New techniques are required to apply atomic scale simulation to study the physics of nanoscale friction. One of the primary limitations of current simulation methods is the limited time scales they can access.  Imagine, you can study a single molecule in isolation and watch it evolve for seconds at a time, but if you want to get a more complete picture of a system (i.e. tens of thousands of atoms), the time you can watch the system decreases dramatically, down to the order of microseconds (typically less).  It’s very difficult to watch systems realistically evolve with this time constraint.  For example, AFM and MEM experiments’ sliding speeds clock in at speeds of 10^-6 to 10^-9 m/s.  Current methods are unsuitable for simulating processes like these that take place at sliding rates considerably slower than 0.1 m/s.  So to solve this issue, we’re working on developing techniques that aim to extend the time scales accessible with simulation.  These novel simulation methods will also be extended to inherently non-equilibrium simulations. We anticipate that such long-time non-equilibrium simulations will be useful for testing theories of friction against simulations in which a single-asperity contact is realistically modeled,, something that has not yet been realized.

The goal of this project is to expand the base of knowledge regarding the fundamental physics and chemistry of friction on the nanoscale. Expanding this knowledge base is critical for the future design of micro- and nano- electromechanical devices (MEMS/NEMS), for interpreting the results of atomic force microscopy (AFM) for surface characterization and for developing effective methods for lubrication in precision applications. It is our hope that these investigations will enable the analysis of transitions in frictional response with respect to sliding rate and temperature. Further, these methods should also lay the groundwork for investigations into the effect of adsorbates such as hydrocarbons and the influence of surface chemistry on friction and wear, with the potential to be extended to a variety of other systems including studies of fracture, fatigue, adhesion and other non-equilibrium materials processes.