論文 - 荒井　規允

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

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© 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

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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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Nanochannel with uniform and Janus surfaces: Shear thinning and thickening in surfactant solution

N Arai, K Yasuoka, XC Zeng

Langmuir 28 (5), 2866-2872 （Langmuir）  28 （ 5 ） 2866 - 2872 2012年

研究論文（学術雑誌）, 共著, 査読有り,  ISSN  0743-7463

　概要を見る

On basis of molecular simulation of confined surfactant solutions, we show that by adding chemical patterns on the inner surface of nanochannels dynamical properties of the confined surfactant solutions could be modified from shear thinning to shear thickening. To this end, we select uniformly hydrophobic and hydrophilic surfaces as well as a stripe-patterned Janus surface as three prototype confining surfaces of nanochannels. In all three nanochannels, when the surfactant solution is under relatively low shear rates, it shears thin. Under moderate shear rates, a sharp decrease in the shear viscosity could occur due to surfactant morphology transition. Under relatively high shear rates, a shear-thinning-to-thickening transition can emerge due to the tendency of stratification normal to the confining surface. Our simulation study offers a guide to steering dynamic properties of surfactant fluids in nanofluidic devices through engineering surfaces of nanochannels by design. © 2012 American Chemical Society.

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Atomistic study of the morphology of graphene on Si and SiC substrates

S Seto, N Arai, K Shintani

MRS Online Proceedings Library Archive 1407 （Materials Research Society Symposium Proceedings）  1407   91 - 96 2012年

研究論文（国際会議プロシーディングス）, 共著, 査読有り

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The morphology of graphene on Si and SiC substrates is investigated using molecular-dynamics simulation. The effects of the size and orientation of graphene on its roughness, distance from the substrate, and periodic structure are examined. The roughness and distance show the size dependency which agrees with the size dependency of the ratio of the periphery length of graphene to its area. It is found there are some cases in which the roughness of graphene can be suppressed. © 2012 Materials Research Society.

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3PT155 フリップフロップのダイナミクスの直接的観察 (日本生物物理学会第 50 回年会 (2012 年度))

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

生物物理 52, S167 （一般社団法人 日本生物物理学会）  52 （ 0 ） S167 2012年

研究論文（研究会，シンポジウム資料等）, 共著, 査読有り,  ISSN  0582-4052

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Molecular dynamics of carbon nanobearings

Sato K., Arai N., Shintani K.

Materials Research Society Symposium Proceedings （Materials Research Society Symposium Proceedings）  1204   103 - 108 2010年08月

研究論文（国際会議プロシーディングス）, 査読有り

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A concept of nanoscale bearing structures utilizing nanocarbon materials is presented based on the prediction via molecular dynamics simulations. The proposed mechanism consists of a graphene layer, intercalated single walled carbon nanotubes (SWNTs), and substrate graphenes. It is found that the friction against the movement of the uppermost graphene is smallest for the 1 SWNT model. © 2010 Materials Research Society.

Asymmetric Brownian motor driven by bubble formation in a hydrophobic channel

N Arai, K Yasuoka, T Koishi, T Ebisuzaki

ACS nano 4 (10), 5905-5913 （ACS Nano）  4 （ 10 ） 5905 - 5913 2010年

研究論文（学術雑誌）, 共著, 査読有り,  ISSN  1936-0851

　概要を見る

The "asymmetric Brownian ratchet model" is a variation of Feynman's ratchet and pawl system proposed. In this model, a system consisting of a motor and a rail has two binding states. One is the random Brownian state, and the other is the asymmetric potential state. When the system is alternatively switched between these states, the motor can be driven in one direction. This model is believed to explain nanomotor behavior in biological systems. The feasibility of the model has been demonstrated using electrical and magnetic forces; however, switching of these forces is unlikely to be found in biological systems. In this paper, we propose an original mechanism of transition between states by bubble formation in a nanosized channel surrounded by hydrophobic atoms. This amounts to a nanoscale motor system using bubble propulsion. The motor system consists of a hydrophobic motor and a rail on which hydrophobic patterns are printed. Potential asymmetry can be produced by using a left-right asymmetric pattern shape. Hydrophobic interactions are believed to play an important role in the binding of biomolecules and molecular recognition. The bubble formation is controlled by changing the width of the channel by an atomic distance (∼0.1 nm). Therefore, the motor is potentially more efficient than systems controlled by other forces, in which a much larger change in the motor position is necessary. We have simulated the bubble-powered motor using dissipative particle dynamics and found behavior in good agreement with that of motor proteins. Energy efficiency is as high as 60%. © 2010 American Chemical Society.

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Molecular simulation at solid-liquid interface

K Yasuoka, T Koishi, T Mlma, N Arai

Toraibarojisuto/Journal of Japanese Society of Tribologists 55 (4), 236-241 （Toraibarojisuto/Journal of Japanese Society of Tribologists）  55 （ 4 ） 236 - 241 2010年

研究論文（学術雑誌）, 共著, 査読有り,  ISSN  0915-1168

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Molecular dynamics of carbon nanobearings

K Sato, N Arai, K Shintani

2009 MRS Fall Meeting, 103-108 2010年

研究論文（国際会議プロシーディングス）, 査読有り

固液界面の物理 固液界面現象の分子シミュレーション

K YASUOKA, T KOISHI, T MIMA, N ARAI

トライボロジスト 55 (4), 236-241 2010年

研究論文（研究会，シンポジウム資料等）, 査読有り