Faculty Profiles - ZHANG, Hedong

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

Characterization of organic friction modifiers using lateral force microscopy and Eyring activation energy model Reviewed

Other Link： https://link.springer.com/article/10.1007/s40544-022-0610-0/fulltext.html

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

Enhancing pressure consistency and transferability of structure-based coarse-graining Reviewed

Tang, JH; Kobayashi, T; Zhang, HD; Fukuzawa, K; Itoh, S

PHYSICAL CHEMISTRY CHEMICAL PHYSICS Vol. 25 ( 3 ) page： 2256 - 2264 2023.1

Language：English Publisher：Physical Chemistry Chemical Physics

Coarse-graining, which models molecules with coarse-grained (CG) beads, allows molecular dynamics simulations to be applied to systems with large length and time scales while preserving the essential molecular structure. However, CG models generally have insufficient representability and transferability. A commonly used method to resolve this problem is multi-state iterative Boltzmann inversion (MS-IBI) with pressure correction, which matches both the structural properties and pressures at different thermodynamic states between CG and all-atom (AA) simulations. Nevertheless, this method is usually effective only in a narrow pressure range. In this paper, we propose a modified CG scheme to overcome this limitation. We find that the fundamental reason for this limitation is that CG beads at close distances are ellipsoids rather than isotropically compressed spheres, as described in conventional CG models. Hence, we propose a method to compensate for such differences by slightly modifying the radial distribution functions (RDFs) derived from AA simulations and using the modified RDFs as references for pressure-corrected MS-IBI. We also propose a method to determine the initial non-bonded potential using both the target RDF and pressure. Using n-dodecane as a case study, we demonstrate that the CG model developed using our scheme reproduces the RDFs and pressures over a wide range of pressure states, including three reference low-pressure states and two test high-pressure states. The proposed scheme allows for accurate CG simulations of systems in which pressure or density varies with time and/or position.

DOI： 10.1039/d2cp04849c

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

PubMed

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

Trimethylolpropane trioleate as eco-friendly lubricant additive Reviewed International coauthorship Open Access

Lee, CT; Lee, MB; Hamdan, SH; Chong, WWF; Chong, CT; Zhang, H; Chen, AWL

ENGINEERING SCIENCE AND TECHNOLOGY-AN INTERNATIONAL JOURNAL-JESTECH Vol. 35 page： 101068 2022.11

Language：English Publisher：Engineering Science and Technology, an International Journal

Approximately 17.9% of fuel energy is used to overcome engine friction in passenger cars with engine frictional losses further broken down into losses along hydrodynamic (40%), elastohydrodynamic – due to pure sliding motion (40%), mixed (10%) and boundary (10%) lubrication regimes. Therefore, to assess the tribological influence of TMP trioleate as an eco-friendly additive to a low viscosity Polyalphaolefin (PAO) at different lubrication regimes, the present study adopted a Stribeck-type analysis. Through this study, the viscosity index of PAO was found to increase significantly when blended with 5-vol% TMP trioleate. Tribologically, across the tested conditions at different sliding velocities and applied normal loads, it was determined that this blend could potentially reduce friction power and wear scar diameter by up to 6.09% and 39.65%, respectively, when compared with the neat PAO. Such an improvement was demonstrated to also synergistically enhance the friction modifier effect of this blend at the mixed lubrication regime, delaying the onset of boundary lubrication regime when the contact is lubricated by this mixture.

DOI： 10.1016/j.jestch.2021.09.014

Open Access

Adsorption Behavior of TEMPO-Based Organic Friction Modifiers during Sliding between Iron Oxide Surfaces: A Molecular Dynamics Study Reviewed

水和ポリマーブラシ膜のせん断すき間に依存した動的ずり粘弾性

林楓昌，伊藤伸太郎，福澤健二，東直輝，張賀東

トライボロジー会議2022 春東京　予稿集 2022.5

ポリアルキルメタクリレート添加潤滑油のナノすき間におけるずり粘弾性の温度依存性

野末拓海，伊藤伸太郎，大久保尚哉，福澤健二，東直輝，張賀東

トライボロジー会議2022 春東京　予稿集 2022.5

Effects of polarity of polyalkylmethacrylate (PAMA) polymer additives on adsorbed film’s thickness and durability

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

トライボロジー会議2022 春東京　予稿集 2022.5

フラーレン添加潤滑油の境界潤滑特性における基材性状依存性の解明

伊藤伸太郎，エン子昂，福澤健二，東直輝，張賀東

トライボロジー会議2022 春東京　予稿集 2022.5

TEMPO系有機摩擦調整剤の酸化鉄表面への吸着挙動に関する分子動力学解析

陳星宇，楊俊韜，安田耕二，古賀伸明，張賀東

トライボロジー会議2022 春東京　予稿集 2022.5

Xingyu Chen, Juntao Yang, Koji Yasuda, Nobuaki Koga, Hedong Zhang

Langmuir Vol. 38 ( 10 ) page： 3170 - 3179 2022.3

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

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