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Wang Y, Wang J, Wu T, Chen W, Peng D, Wu Z, Ma M, Zheng Q. The anomalous effect of electric field on friction for microscale structural superlubric graphite/Au contact. Natl Sci Rev 2024; 11:nwae019. [PMID: 39144740 PMCID: PMC11321252 DOI: 10.1093/nsr/nwae019] [Citation(s) in RCA: 0] [Impact Index Per Article: 0] [Reference Citation Analysis] [Abstract] [Key Words] [Grants] [Track Full Text] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 08/04/2023] [Revised: 12/18/2023] [Accepted: 12/18/2023] [Indexed: 08/16/2024] Open
Abstract
The current-carrying friction characteristics are crucial for the performance of a sliding electrical contact, which plays critical roles in numerous electrical machines and devices. However, these characteristics are influenced by multiple factors such as material surface quality, chemical reactions, and atmospheric environment, leading to a challenge for researchers to comprehensively consider these impacts. Structural superlubricity (SSL), a state of nearly zero friction and no wear between contact solid surfaces, provides an ideal experimental system for these studies. Here, with microscale graphite flakes on atomic-flattened Au surface under applied voltages, we observed two opposite friction phenomena, depending only on whether the edge of graphite flake was in contact with the Au substrate. When in contact the friction force would increase with an increasing voltage, otherwise, the friction force would decrease. Notably, when the voltage was turned off, the friction force quickly recovered to its original level, indicating the absence of wear. Through atmosphere control and molecular dynamics simulations, we revealed the mechanism to be the different roles played by the water molecules confined at the interface or adsorbed near the edges. Our experimental results demonstrate the remarkable tunable and robust frictional properties of SSL under an electrical field, providing an ideal system for the fundamental research of not only sliding electrical contacts, but also novel devices which demand tunable frictions.
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Affiliation(s)
- Yelingyi Wang
- Center for Nano and Micro Mechanics, School of Aerospace Engineering, Tsinghua University, Beijing 100084, China
- Department of Engineering Mechanics, School of Aerospace Engineering, Tsinghua University, Beijing 100084, China
| | - Jin Wang
- International School for Advanced Studies (SISSA), Trieste 34136, Italy
- International Centre for Theoretical Physics (ICTP), Trieste 34151, Italy
| | - Tielin Wu
- Center for Nano and Micro Mechanics, School of Aerospace Engineering, Tsinghua University, Beijing 100084, China
- Department of Engineering Mechanics, School of Aerospace Engineering, Tsinghua University, Beijing 100084, China
| | - Weipeng Chen
- Center for Nano and Micro Mechanics, School of Aerospace Engineering, Tsinghua University, Beijing 100084, China
- Department of Engineering Mechanics, School of Aerospace Engineering, Tsinghua University, Beijing 100084, China
| | - Deli Peng
- Department of Engineering Mechanics, School of Aerospace Engineering, Tsinghua University, Beijing 100084, China
- Institute of Superlubricity Technology, Research Institute of Tsinghua University in Shenzhen, Shenzhen 518057, China
| | - Zhanghui Wu
- Department of Engineering Mechanics, School of Aerospace Engineering, Tsinghua University, Beijing 100084, China
| | - Ming Ma
- Center for Nano and Micro Mechanics, School of Aerospace Engineering, Tsinghua University, Beijing 100084, China
- Institute of Superlubricity Technology, Research Institute of Tsinghua University in Shenzhen, Shenzhen 518057, China
- Department of Mechanical Engineering, State Key Lab of Tribology in Advanced Equipment (SKLT), Tsinghua University, Beijing 10084, China
| | - Quanshui Zheng
- Center for Nano and Micro Mechanics, School of Aerospace Engineering, Tsinghua University, Beijing 100084, China
- Department of Engineering Mechanics, School of Aerospace Engineering, Tsinghua University, Beijing 100084, China
- Institute of Superlubricity Technology, Research Institute of Tsinghua University in Shenzhen, Shenzhen 518057, China
- Institute of Materials Research, Tsinghua Shenzhen International Graduate School, Shenzhen 518057, China
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2
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Dašić M, Almog R, Agmon L, Yehezkel S, Halfin T, Jopp J, Ya'akobovitz A, Berkovich R, Stanković I. Role of Trapped Molecules at Sliding Contacts in Lattice-Resolved Friction. ACS APPLIED MATERIALS & INTERFACES 2024. [PMID: 39105730 DOI: 10.1021/acsami.4c08226] [Citation(s) in RCA: 0] [Impact Index Per Article: 0] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Subscribe] [Scholar Register] [Indexed: 08/07/2024]
Abstract
