Molybdenum disulfide(MoS_(2)) films are widely deployed in industrial applications owing to their inherent interlayer slip characteristics, offering energy consumption savings and prolonged mechanical part performance...Molybdenum disulfide(MoS_(2)) films are widely deployed in industrial applications owing to their inherent interlayer slip characteristics, offering energy consumption savings and prolonged mechanical part performance. Nevertheless, their practical utility is limited by environmental constraints and the limitations of preparation techniques, which hinder the attainment of robust superlubricity(friction coefficient < 0.01). Herein, through magnetron sputtering technology, we synthesize a core-shell-like nanocomposite composed of MoS_(2)nanosheets encapsulating B_(4)C. The core-shell-like structure enables the resulting films to preferentially grow crystalline MoS_(2), providing them with outstanding mechanical properties and efficient lubrication over a wide range of temperatures. Remarkably, such film achieves robust macroscale superlubricity and an ultralow wear rate(1.7 ×10^(-8)mm^(3)N-1m^(-1)) under high contact stress in a mild vacuum environment. This noteworthy outcome is primarily attributable to the self-segmentation of the macroscale contact interface during the friction process, involving:(1) a large amount of wear debris is embedded into the wear track to create extensive micro-sized asperities;(2) a nanolayer of amorphous carbon enriched with oxide nanoparticles is formed on the uppermost part of these asperities;(3) numerous incommensurate nanocontacts comprising nanoparticles and highly oriented MoS_(2)nanosheets are established, culminating in the achievement of robust superlubricity. Our pioneering design, coupled with the elucidation of the underlying superlubricity mechanism, holds significant promise for advancing the development of robust and high-performance lubricants.展开更多
Currently,macroscale liquid superlubricity remains limited to low applied loads and typical ceramic friction pairs.In this study,a robust macroscale superlubricity with a coefficient of friction(COF)of approximately 0...Currently,macroscale liquid superlubricity remains limited to low applied loads and typical ceramic friction pairs.In this study,a robust macroscale superlubricity with a coefficient of friction(COF)of approximately 0.006 is realized at the bearing steel interface induced by protic ionic liquids(ILs)in propylene glycol aqueous solution,and the lubrication system exhibits excellent anti-corrosion properties.Results show that superlubricity can be achieved by employing ILs with longer alkyl chains over a wide load(<350 N)and speed(>700 r/min)range.By systematically investigating factors affecting superlubricity,including the IL structure,ionization degree,test conditions,polyol,water-to-alcohol ratio,and lubrication state,the superlubricity mechanism is discussed.Notably,a thicker and denser stern layer can be formed using ILs with longer alkyl chains,which participates in the tribochemical reaction with the metal substrate to form a tribofilm during rubbing.The hydrogen bond network layer formed by the hydrogen ion and polycol aqueous solution can withstand high applied loads.Water can be used to reduce the shear stress of polyols,and enable superlubricity to be achieved under high-speed rotations.Moreover,an inevitable running-in period serves as a dispersing contact stress and dynamically forms a lubricating film,where the lubrication state locates mixed lubrication and then transforms into boundary lubrication as the roughness of the contact surface increases.This study is expected to significantly promote the development and application of superlubricity in the engineering field.展开更多
Macroscale superlubricity is a prospective strategy in modern tribology to dramatically reduce friction and wear of mechanical equipment;however,it is mainly studied for point-to-surface contact or special friction pa...Macroscale superlubricity is a prospective strategy in modern tribology to dramatically reduce friction and wear of mechanical equipment;however,it is mainly studied for point-to-surface contact or special friction pairs in experiments.In this study,a robust macroscale superlubricity for point-to-point contact on a steel interface was achieved for the first time by using hydroxylated modified boron nitride nanosheets with proton-type ionic liquids(ILs)as additives in ethylene glycol aqueous(EG_(aq)).The detailed superlubricity process and mechanism were revealed by theoretical calculations and segmented experiments.The results indicate that hydration originating from hydrated ions can significantly reduce the shear stress of EG_(aq),which plays an essential role in achieving superlubricity.Moreover,the IL induces a tribochemical reaction to form a friction-protective film.Hydroxylated boron nitride nanosheets(HO-BNNs)function as a polishing and self-repairing agent to disperse the contact stress between friction pairs.Superlubricity involves the change in lubrication state from boundary lubrication to mixed lubrication.This finding can remarkably extend the application of superlubricity for point-to-point contact on steel surfaces for engineering applications.展开更多
