Current perspective towards a general framework to describe and harness friction at the nanoscale

Macroscopic friction is the result of the interplay of several processes occurring at different scales; an atom-scale description of the tribological interactions is then paramount for the explanation of the elementary phenomena at the basis of such processes, and finds immediate application in technological fields involving nanostructured devices. At the moment, there is no theory which tells us what is the friction coefficient given the atomic description of two surfaces in contact: it is measured experimentally or computationally case by case at specific environmental parameters and chemical composition of the moving surfaces. A general theory describing nanoscale friction is then desirable to reduce human effort, search time and material costs necessary to design new tribological materials with target response. We here provide a selective overview of theoretical and computational models which, from our perspective, may pave the avenue towards a unified theoretical framework of nanofriction. In this respect, we believe that the key aspect is to identify a novel mathematical formulation of friction based on its energetic aspects, i.e. energy dissipation, rather than its dynamical effects, i.e. hindering the relative motion of interacting surfaces. Ultimately, such avenue might lead to a way to predict the value of the friction coefficient of two surfaces in contact from the sole knowledge of the atom types and their arrangement, without the need to measure it in operative conditions: one of the biggest challenges in the field of nanotribology.