Faculty Profiles - ZHANG, Hedong

Papers - ZHANG, Hedong

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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

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

Coarse-Grained Molecular Dynamics Study of Lubrication Properties of Nanometer-Thick Liquid Films Invited Reviewed

ZHANG Hedong, KOBAYASHI Takayuki

JOURNAL OF JAPANESE SOCIETY OF TRIBOLOGISTS Vol. 66 ( 4 ) page： 294 - 299 2021.4

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

The establishment of effective lubrication with nanometer-thick liquid films is crucial for the development of advanced miniaturized mechanical systems. Complementary to experiments, molecular dynamics (MD) simulations provide atomic-level insights into the structure and movement of nanometer-thick liquid films. However, conventional all-atom MD simulations are computationally expensive for studying systems over extended length and time scales. Coarse graining, which eliminates some degrees of freedom by grouping several atoms to one bead, is one effective method to reduce computational cost. In this review, the procedure of coarse graining and some points to note for accurate modeling of lubrication phenomena are presented through a concrete example of coarse-grained MD simulations of confined shear of nanometer-thick polar liquid lubricant films at the head-disk interface of magnetic disk drives.

DOI： 10.18914/tribologist.66.04_294

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 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

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 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 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

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 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

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

X. Chen, K. Kawai, H. Zhang, K. Fukuzawa, N. Koga, S. Itoh, N. Azuma

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

Effect of Transverse Dissipative Particle Dynamics on Dynamic Properties of Nanometer-thick Liquid Films on Solid Surfaces Reviewed Open Access

T. Kobayashi, H. Zhang, K. Fukuzawa, S. Itoh

Molecular Simulation Vol. 146 page： 1281–1290 2020.9

Experimental Study of Application of Molecules with a Cyclic Head Group Containing a Free Radical as Organic Friction Modifiers Reviewed Open Access

X. Zhang, M. Tsukamoto, H. Zhang, Y. Mitsuya, S. Itoh, K. Fukuzawa

Journal of Advanced Mechanical Design, Systems, and Manufacturing Vol. 14 page： JAMDSM0044 2020.4

Extension of Measurement Range of Lubrication Gap Shape using Vertical-Objective-Type Ellipsometric Microscopy with Two Compensator Angles Reviewed

K. Namba, K. Fukuzawa, S. Itoh, H. Zhang, N. Azuma

Tribology International Vol. 142 page： 105980 2020.2

Frictional Behaviour of Trimethylolpropane (TMP) Oleate at Different Regimes of Lubrication Reviewed

A.F. Maarof, S.H. Hamdan, C.T. Lee, W.W.F. Chong, C.T. Chong, H. Zhang

Journal of Mechanical Engineering Vol. 8 page： 1-9 2019.12

Validation of Correction Method for Gap Shape Measurement by Vertical-Objective-Type Ellipsometric Microscopy with Rotating-Compensator Ellipsometry Reviewed Open Access

K. Namba, Y. Sasao, K. Fukuzawa, S. Itoh, H. Zhang

Journal of Advanced Mechanical Design, Systems, and Manufacturing Vol. 13 ( 2 ) page： 18-00434 2019.4

Nano-tribological Characterisation of Palm Oil-based Trimethylolpropane Ester for Application as Boundary Lubricant Reviewed

S.H. Hamdan, W.W.F. Chong, J.-H. Ng, C.T. Chong, H. Zhang

Tribology International Vol. 127 page： 1-9 2018.11

Simultaneous in situ Measurements of Contact Behavior and Friction to Understand the Mechanism of Lubrication with Nanometer-thick Liquid Lubricant Films Reviewed

H. Zhang, Y. Takeuchi, W.W.F. Chong, Y. Mitsuya, K. Fukuzawa, S. Itoh

Tribology International Vol. 127 page： 138-146 2018.11

Measurement of Nanometer-thick Lubricating Films using Ellipsometric Microscopy Reviewed Open Access

K. Fukuzawa, Y. Sasao, K. Namba, C. Yamashita, S. Itoh, H. Zhang

Tribology International Vol. 122 page： 8-14 2018.6

Enhanced Viscoelasticity of Polyalphaolefins Confined and Sheared in Submicron-to-nanometer-sized Gap Range and Its Dependence on Shear Rate and Temperature Reviewed

S. Itoh, Y. Ohta, K. Fukuzawa, H. Zhang

Tribology International Vol. 120 page： 210-217 2018.4

Is the Trend of Stribeck Curves Followed by Nano-Lubrication with Molecularly Thin Liquid Lubricant Films? Reviewed

Hedong Zhang, Takahiro Yoshimi, Kenji Fukuzawa, Shintaro Itoh

Tribology International Vol. 119 page： 82-87 2018.3

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. 27 ( 027002 ) 2018.1

Real-time Observation of Molecularly Thin Lubricant Films on Head Sliders Using Rotating-Compensator-Based Ellipsometric Microscopy Reviewed Open Access

Kenji Fukuzawa, Ken Miyata, Chihiro Yamashita, Shintaro Itoh, Hedong Zhang

IEEE Transactions on Magnetics Vol. 53 ( 11 ) page： 1-4 2017.11

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Papers - ZHANG, Hedong