論文 - 荒井　規允

Molecular modelling of active oil droplet propulsion: Insights from dissipative particle dynamics simulation

Sasaki, K; Ishiwatari, Y; Ueno, K; Kojima, T; Banno, T; Arai, N

CHEMICAL PHYSICS LETTERS 857 2024年12月

研究論文（学術雑誌）, 最終著者, 査読有り,  ISSN  0009-2614

　概要を見る

This study employed dissipative particle dynamics (DPD) simulations to investigate the self-propelled motion of oil droplets in water–oil–surfactant systems. It is the first attempt to replicate self-propulsion models of oil droplets at the molecular level, contrasting previous simulations focused on Brownian motion and hydrodynamic behaviour of colloidal particles. The DPD model reproduced droplet propulsion and visualised internal Marangoni flow, showing that larger droplet radii and greater interfacial tension differences increase propulsion speeds. Additionally, surfactants with stronger oil–oil repulsion enhanced propulsion speed, suggesting that surfactant-induced local structures are crucial for the self-propulsion mechanism.

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Corrigendum to “Poly(vinyl alcohol)-modified poly(methyl methacrylate) particles for solid-stabilized oil-in-water emulsions” [Colloids Surf. A: Physicochem. Eng. Asp. 697 (2024) 134433]

Takashi Yamazaki, Kojiro Suzuki, Yusei Kobayashi, Noriyoshi Arai, Toshikazu Tsuji

Colloids and Surfaces A: Physicochemical and Engineering Aspects （Elsevier BV）     135683 - 135683 2024年11月

研究論文（学術雑誌）, 査読有り,  ISSN  0927-7757

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Poly(vinyl alcohol)-modified poly(methyl methacrylate) particles for solid-stabilized oil-in-water emulsions

Yamazaki, T; Suzuki, K; Kobayashi, Y; Arai, N; Tsuji, T

COLLOIDS AND SURFACES A-PHYSICOCHEMICAL AND ENGINEERING ASPECTS （Elsevier BV）  697   134433 - 134433 2024年09月

研究論文（学術雑誌）, 査読有り,  ISSN  0927-7757

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In this study, submicron poly(methyl methacrylate) (PMMA) particles with surfaces modified using poly(vinyl alcohol) (PVA) (PMMA-PVA) were produced to formulate solid-stabilized oil-in-water (O/W) emulsions including high internal phase emulsions with a dispersed phase of over 74 %. The high-internal phase emulsions stabilized by PMMA–PVA exhibited gel-like behavior, and the oil droplets exhibited faceted shapes. PVA with a degree of saponification of 80 and 88 mol% was used as the surface modifier rather than PVA with > 96 mol%, assisting in the formation of a robust adsorbed layer on the PMMA particles. Coarse-grained molecular simulations revealed that the partially-hydrolyzed PVA exhibited a better adsorption behavior compared to the fully-hydrolyzed PVA, being thermodynamically adsorbed onto the PMMA surface in water owing to stable adsorption via its hydrophobic acetyl groups. Furthermore, PMMA–PVA reduced the interfacial tension as the degree of saponification of PVA decreased. Simulation and experimental results suggested that the acetyl groups of PVA not only adsorbed onto the PMMA surface but also promoted adsorption between PMMA and the oil–water interface. Overall, the findings of this study underscore the potency of PMMA–PVA as a particulate stabilizer for formulating O/W high internal phase emulsions.

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Coarse-grained molecular simulation of the effect of liquid crystal molecular pitch on structure in cylindrical confinement

Sato, T; Tsujinoue, H; Arai, N; Takahashi, KZ

PHYSICAL REVIEW E 110 （ 1 ） 014701 2024年07月

研究論文（学術雑誌）, 査読有り,  ISSN  2470-0045

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Blue phases (BPs) consist of three-dimensional self-assembled structures formed by a double-twisted columnar arrangement of liquid crystal molecules. Although their unique optical and structural properties render BPs particularly useful for applications such as liquid crystal displays, BPs typically appear in a narrow temperature range between the isotropic and nematic phases. This thermodynamic instability impedes their practical applicability. However, the simulations we present here showed that, in a quasi-one-dimensional system confined to nanospace, a phase equivalent to the BP appears and persists between the nematic and smectic phases. Confinement to a nanotube (NT) with a relatively small radius enables the BP to be maintained over a wide temperature range, whereas for an NT with a relatively larger radius, the BP appears only in a very narrow temperature range between the aforementioned phases. We additionally showed that the pitch of the BP is dependent on and can be controlled by adjusting the radius of the NTs. This finding has significant implications for the potential application of these materials in fields such as photonics and chiral separation technologies.

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Design strategy for blends of biodegradable polyester and thermoplastic starch based on a molecular dynamics study of the phase-separated interface

Yamaguchi, A; Arai, S; Arai, N

CARBOHYDRATE POLYMERS （Carbohydrate Polymers）  333   122005 2024年06月

研究論文（学術雑誌）, 最終著者, 査読有り,  ISSN  0144-8617

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Molecular insight into the phase-separated interface formed when biodegradable polyesters and thermoplastic starch (TPS) are melt-blended is valuable for the design of composites. In this study, eight different interfaces combining four major biodegradable polyesters (PLA, PBS, PHB and PBAT) and two TPSs [unmodified TPS (nTPS) and citrate-modified TPS (cTPS)] were investigated by using molecular dynamics (MD) simulations. According to the MD simulation results, PBS, PHB and PBAT diffuse readily into the TPS and form compatible interfaces, whereas PLA is less compatible with the TPS. The results of tensile simulations show that PBS and PBAT adhere well to TPS; in particular, PBS/cTPS and PBAT/cTPS exhibit high interfacial-fracture energy (G). Both PLA and PHB blended with TPS exhibit low G because PLA is less compatible with TPS and PHB and TPS have low electrostatic interaction. The reason for the high G of PBS/cTPS and PBAT/cTPS is thought to be a combination of three factors: (i) formation of a deep compatible interface, (ii) suppression of void growth by electrostatic interactions and (iii) absorption of strain energy by a change in the conformation of the molecular chains. These three interfacial adhesion mechanisms should be considered when designing biodegradable polyester/TPS blends with good mechanical properties.

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In-layer inhomogeneity of molecular dynamics in quasi-liquid layers of ice.

Yasuda I, Endo K, Arai N, Yasuoka K

Communications chemistry 7 （ 1 ） 117 2024年05月

研究論文（学術雑誌）, 査読有り,  ISSN  2399-3669

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Quasi-liquid layers (QLLs) are present on the surface of ice and play a significant role in its distinctive chemical and physical properties. These layers exhibit considerable heterogeneity across different scales ranging from nanometers to millimeters. Although the formation of partially ice-like structures has been proposed, the molecular-level understanding of this heterogeneity remains unclear. Here, we examined the heterogeneity of molecular dynamics on QLLs based on molecular dynamics simulations and machine learning analysis of the simulation data. We demonstrated that the molecular dynamics of QLLs do not comprise a mixture of solid- and liquid water molecules. Rather, molecules having similar behaviors form dynamical domains that are associated with the dynamical heterogeneity of supercooled water. Nonetheless, molecules in the domains frequently switch their dynamical state. Furthermore, while there is no observable characteristic domain size, the long-range ordering strongly depends on the temperature and crystal face. Instead of a mixture of static solid- and liquid-like regions, our results indicate the presence of heterogeneous molecular dynamics in QLLs, which offers molecular-level insights into the surface properties of ice.

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Cholesteric liquid crystal phase variations within nanotubes: an in-depth analysis of the influences of twist radius and molecular pitch

Yamada, K; Arai, N

LIQUID CRYSTALS （Liquid Crystals）  51 （ 7 ） 1204 - 1214 2024年05月

研究論文（学術雑誌）, 最終著者, 責任著者, 査読有り,  ISSN  0267-8292

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This study investigates the self-assembly and phase transitions of cholesteric liquid crystals (CLCs) when confined in nanotubes, specifically focusing on the variations in their molecular structures. A dissipative particle dynamics method was used to investigate how the changes in helix radius ((Formula presented.)) and pitch ((Formula presented.)) affect the behaviour of the LCs. For pitches of 24, 12, and 6, the orientation order parameter ((Formula presented.)) showed distinct trends during cooling. Smaller helix radii resulted in isotropic to nematic to smectic phase transitions, whereas larger radii resulted in a novel smectic phase with spiral structures (Sm (Formula presented.)). Circumferential local-order parameters ((Formula presented.) and (Formula presented.)) were introduced to better characterise the phases, and a disordered spiral-structure phase (Sm (Formula presented.)) with local perturbations was observed. The transitions between isotropic, nematic, and smectic phases, highlighting the influence of the pitch and helix radius, were observed from the phase diagrams. Smaller pitches and radii prevented the formation of stable structures; however, specific combinations induced characteristic spiral structures in the smectic phase. These results provide new insights into the self-assembly of confined CLCs, which have potential applications in the design of photonic devices and LC-based sensors. This study advances our understanding of phase control in quasi-one-dimensional systems and highlights the importance of molecular variations in liquid crystal behaviour.

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Supramolecular copolymerization of hydrophobic and hydrophilic monomers in liquid crystalline media

Morishita, D; Itoh, Y; Furukawa, K; Arai, N; Zhang, XJ; Aida, T

CHEMICAL SCIENCE （Chemical Science）  15 （ 11 ） 4068 - 4074 2024年

研究論文（学術雑誌）, 査読有り,  ISSN  2041-6520

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In the case of covalent polymers, immiscible polymers can be integrated by covalently linking them together, but such a strategy is not possible in supramolecular polymers. Here we report the supramolecular copolymerization of two porphyrin-based monomers, C10P2H and TEGPCu with side chains bearing cyanobiphenyl (CB) groups at the ends of hydrophobic alkyl or hydrophilic tetraethylene glycol chains, respectively. These monomers undergo self-sorting supramolecular polymerization in highly diluted solutions ([monomer] = 3.4 × 10−9 mol% (2.0 × 10−8 mol L−1)) in nonpolar media due to the incompatibility of the side chains. Surprisingly, these monomers undergo supramolecular copolymerization under high concentration conditions ([monomer] = 7.7 mol%) in the medium of 4-cyano-4′-pentyloxybiphenyl (5OCB) to form a columnar liquid crystalline phase under thermodynamic conditions, where the individual columns are composed of supramolecular block copolymers. The combination of CB ends of both monomers and the 5OCB medium is essential for the two monomers to form an integrated structure in a condensed system without phase separation.

