Papers - AZUMA Naoki

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

Naoki Azuma, Ryotaro Suzuki, Kenji Fukuzawa, Shintaro Itoh, Hedong Zhang

AIP Advances   Vol. 15 ( 1 )   2025.1

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Authorship：Lead author,　Corresponding author   Language：English   Publishing type：Research paper (scientific journal)   Publisher：AIP Publishing  

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 nano-gaps Invited Reviewed

Naoki Azuma

Bioscience, Biotechnology, and Biochemistry   Vol. 89 ( 4 ) page： 508 - 514   2024.12

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Authorship：Lead author,　Corresponding author   Language：English   Publishing type：Research paper (scientific journal)   Publisher：Oxford University Press (OUP)  

Abstract

Manipulation and analysis methods for large DNAs are critical for epidemiological, clinical, diagnostic, and fundamental research on bacteria, membrane vesicles, plants, yeast, and human cells. However, the physical properties of large DNAs often challenge their manipulation and analysis with high accuracy and speed using the conventional methods such as gel electrophoresis and column-based methods. This review presents the approaches that leverage micrometer- and nanometer-sized gaps within microchannels to control the dynamics and conformations of large DNAs, thereby overcoming these challenges. By designing gap structures and migration conditions based on the relationship between gap parameters and the physical characteristics of large DNAs—such as diameter and persistence length—these methods enable swifter and more precise manipulation and analysis of large DNAs, including size separation, concentration, purification, and single-molecule analysis.

DOI： 10.1093/bbb/zbae179

Web of Science

PubMed

Temperature Dependence of Viscoelasticity of Lubricating Oil with Adsorptive Polymer Additives Sheared in Nanogaps Reviewed Open Access

Takumi Nozue, Shintaro Itoh, Naoya Okubo, Kenji Fukuzawa, Hedong Zhang, Naoki Azuma

Tribology Letters   Vol. 72 ( 3 )   2024.9

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Language：English   Publishing type：Research paper (scientific journal)   Publisher：Springer Science and Business Media LLC  

Abstract

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

DOI： 10.1007/s11249-024-01884-y

Open Access

Web of Science

Scopus

Other Link： 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 Reviewed

Fengchang Lin, Shintaro Itoh, Tomoko Hirayama, Chizuru Hirooka, Yuxi Song, Kenji Fukuzawa, Hedong Zhang, Naoki Azuma

Tribology International   Vol. 191   page： 109189 - 109189   2024.3

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Language：English   Publishing type：Research paper (scientific journal)   Publisher：Elsevier BV  

DOI： 10.1016/j.triboint.2023.109189

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Scopus

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

Fengchang Lin, Shintaro Itoh, Kenji Fukuzawa, Hedong Zhang, Naoki Azuma

Journal of Colloid and Interface Science   Vol. 655   page： 253 - 261   2024.2

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Language：English   Publishing type：Research paper (scientific journal)   Publisher：Elsevier BV  

DOI： 10.1016/j.jcis.2023.11.013

Open Access

Web of Science

Scopus

PubMed

Quantitative Measurement of Squeeze Flow Distribution in Nanogaps by Particle Image Velocimetry Using Quantum Dots Reviewed

Naoki Azuma, Hidetaka Ozeki, Katsuki Miki, Kenji Fukuzawa, Shintaro Itoh, Hedong Zhang

Tribology Letters   Vol. 71 ( 4 )   2023.12

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Authorship：Lead author,　Corresponding author   Language：English   Publishing type：Research paper (scientific journal)   Publisher：Springer Science and Business Media LLC  

DOI： 10.1007/s11249-023-01783-8

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Scopus

Other Link： 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 Reviewed

Xingyu Chen, Koya Inayoshi, Hedong Zhang, Nobuaki Koga, Kenji Fukuzawa, Shintaro Itoh, Naoki Azuma

Tribology International   Vol. 187   page： 108674 - 108674   2023.9

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Publishing type：Research paper (scientific journal)   Publisher：Elsevier BV  

DOI： 10.1016/j.triboint.2023.108674

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Scopus

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

Shintaro Itoh, Kohei Aratani, Fengchang Lin, Kenji Fukuzawa, Naoki Azuma, Hedong Zhang

Applied Physics Express   Vol. 16 ( 7 )   2023.7

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DOI： 10.35848/1882-0786/ace7ad

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Scopus

Effects of Polarity of Polymers on Conformation and Lubricating Film Formation of Adsorbed Films Reviewed

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

MACROMOLECULES   Vol. 56 ( 5 ) page： 1954 - 1964   2023.3

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Language：English   Publishing type：Research paper (scientific journal)   Publisher：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 Reviewed Open Access

Jinchi Hou, Masaki Tsukamoto, Seanghai Hor, Xingyu Chen, Juntao Yang, Hedong Zhang, Nobuaki Koga, Koji Yasuda, Kenji Fukuzawa, Shintaro Itoh, Naoki Azuma

Friction   Vol. 11 ( 2 ) page： 316 - 332   2023.2

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Language：English   Publishing type：Research paper (scientific journal)   Publisher：Springer Science and Business Media LLC  

Abstract

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.