The Xin'anjiang Model is used as the basic model to develop a monthly grid-based macroscale hydrological model for the assessment of the effects of climate change on water resources.The monthly discharge from 1953...The Xin'anjiang Model is used as the basic model to develop a monthly grid-based macroscale hydrological model for the assessment of the effects of climate change on water resources.The monthly discharge from 1953 through 1985 in the Huaihe River Basin is simulated.The sensitivity analysis on runoff is made under assumed climatic scenarios.There is a good agreement between the observed and simulated runoff.Due to the increase of time interval and decrease of precipitation intensity on monthly time scale,there is no monthly runoff in some model girds as the momhly hydrological model is applied to the Huaihe River Basin.Two methods of downscaling monthly precipitation to daily resolution are validated by running the Xin'anjiang model with monthly data at a daily time step.and the model outputs are more realistic than the monthly hydrological model.The metbods of downscaling of monthly precipitation to daily resolution may provide an idea in solving the problem of the shortage of daily data.In the research of the climate change on water resources,the daily hydrological model can be used instead of the monthly one.展开更多
Recent studies have reported that adding nanoparticles to graphene enables macroscale superlubricity to be achieved.This study focuses on the role of nanoparticles in achieving superlubricity.First,because graphene na...Recent studies have reported that adding nanoparticles to graphene enables macroscale superlubricity to be achieved.This study focuses on the role of nanoparticles in achieving superlubricity.First,because graphene nanoscrolls can be formed with nanoparticles as seeds under shear force,the applied load(or shear force)is adjusted to manipulate the formation of graphene nanoscrolls and to reveal the relationship between graphene-nanoscroll formation and superlubricating performance.Second,the load-carrying role of spherical nano-SiO_(2)particles during the friction process is verified by comparison with an elaborately designed fullerene that possesses a hollow-structured graphene nanoscroll.Results indicate that the incorporated nano-SiO_(2)particles have two roles in promoting the formation of graphene nanoscrolls and exhibiting load-carrying capacity to support macroscale forces for achieving macroscale superlubricity.Finally,macroscale superlubricity(friction coefficient:0.006–0.008)can be achieved under a properly tuned applied load(2.0 N)using a simple material system in which a graphene/nano-SiO_(2)particle composite coating slides against a steel counterpart ball without a decorated diamond-like carbon film.The approach described in this study could be of significance in engineering.展开更多
Construction of macro-materials with highly oriented microstructures and well-connected interfaces between building blocks is significant for a variety of applications. However, it is still challenging to confine the ...Construction of macro-materials with highly oriented microstructures and well-connected interfaces between building blocks is significant for a variety of applications. However, it is still challenging to confine the desired structures. Thus, well-defined building blocks would be crucial to address this issue. Herein, we present a facile process based on 1.8 nm Pd nanoclusters （NCs） to achieve centimeter-size assemblages with aligned honeycomb structures, where the diameter of a single tubular moiety is -4 μm. Layered and disordered porous assemblages were also obtained by modulating the temperature in this system. The reconciled interactions between the NCs were crucial to the assemblages. As a comparison, 14 nm Pd nanoparticles formed only aggregates. This work highlights the approach of confining the size of the building blocks in order to better control the assembly process and improve the stability of the structures.展开更多
It is difficult to achieve macroscale superlubricity under high contact pressures and high normal loads.Layered double hydroxide(LDH)nanoadditives were introduced into an ionic liquid alcohol solution(IL(as))with cont...It is difficult to achieve macroscale superlubricity under high contact pressures and high normal loads.Layered double hydroxide(LDH)nanoadditives were introduced into an ionic liquid alcohol solution(IL(as))with contact pressures up to 1.044 GPa,which resulted in a friction coefficient(COF)of 0.004 and a robust superlubricity state lasting for 2 h.Compared with the LDH particles(LDH-Ps)with ca.90-nm widths and 18-nm thickness,micron-scale LDH nanosheet(LDH-N)additives with ca.1.5-pm width and 6-nm thickness increased the load-bearing capacity by approximately three times during superlubricity.The lubricant film thickness and the ultrathin longitudinal dimension of the LDH-N additives did not influence the continuity of the fluid film on the contact surface.These improvements resulted from the protective adsorption layer and ion distribution formed on the contact interface,as revealed by detailed surface analyses and simulation studies.In particular,the sliding energy barrier and Bader charge calculation revealed that weak shear sliding between the nanosheet and the solid surface formed easily and the anions in the liquid adsorbed on the solid surface exhibited electrostatic repulsion forces,which generated stable tribological properties synergistically.This research provides a novel method for obtaining macroscale superlubricity for practical industrial applications.展开更多