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Machine learning prediction of self-assembly and analysis of molecular structure dependence on the critical packing parameter

Ishiwatari, Y; Yokoyama, T; Kojima, T; Banno, T; Arai, N

MOLECULAR SYSTEMS DESIGN & ENGINEERING （Molecular Systems Design and Engineering）  9 （ 1 ） 20 - 28 2024年

研究論文（学術雑誌）, 査読有り,  ISSN  2058-9689

　概要を見る

Amphiphilic molecules spontaneously form self-assembly structures depending on physical conditions such as the molecular structure, concentration, and temperature. These structures exhibit various functionalities according to their morphology. The critical packing parameter (CPP) is used to correlate self-organized structures with the chemical composition. However, accurately calculating it requires information about both the molecular shape and molecular aggregates, making it challenging to apply directly in molecular design. We aimed to predict the self-assembled structure of a molecule directly from its chemical structure and to analyze the factors influencing it using machine learning. Dissipative particle dynamics simulations were used to reproduce many self-assembly structures comprising various chemical structures, and their CPPs were calculated. Machine learning models were built using the chemical structures as input data and the CPPs as output data. As a result, both random forest and the gated recurrent unit showed high prediction accuracy. Feature importance analysis and sample size dependence revealed that the amphiphilic nature of molecules significantly influences the self-assembly structures. Additionally, selecting an appropriate molecular structure representation for each algorithm is crucial. The study results should contribute to product development in the fields of materials science, materials chemistry, and medical materials.

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Mechanisms underlying the stability and instability of concentrated oil-in-water emulsions: Effect of the chemical structure of amphiphilic polymers

Suzuki, K; Kobayashi, Y; Yamazaki, T; Tsuji, T; Arai, N

JOURNAL OF MOLECULAR LIQUIDS （Journal of Molecular Liquids）  394   123749 - 123749 2023年12月

研究論文（学術雑誌）, 査読有り,  ISSN  0167-7322

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Despite extensive experimentation to efficiently prepare concentrated oil-in-water (O/W) emulsions with sufficient stability, the effect of the chemical structure of the polymeric surfactants on the emulsion stability is not yet understood in detail at the molecular level. We investigated the effect of the degree of saponification and arrangement of the hydrophobic (acetyl) groups of poly(vinyl alcohol) (PVA) on the stability of the concentrated emulsion via a combination of experiments and coarse-grained molecular simulations. This was accomplished by varying the degree of saponification and the arrangement of the hydrophobic groups on PVA, and by systematically changing the volume fraction of PVA molecules. The stability of the emulsion was adversely affected by the presence of an excess or the complete absence of hydrophobic groups on PVA. The former situation promotes the aggregation of PVA molecules with each other; conversely, fully saponified PVA molecules penetrate the water phase, thereby decreasing the number of PVA molecules at the O/W interface. Thus, the depletion of the interface of PVA molecules increases the interfacial tension, and, consequently, destabilizes the interface. Adjustment of the degree of saponification to a suitable value (80%) led to the formation of stable, concentrated emulsions with a smaller amount of PVA. For PVA with an appropriate degree of saponification, the interfacial behavior of concentrated O/W emulsions was to a lesser extent affected by the arrangement of the hydrophobic groups of PVA compared to the degree of saponification. Furthermore, the individual PVA chains at the interface had planar conformations, regardless of the arrangement of the hydrophobic groups. Our results indicate that careful tuning of the degree of saponification, rather than the arrangement of the hydrophobic groups of PVA, is necessary to control the interfacial stability of concentrated O/W emulsions using PVA. The findings of this study provide support for departing from empirical trial-and-error approaches and may facilitate the development of emulsifiers with enhanced performance.

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Predicting the Performance of Functional Materials Composed of Polymeric Multicomponent Systems Using Artificial Intelligence—Formulations of Cleansing Foams as an Example

Masugu Hamaguchi, Hideki Miwake, Ryoichi Nakatake, Noriyoshi Arai

Polymers 2023年10月

研究論文（学術雑誌）, 査読有り

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The Relationship between Nanostructured Bio-Inspired Material Surfaces and the Free Energy Barrier Using Coarse-Grained Molecular Dynamics

Meng, F; Arai, N

BIOMIMETICS （Biomimetics）  8 （ 6 ）  2023年09月

研究論文（学術雑誌）, 査読有り

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Bio-inspired (biomimetic) materials, which are inspired by living organisms, offer exciting opportunities for the development of advanced functionalities. Among them, bio-inspired superhydrophobic surfaces have attracted considerable interest due to their potential applications in self-cleaning surfaces and reducing fluid resistance. Although the mechanism of superhydrophobicity is understood to be the free energy barrier between the Cassie and Wenzel states, the solid-surface technology to control the free energy barrier is still unclear. Therefore, previous studies have fabricated solid surfaces with desired properties through trial and error by measuring contact angles. In contrast, our study directly evaluates the free energy barrier using molecular simulations and attempts to relate it to solid-surface parameters. Through a series of simulations, we explore the behavior of water droplets on surfaces with varying values of surface pillar spacing and surface pillar height. The results show that the free energy barrier increases significantly as the pillar spacing decreases and/or as the pillar height increases. Our study goes beyond traditional approaches by exploring the relationship between free energy barriers, surface parameters, and hydrophobicity, providing a more direct and quantified method to evaluate surface hydrophobicity. This knowledge contributes significantly to material design by providing valuable insights into the relationship between surface parameters, free energy barriers, and hydrophilicity/hydrophobicity.

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Molecular insight into toughening induced by core-shell structure formation in starch-blended bioplastic composites

Yamaguchi Akihiro, Arai Satoshi, Arai Noriyoshi

CARBOHYDRATE POLYMERS （Carbohydrate Polymers）  315   120974 2023年09月

研究論文（学術雑誌）, 査読有り,  ISSN  0144-8617

　概要を見る

Binary and ternary blends with poly(lactic acid) (PLA), poly(butylene succinate) (PBS), and thermoplastic starch (TPS) were prepared by a melt process to produce biodegradable biomass plastics with both economical and good mechanical properties. The mechanical and structural properties of each blend were evaluated. Molecular dynamics (MD) simulations were also conducted to examine the mechanisms underlying the mechanical and structural properties. PLA/PBS/TPS blends showed improved mechanical properties compared with PLA/TPS blends. The PLA/PBS/TPS blends with a TPS ratio of 25–40 wt% showed higher impact strength than PLA/PBS blends. Morphology observations showed that in the PLA/PBS/TPS blends, a structure similar to that of core-shell particles with TPS as the embedding phase and PBS as the coating phase was formed, and that the trends in morphology and impact strength changes were consistent. The MD simulations suggested that PBS and TPS tightly adhered to each other in a stable structure at a specific intermolecular distance. From these results, it is clear that PLA/PBS/TPS blends are toughened by the formation of a core-shell structure in which the TPS core and the PBS shell adhered well together and stress concentration and energy absorption occurred in the vicinity of the core-shell structure.

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Aggregation of amphiphilic nanocubes in equilibrium and under shear

Yokoyama Takahiro, Kobayashi Yusei, Arai Noriyoshi, Nikoubashman Arash

SOFT MATTER （Soft Matter）  19 （ 34 ） 6480 - 6489 2023年08月

研究論文（学術雑誌）, 査読有り,  ISSN  1744-683X

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We investigate the self-assembly of amphiphilic nanocubes into finite-sized aggregates in equilibrium and under shear, using molecular dynamics (MD) simulations and kinetic Monte Carlo (KMC) calculations. These patchy nanoparticles combine both interaction and shape anisotropy, making them valuable models for studying folded proteins and DNA-functionalized nanoparticles. The nanocubes can self-assemble into various finite-sized aggregates ranging from rods to self-avoiding random walks, depending on the number and placement of the hydrophobic faces. Our study focuses on suspensions containing multi- and one-patch cubes, with their ratio systematically varied. When the binding energy is comparable to the thermal energy, the aggregates consist of only few cubes that spontaneously associate/dissociate. However, highly stable aggregates emerge when the binding energy exceeds the thermal energy. Generally, the mean aggregation number of the self-assembled clusters increases with the number of hydrophobic faces and decreases with increasing fraction of one-patch cubes. In sheared suspensions, the more frequent collisions between nanocube clusters lead to faster aggregation dynamics but also to smaller terminal steady-state mean cluster sizes. The results from the MD and KMC simulations are in excellent agreement for all investigated two-patch cases, whereas the three-patch cubes form systematically smaller clusters in the MD simulations compared to the KMC calculations due to finite-size effects and slow aggregation kinetics. By analyzing the rate kernels, we are able to identify the primary mechanisms responsible for (shear-induced) cluster growth and breakup. This understanding allows us to tune nanoparticle and process parameters to achieve desired cluster sizes and shapes.

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Reproduction of super-multicomponent self-assembled structures and their functionality using coarse-grained molecular simulation - the example of cleansing agents

Yokoyama Takahiro, Miwake Hideki, Hamaguchi Masugu, Nakatake Ryoichi, Arai Noriyoshi

MOLECULAR SYSTEMS DESIGN & ENGINEERING （Molecular Systems Design and Engineering）  8 （ 4 ） 538 - 550 2023年04月

研究論文（学術雑誌）, 査読有り,  ISSN  2058-9689

　概要を見る

Self-assembly of multi-component systems can provide a large variety of functions, which is impossible for a single-component system, and those multi-component derived functional materials attract attention in various fields such as biomedical, engineering, and materials science. This gives multi-component systems importance, but molecular elucidation of such systems is a major challenge, since this type of complex system has large degrees of freedom. In this study, we focused on cleansing agents as multi-component systems, which are cosmetics products mainly used to remove oily compounds such as makeup, and are multi-component aqueous solutions consisting of many surfactants, moisturizers, and pH regulators. Our aim is to link the macroscopic properties of multi-component systems with the mesoscale structures to elucidate the molecular evidence of functions. We have studied the self-assembled morphologies of cleansing agents using coarse-grained molecular simulations as mesoscale structures and compared them to cleansing performance as a macroscopic property. From the simulation results of morphologies and the experimental results of performance, the key features which explain their functionalities were examined. As a result, it was quantitatively shown that the distribution of specific particles or molecules such as hydrophobic particles both in the bulk state and when they are applied on dirty surfaces is one of the clues to explain the performance. Through molecular designing based on this result, it will be much easier to reach the desired property or performance in the field of multi-component functional materials. Thus, this molecular simulation method will push the field of materials science and materials informatics forward.

