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Lubricants
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Superlubricity: From Nanoscale to Macroscale
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Superlubricity: From Nanoscale to Macroscale

A special issue of Lubricants (ISSN 2075-4442).

Deadline for manuscript submissions: closed (23 September 2023) | Viewed by 4808

Special Issue Editors

Dr. Wei Cao

E-Mail Website
Guest Editor
Department of Physical Chemistry, School of Chemistry, Tel Aviv University, Tel Aviv 6997801, Israel
Interests: nanotribology; nanofluidics
Special Issues, Collections and Topics in MDPI journals
Dr. Caixia Zhang

E-Mail Website
Guest Editor
Institute of Advanced Manufacturing and Intelligent Technology, Faculty of Materials and Manufacturing, Beijing University of Technology, Beijing 100124, China
Interests: superlubricity; friction regulation; intelligent production line

Special Issue Information

Dear Colleagues,

Outstanding works have been published in the field of superlubricity in recent decades. Most of them have reported materials/interfaces at nanoscale or macroscale ( µm scale) achieving ultra-low friction and wearless phenomena. With the rapid development of this area, the central issue—how to promote superlubricity from the experimental level to application in real life—should be readily raised to all researchers. Generally, the first point to consider is to clarify the time (or velocity) and size dependence for a superlubric system. From the theoretical perspective, this calls for the understanding of the physical origin of superlubricity, e.g., theoretical models and numerical computations to explore the time/size scaling of friction behavior from nanoscale to macroscale. From the experimental perspective, to the goal is the measurement of friction at a wide range of velocities and contact area sizes for a certain superlubric sample. In addition, materials showing superlubricity at macroscale (µm to m) or high sliding speed (µm/s to m/s) should be highly emphasized.

The Special Issue aims to promote the application of superlubrication. It reports the recent advances of both the solid-solid structural superlubricity and the solid-liquid hydration superlubricity from nanoscale to macroscale.

Dr. Wei Cao
Dr. Caixia Zhang
Guest Editors

Manuscript Submission Information

Manuscripts should be submitted online at www.mdpi.com by registering and logging in to this website. Once you are registered, click here to go to the submission form. Manuscripts can be submitted until the deadline. All submissions that pass pre-check are peer-reviewed. Accepted papers will be published continuously in the journal (as soon as accepted) and will be listed together on the special issue website. Research articles, review articles as well as short communications are invited. For planned papers, a title and short abstract (about 100 words) can be sent to the Editorial Office for announcement on this website.

Submitted manuscripts should not have been published previously, nor be under consideration for publication elsewhere (except conference proceedings papers). All manuscripts are thoroughly refereed through a single-blind peer-review process. A guide for authors and other relevant information for submission of manuscripts is available on the Instructions for Authors page. Lubricants is an international peer-reviewed open access monthly journal published by MDPI.

Please visit the Instructions for Authors page before submitting a manuscript. The Article Processing Charge (APC) for publication in this open access journal is 2600 CHF (Swiss Francs). Submitted papers should be well formatted and use good English. Authors may use MDPI's English editing service prior to publication or during author revisions.

Keywords

  • structural superlubricity
  • hydration lubrication
  • boundary lubrication
  • ultra-low friction
  • size scaling
  • velocity dependence

Published Papers (3 papers)