In recent studies of two-dimensional(2D)nanomaterial-based solid lubricants,the importance of durability has been emerging for real engineering-scale applications.To achieve this,a transfer layer formation is essentia...In recent studies of two-dimensional(2D)nanomaterial-based solid lubricants,the importance of durability has been emerging for real engineering-scale applications.To achieve this,a transfer layer formation is essential to prevent the wear of the mechanical systems.However,it has been challenging for pristine graphene(PG)to induce a material transfer due to chemical inertness.In this study,we suggest an easy-to-process strategy to promote the huge material transfer of the PG onto the counterpart contacting material.We utilized graphene oxide(GO)as a gluing layer between the PG film and the counterpart contact surface to realize the superior tribological performance.The high interaction energy of the GO from its functional groups makes a contribution to the material transfer of PG,which is unveiled by a systematic analysis of the counterpart contact surface and the wear track.The huge solid transfer layer not only makes a wear-resistant contact interface between the transfer layer and the underlying film by densification and oxidation,but also reduces surface interaction energies,finally resulting in a significant improvement in durability.展开更多
The cause of substorm onset is not yet understood. Chen CX(2016) proposed an entropy switch model, in which substorm onset results from the development of interchange instability. In this study, we sought observationa...The cause of substorm onset is not yet understood. Chen CX(2016) proposed an entropy switch model, in which substorm onset results from the development of interchange instability. In this study, we sought observational evidence for this model by using Time History of Events and Macroscale Interactions during Substorms(THEMIS) data. We examined two events, one with and the other without a streamer before substorm onset. In contrast to the stable magnetosphere, where the total magnetic field strength is a decreasing function and entropy is an increasing function of the downtail distance, in both events the total magnetic field strength and entropy were reversed before substorm onset. After onset, the total magnetic field strength, entropy, and other plasma quantities fluctuated. In addition, a statistical study was performed. By confining the events with THEMIS satellites located in the downtail region between ~8 and ~12 Earth radii, and 3 hours before and after midnight, we found the occurrence rate of the total magnetic field strength reversal to be 69% and the occurrence rate of entropy reversal to be 77% of the total 205 events.展开更多
Archimedes number(Ar)is the most important parameter characterizing the fluid-particle two-phase-flow system,which determines the ratio of terminal velocity of single particle to minimum gas velocity for fluidization,...Archimedes number(Ar)is the most important parameter characterizing the fluid-particle two-phase-flow system,which determines the ratio of terminal velocity of single particle to minimum gas velocity for fluidization,and then the possibility of two fluidized systems being similar in fast-fluidization flow-regime.After brief revisit of the scaling laws reported in literatures,the problem/limitations of missing Ar were revealed/identified.Starting from Glicksman's full set scaling laws,new simplified four identities scaling laws for mesoscale similarity were derived.They were confirmed,also,by the unified model for fast fluidization dynamics established by the present author and his co-workers.When the new criteria were applied for scaling-down a high-temperature CFB combustor to a cold-air model,about one tenth semi-spontaneous scaling for bed size was identified and declared.With this benefit,scaling down from a large CFB combustor,of 15 m in diameter,to a 1/20 cold model was demonstrated successfully.Further simplification was also conducted to the beds using same gas and particles for partial/macroscale similarity.With guidance of the unified model,the simplest scaling laws having two similitude identities were obtained.And this is coincident well with Qi and Zhu's empirical correlation,deduced from dozens more literature data sets and their own.展开更多
Macroscale rolling/sliding conditions are in the superlubricity,a little-studied topic so far.The purpose of this paper is to examine the formation of elastohydrodynamic lubrication(EHL)films by water-based lubricants...Macroscale rolling/sliding conditions are in the superlubricity,a little-studied topic so far.The purpose of this paper is to examine the formation of elastohydrodynamic lubrication(EHL)films by water-based lubricants(glycerol and polyethylene glycol(PEG)),providing superlubricous friction.Experiments were carried out on an optical ball-on-disc tribometer under rolling/sliding conditions.The film thickness was measured by the thin film colorimetric interferometry,and the viscosity of liquids was measured by rotational and high-pressure falling body viscometers.The results show that tribochemical reactions are not the mandatory reason for friction to reach the superlubricity level when using the water-based lubricants.The studied liquids themselves are almost Newtonian.With the addition of water,the signs of shear thinning behavior disappear even more.Suitable conditions for this type of lubricant can be predicted using the known Hamrock–Dowson equations.An anomaly in the thickness of the lubricants was observed as an abrupt change at certain conditions.The more PEG there is in the lubricant,the higher the thickness at the beginning of the jump.展开更多
