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Li J, Li J, Yi S, Wang K. Boundary Slip of Oil Molecules at MoS 2 Homojunctions Governing Superlubricity. ACS APPLIED MATERIALS & INTERFACES 2022; 14:8644-8653. [PMID: 35119817 DOI: 10.1021/acsami.2c00693] [Citation(s) in RCA: 5] [Impact Index Per Article: 2.5] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Subscribe] [Scholar Register] [Indexed: 06/14/2023]
Abstract
Molybdenum disulfide (MoS2) nanoflakes are widely used as nano-additives in oil for the excellent lubrication performance. However, the molecular mechanism of MoS2 nanoflakes in oil governing the friction properties remains elusive. In this study, MoS2 homojunctions were constructed by combining the fabricated MoS2 probe and MoS2 crystal with an atomic force microscope (AFM), and the superlubricity with an ultralow friction coefficient of approximately 0.003 at MoS2 homojunctions was attained after the formation of a confined oil layer, exhibiting a 67% reduction of the friction coefficient in comparison to that under a nitrogen atmosphere. The boundary slip of oil molecules on the MoS2 crystal with a small energy barrier was observed, causing the shear to occur at the interface of oil/MoS2 crystal with an extremely low shear strength, which contributes to the achievement of superlubricity. This boundary slip of oil molecules at MoS2 homojunctions can be extended to the macroscale for friction reduction, supplying a fundamental insight into the lubrication mechanism of MoS2 nanoflakes in oil, which has potential applications for designing an efficient lubrication system with nano-additives.
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Affiliation(s)
- Jianfeng Li
- State Key Laboratory of Tribology, Tsinghua University, Beijing 100084, China
| | - Jinjin Li
- State Key Laboratory of Tribology, Tsinghua University, Beijing 100084, China
| | - Shuang Yi
- State Key Laboratory of Tribology, Tsinghua University, Beijing 100084, China
| | - Kaiqiang Wang
- State Key Laboratory of Tribology, Tsinghua University, Beijing 100084, China
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Cafolla C, Foster W, Voïtchovsky K. Lubricated friction around nanodefects. SCIENCE ADVANCES 2020; 6:eaaz3673. [PMID: 32284981 PMCID: PMC7124950 DOI: 10.1126/sciadv.aaz3673] [Citation(s) in RCA: 8] [Impact Index Per Article: 2.0] [Reference Citation Analysis] [Abstract] [Grants] [Track Full Text] [Figures] [Subscribe] [Scholar Register] [Received: 09/03/2019] [Accepted: 01/08/2020] [Indexed: 06/11/2023]
Abstract
The lubrication properties of nanoconfined liquids underpin countless natural and industrial processes. However, our current understanding of lubricated friction is still limited, especially for nonideal interfaces exhibiting nanoscale chemical and topographical defects. Here, we use atomic force microscopy to explore the equilibrium and dynamical behavior of a model lubricant, squalane, confined between a diamond tip and graphite in the vicinity of an atomic step. We combine high-resolution imaging of the interface with highly localized shear measurements at different velocities and temperatures to derive a quantitative picture of the lubricated friction around surface defects. We show that defects tend to promote local molecular order and increase friction forces by reducing the number of stable molecular configurations in their immediate vicinity. The effect is general, can propagate over hundreds of nanometers, and can be quantitatively described by a semiempirical model that bridges the molecular details and mesoscale observations.
