(393h) Effects of Environmental Species on Tribological Properties of MoS2: Using Simulations to Interpret Experimental Observations

Molybdenum disulfide (MoS₂) is a lamellar solid with applications in semiconductor devices, catalysis, and lubrication. The layers of MoS₂ interact via weak van der Waals forces, enabling the layers to slide with a low coefficient of friction in dry or vacuum environments. This makes MoS₂ an attractive solid lubricant for use in satellites and other aerospace applications. However, exposure to environmental species, e.g. oxygen and water, has been shown to degrade the lubricating properties of MoS₂. The precise mechanisms of the interactions between MoS₂ and water and how these interactions affect its tribological properties remain poorly understood.

In this talk, we will present our theory for how adsorbed water impacts the tribology of MoS₂ lubricants, based on experiments and simulations. We report the coefficient of friction over a wide range of humidities using vacuum-based tribological experiments and describe how different types of molecular simulation (density functional theory, Monte Carlo, and molecular dynamics) augment our interpretation of those experiments. We will present computed adsorption isotherms for water adsorption on MoS₂ under realistic atmospheric conditions We will discuss the interaction of water and oxygen with common defects in MoS2, including sulfur vacancies, edge defects, grain boundaries, and oxidized sites. Finally, we will discuss how water adsorption on MoS₂ impacts the tribological performance of the material.

SNL is managed and operated by NTESS under DOE NNSA contract DE-NA0003525