Molecular Tribology: Chemically Engineering Energy Dissipation at the Nanoscale

Friction is a phenomenon which is present in our everyday life although we tend to remember it only when it is nearly absent such as when “slipping on ice”. Its presence across disparate length scales (earthquakes, car engines down to molecular machines) reminds us of its ubiquity which endows friction of an utmost practical importance. Therefore, attempts to control it are almost as old as civilization and intrinsically tied to our technological progress. Interestingly, during the past decades we have witnessed a growing progress in miniaturization of devices down to the nanometer scale. “Special problems occur when things get small […] and it might turn out to be advantages if we knew how to design for them”, said Feynman when discussing the prospects of building “infinitesimal machinery”. To achieve this goal, and to design efficient molecular nano-engines, it becomes imperative to unveil the non-equilibrium processes governing friction and energy dissipation at a molecular level. This chapter provides a comprehensive review of recent advancements in understanding nanoscale friction and the role of internal molecular degrees of freedom in controlling energy dissipation during friction. We discuss how recent advancements in experimental techniques, particularly those linked to Scanning Probe Microscopy, have significantly enhanced our comprehension of the mechanical characteristics of individual molecules and their influence on dissipation processes. We delve into how these internal degrees of freedom facilitate control over energy dissipation, unlocking various pathways to achieve different applications at the nanoscale, such as superlubric states through molecular flexibility. Furthermore, we analyze potential applications of the energy dissipation pathways in novel mechanisms for achieving controlled locomotion of molecular machines.