Micro-sized silicon anodes have shown much promise in large-scale industrial production of high-energy lithium batteries.However,large volume change(>300%)of silicon anodes causes severe particle pulverization and ...Micro-sized silicon anodes have shown much promise in large-scale industrial production of high-energy lithium batteries.However,large volume change(>300%)of silicon anodes causes severe particle pulverization and the formation of unstable solid electrolyte interphases during cycling,leading to rapid capacity decay and short cycle life of lithium-ion batteries.When addressing such issues,binder plays key roles in obtaining good structural integrity of silicon anodes.Herein,we report a biopolymer composite binder composed of rigid poly(acrylic acid)(PAA)and flexible silk fibroin(SF)tailored for micro-sized silicon anodes.The PAA/SF binder shows robust gradient binding energy via chemical interactions between carboxyl and amide groups,which can effectively accommodate large volume change of silicon.This PAA/SF binder also shows much stronger adhesion force and improved binding towards high-surface/defective carbon additives,resulting in better electrochemical stability and higher coulombic efficiency,than conventional PAA binder.As such,micro-sized silicon/carbon anodes fabricated with novel PAA/SF binder exhibit much better cyclability(up to 500 cycles at 0.5 C)and enhanced rate capability compared with conventional PAA-based anodes.This work provides new insights into the design of functional binders for high-capacity electrodes suffering from large volume change for the development of nextgeneration lithium batteries.展开更多
Interparticle adhesion force has a controlling effect on the physical and mechanical properties of planetary regolith and rocks.The current research on the adhesion force of planetary regolith and rock particles has b...Interparticle adhesion force has a controlling effect on the physical and mechanical properties of planetary regolith and rocks.The current research on the adhesion force of planetary regolith and rock particles has been primarily based on the assumption of smooth spherical particles to calculate the intergranular adhesion force;this approach lacks consideration for the adhesion force between irregular shaped particles.In our study,an innovative approach was established to directly measure the adhesion force between the arbitrary irregular shaped particles;the probe was modified using simulated lunar soil particles that were a typical representation of planetary regolith.The experimental results showed that for irregular shaped mineral particles,the particle size and mineral composition had no significant influence on the interparticle adhesion force;however,the complex morphology of the contact surface predominantly controlled the adhesion force.As the contact surface roughness increased,the adhesion force gradually decreased,and the rate of decrease gradually slowed;these results were consistent with the change trend predicted via the theoretical models of quantum electrodynamics.Moreover,a theoretical model to predict the adhesion force between the irregular shaped particles was constructed based on Rabinovich’s theory,and the prediction results were correlated with the experimental measurements.展开更多
Surface roughness plays a significant role in floatability of coal.In the present paper,coking coal surface was polished by three different sandpapers and the surface properties were characterized by contact angle and...Surface roughness plays a significant role in floatability of coal.In the present paper,coking coal surface was polished by three different sandpapers and the surface properties were characterized by contact angle and roughness measurements.The effect of surface roughness on floatability was investigated by adhesion force measurement system for measuring interaction forces between droplets/bubbles and coking coal surfaces with different roughness.The results showed that the contact angle decreased with increasing roughness yet the adhesion force between the water droplet and coal surface increased owing to the increased contact line and the appearance of line pinning.Maximum adhesion forces between water and surfaces were 111.70,125.48,and 136.42μN when the roughness was 0.23,0.98,and 2.79 μm,respectively.In contrast,under a liquid environment,the adhesion forces between air bubble/oil droplet and coal surfaces were decreased with increasing roughness because of the restriction by water.Maximum adhesion forces of increasing roughness were 97.14,42.76,and 17.86 μN measured at interfaces between air bubble and coal surfaces and 169.48,145.84,and 121.02 lN between oil droplet and surfaces,respectively.Decreasing roughness could be beneficial to the spreading of oil droplets and the adhesion of bubbles which is conducive to flotation separation.展开更多
In micro-manipulation, the adhesion force has very important influence on behaviors of micro-objects. Here, a theoretical study on the effects of humidity on the adhesion force is presented between atomic force micros...In micro-manipulation, the adhesion force has very important influence on behaviors of micro-objects. Here, a theoretical study on the effects of humidity on the adhesion force is presented between atomic force microscope(AFM) tips and substrate.The analysis shows that the precise tip geometry plays a critical role on humidity dependence of the adhesion force, which is the dominant factor in manipulating micro-objects in AFM experiments. For a blunt(paraboloid) tip, the adhesion force versus humidity curves tends to the apparent contrast(peak-to-valley corrugation) with a broad range.This paper demonstrates that the abrupt change of the adhesion force has high correlation with probe curvatures, which is mediated by coordinates of solid-liquid-vapor contact lines(triple point) on the probe profiles. The study provides insights for further understanding nanoscale adhesion forces and the way to choose probe shapes in manipulating micro-objects in AFM experiments.展开更多
Nanoparticle-reinforced metal matrix composite coatings have significant potential in mechanical part surface strengthening owing their excellent mechanical properties.This paper reports a phenomenon in which the grai...Nanoparticle-reinforced metal matrix composite coatings have significant potential in mechanical part surface strengthening owing their excellent mechanical properties.This paper reports a phenomenon in which the grain orientation gradually evolves to(220)as the deposition current density increases when preparing nanoparticle-reinforced nickel-based composite coatings through jet electrodeposition(JED).During the preparation of the Ni-SiC composite coatings,the deposition current density increased from 180 A/dm2 to 220 A/dm2,and TC(220)gradually increase from 41.4%to 97.7%.With an increase of TC(220),the self-corrosion potential increases from−0.575 to−0.477 V,the corrosion current density decreases from 9.52μA/cm^2 to 2.76μA/cm^2,the diameter of the corrosion pits that after 10 days of immersion in a 3.5 wt%NaCl solution decreases from 278–944 nm to 153–260 nm,and the adhesion of the coating increases from 24.9 N to 61.6 N.Compared a conventional electrodeposition(CED),the Ni-SiC composite coating using JED has the advantages of a smooth surface morphology,high corrosion resistance,and strong adhesion,which are more obvious with an increase in TC(220).展开更多
