Abstract:The application of ionic liquids as lubricants has attracted substantial interest over the past decade and this has produced a rich literature. The aim of this review is to summarize the main findings about frictional behavior of ionic liquids in the boundary lubrication regime. We first recall why the unusual properties of ionic liquids make them very promising lubricants, and the molecular mechanisms at the origin of their lubricating behavior. We then point out the main challenges to be overcome in order to optimise ionic liquid lubricant performance for common applications. We finally discuss their use in the context of electroactive lubrication.

Buckminsterfullerenes (C 60) are near-spherical 2 molecules which freely rotate at room temper-3 ature in the solid state and when dissolved in 4 solution. An intriguing question arises as to 5 whether C 60 molecules can act as molecular 6 ball bearings, i.e. preventing direct contact 7 between two solid surfaces whilst simultane-8 ously dissipating shear stress through fast ro-9 tation. To explore this, we performed measure-10 ments of friction across a solution of C 60 in the 11 boundary lubrication regime. High resolution 12 shear and normal force measurements between 13 mica sheets separated by the C 60 solution were 14 made using a Surface Force Balance to provide a 15 single-asperity contact and sub-nanometer res-16 olution in lm thickness. We nd that, even 17 at small volume fraction, C 60 forms a solid-like 18 amorphous boundary lm sustaining high nor-19 mal load, suggesting that this system undergoes 20 a glass transition under connement. The C 60 21 lm gives rise to a low friction coecient up 22 to moderate applied loads, and we discuss the 23 possible relevance of the ball bearing eect at 24 the molecular scale. 25 2 Ball bearings, consisting of 40 balls running along a groove (e.g. in an axle 41 assembly), are designed to reduce the friction 42 further by transforming sliding into rolling. It 43