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Research

14 pages, 5539 KiB  
Article
Impact of Water Content on the Superlubricity of Ethylene Glycol Solutions
by Lvzhou Li, Peng Gong, Pengpeng Bai, Xiangli Wen, Yonggang Meng, Jianning Ding and Yu Tian
Lubricants 2023, 11(11), 466; https://doi.org/10.3390/lubricants11110466 - 31 Oct 2023
Cited by 1 | Viewed by 1438
Abstract
Aqueous solutions of water and ethylene glycol (EG) are prevalently employed in braking, heat transfer, and lubrication systems. However, the precise mechanism through which water content affects the lubricative attributes of EG solutions remains elusive. This research systematically examines the tribological characteristics of [...] Read more.
Aqueous solutions of water and ethylene glycol (EG) are prevalently employed in braking, heat transfer, and lubrication systems. However, the precise mechanism through which water content affects the lubricative attributes of EG solutions remains elusive. This research systematically examines the tribological characteristics of EG solutions at varying concentrations using a ceramic–TiAlN friction-pair system. As the concentration of EG increases, the sequential transformation of the associated molecular complex structure in the lubricating medium can be described as follows: [H2O]m·EG → [H2O]m·[EG]n → H2O·[EG]n. Among them, the stoichiometric coefficients “m” and “n” are the simplest mole ratio of H2O and EG in the molecular complex structure, respectively. The most favorable EG concentration was determined to be 50 wt.%. At this concentration, a flexible molecular complex adsorption structure ([H2O]m·[EG]n) with a significant bearing capacity (due to intense hydrogen bonding) forms on the surface of the friction pair, which results in a reduction in the running-in duration and facilitates the achievement of superlubricity, and the coefficient of friction (COF) is about 0.0047. Solutions containing 50 wt.% EG enhance the load-bearing ability and hydrophilicity of the lubricating medium. Moreover, they minimize the roughness of the worn region and curtail the adhesive forces and shear stress at the frictional interface, enabling the realization of superlubricity. Consequently, this research offers valuable insights into the optimal water-to-EG ratio, revealing the mechanism of a superlubricity system that possesses exceptional tribological attributes and holds significant potential for practical applications. Full article
(This article belongs to the Special Issue Superlubricity: From Nanoscale to Macroscale)
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11 pages, 7680 KiB  
Article
Low Friction Achieved on Plasma Electrolytic Oxidized TC4 Alloy in the Presence of PAO Base Oil Containing MoDTC
by Huilai Sun, Shengrui Zhou, Lupeng Shao, Junji Luan, Yong Wan and Chao Wang
Lubricants 2023, 11(1), 4; https://doi.org/10.3390/lubricants11010004 - 21 Dec 2022
Viewed by 1141
Abstract
Surface engineering is required to improve the poor lubrication performance of titanium alloys in many applications. In this study, an oxide coating with high-hardness was created on TC4 titanium alloy by using plasma electrolytic oxidation (PEO). The composition and structure of the PEO [...] Read more.
Surface engineering is required to improve the poor lubrication performance of titanium alloys in many applications. In this study, an oxide coating with high-hardness was created on TC4 titanium alloy by using plasma electrolytic oxidation (PEO). The composition and structure of the PEO coatings were analyzed by scanning electron microscopy (SEM), X-ray diffraction (XRD), and Raman spectroscopy. The tribological properties of the PEO-treated TC4 were investigated in the presence of a polyalphaolefin (PAO) base oil with addition of molybdenum dialkyldithiocarbamate (MoDTC). The results show that the PEO-treated TC4 exhibits excellent lubrication performance in the presence of MoDTC. The oxide coating on the PEO-treated TC4 sample shows a tribo-induced catalysis effect enabling the decomposition of MoDTC to forms an effective lubricating film containing MoS2, resulting in reduced friction and wear. Full article
(This article belongs to the Special Issue Superlubricity: From Nanoscale to Macroscale)
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14 pages, 5169 KiB  
Article
Regulation Mechanism of Trivalent Cations on Friction Coefficient of a Poly(Vinylphosphonic Acid) (PVPA) Superlubricity System
by Mengmeng Liu, Caixia Zhang, Lihui Wang, Yanhong Cheng, Ying Li, Lianpeng Bai and Zhifeng Liu
Lubricants 2022, 10(8), 191; https://doi.org/10.3390/lubricants10080191 - 19 Aug 2022
Viewed by 1423
Abstract
The application range of superlubricity systems can be extended effectively by realizing an adjustable friction coefficient. In this study, a stable poly(vinylphosphonic acid) (PVPA) superlubricity system was developed using sodium chloride (NaCl) solution as the lubricant. A sudden increase in the friction coefficient [...] Read more.
The application range of superlubricity systems can be extended effectively by realizing an adjustable friction coefficient. In this study, a stable poly(vinylphosphonic acid) (PVPA) superlubricity system was developed using sodium chloride (NaCl) solution as the lubricant. A sudden increase in the friction coefficient occurred when a trivalent salt solution was introduced to the base lubricant during the friction process. The changes in surface microstructure and interfacial molecular behavior induced by trivalent cations were studied by scanning electron microscopy (SEM), energy dispersive spectroscopy (EDS) and molecular dynamics simulation. The regulation mechanism of trivalent cations with respect to the friction coefficient of the PVPA superlubricity system was explored. Although La3+ and Fe3+ in solutions exist in two forms (La3+ and Fe(OH)3), both can destroy the stable coating structure through a bridging effect, resulting in a sudden increase in the friction coefficient. The ability of various cations to attract the surrounding water molecules is an important reason for the varying degree of change of the friction coefficient. In addition, the degree of sudden increase in the friction coefficient is dependent on the concentration of trivalent cations. There is an extreme concentration at which the maximum sudden increase degree in friction coefficient can be obtained. This study provides insights into the realization of oil-based superlubricity through interface regulation. Full article
(This article belongs to the Special Issue Superlubricity: From Nanoscale to Macroscale)
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