core-shell and pure nanoparticles

Tamura Y., Arai N.

Molecular Simulation （Molecular Simulation）  41 （ 10-12 ） 905 - 912 2015年08月

研究論文（学術雑誌）, 査読有り,  ISSN  08927022

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© 2014 Taylor and Francis. Core-shell nanoparticles are nanosized particles that consist of a core and a shell, constructed from different metallic elements. Core-shell nanoparticles have received extensive attention, owing to their various potential applications such as paints, optical films and catalysts. Herein, we investigate the melting behaviours of different core-shell nanoparticles under continuous heating using molecular dynamics simulation. Different metallic elements were examined as core-shell and pure nanoparticles. Five different processes were observed during the melting of core-shell nanoparticles. In contrast, only one process was identified during the melting of pure nanoparticles. These processes were influenced by the nanoparticle size, shell thickness and differences between the lattice constants and melting point temperatures of the metallic elements. Our simulation provides microscopic insights into the melting behaviours of existing and proposed core-shell nanoparticles that would be highly beneficial towards the fabrication of materials with different chemical coatings.

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

Y Kobayashi, N Arai

Soft Matter 12 (2), 378-385 （Soft Matter）  12 （ 2 ） 378 - 385 2015年

研究論文（学術雑誌）, 共著, 査読有り,  ISSN  1744683X

　概要を見る

© 2016 The Royal Society of Chemistry. We performed molecular simulations to investigate the morphologies and phase diagrams of self-assembled diblock Janus nanoparticles (JNPs) confined in nanotubes. A JNP is a unique anisotropic nanoparticle, which typically has more than two distinct surfaces, each with different properties. We derived qualitative phase diagrams of axial pressure versus the ratio of the diameter of the nanoparticle and the nanotube. Three distinct types of nanotube walls were considered: hydrophobic, hydrophilic, and hydroneutral. We observed diverse morphologies in JNP solutions, many of which have not been observed in bulk solutions. We also compared the self-assembled structures of diblock and triblock patchy particles. Under weak confinement, significant differences were observed between the different JNP designs. The orientation ordering and self-assembly behaviours of the JNPs can be qualitatively predicted based on the chemical nature of the nanotube wall and the JNP design.

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Molecular dynamics simulation of the melting processes of core–shell and pure nanoparticles

Y Tamura, N Arai

Molecular Simulation 41 (10-12), 905-912 2015年

研究論文（学術雑誌）, 査読有り

分子シミュレーションによるソフトマター領域のスマートプロセス技術開発を目指して

荒井 規允

スマートプロセス学会誌 （一般社団法人 スマートプロセス学会 （旧高温学会））  4 （ 1 ） 40 - 45 2015年

研究論文（研究会，シンポジウム資料等）, 単著, 査読有り,  ISSN  2186-702X

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Structural analysis of telechelic polymer solution using dissipative particle dynamics simulations

N Arai

Molecular Simulation 41 (10-12), 996-1001 （Molecular Simulation）  41 （ 10-12 ） 996 - 1001 2015年

研究論文（学術雑誌）, 単著, 査読有り,  ISSN  08927022

　概要を見る

© 2014 Taylor and Francis. A telechelic polymer is an amphiphilic polymer that can form micellar structures when dissolved in water. A telechelic polymer solution shows viscoelastic behaviour owing to the formation of characteristic networks, i.e. loops, bridges and dangling chains. For industrial purposes, telechelic polymers have many applications as thickening agents, such as in paints and cosmetics. Thus, it is desirable to predict and control the rheological properties of telechelic polymers. However, detailed studies at the molecular level have not yet been performed. In this study, I use the dissipative particle dynamics (DPD) method to investigate the relationship between the characteristic structural properties and the molecular structure in telechelic polymer solutions. I show that the morphology of telechelic polymer solutions depends on the concentration and chain length, the distribution of the end-to-end distance, the mean square end-to-end distance, the mean square radius of gyration and the time-averaged mean square displacement. Although an effect of entanglement is important for properties of polymer melts, the polymer chain composed of DPD particles cannot reproduce it. Therefore, I compare telechelic polymer solutions with and without the segmental repulsive potential (SRP), which can simulate the effect of entanglement in DPD simulations. The results indicate that it is necessary to include the SRP in DPD simulations to correctly analyse the behaviour of telechelic polymer solutions.