Understanding atomic friction within a liquid environment is crucial for engineering friction mechanisms and characterizing surfaces. It has been suggested that the lattice resolution of friction force microscope in liquid environments stems from a dry contact state, with all liquid molecules expelled from the area of closest approach between the tip and substrate. Here, we revisit this assertion by performing in-depth friction force microscopy experiments and molecular dynamics simulations of the influence of surrounding water molecules on the dynamic behavior of the nanotribological contact between an amorphous SiO2 probe and a monolayer MoS2 substrate. An analysis of simulation and experimental stick-slip patterns demonstrates the entrapment of water molecules at the contact interface. These trapped water molecules behave as an integral component of the probe and participate in its interaction with the substrate, affecting the dynamics of the probe and preventing long slips. Significantly, surrounding water from the capillary or layer exhibits a replenishing effect, acting as a water reservoir during sliding. This phenomenon facilitates the preservation of lattice-scale resolution across a range of applied normal loads.
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Affiliation(s)
- Miljan Dašić
- Scientific Computing Laboratory, Center for the Study of Complex Systems, Institute of Physics Belgrade, University of Belgrade, Pregrevica 118, Belgrade 11080, Serbia
| | - Roy Almog
- Department of Chemical Engineering, Ben-Gurion University of the Negev, Beer Sheva Blvd 1, Beer Sheva 84105, Israel
| | - Liron Agmon
- Department of Chemical Engineering, Ben-Gurion University of the Negev, Beer Sheva Blvd 1, Beer Sheva 84105, Israel
| | - Stav Yehezkel
- Department of Chemical Engineering, Ben-Gurion University of the Negev, Beer Sheva Blvd 1, Beer Sheva 84105, Israel
| | - Tal Halfin
- Department of Chemical Engineering, Ben-Gurion University of the Negev, Beer Sheva Blvd 1, Beer Sheva 84105, Israel
| | - Jürgen Jopp
- The Ilse Katz Institute for Nanoscale Science and Technology, Ben-Gurion University of the Negev, Beer Sheva Blvd 1, Beer Sheva 84105, Israel
| | - Assaf Ya'akobovitz
- The Ilse Katz Institute for Nanoscale Science and Technology, Ben-Gurion University of the Negev, Beer Sheva Blvd 1, Beer Sheva 84105, Israel
- Department of Mechanical Engineering, Ben-Gurion University of the Negev, Beer Sheva Blvd 1, Beer Sheva 84105, Israel
| | - Ronen Berkovich
- Department of Chemical Engineering, Ben-Gurion University of the Negev, Beer Sheva Blvd 1, Beer Sheva 84105, Israel
- The Ilse Katz Institute for Nanoscale Science and Technology, Ben-Gurion University of the Negev, Beer Sheva Blvd 1, Beer Sheva 84105, Israel
| | - Igor Stanković
- Scientific Computing Laboratory, Center for the Study of Complex Systems, Institute of Physics Belgrade, University of Belgrade, Pregrevica 118, Belgrade 11080, Serbia
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Liu J, Yang X, Fang H, Yan W, Ouyang W, Liu Z. In Situ Twistronics: A New Platform Based on Superlubricity. ADVANCED MATERIALS (DEERFIELD BEACH, FLA.) 2023:e2305072. [PMID: 37867201 DOI: 10.1002/adma.202305072] [Citation(s) in RCA: 0] [Impact Index Per Article: 0] [Reference Citation Analysis] [Abstract] [Key Words] [Grants] [Track Full Text] [Subscribe] [Scholar Register] [Received: 05/29/2023] [Revised: 07/19/2023] [Indexed: 10/24/2023]
Abstract
Twistronics, an emerging field focused on exploring the unique electrical properties induced by twist interface in graphene multilayers, has garnered significant attention in recent years. The general manipulation of twist angle depends on the assembly of van der Waals (vdW) layered materials, which has led to the discovery of unconventional superconductivity, ferroelectricity, and nonlinear optics, thereby expanding the realm of twistronics. Recently, in situ tuning of interlayer conductivity in vdW layered materials has been achieved based on scanning probe microscope. In this Perspective, the advancements in in situ twistronics are focused on by reviewing the state-of-the-art in situ manipulating technology, discussing the underlying mechanism based on the concept of structural superlubricity, and exploiting the real-time twistronic tests under scanning electron microscope (SEM). It is shown that the real-time manipulation under SEM allows for visualizing and monitoring the interface status during in situ twistronic testing. By harnessing the unique tribological properties of vdW layered materials, this novel platform not only enhances the fabrication of twistronic devices but also facilitates the fundamental understanding of interface phenomena in vdW layered materials. Moreover, this platform holds great promise for the application of twistronic-mechanical systems, providing avenues for the integration of twistronics into various mechanical frameworks.
