Richard Kouitat Njiwa

Abstract:

Friction is known to be a multi-scale phenomenon which starts at the atomic or molecular scale, and emerges at the macro-scale by means of the so-called real contact area. This multi-scale process generally involves some self-organization processes within this real contact area, which generally occurs with the reduction of the number of degrees of freedom. Hence, macro-scale properties of physical systems – such as the coefficient of friction, the Young modulus, the yield strength, or the fracture toughness – cannot be deduced directly from the molecular scale properties because these properties are defined by meso-scale objects such as defects, grains, and asperities – especially, roughness for tribological purpose. Thus, (i) tribological properties – including friction and wear processes – need to be studied by considering a multi-scale approach, in order to understand how these phenomena emerge from atomic to macroscopic scale; (ii) specific emerging tribological behaviors can be tailored or adjusted by means of self-assembled monolayers or hierarchical surfaces or materials. In this paper, this approach will be illustrated by considering various tribological studies, which have been investigated at various scales in our respective teams.