| In practical engineering applications,the components of equipment often lose lubrication due to lubricant loss or insufficient supply,thus reducing its service life.How to resolve the problem of oil starvation caused by insufficient lubricant supply has become an urgent problem in industry.In this thesis,three kinds of surfaces with gradient wettability were prepared based on silicon by chemical vapor deposition of silane,local vacuum ultraviolet light,acid/alkali etching and other technical means.Using the driving force provided by its own surface energy gradient,the lubricant,which drained on both sides of the contact track,automatically migrated and returned to the contact track.Therefore,the problem of insufficient lubrication in the contact area was resolved.Their antifriction performance was studied by using the point contact reciprocating cycle friction and wear testing machine.First of all,in order to prevent the loss of oil droplets,a wettability gradient surface with high oil collection performance was prepared on silicon wafer by chemical vapor deposition silane and local vacuum ultraviolet photography.It is found that when the oil droplets are placed at the oil-repellent/lipophilic junction,the oil droplets can rapidly migrate from the oil-repellent region to the lipophilic region within 5 s.The research of Point contact reciprocating cycle friction and wear testing machine(with a load of 8 N and 30 minutes)shows that its friction coefficient is effectively reduced by about 14%compared with the original untreated silicon wafer.The surface morphology observed by confocal microscope showed that the depth of the wear marks was shallower than that of the original untreated silicon wafer.In order to keep the lubricant flowing back to the contact track,a wedge pattern mask was arranged on the silicon substrate,and then a wedge pattern functional surface that can realize the spontaneous migration and backflow of oil droplets was prepared by combining chemical vapor deposition silane and local ultraviolet photography.The effects of oil droplet volume,wedge angle and wedge length on the migration characteristics of oil droplets were studied.The results showed that with the increase of oil droplet volume,the migration distance and velocity of oil droplets first increased and then decreased;With the increase of wedge angle,the migration distance and velocity of oil droplets continued to decrease;However,the wedge length had no obvious effect on the oil droplet migration speed.Then the wedge pattern functional surface was prepared on both sides of the contact pair running track.It was found that the friction coefficient of the surface could be maintained below 0.05 for a long time,while the friction coefficient of the surface without wettability gradient was as high as 0.195.This confirms that the wedge pattern functional surface can lead to the spontaneous backflow of lubricant and has an effective antifriction effect.Finally,a wedge-shaped SLIPS(Slippery Liquid Infused Porous Surface)that can realize the spontaneous migration and backflow of oil droplets as a whole was prepared by combining acid/alkali etching,chemical vapor deposition of silane monolayer and local vacuum ultraviolet photography.Its spontaneous migration and backflow performance of oil droplets on the surface was studied.It is found that both water droplets with high surface tension and lubricating oil with low surface tension can eliminate the pinning phenomenon of liquid droplets on the surface due to contact angle hysteresis and realize the overall directional migration of liquid droplets during the migration process on the wedge-shaped SLIPS.The point contact reciprocating cycle friction and wear testing machine were carried out to compare the wedge-shaped SLIPS with the nonwedge-shaped SLIPS.The wedge-shaped SLIPS can significantly slow down the time of the destruction of the silane monolayer: at 633 s,lots of signs of the destruction of the monolayer were found on the non-wedge-shaped SLIPS,while the wedge-shaped SLIPS did not appear until 3034 s;Correspondingly,the friction coefficient of the wedge-shaped SLIPS was reduced by 43%,which showed a obvious antifriction performance. |
