Faculty Profiles - ZHANG, Hedong

Papers - ZHANG, Hedong

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ReaxFF molecular dynamics study of mechanochemical degradation of PFPE lubricants on DLC in heat-assisted magnetic recording Reviewed Open Access

RSC MECHANOCHEMISTRY Vol. 2 ( 5 ) page： 745 - 755 2025.9

Size analysis of large DNA molecules by relaxation time measurement using a nanoslit channel Reviewed Open Access

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

LAB ON A CHIP Vol. 25 ( 16 ) page： 4048 - 4058 2025.8

Language：English Publishing type：Research paper (scientific journal) Publisher：Lab on A Chip

Determining the size of DNA molecules >10 kbp continues to be challenging, as conventional methods, such as pulsed-field gel electrophoresis require time-consuming analysis and artificial gel structures increase the risk of mechanical fragmentation to DNA molecules during repeated hooking and stretching. Herein, we developed a new analytical method for identifying the size of DNA molecules by measuring the time required for a stretched large DNA molecule to relax into a random coil, using nanoslit channels with depths of 130-49 nm. By maintaining the initial stretching ratio of the collected DNA molecules at <30%, we successfully differentiated a mixed DNA sample containing λ and T4 DNAs into two distinct peaks in the relaxation-time histogram. Furthermore, we explored the influence of the number of collected relaxation times and nanoslit depths on the resolution of size analysis. Our findings indicated that the nanoslit depth was the primary factor affecting the size determination resolution. Reducing the nanoslit depth enhanced resolution, whereas the number of effective relaxation times did not impact the resolution once a critical data threshold was reached. A nanoslit channel of depth 49 nm exhibited superior performance, with a maximum resolution of 2.33 and a short analysis time of 60 s, surpassing both conventional methods in terms of resolution and time efficiency. The proposed method shows great potential for accurate, large-scale DNA size analysis.

DOI： 10.1039/d4lc00998c

Emergent Tribological Behavior from Concentration-Driven Conformational Transitions in Adsorbed Polymer Films Reviewed

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

NANO LETTERS Vol. 25 ( 29 ) page： 11251 - 11256 2025.7

Language：English Publishing type：Research paper (scientific journal) Publisher：Nano Letters

Adsorbed polymer films on surfaces from lubricant solutions play important roles in preventing direct contacts of solid surfaces during rubbing and govern tribological behavior in nanosliding gaps. Using neutron reflectometry (NR) and self-developed vertical-objective-type ellipsometric microscopy (VEM), we report a concentration-driven emergent transition in the structure and tribological behavior of adsorbed polymer films at solid-liquid interfaces. At low concentrations, polymer chains adopt flattened conformations that show low friction under sliding. Above a critical concentration threshold, competitive adsorption induces a transition to double-layer structures rich in loops and tails, enabling thick lubricating layers to form during sliding but to exhibit increased friction.

DOI： 10.1021/acs.nanolett.5c01973

Web of Science

Scopus

PubMed

Interfacial slip quantification in nanogaps using squeeze flow velocimetry Reviewed

Ozeki H., Azuma N., Fukuzawa K., Itoh S., Zhang H., Song Y.

Physics of Fluids Vol. 37 ( 5 ) 2025.5

Language：English Publishing type：Research paper (scientific journal) Publisher：Physics of Fluids

Understanding interfacial slip in nanogaps is crucial for modeling fluid flow in mechanical and analytical systems. To quantify slip length and shear stress at the liquid-solid interface, we measured the velocity of squeeze flow as fluid was pressed between solid surfaces. Our results showed that slip length varied with lateral positions and gap heights, while shear stress had a noticeable threshold beyond which slip begins, indicating the limiting shear stress model for interfacial slip in nanogaps. These insights enhance our understanding of interfacial slip phenomena in nanogaps and provide a foundation for modeling their influence on fluid flow.

DOI： 10.1063/5.0271999

Scopus

Detection and Behaviors of TEMPO Derivatives in Seven Mass Spectrometry Ionization Methods Reviewed Open Access

Oyama, KI; Hor, S; Tsukamoto, M; Zhang, HD

JOURNAL OF MASS SPECTROMETRY Vol. 60 ( 4 ) page： e5122 2025.4

Language：English Publishing type：Research paper (scientific journal) Publisher：Journal of Mass Spectrometry

Four 2,2,6,6-tetramethylpiperidinyloxyl (TEMPO) derivatives with molecular weights of 339–1131 Da were synthesized to investigate their ionization behaviors in fast atom bombardment (FAB), electron ionization (EI), direct analysis in real time (DART), electrospray ionization (ESI), atmospheric pressure chemical ionization (APCI), atmospheric pressure photoionization (APPI), and matrix-assisted laser desorption/ionization mass spectrometry (MALDI-MS). These include 4-dodecanoylamino-2,2,6,6-tetramethyl-1-piperidinyloxy (1), 4-dodecylamino-2,2,6,6-tetramethyl-1-piperidinyloxy (2), N,N′-bis(2,2,6,6-tetramethyl-1-oxyl-4-piperidinyl)dodecanediamide (3), and bis-cholesterol TEMPO derivative 4. For TEMPO derivatives 1 and 2 (molecular weights: 353 Da and 339 Da), [M]+, [M+H]+•, and [M+2H]+ peaks were detected. TEMPO derivative 3, containing two TEMPO moieties, showed [M]+•, [M+H]+, [M+2H]+•, and [M+3H]+ peaks. EI was optimal for smaller derivatives, as molecular ion peaks were predominant. For larger analytes, molecular ion intensities weakened, favoring hydrogen adduct peaks. EI and DART-MS failed to detect bis-cholesterol TEMPO derivative 4. Under APCI and APPI-MS, N–O bond cleavage was observed. MALDI-MS detected only hydrogen adduct peaks. FAB, ESI, APCI, and APPI-MS detections varied with scan numbers, unlike EI, DART, and MALDI-MS.