It is necessary to know the status of adhesion conditions between wheel and rail for efficient accelerating and decelerating of railroad vehicle.The proper estimation of adhesion conditions and their real-time impleme...It is necessary to know the status of adhesion conditions between wheel and rail for efficient accelerating and decelerating of railroad vehicle.The proper estimation of adhesion conditions and their real-time implementation is considered a challenge for scholars.In this paper,the development of simulation model of extended Kalman filter(EKF)in MATLAB/Simulink is presented to estimate various railway wheelset parameters in different contact conditions of track.Due to concurrent in nature,the Xilinx®System-on-Chip Zynq Field Programmable Gate Array(FPGA)device is chosen to check the onboard estimation ofwheel-rail interaction parameters by using the National Instruments(NI)myRIO®development board.The NImyRIO®development board is flexible to deal with nonlinearities,uncertain changes,and fastchanging dynamics in real-time occurring in wheel-rail contact conditions during vehicle operation.The simulated dataset of the railway nonlinear wheelsetmodel is tested on FPGA-based EKF with different track conditions and with accelerating and decelerating operations of the vehicle.The proposed model-based estimation of railway wheelset parameters is synthesized on FPGA and its simulation is carried out for functional verification on FPGA.The obtained simulation results are aligned with the simulation results obtained through MATLAB.To the best of our knowledge,this is the first time study that presents the implementation of a model-based estimation of railway wheelset parameters on FPGA and its functional verification.The functional behavior of the FPGA-based estimator shows that these results are the addition of current knowledge in the field of the railway.展开更多
AIM:To introduce a modified technique of internal limiting membrane(ILM)centripetal dragging and peeling to treat idiopathic macular hole(IMH)and to observe the ILM-retina adhesive forces.METHODS:Twenty-six consecutiv...AIM:To introduce a modified technique of internal limiting membrane(ILM)centripetal dragging and peeling to treat idiopathic macular hole(IMH)and to observe the ILM-retina adhesive forces.METHODS:Twenty-six consecutive patients with stage 3 to 4 IMH and followed up at least six months were enrolled.All patients underwent complete par plana vitrectomy,ILM dragging and peeling,fluid and gas exchange,15%C3 F8 tamponade and 2-week prone position.The best corrected visual acuity,macular hole evaluation by optical coherence tomography,and complications were evaluated.RESULTS:The mean diameter of IMH was 524±148μm(range:201-683μm),with 21 cases(80.8%)greater than 400μm.ILM dragging and peeling were successfully performed in all cases.Most of the ILM-retina adhesive forces are severe(42.3%,11/26),followed by mild(38.5%,10/26),and moderate(19.2%,5/26).The mean follow-up duration was 21.2±6.1 mo.The IMH was closed in 25(96.3%)eyes.Visual acuity(logMAR)improved significantly from 1.2±0.6 preoperatively to 0.7±0.5 postoperatively(P<0.001).CONCLUSION:Preexisting ILM-retina adhesive force is found in IMH patients.With assistance of this force,this modified technique may help to release the IMH edges and improve the closure rate of large IMH.展开更多
To expand the future clinic applications of biodegradable magnesium alloy,polymer coatings with excellent biocompatibility are the keys to solve the local alkalinity and rapid hydrogen release.Natural-organic silk fib...To expand the future clinic applications of biodegradable magnesium alloy,polymer coatings with excellent biocompatibility are the keys to solve the local alkalinity and rapid hydrogen release.Natural-organic silk fibroin provides an approach to fabricate a protective coating on biomedical Mg-Zn-Ca alloy,however,the adhesion force and mechanical properties of the coating on substrates are ought to be further improved without any chemical conversion/intermediate layer.Hereby,based on VUV/O;surface activation,a hybrid of silk fibroin and sodium alginate is proposed to enhance the adhesion force and mechanical properties of the composite coatings on hydrophilic Mg-Zn-Ca alloy surfaces.Various mass ratios of sodium alginate addition were investigated to achieve the optimum coating strategy.The nanoscratch test and nanoindentation test confirmed that the adhesion force was tripled and mechanical properties index was significantly improved when the mass ratio of silk fibroin/sodium alginate was 70/30 compared to pure silk fibroin or sodium alginate coatings.Meanwhile,the corrosion rate of the coated Mg-Zn-Ca alloy was significantly delayed with the addition of sodium alginate,resulting in a reaction layer during corrosion process.Furthermore,the mechanisms for both adhesion and corrosion processes were discussed in detail.Our findings offer more possibilities for the controllable surface performance of degradable metals.展开更多
Properties of shale in an acid environment are important when acid or CO2 is injected into geologic formations as a working fluid for enhanced oil and gas recovery,hydraulic fracturing and reduced fracture initiation ...Properties of shale in an acid environment are important when acid or CO2 is injected into geologic formations as a working fluid for enhanced oil and gas recovery,hydraulic fracturing and reduced fracture initiation pressure.It has previously been shown that acid fluids can enhance the formation conductivity and decrease the hardness of shale.However,less is known about the effect of dilute acid on the adhesion properties of shale.In the study,shale samples are characterized in detail with advanced analysis.Adhesion properties of shale via dilute acid treatment were revealed by atomic force microscopy(AFM)for the first time.Results indicate that acid treatment can greatly enhance adhesion forces of the shale surface.After acid treatment,the average adhesion forces show a platform-like growth with an increase in loading force.Through analysis of results from AFM,scanning electron microscopy,and X-ray diffraction,we affirm that the enhanced adhesion forces are mainly from increased specific surface area and reduced elastic modulus.The results presented in this work help understand the adhesion properties of shale oil/gas present in an acidic environment,which have great significance in unconventional resources development.展开更多
To address proppant flowback issues during post-fracturing treatments and production,self-healing elastomer modified proppants(SMPs)are proposed.Owing to their inherent self-aggregation behavior,the SMPs can aggregate...To address proppant flowback issues during post-fracturing treatments and production,self-healing elastomer modified proppants(SMPs)are proposed.Owing to their inherent self-aggregation behavior,the SMPs can aggregate together spontaneously to prevent proppant flowback and increase the pack porosity.It is noteworthy that the SMPs have a firm and dry self-healing elastomer(SE)coating,making their storage,transport and use as conventional proppants possible.The SE synthesized through polymerization is rich in amidogens and carbonyl groups as characterized by Fourier transform infrared spectroscopy and the proton nuclear magnetic resonance.Thermal and thermomechanical properties of the SE coating are revealed by the thermogravimetric analysis,the differential scanning calorimetry and the rheological tests.The self-aggregation behavior of the SMPs is demonstrated by the adhesion force tests.The reversible hydrogen bonding interactions in SE coating contribute to the self-aggregation behavior of the SMPs,which is revealed by the thixotropy test and the FTIR analysis at different temperatures.With the self-aggregation behavior,the crushed proppants can aggregate in situ to form a stable structure again and therefore reduce the threat of narrowing down the fracture and proppant flowback,which has an important practical significance during oil and gas production.展开更多