Superlubricity,or structural lubricity,is a state that has two contacting surfaces exhibiting no resistance to sliding.This effect has been theoretically described to be possible between two completely clean single cr...Superlubricity,or structural lubricity,is a state that has two contacting surfaces exhibiting no resistance to sliding.This effect has been theoretically described to be possible between two completely clean single crystalline solid surfaces.However,experimental observations of superlubricity were limited to nanoscale and under high vacuum or inert gas environments even after twenty years since the concept of superlubricity has been suggested in 1990.In the last two years,remarkable advances have been achieved in experimental observations of superlubricity ranging from micro-scale to centimeters and in ambient environment.This study aims to report a comprehensive understanding of the superlubricity phenomenon.展开更多
Shear responses of dense granular mixtures of spherical coarse particles with the rolling resistance and spherical fine particles are studied via triaxial compression tests using the discrete element method.The macros...Shear responses of dense granular mixtures of spherical coarse particles with the rolling resistance and spherical fine particles are studied via triaxial compression tests using the discrete element method.The macroscale responses(shear strength and dilatancy)are examined.Comparing the results with those in the literature indicates that granular mixtures with a rolling resistance coefficient of 0.5 have similar macroscale responses to those of gravel-shaped coarse particle mixtures.We quantify the microscale responses including the percentage contributions of contact types,partial coordination number,average particle rotation,average degree of interlocking,and local structural properties,A detailed analysis of the force-fabric anisotropy reveals the mechanisms of the variations in the shear strength with the rolling resistance coefficient and the fines content.The mechanism of the variation in the shear strength with the fines content for granular mixtures with a rolling resistance coefficient of 0.5 is different from that for gravel-shaped coarse particle mixtures.Finally,we find that a rolling resistance linear model weakens the linear relationship between the stress ratio and the fabric anisotropy of strong and non-sliding contacts when the fines content is 30% and 40%.展开更多
Though increasing understanding and remarkable clinical successes have been made, enormous challenges remain to be solved in the field of cancer immunotherapy. In this context, biomaterial-based immunomodulatory strat...Though increasing understanding and remarkable clinical successes have been made, enormous challenges remain to be solved in the field of cancer immunotherapy. In this context, biomaterial-based immunomodulatory strategies are being developed to boost antitumor immunity. For the local immunotherapy, macroscale bioma-terial scaffolds with 3D network structures show great superiority in the following aspects: facilitating the encapsulation, localized delivery, and controlled release of immunotherapeutic agents and even immunocytes for more efficient immunomodulation. The concentrating immunomodulation in situ could minimize systemic tox-icities, but still exert abscopal effects to harness the power of overall anticancer immune response for eradicating malignancy. To promote such promising immunotherapies, the design requirements of macroscale 3D scaffolds should comprehensively consider their physicochemical and biological properties, such as porosity, stiffness, surface modification, cargo release kinetics, biocompatibility, biodegradability, and delivery modes. To date, increasing studies have focused on the relationships between these parameters and the biosystems which will guide/assist the 3D biomaterial scaffolds to achieve the desired immunotherapeutic outcomes. In this review, by highlighting some recent achievements, we summarized the latest advances in the development of various 3D scaffolds as niches for cancer immunotherapy. We also discussed opportunities, challenges, current trends, and future perspectives in 3D macroscale biomaterial scaffold-assisted local treatment strategies. More importantly, this review put more efforts to illustrate how the 3D biomaterial systems affect to modulate antitumor immune activities, where we discussed how significant the roles and behaviours of 3D macroscale scaffolds towards in situ cancer immunotherapy in order to direct the design of 3D immunotherapeutic.展开更多
Macroscale superlubricity has attracted increasing attention owing to its high significance in engineering and economics.We report the superlubricity of engineering materials by the addition of partially oxidized blac...Macroscale superlubricity has attracted increasing attention owing to its high significance in engineering and economics.We report the superlubricity of engineering materials by the addition of partially oxidized black phosphorus(oBP)in an oleic acid(OA)oil environment.The phosphorus oxides produced by active oxidation exhibit lower friction and quick deposition performance compared to BP particles.The H-bond(–COOH…O–P,or–COOH…O=P)formed between P–O bond(or P=O)and OA molecule could benefit the lubricating state and decrease the possibility of direct contact between rough peaks.The analysis of the worn surface indicates that a three-layer tribofilm consisting of amorphous carbon,BP crystal,and phosphorus oxide forms during the friction,which replaces the shear interface from the steel/steel to carbon–oBP/carbon–oBP layer and enables macroscale superlubricity.展开更多