DOI： 10.1007/s40544-022-0610-0

Open Access

Web of Science

Scopus

Other Link： 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 Reviewed Open Access

Jinchi Hou, Masaki Tsukamoto, Hedong Zhang, Kenji Fukuzawa, Shintaro Itoh, Naoki Azuma

Tribology International   Vol. 178   2023.2

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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

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Scopus

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

Kyosuke Uchida, Shintaro Itoh, Kenji Fukuzawa, Naoki Azuma, Hedong Zhang

Tribology Online   Vol. 18 ( 3 ) page： 91 - 96   2023

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Language：English   Publishing type：Research paper (scientific journal)   Publisher：Japanese Society of Tribologists  

<p>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.</p>

DOI： 10.2474/trol.18.91

Open Access

Web of Science

Scopus

CiNii Research

Effect of Water on Mechanochemical Reactions of PFPE Lubricant Films: A Reactive Molecular Dynamics Study

CHEN Xingyu, INAYOSHI Koya, ZHANG Hedong, FUKUZAWA Kenji, ITOH Shintaro, AZUMA Naoki

The Proceedings of the Conference on Information, Intelligence and Precision Equipment : IIP   Vol. 2023 ( 0 ) page： IIPA-1-10   2023

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Language：Japanese   Publisher：The Japan Society of Mechanical Engineers  

<p>Using molecular dynamics with our developed reactive force field, we investigated the effect of water on the mechanochemical reaction of nanometer-thick perfluoropolyether D-4OH films at the head–disk interface of heat-assisted magnetic recording. Three types of reactions were observed: hydrolysis, end group–end group association (EEA) reaction, and end group–main chain association (EMA) reaction. The simulation results showed that water molecules accelerate the decomposition of D-4OH and such effect is more noticeable at low pressures than at high pressures. The presence of water induces hydrolysis and accelerates the EEA reaction, whereas the EMA reaction is greatly accelerated by pressure rather than water.</p>

DOI： 10.1299/jsmeiip.2023.iipa-1-10

CiNii Research

Elucidation of Correlation between Molecular Structure and Viscosity by Measuring Temperature Dependence of Dielectric Relaxation Spectra and Shear Viscosity

UCHIDA Kyosuke, ITOH Shintaro, FUKUZAWA Kenji, AZUMA Naoki, ZHANG Hedong

The Proceedings of the Conference on Information, Intelligence and Precision Equipment : IIP   Vol. 2023 ( 0 ) page： IIPA-6-16   2023

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Language：Japanese   Publisher：The Japan Society of Mechanical Engineers  

<p>Reducing lubricant viscosity is one effective way to improve the energy efficiency of automobiles. Designing a lubricant with the desired properties requires elucidating the relation between viscosity and molecule structure. In this study, we measured the temperature dependence of dielectric relaxation for lubricants with different molecular structures. The dielectric relaxation measurements can evaluate the motility of single molecules influenced by the ambient viscosity. Additionally, we measured the temperature dependence of lubricant viscosity with a rotational viscometer. By comparing the results of both flow viscosity and dielectric relaxation measurements, we find a correlation between flow activation energy and single-molecule mobility when viscosity is dependent on molecular weight, while there is no correlation between them when polarity dominantly affects viscosity.</p>

DOI： 10.1299/jsmeiip.2023.iipa-6-16

CiNii Research

Estimation of surface slippage in nanogap based on flow velocity distributions obtained by nanoparticle image velocimetry

OZEKI Hidetaka, AZUMA Naoki, FUKUZAWA Kenji, ITOH Shintaro, ZHANG Hedong

The Proceedings of the Conference on Information, Intelligence and Precision Equipment : IIP   Vol. 2023 ( 0 ) page： IIPA-6-5   2023

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Language：Japanese   Publisher：The Japan Society of Mechanical Engineers  

<p>With the development of microfabrication and surface treatment technologies, the gaps between elements in mechanical and electronic components have narrowed from the micrometer to the nanometer-sized. Fluid slippage at the solid/liquid interface is one of the phenomena that are considered to occur in micro/nanometer-sized gaps, and frictional properties there are expected to be different from those in macro gaps. For proper lubrication design in nanometer-sized gap, it is necessary to quantify the slippage at the interface. In this study, we used the fluorescence tracking of quantum dots with diameters of a few nanometers to measure the squeezed flow in nanometer-sized gap. Quantitative lateral velocity distributions were measured, and we estimated the slippage based on our proposed analysis of the number distribution of measured velocity values that depends on the flow profile in the depth direction. Our obtained results suggested that interfacial slippage occurred in the gap about less than 200 nm.</p>

DOI： 10.1299/jsmeiip.2023.iipa-6-5

CiNii Research

Development of a Temperature Control Stage for Nano Rheology Measurement Suppressing Positional Fluctuations Caused by Environmental Temperature Changes

NOZUE Takumi, ITOH Shintaro, FUKUZAWA Kenji, AZUMA Naoki, ZHANG Hedong

The Proceedings of the Conference on Information, Intelligence and Precision Equipment : IIP   Vol. 2023 ( 0 ) page： IIPA-6-11   2023

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Language：Japanese   Publisher：The Japan Society of Mechanical Engineers  

<p>Polymer additives in lubrication oils are known to play a role as viscosity index improvers that change the temperature dependence of viscosity. On the other hand, it is assumed that polymers adsorbed on surfaces contribute to low friction, and clarification of their mechanical properties and temperature dependence is essential for lubrication design. In our previous research, we have successfully measured the gap dependence of mechanical properties (shear viscoelasticity) of base oils by applying the fiber wobbling method (FWM), a nano-rheological measurement method that we originally developed. In this study, we developed a temperature-control stage for FWM to measure the temperature dependence of shear viscoelasticity in nano-gaps of polymer-added lubricants.</p>

