MolNanoTribology · Tuning molecular friction and adhesion by atomic/chemical design

Tuning molecular friction and adhesion by atomic/chemical design

Friction is a phenomenon that is in our everyday life although we tend to remember it only when it is nearly absent such as in the comical popular staple of slipping on a banana peel. Its presence across disparate length scales (earth-quakes, car engines down to molecular machines) reminds us of its ubiquity which endows friction of an utmost practical importance and therefore attempts to control it are almost as old as civilization. Through the works of da Vinci, Amonton and Coulomb the fundamental laws of friction were established and although they hold remarkably well for a wide set of conditions they do not provide any insight into the underlying principles that govern friction. This lack of fundamental understanding has proven to be the Achilles heel of tribology as it hinders our predictive power, e.g. “it is impossible to predict a priori the friction coefficient for a given system”. In a renewed attempt to control friction by atomistic design and aiming to bridge the gap across different length scales, the fields of nanotribology and nanomanipulation were established. Powered by major advances in nanotechnology, they allowed for a nanometer scale control of sliding interfaces, e.g. through Ultra-High-Vacuum (UHV) and Low-Temperature (LT) experiments, which resulted in major advances on our understanding of friction at an atomic scale. Interestingly, during the past decades we have also witnessed a growing desire in miniaturization of devices down to the nanometer scale. Examples such as auto-assembling of molecular structures capable of meeting specific needs (e.g. synthetic photosynthesis, catalysis and molecular electronics) up to molecular-machines (recipient of 2016 Nobel prize in Chemistry) are showing to be promising avenues with a huge technological and economic interest in the decades to come. “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”. The unavoidable downsizing technological roadmap shall certainly call for novel paradigms to mitigate energy dissipation in such small devices. Hand-in-hand with major advances of synthetic organic chemistry allowing us to build nanoarchitectures almost in a atom-by-atom fashion, we urgently need to explore how energy dissipation can be controlled at molecular scale so to guide these efforts into more efficient/greener technologies. In this project we set up a road-map to address this challenge by combining state-of-the-art atomistic Molecular Dynamics (MD) simulations with the unparalleled resolution provided by LT-UHV experiments. Through carefully designed molecules we have shown that friction and adhesion at single molecule can be tuned via chemical design.

Data: CORDIS, © European Union