Thin silver films are deposited by radio frequency magnetron sputtering on glass ceramic at room temperature.Variations of sputtering power,bios voltage and power density are carried out for each deposition,then parts...Thin silver films are deposited by radio frequency magnetron sputtering on glass ceramic at room temperature.Variations of sputtering power,bios voltage and power density are carried out for each deposition,then parts of as-deposited samples are subjected to annealing at 600 ℃ within a vacuum chamber.Structural properties are studied by X-ray diffraction(XRD),scanning electron microscope(SEM)and laser scanning confocal microscope(LSCM).It is shown that structural properties have a strong dependency on sputtering power and annealing temperature.Electrical contact resistance measured by a four point probe instrument is directly affected by the thickness of films.It is also found that the film conductivity,especially in thinner films,is improved by the increasing grain size.Finally,the film adhesion is observed by scratch tests.And the adhesive ability deposited by radio frequency magnetron sputtering shows a better performance than that produced by traditional methods.展开更多
Maintenance of wind turbine farms is a huge task,with associated significant risks and potential hazard to the safety and well-being of people who are responsible for carrying the tower inspection tasks.Periodic inspe...Maintenance of wind turbine farms is a huge task,with associated significant risks and potential hazard to the safety and well-being of people who are responsible for carrying the tower inspection tasks.Periodic inspections are required for wind turbine tower to ensure that the wind turbines are in full working order,with no signs of potential failure.Therefore,the development of an automated wind tower inspection system has been very cnucial for the overall performance of the renewable wind power generation industry.In order to determine the life span of the tower,an investigation of robot design is discussed in this paper.It presents how a mechanical spring-loaded climbing robot can be designed and constructed to climb and rotate 360°around the tower.An adjustable circular shape robot is designed that allows the device to fit in different diameters of the wind generator tower.The rotational module is designed to allow the wheels to rotate and be able to go in a circular motion.The design further incorporates a suspension that allows the robot to go through any obstacle.This paper also presents a finite element spring stress analy sis and Simulink control system model to find the optimal parameters that are required for the wind tower climbing robot.展开更多
The triboelectric nanogenerator(TENG)is a new mechanical energy harvesting technology in which the typical viscoelastic material polydimethylsiloxane(PDMS)is widely used.Micro-/nano-textures are often fabricated on th...The triboelectric nanogenerator(TENG)is a new mechanical energy harvesting technology in which the typical viscoelastic material polydimethylsiloxane(PDMS)is widely used.Micro-/nano-textures are often fabricated on the PDMS surface to enhance the electrical performance of TENG.As the contact region decreases to micro/nano scale,the adhesive forces become dominant.However,there is still a lack of contact mechanics model considering both material viscoelasticity and the adhesive forces to guide the surface texture design.In this paper,the explicit data-fitting formulas based on the fractional derivative Zener model are firstly derived to identify the viscoelastic constitutive parameters,which can not only avoid the influence of the initial contact point,but also ensure the accurate conversion between the creep compliance and the relaxation modulus function.Then a viscoelastic-adhesive contact model based on the fitted constitutive parameters is established,and the numerical algorithms such as bi-conjugate stabilized(Bi-CGSTAB)method and fast Fourier transform(FFT)technique are employed to analyze the effects of material viscoelasticity and texture sizes on the contact and electrical performance.It is shown that,compared with results from the elastic-adhesive contact model,the contact area ratio based on the viscoelastic-adhesive contact model is significantly larger,which is much closer to the experimental results.Among the selected sizes of pyramid texture,the higher electrical performance can be obtained from the textures with a smaller pitch and a larger width under the heavier applied load.This study can provide a theoretical reference for the design of viscoelastic surface texture of TENG.展开更多
90°is the limitation oflyophilicity and lyophobicity for ideal surface for centuries,but it has been proved to be contradictory on some occasions.The symmetrical surfaces with different surface tensions can attra...90°is the limitation oflyophilicity and lyophobicity for ideal surface for centuries,but it has been proved to be contradictory on some occasions.The symmetrical surfaces with different surface tensions can attract or repel each other in water.Therefore,at the molecular level,the Iyophilicity or lyophobicity is the results of interactions between the liquids and substrates.Here,using atomic force microscope(AFM)to measure interaction forces between symmetrical self-assembled monolayers(SAMs)in different liquids,we found that the SAMs repel each other when the surfaces are hydrophilic whereas attract when hydrophobic in water.The contact angle corresponding to the transition of attraction to repulsion is approximate to 65°,defined as the intrinsic wetting threshold(IWT)of water.For ethylene glycol(EG),dimethyl sulfoxide(DMSO),N,N-dimethyl formamide(DMF),the IWTs could be determined by changes of adhesion forces between SAMs.This research redefined the IWTs for liquids,which is the essential guide to both basic theory and applications of wettability.展开更多
Light carries energy and momentum,laying the physical foundation of optical manipulation that has facilitated advances in myriad scientific disciplines,ranging from biochemistry and robotics to quantum physics.Utilizi...Light carries energy and momentum,laying the physical foundation of optical manipulation that has facilitated advances in myriad scientific disciplines,ranging from biochemistry and robotics to quantum physics.Utilizing the momentum of light,optical tweezers have exemplified elegant light–matter interactions in which mechanical and optical momenta can be interchanged,whose effects are the most pronounced on micro and nano objects in fluid suspensions.In solid domains,the same momentum transfer becomes futile in the face of dramatically increased adhesion force.Effective implementation of optical manipulation should thereupon switch to the“energy”channel by involving auxiliary physical fields,which also coincides with the irresistible trend of enriching actuation mechanisms beyond sole reliance on light-momentum-based optical force.From this perspective,this review covers the developments of optical manipulation in schemes of both momentum and energy transfer,and we have correspondingly selected representative techniques to present.Theoretical analyses are provided at the beginning of this review followed by experimental embodiments,with special emphasis on the contrast between mechanisms and the practical realization of optical manipulation in fluid and solid domains.展开更多
Zero-dimensional(0D)carbon dots exhibit excellent potential as a new oil-displacing agent for unconventional reservoir development.However,the difficulty in size/surface properties control and unclear mechanism hinder...Zero-dimensional(0D)carbon dots exhibit excellent potential as a new oil-displacing agent for unconventional reservoir development.However,the difficulty in size/surface properties control and unclear mechanism hinder their further applications.In this study,amino-modified carbon dots(am-CDs)for oil displacement were facilely synthesized through the rapid polymerization of D-glucose(D-Glc)and 3-aminopropyltriethoxysilane(APTES).The size of am-CDs could be precisely controlled by the reaction condition and quenching achieved by adjusting the pH value to neutral.The surface amine groups endow am-CDs with excellent hydrophilicity and dispersion stability.The 0.30 wt.%nanofluid based on am-CDs with an average size of 2.6±0.040 nm showed remarkable oil recovery efficiency(54.09%)without the addition of surfactant.The oil recovery efficiency of am-CDs is much higher than those of water flooding(30.25%),nano-SiO_(2) flooding(36.45%),and amino-free carbon dots(af-CDs)flooding(37.80%).Experimental and theoretical results reveal that am-CDs can be favorably adsorbed on the core surface to modulate the micro-scale wettability,changing the surface from oil-wet to relatively uniform water-wet.Meanwhile,am-CDs can effectively reduce the adhesion force between alkanes and sandstone surfaces,contributing to oil droplets peeling off and oil displacement.This study provides a new strategy for developing efficient carbon dots-based nanofluids for enhanced oil recovery.展开更多