DOI： 10.1299/jsmeiip.2023.iipa-6-11

CiNii Research

Quantifying Shear Properties of Nano-Confined Liquids Using Vertical Objective Ellipsometric Microscopy

KATO Tsuyohi, FUKUZAWA Keji, AZUMA Noaki, Itoh Shintaro, ZHANG Hedong, NAKAGAWA Masaru, NAWATA Ryo, SEKI Junichi, ASANO Toshiya

The Proceedings of the Conference on Information, Intelligence and Precision Equipment : IIP   Vol. 2023 ( 0 ) page： IIPA-6-15   2023

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Language：Japanese   Publisher：The Japan Society of Mechanical Engineers  

<p>To elucidate the cause of increase in shear resistance in alignment process for nano imprint lithography (NIL), by using vertical-objective-type ellipsometric microscopy (VEM) combined with a micro-cylinder structure and gap feedback-control, shear response of nano-confined liquid film mimicking a NIL resist film were measured. The three kinds of samples were prepared; monomer, monomer with release agent, and monomer with polymerization initiator. The increase in the shear resistance force was not detected with the monomer alone, but with the addition of additives. The shear response waveforms indicated that the resist solidifies at nanometer gaps and may melt above the yield shear force. These results suggest that the additive is unevenly distributed near the sliding solid surfaces and changes the physical properties of the monomer near the solid surfaces, resulting in a significant increase in shear resistance force at the nano gaps. This mechanism is thought to be responsible for the increased shear resistance force in the NIL alignment process as well.</p>

DOI： 10.1299/jsmeiip.2023.iipa-6-15

CiNii Research

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

Yuxi Song, Kenji Fukuzawa, Shintaro Itoh, Hedong Zhang, Naoki Azuma

Tribology International   Vol. 165   page： 107341 - 107341   2022.1

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Language：English   Publishing type：Research paper (scientific journal)   Publisher：Elsevier BV  

DOI： 10.1016/j.triboint.2021.107341

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Scopus

Simultaneous Measurement of Shear Viscoelasticity and Dielectric Relaxation of Lubricant Oil Sheared in Nanometer-sized Gaps

KATSUNO Shotaro, ITOH Shintaro, FUKUZAWA Kenji, AZUMA Naoki, ZHANG Hedong

The Proceedings of the Conference on Information, Intelligence and Precision Equipment : IIP   Vol. 2022 ( 0 ) page： IIP2R3-H11   2022

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Language：Japanese   Publisher：The Japan Society of Mechanical Engineers  

DOI： 10.1299/jsmeiip.2022.iip2r3-h11

CiNii Research

Observing squeeze flow in nanometer-sized gap using fluorescent images of quantum dots

AZUMA Naoki, MIKI Katsuki, FUKUZAWA Kenji, ITOH Shintaro, ZHANG Hedong

The Proceedings of the Conference on Information, Intelligence and Precision Equipment : IIP   Vol. 2022 ( 0 ) page： IIP2R3-H12   2022

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Language：Japanese   Publisher：The Japan Society of Mechanical Engineers  

<p>With the development of microfabrication and surface processing technologies, gap between two solid surfaces in Micro electro mechanical systems (MEMS) and Micro total analysis system (μTAS) becomes microgap to nanogap. For designing the devices and verifying the principle of MEMS and μTAS, experimental method to measure flow distribution of fluid confined in nanogap is required. In this study, we aim to realize the measurement of the flow distribution of squeezed flow in the nanogap using fluorescence images of nanoparticles. We evaluated the validity of our experimental method by comparing our experimental results with the theoretical results and clarified the size of nanogap that can be measured using our method.</p>

DOI： 10.1299/jsmeiip.2022.iip2r3-h12

CiNii Research

Molecular Dynamics Study of Mechanochemical Reactions of PFPE Lubricant Films in the Presence of Water and Oxygen

INAYOSHI Koya, AOTO Takumi, CHEN Xingyu, ZHANG Hedong, FUKUZAWA Kenji, ITOH Shintaro, AZUMA Naoki

The Proceedings of the Conference on Information, Intelligence and Precision Equipment : IIP   Vol. 2022 ( 0 ) page： IIP2R1-A06   2022

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Language：Japanese   Publisher：The Japan Society of Mechanical Engineers  

<p>Using molecular dynamics with our developed reactive force field, we investigated the effect of water and/or oxygen on the mechanochemical reaction of nanometer-thick perfluoropolyether D-4OH films at the head–disk interface of heat-assisted magnetic recording. The simulation results showed that the presence of oxygen, water, or both accelerated the mechanochemical reaction of D-4OH. For oxygen only, no decomposition reaction occurred, and oxidation reactions were observed in which an oxygen molecule was inserted between the C–C bond in the end group of D-4OH. In contrast, in the presence of water, hydrolysis decomposition reactions at the C–O bond in the end group of D-4OH occurred frequently, and polymerization reactions were also observed.</p>

DOI： 10.1299/jsmeiip.2022.iip2r1-a06

CiNii Research

Thickness control method of liquid films with nanometer resolution using molecular interaction between solid and liquid

Saitoh Yuki, Fukuzawa Kenji, Itoh Shintaro, Azuma Naoki, Zhang Hedong

The Proceedings of the Conference on Information, Intelligence and Precision Equipment : IIP   Vol. 2022 ( 0 ) page： IIP2R3-H05   2022

