Mechanical and tribological properties of layered epoxy coatings synergistically enhanced by graphene and polytetrafluoroethylene: molecular dynamics simulations and experimental verification

Epoxy resin coatings have high adhesion properties and excellent chemical resistance, and are widely used in the fields of ships, automobiles and electronic appliances. However, the shortcomings of epoxy resin, such as high brittleness, poor thermal stability and insufficient abrasion resistance, seriously affect the durability of the coating. In this paper, the mechanisms of mechanical and tribological properties of graphene (Gr) and polytetrafluoroethylene (PTFE) synergistically reinforced epoxy resin (EP) double layer coatings (with pure epoxy resin as the bottom layer) on Cu substrates were investigated by molecular dynamics simulations. The modeling includes pure epoxy double layer coating (Pure EP-EP), PTFE reinforced epoxy double layer coating (PTFE/EP-EP), and graphene and PTFE synergistically reinforced epoxy double layer coating (Gr/PTFE/EP-EP). The counter frictional part for these coatings is Cu metal. The simulation results show that by analyzing the interaction energy between the coating and the Cu substrate, the double layer coating with Pure EP as the bottom layer is found to have a better adsorption capacity, which can effectively extend the service life of the coating, compared with those with PTFE/EP or Gr/PTFE/EP as bottom layer. By calculating the shear modulus, Young's modulus and bulk modulus of the Gr/PTFE/EP-EP coating, the synergistic enhancement mechanism of the mechanical properties of the Gr/PTFE/EP-EP coating was revealed. In particular, the PTFE/EP-EP coating exhibited a reduction in mechanical properties and the mechanical property simulation results were verified experimentally. Compared with the Pure EP-EP double layer coating, the PTFE/EP-EP and Gr/PTFE/EP-EP double layer coatings showed a reduction in friction coefficient of 9.52% and 23.81%, wear rate of 46.69% and 76.63%, and mean square displacements (MSD) of 22.4% and 81.34%, respectively. The synergistic effect of Gr and PTFE on the tribological performance of Gr/PTFE/EP-EP coatings was better than that of PTFE/EP-EP coatings with PTFE only. The interaction of Gr and PTFE with EP was analyzed by comparing the changes in radius distribution function (RDF), relative concentration, temperature and velocity in the thickness direction of PTFE/EP-EP coatings and Gr/PTFE/EP-EP coatings, which further revealed the synergistic enhancement mechanism by Gr and PTFE.