Design of Low Wear Polymer Composites

Multifunctional tribological coatings rely on combinations of materials to improve properties, such as lubricity and wear resistance. For example, some polymer composites exhibit favorable tribological performance as solid lubricants. Here, classical molecular dynamics simulations are used to investigate the tribological behaviors of a mixed system of polyethylene (PE) sliding over polytetrafluoroethylene (PTFE) with the results compared with the sliding of the relevant homogeneous systems. In particular, oriented cross-linked PTFE and PE surfaces are slid in several relative sliding directions such that the surface chains are in-registry or out-of-registry and at various applied normal loads. The simulation results quantify the ways in which the mixed PTFE-PE system behaves differently than either of the homogeneous systems due to the lack of interlocking phases at the interface. These findings are compared with experimental production of polyetheretherketone (PEEK)-PTFE composites that have unusually low wear rates of 7.0 x 10(-8) mm(3)/Nm, coupled with a steady, low friction coefficient of mu = 0.11 for over two million sliding cycles. The simulation results explain the atomic-scale origins of the frictional properties of this composite.