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Language：Japanese   Publisher：The Japan Society of Mechanical Engineers  

<p>Thickness control of thin liquid films is useful in various fields for the control of physical properties of solid surfaces such as wettability and multilayer fabrication using light-curing resin liquid films. In this report, we propose a precise thickness control method with nanometer-order resolution using intermolecular interaction between solid and liquid, and report its experimental verification.</p>

DOI： 10.1299/jsmeiip.2022.iip2r3-h05

CiNii Research

Fabrication of Microfluidic Device by Reactive Ion Etching and Focused Ion Beam Milling Invited

AZUMA Naoki

JOURNAL OF JAPANESE SOCIETY OF TRIBOLOGISTS   Vol. 66 ( 10 ) page： 762 - 767   2021.10

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Language：Japanese   Publishing type：Research paper (other academic)   Publisher：Japanese Society of Tribologists  

<p>Microfluidic devices are technologies that integrate micro- and nano-meter sized structures in a microchannel using a microfabrication technique. In this article, I focused on the fabrication process of our developed microfluidic device which is based on the principle of size exclusion chromatography for DNA separation. Since this device has microfence structures and nanoslit structures in a microchannel, its fabrication process consists of a photolithography and a reactive ion etching for creating the microfence structures and a focused ion beam milling for creating the nanoslit structures. Additionally, I introduced the experimental results of DNA separation using our fabricated microfluidic device. Beyond the research field of analytical chemistry, microfluidic devices have been utilized to other research fields such as rheology for the measurement of viscosity and flow distribution of liquids. I hope that this article will be of interest to the readership in the research field of tribology.</p>

DOI： 10.18914/tribologist.66.10_762

CiNii Research

Prologue to the Special Issue on “Fabrication Technologies of Micro and Nano Structures and Their Applications” Invited

AZUMA Naoki

JOURNAL OF JAPANESE SOCIETY OF TRIBOLOGISTS   Vol. 66 ( 10 ) page： 737 - 737   2021.10

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Language：Japanese   Publishing type：Research paper (other academic)   Publisher：Japanese Society of Tribologists  

DOI： 10.18914/tribologist.66.10_737

CiNii Research

Super-localization of individual fluorophores along a DNA strand in a microchannel Reviewed

Naoki Azuma, Kenji Fukuzawa, Shintaro Itoh

Applied Physics Letters   Vol. 119 ( 2 ) page： 023701 - 023701   2021.7

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Authorship：Lead author,　Corresponding author   Language：English   Publishing type：Research paper (scientific journal)  

DOI： 10.1063/5.0046939

Measurement of escape time of concentrated DNA molecules in front of a nanogap Reviewed

Naoki Azuma, Kenji Fukuzawa, Shintaro Itoh

Applied Physics Express   Vol. 14 ( 1 ) page： 015001 - 015001   2021.1

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Language：Japanese   Publishing type：Research paper (scientific journal)   Publisher：{IOP} Publishing  

DOI： 10.35848/1882-0786/abd199

Scopus

Other Link： https://iopscience.iop.org/article/10.35848/1882-0786/abd199/pdf

Simultaneous Measurement of Viscoelasticity and Film Thickness during Shearing of Patterned Hydrated Polymer Brush Film

LIN Fengchang, ITOH Shintaro, FUKUZAWA Kenji, ZHANG Hedong, AZUMA Naoki

The Proceedings of the Conference on Information, Intelligence and Precision Equipment : IIP   Vol. 2021 ( 0 ) page： IIP1B1-4   2021

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Language：Japanese   Publishing type：Research paper (other academic)   Publisher：The Japan Society of Mechanical Engineers  

<p>2-methacryloyloxyethyl phosphorylcholine (MPC) polymer is a promising coating material for extending the useful life of artificial joints due to its biocompatibility and lubricity. Especially, the hydrated brush-like MPC polymer film showed a low coefficient of friction. However, the mechanism of the lubricity is not fully understood. Friction coefficients of the MPC polymer films showed dependency on the shear gap, which must be caused by the thickness dependence of the film's mechanical properties (viscoelasticity). However, due to the thin film thickness (around 100 nm), it was difficult to measure the viscoelasticity. Thus, this research aimed to measure the hydrated MPC polymer brush film's viscoelasticity and elucidate its gap dependency. We established a measurement method that realizes simultaneous measurement of shear viscoelasticity and film thickness.</p>

DOI： 10.1299/jsmeiip.2021.iip1b1-4

CiNii Research

Measurement of Surface Adsorption Characteristics to Elucidate the Action Mechanism of Organic Friction Modifiers in Lubricating Oil

KUZUYA Kohei, ZHANG Hedong, FUKUZAWA Kenji, ITOH Shintaro, AZUMA Naoki, HOR Seanghai, TSUKAMOTO Masaki

The Proceedings of the Conference on Information, Intelligence and Precision Equipment : IIP   Vol. 2021 ( 0 ) page： IIP1B1-2   2021

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Language：Japanese   Publishing type：Research paper (other academic)   Publisher：The Japan Society of Mechanical Engineers  