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Wetting hysteresis induces effective unidirectional water transport through a fluctuating nanochannel

Arai Noriyoshi, Yamamoto Eiji, Koishi Takahiro, Hirano Yoshinori, Yasuoka Kenji, Ebisuzaki Toshikazu

NANOSCALE HORIZONS （Nanoscale Horizons）  8 （ 5 ） 652 - 661 2023年02月

研究論文（学術雑誌）, 査読有り,  ISSN  2055-6756

　概要を見る

We propose a water pump that actively transports water molecules through nanochannels. Spatially asymmetric noise fluctuations imposed on the channel radius cause unidirectional water flow without osmotic pressure, which can be attributed to hysteresis in the cyclic transition between the wetting/drying states. We show that the water transport depends on fluctuations, such as white, Brownian, and pink noises. Because of the high-frequency components in white noise, fast switching of open and closed states inhibits channel wetting. Conversely, pink and Brownian noises generate high-pass filtered net flow. Brownian fluctuation leads to a faster water transport rate, whereas pink noise has a higher capability to overcome pressure differences in the opposite direction. A trade-off relationship exists between the resonant frequency of the fluctuation and the flow amplification. The proposed pump can be considered as an analogy for the reversed Carnot cycle, which is the upper limit of the energy conversion efficiency.

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Combining Molecular Dynamics and Machine Learning to Analyze Shear Thinning for Alkane and Globular Lubricants in the Low Shear Regime

Yasuda I., Kobayashi Y., Endo K., Hayakawa Y., Fujiwara K., Yajima K., Arai N., Yasuoka K.

ACS Applied Materials and Interfaces （ACS Applied Materials and Interfaces）  15 （ 6 ） 8567 - 8578 2023年02月

研究論文（学術雑誌）, 査読有り,  ISSN  19448244

　概要を見る

Lubricants with desirable frictional properties are important in achieving an energy-saving society. Lubricants at the interfaces of mechanical components are confined under high shear rates and pressures and behave quite differently from the bulk material. Computational approaches such as nonequilibrium molecular dynamics (NEMD) simulations have been performed to probe the molecular behavior of lubricants. However, the low-shear-velocity regions of the materials have rarely been simulated owing to the expensive calculations necessary to do so, and the molecular dynamics under shear velocities comparable with that in the experiments are not clearly understood. In this study, we performed NEMD simulations of extremely confined lubricants, i.e., two molecular layers for four types of lubricants confined in mica walls, under shear velocities from 0.001 to 1 m/s. While we confirmed shear thinning, the velocity profiles could not show the flow behavior when the shear velocity was much slower than thermal fluctuations. Therefore, we used an unsupervised machine learning approach to detect molecular movements that contribute to shear thinning. First, we extracted the simple features of molecular movements from large amounts of MD data, which were found to correlate with the effective viscosity. Subsequently, the extracted features were interpreted by examining the trajectories contributing to these features. The magnitude of diffusion corresponded to the viscosity, and the location of slips that varied depending on the spherical and chain lubricants was irrelevant. Finally, we attempted to apply a modified Stokes-Einstein relation at equilibrium to the nonequilibrium and confined systems. While systems with low shear rates obeyed the relation sufficiently, large deviations were observed under large shear rates.

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Effect of temperature on the structure and drug-release behaviour of inclusion complex of beta-cyclodextrin with cyclophosphamide: a molecular dynamics study

Sakai Seiga, Hirano Yoshinori, Kobayashi Yusei, Arai Noriyoshi

SOFT MATTER （Soft Matter）  19 （ 16 ） 2902 - 2907 2023年

研究論文（学術雑誌）, 査読有り,  ISSN  1744-683X

　概要を見る

Cyclodextrins (CDs) are suitable drug carriers because of their doughnut-shaped cavities with hydrophilic outer and hydrophobic inner surfaces. Temperature-responsive CD-based drug carriers are expected to be one of the most promising candidates for drug delivery systems. In this study, we performed molecular dynamics simulations of the inclusion complex of β-CD with cyclophosphamide (CP) at temperatures from 300 K to 400 K to investigate the temperature dependency of the release behaviour of CP and structural changes of β-CD in an aqueous solution. We analysed the distance between the centres of mass of β-CD and CP and the radius of gyration of β-CD. The CP molecule was released from the β-CD cavity at 400 K, whereas two different inclusion complexes, partially and completely, were observed at T < 400 K. β-CD encapsulating a CP molecule had a more spherical shape and rigidity than β-CD without a CP, and the rigidity of their inclusion complex decreased with increasing temperature. Our findings provide fundamental insights into the behaviours of the β-CD/CP complex and drug release at the molecular level and can facilitate the development of new temperature-responsive drug delivery systems with CD nanocarriers triggered by localised temperature increases using focused ultrasound.

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Unsupervised deep learning for molecular dynamics simulations: a novel analysis of protein-ligand interactions in SARS-CoV-2 M<SUP>pro</SUP>

Mustali, J; Yasuda, I; Hirano, Y; Yasuoka, K; Gautieri, A; Arai, N

RSC ADVANCES （RSC Advances）  13 （ 48 ） 34249 - 34261 2023年

研究論文（学術雑誌）, 査読有り

　概要を見る

Molecular dynamics (MD) simulations, which are central to drug discovery, offer detailed insights into protein-ligand interactions. However, analyzing large MD datasets remains a challenge. Current machine-learning solutions are predominantly supervised and have data labelling and standardisation issues. In this study, we adopted an unsupervised deep-learning framework, previously benchmarked for rigid proteins, to study the more flexible SARS-CoV-2 main protease (Mpro). We ran MD simulations of Mpro with various ligands and refined the data by focusing on binding-site residues and time frames in stable protein conformations. The optimal descriptor chosen was the distance between the residues and the center of the binding pocket. Using this approach, a local dynamic ensemble was generated and fed into our neural network to compute Wasserstein distances across system pairs, revealing ligand-induced conformational differences in Mpro. Dimensionality reduction yielded an embedding map that correlated ligand-induced dynamics and binding affinity. Notably, the high-affinity compounds showed pronounced effects on the protein's conformations. We also identified the key residues that contributed to these differences. Our findings emphasize the potential of combining unsupervised deep learning with MD simulations to extract valuable information and accelerate drug discovery.

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Correlation between ordering and shear thinning in confined OMCTS liquids

Kobayashi Yusei, Arai Noriyoshi, Yasuoka Kenji

JOURNAL OF CHEMICAL PHYSICS （Journal of Chemical Physics）  157 （ 11 ） 114506 2022年09月

研究論文（学術雑誌）, 査読有り,  ISSN  0021-9606

　概要を見る

Despite decades of extensive research, the behavior of confined liquids, particularly in the mixed/boundary lubrication regime, remains unelucidated. This can be attributed to several factors, including the difficulty to make direct experimental observations of the behavior of lubricant molecules under nonequilibrium conditions, the high computational cost of molecular simulations to reach steady state, and the low signal-to-noise ratio at extremely low shear rates corresponding to actual operating conditions. In this regard, we studied the correlation between the structure formation and shear viscosity of octamethylcyclotetrasiloxane confined between two mica surfaces in a mixed/boundary lubrication regime. Three different surface separations - corresponding to two-, three-, and five-layered structures - were considered to analyze the effect of confinement. The orientational distributions with one specific peak for n = 2 and two distributions, including a parallel orientation with the surface normal for n > 2, were observed at rest. The confined liquids exhibited a distinct shear-thinning behavior independent of surface separations for a relatively low shear rate, γ˙≲108s-1. However, the shear viscosities at γ˙≲108s-1 depended on the number of layered structures. Newtonian behavior was observed with further increase in the shear rate. Furthermore, we found a strong correlation between the degree of molecular orientation and the shear viscosity of the confined liquids. The magnitude of the shear viscosity of the confined liquids can primarily be determined by the degree of molecular orientation, and shear thinning originates from the vanishing of specific orientational distributions with increasing shear rate.

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A stochastic Hamiltonian formulation applied to dissipative particle dynamics

Peng L., Arai N., Yasuoka K.

Applied Mathematics and Computation （Applied Mathematics and Computation）  426   127126 - 127126 2022年08月

研究論文（学術雑誌）, 査読有り,  ISSN  00963003

　概要を見る

In this paper, a stochastic Hamiltonian formulation (SHF) is proposed and applied to dissipative particle dynamics (DPD) simulations. As an extension of Hamiltonian dynamics to stochastic dissipative systems, the SHF provides necessary foundations and great convenience for constructing efficient numerical integrators. As a first attempt, we develop the Störmer–Verlet type of schemes based on the SHF, which are structure-preserving for deterministic Hamiltonian systems without external forces, the dissipative forces in DPD. Long-time behaviour of the schemes is shown numerically by studying the damped Kubo oscillator. In particular, the proposed schemes include the conventional Groot–Warren's modified velocity-Verlet method and a modified version of Gibson–Chen–Chynoweth as special cases. The schemes are applied to DPD simulations and analysed numerically.