基金supported by the National Natural Science Foundation of China (Grant Nos. U21A20127, 52375220)the Strategic Priority Research Program of the Chinese Academy of Sciences (Grant No. XDB 0470302)the Natural Science Foundation of Ningbo (Grant No. 2022J300)。
文摘Molybdenum disulfide(MoS_(2)) films are widely deployed in industrial applications owing to their inherent interlayer slip characteristics, offering energy consumption savings and prolonged mechanical part performance. Nevertheless, their practical utility is limited by environmental constraints and the limitations of preparation techniques, which hinder the attainment of robust superlubricity(friction coefficient < 0.01). Herein, through magnetron sputtering technology, we synthesize a core-shell-like nanocomposite composed of MoS_(2)nanosheets encapsulating B_(4)C. The core-shell-like structure enables the resulting films to preferentially grow crystalline MoS_(2), providing them with outstanding mechanical properties and efficient lubrication over a wide range of temperatures. Remarkably, such film achieves robust macroscale superlubricity and an ultralow wear rate(1.7 ×10^(-8)mm^(3)N-1m^(-1)) under high contact stress in a mild vacuum environment. This noteworthy outcome is primarily attributable to the self-segmentation of the macroscale contact interface during the friction process, involving:(1) a large amount of wear debris is embedded into the wear track to create extensive micro-sized asperities;(2) a nanolayer of amorphous carbon enriched with oxide nanoparticles is formed on the uppermost part of these asperities;(3) numerous incommensurate nanocontacts comprising nanoparticles and highly oriented MoS_(2)nanosheets are established, culminating in the achievement of robust superlubricity. Our pioneering design, coupled with the elucidation of the underlying superlubricity mechanism, holds significant promise for advancing the development of robust and high-performance lubricants.
基金This work was supported by the Youth Innovation Promotion Association of Chinese Academy of Sciences(No.2021422).
文摘Currently,macroscale liquid superlubricity remains limited to low applied loads and typical ceramic friction pairs.In this study,a robust macroscale superlubricity with a coefficient of friction(COF)of approximately 0.006 is realized at the bearing steel interface induced by protic ionic liquids(ILs)in propylene glycol aqueous solution,and the lubrication system exhibits excellent anti-corrosion properties.Results show that superlubricity can be achieved by employing ILs with longer alkyl chains over a wide load(<350 N)and speed(>700 r/min)range.By systematically investigating factors affecting superlubricity,including the IL structure,ionization degree,test conditions,polyol,water-to-alcohol ratio,and lubrication state,the superlubricity mechanism is discussed.Notably,a thicker and denser stern layer can be formed using ILs with longer alkyl chains,which participates in the tribochemical reaction with the metal substrate to form a tribofilm during rubbing.The hydrogen bond network layer formed by the hydrogen ion and polycol aqueous solution can withstand high applied loads.Water can be used to reduce the shear stress of polyols,and enable superlubricity to be achieved under high-speed rotations.Moreover,an inevitable running-in period serves as a dispersing contact stress and dynamically forms a lubricating film,where the lubrication state locates mixed lubrication and then transforms into boundary lubrication as the roughness of the contact surface increases.This study is expected to significantly promote the development and application of superlubricity in the engineering field.
基金The authors are gratefully for the financial support provided by the Youth Innovation Promotion Association CAS(2021422).
文摘Macroscale superlubricity is a prospective strategy in modern tribology to dramatically reduce friction and wear of mechanical equipment;however,it is mainly studied for point-to-surface contact or special friction pairs in experiments.In this study,a robust macroscale superlubricity for point-to-point contact on a steel interface was achieved for the first time by using hydroxylated modified boron nitride nanosheets with proton-type ionic liquids(ILs)as additives in ethylene glycol aqueous(EG_(aq)).The detailed superlubricity process and mechanism were revealed by theoretical calculations and segmented experiments.The results indicate that hydration originating from hydrated ions can significantly reduce the shear stress of EG_(aq),which plays an essential role in achieving superlubricity.Moreover,the IL induces a tribochemical reaction to form a friction-protective film.Hydroxylated boron nitride nanosheets(HO-BNNs)function as a polishing and self-repairing agent to disperse the contact stress between friction pairs.Superlubricity involves the change in lubrication state from boundary lubrication to mixed lubrication.This finding can remarkably extend the application of superlubricity for point-to-point contact on steel surfaces for engineering applications.