<p>High performance environment-friendly organic friction modifier (OFM) additives are crucial for reducing energy loss and greenhouse gases due to friction and wear. In this study, we designed and synthesized a new type of TEMPO-based OFMs which contain a cyclic structure and free radical. In addition to friction and wear measurements, surface adsorption characteristics of the OFMs were measured with quartz crystal microbalance (QCM). We confirmed that Amide-TEMPO exhibits better friction and wear reduction effect than the conventional glyceryl monooleate. The friction coefficient correlated negatively with the adsorption equilibrium constant, but it showed no correlation with the adsorption density. The anti-wear performance showed no correlation with both adsorption equilibrium constant and adsorption density, suggesting that it is difficult to interpret the wear characteristics simply from the static adsorption characteristics measured by QCM.</p>

DOI： 10.1299/jsmeiip.2021.iip1b1-2

CiNii Research

Measurement of squeeze flow in micrometer-sized gap using single molecule tracking of quantum dot

MIKI Katsuki, AZUMA Naoki, FUKUZAWA Kenji, ITOH Shintaro, ZHANG Hedong

The Proceedings of the Conference on Information, Intelligence and Precision Equipment : IIP   Vol. 2021 ( 0 ) page： IIP1B1-3   2021

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Language：Japanese   Publishing type：Research paper (other academic)   Publisher：The Japan Society of Mechanical Engineers  

<p>The lubrication phenomena of lubricants confined in a nanometer-sized gap are different from those in the bulk state. Clarifying the mechanism of them requires the method to measure the lubricant flow in the nanometer-sized gap. Therefore, we proposed the method to measure the lubricant flow using single molecule tracking of quantum dots with the fluorescence microscope. A single quantum dot has the diameter of several tens of nm and can be applied to measure the lubricant flow in nanometer-sized gap. In this study, we tried to measure the squeeze flow of lubricants in micrometer-sized gap to verify the validity of our proposed method. Our obtained velocities of the squeeze flow were good agreement with those of theoretical model, that indicated the validity of our method.</p>

DOI： 10.1299/jsmeiip.2021.iip1b1-3

CiNii Research

Reactive Molecular Dynamics Study of Effect of Water and Oxygen Molecules on Decomposition of PFPE Lubricant Films in Heat-Assisted Magnetic Recording

AOTO Takumi, CHEN Xingyu, ZHANG Hedong, FUKUZAWA Kenji, ITOH Shintaro, AZUMA Naoki

The Proceedings of the Conference on Information, Intelligence and Precision Equipment : IIP   Vol. 2021 ( 0 ) page： IIP2A3-3   2021

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Language：Japanese   Publishing type：Research paper (other academic)   Publisher：The Japan Society of Mechanical Engineers  

<p>To realize heat-assisted magnetic recording (HAMR), which can largely increase the recording density of hard disk drives, it is crucial to ensure the reliability and durability of the head disk interface (HDI) that involves high temperature and high-speed shear. In this study, we performed reactive molecular dynamics simulations to clarify the effects of water and oxygen molecules on the decomposition of nanometer-thick perfluoropolyether D-4OH films that lubricate the HDI of HAMR. From the simulation results, we found that water molecules accelerate the decomposition of D-4OH and this effect is suppressed by the presence of oxygen molecules. We also found that high normal pressures and concentrations of water and oxygen molecules lead to fast decomposition of D-4OH molecules.</p>

DOI： 10.1299/jsmeiip.2021.iip2a3-3

CiNii Research

Optimizing on-chip concentration of DNA molecules against a nanoslit barrier Reviewed

Naoki Azuma, Shintaro Itoh, Kenji Fukuzawa

Microfluidics and Nanofluidics   Vol. 24 ( 86 ) page： 13   2020.10

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DOI： 10.1007/s10404-020-02392-w

Scopus

ReaxFF Reactive Molecular Dynamics Simulations of Mechano-chemical Decomposition of Perfluoropolyether Lubricants in Heat-assisted Magnetic Recording Reviewed

Xingyu Chen, Kento Kawai, Hedong Zhang, Kenji Fukuzawa, Nobuaki Koga, Shintaro Itoh, Naoki Azuma

Journal of Physical Chemistry C   Vol. 124 ( 41 ) page： 22496–22505   2020.9

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DOI： 10.1021/acs.jpcc.0c06486

Extension of measurement range of lubrication gap shape using vertical-objective-type ellipsometric microscopy with two compensator angles Reviewed

Katsuya Namba, Kenji Fukuzawa, Shintaro Itoh, Hedong Zhang, Naoki Azuma

Tribology International   Vol. 142 ( 105980 ) page： 8   2020.2

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Language：Japanese   Publishing type：Research paper (scientific journal)  

DOI： 10.1016/j.triboint.2019.105980

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Scopus

Viscosity measurement of lubricant at uniform small gaps by combining microfluidic device and fluorescence correlation spectroscopy

KIMOTO Takayuki, FUKUZAWA Kenji, ITOH Shintrao, AZUMA Naoki, ZHANG Hedong

The Proceedings of the Conference on Information, Intelligence and Precision Equipment : IIP   Vol. 2020 ( 0 ) page： 2C08   2020

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Measurement of the viscosity of the lubricant in the minute gap is important for elucidating the boundary and mixed lubrication characteristics. It has become clear that the lubricant has a specific viscosity depending on the small gap. Since the viscosity depends on the gap, measurement at a constant (uniform) gap in the measurement region was essential, but it was difficult with a gap of the order of 10 nm. In this study, we propose a method for measuring the viscosity of lubricant in a uniform small gap by combining microfluidic device and fluorescence correlation spectroscopy.

