| Polyimide,as a high-performance engineering polymer,has outstanding high and low temperature,mechanical properties,chemical stability and radiation resistance,which has great application in aerospace,thin film,microelectronics,medicine and insulation coating.However,the tribological performance of pure polyimide is too poor to meet the actual demand.As an emerging two-dimensional layered nanomaterial,fluorosinolene not only inherits the unique molecular structure and excellent properties of graphene,but also has excellent lubricating performance and low surface energy from the formation of C-F bond,which has great potential in enhancing the tribological properties of polymers.Nevertheless,it is still difficult to realize the high dispersion of graphene in polyimide to enhance its comprehensive properties.Based on these problems,In this paper,fluorinated graphene is chemically modified to achieve stable dispersion in polyimide matrix.We construct a fluorinated graphene modified polyimide composite coating system,and systematically study the influence of doping concentration,fluorination degree and carbon nanotube load on the performance of the polyimide composite coating.Moreover,we investigate the friction behavior of the polyimide composite coating modified by fluorinated graphene,and ultimately,the mechanism of anti-friction and anti-wear of fluorinated graphene is revealed on the micro sacle.First,FG nanosheets were treated with chloroform to reduce the interlayer molecular forces.FG nanosheet modified PI composite coatings with different contents(0.0 wt%,0.25% wt,0.5 wt%,1.0 wt% and 2.0 wt%)were prepared by in-situ polymerization.The tribological behaviors of PI composite coatings with different FG doping contents under seawater lubrication and dry friction conditions were systematically investigated.The experimental results showed that both of the mechanical and thermal properties of PI composite coatings were significantly improved,and the COF under different friction condition was slightly reduced.In the dry friction environment,the PI composite coating with a doping concentration of 0.5 wt% showed a dense transfer film to obtain the best tribological properties,and its wear rate was 51.2% lower than that of pure PI.Under seawater lubrication conditions,the friction coefficient was significantly reduced compared to dry grinding,but the softening effect of seawater on the polyimide caused the wear rate of the PI composite coating to deteriorate.Second,graphene was treated with different gas fluorination time to prepare FG with different fluorination levels.Modify the FG nanosheets with ionic liquids to enhance the stable dispersion of FG in the PI matrix.And then,FG modified PI composite coatings with different fluorination degrees were successfully synthesized by in-situ polymerization.The effects of the degree of fluorination of FG on the chemical state of FG and the properties of PI composite coatings were investigated.The results showed that as the fluorination degree increased,the more stable the C-F bond,the crosslink density between the PI molecules was strengthened to obtain excellent thermal stability and mechanical strength.At the same time,the existence of F was beneficial to produce a lubricating transfer film and promoted the enhancement of tribological properties.Finally,the FG and CNTs modified by ionic liquid were loaded and blended by physical adsorption method,and compounded with PI by in-situ polymerization.The results showed that the loading of CNTs enhanced the dispersibility of FG in organic solvents.Both the cross-linked network of CNTs and the two-dimensional layered structure of FG could improve the mechanical and tribological properties of PI,but the CNT effect was more significant,resulting in FG/CNT modified PI composites with the best mechanical properties and wear resistance.Due to the excellent lubricating properties of FG,FG+CNT modified PI composites showed the best friction reduction ability. |
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