文摘The Xin'anjiang Model is used as the basic model to develop a monthly grid-based macroscale hydrological model for the assessment of the effects of climate change on water resources.The monthly discharge from 1953 through 1985 in the Huaihe River Basin is simulated.The sensitivity analysis on runoff is made under assumed climatic scenarios.There is a good agreement between the observed and simulated runoff.Due to the increase of time interval and decrease of precipitation intensity on monthly time scale,there is no monthly runoff in some model girds as the momhly hydrological model is applied to the Huaihe River Basin.Two methods of downscaling monthly precipitation to daily resolution are validated by running the Xin'anjiang model with monthly data at a daily time step.and the model outputs are more realistic than the monthly hydrological model.The metbods of downscaling of monthly precipitation to daily resolution may provide an idea in solving the problem of the shortage of daily data.In the research of the climate change on water resources,the daily hydrological model can be used instead of the monthly one.
基金The authors thank the National Natural Science Foundation of China(Grant No.51775537)Youth Innovation Promotion Association of Chinese Academy of Sciences(Grant No.Y202084)for financial support.
文摘Recent studies have reported that adding nanoparticles to graphene enables macroscale superlubricity to be achieved.This study focuses on the role of nanoparticles in achieving superlubricity.First,because graphene nanoscrolls can be formed with nanoparticles as seeds under shear force,the applied load(or shear force)is adjusted to manipulate the formation of graphene nanoscrolls and to reveal the relationship between graphene-nanoscroll formation and superlubricating performance.Second,the load-carrying role of spherical nano-SiO_(2)particles during the friction process is verified by comparison with an elaborately designed fullerene that possesses a hollow-structured graphene nanoscroll.Results indicate that the incorporated nano-SiO_(2)particles have two roles in promoting the formation of graphene nanoscrolls and exhibiting load-carrying capacity to support macroscale forces for achieving macroscale superlubricity.Finally,macroscale superlubricity(friction coefficient:0.006–0.008)can be achieved under a properly tuned applied load(2.0 N)using a simple material system in which a graphene/nano-SiO_(2)particle composite coating slides against a steel counterpart ball without a decorated diamond-like carbon film.The approach described in this study could be of significance in engineering.
文摘Construction of macro-materials with highly oriented microstructures and well-connected interfaces between building blocks is significant for a variety of applications. However, it is still challenging to confine the desired structures. Thus, well-defined building blocks would be crucial to address this issue. Herein, we present a facile process based on 1.8 nm Pd nanoclusters （NCs） to achieve centimeter-size assemblages with aligned honeycomb structures, where the diameter of a single tubular moiety is -4 μm. Layered and disordered porous assemblages were also obtained by modulating the temperature in this system. The reconciled interactions between the NCs were crucial to the assemblages. As a comparison, 14 nm Pd nanoparticles formed only aggregates. This work highlights the approach of confining the size of the building blocks in order to better control the assembly process and improve the stability of the structures.
基金This project was supported by the National Natural Science Foundation of China(Nos.51875303,51905294,and 52105194)the Tribology Science Fund of the State Key Laboratory of Tribology(No.SKLTKF20A01).
文摘It is difficult to achieve macroscale superlubricity under high contact pressures and high normal loads.Layered double hydroxide(LDH)nanoadditives were introduced into an ionic liquid alcohol solution(IL(as))with contact pressures up to 1.044 GPa,which resulted in a friction coefficient(COF)of 0.004 and a robust superlubricity state lasting for 2 h.Compared with the LDH particles(LDH-Ps)with ca.90-nm widths and 18-nm thickness,micron-scale LDH nanosheet(LDH-N)additives with ca.1.5-pm width and 6-nm thickness increased the load-bearing capacity by approximately three times during superlubricity.The lubricant film thickness and the ultrathin longitudinal dimension of the LDH-N additives did not influence the continuity of the fluid film on the contact surface.These improvements resulted from the protective adsorption layer and ion distribution formed on the contact interface,as revealed by detailed surface analyses and simulation studies.In particular,the sliding energy barrier and Bader charge calculation revealed that weak shear sliding between the nanosheet and the solid surface formed easily and the anions in the liquid adsorbed on the solid surface exhibited electrostatic repulsion forces,which generated stable tribological properties synergistically.This research provides a novel method for obtaining macroscale superlubricity for practical industrial applications.
基金supported by the National Research Foundation of Korea(NRF)Global Basic Research Laboratory grant funded by the Korea government(MSIT)(No.RS-2025-02216195)by the Korea Institute of Energy Technology Evaluation and Planning(KETEP)grant funded by the Korea government(MOTIE)(No.20214000000140).
