Computational tribology: a case study about molybdenum disulfide

Abstract: One third of energy produced by industrial countries is lost as friction. High wear caused by friction means that ca. 35% of the industrial production is used to replace degraded products, whilst causing the breakdown of machinery, resulting in safety risks and environmental pollution. Controlling and reducing friction is a fundamental step in attaining the sustainable development of our society, as detailed in the Brundtland report[1].
This goal is typically achieved by introducing a liquid-based lubricant to the interfacial region. To circumvent any potential shortcomings associated with wet lubrication (risk of contamination, failure to perform under extreme conditions etc.) engineers began to exploit solid state lubricants such as graphene, boron nitride, and transition metal dichalcogenides (TMDs). Solid lubricants proffer a number of advantages over wet lubricants, such as low evaporation rate, increased working temperature range and corrosion resistance.
Molybdenum disulfide, the most studied member of the TMD family, has been used as solid lubricant for decades, showing one of the lowest known coefficient of friction among solids. Moreover, MoS2 was the first material able to reach the so-called superlubricity regime (i.e., an apparent loss of frictional force, that decreases below detection limits in macroscopic measurements)[2].
In this seminar, I will show that classical molecular dynamics simulations can be used as “magnification glasses” to investigate phenomena which are typically hard to follow experimentally. Starting from an open question from mechanical engineering about how the lubrication mechanism of molybdenum disulfide takes place, I will guide you through the computational study that we performed[3], focusing on how structural rearrangements (i.e., the formation of ordered phases from amorphous structures) can finally affect the tribological properties of the material.

[1] K. Holmberg, A. Erdemir, Friction, 5, 263 (2017).
[2] J.M. Martin, C. Donnet, Th. Le Mogne, Th. Epicier, Phys. Rev. B, 48, 10583(R) (1993).
[3] P. Nicolini, R. Capozza, P. Restuccia, T. Polcar, ACS Appl. Mater. Interfaces, 10, 8937 (2018).