論文 - 荒井　規允

Molecular Dynamics Investigation of Static and Dynamic Interfacial Properties in Ice-Polymer Premelting Layers

T Sato, I Yasuda, N Arai, K Yasuoka

arXiv preprint arXiv:2504.19628 2025年

Machine learning-enabled exploration of mesoscale architectures in amphiphilic-molecule self-assembly

T Sudo, S Ishiai, Y Ishiwatari, T Yokoyama, K Yasuoka, N Arai

Next Research 2 (1), 100150 2025年

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

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

Colloids and Surfaces A: Physicochemical and Engineering Aspects 704, 135683 2025年

Composition-agnostic prediction of self-assembly in multicomponent amphiphile mixtures from molecular structure

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

arXiv preprint arXiv:2512.19724 2025年

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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Poly(vinyl alcohol)-modified poly(methyl methacrylate) particles for solid-stabilized oil-in-water emulsions (vol 697, 134433, 2024)

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

COLLOIDS AND SURFACES A-PHYSICOCHEMICAL AND ENGINEERING ASPECTS （Elsevier BV）  704   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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The authors regret to inform you that we have discovered a mistake in our original modeling of poly(methyl methacrylate) (PMMA) shown in Fig. 1(b) in Ref. [1]. We reran all-atomistic molecular dynamics (MD) simulations with the corrected molecular structure of PMMA (Fig. 1(b)) to obtain interaction parameters, a<inf>ij</inf>, and have revised a<inf>ij</inf> as shown in Table 1. In addition, the dissipative particle dynamics (DPD) simulations of the biphasic system with this corrected a<inf>ij</inf> were performed to see the behavior of poly(vinyl alcohol) (PVA) adsorbed onto the PMMA surface. We found no deviations from Fig. 10 and Fig. 11 in Ref. [1]. Therefore, the conclusion of the article [1] is unaffected. The authors would like to apologize for any inconvenience caused.

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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

　概要を見る

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

　概要を見る

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

　概要を見る

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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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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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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Investigating the Molecular Design Mechanism Behind the Hydrophobicity of Biological Surface Nanostructures: Insights from Butterfly and Mosquito Systems

F Meng, N Arai

arXiv preprint arXiv:2404.11899 2024年

Novel stabilization mechanisms for concentrated emulsions with tunable morphology via amphiphilic polymer-grafted nanoparticles

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

arXiv preprint arXiv:2408.11320 2024年

Molecular understanding for motion modes of oil droplets in aqueous solutions of ester-and amide-containing cationic surfactants

K Ueno, Y Ishiwatari, K Sasaki, T Kojima, A Takai, K Asakura, N Arai, ...

ChemRxiv 2024 (1001) 2024年

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

　概要を見る

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

　概要を見る

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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