Investigation of programmable friction with ionic liquid mixtures at the nano- and macroscales

Non-mechanical stimuli are used to directly control or program the friction properties of tribosystems. For this purpose, an ionic liquid is used as a lubricant that affects and controls the friction in the presence of external triggers. Here, it is shown that the friction behavior of two surfaces in sliding contact can be controlled and permanently changed by applying an electrical potential to an ionic liquid mixture (ILM). This change in the friction properties was demonstrated both at the nanoscale using an atomic force microscopy (AFM)-based friction force microscopy (FFM) and at the macroscale using a specially designed tribo-setup cell. In tribology, the linking of these two scales of magnitude represents one of the greatest obstacles between basic research and the step towards application-oriented system development and is therefore of fundamental importance. In addition, other parameters affecting the tribological behavior of the system, such as roughness, lubricant film thickness, and wear behavior, were investigated as a function of the electrical potentials. The correlation between the structure of surface-bound ionic liquid layers and the friction behavior can be used to control friction, thus enabling a first step towards tribosystems that automatically adapt to changing conditions.