研究者詳細 - 東　直輝

論文 - 東　直輝

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Stretching and immobilizing a single DNA molecule on a glass surface using pressure flow in a microchannel for super-resolution imaging 査読有り

Azuma, N; Suzuki, R; Fukuzawa, K; Itoh, S; Zhang, HD

AIP ADVANCES 15 巻 ( 1 ) 2025年1月

担当区分：筆頭著者,　責任著者記述言語：英語掲載種別：研究論文（学術雑誌）出版者・発行元：AIP Advances

Single-DNA analysis combines fluorescence microscopy with a method of stretching a single DNA molecule from its random coil shape to a linear shape. Although super-resolution imaging methods can be used for analyzing the DNA with a higher lateral resolution, these methods require several seconds to minutes to obtain a super-resolution image of the entire DNA molecule. Therefore, immobilizing the stretched DNA molecules on the substrate surface is essential for preventing the decrease in the lateral resolution caused by thermal fluctuations of the molecule. Previous studies utilized a method to use super-resolution imaging methods, in which a DNA molecule can be stretched by the surface tension of the air-liquid interface and immobilized on a glass surface treated with a silane coupling agent. However, achieving control over the stretch ratio of the DNA molecule poses challenges because of the difficulty in accurately adjusting the surface tension. In this study, we used the combination of stretching DNA molecules using pressure flow in a microchannel and immobilizing them on a glass surface treated with a silane coupling agent. Our results indicated that this method enabled the control of the stretch ratio of the molecule by adjusting the flow velocity and the super-resolution imaging while reducing thermal fluctuation by immobilizing the molecule on the surface. Combining the method with the super-resolution imaging method enables the analysis of single DNA molecules with higher accuracy.

DOI： 10.1063/5.0223375

Web of Science

Scopus

Manipulation and analysis of large DNA molecules by controlling their dynamics using micro and nanogaps 招待有り査読有り

Azuma, N

BIOSCIENCE BIOTECHNOLOGY AND BIOCHEMISTRY 89 巻 ( 4 ) 頁： 508 - 514 2024年12月

Temperature Dependence of Viscoelasticity of Lubricating Oil with Adsorptive Polymer Additives Sheared in Nanogaps 査読有り Open Access

Nozue, T; Itoh, S; Okubo, N; Fukuzawa, K; Zhang, HD; Azuma, N

TRIBOLOGY LETTERS 72 巻 ( 3 ) 2024年9月

記述言語：英語掲載種別：研究論文（学術雑誌）出版者・発行元：Tribology Letters

Adsorptive polymer additives have been reported to improve the retention capacity of oil films under hydrodynamic lubrication and to reduce friction under boundary lubrication. These effects are believed to result from the formation of a polymer adsorption film on the surface that acts as a lubricious coating. Polymer adsorption films have become dominant in nanometer-order microscopic gaps. However, their mechanical properties are difficult to quantify. This hinders the development of polymer additives. In our previous study, we successfully measured the shear viscoelasticity of lubricants (base oils) sheared in nanogaps using an originally developed measurement method called the fiber wobbling method (FWM). In this study, we measured the shear viscoelasticity of polymer-added lubricants in nanogaps by using FWM. In addition, we developed a heating stage in the FWM to quantify the temperature dependence of shear viscoelasticity in nanogaps. As a result, the viscosity index improved and elasticity was observed in the nanogap, where the polymer adsorption film was dominant. Furthermore, our results indicated that the elasticity of the adsorbed polymer film originated from entropic elasticity. Graphical Abstract: (Figure presented.)

DOI： 10.1007/s11249-024-01884-y

Open Access

Web of Science

Scopus

その他リンク： https://link.springer.com/article/10.1007/s11249-024-01884-y/fulltext.html

Hydration-lubrication performance improvement via synergistic effects of free polymers and polymer brushes 査読有り

Lin, FC; Itoh, S; Hirayama, T; Hirooka, C; Song, YX; Fukuzawa, K; Zhang, HD; Azuma, N