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Theoretical Design of a Janus-Nanoparticle-Based Sandwich Assay for Nucleic Acids

Sato Takumi, Esashika Keiko, Yamamoto Eiji, Saiki Toshiharu, Arai Noriyoshi

INTERNATIONAL JOURNAL OF MOLECULAR SCIENCES （International Journal of Molecular Sciences）  23 （ 15 ）  2022年08月

研究論文（学術雑誌）, 査読有り,  ISSN  16616596

　概要を見る

Nanoparticles exhibit diverse self-assembly attributes and are expected to be applicable under unique settings. For instance, biomolecules can be sandwiched between dimer nanoparticles and detected by surface-enhanced Raman scattering. Controlling the gap between extremely close dimers and stably capturing the target molecule in the gap are crucial aspects of this strategy. Therefore, polymer-tethered nanoparticles (PTNPs), which show promise as high-performance materials that exhibit the attractive features of both NPs and polymers, were targeted in this study to achieve stable biomolecule sensing. Using coarse-grained molecular dynamics simulations, the dependence of the PTNP interactions on the length of the grafted polymer, graft density, and coverage ratio of a hydrophobic tether were examined. The results indicated that the smaller the tether length and graft density, the smaller was the distance between the PTNP surfaces ((Formula presented.)). In contrast, (Formula presented.) decreased as the coverage ratio of the hydrophobic surface ((Formula presented.)) increased. The sandwiching probability of the sensing target increased in proportion to the coverage ratio. At high (Formula presented.) values, the PTNPs aggregated into three or more particles, which hindered their sensing attributes. These results provide fundamental insight into the sensing applications of NPs and demonstrate the usefulness of PTNPs in sensing biomolecules.

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ソフトマターの粗視化分子シミュレーション

荒井 規允

色材協会誌 （一般社団法人 色材協会）  95 （ 4 ） 92 - 97 2022年04月

研究論文（研究会，シンポジウム資料等）, 査読有り,  ISSN  0010-180X

　概要を見る

<p>ソフトマターは与えられた外力に対して特異な応答を示す。この性質を利用し，洗剤や化粧品，ゴムタイヤ，液晶ディスプレイなどさまざまな機能性材料として用いられている。これらの材料の性質は分子構造だけでなく，それらが集まって形成される自己集合構造にも強く影響することが知られている。ゆえに所望の機能をもつ材料の設計には，ソフトマターの自己集合構造を予測・制御することが重要となる。われわれは粗視化分子シミュレーションを用い，さまざまなソフトマターの自己集合挙動，さらには自己集合構造と物性の関係性について研究してきた。ここではこれまで取り組んできた研究の中からいくつかについて紹介する。</p>

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散逸粒子動力学法を用いたナノ空間内における高分子グラフトナノ粒子の自己組織化に関する研究

佐藤 碧海, 小林 祐生, 荒井 規允

日本機械学会関東支部総会講演会講演論文集 （一般社団法人 日本機械学会）  2022.28 （ 0 ） 15F17 2022年

研究論文（研究会，シンポジウム資料等）, 査読有り

　概要を見る

<p>In this study, we investigate the morphology and phase diagram of self-assembled polymeric nanoparticles (NPs) confined within nanotubes (NTs) by dissipative particle dynamics simulations. There is a clear relationship between the self-assembling architecture of nanoparticles (NPs) and their physical properties, and Polymer-tethered NPs, which are created by grafting polymers onto NPs to control the self-assembly of NPs, have attracted considerable attention. However, self-assembled structures have not been systematically classified because of the large number of tuning parameters such as the polymer length and graft density. In this study, we investigated the confinement of NPs grafted with three types of polymers: hydrophilic, hydrophobic and Janus surface, hydrophilic and hydrophobic walls. First, we derived the qualitative phase diagram of the axial pressure Pz and the ratio L of NT radius to NP radius. As a result, in polymer-grafted NPs with Janus amphiphilic surface, hydrophobic and hydrophilic polymer tether NPs were found to assemble axially to form an ordered structure, and in hydrophobic NTs, a double helical structure was formed at L=3.0. These simulation results show that the self-assembled structure of polymer tether NPs can be qualitatively predicted based on the chemical properties of NT walls and the surface design of polymer tether NPs.</p>

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雲母表面間に閉じ込められた OMCTS の構造とせん断粘度に関する分子動力学シミュレーション

小林 祐生, 荒井 規允, 泰岡 顕治

日本機械学会関東支部総会講演会講演論文集 （一般社団法人 日本機械学会）  2022.28 （ 0 ） 15F20 2022年

研究論文（研究会，シンポジウム資料等）, 査読有り

　概要を見る

<p>Fluids confined in nanochannel exhibit distinct phases and flow properties not shown in the bulk. These confined systems are involved in many industrial and engineering applications such as nanofluidic devices, biological membranes and therefore understanding and controlling the molecular behavior of confined liquids is important. Octamethylcyclotetrasiloxane (OMCTS) is a small macrocycle made of four covalently linked Si(Me)2O units which have been used as a model liquid in the experimental studies. However, much less is known about the mechanisms related to external stimuli such as shear and how those molecular behaviors in a confined system impact the flow properties of the whole liquid. In this study, we have investigated the structure and shear viscosity of OMCTS confined between two mica walls under shear, using molecular dynamics simulation. The results showed layering of OMCTS molecules, depending on the distance between two mica surfaces. In addition to this, the structural changes were observed accompanied by shear-thinning behavior when we applied shear to the system.</p>

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Simulation study on the effects of the self-assembly of nanoparticles on thermal conductivity of nanofluids

Tanaka Shogo, Arai Noriyoshi, Kobayashi Yusei

CHEMICAL PHYSICS LETTERS （Chemical Physics Letters）  785 （ 139129 ）  2021年12月

研究論文（学術雑誌）, 査読有り,  ISSN  0009-2614

　概要を見る

The mechanisms underlying the thermal conductivity behavior of nanofluids have not been completely clarified thus far. This is due to the various competing factors and the lack of a molecular-level understanding of the heat transfer enhancement of nanofluids. In this study, energy-conserving dissipative particle dynamics simulations were conducted to investigate the effects of the self-assembly of nanoparticles (NPs) on the nanoscale heat transfer properties. We demonstrated that considering the balance between the effects of the distance between the NPs and the solvent and the enhancement in thermal conductivity on adding NPs is important for controlling the thermal conductivity of nanofluids.

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慶應義塾大学理工学部機械工学科 荒井研究室

荒井 規允

アンサンブル （分子シミュレーション学会）  23 （ 4 ） 290 - 293 2021年10月

研究論文（研究会，シンポジウム資料等）, 査読有り,  ISSN  18846750

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Effect of chemical design of grafted polymers on the self-assembled morphology of polymer-tethered nanoparticles in nanotubes

Sato Takumi, Kobayashi Yusei, Arai Noriyoshi

JOURNAL OF PHYSICS-CONDENSED MATTER （Journal of Physics Condensed Matter）  33 （ 36 ）  2021年09月

研究論文（学術雑誌）, 査読有り,  ISSN  0953-8984

　概要を見る

There is a clear relationship between the self-assembling architecture of nanoparticles (NPs) and their physical properties, and they are currently used in a variety of applications, including optical sensors. Polymer-tethered NPs, which are created by grafting polymers onto NPs to control the self-assembly of NPs, have attracted considerable attention. Recent synthetic techniques have made it possible to synthesize a wide variety of polymers and thereby create NPs with many types of surfaces. However, self-assembled structures have not been systematically classified because of the large number of tuning parameters such as the polymer length and graft density. In this study, by using coarse-grained molecular simulation, we investigated the changes in the self-assembled structure of polymer-tethered NP solutions confined in nanotubes due to the chemical properties of polymers. Three types of tethered polymer NP models were examined: homo hydrophilic, diblock hydrophilic-hydrophobic (HI-HO), and diblock hydrophobic-hydrophilic. Under strong confinement, the NPs were dispersed in single file at low axial pressure. As the pressure increased, multilayered lamellar was observed in the HI-HO model. In contrast, under weak confinement, the difference in the pressure at which the phases emerge, depending on the model, was significant. By changing the chemical properties of the grafted polymer, the thermodynamic conditions (the axial pressure in this study) under which the phases appear is altered, although the coordination of NPs remains almost unchanged. Our simulation offers a theoretical guide for controlling the morphologies of self-assembled polymer-tethered NPs, a novel system that may find applications in nanooptical devices or for nanopatterning.

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Molecular Insight into the Possible Mechanism of Drag Reduction of Surfactant Aqueous Solution in Pipe Flow

Kobayashi Yusei, Gomyo Hirotaka, Arai Noriyoshi

INTERNATIONAL JOURNAL OF MOLECULAR SCIENCES （International Journal of Molecular Sciences）  22 （ 14 ） 7573 - 7573 2021年07月

研究論文（学術雑誌）, 査読有り,  ISSN  16616596

　概要を見る

The phenomenon of drag reduction (known as the “Toms effect”) has many industrial and engineering applications, but a definitive molecular-level theory has not yet been constructed. This is due both to the multiscale nature of complex fluids and to the difficulty of directly observing self-assembled structures in nonequilibrium states. On the basis of a large-scale coarse-grained molecular simulation that we conducted, we propose a possible mechanism of turbulence suppression in surfactant aqueous solution. We demonstrate that maintaining sufficiently large micellar structures and a homogeneous radial distribution of surfactant molecules is necessary to obtain the drag-reduction effect. This is the first molecular-simulation evidence that a micellar structure is responsible for drag reduction in pipe flow, and should help in understanding the mechanisms underlying drag reduction by surfactant molecules under nonequilibrium conditions.

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

Sato Takumi, Kobayashi Yusei, Michioka Takenobu, Arai Noriyoshi

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

研究論文（学術雑誌）, 査読有り,  ISSN  1744-683X

　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.

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Nanotube Active Water Pump Driven by Alternating Hydrophobicity

Arai Noriyoshi, Koishi Takahiro, Ebisuzaki Toshikazu

ACS NANO （ACS Nano）  15 （ 2 ） 2481 - 2489 2021年02月

研究論文（学術雑誌）, 査読有り,  ISSN  1936-0851

　概要を見る

Water transport must be efficiency controlled for the future sustainability of life. Various water transport systems using carbon nanotubes have been proposed in recent years. Although these systems are more permeable than aquaporins, their water transport is passive. In this study, we successfully demonstrate an active water pump driven by simple hydrophobic interaction through computer simulation. Even in the absence of a pressure- or density-gradient, the proposed pump can actively transport water molecules by alternately switching the hydrophobicity of the pump surface. The water transport rate can be easily controlled by varying the time interval of switching. The pump with optimized switching time exhibits prominent water permeance. The results obtained herein can be applied in various water transport technologies because of the simple mechanics. The proposed water pump has the potential to realize an effective device such as a low-energy artificial purification system.