DOI： 10.1002/jms.5122

Bulk conformation and shear-induced transitions in bottlebrush poly(alkyl methacrylate): The role of side chain length and polymer flexibility Reviewed Open Access

Himanshu Shekhar, Yuma Chikazawa, Yuxi Song, Hedong Zhang

Tribology International Vol. 204 page： 110476 - 110476 2025.4

Wearable PZT Piezoelectric Sensor Device for Accurate Arterial Pressure Pulse Waveform Measurement Reviewed Open Access

Li, MY; Aoyama, J; Inayoshi, K; Zhang, HD

ADVANCED ELECTRONIC MATERIALS 2025.1

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

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

AIP Advances Vol. 15 ( 1 ) 2025.1

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

Open Access

Web of Science

Scopus

Mechanism of Hydrogen Generation by Decomposition of Lubricating Oils: Effect of Lubricating Oils on Hydrogen Brittle Flaking Reviewed Open Access

Ito Motohiro, Kawamura Takayuki, Sakaguchi Tomoya, Suzuki Yuichi, Zhang Hedong, Nagaoka Masataka

Tribology Online Vol. 19 ( 6 ) page： 517 - 524 2024.11

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

<p>In the rolling bearings used in automotive electrical instruments and auxiliary devices such as alternators, it is well-known that brittle flaking occurs earlier than expected due to hydrogen embrittlement. Despite this, in the flaking mechanism, the generation process of hydrogen atoms in lubricating oils has not been clarified microscopically. In this study, we theoretically elucidated the reaction processes of poly-α-olefin (PAO) and alkyl diphenyl ether (ADE) molecules using quantum mechanical (QM) calculations. The basic and important mechanism for the generation of hydrogen molecules was clarified for the first time at the atomic level. Upon considering the generation mechanism on ceramics and nascent steel surfaces, it was found that the reason why the amount of hydrogen generation is similar regardless of the type of lubricant is because the energy required for hydrogen generation is almost the same. Furthermore, it was suggested that the suppression of hydrogen brittle flaking by ADE was due to the low exposure frequency of the nascent steel surface.</p>

DOI： 10.2474/trol.19.517

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

Web of Science

Scopus

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

Ionic liquid lubricity enhancement with bio-oil derived from microwave pyrolysis of bamboo Reviewed International coauthorship

Ariffin, NAAM; Foong, SY; Chong, WWF; Lam, SS; Ng, JH; Zhang, HD

INDUSTRIAL CROPS AND PRODUCTS Vol. 214 2024.8

Molecular dynamics study of confined liquid film viscosity in Constant-Pressure and Constant-Distance systems Reviewed International coauthorship Open Access

Chen, XY; Zhang, HD; Yokoyama, H; Chong, WWF; Fukuzawa, K; Itoh, S

JOURNAL OF MOLECULAR LIQUIDS Vol. 404 page： 124955 - 124955 2024.6

Numerical modelling of macro lubricity in conjunctions with nanometer-thick films Reviewed International coauthorship

Chong, WWF; Zhang, HD; Li, YR

TRIBOLOGY INTERNATIONAL Vol. 193 2024.5

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

Coarse-Grained Molecular Dynamics Simulations of Organic Friction Modifier Adsorption on Rough Surfaces under Shear Reviewed International coauthorship Open Access

J. Tang, W.W.F. Chong, H. Zhang

Lubricants Vol. 12 ( 2 ) page： 30 2024.1

Enhancing boundary friction and wear reduction through adsorption control in protic ionic liquid and carbon mixtures Reviewed International coauthorship

Ariffin, NAAM; Lee, CT; Lee, MB; Halid, I; Hamdan, SH; Ismail, MI; Chong, WWF; Zhang, HD

JOURNAL OF MATERIALS SCIENCE Vol. 59 ( 3 ) page： 794 - 809 2024.1

Language：English Publishing type：Research paper (scientific journal) Publisher：Journal of Materials Science

This study addresses the challenge of enhancing lubrication performance by exploring the potential of a protic ionic liquid (IL), [Oley][Oleic], in conjunction with carbon nanotube (CNT) mixtures. The primary objective is to determine the optimal CNT concentration that achieves effective lubrication for the IL-based lubricant. Through experimental investigation, notable reductions of 19.8 % in friction and 67.2% in wear are demonstrated when [Oley][Oleic] is blended with the optimum CNT concentration at 0.10 wt%. This study employs a friction-derived adsorption model to elucidate the underlying mechanisms of friction. The results indicate that the addition of CNTs leads to a larger adsorption surface coverage area of the lubricant molecules, resulting in decreased friction and wear. Synergistic attractive cooperative interactions among the IL molecules in the presence of CNTs are identified as a key factor in enhancing adsorption efficiency. These findings provide insights into the interaction between [Oley][Oleic] and CNTs when sheared, offering a predictive framework for understanding friction and wear behaviour specific to IL-based lubricants. By presenting a solution for reducing friction and wear, this study contributes to the development of energy-efficient and environmentally-friendly lubrication practices, opening avenues for further advancements in the field of lubrication and promoting sustainable tribological solutions for diverse applications.

DOI： 10.1007/s10853-023-09257-x

Web of Science

Scopus

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

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

Tribology International Vol. 191 page： 109189 2023.12

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 page： 112 2023.9

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

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

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

Tribology Online Vol. 18 ( 3 ) page： 91 - 96 2023.7

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

Web of Science

Scopus

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Papers - ZHANG, Hedong