TRIBOLOGY INTERNATIONAL 191 巻頁： 109189 - 109189 2024年3月

記述言語：英語掲載種別：研究論文（学術雑誌）出版者・発行元：Tribology International

In this study, we demonstrated hydration lubricity improvement via the synergistic effects of free polymers and brush films formed on a surface. We analyzed the hydration interfacial structure using neutron reflectometry and measured the shear viscoelasticity of the film using the fiber wobbling method. The results revealed that the volume fraction of the free polymer adsorbed on the brush film increased, leading to an improvement in the load-carrying capacity. Additionally, a water-rich layer formed on the surface owing to the brush film's exclusion-volume effect, and this layer reduced the shear resistance and increased the lubricity. These insights into the composite films of polymer brushes and adsorbed free polymers offer new perspectives and design principles for the development of hydration lubrication.

DOI： 10.1016/j.triboint.2023.109189

Web of Science

Scopus

Correlation between viscoelastic response and frictional properties of hydrated zwitterionic polymer brush film in narrowing shear gap 査読有り Open Access

Lin, FC; Itoh, S; Fukuzawa, K; Zhang, HD; Azuma, N

JOURNAL OF COLLOID AND INTERFACE SCIENCE 655 巻頁： 253 - 261 2024年2月

記述言語：英語掲載種別：研究論文（学術雑誌）出版者・発行元：Journal of Colloid and Interface Science

Hypothesis: A hydrated 2-methacryloyloxyethyl phosphorylcholine (MPC) polymer brush exhibits exceptional lubricity. This lubrication mechanism has traditionally been attributed to either the inherent fluidity of the brush or the water film that forms owing to its hydrophilic nature. Given previous findings that the frictional properties of the MPC polymer brush film show load dependence, we hypothesize that the lubrication mechanism can be elucidated by examining the shear gap (varies owing to the load) dependence of the brush's viscoelastic response. Experiments: MPC polymer brush films with different thicknesses were prepared. Their viscoelastic responses were evaluated across different shear gap widths, and the frictional properties were subsequently compared across states with distinct viscoelastic behaviors. Findings: The observed shear viscoelasticity demonstrated a clear gap dependence that correlated with frictional attributes. Our data suggests that the lubrication mechanism shifts based on the shear gap. Specifically, two states exhibited low coefficients of friction: one where the osmotic pressure supports the load while allowing flexible deformation of the brush film, and the other where the brush film undergoes compression and transitions to a fully elastic state.

DOI： 10.1016/j.jcis.2023.11.013

Quantitative Measurement of Squeeze Flow Distribution in Nanogaps by Particle Image Velocimetry Using Quantum Dots 査読有り

Azuma, N; Ozeki, H; Miki, K; Fukuzawa, K; Itoh, S; Zhang, HD

TRIBOLOGY LETTERS 71 巻 ( 4 ) 2023年12月

担当区分：筆頭著者,　責任著者記述言語：英語掲載種別：研究論文（学術雑誌）出版者・発行元：Tribology Letters

The development of microfabrication and surface machining techniques has made solid surfaces more precise, and the gap dimensions in mechanical systems such as Micro Electro Mechanical Systems and Micro Total Analysis Systems have decreased from the order of micrometers to the order of nanometers. Because the fluid flow properties in nanogaps are different from those in the bulk, experimental measurement of flow velocity in nanogaps is necessary to design nanogap mechanical systems and verify the principle of their operation. In general, the lateral flow velocity distribution can be measured by mixing fluorescent particles with the fluid and tracking the particles with a microscope with high lateral and temporal resolution. However, in previous studies, quantitative measurement of flow velocity in nanogaps could not be achieved due to the influence of the interaction between the fluorescent particles and solid surfaces because the diameters of the particles were large, and ranged from tens of nm to tens of µm. The objective of this study is to quantitatively measure the lateral flow velocity distribution in nanogaps by particle image velocimetry using quantum dots with diameters in the single-digit nanometer range. We have implemented a simultaneous quantitative measurement of the nanogap shape by optical interferometry, and the flow velocity distribution by PIV using quantum dots. Focusing on the squeeze flow caused by narrowing the gap, we have shown that PIV using quantum dots can achieve quantitative measurement of velocity distribution in 100 nm-level-gaps. Graphical Abstract: [Figure not available: see fulltext.]