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準一次元閉じ込め系におけるコレステリック液晶が形成する自己集合構造に関する散逸粒子動力学シミュレーション

辻之上 弘晃, 野澤 拓磨, 高橋 和義, 荒井 規允

日本機械学会関東支部総会講演会講演論文集 （一般社団法人 日本機械学会）  2021.27 （ 0 ） 10C14 2021年

研究論文（研究会，シンポジウム資料等）, 査読有り

　概要を見る

<p>Blue phases (BPs) are three-dimensional self-assembly structures of liquid crystals with a lattice of line defects. They have attracted considerable interest as the potential in next generation displays. It is well known that BPs occur in cholesteric liquid crystals (CLCs) under certain thermodynamic conditions. However, previous studies have indicated that confining surfaces may induce distinctive structural changes. For example, a quasi-two-dimensional (Q2D) confinement system was investigated with the aid of numerical calculations, and a stable Q2D Skyrmion structure was attained. In this study, we investigated the CLC phase behavior at the molecular scale for a quasi-one-dimensional (Q1D) nanotube system using molecular simulations. We observed the various morphological behaviors of CLCs by changing the temperature and the radius of nanotube. Specially, we discovered a self-assembly structures with cylindrical defects rather than lines by introducing a novel local orientation analysis. Our results show that the self-assembly of CLCs offers a guide to control the intensity in one-dimensional confinement and fundamental knowledge for application to optical devices.</p>

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粗視化分子シミュレーションを用いたコロイド-ポリマー混合溶液の自己集合と粘性挙動に関する研究

小林 祐生, 荒井 規允, Arash Nikoubashman

日本機械学会関東支部総会講演会講演論文集 （一般社団法人 日本機械学会）  2021.27 （ 0 ） 10C12 2021年

研究論文（研究会，シンポジウム資料等）, 査読有り

　概要を見る

<p>We investigate the structure and rheological properties of dilute colloid-polymer mixtures at rest and under shear <i>via</i> 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 colloidal micelles, and small 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 small shear rates, all mixtures exhibit a Newtonian-like response with intrinsic shear viscosities that are up to two times as large as of pure suspensions of non-adsorbing colloids at the same concentration. Further, 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 become shear-thinning. This shear-induced breakup occurs at stronger shear compared to pure JC suspensions, indicating that the adsorbed polymers reinforce the hybrid aggregates.</p>

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

Kobayashi Yusei, Arai Noriyoshi, Nikoubashman Arash

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

研究論文（学術雑誌）, 査読有り,  ISSN  0743-7463

　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.

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

Tsujinoue H, Kobayashi Y, Arai N

Langmuir : the ACS journal of surfaces and colloids （Langmuir : the ACS journal of surfaces and colloids）  36 （ 36 ） 10690 - 10698 2020年09月

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

　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.

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Cylindrical defect structures formed by chiral nematic liquid crystals in quasi-one-dimensional systems.

Tsujinoue H, Nozawa T, Arai N

Physical chemistry chemical physics : PCCP （Physical Chemistry Chemical Physics）  22 （ 29 ） 16896 - 16904 2020年08月

研究論文（学術雑誌）, 共著, 査読有り,  ISSN  1463-9076

　概要を見る

© the Owner Societies. Blue phases are three-dimensional self-assembly structures of liquid crystals with a lattice of line defects. They have attracted considerable interest as photonic materials. It is well known that blue phases occur in cholesteric liquid crystals (CLCs) under certain thermodynamic conditions; however, recent studies have indicated that confining surfaces may induce distinctive structural changes. For example, in a previous study, a quasi-two-dimensional (Q2D) confinement system was investigated with the aid of numerical calculations, and a stable Q2D Skyrmion structure was attained. Here, we performed molecular simulations to investigate the CLC phase behavior at the molecular scale for a quasi-one-dimensional (Q1D) nanotube system. Various morphological behaviors of CLCs were observed by changing the temperature and the radius of the nanotubes. In particular, we discovered a self-assembled structure with cylindrical (or ring-like) defects rather than lines by introducing a novel local orientation analysis. Our simulation results show that the self-assembly of CLCs offers a guide to control the intensity in Q1D systems and fundamental knowledge for their application to optical devices. This journal is

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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

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

　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.

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Performance of Coarse Graining in Estimating Polymer Properties: Comparison with the Atomistic Model

Miwatani Ryota, Takahashi Kazuaki Z., Arai Noriyoshi

POLYMERS （Polymers）  12 （ 2 ） 382 - 382 2020年02月

研究論文（学術雑誌）, 共著, 査読有り

　概要を見る

© 2020 by the authors. Combining atomistic and coarse-grained (CG) models is a promising approach for quantitative prediction of polymer properties. However, the gaps between the length and time scales of atomistic and CG models still need to be bridged. Here, the scale gaps of the atomistic model of polyethylene melts, the bead-spring Kremer-Grest model, and dissipative particle dynamics with the slip-spring model were investigated. A single set of spatial and temporal scaling factors was determined between the atomistic model and each CG model. The results of the CG models were rescaled using the set of scaling factors and compared with those of the atomistic model. For each polymer property, a threshold value indicating the onset of static or dynamic universality of polymers was obtained. The scaling factors also revealed the computational efficiency of each CG model with respect to the atomistic model. The performance of the CG models of polymers was systematically evaluated in terms of both the accuracy and computational efficiency.

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Structure and dynamics of amphiphilic Janus spheres and spherocylinders under shear

Kobayashi Yusei, Arai Noriyoshi, Nikoubashman Arash

SOFT MATTER （Soft Matter）  16 （ 2 ） 476 - 486 2020年01月

研究論文（学術雑誌）, 共著, 査読有り,  ISSN  1744-683X

　概要を見る

This journal is © The Royal Society of Chemistry. We study the structure formation and flow properties of colloidal dispersions comprised of Janus spheres, Janus spherocylinders, and their mixtures, using hybrid molecular dynamics simulations that take into account hydrodynamic interactions. We systematically vary the Janus balance and the shape anisotropy of the particles, and explore a range of colloid volume fractions in the liquid regime of the phase diagram. At rest, Janus spheres with small hydrophobic patches form spherical micelles for all investigated colloid concentrations. In contrast, Janus spheres with an entirely hydrophobic hemisphere aggregate to larger worm-like micelles and network-like structures. Janus spherocylinders exhibit a similar self-assembly behavior. At small and intermediate shear, we observe deformation and rearrangement of the micelles, accompanied by a Newtonian-like rheology with slightly higher shear viscosity compared to homoparticle dispersions at the same concentration. As the shear rate is increased further, the micelles eventually break up into small dimers and free particles, causing a distinct shear-thinning of the dispersions. The network-like structures exhibit a similar flow behavior at high shear rates, but for weak shear we find an almost threefold increase of the shear viscosity and a distinct shear-thinning behavior due to the fracturing of the intertwined networks. In general, we identify a strong correlation between the size of the aggregates and the rheology of the dispersions, allowing for the determination of dynamic properties solely based on structural information.

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界面活性剤水溶液およびコロイド懸濁液における自己集合と流動ダイナミクス

小林 祐生, 荒井 規允

混相流 （日本混相流学会）  34 （ 1 ） 11 - 18 2020年

研究論文（研究会，シンポジウム資料等）, 共著, 査読有り,  ISSN  0914-2843

　概要を見る

<p>In recent years, self-assembly of complex fluids has received considerable attention in the fields of nanoscience and nanotechnology. Self-assembly is involved in various functional materials that are widely used in industry and there is a strong relationship between self-assembled structures and specific functions. Hence, the understanding and controlling of the self-assembly controlling of complex fluids is important and a useful process in materials chemistry and engineering. In this paper, the recent developments on studies of the structure formation and flow properties of amphiphilic molecules and Janus colloids in solution, using coarse-grained simulation that takes into account hydrodynamic interactions are reviewed. We first briefly introduce the dissipative particle dynamics method and discuss in detail the self-assembly behavior and viscosity properties of surfactant aqueous solution in nanotubes. Following this, we describe another simulation method in which solvent particles are modeled explicitly as point particles, which is the so-called "the multi-particle collision dynamics (MPCD)". The relation between the structural and rheological properties of Janus colloids in solution, using molecular dynamics simulations coupled to MPCD is reported. In general, the shear viscosity of the dispersion correlates strongly with the size of the aggregates not aggregates shape. These results allow us to determine the dynamic properties solely based on structural information.</p>

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最近の研究から「散逸粒子動力学シミュレーションによる両親媒性テトラポッド型ナノ粒子の自己集合制御」

荒木 雄介, 荒井 規允

アンサンブル （分子シミュレーション学会）  22 （ 1 ） 55 - 60 2020年

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

　概要を見る

<p>近年，合成技術の発達によって様々な形状や表面を有すナノ粒子の作製が可能となった．そのようなナノ粒子は複雑な自己集合構造を示すことが報告されている．ナノ粒子の自己集合の制御や予測は，分子レベルからの機能性材料の設計に必要不可欠である．本研究では，両親媒性テトラポッド型ナノ粒子に着目し，腕の長さや親水/疎水比が自己集合へどのような影響を及ぼすか，散逸粒子動力学シミュレーションによって調べた．</p><p></p><p></p>

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Self-assembly of spheroidal triblock Janus nanoparticle solutions in nanotubes

Kobayashi Y., Inokuchi T., Nishimoto A., Arai N.