Ni-P(-SiC)composite coatings were successfully deposited on 70 vol%SiC_(p)/Al composite by electroless plating.The surface microstructures and the phase structures of the Ni-P(-SiC)coatings were examined and analyzed ...Ni-P(-SiC)composite coatings were successfully deposited on 70 vol%SiC_(p)/Al composite by electroless plating.The surface microstructures and the phase structures of the Ni-P(-SiC)coatings were examined and analyzed by scanning electron microscopy(SEM)and X-ray diffraction(XRD)before and after heat-treatment at200-400℃for 2 h.The thermal diffusivity of the deposited samples and the interface adhesion between the coating and the substrate were investigated.The experimental results show that SiC content in the coatings increases obviously and XRD peaks are enhanced with SiC content in the bath increasing from 3 to 9 g·L^(-1).After heat-treatment,the surface of the coating becomes smoother and no diffusion layer is produced at the interface.A new phase Ni3P forms in the coating during heat-treatment at 400℃.The critical load(L_(c))of Ni-P-SiC composite coating on SiC_(p)/Al composite reaches the maximum value of 84.9 N with SiC content of 3 g·L^(-1)after heat-treatment at 200℃and more or less decreases with the increase in SiC content and heat-treatment temperature.The thermal diffusivity of deposited samples gradually increases as the temperature increases;however,it reduces firstly and then climbs with the increase in SiC content.展开更多
Agglomeration with improved flowability for platy crystals is desirable in pharmaceutical downstream processing. The formation of agglomerates in pure solvents without the aid of bridging liquids is a convenient and l...Agglomeration with improved flowability for platy crystals is desirable in pharmaceutical downstream processing. The formation of agglomerates in pure solvents without the aid of bridging liquids is a convenient and low-cost method compared with complex spherical crystallization. In this work, the adhesion free energies between aspirin crystals in six solvents were calculated using Lifshitz-van der Waals acid-base theory to screen suitable solvents for agglomeration. The maximum stirring rate for agglomeration was determined by adhesion forces and dispersion forces. Then the agglomerates of plate-shaped aspirin were successfully prepared in acetone, methanol, ethanol, 2-propanol, and ethylene glycol without additives by simple cooling crystallization. The interactions between solvent and crystal surfaces were also used to explain the outcomes. A feasible mechanism for the agglomeration process of platy crystals was elucidated, involving the adhesion of dominant crystal facets at the beginning. The effect of stirring rate, cooling rate, and initial supersaturation on agglomeration degree and particle size of aspirin agglomerates were studied. The obtained aspirin agglomerates under the optimal conditions exhibited a uniform particle size distribution, a high agglomeration degree, and superior flowability.展开更多
The motion of droplets on a super‐hydrophobic surface,whether by sliding or rolling,is a hot research topic.It affects the performance of super‐hydrophobic materials in many industrial applications.In this study,a s...The motion of droplets on a super‐hydrophobic surface,whether by sliding or rolling,is a hot research topic.It affects the performance of super‐hydrophobic materials in many industrial applications.In this study,a super‐hydrophobic surface with a varied roughness is prepared by chemical‐etching.The adhesive force of the advancing and receding contact angles for a droplet on a super‐hydrophobic surface is characterized.The adhesive force increases with a decreased contact angle,and the minimum value is 0.0169 mN when the contact angle is 151.47°.At the same time,the motion of a droplet on the superhydrophobic surface is investigated by using a high‐speed camera and fluid software.The results show that the droplet rolls instead of sliding and the angular acceleration increases with an increased contact angle.The maximum value of the angular acceleration is 1,203.19 rad/s^(2) and this occurs when the contact angle is 151.47°.The relationship between the etching time,roughness,angular acceleration,and the adhesion force of the forward and backward contact angle are discussed.展开更多
Load-dependent friction hysteresis is an intriguing phenomenon that occurs in many materials,where the friction measured during unloading is larger than that measured during loading for a given normal load.However,the...Load-dependent friction hysteresis is an intriguing phenomenon that occurs in many materials,where the friction measured during unloading is larger than that measured during loading for a given normal load.However,the mechanism underlying this behavior is still not well understood.In this work,temperaturecontrolled friction force microscopy was utilized to explore the origin of friction hysteresis on exfoliated monolayer graphene.The experimental observations show that environmental adsorbates from ambient air play an important role in the load dependence of friction.Specifically,the existence of environmental adsorbates between the tip and graphene surface gives rise to an enhanced tip–graphene adhesion force,which leads to a positive friction hysteresis where the friction force is larger during unloading than during loading.In contrast to positive friction hysteresis,a negative friction hysteresis where the friction force is smaller during unloading than during loading is observed through the removal of the environmental adsorbates upon in situ annealing.It is proposed that the measured friction hysteresis originates from the hysteresis in the contact area caused by environmental adsorbates between the tip and graphene.These findings provide a revised understanding of the friction hysteresis in monolayer graphene in terms of environmental adsorbates.展开更多
文摘Micro-sized silicon anodes have shown much promise in large-scale industrial production of high-energy lithium batteries.However,large volume change(>300%)of silicon anodes causes severe particle pulverization and the formation of unstable solid electrolyte interphases during cycling,leading to rapid capacity decay and short cycle life of lithium-ion batteries.When addressing such issues,binder plays key roles in obtaining good structural integrity of silicon anodes.Herein,we report a biopolymer composite binder composed of rigid poly(acrylic acid)(PAA)and flexible silk fibroin(SF)tailored for micro-sized silicon anodes.The PAA/SF binder shows robust gradient binding energy via chemical interactions between carboxyl and amide groups,which can effectively accommodate large volume change of silicon.This PAA/SF binder also shows much stronger adhesion force and improved binding towards high-surface/defective carbon additives,resulting in better electrochemical stability and higher coulombic efficiency,than conventional PAA binder.As such,micro-sized silicon/carbon anodes fabricated with novel PAA/SF binder exhibit much better cyclability(up to 500 cycles at 0.5 C)and enhanced rate capability compared with conventional PAA-based anodes.This work provides new insights into the design of functional binders for high-capacity electrodes suffering from large volume change for the development of nextgeneration lithium batteries.