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Moriguchi S, Tsujimoto T, Sasahara A, Kokawa R, Onishi H. Nanometer-Scale Distribution of a Lubricant Modifier on Iron Films: A Frequency-Modulation Atomic Force Microscopy Study Combined with a Friction Test. ACS OMEGA 2019; 4:17593-17599. [PMID: 31656935 PMCID: PMC6812132 DOI: 10.1021/acsomega.9b02821] [Citation(s) in RCA: 1] [Impact Index Per Article: 0.2] [Reference Citation Analysis] [Abstract] [Track Full Text] [Figures] [Subscribe] [Scholar Register] [Received: 09/01/2019] [Accepted: 09/24/2019] [Indexed: 06/10/2023]
Abstract
Liquid lubricants used in mechanical applications are low-vapor-pressure hydrocarbons modified with a small quantity of polar compounds. The polar modifiers adsorbed on the surface of sliding solids dominate the friction properties when the sliding surfaces are in close proximity. However, a few methods are available for the characterization of the adsorbed modifiers of a nanometer-scale thickness. In this study, we applied frequency-modulation atomic force microscopy to evaluate the vertical and lateral density distributions of the adsorbed modifier in a real lubricant, namely, poly-α-olefin (PAO) modified with an orthophosphoric acid oleyl ester. The liquid-induced force on the probing tip was mapped on a plane that was perpendicular to the lubricant-iron interface with a force sensitivity on the order of 10 pN. The PAO in the absence of the ester modifier was directly exposed to the film, which produced a few liquid layers parallel to the film surface with layer-to-layer distances of 0.6-0.7 nm. A monomolecular layer of the modifier was intermittently adsorbed with increasing ester concentration in the bulk lubricant, with complete coverage seen at 20 ppm. The C18H35 chains of the oleyl esters fluctuating in the lubricant produced a repulsive force on the tip, which monotonically decayed with the tip-to-surface distance. The dynamic friction coefficient of sliding steel-lubricant-steel interfaces, which was separately determined using a friction tester, was compared with the force map determined on the iron film immersed in the corresponding lubricant. The complete monomolecular layer of the ester modifier on the static lubricant-iron boundary is a requirement for achieving smooth and stable friction at the sliding interface.
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Affiliation(s)
- Shiho Moriguchi
- Department
of Chemistry, School of Science, Kobe University, Rokko-dai, Nada-ku, Kobe 657-8501, Japan
- Shimadzu
Techno-Research Incorporated, Nishinokyo-shimoaicho, Nakagyo-ku, Kyoto 604-8436, Japan
| | - Teppei Tsujimoto
- JXTG
Nippon Oil & Energy Corporation, Chidoricho, Naka-ku, Yokohama 231-0815, Japan
| | - Akira Sasahara
- Department
of Chemistry, School of Science, Kobe University, Rokko-dai, Nada-ku, Kobe 657-8501, Japan
| | - Ryohei Kokawa
- Shimadzu
Corporation, Nishinokyo-Kuwabaracho, Nakagyo-ku, Kyoto 604-8511, Japan
| | - Hiroshi Onishi
- Department
of Chemistry, School of Science, Kobe University, Rokko-dai, Nada-ku, Kobe 657-8501, Japan
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Xu RG, Xiang Y, Leng Y. Computational simulations of solvation force and squeezing out of dodecane chain molecules in an atomic force microscope. J Chem Phys 2017; 147:054705. [DOI: 10.1063/1.4996886] [Citation(s) in RCA: 9] [Impact Index Per Article: 1.3] [Reference Citation Analysis] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/14/2022] Open
Affiliation(s)
- Rong-Guang Xu
- Department of Mechanical and Aerospace Engineering, The George Washington University, Washington, DC 20052, USA
| | - Yuan Xiang
- Department of Mechanical and Aerospace Engineering, The George Washington University, Washington, DC 20052, USA
| | - Yongsheng Leng
- Department of Mechanical and Aerospace Engineering, The George Washington University, Washington, DC 20052, USA
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Voïtchovsky K. Effect of temperature on the viscoelastic properties of nano-confined liquid mixtures. NANOSCALE 2016; 8:17472-17482. [PMID: 27714164 DOI: 10.1039/c6nr05879e] [Citation(s) in RCA: 1] [Impact Index Per Article: 0.1] [Reference Citation Analysis] [Abstract] [Track Full Text] [Subscribe] [Scholar Register] [Indexed: 06/06/2023]
Abstract
The behaviour of fluids confined in nanoscale gaps plays a central role in molecular science and nanofluidics, with applications ranging from biological function to multiscale printing, osmosis and filtration, lab-on-chip technology and friction reduction. Here atomic force microscopy is used to shear five different mixtures of hexadecane and squalane confined between the tip apex and atomically flat graphite. The shearing amplitudes are typically <2 nm, hence reflecting highly localised information at the interface. The evolution of each mixture's viscoelastic properties is studied as a function of temperature, between 20 °C and 100 °C. The results, complemented by sub-nanometre resolution images of the interface, show that spatial organisation of the liquid molecules at the surface of graphite largely dominates the measurements. Squalane presents a higher effective affinity for the surface by forming a robust self-assembled layer in all mixtures. This results in a step-like change of the viscous and elastic response of the confined liquid as the confining pressure increases. In contrast, measurements in pure hexadecane show a continuous and linear increase in the apparent viscosity with pressure at all temperatures. This is interpreted as a more fragile interfacial layer and images show that it can be completely removed at high temperatures. Depending on the mixture composition, measurements can be strongly location-dependent which suggests molecular clustering and nanoscale phase separation at the interface.