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Poisson property of the occurrence of flip-flops in a model membrane

N Arai, T Akimoto, E Yamamoto, M Yasui, K Yasuoka

The Journal of chemical physics 140 (6), 02B609_1 （Journal of Chemical Physics）  140 （ 6 ） 064901 2014年

研究論文（学術雑誌）, 共著, 査読有り,  ISSN  0021-9606

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How do lipid molecules in membranes perform a flip-flop? The flip-flops of lipid molecules play a crucial role in the formation and flexibility of membranes. However, little has been determined about the behavior of flip-flops, either experimentally, or in molecular dynamics simulations. Here, we provide numerical results of the flip-flops of model lipid molecules in a model membrane and investigate the statistical properties, using millisecond-order coarse-grained molecular simulations (dissipative particle dynamics). We find that there are three different ways of flip-flops, which can be clearly characterized by their paths on the free energy surface. Furthermore, we found that the probability of the number of the flip-flops is well fitted by the Poisson distribution, and the probability density function for the inter-occurrence times of flip-flops coincides with that of the forward recurrence times. These results indicate that the occurrence of flip-flops is a Poisson process, which will play an important role in the flexibilities of membranes. © 2014 AIP Publishing LLC.

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Self-assembly of triblock Janus nanoparticle in nanotube

N Arai, K Yausoka, XC Zeng

Journal of chemical theory and computation 9 (1), 179-187 （Journal of Chemical Theory and Computation）  9 （ 1 ） 179 - 187 2013年

研究論文（学術雑誌）, 共著, 査読有り,  ISSN  1549-9618

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We have performed molecular simulations to investigate morphologies and the phase diagram of the self-assembled triblock Janus nanoparticle confined to nanotubes. The triblock Janus nanoparticle is decorated with two hydrophobic caps at the north and south poles with a tunable area, separated by an electrically charged middle band. On the basis of the observed pressure- and tube-radius-dependent morphologies, we derive semiquantitative phase diagrams of the axial pressure versus the ratio of the radius of the nanoparticle to the radius of the nanotube. Three distinct walls of the nanotube, namely, hydrophobic, hydrophilic, and hydroneutral, are considered. We find that the three phase diagrams corresponding to three chemically different walls of the nanotube show some universal features. These features can be illustrated through a schematic assembly map and a roadmap on the variation of coordination number of the nanoparticles. In particular, we find that highly ordered morphologies tend to form when the coordination number of Janus particles is a multiple of 2. The orientation ordering and self-assembly behavior of the Janus nanoparticles can be qualitatively predicted when the chemical nature of the nanotube wall is known. © 2012 American Chemical Society.

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Understanding molecular motor walking along a microtubule: A themosensitive asymmetric brownian motor driven by bubble formation

N Arai, K Yasuoka, T Koishi, T Ebisuzaki, XC Zeng

Journal of the American Chemical Society 135 (23), 8616-8624 （Journal of the American Chemical Society）  135 （ 23 ） 8616 - 8624 2013年

研究論文（学術雑誌）, 単著, 査読有り,  ISSN  0002-7863

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The "asymmetric Brownian ratchet model", a variation of Feynman's ratchet and pawl system, is invoked to understand the kinesin walking behavior along a microtubule. The model system, consisting of a motor and a rail, can exhibit two distinct binding states, namely, the random Brownian state and the asymmetric potential state. When the system is transformed back and forth between the two states, the motor can be driven to "walk" in one direction. Previously, we suggested a fundamental mechanism, that is, bubble formation in a nanosized channel surrounded by hydrophobic atoms, to explain the transition between the two states. In this study, we propose a more realistic and viable switching method in our computer simulation of molecular motor walking. Specifically, we propose a thermosensitive polymer model with which the transition between the two states can be controlled by temperature pulses. Based on this new motor system, the stepping size and stepping time of the motor can be recorded. Remarkably, the "walking" behavior observed in the newly proposed model resembles that of the realistic motor protein. The bubble formation based motor not only can be highly efficient but also offers new insights into the physical mechanism of realistic biomolecule motors. © 2013 American Chemical Society.