基金supported by the National Natural Science Foundation of China(Nos.U22A20166,52104141,12172230 and U2013603)the Department of Science and Technology of Guangdong Province(No.2019ZT08G315)the Guangdong Basic and Applied Basic Research Foundation(No.2023A1515012654).
文摘Interparticle adhesion force has a controlling effect on the physical and mechanical properties of planetary regolith and rocks.The current research on the adhesion force of planetary regolith and rock particles has been primarily based on the assumption of smooth spherical particles to calculate the intergranular adhesion force;this approach lacks consideration for the adhesion force between irregular shaped particles.In our study,an innovative approach was established to directly measure the adhesion force between the arbitrary irregular shaped particles;the probe was modified using simulated lunar soil particles that were a typical representation of planetary regolith.The experimental results showed that for irregular shaped mineral particles,the particle size and mineral composition had no significant influence on the interparticle adhesion force;however,the complex morphology of the contact surface predominantly controlled the adhesion force.As the contact surface roughness increased,the adhesion force gradually decreased,and the rate of decrease gradually slowed;these results were consistent with the change trend predicted via the theoretical models of quantum electrodynamics.Moreover,a theoretical model to predict the adhesion force between the irregular shaped particles was constructed based on Rabinovich’s theory,and the prediction results were correlated with the experimental measurements.
基金This work was supported by the Jiangsu Natural Science Fund-Youth Fund(BK20190639)National Nature Science Foundation of China(Nos.21978318,51904300,and 51922106)National Key R&D Program of China(2020YFC1908803).
文摘Surface roughness plays a significant role in floatability of coal.In the present paper,coking coal surface was polished by three different sandpapers and the surface properties were characterized by contact angle and roughness measurements.The effect of surface roughness on floatability was investigated by adhesion force measurement system for measuring interaction forces between droplets/bubbles and coking coal surfaces with different roughness.The results showed that the contact angle decreased with increasing roughness yet the adhesion force between the water droplet and coal surface increased owing to the increased contact line and the appearance of line pinning.Maximum adhesion forces between water and surfaces were 111.70,125.48,and 136.42μN when the roughness was 0.23,0.98,and 2.79 μm,respectively.In contrast,under a liquid environment,the adhesion forces between air bubble/oil droplet and coal surfaces were decreased with increasing roughness because of the restriction by water.Maximum adhesion forces of increasing roughness were 97.14,42.76,and 17.86 μN measured at interfaces between air bubble and coal surfaces and 169.48,145.84,and 121.02 lN between oil droplet and surfaces,respectively.Decreasing roughness could be beneficial to the spreading of oil droplets and the adhesion of bubbles which is conducive to flotation separation.
基金Project supported by the National Natural Science Foundation of China(Nos.11105088 and 81060307)the Innovation Program of Shanghai Municipal Education Commission(No.11YZ20)+1 种基金the Guangxi Natural Science Foundation Program(No.2013GXNSFBA019006)the Guangxi Province Higher Educational Science and Technology Program(No.2013YB033)
文摘In micro-manipulation, the adhesion force has very important influence on behaviors of micro-objects. Here, a theoretical study on the effects of humidity on the adhesion force is presented between atomic force microscope(AFM) tips and substrate.The analysis shows that the precise tip geometry plays a critical role on humidity dependence of the adhesion force, which is the dominant factor in manipulating micro-objects in AFM experiments. For a blunt(paraboloid) tip, the adhesion force versus humidity curves tends to the apparent contrast(peak-to-valley corrugation) with a broad range.This paper demonstrates that the abrupt change of the adhesion force has high correlation with probe curvatures, which is mediated by coordinates of solid-liquid-vapor contact lines(triple point) on the probe profiles. The study provides insights for further understanding nanoscale adhesion forces and the way to choose probe shapes in manipulating micro-objects in AFM experiments.
基金Supported by National Natural Science Foundation of China(Grant No.51675535)Major Research Project of Shandong Province of China(Grant No.2019GGX104068)+3 种基金Key Pre-Research Foundation of Military Equipment of China(Grant No.6140923030702)National Science and Technology Major Project of China(Grant No.2017ZX05072)Graduate Innovation Protect of China University of Petroleum(East China)(Grant No.YCX2020059)Science and Technology Support Plan for Youth Innovation of Universities in Shandong Province of China(Grant No.2019KJB016).
文摘Nanoparticle-reinforced metal matrix composite coatings have significant potential in mechanical part surface strengthening owing their excellent mechanical properties.This paper reports a phenomenon in which the grain orientation gradually evolves to(220)as the deposition current density increases when preparing nanoparticle-reinforced nickel-based composite coatings through jet electrodeposition(JED).During the preparation of the Ni-SiC composite coatings,the deposition current density increased from 180 A/dm2 to 220 A/dm2,and TC(220)gradually increase from 41.4%to 97.7%.With an increase of TC(220),the self-corrosion potential increases from−0.575 to−0.477 V,the corrosion current density decreases from 9.52μA/cm^2 to 2.76μA/cm^2,the diameter of the corrosion pits that after 10 days of immersion in a 3.5 wt%NaCl solution decreases from 278–944 nm to 153–260 nm,and the adhesion of the coating increases from 24.9 N to 61.6 N.Compared a conventional electrodeposition(CED),the Ni-SiC composite coating using JED has the advantages of a smooth surface morphology,high corrosion resistance,and strong adhesion,which are more obvious with an increase in TC(220).