DOI： 10.1007/s11249-023-01783-8

Web of Science

Scopus

その他リンク： https://link.springer.com/article/10.1007/s11249-023-01783-8/fulltext.html

Effect of water on mechano-chemical reactions of perfluoropolyether lubricant films in heat-assisted magnetic recording: A reactive molecular dynamics study 査読有り

Chen, XY; Inayoshi, K; Zhang, HD; Koga, N; Fukuzawa, K; Itoh, S; Azuma, N

TRIBOLOGY INTERNATIONAL 187 巻頁： 108674 - 108674 2023年9月

掲載種別：研究論文（学術雑誌）出版者・発行元：Tribology International

A comprehensive understanding of the decomposition of perfluoropolyether (PFPE) films is crucial for establishing effective lubrication of heat-assisted magnetic recording (HAMR) systems. In this study, to examine the combined influence of heat, mechanical stress, and water, we conducted nonequilibrium reactive molecular dynamics simulations using our ReaxFF force field for the PFPE D-4OH films mixed with water. We thoroughly analyzed the reaction rates, types, pathways, and products, and identified vulnerable bonds. The results demonstrate that water significantly accelerates the reactions of D-4OH, particularly at lower normal pressures. We found that water molecules form clusters and are surrounded by the D-4OH end groups. Consequently, water induces hydrolysis of D-4OH or catalyzes reactions between D-4OH by dissociating C–O bonds in the end groups.

DOI： 10.1016/j.triboint.2023.108674

Web of Science

Scopus

High temporal resolution measurement of the curing process of nanometer-thick photocurable liquid films using the fiber wobbling method 査読有り

Itoh, S; Aratani, K; Lin, FC; Fukuzawa, K; Azuma, N; Zhang, HD

APPLIED PHYSICS EXPRESS 16 巻 ( 7 ) 2023年7月

掲載種別：研究論文（学術雑誌）出版者・発行元：Applied Physics Express

We established a method for assessing the curing process of a nanometer-thick photocurable liquid film by monitoring changes in shear viscoelasticity at a high temporal resolution. The originally developed nano-rheometry method (the fiber wobbling method) was applied for the viscoelastic measurements. We succeeded in measuring the curing process of a 100 nm thick liquid film with a time resolution of 1 ms. The experimental results suggested that the confinement effect in the nanogap suppresses liquid curing. Thus, the proposed evaluation method can be used for developing nanoimprint lithography and high-precision 3D printing. © 2023 The Japan Society of Applied Physics

DOI： 10.35848/1882-0786/ace7ad

Web of Science

Scopus

Effects of Polarity of Polymers on Conformation and Lubricating Film Formation of Adsorbed Films 査読有り

Song, YX; Fukuzawa, K; Hirayama, T; Yamashita, N; Yamada, NL; Itoh, S; Azuma, N; Zhang, HD

MACROMOLECULES 56 巻 ( 5 ) 頁： 1954 - 1964 2023年3月

記述言語：英語掲載種別：研究論文（学術雑誌）出版者・発行元：Macromolecules

The conformations and lubricating film formation ability of adsorbed films on metal surfaces formed by poly(alkyl methacrylate) (PAMA) homopolymers with different polarities from nonpolar lubricant oil were investigated. It was found that as the polarity of the polymers became higher, the chains in the adsorbed films adsorbed more loosely to the surfaces (i.e., they formed more loops and tails). The loosely adsorbed chains temporarily trapped free polymer chains flowing into the gap between sliding surfaces, resulting in a much thicker lubricating film. Thus, the sliding surfaces were better protected from wear caused by direct contact. On the other hand, flattened chains occupying in the adsorbed film formed by low polarity-polymers could not trap free polymer chains, resulting in a thinner lubricating film.

