An Atomistic\nLevel Investigation of the PFDTES–Graphene\nInterfacial Shear Strength and the Stick–Slip Mechanism

1<i>H</i>,1<i>H</i>,2<i>H</i>,2<i>H</i>-Perfluorodecyltriethoxysilane (PFDTES) is the\nmost widely\nused coating material with low surface energy and has the potential\nto be used as a dust-mitigating coating material during lunar landing\nmissions. Graphene can be added to the PFDTES matrix to improve its\nmechanical properties. In this study, molecular dynamics simulations\nwere performed to investigate the interfacial shear strength and friction\nmechanism between the PFDTES matrix and graphene. A systematic molecular\ndynamics (MD) simulation has been performed to calculate the interfacial\nshear strength of the PFDTES–graphene interface with considering\nthe effect of graphene sliding velocity and vacancy defect density.\nFor a pristine graphene layer with a size of 10 nm × 10 nm, the\ninterfacial force between graphene and the PFDTES matrix is around\n3 nN. Like other polymeric materials, the interfacial shear force\nexhibited stick–slip behavior under loading. The interfacial\nshear force will start to increase after the graphene starts sliding\nagainst the PFDTES matrix and reaches a stable plateau in a very short\ndistance. It has been found that the influence of the interfacial\nshear strength from the sliding velocity of graphene is minimal. However,\na significant increase in the interfacial shear strength has been\nobserved after the graphene defect density increased; i.e., the magnitude\nof the shear force increased from 3 nN to around 14 nN after the defect\ndensity increased from 0% for pristine graphene to 40%. It has been\nfound that vacancy defects will increase the fluctuation in the interfacial\nshear force, and it is due to not only the increased roughness near\ndefects but also the stretched bonds in graphene under loading according\nto the distribution of the bond length. This study concluded that\ninterfacial stick–slip behavior also exists in the PFDTES–graphene\ninterface, and vacancy defects will have a significant improvement\nin the interfacial shear strength.