Molecular Systems Design and Engineering （Molecular Systems Design and Engineering）  4 （ 1 ） 122 - 132 2019年02月

研究論文（学術雑誌）, 共著, 査読有り,  ISSN  2058-9689

　概要を見る

© 2019 The Royal Society of Chemistry. We have performed coarse-grained molecular simulations to investigate the morphologies and phase diagrams of self-assembled spheroidal triblock Janus nanoparticles (JNPs) confined in nanotubes. Nanoparticles exhibit several unique behaviours through shape changes, such as high thermal conductivity in heat pipes, high strength of binding avidity in ligand-receptor interactions, high amounts of uptake between cells during endocytosis processes, and so on. In this study, we focus on the effect of shape on self-assembled structures or phases within nanospaces. We derived qualitative phase diagrams of axial pressure versus the ratio of the diameter of the nanoparticles and nanotubes. Two distinct types of nanotube walls and three types of JNP shapes were considered: hydrophobic and hydrophilic walls, and NP aspect ratios of 1.5, 2.0, and 2.5. We observed diverse morphologies in spheroidal JNP solutions, many of which have not been observed before in bulk solutions. We also compared the self-assembled structures of spherical triblock JNPs. By increasing the aspect ratio of the NPs, clusters of unique structures, such as tripods, tetrapods, and hexapods, were formed. Moreover, we found that an increase in the value of the aspect ratio leads to a shift in the multilayer toroidal stacking phases to a weaker confinement effect. The self-assembly behaviours of the spheroidal JNPs can be qualitatively predicted based on the chemical nature of the nanotube walls and shapes of the JNPs.

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Self-assembly of spheroidal triblock Janus nanoparticle solutions in nanotube

Y Kobayashi, T. Inokuchi, A. Nishimoto, N. Arai

Molecular Systems Design and Engineering 4   122 - 132 2019年02月

研究論文（学術雑誌）, 共著, 査読有り

Polymodal rheological behaviors induced by self-assembly of surfactants confined in nanotubes

Kobayashi Y., Arai N.

Journal of Molecular Liquids （Journal of Molecular Liquids）  274   328 - 337 2019年01月

研究論文（学術雑誌）, 単著, 査読有り,  ISSN  01677322

　概要を見る

© 2018 Elsevier B.V. Self-assembly is currently one of the most studied branches of materials chemistry, and has attracted a lot of attention due to its diverse potential applications in electronics, engineering, biomedical, and optical fields. Thus far, many previous studies have reported on the self-assembly of surfactants for developing various functional materials. In this study, we focus 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 chemically distinct nanotubes using a computer simulation. Graphs of the Weissenberg number (Wi) versus the viscosity (η) in hydrophilic, hydroneutral, and hydrophobic nanotubes at different concentrations of surfactant were derived. We found that differences in the viscosity can be obtained depending on the chemical nature of the wall surface, even in systems without surfactant molecules. With the surfactant molecules, characteristic viscosity behaviors were observed with rich steady-state morphologies. For example, although the concentration of the surfactant is the same (c = 30%), completely different viscosity behaviors were observed in hydrophilic (shear-thinning) and hydrophobic (shear-thickening) nanotubes. Our simulations offer a guide to controlling the rheological properties of surfactant aqueous solutions by altering the chemical nature of the wall surface and elucidating the effects of confinement, the concentration of the surfactant aqueous solution, and the self-assembled structure.

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Polymorphic transitions mediated by surfactants in liquid crystal nanodroplet

Tsujinoue H., Inokuchi T., Arai N.

Liquid Crystals （Liquid Crystals）  46 （ 9 ） 1428 - 1439 2019年

研究論文（学術雑誌）, 共著, 査読有り,  ISSN  02678292

　概要を見る

© 2019, © 2019 Informa UK Limited, trading as Taylor & Francis Group. Recently, various techniques have been developed using photonic crystals. Liquid crystals (LC) confined in a nanodroplet mimicked photonic crystals, such as those of opal. Therefore, investigating the phase behaviour of LC molecules in nanodroplets is very important in the next-generation optical field. In this study, the chemical interaction between surfactants and LCs in nanodroplets is reproduced using a dissipative particle dynamics method. We identify the phase behaviour of LCs and investigate how the chemical interaction affect on the orientation of LCs. In particular, by adding surfactant molecules, various morphological behaviours were observed in the LC nanodroplet. The phase transition temperature varied depending on RND (amount of surfactant molecules). Furthermore, difference of the self-assembly structure also appeared inside the droplet depending on RND. Our simulation offers a theoretical guide to control morphologies of self-assembled LCs inside a nanodroplet, a novel system that may find applications in nanofluidic devices or in photonic crystal technology.

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Dissociation effect of non-covalent bond for morphological behavior of triblock copolymers: a dissipative particle dynamics study

Y Araki, N Arai

Chemical Engineering Communications, 1-13 （Chemical Engineering Communications）  208 （ 1 ） 1 - 13 2019年

研究論文（学術雑誌）, 共著, 査読有り,  ISSN  0098-6445

　概要を見る

© 2019, © 2019 Taylor & Francis Group, LLC. The nanophase separation structure produced by block polymers is used for highly functional materials and has been studied for 50 years. In recent years, researchers have shown interest in introducing non-covalent bonds, such as hydrogen bonds and metal–ligand bonds, to polymers. The non-covalent bond dissociates or recombines in response to physical conditions, including temperature and concentration. The non-covalent bond freely controls the phase separation structure, namely, the physical properties of the polymer material. However, various interactions are involved in the formation process, for example, polymer–polymer, polymer–solvent, bonding and bending in the polymer. To control the self-assembled structure, it is necessary to understand the influence of the non-covalent bond at the molecular level. In this study, we investigated the effect of the non-covalent bond on a stage of phase separation immediately after dissociation (early-stage) of self-assembled morphologies by introducing the binding site to the triblock polymers. Various stable morphologies, including lamellar, lamellar with a grain boundary, and pre-lamellar, were observed by changing the positions of the non-covalent bond, their dissociation ratio, and the initial configurations. Moreover, we calculated the radial distribution function and static structure factor to identify the structural features. The results suggested that the early-stage of self-assembled morphology in polymer melt could be controlled by the position of the non-covalent bond and its dissociation ratio.

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Replica exchange dissipative particle dynamics method on threadlike micellar aqueous solutions

Y Kobayashi, K Nomura, T Kaneko, N Arai

Journal of Physics: Condensed Matter 32 (11), 115901 （Journal of Physics Condensed Matter）  32 （ 11 ） 115901 2019年

研究論文（学術雑誌）, 共著, 査読有り,  ISSN  0953-8984

　概要を見る

© 2019 IOP Publishing Ltd. 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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Programmed self-assembly of tetrapod nanoparticles with an amphiphilic surface pattern: the effect of arm length and hydrophobic ratio

Y Araki, Y Kobayashi, N Arai

Molecular Systems Design & Engineering 4 (6), 1095-1102 （Molecular Systems Design and Engineering）  4 （ 6 ） 1095 - 1102 2019年

研究論文（学術雑誌）, 共著, 査読有り,  ISSN  2058-9689

　概要を見る

© 2019 The Royal Society of Chemistry. We studied the self-assembly processes and morphologies of tetrapod nanoparticle solutions using dissipative particle dynamics (DPD) simulations. Composite-shaped nanoparticles, such as a tetrapod model with an amphiphilic surface pattern, were also synthesised experimentally. We programmed nanoparticle self-assembly using the DPD results at various values of the hydrophobic ratio (HR) and arm length (AL). Considering these two parameters, we observed the self-assembly processes and morphologies in a tetrapod nanoparticle solution. As a result, it was found that the HR and AL of tetrapod nanoparticles were effective parameters for controlling their self-assembly processes or structures under equilibrium. In this study, we programmed the AL or HR parameters, and we report their influences on self-assembly. Our simulations offer a guide to controlling the morphologies of self-assembled tetrapod nanoparticles, which constitute novel systems that may find applications in nanofluidic devices.

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Predominant factor determining thermal conductivity behavior of nanofluid: Effect of cluster structures with various nanoparticles

Y Kobayashi, N Arai

Journal of The Electrochemical Society 166 (9), B3223-B3227 （Journal of the Electrochemical Society）  166 （ 9 ） B3223 - B3227 2019年

研究論文（学術雑誌）, 共著, 査読有り,  ISSN  0013-4651

　概要を見る

© The Author(s) 2019. Despite several research efforts, the detailed mechanism that dominates the thermal conductivity of nanofluids has not been explained. We investigated the effect of the chemical surface design of NPs (hydrophobic–hydrophilic balance of the NPs containing Janus surface) and verified the influence of their self–assembled structures on the thermal conductivity of a nanofluid using molecular simulation. When hydrophobic (HO) NPs are added to a nanofluid, they only form one large cluster because they do not prefer to be in contact with water molecules. Hence, an increment in the thermal conductivity of the nanofluid added with HO NPs was observed. On the contrary, the mean cluster size of Janus NPs was limited because of their limited HO superficial areas (attractive domains). Hence, an increment in the enhancement ratio of thermal conductivity was not observed even when the volume fraction of the NPs (φNP) was increased. Thus, our results demonstrate that the mean cluster size of NPs is the key factor for thermal conductivity enhancement. In addition, this study reveals that it is possible to control the thermal conductivity of nanofluids (or the mean cluster size of Janus NPs) using Janus NPs with surfaces designed using anisotropic chemical interactions.

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Predicting molecular ordering in a binary liquid crystal using machine learning

T Inokuchi, R Okamoto, N Arai

Liquid Crystals, 1-11 （Liquid Crystals）  47 （ 3 ） 438 - 448 2019年

研究論文（学術雑誌）, 共著, 査読有り,  ISSN  0267-8292

　概要を見る

© 2019, © 2019 Informa UK Limited, trading as Taylor & Francis Group. Machine learning is a category of AI technology that is utilized in the product development cycle in numerous industries. It was reported that machine learning can be applied to predict the chemical properties of functional materials, for example, the self-assembly of surfactant solutions (Nanoscale, 2018, 10, 16013) and the chemical reactions of copper nanoparticles (ACS Energy Lett., 2018, 3, 2983). A liquid crystal (LC) molecule is a representative functional material. Monodisperse systems have been targeted in many theoretical studies; however, the resulting products usually have a polydisperse distribution. It has been reported in several studies that the properties exhibited by polydisperse systems are different from those observed in monodisperse systems. In this study, we focus on the physical properties of polydisperse systems i.e. the ratio of binary LC molecules on the phase transition temperature and the possibility of predicting the physical properties of the system using machine learning. A relatively high prediction accuracy was obtained using machine learning. This study demonstrates that machine learning can be utilized to predict the phase transition temperature of polydispersed LC systems. The results of this study will contribute to the further development of material science and molecular design via the application of machine learning.