文摘It is necessary to know the status of adhesion conditions between wheel and rail for efficient accelerating and decelerating of railroad vehicle.The proper estimation of adhesion conditions and their real-time implementation is considered a challenge for scholars.In this paper,the development of simulation model of extended Kalman filter(EKF)in MATLAB/Simulink is presented to estimate various railway wheelset parameters in different contact conditions of track.Due to concurrent in nature,the Xilinx®System-on-Chip Zynq Field Programmable Gate Array(FPGA)device is chosen to check the onboard estimation ofwheel-rail interaction parameters by using the National Instruments(NI)myRIO®development board.The NImyRIO®development board is flexible to deal with nonlinearities,uncertain changes,and fastchanging dynamics in real-time occurring in wheel-rail contact conditions during vehicle operation.The simulated dataset of the railway nonlinear wheelsetmodel is tested on FPGA-based EKF with different track conditions and with accelerating and decelerating operations of the vehicle.The proposed model-based estimation of railway wheelset parameters is synthesized on FPGA and its simulation is carried out for functional verification on FPGA.The obtained simulation results are aligned with the simulation results obtained through MATLAB.To the best of our knowledge,this is the first time study that presents the implementation of a model-based estimation of railway wheelset parameters on FPGA and its functional verification.The functional behavior of the FPGA-based estimator shows that these results are the addition of current knowledge in the field of the railway.
基金Supported by the National Natural Science Foundation of China(No.81470642No.81770964)the Science and Technology Commission of Shanghai Municipality(No.17411952900)。
文摘AIM:To introduce a modified technique of internal limiting membrane(ILM)centripetal dragging and peeling to treat idiopathic macular hole(IMH)and to observe the ILM-retina adhesive forces.METHODS:Twenty-six consecutive patients with stage 3 to 4 IMH and followed up at least six months were enrolled.All patients underwent complete par plana vitrectomy,ILM dragging and peeling,fluid and gas exchange,15%C3 F8 tamponade and 2-week prone position.The best corrected visual acuity,macular hole evaluation by optical coherence tomography,and complications were evaluated.RESULTS:The mean diameter of IMH was 524±148μm(range:201-683μm),with 21 cases(80.8%)greater than 400μm.ILM dragging and peeling were successfully performed in all cases.Most of the ILM-retina adhesive forces are severe(42.3%,11/26),followed by mild(38.5%,10/26),and moderate(19.2%,5/26).The mean follow-up duration was 21.2±6.1 mo.The IMH was closed in 25(96.3%)eyes.Visual acuity(logMAR)improved significantly from 1.2±0.6 preoperatively to 0.7±0.5 postoperatively(P<0.001).CONCLUSION:Preexisting ILM-retina adhesive force is found in IMH patients.With assistance of this force,this modified technique may help to release the IMH edges and improve the closure rate of large IMH.
基金supported by the National Natural Science Foundation of China(Grant No.51975151)the China Postdoctoral Science Foundation(Grant No.2017M610207)+1 种基金the Heilongjiang Provincial Natural Science Foundation of China(Grant No.LH2019E041)the Fundamental Research Funds for Central Universities(Grant No.HIT.NSRIF.2019005)。
文摘To expand the future clinic applications of biodegradable magnesium alloy,polymer coatings with excellent biocompatibility are the keys to solve the local alkalinity and rapid hydrogen release.Natural-organic silk fibroin provides an approach to fabricate a protective coating on biomedical Mg-Zn-Ca alloy,however,the adhesion force and mechanical properties of the coating on substrates are ought to be further improved without any chemical conversion/intermediate layer.Hereby,based on VUV/O;surface activation,a hybrid of silk fibroin and sodium alginate is proposed to enhance the adhesion force and mechanical properties of the composite coatings on hydrophilic Mg-Zn-Ca alloy surfaces.Various mass ratios of sodium alginate addition were investigated to achieve the optimum coating strategy.The nanoscratch test and nanoindentation test confirmed that the adhesion force was tripled and mechanical properties index was significantly improved when the mass ratio of silk fibroin/sodium alginate was 70/30 compared to pure silk fibroin or sodium alginate coatings.Meanwhile,the corrosion rate of the coated Mg-Zn-Ca alloy was significantly delayed with the addition of sodium alginate,resulting in a reaction layer during corrosion process.Furthermore,the mechanisms for both adhesion and corrosion processes were discussed in detail.Our findings offer more possibilities for the controllable surface performance of degradable metals.
基金supported by National Natural Science Foundation of China(No.51674275)National Science and Technology Major Project(2017ZX05009-003)PetroChina Innovation Foundation(2018D-5007-0308)
文摘Properties of shale in an acid environment are important when acid or CO2 is injected into geologic formations as a working fluid for enhanced oil and gas recovery,hydraulic fracturing and reduced fracture initiation pressure.It has previously been shown that acid fluids can enhance the formation conductivity and decrease the hardness of shale.However,less is known about the effect of dilute acid on the adhesion properties of shale.In the study,shale samples are characterized in detail with advanced analysis.Adhesion properties of shale via dilute acid treatment were revealed by atomic force microscopy(AFM)for the first time.Results indicate that acid treatment can greatly enhance adhesion forces of the shale surface.After acid treatment,the average adhesion forces show a platform-like growth with an increase in loading force.Through analysis of results from AFM,scanning electron microscopy,and X-ray diffraction,we affirm that the enhanced adhesion forces are mainly from increased specific surface area and reduced elastic modulus.The results presented in this work help understand the adhesion properties of shale oil/gas present in an acidic environment,which have great significance in unconventional resources development.
基金the support from the National Key R&D Program of China(grant number 2018YFA0702400)the Major Scientific and Technological Projects of CNPC(grant number ZD2019-183-007)the Fundamental Research Funds for the Central Universities(grant number No.19CX02017A)。
文摘To address proppant flowback issues during post-fracturing treatments and production,self-healing elastomer modified proppants(SMPs)are proposed.Owing to their inherent self-aggregation behavior,the SMPs can aggregate together spontaneously to prevent proppant flowback and increase the pack porosity.It is noteworthy that the SMPs have a firm and dry self-healing elastomer(SE)coating,making their storage,transport and use as conventional proppants possible.The SE synthesized through polymerization is rich in amidogens and carbonyl groups as characterized by Fourier transform infrared spectroscopy and the proton nuclear magnetic resonance.Thermal and thermomechanical properties of the SE coating are revealed by the thermogravimetric analysis,the differential scanning calorimetry and the rheological tests.The self-aggregation behavior of the SMPs is demonstrated by the adhesion force tests.The reversible hydrogen bonding interactions in SE coating contribute to the self-aggregation behavior of the SMPs,which is revealed by the thixotropy test and the FTIR analysis at different temperatures.With the self-aggregation behavior,the crushed proppants can aggregate in situ to form a stable structure again and therefore reduce the threat of narrowing down the fracture and proppant flowback,which has an important practical significance during oil and gas production.