文摘In recent studies of two-dimensional(2D)nanomaterial-based solid lubricants,the importance of durability has been emerging for real engineering-scale applications.To achieve this,a transfer layer formation is essential to prevent the wear of the mechanical systems.However,it has been challenging for pristine graphene(PG)to induce a material transfer due to chemical inertness.In this study,we suggest an easy-to-process strategy to promote the huge material transfer of the PG onto the counterpart contacting material.We utilized graphene oxide(GO)as a gluing layer between the PG film and the counterpart contact surface to realize the superior tribological performance.The high interaction energy of the GO from its functional groups makes a contribution to the material transfer of PG,which is unveiled by a systematic analysis of the counterpart contact surface and the wear track.The huge solid transfer layer not only makes a wear-resistant contact interface between the transfer layer and the underlying film by densification and oxidation,but also reduces surface interaction energies,finally resulting in a significant improvement in durability.
基金supported by the National Natural Science Foundation of China(Grant No.NSFC41974204)。
文摘The cause of substorm onset is not yet understood. Chen CX(2016) proposed an entropy switch model, in which substorm onset results from the development of interchange instability. In this study, we sought observational evidence for this model by using Time History of Events and Macroscale Interactions during Substorms(THEMIS) data. We examined two events, one with and the other without a streamer before substorm onset. In contrast to the stable magnetosphere, where the total magnetic field strength is a decreasing function and entropy is an increasing function of the downtail distance, in both events the total magnetic field strength and entropy were reversed before substorm onset. After onset, the total magnetic field strength, entropy, and other plasma quantities fluctuated. In addition, a statistical study was performed. By confining the events with THEMIS satellites located in the downtail region between ~8 and ~12 Earth radii, and 3 hours before and after midnight, we found the occurrence rate of the total magnetic field strength reversal to be 69% and the occurrence rate of entropy reversal to be 77% of the total 205 events.
基金support from the National Natural Science Foundation of China(grant No.52076138),。
文摘Archimedes number(Ar)is the most important parameter characterizing the fluid-particle two-phase-flow system,which determines the ratio of terminal velocity of single particle to minimum gas velocity for fluidization,and then the possibility of two fluidized systems being similar in fast-fluidization flow-regime.After brief revisit of the scaling laws reported in literatures,the problem/limitations of missing Ar were revealed/identified.Starting from Glicksman's full set scaling laws,new simplified four identities scaling laws for mesoscale similarity were derived.They were confirmed,also,by the unified model for fast fluidization dynamics established by the present author and his co-workers.When the new criteria were applied for scaling-down a high-temperature CFB combustor to a cold-air model,about one tenth semi-spontaneous scaling for bed size was identified and declared.With this benefit,scaling down from a large CFB combustor,of 15 m in diameter,to a 1/20 cold model was demonstrated successfully.Further simplification was also conducted to the beds using same gas and particles for partial/macroscale similarity.With guidance of the unified model,the simplest scaling laws having two similitude identities were obtained.And this is coincident well with Qi and Zhu's empirical correlation,deduced from dozens more literature data sets and their own.
基金supported by the Czech Science Foundation(No.21-28352S).
文摘Macroscale rolling/sliding conditions are in the superlubricity,a little-studied topic so far.The purpose of this paper is to examine the formation of elastohydrodynamic lubrication(EHL)films by water-based lubricants(glycerol and polyethylene glycol(PEG)),providing superlubricous friction.Experiments were carried out on an optical ball-on-disc tribometer under rolling/sliding conditions.The film thickness was measured by the thin film colorimetric interferometry,and the viscosity of liquids was measured by rotational and high-pressure falling body viscometers.The results show that tribochemical reactions are not the mandatory reason for friction to reach the superlubricity level when using the water-based lubricants.The studied liquids themselves are almost Newtonian.With the addition of water,the signs of shear thinning behavior disappear even more.Suitable conditions for this type of lubricant can be predicted using the known Hamrock–Dowson equations.An anomaly in the thickness of the lubricants was observed as an abrupt change at certain conditions.The more PEG there is in the lubricant,the higher the thickness at the beginning of the jump.
基金supports from the National Natural Science Foundation of China(NSFC)(Grant No.10832005)the the National Key Basic Research(973)Program of China(Grants Nos.2007CB936803 and 2013CB934200)are acknowledged.