DOI： 10.1299/jsmeiip.2020.2c08

CiNii Research

Shear gap determination method by optical interference fringes measurement for quantifying shear viscoelasticity of nanometer-thick phospholipid polymer brush films

LIN Fengchang, ITOH Shintaro, FUKUZAWA Kenji, ZHANG Hedong, AZUMA Naoki

The Proceedings of Mechanical Engineering Congress, Japan   Vol. 2020 ( 0 ) page： J13111   2020

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<p>2-Methacryloyloxyethyl phosphorylcholine (MPC) polymer is used as coating material on artificial joint for its hydrated lubricity. In order to elucidate the mechanism of the hydrated lubrication, in this research, we measure the shear viscoelasticity of hydrated MPC polymer films by using a fiber wobbling method (FWM). Simultaneously, we measure the shearing gap by combining microscope underneath the FWM setup and observing the interference fringe. We found that both viscosity and elasticity increased along with the decreasing of gap width. However, the MPC polymer showed a transition from viscous dominant to elastic dominant when the gap is smaller than a certain gap width. This implies that MPC films reduce friction as a low viscos fluid in large shearing gaps and prevent contact between surfaces in small gaps for reducing friction and wear. This may explain the mechanism of hydrated lubrication of MPC film coated on a surface of artificial joint.</p>

DOI： 10.1299/jsmemecj.2020.j13111

CiNii Research

Molecular Elongation of Large Molecular Weight DNA Electrophoresed in Nanoslit Channel and Its Voltage Dependence

NAGATA Haruka, ITOH Shintaro, AZUMA Naoki, FUKUZAWA Kenji, ZHANG Hedong

The Proceedings of the Conference on Information, Intelligence and Precision Equipment : IIP   Vol. 2020 ( 0 ) page： 2C05   2020

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Nanopore sequencer is expected as a core technology for realizing medical treatment based on genome information. In order to improve the analysis efficiency, it is necessary to be able to analyze a large molecular size genomic DNA (large molecular weight DNA) with one molecule. Large molecular weight DNA has a random coil structure in a stable state. Therefore, it is indispensable to establish the technology to extend the random coil-shaped DNA molecule linearly in order to realize the analysis with the nanopore sequencer. In this study, we experimentally verified the effect of migration conditions on the elongation rate of DNA molecules that elongate during electrophoresis in a nanoslit. The results showed that DNA elongation was significantly affected not only by the geometric conditions of the flow channel, but also by the electric field distribution (position within the nanoslit) and the migration speed.

DOI： 10.1299/jsmeiip.2020.2c05

CiNii Research

Dependence of stretching rate of DNA molecules on gas/liquid interface velocity in combing method using microchannel

AZUMA Naoki, ASAI Taihei, FUKUZAWA Kenji, ITOH Shintaro, ZHANG Hedong

The Proceedings of the Conference on Information, Intelligence and Precision Equipment : IIP   Vol. 2020 ( 0 ) page： 2C06   2020

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In this study, we stretched and immobilized a 48.5 kbp-DNA molecule using a pressure flow and a gas-liquid interface movement in a microchannel. A chip device with a straight microchannel was fabricated by transfering Si mold created by a photolithography to PDMS. The depth and width of the microchannel were 2 μm and 100 μm, respectively. We controlled the velocities of the pressure flow and the gas-liquid interface by controlling applied pressures into the microchannel in order to investigate the dependence of stretched rate of the DNA molecule on the velocities. We measured the sizes of stretched and immobilized DNA molecules in the microchannel at each applied pressure by analysing the fluorescent images obtained using a fluorescence microscope. We indicated that the increase of the applied pressure improved the stretched rate of DNAs and achieved the stretched rate of 70 % under the condition of 1150 μm / s (600 mbar).

DOI： 10.1299/jsmeiip.2020.2c06

CiNii Research

Viscosity measurement of lubricant at uniform small gaps by fluorescence correlation spectroscopy with micro-fluidic device

HASEGAWA Sho, KIMOTO Takayuki, FUKUZAWA Kenji, ITOH Shintaro, ZHANG Hedong

The Proceedings of Mechanical Engineering Congress, Japan   Vol. 2020 ( 0 ) page： J13112   2020

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DOI： 10.1299/jsmemecj.2020.j13112

CiNii Research

Verification of the effect of electric field strength and gradient on the elongation of DNA molecules using the confinement effect

NAGATA Haruka, Itoh Shintaro, Azuma Naoki, Fukuzawa Kenji, Zhang Hedong

The Proceedings of Mechanical Engineering Congress, Japan   Vol. 2020 ( 0 ) page： J13115   2020

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<p>For reading out genomic information from a single molecule of DNA, it is required to establish a DNA extension method that stretches a DNA molecule existing in a random coil state in a solution. To achieve highly stretched DNA molecules, we utilized and experimentally verified the effect of hydrodynamic drag force and electric field gradient in addition to the effect of nano-confinement; channels heights smaller than the persistence length of DNA molecules. In our experimental results, we revealed that the higher the migration velocity, the higher the elongation rate of DNA molecules. Moreover, by comparing the elongation rate of molecules measured in rectangular and taper-shaped nanoslits, we were able to achieve a higher degree of elongation in the latter type, which had the electric field gradient.</p>

DOI： 10.1299/jsmemecj.2020.j13115

CiNii Research

Friction Properties of Hydrated Phospholipid Polymer Brush Films Prepared by Surface Initiated Graft Polymerization