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Affiliation(s)
- Jianxin Liu
- Department of Engineering Mechanics, School of Civil Engineering, Wuhan University, Wuhan, Hubei, 430072, China
| | - Xiaoqi Yang
- Department of Engineering Mechanics, School of Civil Engineering, Wuhan University, Wuhan, Hubei, 430072, China
| | - Hui Fang
- Department of Engineering Mechanics, School of Civil Engineering, Wuhan University, Wuhan, Hubei, 430072, China
| | - Weidong Yan
- Department of Engineering Mechanics, School of Civil Engineering, Wuhan University, Wuhan, Hubei, 430072, China
| | - Wengen Ouyang
- Department of Engineering Mechanics, School of Civil Engineering, Wuhan University, Wuhan, Hubei, 430072, China
- State Key Laboratory of Water Resources Engineering and Management, Wuhan University, Wuhan, Hubei, 430072, P. R. China
| | - Ze Liu
- Department of Engineering Mechanics, School of Civil Engineering, Wuhan University, Wuhan, Hubei, 430072, China
- State Key Laboratory of Water Resources Engineering and Management, Wuhan University, Wuhan, Hubei, 430072, P. R. China
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4
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Zhang D, Huang M, Klausen LH, Li Q, Li S, Dong M. Liquid-Phase Friction of Two-Dimensional Molybdenum Disulfide at the Atomic Scale. ACS APPLIED MATERIALS & INTERFACES 2023; 15:21595-21601. [PMID: 37070722 DOI: 10.1021/acsami.3c00221] [Citation(s) in RCA: 1] [Impact Index Per Article: 1.0] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Subscribe] [Scholar Register] [Indexed: 05/05/2023]
Abstract
Tribological properties depend strongly on environmental conditions such as temperature, humidity, and operation liquid. However, the origin of the liquid effect on friction remains largely unexplored. Herein, taking molybdenum disulfide (MoS2) as a model system, we explored the nanoscale friction of MoS2 in polar (water) and nonpolar (dodecane) liquids through friction force microscopy. The friction force exhibits a similar layer-dependent behavior in liquids as in air; i.e., thinner samples have a larger friction force. Interestingly, friction is significantly influenced by the polarity of the liquid, and it is larger in polar water than in nonpolar dodecane. Atomically resolved friction images together with atomistic simulations reveal that the polarity of the liquid has a substantial effect on friction behavior, where liquid molecule arrangement and hydrogen-bond formation lead to a higher resistance in polar water in comparison to that in nonpolar dodecane. This work provides insights into the friction on two-dimensional layered materials in liquids and holds great promise for future low-friction technologies.