基金Supported by the National Natural Science Foundation of China(50975134)
文摘Thin silver films are deposited by radio frequency magnetron sputtering on glass ceramic at room temperature.Variations of sputtering power,bios voltage and power density are carried out for each deposition,then parts of as-deposited samples are subjected to annealing at 600 ℃ within a vacuum chamber.Structural properties are studied by X-ray diffraction(XRD),scanning electron microscope(SEM)and laser scanning confocal microscope(LSCM).It is shown that structural properties have a strong dependency on sputtering power and annealing temperature.Electrical contact resistance measured by a four point probe instrument is directly affected by the thickness of films.It is also found that the film conductivity,especially in thinner films,is improved by the increasing grain size.Finally,the film adhesion is observed by scratch tests.And the adhesive ability deposited by radio frequency magnetron sputtering shows a better performance than that produced by traditional methods.
文摘Maintenance of wind turbine farms is a huge task,with associated significant risks and potential hazard to the safety and well-being of people who are responsible for carrying the tower inspection tasks.Periodic inspections are required for wind turbine tower to ensure that the wind turbines are in full working order,with no signs of potential failure.Therefore,the development of an automated wind tower inspection system has been very cnucial for the overall performance of the renewable wind power generation industry.In order to determine the life span of the tower,an investigation of robot design is discussed in this paper.It presents how a mechanical spring-loaded climbing robot can be designed and constructed to climb and rotate 360°around the tower.An adjustable circular shape robot is designed that allows the device to fit in different diameters of the wind generator tower.The rotational module is designed to allow the wheels to rotate and be able to go in a circular motion.The design further incorporates a suspension that allows the robot to go through any obstacle.This paper also presents a finite element spring stress analy sis and Simulink control system model to find the optimal parameters that are required for the wind tower climbing robot.
基金This work is financially supported by National Natural Science Foundation of China(Nos.51735001 and 11472046).
文摘The triboelectric nanogenerator(TENG)is a new mechanical energy harvesting technology in which the typical viscoelastic material polydimethylsiloxane(PDMS)is widely used.Micro-/nano-textures are often fabricated on the PDMS surface to enhance the electrical performance of TENG.As the contact region decreases to micro/nano scale,the adhesive forces become dominant.However,there is still a lack of contact mechanics model considering both material viscoelasticity and the adhesive forces to guide the surface texture design.In this paper,the explicit data-fitting formulas based on the fractional derivative Zener model are firstly derived to identify the viscoelastic constitutive parameters,which can not only avoid the influence of the initial contact point,but also ensure the accurate conversion between the creep compliance and the relaxation modulus function.Then a viscoelastic-adhesive contact model based on the fitted constitutive parameters is established,and the numerical algorithms such as bi-conjugate stabilized(Bi-CGSTAB)method and fast Fourier transform(FFT)technique are employed to analyze the effects of material viscoelasticity and texture sizes on the contact and electrical performance.It is shown that,compared with results from the elastic-adhesive contact model,the contact area ratio based on the viscoelastic-adhesive contact model is significantly larger,which is much closer to the experimental results.Among the selected sizes of pyramid texture,the higher electrical performance can be obtained from the textures with a smaller pitch and a larger width under the heavier applied load.This study can provide a theoretical reference for the design of viscoelastic surface texture of TENG.
基金This research is supported by the National Natural Science Foundation of China(Nos.21972154,21988102,and 22090052)Frontier Science Key Projects of CAS(ZDBS-LY-SLH022)+1 种基金the National Research Fund of China for Fundamental Key Projects(No.2019YFA0708700)Project funded by China Postdoctoral Science Foundation(No.2020M670091).
文摘90°is the limitation oflyophilicity and lyophobicity for ideal surface for centuries,but it has been proved to be contradictory on some occasions.The symmetrical surfaces with different surface tensions can attract or repel each other in water.Therefore,at the molecular level,the Iyophilicity or lyophobicity is the results of interactions between the liquids and substrates.Here,using atomic force microscope(AFM)to measure interaction forces between symmetrical self-assembled monolayers(SAMs)in different liquids,we found that the SAMs repel each other when the surfaces are hydrophilic whereas attract when hydrophobic in water.The contact angle corresponding to the transition of attraction to repulsion is approximate to 65°,defined as the intrinsic wetting threshold(IWT)of water.For ethylene glycol(EG),dimethyl sulfoxide(DMSO),N,N-dimethyl formamide(DMF),the IWTs could be determined by changes of adhesion forces between SAMs.This research redefined the IWTs for liquids,which is the essential guide to both basic theory and applications of wettability.
基金supported by the National Natural Science Foundation of China (Nos.61927820,61905201,and 62275221).
文摘Light carries energy and momentum,laying the physical foundation of optical manipulation that has facilitated advances in myriad scientific disciplines,ranging from biochemistry and robotics to quantum physics.Utilizing the momentum of light,optical tweezers have exemplified elegant light–matter interactions in which mechanical and optical momenta can be interchanged,whose effects are the most pronounced on micro and nano objects in fluid suspensions.In solid domains,the same momentum transfer becomes futile in the face of dramatically increased adhesion force.Effective implementation of optical manipulation should thereupon switch to the“energy”channel by involving auxiliary physical fields,which also coincides with the irresistible trend of enriching actuation mechanisms beyond sole reliance on light-momentum-based optical force.From this perspective,this review covers the developments of optical manipulation in schemes of both momentum and energy transfer,and we have correspondingly selected representative techniques to present.Theoretical analyses are provided at the beginning of this review followed by experimental embodiments,with special emphasis on the contrast between mechanisms and the practical realization of optical manipulation in fluid and solid domains.
基金the National Key Research and Development Program of China(No.2019YFA0708700)the China National Petroleum Corporation Innovation Found(No.2021DQ02-0205).
