Faculty Profiles - AZUMA Naoki

Papers - AZUMA Naoki

Division display 21 - 40 of about 53 ／ All the affair displays >>

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

Language：Japanese Publisher：The Japan Society of Mechanical Engineers

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.

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

Language：Japanese Publisher：The Japan Society of Mechanical Engineers

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.

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

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

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.

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

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

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

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

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

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.

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

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

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.

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

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

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.

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

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

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.

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

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

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

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

Language：Japanese Publisher：The Japan Society of Mechanical Engineers

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

Language：Japanese Publisher：The Japan Society of Mechanical Engineers

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.

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

Language：Japanese Publisher：The Japan Society of Mechanical Engineers

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

Language：Japanese Publisher：The Japan Society of Mechanical Engineers

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

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

Language：Japanese Publisher：The Japan Society of Mechanical Engineers

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.

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

　 PREV - NEXT 　

<AZUMA Naoki>

Papers - AZUMA Naoki