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Affiliation(s)
- Deliang Zhang
- Key Laboratory of Colloid and Interface Chemistry of the Ministry of Education, School of Chemistry and Chemical Engineering, Shandong University, Jinan 250100, China
| | - Mingzheng Huang
- State Key Laboratory for Mechanical Behavior of Materials, Xi'an Jiaotong University, Xi'an 710049, China
| | | | - Qiang Li
- Key Laboratory of Colloid and Interface Chemistry of the Ministry of Education, School of Chemistry and Chemical Engineering, Shandong University, Jinan 250100, China
| | - Suzhi Li
- State Key Laboratory for Mechanical Behavior of Materials, Xi'an Jiaotong University, Xi'an 710049, China
| | - Mingdong Dong
- Interdisciplinary Nanoscience Center (iNANO), Aarhus University, Aarhus C DK-8000, Denmark
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5
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Zhou X, Chen P, Xu RG, Zhang C, Zhang J. Interfacial friction of vdW heterostructures affected by in-plane strain. NANOTECHNOLOGY 2022; 34:015708. [PMID: 36174390 DOI: 10.1088/1361-6528/ac962a] [Citation(s) in RCA: 0] [Impact Index Per Article: 0] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Subscribe] [Scholar Register] [Received: 06/17/2022] [Accepted: 09/28/2022] [Indexed: 06/16/2023]
Abstract
Interfacial properties of van der Waals (vdW) heterostructures dominate the durability and function of their booming practical and potential applications such as opoelectronic devices, superconductors and even pandemics research. However, the strain engineering modulates of interlayer friction of vdW heterostructures consisting of two distinct materials are still unclear, which hinders the applications of vdW heterostructures, as well as the design of solid lubricant and robust superlubricity. In the present paper, a molecular model between a hexagonal graphene flake and a rectangular SLMoS2sheet is established, and the influence of biaxial and uniaxial strain on interlayer friction is explored by molecular dynamics. It is found that the interlayer friction is insensitive to applied strains. Strong robustness of superlubricity between distinct layers is owed to the structure's intrinsic incommensurate characteristics and the existence of Moiré pattern. In engineering practice, it is of potential importance to introduce two distinct 2D materials at the sliding contact interface to reduce the interfacial friction of the contact pair and serve as ideal solid lubricants. Our research provides a further basis to explore the nanotribology and strain engineering of 2D materials and vdW heterostructures.
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Affiliation(s)
- Xuanling Zhou
- State Key Laboratory for Geomechanics and Deep Underground Engineering, School of Mechanics and Civil Engineering, China University of Mining and Technology, Xuzhou, Jiangsu, 221116, People's Republic of China
| | - Peijian Chen
- State Key Laboratory for Geomechanics and Deep Underground Engineering, School of Mechanics and Civil Engineering, China University of Mining and Technology, Xuzhou, Jiangsu, 221116, People's Republic of China
- State Key Laboratory of Mechanics and Control of Mechanical Structures, Nanjing University of Aeronautics and astronautics, Nanjing, Jiangsu, 210016, People's Republic of China
- State Key Laboratory of Solid Lubrication, Lanzhou Institute of Chemical Physics, Chinese Academy of Sciences, Lanzhou 730000, People's Republic of China
| | - Rong-Guang Xu
- School of Engineering & Applied Science, The George Washington University, Washington DC, WA-20052, United States of America
| | - Cun Zhang
- Department of Engineering Mechanics, Shijiazhuang Tiedao University, Shijiazhuang, 050043, People's Republic of China
| | - Jiazhen Zhang
- State Key Laboratory for Geomechanics and Deep Underground Engineering, School of Mechanics and Civil Engineering, China University of Mining and Technology, Xuzhou, Jiangsu, 221116, People's Republic of China
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Noël O, Mazeran PE, Stanković I. Nature of Dynamic Friction in a Humid Hydrophobic Nanocontact. ACS NANO 2022; 16:10768-10774. [PMID: 35731935 DOI: 10.1021/acsnano.2c02665] [Citation(s) in RCA: 0] [Impact Index Per Article: 0] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Subscribe] [Scholar Register] [Indexed: 06/15/2023]
Abstract
The physics of dynamic friction on water molecule contaminated surfaces is still poorly understood. In line with the growing interest in hydrophobic contact for industrial applications, this paper focuses on friction mechanisms in such interfaces. As a commonly used material, contact with graphite is considered in a twin-fold approach based on experimental investigations using the circular mode atomic force microscopy technique combined with molecular dynamic simulations. We demonstrate that an intuitive paradigm, which asserts that water molecules are squeezed out of a hydrophobic contact, should be refined. As a consequence, we introduce a mechanism considering a droplet produced within the sliding nanocontact by the accumulation of water adsorbed on the substrate. Then we show that a full slip regime of the droplet sliding on the hydrophobic substrate explains the experimental tribological behavior.