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散逸粒子動力学（DPD）法を用いたソフトマターの分子シミュレーション

荒井 規允

可視化情報学会誌 （社団法人 可視化情報学会）  39 （ 154 ） 19 - 25 2019年

研究論文（研究会，シンポジウム資料等）, 単著, 査読有り,  ISSN  0916-4731

　概要を見る

<p>近年，コンピュータシミュレーション技術の発達によって，これまで取り扱うことのできなかった様々なシステムの再現，可視化が行われるようになってきた．散逸粒子動力学(DPD)法は分子シミュレーションの一種だが，原子や分子をある程度一纏めとして扱うことで，従来の分子シミュレーションよりも大きな時空間スケールの現象を再現できる．本稿では，DPD法の歴史，アルゴリズムを簡単に説明したあと，これまで筆者が対象としてきたいくつかのソフトマター材料(界面活性剤，ナノ粒子，液晶，高分子膜・生体膜)に対するDPDシミュレーションについて紹介する．</p>

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Water permeation in polymeric membranes: Mechanism and synthetic strategy for water-inhibiting functional polymers

Araki Y., Kobayashi Y., Kawaguchi T., Kaneko T., Arai N.

Journal of Membrane Science （Journal of Membrane Science）  564   184 - 192 2018年10月

研究論文（学術雑誌）, 単著, 査読有り,  ISSN  03767388

　概要を見る

© 2018 Elsevier B.V. The prediction and control of penetration in a polymeric membrane is of critical importance in green chemistry and energy technology, including gas separation, water purification, and desalination. We performed molecular simulations of water transport through a polymeric membrane to clarify the key factors that dominate water permeation. The effects of additives and chemical interaction (solubility) on water inhibition were investigated. We found that additives reduce water permeability into the membrane. Upon incorporation of the additive, strength of coordination of water molecules near the membrane surface increases. Thus, the penetration frequency of water molecules into the membrane decreases. It is suggested that the local environment near the membrane surface plays a significant role in controlling water permeability. In order to gain deeper insights into the polymer design, we discussed the chemical interaction (solubility) parameter change between polymer chains and additives. Using a repulsive chemical species of a polymer chain for additives can lead to higher water inhibition. The ability to control water permeability into the membrane by polymer design can be exploited for applications in water separation technology.

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Multiscale prediction of functional self-assembled materials using machine learning: High-performance surfactant molecules

Inokuchi T., Li N., Morohoshi K., Arai N.

Nanoscale （Nanoscale）  10 （ 34 ） 16013 - 16021 2018年09月

研究論文（学術雑誌）, 共著, 査読有り,  ISSN  20403364

　概要を見る

© 2018 The Royal Society of Chemistry. Various physical properties of functional materials can be induced by controlling their chemical molecular structures. Therefore, molecular design is crucial in the fields of engineering and materials science. With its remarkable development in various fields, machine learning combined with molecular simulation has recently been found to be effective at predicting the electronic structure of materials (Nat. Commun., 2017, 8, 872 and Nat. Commun., 2017, 8, 13890). However, previous studies have used similar microscale information as input and output data for machine learning, i.e., molecular structures and electronic structures. In this study, we determined whether multiscale data can be predicted using machine learning via a self-assembly functional material system. In particular, we investigated whether machine learning can be used to predict dispersion and viscosity, as the representative physical properties of a self-assembled 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 of this study will aid in further development of the application of machine learning to materials science and molecular design.

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Self-assembled morphology of tripod nanoparticle solutions: the effect of arm length and hydrophobic ratio

Bin Sazali M., Kobayashi Y., Taniguchi Y., Nakashima T., Arai N.

Molecular Systems Design and Engineering （Molecular Systems Design and Engineering）  3 （ 3 ） 572 - 580 2018年06月

研究論文（学術雑誌）, 共著, 査読有り,  ISSN  2058-9689

　概要を見る

© 2018 The Royal Society of Chemistry. We have studied the self-assembled morphologies of tripod nanoparticle solutions confined in nanoslits using dissipative particle dynamics (DPD) simulations. In the present study, composite-shaped nanoparticles, like a planar tripod model with an amphiphilic surface pattern, were also synthesized experimentally. Using the DPD results at various values of a hydrophobic ratio (HR) and arm length (AL), we create phase diagrams of the self-assembled morphologies of tripod nanoparticles. With each of the two parameters, we observe three morphologies in the tripod nanoparticle solution. Further, potential energy vs. temperature for various tripod nanoparticle solutions is compared for different self-assembled structures. Our simulations offer a guide to control the morphologies of self-assembled tripod nanoparticles, which constitute novel systems that may find applications in nanofluidic devices.

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Dissipative particle dynamics simulation of the relaxation behaviour of a triblock copolymer supramolecular network

Wakimoto K., Sasaki H., Arai N.

Molecular Simulation （Molecular Simulation）  44 （ 7 ） 534 - 539 2018年05月

研究論文（学術雑誌）, 単著, 査読有り,  ISSN  08927022

　概要を見る

© 2017 Informa UK Limited, trading as Taylor & Francis Group. Since block copolymers self-assemble into various nanostructures and these are widely used in soft materials such as cosmetics and paints, these continue to be the subjects of fundamental studies that progress new technologies. ABA triblock copolymers self-organise into supramolecular networks in which crosslinked structures change upon heating and other external stimulation. Supramolecular networks that consist of ABA triblock copolymers have three components: bridges, loops and dangles. These supramolecular networks have structural regions (clusters) in which end blocks of polymer chains are aggregated and connected by the internal blocks of the polymer chains. Despite of the importance of relaxation behaviour during the measurement and control of polymer materials, the molecular-level behaviour of these systems has not been addressed. We observed pull-out phenomenon that the ends of these polymers detach from clusters, and estimated characteristic detachment times by counting the number of detachments and compared it with the time of longest relaxation in that system.

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Understanding a molecular motor walking along a microtubule: an asymmetric Brownian motor driven by bubble formation with a focus on binding affinity

Hojo M., Arai N., Ebisuzaki T.

Molecular Simulation （Molecular Simulation）  44 （ 7 ） 523 - 529 2018年05月

研究論文（学術雑誌）, 単著, 査読有り,  ISSN  08927022

　概要を見る

© 2017 Informa UK Limited, trading as Taylor & Francis Group. In recent years, many studies on a molecular motor have been conducted in the fields of biorheology and nanoengineering. The molecular motor is a molecule that converts the chemical energy obtained by ATP hydrolysis into mechanical energy. Explaining this mechanism is important for nanoengineering. A kinesin, which is a type of molecular motor, has the characteristics to move on a microtubule with hand-over-hand steps. The kinesin walking behaviour is explained by the ‘asymmetric Brownian ratchet model’. Previously, we had suggested that the walking mechanism was achieved by the bubble formation in a nanosized channel surrounded by hydrophobic atoms with the transition between the two states–bubble state and liquid state. However, the walking behaviour of the model motor was different from that of a single molecule measurement of a kinesin. In this study, we constructed a new motor system focused on the asymmetric binding affinity of a motor protein and performed a model simulation using the dissipative particle dynamics method. As a result, it was observed that hand-over-hand walking depends on the transition position ratio and the transition frequency coefficient. Moreover, the efficiency of the new motor system is higher than that of the previous motor systems. The new motor model can provide a simulation guide for the design of biomimetic nanomachines.

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Self-assembly of peptide amphiphiles by vapor pressure osmometry and dissipative particle dynamics

Seki T., Arai N., Suh D., Ozawa T., Shimada T., Yasuoka K., Hotta A.

RSC Advances （RSC Advances）  8 （ 47 ） 26461 - 26468 2018年

研究論文（学術雑誌）, 共著, 査読有り,  ISSN  2046-2069

　概要を見る

© The Royal Society of Chemistry. Peptide amphiphiles are one of the most promising materials in the biomedical field, so much effort has been devoted to characterizing the mechanism of their self-assembly and thermosensitive gelation. In this work, vapor pressure osmometry measurements were carried out to parameterize the thermosensitivity of interactions between peptide amphiphiles in an aqueous solution. The osmometry measurement verified that the peptides became more hydrophobic as temperature increased, which was quantitatively described with the Flory-Huggins χ parameter. Thereafter, a coarse-grained molecular model was used to simulate peptide amphiphiles dissolved in an aqueous solution. The temperature sensitive coarse-grained parameter aHW, which is the repulsive force between the hydrophilic head of the peptide amphiphile and water was estimated from the aforementioned experimentally obtained χ. Furthermore, the effects of concentration and temperature on the self-assembly behavior of peptide amphiphiles were quantitatively studied by dissipative particle dynamics. The simulation results revealed that aHW plays an important role in self-assembly characteristics and in the resulting microstructure of the peptide amphiphiles, which coincides with previous experimental and computational findings. The methodology in quantitatively linking the coarse-grained parameter from experiment and theory provides a sensible foundation for bridging future simulation studies with experimental work on macromolecules.

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Relationship between water permeation and flip-flop motion in a bilayer membrane

Inokuchi T., Arai N.

Physical Chemistry Chemical Physics （Physical Chemistry Chemical Physics）  20 （ 44 ） 28155 - 28161 2018年

研究論文（学術雑誌）, 共著, 査読有り,  ISSN  14639076

　概要を見る

© 2018 the Owner Societies. The lipid bilayer membrane facilitates various biological reactions and is thus an essential structure that sustains all higher forms of life. The unique local environment of the lipid bilayer plays critical roles for the diffusion of biomolecules as well as water molecules in biological reactions. Although fluctuation of the cell membrane is expected to allow for the transport of some water molecules, the flip-flop of lipid molecules corresponds to lipid transport between membrane leaflets, and is considered to be an important process to regulate the lipid composition of biological membranes. However, the relationship between these flip-flop phenomena and surrounding water molecules remains poorly understood. We hypothesized that the flip-flop is caused by water molecules permeating through the cell membrane. To test this hypothesis, we used millisecond-order coarse-grained molecular simulations (dissipative particle dynamics) to investigate the distance between water molecules and lipid molecules depending on the position of the lipid molecule. The results clearly showed that water molecules affect the flip-flop motion in the early stage, but have minimal contribution to the subsequent behavior. Moreover, based on the results of dissipative particle dynamics simulation, we computed several first-passage-time (FPT) quantities to describe the detailed dynamics of water permeation. We modeled arrangements in the middle of the flip-flop process, which were compared with the arrangement without lipid molecules. Overall, our results indicate that lipid molecules located both in perpendicular and parallel arrangements largely affect water permeation. These findings provide new insight into the detailed relationship between water permeation and the flip-flop motion.