HIROOKA Chizuru, ITOH Shintaro, FUKUZAWA Kenji, Zhang Hedong, AZUMA Naoki

The Proceedings of Mechanical Engineering Congress, Japan   Vol. 2020 ( 0 ) page： J13121   2020

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DOI： 10.1299/jsmemecj.2020.j13121

CiNii Research

Coarse-grained Molecular Dynamics Study of Effect of Surface Roughness on Adsorption Behavior of Fatty Acid Additives in Lubricating Oil

TANG Jiahao, ZHANG Hedong, FUKUZAWA Kenji, ITOH Shintaroh, AZUMA Naoki

The Proceedings of Mechanical Engineering Congress, Japan   Vol. 2020 ( 0 ) page： J13109   2020

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<p>Coarse-grained molecular dynamics simulations were performed to compare the adsorption of organic friction modifier (OFM) added in lubricating oil to flat and corrugated surfaces. Stearic acid, dodecane, and hematite were used as the OFM, lubricating oil, and solid surfaces, respectively. The simulation results showed that the increase in the surface number density of adsorbed stearic acid molecules in 100 ns simulations at 353 K was approximately four times faster on the corrugated surface than on the flat surface. We infer that surface roughness may promote adsorption of OFM additives, owing to the enhanced liquid–solid interactions at the corners formed between adjacent layers of solid surfaces.</p>

DOI： 10.1299/jsmemecj.2020.j13109

CiNii Research

Reactive Molecular Dynamics Study of Thermal Decomposition and Transfer of Perfluoropolyether Lubricant in Heat-assisted Magnetic Recording

CHEN Xingyu, ZHANG Hedong, FUKUZAWA Kenji, ITOH Shintaro, AZUMA Naoki

The Proceedings of Mechanical Engineering Congress, Japan   Vol. 2020 ( 0 ) page： S16102   2020

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<p>To achieve reliable heat-assisted magnetic recording (HAMR), it is crucial to understand the decomposition of perfluoropolyether (PFPE) lubricant films. In this study, we performed reactive all-atom molecular dynamics simulations to investigate the thermal decomposition of PFPE D-4OH using our original ReaxFF force field. The results showed that the thermal decomposition of D-4OH molecules is mainly attributed to the dissociation of C–O bond in the polar end groups and the dissociated fragments transfer from the disk to head and form smears. On the other hand, by quantifying the decomposition time constants at 700 and 800 K, we infer that the thermal decomposition of D-4OH films hardly occurs within the HAMR heating time of ~1 ns.</p>

DOI： 10.1299/jsmemecj.2020.s16102

CiNii Research

Reactive Molecular Dynamics Study of Mechano-chemical Decomposition of Perfluoropolyether Lubricants in Heat-assisted Magnetic Recording

CHEN Xingyu, KAWAI Kento, ZHANG Hedong, FUKUZAWA Kenji, ITOH Shintaro, AZUMA Naoki

The Proceedings of the Conference on Information, Intelligence and Precision Equipment : IIP   Vol. 2020 ( 0 ) page： 1A06   2020

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Language：Japanese   Publisher：The Japan Society of Mechanical Engineers  

To achieve effective lubrication of head-disk interface in heat-assisted magnetic recording (HAMR),
mechano-chemical decomposition of nonpolar and polar perfluoropolyether (PFPE) lubricant films, i.e., Z, Z-tetraol, Demnum, and D-4OH, was investigated using reactive molecular dynamics. By fitting with quantum calculation results, the reactive force field (ReaxFF) for PFPE was developed, allowing simulation of chemical reactions of PFPE lubricants. The results showed that at a temperature of 700 K, pure thermal decomposition of PFPE hardly occurs within the nanosecond heating time of HAMR, whereas mechano-chemical decomposition is highly possible to occur when normal pressure and shear are applied by the head and disk. We confirmed that thermal decomposition is mainly caused by the dissociation of C–O bond at the polar end groups and mechano-chemical decomposition is caused by dissociation of C–O bonds at both the polar end groups and main chains.

DOI： 10.1299/jsmeiip.2020.1a06

CiNii Research

Dynamic Viscoelasticity of Hydrated Phospholipid Polymer Brush Measured by Fiber Wobbling Method Invited Reviewed

S. Itoh, S. Aoyama, Y. Higashizaka, K. Fukuzawa, H. Zhang, N. Azuma

Proceedings of the STLE/ASME International Joint Tribology Conference     2019.10

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Gap and Shear Rate Dependence of Viscoelasticity of Lubricants with Polymer Additives Sheared in Nano Gaps Invited Reviewed

S Itoh, R Aoki, K Fukuzawa, H Zhang, N Azuma, Y Onumata

Proceedings of the STLE/ASME International Joint Tribology Conference     2019.10

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Measurement of Trapping Time of DNA Molecule in front of Nanogap Using Concentration Method

AZUMA Naoki, FUKUZAWA Kenji, ITOH Shintaro, ZHANG Hedong

The Proceedings of the Symposium on Micro-Nano Science and Technology   Vol. 2019.10 ( 0 ) page： 21pm1PN319   2019

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<p>When a DNA molecule passes through a nanochannel which depth is smaller than its size, the molecule is trapped in front of the nanochannel based on an entropy trap. Trapping time τ is a parameter to characterize the entropy trap and measuring trapping time τ accurately is required to design DNA separation and concentration methods based on the entropy trap. In this study, we proposed an experimental measurement method of trapping time τ using DNA concentration method. We fabricated a chip device with a nanogap of 25-nm depth in a microchannel using microfabrication technique and succeeded in determining the voltage V dependence of trapping time τ of 48.5-kbp DNA by experiments with 0.8 - 1.2 V.</p>