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Affiliation(s)
- Olivier Noël
- IMMM, UMR CNRS 6283, Le Mans Université, Avenue O. Messiaen, 72085 Cedex 09, Le Mans, France
| | - Pierre-Emmanuel Mazeran
- Sorbonne Universités, Université de Technologie de Compiègne, Laboratoire Roberval, FRE UTC-CNRS 2012, Centre de Recherche de Royallieu, CS 60319, 60203, Compiègne Cedex, France
| | - Igor Stanković
- Scientific Computing Laboratory, Center for the Study of Complex Systems, Institute of Physics Belgrade, University of Belgrade, Pregrevica 118, 11080 Belgrade, Serbia
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7
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Park I, Hausen F, Baltruschat H. Friction on I‐modified Au(111) in a Tetraglyme Electrolyte. ChemElectroChem 2022. [DOI: 10.1002/celc.202101660] [Citation(s) in RCA: 0] [Impact Index Per Article: 0] [Reference Citation Analysis] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/08/2022]
Affiliation(s)
- Inhee Park
- University of Bonn: Rheinische Friedrich-Wilhelms-Universitat Bonn Institute of Physical and Theoretical Chemistry 53117 Bonn GERMANY
| | - Florian Hausen
- RWTH Aachen University: Rheinisch-Westfalische Technische Hochschule Aachen Institute of Physical Chemistry 52425 Jülich GERMANY
| | - Helmut Baltruschat
- University of Bonn Inst. f. Physikalische u.Theoret. Chemie R�merstra�e 164-Abteilung Elektrochemie- 53117 Bonn GERMANY
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8
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Claerbout VEP, Nicolini P, Polcar T. Exploring Nanoscale Lubrication Mechanisms of Multilayer MoS 2 During Sliding: The Effect of Humidity. Front Chem 2021; 9:684441. [PMID: 34249859 PMCID: PMC8265273 DOI: 10.3389/fchem.2021.684441] [Citation(s) in RCA: 4] [Impact Index Per Article: 1.3] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 03/23/2021] [Accepted: 05/31/2021] [Indexed: 12/03/2022] Open
Abstract
Solid lubricants have received substantial attention due to their excellent frictional properties. Among others, molybdenum disulfide (MoS2) is one of the most studied lubricants. Humidity results in a deterioration of the frictional properties of MoS2. The actual mechanism at the nanoscale is still under debate, although there are indications that chemical reactions are not likely to occur in defect-free structures. In this study, we performed nonequilibrium molecular dynamics simulations to study the frictional properties of multilayer MoS2 during sliding in the presence of water. Moreover, we also investigated the effect of sliding speed and normal load. We confirmed earlier results that a thin layer of water organizes as a solidified, ice-like network of hydrogen bonds as a result of being confined in a two-dimensional fashion between MoS2. Moreover, we found that there exists an energy-driven, rotational dependence of the water network atop/beneath MoS2. This orientational anisotropy is directly related to the dissipative character of MoS2 during sliding. Finally, three distinct frictional regimes were identified, two for a thin layer of water and one for bulk water. In the case of a thin layer and low coverage, water represents a solid-like contaminant, causing high energy dissipation. For a thin layer and high coverage, water starts to act as a solid-like lubricant, reducing dissipation during sliding. Finally, a regime where water acts as a liquid lubricant, characterized by a clear velocity dependence was found.
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Affiliation(s)
- Victor E P Claerbout
- Department of Control Engineering, Faculty of Electrical Engineering, Czech Technical University in Prague, Prague, Czechia
| | - Paolo Nicolini
- Department of Control Engineering, Faculty of Electrical Engineering, Czech Technical University in Prague, Prague, Czechia
| | - Tomas Polcar
- Department of Control Engineering, Faculty of Electrical Engineering, Czech Technical University in Prague, Prague, Czechia
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9
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Park I, Baltruschat H. In situ friction study of Ag Underpotential deposition (UPD) on Au(111) in aqueous electrolyte. Chemphyschem 2021; 22:952-959. [PMID: 33734530 PMCID: PMC8252634 DOI: 10.1002/cphc.202100130] [Citation(s) in RCA: 1] [Impact Index Per Article: 0.3] [Reference Citation Analysis] [Abstract] [Key Words] [Grants] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 02/16/2021] [Revised: 03/15/2021] [Indexed: 11/29/2022]
Abstract
The electrodeposition of silver on Au(111) was investigated using lateral force microscopy (LFM) in Ag+ containing sulfuric acid. Friction force images show that adsorbed sulfate forms3 × 7 R 19 . 1 ∘ structure (θ s u l f a t e = 0 . 2 ) on Au(111) prior to Ag underpotential deposition (UPD) and ( 3 × 3 R 30 ∘ ) structure (θ s u l f a t e = 0 . 33 ) on a complete monolayer or bilayer of Ag. Variation of friction with normal load shows a non-monotonous dependence, which is caused by increasing penetration of the tip into the sulfate adlayer. In addition, the friction force is influenced by the varying coverage and mobility of Ag atoms on the surface. Before Ag coverage reaches the critical value, the deposited silver atoms may be mobile enough to be dragged by the movement of AFM tip. Possible penetration of the tip into the UPD layer at very high loads is discussed as a model for self-healing wear. However, when the coverage of Ag is close to 1, the deposited Ag atoms are tight enough to resist the influence of the AFM tip and the tip penetrates only into the sulfate adlayer.