DOI： 10.1021/acs.macromol.2c02238

Web of Science

Scopus

Molecules with a TEMPO-based head group as high-performance organic friction modifiers 査読有り Open Access

Hou, J; Tsukamoto, M; Hor, S; Chen, X; Yang, J; Zhang, H; Koga, N; Yasuda, K; Fukuzawa, K; Itoh, S; Azuma, N

FRICTION 11 巻 ( 2 ) 頁： 316 - 332 2023年2月

記述言語：英語掲載種別：研究論文（学術雑誌）出版者・発行元：Friction

High-performance organic friction modifiers (OFMs) added to lubricating oils are crucial for reducing energy loss and carbon footprint. To establish a new class of OFMs, we measured the friction and wear properties of N-(2,2,6,6-tetramethyl-1-oxyl-4-piperidinyl)dodecaneamide referred to as C12Amide-TEMPO. The effect of its head group chemistry, which is characterized by a rigid six-membered ring sandwiched by an amide group and a terminal free oxygen radical, was also investigated with both experiments and quantum mechanical (QM) calculations. The measurement results show that C12Amide-TEMPO outperforms the conventional OFMs of glyceryl monooleate (GMO) and stearic acid, particularly for load-carrying capacity, wear reduction, and stability of friction over time. The friction and wear reduction effect of C12Amide-TEMPO is also greatly superior to those of C12Ester-TEMPO and C12Amino-TEMPO, in which ester and amino groups replace the amide group, highlighting the critical role of the amide group. The QM calculation results suggest that, in contrast to C12Ester-TEMPO, C12Amino-TEMPO, and the conventional OFMs of GMO and stearic acid, C12Amide-TEMPO can form effective boundary films on iron oxide surfaces with a unique double-layer structure: a strong surface adsorption layer owing to the chemical interactions of the amide oxygen and free radical with iron oxide surfaces, and an upper layer owing to the interlayer hydrogen-bonding between the amide hydrogen and free radical or between the amide hydrogen and oxygen. Moreover, the intralayer hydrogen-bonding in each of the two layers is also possible. We suggest that in addition to strong surface adsorption, the interlayer and intralayer hydrogen-bonding also increases the strength of the boundary films by enhancing the cohesion strength, thereby resulting in the high tribological performance of C12Amide-TEMPO. The findings in this study are expected to provide new hints for the optimal molecular design of OFMs. [Figure not available: see fulltext.]

DOI： 10.1007/s40544-022-0610-0

Open Access

Web of Science

Scopus

その他リンク： https://link.springer.com/article/10.1007/s40544-022-0610-0/fulltext.html

Characterization of organic friction modifiers using lateral force microscopy and Eyring activation energy model 査読有り Open Access

Hou, JC; Tsukamoto, M; Zhang, HD; Fukuzawa, K; Itoh, S; Azuma, N

TRIBOLOGY INTERNATIONAL 178 巻 2023年2月

記述言語：英語掲載種別：研究論文（学術雑誌）出版者・発行元：Tribology International

High-performance organic friction modifiers (OFMs) added to lubricating oils are crucial for reducing friction and wear under boundary lubrication. To guide the development of higher-performance OFMs, the boundary lubrication characteristics and working mechanisms of existing OFMs should be elucidated. In this study, the nanoscale frictional properties of conventional and recently developed TEMPO-based OFMs were measured using lateral force microscopy and interpreted using the Eyring activation energy model. We found that the parameters in this model provided insights into the characteristics of OFMs during loaded sliding, including the load-carrying capacity, adsorption speed, and shear-motion location. Therefore, analysis using the Eyring activation energy model effectively complements the LFM measurements and provides a new perspective for evaluating the boundary lubrication characteristics of OFMs beneficial for the development of high-performance OFMs.

DOI： 10.1016/j.triboint.2022.108052

Web of Science

Scopus

Revealing the Dependence of Lubricant Viscosity on Molecular Structure by Measuring the Temperature Dependence of Dielectric Relaxation and Viscosity 査読有り Open Access

Uchida, K; Itoh, S; Fukuzawa, K; Azuma, N; Zhang, HD

TRIBOLOGY ONLINE 18 巻 ( 3 ) 頁： 91 - 96 2023年

記述言語：英語掲載種別：研究論文（学術雑誌）出版者・発行元：Tribology Online

Reducing the viscosity of the lubricant is an effective way to improve the energy efficiency of automobiles. However, designing a lubricant with the desired properties requires elucidating the relationship between viscosity and molecular structure. In this study, we measured the temperature dependence of the dielectric relaxation of model lubricants with different molecular structures. Dielectric relaxation measurements were used to evaluate the influence of ambient viscosity on the motility of single molecules. In addition, we measured the temperature dependence of the lubricant viscosity using a rotational viscometer. By comparing the flow viscosity and dielectric relaxation measurement results, we showed that the activation volume and energy of the luburicant, which determine viscosity, can be resolved. As a result, we succeeded in quantitatively evaluating the contribution of molecular structure to changes in the activation energy, and elucidated the effect of the density of polar groups per molecule on changes in the activation volume.

