Tribochemistry of Solid Lubricants by ab initio Molecular Dynamics, Effects of Mechanical Stresses on Reaction Kinetics

摘要

We perform ab initio molecular dynamics simulations to monitor the chemical reactions occurring at the interface of important solid lubricants interacting with water molecules under the effects of mechanical stresses (load and shear). We considered molybdenum disulfide (MoS_2) and graphite, whose lubricating properties are affected by air humidity in opposite ways for reasons that are not fully understood. Our simulations show that water molecules are attracted by defects in MoS_2, but we never observe chemical reactions that lead to MoS_2 oxidation. We also find that water molecules physically interacting with MoS_2 layers significantly impede sliding. The tribological properties of MoS_2 are compared to those of few-layer graphene both in terms of interlayer slipperiness and interaction with water. We investigate the role of mechanical stress on reaction kinetics by systematic analysis of the effects of load and shear on water dissociation at diamond interfaces.