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Affiliation(s)
- Inhee Park
- Institut für physikalische und Theoretische ChemieUniversität BonnRömerstraße 164D-53117BonnGermany
| | - H. Baltruschat
- Institut für physikalische und Theoretische ChemieUniversität BonnRömerstraße 16453117BonnGermany
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10
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Gao H, Ewen JP, Hartkamp R, Müser MH, Dini D. Scale-Dependent Friction-Coverage Relations and Nonlocal Dissipation in Surfactant Monolayers. LANGMUIR : THE ACS JOURNAL OF SURFACES AND COLLOIDS 2021; 37:2406-2418. [PMID: 33545003 DOI: 10.1021/acs.langmuir.0c03403] [Citation(s) in RCA: 2] [Impact Index Per Article: 0.7] [Reference Citation Analysis] [Abstract] [Track Full Text] [Subscribe] [Scholar Register] [Indexed: 06/12/2023]
Abstract
Surfactant molecules, known as organic friction modifiers (OFMs), are routinely added to lubricants to reduce friction and wear between sliding surfaces. In macroscale experiments, friction generally decreases as the coverage of OFM molecules on the sliding surfaces increases; however, recent nanoscale experiments with sharp atomic force microscopy (AFM) tips have shown increasing friction. To elucidate the origin of these opposite trends, we use nonequilibrium molecular dynamics (NEMD) simulations and study kinetic friction between OFM monolayers and an indenting nanoscale asperity. For this purpose, we investigate various coverages of stearamide OFMs on iron oxide surfaces and silica AFM tips with different radii of curvature. We show that the differences between the friction-coverage relations from macroscale and nanoscale experiments are due to molecular plowing in the latter. For our small tip radii, the friction coefficient and indentation depth both have a nonmonotonic dependence on OFM surface coverage, with maxima occurring at intermediate coverage. We rationalize the nonmonotonic relations through a competition of two effects (confinement and packing density) that varying the surface coverage has on the effective stiffness of the OFM monolayers. We also show that kinetic friction is not very sensitive to the sliding velocity in the range studied, indicating that it originates from instabilities. Indeed, we find that friction predominately originates from plowing of the monolayers by the leading edge of the tip, where gauche defects are created, while thermal dissipation is mostly localized in molecules toward the trailing edge of the tip, where the chains return to a more extended conformation.
