查看更多>>摘要：The separation of oil-in-water emulsion is an urgent challenge because its massive production and discharge from daily and industrial activities have caused severe hazards to the ecosystem and serious threats to human health.Membrane technology is considered an outstanding solution strategy for the separation of oil-in-water emulsions due to its unique advantages of low cost,high efficiency,easy operation,and environmental friendliness.However,the membrane is easily fouled by the emulsion oil droplets during the separation process,causing a sharp decline in permeation flux,which greatly inhibits the long-term use of the membrane and largely shortens the membrane's life.Recently,it was found that endowing the membranes with special wettability e.g.,superhydrophilic and superoleophobic can greatly enhance the permeability of the continuous water phase and inhibit the adhesion of oil droplets,thus promoting the separation performance and anti-oil-fouling property of membrane for oily emulsions.In this paper,we review and discuss the recent developments in membranes with special wettability for separating oil-in-water emulsions,including the mechanism analysis of emulsion separation membrane,membrane fouling issues,design strategies,and representative studies for enhancing the membrane's anti-oil-fouling ability and emulsion separation performance.
查看更多>>摘要：The ocular lubrication,where the eyelid constantly slides on the curved corneal surface,is considered as one of primary lubrication systems in bio-tribology.Under reliable lubrication conditions,sensitive ocular tissues remain intact from fatigue damage during spontaneous blink cycles.The tear film,evenly filled between cornea and conjunctiva,is a biological fluid with dynamic adjustment ability,which provides superior lubrication with the friction coefficient of below 0.01.However,the lubrication failure may result in a variety of uncomfortable symptoms such as inflammatory reactions,tissue damage and neurological abnormalities.Therefore,it is essential to clarify the fundamental mechanism of ocular lubrication,which helps to alleviate and even recover from various ocular symptoms.This review firstly demonstrates that the ocular components,containing lipids and mucins,contribute to maintaining the lubrication stability of tear film.Furthermore,the ocular lubrication state in various physiological environments and the physical effect on tear film dynamics are further discussed.As typical applications,the therapeutic agents of dry eye syndrome and contact lens with superior lubrication effects are introduced and their lubrication mechanisms are clarified.Finally,this review summarizes a series of the latest research inspired by ocular lubrication.Overall,this work will provide a valuable guidance on the theoretical research and extensive applications in the field of biological lubrication.
查看更多>>摘要：Humans rely on their fingers to sense and interact with external environment.Understanding the tribological behavior between finger skin and object surface is crucial for various fields,including tactile perception,product appearance design,and electronic skin research.Quantitatively describing finger frictional behavior is always challenging,given the complex structure of the finger.In this study,the texture and sliding direction dependence of finger skin friction was quantified based on explicit mathematic models.The proposed double-layer model of finger skin effectively described the nonlinear elastic response of skin and predicted the scaling-law of effective elastic modulus with contact radius.Additionally,the skin friction model on textured surface considering adhesion and deformation factors was established.It revealed that adhesive term dominated finger friction behavior in daily life,and suggested that object texture size mainly influenced friction-induced vibrations rather than the average friction force.Combined with digital image correlation(DIC)technique,the effect of sliding direction on finger friction was analyzed.It was found that the anisotropy in finger friction was governed by the finger's ratchet pawl structure,which also contributes to enhanced stick-slip vibrations in the distal sliding direction.The proposed friction models can offer valuable insights into the underlying mechanism of skin friction under various operating conditions,and can provide quantitative guidance for effectively encoding friction into haptics.
查看更多>>摘要：Lubrication failure accompanying with blackening phenomenon significantly reduces the long-running operational reliability of porous polymide(PPI)lubricated with poly-α-olefin(PAO)oil.Here,the effects of lubrication condition and counter-surface chemistry on the blackening failure of PAO impregnated PPI were studied through the comparison of the tribological tests against GCr15 steel ball and Al2O3 ceramic ball with and without PAO oil lubrication.Black products were found to be formed on the PAO impregnated PPI surface slid against steel ball or Al2O3 ball added with iron nano-particles,but be absent under the conditions without iron or PAO oil.Further analysis indicated that the iron-catalyzed splitting of PAO oil into small molecule alkanes and following the formation of black organic matter should be mainly responsible for the blackening phenomenon.Molecular dynamic(MD)simulations demonstrated that the iron facilitated the separation of hydrogen atom and the following broken of C-C bonds in PAO molecules,final resulting in the splitting of PAO oil.
查看更多>>摘要：Friction remains as the primary mode of energy dissipation and components wear,and achieving superlubricity shows high promise in energy conservation and lifetime wear protection.The results in this work demonstrate that direct superlubricity combined with superlow wear can be realized for steel/Si3N4 contacts on engineering scale when polyhydroxy alcohol solution was selectively modified by amino group.Macroscopic direct superlubricity occurs because 3-amino-1,2-propanediol molecules at the friction interface could be induced to rotate and adsorb vertically on the friction surface,forming in-situ thick and dense molecular films to passivate the asperity contacts.Furthermore,amino modification is also conducive to improving the lubrication state from boundary to mixed lubrication regime by strengthening the intermolecular hydrogen bonding interaction,presenting enhanced load-bearing capability and reduced direct solid asperity contacts.Thus,direct superlow average friction of 0.01 combined with superlow wear are achieved simultaneously.The design principle of direct superlubricity and superlow wear in this work indeed offers an effective strategy to fundamentally improve energy efficiency and provide lifetime wear protection for moving mechanical assemblies.