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Phase diagrams of confined solutions of dimyristoylphosphatidylcholine (DMPC) lipid and cholesterol in nanotubes

N Arai, K Yasuoka, XC Zeng

Microfluidics and nanofluidics 14 (6), 995-1010 （Microfluidics and Nanofluidics）  14 （ 6 ） 995 - 1010 2013年

研究論文（学術雑誌）, 共著, 査読有り,  ISSN  1613-4982

　概要を見る

We have studied equilibrium morphologies of dimyristoylphosphatidylcholine lipid solution and cholesterol solution confined to nanotubes using dissipative particle dynamics (DPD) simulations. Phase diagrams regarding monomer concentration c versus radius of nanotube r for both solutions are attained. Three types of the inner surface of nanotubes, namely hydrophobic, hydrophilic, and hydroneutral are considered in the DPD simulations. A number of phases and molecular assemblies for the confined solutions are revealed, among others, such as the spiral wetting and bilayer helix. Several phases and assemblies have not been reported in the literature, and some are non-existence in bulk solutions. The ability to control the morphologies and self-assemblies within nanoscale confinement can be exploited for patterning interior surface of nanochannels for application in nanofluidics and nanomedical devices. © 2012 Springer-Verlag Berlin Heidelberg.

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A vesicle cell under collision with a Janus or homogeneous nanoparticle: translocation dynamics and late-stage morphology

N Arai, K Yasuoka, XC Zeng

Nanoscale 5 (19), 9089-9100 （Nanoscale）  5 （ 19 ） 9089 - 9100 2013年

研究論文（学術雑誌）, 共著, 査読有り,  ISSN  2040-3364

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We investigate translocation dynamics of a vesicle cell under collision with a Janus or a homogeneous hydrophobic/hydrophilic nanoparticle. To this end, we perform dissipative particle dynamics simulation by setting the nanoparticle with different initial velocities, different chemical patterns of the surface for the nanoparticle, and different orientations (for the Janus nanoparticle). Particular attention is given to translocation dynamics, in-cell water discharge, and the late-stage morphologies of the vesicle/nanoparticle system after the collision. We observe three late-stage states for the Janus nanoparticle, and four late-stage states for the homogeneous nanoparticles. We find that the late-stage state and the associated dynamical pathway not only depend on the relative velocity but also on the chemical pattern of the nanoparticle surface, as well as on the orientation of the incident Janus nanoparticle. We have examined the time-dependent mean radius of the vesicle, the number of in-cell water beads lost from the vesicle, as well as the collision-induced pore size on the lipid membrane during the course of collision. Our simulation provides microscopic insights into the resilience of the vesicle-cell membrane and dynamical behavior of the vesicle under the attack of a foreign nanoparticle. Knowledge and insights gained through the simulation will have implication to the drug delivery with different chemical coatings. © The Royal Society of Chemistry 2013.

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散逸粒子動力学法によるテレケリックポリマー水溶液の解析

荒井 規允, 畝山 多加志

理論応用力学講演会 講演論文集 （日本学術会議 「機械工学委員会・土木工学・建築学委員会合同IUTAM分科会」）  61 （ 0 ） 11 - 11 2012年

研究論文（研究会，シンポジウム資料等）, 共著, 査読有り

　概要を見る

テレケリックポリマーとは，親水性高分子の両末端を疎水化した会合性のポリマーである．テレケリックポリマーは水溶液中において，特異なネットワーク構造（loop, bridging chain, dangling chain）を形成し，顕著な粘弾性を示す．その性質から我々の身の回りでは，増粘剤として塗装や化粧品等に用いられており，工業的に大きな需要がある．しかし詳細な研究は未だ十分に進んでおらず，例えば末端の1個の分子が異なるだけで，物性や機能が大きく異なるが，それと分子レベルでの構造の関係は明らかになっていない．またテレケリックポリマー溶液にせん断を与え粘度を測定した場合，せん断の速さによって粘度が増加するshear thickeningという非線形な現象が観察される．これを説明するために，これまで様々な理論が提案されたが，現在主流のモデルはどれも理論的・実験的に十分な裏付けがあるわけではなく，その分子論的な由来は不明である．本研究の目的は，散逸粒子動力学シミュレーションを用い，テレケリックポリマーの特異な性質と分子レベルの構造の関係を明らかにすることである．

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