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Affiliation(s)
- Hongyu Gao
- Department of Materials Science and Engineering, Universität des Saarlandes, 66123 Saarbrücken, Germany
| | - James P Ewen
- Department of Mechanical Engineering, Imperial College London, London SW7 2AZ, U.K
| | - Remco Hartkamp
- Process and Energy Department, Delft University of Technology, Leeghwaterstraat 39, 2628 CB Delft, The Netherlands
| | - Martin H Müser
- Department of Materials Science and Engineering, Universität des Saarlandes, 66123 Saarbrücken, Germany
| | - Daniele Dini
- Department of Mechanical Engineering, Imperial College London, London SW7 2AZ, U.K
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11
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Qu C, Wang K, Wang J, Gongyang Y, Carpick RW, Urbakh M, Zheng Q. Origin of Friction in Superlubric Graphite Contacts. PHYSICAL REVIEW LETTERS 2020; 125:126102. [PMID: 33016762 DOI: 10.1103/physrevlett.125.126102] [Citation(s) in RCA: 16] [Impact Index Per Article: 4.0] [Reference Citation Analysis] [Abstract] [Track Full Text] [Subscribe] [Scholar Register] [Received: 04/16/2020] [Accepted: 08/20/2020] [Indexed: 06/11/2023]
Abstract
More than thirty years ago, it was theoretically predicted that friction for incommensurate contacts between atomically smooth, infinite, crystalline materials (e.g., graphite, MoS_{2}) is vanishing in the low speed limit, and this corresponding state was called structural superlubricity (SSL). However, experimental validation of this prediction has met challenges, since real contacts always have a finite size, and the overall friction arises not only from the atoms located within the contact area, but also from those at the contact edges which can contribute a finite amount of friction even when the incommensurate area does not. Here, we report, using a novel method, the decoupling of these contributions for the first time. The results obtained from nanoscale to microscale incommensurate contacts of graphite under ambient conditions verify that the average frictional contribution of an inner atom is no more than 10^{-4} that of an atom at the edge. Correspondingly, the total friction force is dominated by friction between the contact edges for contacts up to 10 μm in lateral size. We discuss the physical mechanisms of friction observed in SSL contacts, and provide guidelines for the rational design of large-scale SSL contacts.
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Affiliation(s)
- Cangyu Qu
- Institute of Superlubricity Technology, Research Institute of Tsinghua University in Shenzhen, Shenzhen 518057, China
- Center for Nano and Micro Mechanics, Tsinghua University, Beijing 100084, China
- Department of Engineering Mechanics, Tsinghua University, Beijing 100084, China
| | - Kunqi Wang
- Center for Nano and Micro Mechanics, Tsinghua University, Beijing 100084, China
- State Key Laboratory of Tribology & Department of Mechanical Engineering, Tsinghua University, Beijing 100084, China
| | - Jin Wang
- Center for Nano and Micro Mechanics, Tsinghua University, Beijing 100084, China
- Department of Engineering Mechanics, Tsinghua University, Beijing 100084, China
| | - Yujie Gongyang
- Center for Nano and Micro Mechanics, Tsinghua University, Beijing 100084, China
- Department of Engineering Mechanics, Tsinghua University, Beijing 100084, China
| | - Robert W Carpick
- Mechanical Engineering and Applied Mechanics Department, University of Pennsylvania, Philadelphia, Pennsylvania 19147, USA
| | - Michael Urbakh
- Department of Physical Chemistry, School of Chemistry, The Raymond and Beverly Sackler Faculty of Exact Sciences, and The Sackler Center for Computational Molecular and Materials Science, Tel Aviv University, Tel Aviv 69978, Israel
| | - Quanshui Zheng
- Institute of Superlubricity Technology, Research Institute of Tsinghua University in Shenzhen, Shenzhen 518057, China
- Center for Nano and Micro Mechanics, Tsinghua University, Beijing 100084, China
- Department of Engineering Mechanics, Tsinghua University, Beijing 100084, China
- State Key Laboratory of Tribology & Department of Mechanical Engineering, Tsinghua University, Beijing 100084, China
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12
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Pang H, Wang H, Li M, Gao C. Atomic-Scale Friction on Monovacancy-Defective Graphene and Single-Layer Molybdenum-Disulfide by Numerical Analysis. NANOMATERIALS 2020; 10:nano10010087. [PMID: 31906488 PMCID: PMC7023280 DOI: 10.3390/nano10010087] [Citation(s) in RCA: 4] [Impact Index Per Article: 1.0] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Download PDF] [Figures] [Subscribe] [Scholar Register] [Received: 12/06/2019] [Revised: 12/23/2019] [Accepted: 12/26/2019] [Indexed: 12/25/2022]
Abstract
Using numerical simulations, we study the atomic-scale frictional behaviors of monovacancy-defective graphene and single-layer molybdenum-disulfide (SLMoS2) based on the classical Prandtl–Tomlinson (PT) model with a modified interaction potential considering the Schwoebel–Ehrlich barrier. Due to the presence of a monovacancy defect on the surface, the frictional forces were significantly enhanced. The effects of the PT model parameters on the frictional properties of monovacancy-defective graphene and SLMoS2 were analyzed, and it showed that the spring constant of the pulling spring cx is the most influential parameter on the stick–slip motion in the vicinity of the vacancy defect. Besides, monovacancy-defective SLMoS2 is found to be more sensitive to the stick–slip motion at the vacancy defect site than monovacancy-defective graphene, which can be attributed to the complicated three-layer-sandwiched atomic structure of SLMoS2. The result suggests that the soft tip with a small spring constant can be an ideal candidate for the observation of stick–slip behaviors of the monovacancy-defective surface. This study can fill the gap in atomic-scale friction experiments and molecular dynamics simulations of 2D materials with vacancy-related defects.
