Faculty Profiles - AZUMA Naoki

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

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

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

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

Hydration–lubrication performance improvement via synergistic effects of free polymers and polymer brushes Reviewed

Other Link： https://link.springer.com/article/10.1007/s11249-024-01884-y/fulltext.html

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

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

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

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

Effect of Water on Mechano-Chemical Reactions of Perfluoropolyether Lubricant Films in Heat-Assisted Magnetic Recording: A Reactive Molecular Dynamics Study Reviewed

Other Link： https://link.springer.com/article/10.1007/s11249-023-01783-8/fulltext.html

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

Tribology International Vol. 187 page： 108674 - 108674 2023.9

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

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

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

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

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

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

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

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

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

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

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

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

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

Language：Japanese Publisher：The Japan Society of Mechanical Engineers

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.

DOI： 10.1299/jsmeiip.2023.iipa-1-10

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

Language：Japanese Publisher：The Japan Society of Mechanical Engineers

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.

DOI： 10.1299/jsmeiip.2023.iipa-6-16

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

Language：Japanese Publisher：The Japan Society of Mechanical Engineers

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.

DOI： 10.1299/jsmeiip.2023.iipa-6-5

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

Language：Japanese Publisher：The Japan Society of Mechanical Engineers

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.

DOI： 10.1299/jsmeiip.2023.iipa-6-11

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

Language：Japanese Publisher：The Japan Society of Mechanical Engineers

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.

DOI： 10.1299/jsmeiip.2023.iipa-6-15

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

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

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

Language：Japanese Publisher：The Japan Society of Mechanical Engineers

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.

DOI： 10.1299/jsmeiip.2022.iip2r3-h12