文摘Superlubricity,or structural lubricity,is a state that has two contacting surfaces exhibiting no resistance to sliding.This effect has been theoretically described to be possible between two completely clean single crystalline solid surfaces.However,experimental observations of superlubricity were limited to nanoscale and under high vacuum or inert gas environments even after twenty years since the concept of superlubricity has been suggested in 1990.In the last two years,remarkable advances have been achieved in experimental observations of superlubricity ranging from micro-scale to centimeters and in ambient environment.This study aims to report a comprehensive understanding of the superlubricity phenomenon.
基金This research was supported by the National Natural Science Foundation of China(grant number 51809292)the Fundamental Research Funds for the Central Universities of Central South University(grant number 2018zzts195).
文摘Shear responses of dense granular mixtures of spherical coarse particles with the rolling resistance and spherical fine particles are studied via triaxial compression tests using the discrete element method.The macroscale responses(shear strength and dilatancy)are examined.Comparing the results with those in the literature indicates that granular mixtures with a rolling resistance coefficient of 0.5 have similar macroscale responses to those of gravel-shaped coarse particle mixtures.We quantify the microscale responses including the percentage contributions of contact types,partial coordination number,average particle rotation,average degree of interlocking,and local structural properties,A detailed analysis of the force-fabric anisotropy reveals the mechanisms of the variations in the shear strength with the rolling resistance coefficient and the fines content.The mechanism of the variation in the shear strength with the fines content for granular mixtures with a rolling resistance coefficient of 0.5 is different from that for gravel-shaped coarse particle mixtures.Finally,we find that a rolling resistance linear model weakens the linear relationship between the stress ratio and the fabric anisotropy of strong and non-sliding contacts when the fines content is 30% and 40%.
基金This work was supported by the National Natural Science Foundation of China(51973243 and 52173150)National Science and Technology Major Project of the Ministry of Science and Technology of China(2018ZX10301402)+2 种基金International Cooperation and Exchange of the National Natural Science Foundation of China(51820105004)Guang-dong Innovative and Entrepreneurial Research Team Program(2016ZT06S029)Fundamental Research Funds for the Central Uni-versities(191gzd35).
文摘Though increasing understanding and remarkable clinical successes have been made, enormous challenges remain to be solved in the field of cancer immunotherapy. In this context, biomaterial-based immunomodulatory strategies are being developed to boost antitumor immunity. For the local immunotherapy, macroscale bioma-terial scaffolds with 3D network structures show great superiority in the following aspects: facilitating the encapsulation, localized delivery, and controlled release of immunotherapeutic agents and even immunocytes for more efficient immunomodulation. The concentrating immunomodulation in situ could minimize systemic tox-icities, but still exert abscopal effects to harness the power of overall anticancer immune response for eradicating malignancy. To promote such promising immunotherapies, the design requirements of macroscale 3D scaffolds should comprehensively consider their physicochemical and biological properties, such as porosity, stiffness, surface modification, cargo release kinetics, biocompatibility, biodegradability, and delivery modes. To date, increasing studies have focused on the relationships between these parameters and the biosystems which will guide/assist the 3D biomaterial scaffolds to achieve the desired immunotherapeutic outcomes. In this review, by highlighting some recent achievements, we summarized the latest advances in the development of various 3D scaffolds as niches for cancer immunotherapy. We also discussed opportunities, challenges, current trends, and future perspectives in 3D macroscale biomaterial scaffold-assisted local treatment strategies. More importantly, this review put more efforts to illustrate how the 3D biomaterial systems affect to modulate antitumor immune activities, where we discussed how significant the roles and behaviours of 3D macroscale scaffolds towards in situ cancer immunotherapy in order to direct the design of 3D immunotherapeutic.
基金supported by the Beijing Natural Science Foundation(Grant No.JQ21008)the National Natural Science Foundation of China(Grant No.52275197)the Tsinghua-Foshan Innovation Special Fund(TFISF)(Grant No.2020THFS0127).
文摘Macroscale superlubricity has attracted increasing attention owing to its high significance in engineering and economics.We report the superlubricity of engineering materials by the addition of partially oxidized black phosphorus(oBP)in an oleic acid(OA)oil environment.The phosphorus oxides produced by active oxidation exhibit lower friction and quick deposition performance compared to BP particles.The H-bond(–COOH…O–P,or–COOH…O=P)formed between P–O bond(or P=O)and OA molecule could benefit the lubricating state and decrease the possibility of direct contact between rough peaks.The analysis of the worn surface indicates that a three-layer tribofilm consisting of amorphous carbon,BP crystal,and phosphorus oxide forms during the friction,which replaces the shear interface from the steel/steel to carbon–oBP/carbon–oBP layer and enables macroscale superlubricity.