DOI： 10.2474/trol.18.91

PFPE潤滑膜のメカノケミカル反応に及ぼす水の影響に関する反応分子動力学解析

陳星宇, 稲吉宏哉, 張賀東, 福澤健二, 伊藤伸太郎, 東直輝

IIP情報・知能・精密機器部門講演会講演論文集 2023 巻 ( 0 ) 頁： IIPA-1-10 2023年

誘電緩和スペクトルとずり粘度の温度依存性計測による分子構造と粘度の相関解明

内田恭輔, 伊藤伸太郎, 福澤健二, 東直輝, 張賀東

IIP情報・知能・精密機器部門講演会講演論文集 2023 巻 ( 0 ) 頁： IIPA-6-16 2023年

蛍光一分子像追跡によって得られた流速分布に基づくナノすきま内の界面スリップの推定

尾関秀隆, 東直輝, 福澤健二, 伊藤伸太郎, 張賀東

IIP情報・知能・精密機器部門講演会講演論文集 2023 巻 ( 0 ) 頁： IIPA-6-5 2023年

環境温度変化による位置変動を抑制したナノレオロジー計測用温度制御ステージの開発

野末拓海, 伊藤伸太郎, 福澤健二, 東直輝, 張賀東

IIP情報・知能・精密機器部門講演会講演論文集 2023 巻 ( 0 ) 頁： IIPA-6-11 2023年

垂直観測型エリプソメトリー顕微鏡によるナノ閉じ込めされた液体のせん断特性の定量化

加藤剛史, 福澤健二, 東直輝, 伊藤伸太郎, 張賀東, 中川勝, 縄田亮, 関淳一, 浅野俊哉

IIP情報・知能・精密機器部門講演会講演論文集 2023 巻 ( 0 ) 頁： IIPA-6-15 2023年

In-situ measurement of temporal changes in thickness of polymer adsorbed films from lubricant oil by vertical-objective-based ellipsometric microscopy 査読有り

Song, YX; Fukuzawa, K; Itoh, S; Zhang, HD; Azuma, N

TRIBOLOGY INTERNATIONAL 165 巻頁： 107341 - 107341 2022年1月

記述言語：英語掲載種別：研究論文（学術雑誌）出版者・発行元：Tribology International

Understanding the formation mechanism and conformation of the adsorbed film formed by additives is critical to clarify the boundary lubrication characteristics. In this study, using the vertical-objective-based ellipsometric microscope (VEM), which can measure nm-gaps between solid surfaces, we proposed a new method for in-situ measuring the thickness of additive adsorbed film in the lubricant oil. In this method, the adsorbed film thickness was measured by measuring the gap between the solids, which was filled by the additive film. The formation process of polyalkylmethacrylate (PAMA) polymer additive adsorbed film was successfully observed. Moreover, we revealed that the PAMA adsorbed films adopted two different conformations depending on the molecular weight and concentration of the polymer: the flattened single-layer conformation and double-layer conformation.

DOI： 10.1016/j.triboint.2021.107341

Web of Science

Scopus

ナノすき間でせん断される潤滑油のずり粘弾性と誘電緩和の同時計測

勝野翔太郎, 伊藤伸太郎, 福澤健二, 東直輝, 張賀東

IIP情報・知能・精密機器部門講演会講演論文集 2022 巻 ( 0 ) 頁： IIP2R3-H11 2022年

量子ドットの蛍光画像追跡を用いたナノすきまのスクイーズ流れ分布計測

東直輝, 美木克貴, 福澤健二, 伊藤伸太郎, 張賀東

IIP情報・知能・精密機器部門講演会講演論文集 2022 巻 ( 0 ) 頁： IIP2R3-H12 2022年

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