Non-empirical law depicting how atomic-scale friction behaves is crucial for facilitating the practical design of tribosystems.However,progress in developing a practically usable friction law has stagnated because ato...Non-empirical law depicting how atomic-scale friction behaves is crucial for facilitating the practical design of tribosystems.However,progress in developing a practically usable friction law has stagnated because atomic-scale friction arises from the continuous formation and rupture of interfacial chemical bonds,and such interfacial chemical reactions are difficult to measure precisely.Here,we propose a usable friction law for atomic-scale contact by using large-scale atomistic simulations to correctly measure the interfacial chemical reactions of a realistic rough surface.This friction model is effective to predict how atomicscale friction force varies with temperature,sliding velocity,and load.As a special example,our model predicts velocity-related mountain-like temperature dependence of friction,and this prediction result is then carefully validated by comparison with ultrahigh-vacuum atomic force microscopy(AFM)experiments.展开更多
To meet the surging needs in energy efficiency and eco-friendly lubricants,a novel superlubricious technology using a vegetable oil and ceramic materials is proposed.By coupling different hydrogen-free amorphous carbo...To meet the surging needs in energy efficiency and eco-friendly lubricants,a novel superlubricious technology using a vegetable oil and ceramic materials is proposed.By coupling different hydrogen-free amorphous carbon coatings with varying fraction of sp^(2) and sp^(3) hybridized carbon in presence of a commercially available silicon nitride bulk ceramic,castor oil provides superlubricity although the liquid vegetable oil film in the contact is only a few nanometres thick at most.Besides a partial liquid film possibly separating surfaces in contact,local tribochemical reactions between asperities are essential to maintain superlubricity at low speeds.High local pressure activates chemical degradation of castor oil generating graphitic/graphenic-like species on top of asperities,thus helping both the chemical polishing of surface and its chemical passivation by H and OH species.Particularly,the formation of the formation of–(CH_(2)–CH_(2))n–noligomers have been evidenced to have a major role in the friction reduction.Computer simulation unveils that formation of chemical degradation products of castor oil on friction surfaces are favoured by the quantity of sp^(2)-hybridized carbon atoms in the amorphous carbon structure.Hence,tuning sp^(2)-carbon content in hydrogen-free amorphous carbon,in particular,on the top layers of the coating,provides an alternative way to control superlubricity achieved with castor oil and other selected green lubricants.展开更多
基金supported by MEXT“Exploratory Challenge on Post-K Computer”(Challenge of Basic Science—Exploring Extremes through Multi-Physics and Multi-Scale Simulations),Japan Science and Technology Agency CREST(No.JPMJCR2191)Japan Society for the Promotion of Science(JSPS)Scientific Research(B)(No.21H01235)+6 种基金Grants-in-Aid for Scientific Research(C)(No.19K05380)Scientific Research(A)(No.18H03751)the National Natural Science Foundation of China(NSFC)(Nos.52305214,52235004,12172309,11890672,and 11602205)the Natural Science Foundation of Sichuan Province(Nos.2023YFSY0004 and 2022NSFSC1917)the New Interdisciplinary Cultivation Fund of Southwest Jiaotong University(No.2682022RC001)the Center for Computational Materials Science(CCMS,Tohoku University)for the use of MAterials science Supercomputing system for Advanced MUlti-scale simulations towards NExtgeneration—Institute for Materials Research(MASAMUNE-IMR)(Nos.18S0403,19S0506,20S0509,and 202012-SCKXX-0502)the Analytical and Testing Center of Southwest Jiaotong University for AFM measurements.
文摘Non-empirical law depicting how atomic-scale friction behaves is crucial for facilitating the practical design of tribosystems.However,progress in developing a practically usable friction law has stagnated because atomic-scale friction arises from the continuous formation and rupture of interfacial chemical bonds,and such interfacial chemical reactions are difficult to measure precisely.Here,we propose a usable friction law for atomic-scale contact by using large-scale atomistic simulations to correctly measure the interfacial chemical reactions of a realistic rough surface.This friction model is effective to predict how atomicscale friction force varies with temperature,sliding velocity,and load.As a special example,our model predicts velocity-related mountain-like temperature dependence of friction,and this prediction result is then carefully validated by comparison with ultrahigh-vacuum atomic force microscopy(AFM)experiments.
基金This research is supported by TOTAL,Solaize Research Center and Federal Ministry of Economic Affairs and Energy Germany(BMWi)within project CHEOPS3(Funding number 03ET1286B).
文摘To meet the surging needs in energy efficiency and eco-friendly lubricants,a novel superlubricious technology using a vegetable oil and ceramic materials is proposed.By coupling different hydrogen-free amorphous carbon coatings with varying fraction of sp^(2) and sp^(3) hybridized carbon in presence of a commercially available silicon nitride bulk ceramic,castor oil provides superlubricity although the liquid vegetable oil film in the contact is only a few nanometres thick at most.Besides a partial liquid film possibly separating surfaces in contact,local tribochemical reactions between asperities are essential to maintain superlubricity at low speeds.High local pressure activates chemical degradation of castor oil generating graphitic/graphenic-like species on top of asperities,thus helping both the chemical polishing of surface and its chemical passivation by H and OH species.Particularly,the formation of the formation of–(CH_(2)–CH_(2))n–noligomers have been evidenced to have a major role in the friction reduction.Computer simulation unveils that formation of chemical degradation products of castor oil on friction surfaces are favoured by the quantity of sp^(2)-hybridized carbon atoms in the amorphous carbon structure.Hence,tuning sp^(2)-carbon content in hydrogen-free amorphous carbon,in particular,on the top layers of the coating,provides an alternative way to control superlubricity achieved with castor oil and other selected green lubricants.