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Gosvami NN, O'Shea SJ. Nanoscale Trapping and Squeeze-Out of Confined Alkane Monolayers. LANGMUIR : THE ACS JOURNAL OF SURFACES AND COLLOIDS 2015; 31:12960-12967. [PMID: 26529283 DOI: 10.1021/acs.langmuir.5b03133] [Citation(s) in RCA: 1] [Impact Index Per Article: 0.1] [Reference Citation Analysis] [Abstract] [Track Full Text] [Subscribe] [Scholar Register] [Indexed: 06/05/2023]
Abstract
We present combined force curve and conduction atomic force microscopy (AFM) data for the linear alkanes CnH2n+2 (n = 10, 12, 14, 16) confined between a gold-coated AFM tip and a graphite surface. Solvation layering is observed in the force curves for all liquids, and conduction AFM is used to study in detail the removal of the confined (mono)layer closest to the graphite surface. The squeeze-out behavior of the monolayer can be very different depending upon the temperature. Below the monolayer melting transition temperatures the molecules are in an ordered state on the graphite surface, and fast and complete removal of the confined molecules is observed. However, above the melting transition temperature the molecules are in a disordered state, and even at large applied pressure a few liquid molecules are trapped within the tip-sample contact zone. These findings are similar to a previous study for branched alkanes [ Gosvami Phys. Rev. Lett. 2008, 100, 076101 ], but the observation for the linear alkane homologue series demonstrates clearly the dependence of the squeeze-out and trapping on the state of the confined material.
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Affiliation(s)
- N N Gosvami
- Department of Mechanical Engineering and Applied Mechanics, University of Pennsylvania , Philadelphia, Pennsylvania 19104, United States
| | - S J O'Shea
- Institute of Materials Research and Engineering, 2 Fusionopolis Way, Innovis #08-03, Singapore 138634
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Xu RG, Leng Y. Solvation force simulations in atomic force microscopy. J Chem Phys 2014; 140:214702. [DOI: 10.1063/1.4879657] [Citation(s) in RCA: 16] [Impact Index Per Article: 1.6] [Reference Citation Analysis] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/14/2022] Open
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Nanomechanics of lipid bilayers by force spectroscopy with AFM: A perspective. BIOCHIMICA ET BIOPHYSICA ACTA-BIOMEMBRANES 2010; 1798:741-9. [DOI: 10.1016/j.bbamem.2009.12.019] [Citation(s) in RCA: 135] [Impact Index Per Article: 9.6] [Reference Citation Analysis] [Track Full Text] [Subscribe] [Scholar Register] [Received: 10/04/2009] [Revised: 12/16/2009] [Accepted: 12/20/2009] [Indexed: 01/11/2023]
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Van LP, Kyrylyuk V, Polesel-Maris J, Thoyer F, Lubin C, Cousty J. Experimental three-dimensional description of the liquid hexadecane/graphite interface. LANGMUIR : THE ACS JOURNAL OF SURFACES AND COLLOIDS 2009; 25:639-642. [PMID: 19072577 DOI: 10.1021/la803665k] [Citation(s) in RCA: 2] [Impact Index Per Article: 0.1] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Subscribe] [Scholar Register] [Indexed: 05/27/2023]
Abstract
By using an atomic force microscope based on a quartz tuning fork sensor, a 3-dimensional description of the interface between liquid hexadecane and a highly oriented pyrolytic graphite surface can be achieved at room temperature. The C16H34 monolayer in contact with the substrate surface exhibits a lamellar structure whereas no observation at the liquid/graphite interface by scanning tunnelling microscopy was reported for this alkane. The second layer shows very weak corrugations corresponding to lamella boundaries. Force/distance curves show at least four oscillations separated by 0.4 nm except for the first period with a 0.38 nm distance that corresponds to the layer closer the substrate. Such a description agrees well with molecular dynamics results obtained on alkane/solid interfaces.
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Affiliation(s)
- L Pham Van
- CEA-Saclay, bat. 462, F-91191 Gif sur Yvette Cedex, France
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