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Affiliation(s)
- Haosheng Pang
- School of Mechanical Engineering and Automation, Fuzhou University, Fuzhou, Fujian 350002, China
| | - Hongfa Wang
- School of Mechanical Engineering and Automation, Fuzhou University, Fuzhou, Fujian 350002, China
| | - Minglin Li
- School of Mechanical Engineering and Automation, Fuzhou University, Fuzhou, Fujian 350002, China
- Fujian Key Laboratory of Medical Instrumentation and Pharmaceutical Technology, Fuzhou University, Fuzhou, Fujian 350002, China
- Correspondence: (M.L.); (C.G.)
| | - Chenghui Gao
- School of Mechanical Engineering and Automation, Fuzhou University, Fuzhou, Fujian 350002, China
- Correspondence: (M.L.); (C.G.)
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Deng H, Ma M, Song Y, He Q, Zheng Q. Structural superlubricity in graphite flakes assembled under ambient conditions. NANOSCALE 2018; 10:14314-14320. [PMID: 30019038 DOI: 10.1039/c7nr09628c] [Citation(s) in RCA: 19] [Impact Index Per Article: 3.2] [Reference Citation Analysis] [Abstract] [Track Full Text] [Subscribe] [Scholar Register] [Indexed: 06/08/2023]
Abstract
To date, structural superlubricity in microscale contacts is mostly observed in intrinsic graphite flakes that are cleaved by shearing from HOPG mesas in situ or friction pairs assembled in vacuum due to the high requirement of ultra clean interface for superlubricity, which severely limits their practical applications. Herein, we report observations on microscale structural superlubricity in graphite flake pairs assembled under ambient conditions, where contaminants are inevitably present at the interfaces. For such friction pairs, we find a novel running-in phenomenon, where the friction decreases with reciprocating motions, but no morphological or chemical changes can be observed. The underlying mechanism for the new running-in process is revealed to be the removal of third bodies confined between the surfaces. Our results improve the understanding of microscale superlubricity and may help extend the practical applications of superlubricity.
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Affiliation(s)
- He Deng
- School of Mechanical Engineering, Southwest Jiaotong University, Chengdu 610031, PR China
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Jana PK, Chen W, Alava MJ, Laurson L. Nanoscale liquid crystal lubrication controlled by surface structure and film composition. Phys Chem Chem Phys 2018; 20:18737-18743. [PMID: 29961781 DOI: 10.1039/c8cp03353f] [Citation(s) in RCA: 6] [Impact Index Per Article: 1.0] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/21/2022]
Abstract
Liquid crystals have emerged as potential candidates for next-generation lubricants due to their tendency to exhibit long-range ordering. Here, we construct a full atomistic model of 4-cyano-4-hexylbiphenyl (6CB) nematic liquid crystal lubricants mixed with hexane and confined by mica surfaces. We explore the effect of the surface structure of mica, as well as lubricant composition and thickness, on the nanoscale friction in the system. Our results demonstrate the key role of the structure of the mica surfaces, specifically the positions of potassium (K+) ions, in determining the nature of sliding friction with monolayer lubricants, including the presence or absence of stick-slip dynamics. With the commensurate setup of confining surfaces, when the grooves created between the periodic K+ ions are parallel to the sliding direction we observe a lower friction force as compared to the perpendicular situation. Random positions of ions exhibit even smaller friction forces with respect to the previous two cases. For thicker lubrication layers the surface structure becomes less important and we observe a good agreement with the experimental data on bulk viscosity of 6CB and the additive hexane. In case of thicker lubrication layers, friction may still be controlled by tuning the relative concentrations of 6CB and hexane in the mixture.
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Affiliation(s)
- Pritam Kumar Jana
- COMP Centre of Excellence, Department of Applied Physics, Aalto University, P.O. Box 11100, FI-00076 Aalto, Espoo, Finland.
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