文摘Zero-dimensional(0D)carbon dots exhibit excellent potential as a new oil-displacing agent for unconventional reservoir development.However,the difficulty in size/surface properties control and unclear mechanism hinder their further applications.In this study,amino-modified carbon dots(am-CDs)for oil displacement were facilely synthesized through the rapid polymerization of D-glucose(D-Glc)and 3-aminopropyltriethoxysilane(APTES).The size of am-CDs could be precisely controlled by the reaction condition and quenching achieved by adjusting the pH value to neutral.The surface amine groups endow am-CDs with excellent hydrophilicity and dispersion stability.The 0.30 wt.%nanofluid based on am-CDs with an average size of 2.6±0.040 nm showed remarkable oil recovery efficiency(54.09%)without the addition of surfactant.The oil recovery efficiency of am-CDs is much higher than those of water flooding(30.25%),nano-SiO_(2) flooding(36.45%),and amino-free carbon dots(af-CDs)flooding(37.80%).Experimental and theoretical results reveal that am-CDs can be favorably adsorbed on the core surface to modulate the micro-scale wettability,changing the surface from oil-wet to relatively uniform water-wet.Meanwhile,am-CDs can effectively reduce the adhesion force between alkanes and sandstone surfaces,contributing to oil droplets peeling off and oil displacement.This study provides a new strategy for developing efficient carbon dots-based nanofluids for enhanced oil recovery.
基金financially supported by the National Natural Science Foundation of China(Nos.51572112,51172177)the Natural Science Foundation of Jiangsu Province(Nos.BK20151340)+2 种基金the Six Talent Peaks Project of Jiangsu Province(No.2014-XCL-002)the Postdoctoral Science Foundation of China(No.2014M551512)the Innovation/Entrepreneurship Program of Jiangsu Province(Nos.[2013]477,[2015]26)。
文摘Ni-P(-SiC)composite coatings were successfully deposited on 70 vol%SiC_(p)/Al composite by electroless plating.The surface microstructures and the phase structures of the Ni-P(-SiC)coatings were examined and analyzed by scanning electron microscopy(SEM)and X-ray diffraction(XRD)before and after heat-treatment at200-400℃for 2 h.The thermal diffusivity of the deposited samples and the interface adhesion between the coating and the substrate were investigated.The experimental results show that SiC content in the coatings increases obviously and XRD peaks are enhanced with SiC content in the bath increasing from 3 to 9 g·L^(-1).After heat-treatment,the surface of the coating becomes smoother and no diffusion layer is produced at the interface.A new phase Ni3P forms in the coating during heat-treatment at 400℃.The critical load(L_(c))of Ni-P-SiC composite coating on SiC_(p)/Al composite reaches the maximum value of 84.9 N with SiC content of 3 g·L^(-1)after heat-treatment at 200℃and more or less decreases with the increase in SiC content and heat-treatment temperature.The thermal diffusivity of deposited samples gradually increases as the temperature increases;however,it reduces firstly and then climbs with the increase in SiC content.
基金supported by the Tianjin Municipal Natural Science Foundation(grant No.21JCYBJC00600).
文摘Agglomeration with improved flowability for platy crystals is desirable in pharmaceutical downstream processing. The formation of agglomerates in pure solvents without the aid of bridging liquids is a convenient and low-cost method compared with complex spherical crystallization. In this work, the adhesion free energies between aspirin crystals in six solvents were calculated using Lifshitz-van der Waals acid-base theory to screen suitable solvents for agglomeration. The maximum stirring rate for agglomeration was determined by adhesion forces and dispersion forces. Then the agglomerates of plate-shaped aspirin were successfully prepared in acetone, methanol, ethanol, 2-propanol, and ethylene glycol without additives by simple cooling crystallization. The interactions between solvent and crystal surfaces were also used to explain the outcomes. A feasible mechanism for the agglomeration process of platy crystals was elucidated, involving the adhesion of dominant crystal facets at the beginning. The effect of stirring rate, cooling rate, and initial supersaturation on agglomeration degree and particle size of aspirin agglomerates were studied. The obtained aspirin agglomerates under the optimal conditions exhibited a uniform particle size distribution, a high agglomeration degree, and superior flowability.
基金The authors acknowledge the financial support from the National Natural Science Foundation of China(Grant Nos.U1809214 and U1809213)the National Basic Research Program of China(973 Program)(Grant No.2013CB632302)+1 种基金the Foundation of Key Laboratory of Marine Materials and Related Technologies,Chinese Academy of Sciences(2018K01)the Foundation of Key Laboratory of Marine Materials and Related Technologies,CAS(2018K01).
文摘The motion of droplets on a super‐hydrophobic surface,whether by sliding or rolling,is a hot research topic.It affects the performance of super‐hydrophobic materials in many industrial applications.In this study,a super‐hydrophobic surface with a varied roughness is prepared by chemical‐etching.The adhesive force of the advancing and receding contact angles for a droplet on a super‐hydrophobic surface is characterized.The adhesive force increases with a decreased contact angle,and the minimum value is 0.0169 mN when the contact angle is 151.47°.At the same time,the motion of a droplet on the superhydrophobic surface is investigated by using a high‐speed camera and fluid software.The results show that the droplet rolls instead of sliding and the angular acceleration increases with an increased contact angle.The maximum value of the angular acceleration is 1,203.19 rad/s^(2) and this occurs when the contact angle is 151.47°.The relationship between the etching time,roughness,angular acceleration,and the adhesion force of the forward and backward contact angle are discussed.
基金This work was financially supported by the Grant for Taishan Scholar Advantage Characteristic Discipline of Shandong Provincethe Start-up Grant for QiLu Young Scholars of Shandong University+2 种基金the Danish National Research Foundation,the AUFF NOVAprojectthe Danish National Research FoundationAUFF NOVA-project,and EU H2020 RISE(MNR4SCell 734174 project).
文摘Load-dependent friction hysteresis is an intriguing phenomenon that occurs in many materials,where the friction measured during unloading is larger than that measured during loading for a given normal load.However,the mechanism underlying this behavior is still not well understood.In this work,temperaturecontrolled friction force microscopy was utilized to explore the origin of friction hysteresis on exfoliated monolayer graphene.The experimental observations show that environmental adsorbates from ambient air play an important role in the load dependence of friction.Specifically,the existence of environmental adsorbates between the tip and graphene surface gives rise to an enhanced tip–graphene adhesion force,which leads to a positive friction hysteresis where the friction force is larger during unloading than during loading.In contrast to positive friction hysteresis,a negative friction hysteresis where the friction force is smaller during unloading than during loading is observed through the removal of the environmental adsorbates upon in situ annealing.It is proposed that the measured friction hysteresis originates from the hysteresis in the contact area caused by environmental adsorbates between the tip and graphene.These findings provide a revised understanding of the friction hysteresis in monolayer graphene in terms of environmental adsorbates.