查看更多>>摘要：Efficient cooperative lubrication can be achieved via the introduction of core‒shell structure lubricant additives with hard core and soft shell,for obtaining the expected anti-wear performance from the structural changes in the friction process.In this study,C@Ag microspheres with a core‒shell structure were prepared by the redox method with carbon spheres as the core and Ag nanoparticles as the shell.Their tribological behaviors as base oil(G1830)additive with different concentrations were investigated in detail.Compared with base oil,the addition of C@Ag particles at 0.5 wt%can reduce the coefficient of friction(COF)and wear volume(Wv)up to 15.5%and 88%,respectively.More importantly,C@Ag particles provide superior lubrication performance to single additive(like carbon sphere(CS)and Ag nanoparticle).C@Ag core‒shell particles contribute to the formation of tribo-film by melt bonding of flexible Ag and carbon sphere(CS)toward excellent self-repair performance and high-efficiency lubrication.Hence,core‒shell structural nanoparticles with hard-core and soft-shell hold bright future for high-performance lubrication application.
查看更多>>摘要：Two-dimensional(2D)van der Waals layered materials have been widely used as lubricant.Penta-graphene(PG),a 2D carbon allotrope exclusively composed of irregular carbon pentagons has recently been predicted to have superlubricating property.In the present study,by combining the molecular dynamics simulation and first-principles calculations,we investigated the frictional property of PG in both commensurate and incommensurate contacts.Our calculations show the ultra-low friction at the interface of relatively rotated bilayer PG with twist angles of more than 10° away from the commensurate configuration.Meanwhile,our calculations demonstrate the isotropy of the ultra-low friction at the interface of incommensurate contact,in contrast to the anisotropic of the commensurate contacting interface.Additionally,the evolution of friction force and the fluctuation of potential energy along sliding path correlate closely with the interface's structure.The energetics and charge density explain the difference between the friction at the interfaces of the commensurate and incommensurate contacts.Not only that,we found the correlation between the intrinsic structural feature and interlayer binding energy.Importantly,our findings on the retainment of the ultra-low friction under work conditions indicates that the superlubricating state of PG has good practical adaptability.
查看更多>>摘要：This study reports on the tribological performance of aromatic thermosetting co-polyester(ATSP)and polyether ether ketone(PEEK)-based polymer composite coatings mixed with PTFE filler.The coatings were tested across a wide temperature range from-180 to 110 ℃ to simulate the environmental temperatures on Titan,Moon,and Mars,which are of particular interest for NASA's future exploratory missions.An experimental setup was developed to conduct the pin-on-disk experiments under dry sliding conditions and extreme temperature and contact pressure.Transfer film formation and its characteristics were found to play significant roles in the tribological performance,and the characteristics of the film were temperature-dependent.The XPS and SEM analysis indicated the increase of the PTFE content in the transfer film as the temperature decreased to cryogenic conditions.The coefficient of friction did not follow a linear trend with temperature and was minimum at 110 ℃ and maximum at-180 ℃.ATSP coating showed superior performance with lower friction and unmeasurable wear at all temperatures,whereas PEEK coating exhibited maximum wear at 25 ℃ followed by-180,and 110 ℃.
查看更多>>摘要：Wind power gears will be excessively worn due to lubrication failure during operation.Herein,the tribological properties of rubbing pairs are improved by filling solid lubricants into surface texture.In texture design,three types of topological textures(Circle(C),Hexagon(H),and Circle/Hexagon(CH))were obtained by cell topology optimization,and then three cases with 20%,30%,and 40%density were designed for each texture.Next,SnAgCu and TiC were deposited in texture of AISI 4140 steel(AS)to obtain 9 kinds of self-lubricating surfaces.Among them,AS with 30%CH density(AS-CH30)exhibits excellent mechanical and tribological properties.Compared with AS-C and AS-H,the maximum equivalent stress of AS-CH was decreased by 10.86%and 5.37%,respectively.Friction coefficient and wear rate of AS-CH30 were 79.68%and 78%lower than those of AS.The excellent tribological performances of AS-CH30 can be attributed to the synergistic effect of topological surface and solid lubricants.Topological surface can not only reduce fluctuation of equivalent stress,but also promote the stored lubricants to be easily transferred at the contact interface to form a 200 nm lubricating film containing solid lubricants(mainly),oxides and wear debris.
查看更多>>摘要：The contact of an elastic quarter-or eighth-space is studied under the condition that the movement of the side surface of the quarter-space is constrained:It can slide freely along the plane of the side surface but its normal movement is blocked(for example,by a rigid wall).The solution of this contact problem can be easily achieved by additionally applying a mirrored load to an elastic half-space.Non-adhesive contact and the Johnson-Kendall-Roberts(JKR)-type adhesive contact between a rigid sphere and an elastic quarter-space under such a boundary condition is numerically simulated using the fast Fourier transform(FFT)-assisted boundary element method(BEM).Contacts of an elastic eighth-space are investigated using the same idea.Depending on the position of the sphere relative to the side edge,different contact behavior is observed.In the case of adhesive contact,the force of adhesion first increases with increasing the distance from the edge of the quarter-space,achieves a maximum,and decreases further to the JKR-value in large distance from the edge.The enhancement of the force of adhesion compared to the half-space-contact is associated with the pinning of the contact area at the edge.We provide the maps of the force of adhesion and their analytical approximations,as well as pressure distributions in the contact plane and inside the quarter-/eighth-space.
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