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Janus or homogeneous nanoparticle mediated self-assembly of polymer electrolyte fuel cell membranes

Kobayashi Y., Arai N.

RSC Advances （RSC Advances）  8 （ 33 ） 18568 - 18575 2018年

研究論文（学術雑誌）, 共著, 査読有り,  ISSN  2046-2069

　概要を見る

© 2018 The Royal Society of Chemistry. The functionality of polymer electrolyte fuel cell membranes depends on the self-assembled structure of the graft polymer. To control self-assembly, nanoparticles (NPs) are often used as catalysts. Hence, we investigate the effect of hydrophilic (HI), hydrophobic (HO), and Janus nanoparticles (JNPs) for the self-assembly of graft polymers using dissipative particle dynamics (DPD) simulations. We found that the differences that appeared among the self-assembled structures of water depended on the concentration of PEFC. We also calculated the diffusion constant of water (D(H2O)) from the slopes of the time-averaged mean square displacement (MSD) curves. HI NPs had the largest effect in suppressing the diffusion of water because the HI NPs incorporated into the water particles. It was also seen that D(H2O) with various NPs gradually decreased as the number of NPs increased for three PEFC concentrations (70%, 80%, and 90%). Thus, a close correlation between the position and chemical composition of NPs in polymer electrolyte fuel cell (PEFC) membrane systems has been found. Moreover, the mean square radius of gyration 〈Rg〉 and the mean square end-to-end distance 〈R〉 was calculated to analyse the self-assembled structures of PEFC. The 〈Rg〉 and 〈R〉 increased as the concentration of PEFC was increased, with and without various NPs.

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Dissipative Particle Dynamics Simulation for Clarifying Mechanism of Water Permeation in Polymeric Membranes

Y Araki, N Arai, Y Kobayashi, T Kawaguchi, T Kaneko

Meeting Abstracts, 187-187 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

表面官能基を有するナノ粒子の自己集合に関する分子シミュレーション

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

　概要を見る

<p>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.</p>

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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

　概要を見る

<p>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．</p>

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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

　概要を見る

<p>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⁾.</p>

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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

　概要を見る

<p>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 (<i>c</i> = 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.</p>

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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

　概要を見る

<p>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．</p>

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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

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© 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

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© 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

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© 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

　概要を見る

© 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.

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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

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© 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

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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

　概要を見る

<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

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

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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

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© 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

　概要を見る

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

　概要を見る

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

　概要を見る

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

　概要を見る

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

散逸粒子動力学法を用いた界面活性剤水溶液の自己組織化の解明および高効率ナノモーターシステムの設計・開発

荒井　規允

2009年03月

学位論文（博士）, 単著, 筆頭著者, 責任著者, 査読有り

Molecular dynamics of carbon nanobearings

K Shintani, N Arai

MRS Online Proceedings Library Archive 1204 2009年

研究論文（国際会議プロシーディングス）, 査読有り

Self-assembly of surfactants and polymorphic transition in nanotubes

N Arai, K Yasuoka, XC Zeng

Journal of the American Chemical Society 130 (25), 7916-7920 （Journal of the American Chemical Society）  130 （ 25 ） 7916 - 7920 2008年

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

　概要を見る

We study self-assembly and polymorphic transitions of surfactant molecules in water within a nanotube and the effect of water-nanotube interactions on the self-assembly morphologies. We present a simulation evidence of a cornucopia of polymorphic structures of surfactant assemblies-many of which have not been observed in bulk solutions-through adjusting the water-nanotube chemical interactions which range from hydrophilic to hydroneutral and to hydrophobic. The ability to control the morphologies of surfactant assemblies within nanoscale confinement can be used for patterning the interior surface of nanochannels for application in nanofluidics and nanomedical devices. © 2008 American Chemical Society.

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Dissipative particle dynamics studies on the self-assembling dynamics of the peptide amphiphiles

T Seki, N Arai, T Ozawa, T Shimada, K Yasuoka, A Hotta

MRS Online Proceedings Library Archive 1135 （Materials Research Society Symposium Proceedings）  1135   143 - 149 2008年

研究論文（学術雑誌）, 共著, 査読有り

　概要を見る

A coarse-grained model of peptide amphiphiles (PA) dissolved in aqueous solution was presented, where the effects of PA concentration, temperature and shear stress upon the selfassembly of PA were numerically studied by dissipative particle dynamics (DPD) simulation. We technically investigate the repulsion parameter ahw which indicates the repulsion force between the hydrophilic head of PA and water molecules, hence, at the same time, indicating the change in temperature. It was found that ahw played an important role in the self-assembly dynamics and in the resulting micro-structures of PA. By imposing shear strain on the simulation system, the formation of wormlike PA micelles was accelerated. The simulation results were in good agreement with our previous experimental results and the mechanism of shear-induced transition was proposed. © 2009 Materials Research Society.

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ナノチューブ内の界面活性剤水溶液の自己組織化

荒井 規允, 泰岡 顕治, Xiao C. Zeng

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」）  57 （ 0 ） 37 - 37 2008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

界面活性剤水溶液はバルクで様々な形態を示す．球状ミセルや棒状ミセル，紐状ミセル，二分子膜，ベシクルなどが存在することが知られている．本研究では，ナノチューブに閉じ込められた界面活性剤水溶液の自己組織化について，散逸粒子動力学シミュレーションを行った．

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Spontaneous self-assembly process for threadlike micelles

N Arai, K Yasuoka, Y Masubuchi

The Journal of chemical physics 126 (24), 244905 （Journal of Chemical Physics）  126 （ 24 ） 244905 - 244905 2007年

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

　概要を見る

More than 100 μs dissipative particle dynamics simulations were carried out to investigate the spontaneous formation process of threadlike micelles from the random configuration for surfactant molecules. Stable spherical micelles were formed during the earlier stage. These spherical micelles fused to each other and grew into rodlike and threadlike micelles during the later stage. The length and radius of a micelle were estimated by tracing the backbone positions and the distance between the head group particles and the backbone of the micelles, respectively. The ratio of the largest to the smallest principal moments of inertia for each micelle was calculated as the micelle shape. © 2007 American Institute of Physics.

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D244 剪断下の散逸粒子動力学シミュレーションによる紐状ミセル水溶液のダイナミクスの解明(分子動力学2)

荒井 規允, 泰岡 顕治, 増渕 雄一

熱工学コンファレンス講演論文集 （一般社団法人 日本機械学会）  2007 （ 0 ） 319 - 320 2007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

A micelle is the self-assembly of surfactant molecules formed in surfactant aqueous solution. The micelle has various forms such as a threadlike, spherical, discoid, and bilayer. Particularly, the threadlike micelle has the great possibility of the application in the industry, utilizing the uniqueness in its formation. However, an overall understanding of the formation dynamics of the threadlike micelle has not been accomplished, because of the so-called 'mesoscopic problem' in dynamics. In this paper to clarify the multiscale dynamics in the threadlike micelles we adopted the Dissipative Particle Dynamics (DPD) simulations. Moreover, the shear stress was put on a similar system, and it comnpared it without shear stress.)

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散逸粒子動力学シミュレーションによる紐状ミセル水溶液のダイナミクスの解明

荒井 規允, 泰岡 顕治, 増渕 雄一

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」）  56 （ 0 ） 246 - 246 2007年

研究論文（研究会，シンポジウム資料等）, 共著, 筆頭著者, 査読有り

　概要を見る

界面活性剤の自己組織体の1つとして<B>紐状ミセル</B>がある．紐状ミセルはその組織形成ダイナミクスの特異性から工業的に様々な応用が模索され，一部実用化されている．しかしながら紐状ミセルを含む系のダイナミクスは時間と空間のスケールが広範囲に渡り，メソスケールダイナミクスの典型的な問題であるため理解が進んでいない．工業的応用の際にコスト等の面から重要だと思われる生成過程も，紐状ミセル系では明らかになっていない．したがって，本研究では紐状ミセルのダイナミクスを明らかにすることを目的として，メソスケールのシミュレーション方法である<B>散逸粒子動力学</B> (DPD:Dissipative Particle Dynamics) 法を用いた．

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散逸粒子動力学シミュレーションによる紐状ミセルの生成過程の解明

荒井　規允

2006年03月

学位論文（修士）, 単著, 筆頭著者, 責任著者, 査読有り

A221 散逸粒子動力学シミュレーションによる剪断流れ下における紐状ミセルの生成過程の解明(マイクロ・ナノスケール7)

荒井 規允, 泰岡 顕治, 増渕 雄一

熱工学コンファレンス講演論文集 （一般社団法人 日本機械学会）  2006 （ 0 ） 231 - 232 2006年

研究論文（研究会，シンポジウム資料等）, 共著, 筆頭著者, 査読有り

　概要を見る

A micelle is the self-assembly of surfactant molecules formed in surfactant aqueous solution. The micelle has various forms such as a threadlike, spherical, discoid, and bilayer. Particularly, the threadlike micelle has the great possibility of the application in the industry, utilizing the uniqueness in its formation. However, an overall understanding of the formation dynamics of the threadlike micelle has not been accomplished, because of the so-called 'mesoscopic problem' in dynamics. In this paper to clarify the multiscale dynamics in the threadlike micelles we adopted the Dissipative Particle Dynamics (DPD) simulations. Moreover, the shear stress was put on a similar system, and it comnpared it without shear stress.

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2807 Dissipative Particle Dynamics(DPD)法を用いた紐状ミセルの生成過程のシミュレーション(OS-28B,OS-28 熱流体の分子シミュレーション)

荒井 規允, 泰岡 顕治, 増渕 雄一

計算力学講演会講演論文集 （一般社団法人 日本機械学会）  2005 （ 0 ） 47 - 48 2005年

研究論文（研究会，シンポジウム資料等）, 共著, 筆頭著者, 査読有り

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