Unveiling the Lubrication Mechanism of Graphene Coating on PEEK: A Molecular Dynamics Study Under Dry Friction and Seawater

Graphene coatings have considerable potential to improve the tribological performance of polyetheretherketone (PEEK) under dry friction conditions. For PEEK components operating in marine environments, direct exposure to seawater introduces water molecules and dissolved ions into the sliding interface, which may alter interfacial interactions and lubrication behavior. However, how seawater alters the lubrication mechanism and protective effect of graphene at the PEEK interface remains poorly understood. To address this issue, molecular dynamics simulations were performed to compare PEEK with and without graphene under dry and seawater conditions, thereby revealing the interfacial deformation and molecular response. The results show that graphene preserved the structural integrity of PEEK, reduced its tangential displacement by more than 99%, and decreased the shear stress transmitted into the polymer matrix by approximately 85% to 90%. In the absence of graphene, seawater reduced the tangential mean square displacement of PEEK by approximately 20%, while increasing the normal mean square displacement by about 17%, indicating that seawater redistributed part of the polymer motion from tangential dragging toward normal and local molecular rearrangement. The combined analysis shows that graphene mainly limits the penetration of sliding loads into PEEK, whereas seawater regulates the direction and spatial distribution of the remaining deformation. This work provides a molecular basis for the design of graphene-protected PEEK interfaces in marine friction applications.