In Situ Fabrication of Low-Friction Sandwich Sheets Through Functionalized Graphene Crosslinked by Ionic Liquids

Graphene is considered a wonder material for fundamental research and industrial application, whereas its poor dispersibility and incompatibility in lubricants have impeded the application for solving lubrication problems. Here, in situ fabrication of effectively functionalized graphene sheets was developed through a moderate electrochemical method for exfoliating graphite into graphene sheets in ionic liquids solution. The as-fabricated graphene sheets with the charged groups of ionic liquids (ILs) could be self-assembled together to form the multilayer sandwich structure through the electrostatic interaction. Self-assembly multilayer graphene (MLG) exhibits so high-density coverage of functional groups that some amorphous regions are formed on the graphene basal plane, which significantly improves its dispersibility and stability in ILs lubricant. Moreover, the functionalized MLG as a novel lubricant additive greatly enhances the friction-reducing and antiwear abilities for the contact of steel/steel (friction coefficient and wear volume lubricated by ILs with MLG at applied load of 200 N and 150 degrees C were reduced by up to 55.9 and 84.2 %, and under high vacuum were reduced by up to 36 and 94.3 % with pure ILs as a comparison, respectively), which is attributed to the synergies of ILs and MLG because ILs with functionalized MLG can form the physical adsorptive film and tribo-chemical reaction film on the rubbing surface during friction process.