DOI： 10.1299/jsmemnm.2019.10.21pm1pn319

CiNii Research

Determination of optimal voltage by theoretical model for DNA concentration using nanoslit

AZUMA Naoki, FUKUZAWA Kenji, ITOH Shintaro, ZHANG Hedong

The Proceedings of the Conference on Information, Intelligence and Precision Equipment : IIP   Vol. 2019 ( 0 ) page： 2C01   2019

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On-chip concentration is a method of concentrating biomolecules using a nanometer-sized structure created into a microchannel, which is effective for improving detection sensitivity for microfluidic devices. As an on -chip concentration method for DNA molecules, we proposed a concentration method using nanoslit, which was a gap smaller than a diameter of a single molecule. Since this concentration method was based on the principle of entropy trap, its concentration amount depended on applied voltage. In this study, we proposed a theoretical model of concentration using nanoslit and determined an optimal voltage at which maximizing the concentration amount. We fabricated a chip device with 25 nm-depth nanoslit using microfabrication technique and experimentally verified the validity of our model. We achieved the concentration of λ DNA molecules at 17 times when we applied 0.6 V for 15 s.

DOI： 10.1299/jsmeiip.2019.2c01

CiNii Research

Separation of large DNA molecules by applying pulsed electric field to size exclusion chromatography-based microchip Reviewed

Naoki Azuma, Shintaro Itoh, Kenji Fukuzawa, Hedong Zhang

Japanese Journal of Applied Physics   Vol. 57 ( 2 ) page： 8   2018.2

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Language：Japanese   Publishing type：Research paper (scientific journal)  

DOI： 10.7567/JJAP.57.027002

Web of Science

Scopus

Optimization of applied voltages for on-chip concentration of DNA using nanoslit Reviewed

Naoki Azuma, Shintaro Itoh, Kenji Fukuzawa, Hedong Zhang

Japanese Journal of Applied Physics   Vol. 56 ( 12 ) page： 8   2017.12

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Language：Japanese   Publishing type：Research paper (scientific journal)  

DOI： 10.7567/JJAP.56.127001

Web of Science

Scopus

Fast size separation of large DNA molecules by applying pulsed electric field to size exclusion chromatography-based electrophoresis microchip

AZUMA Naoki, ITOH Shintaro, FUKUZAWA Kenji, ZHANG Hedong

The Proceedings of the Conference on Information, Intelligence and Precision Equipment : IIP   Vol. 2017 ( 0 ) page： E-01 - 1   2017

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Size separation of large DNA molecules (10 kbp – 1000 kbp) is one of the fundamental procedures for identifying bacterium’s genotypes, which should be fast for quick defection of infectious diseases. In our conventional study, we developed an electrophoresis microchip based on size exclusion chromatography. This separation has an advantage that it does not cause large deformation of DNA, which is important for separation of large DNAs because they can be easily fragmented. We achieved separation of large DNAs (48 kbp + 166 kbp) driven by a direct electric field as electrophoretic condition of DNA. However, it caused long separation time (3000 s) because DNAs migration was slow due to low applied voltage for the separation. In this study, we achieved faster separation of DNAs using a pulsed electric field under which applied voltage can be higher.

DOI： 10.1299/jsmeiip.2017.e-01

CiNii Research

On-chip concentration of DNA samples using a nano-slit fabricated in a microchannel

Azuma Naoki, Itoh Shintaro, Fukuzawa Kenji, Zhang Hedong

The Proceedings of the Symposium on Micro-Nano Science and Technology   Vol. 2017.8 ( 0 ) page： PN-106   2017

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On-chip concentration of samples using nanometer-sized structures fabricated in a microchannel is an effective method to improve detection sensitivity in μTAS. We proposed on-chip concentration of DNA samples using a nano-slit, which is a channel with a depth smaller than a diameter of DNA molecule. The concentration is based on an entropy trap at the boundary between the microchannel and the nano-slit. Therefore, concentration is achieved only by adjusting applied voltages. In this study, we verified the feasibility and the performances of the proposed concentration experimentally. When we applied 0.3 V for 100 s by using 30-nm deep nano-slit, we succeeded in concentration of λ DNA at 25 times the concentration rate.

DOI： 10.1299/jsmemnm.2017.8.pn-106

CiNii Research

Separation of large DNA molecules by size exclusion chromatography-based microchip with on-chip concentration structure Reviewed

Naoki Azuma, Shintaro Itoh, Kenji Fukuzawa, Hedong Zhang

Japanese Journal of Applied Physics   Vol. 55 ( 06GN01 ) page： 8   2016.4

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Improvement of resolution in SEC-type DNA separation microchip by on-chip concentration using nano-slit Reviewed

Naoki Azuma, Shintaro Itoh, Yusuke Sugimoto, Kenji Fukuzawa, Hedong Zhang

Proceedings of the JSME-IIP/ASME-ISPS Joint International Conference on Micromechatronics for Information and Precision Equipment   Vol. 2015 ( MoB-2-4 )   2015.6

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Authorship：Lead author   Language：English   Publishing type：Research paper (international conference proceedings)  

DOI： https://doi.org/10.1299/jsmemipe.2015._MoB-2-4-1