CMSP Section announces seminar

[Cond.Matt. & Stat.Mech.Section]

SEMINAR



Wednesday, 10 June -    4:00 p.m.

 

Luigi Stasi Seminar Room -    ICTP Leonardo Building   (first floor)


André SCHIRMEISEN     ( Institute of Applied Physics, Justus-Liebig University Giessen)


"Pushing nanoparticles:   From superlubric sliding to tiny earthquakes"

 
Abstract


In an effort to reduce the friction between sliding components scientists and engineers have developed a multitude of lubrication schemes. In the field of dry lubrication the idea of superlubricity, i.e. the state of (almost) vanishing friction, has received widespread attention lately. One of the most intriguing concepts in this framework is referred to as `structural lubricity', where flat surfaces are thought to slide past each other virtually frictionless if their atomic structures are incommensurate. In this talk, we analyze the fundamental mechanisms that govern the area-dependence of friction in extended but atomically flat contacts of dissimilar materials. The resulting sublinear power laws, which link mesoscopic friction to atomic principles, are then confirmed by measuring the sliding resistance of gold and antimony particles on graphite [1]. On one hand these findings suggest that engineering surfaces with very low friction can be realized up to mesoscopic contact areas. Furthermore, it is shown that nanoparticles can even co-exist in two frictional states, exhibiting ‘frictional duality’: Some particles show linear scaling with contact area reminiscent of Amonton’s friction law while others remain in the superlow friction state of structural lubricity [2]. This duality phenomenon is explained by a model of partial interface contamination. Lastly, we investigated the effect of contact ageing, detrimental in the field of earthquake modelling: The shear strength of tectonic plates is believed to increase logarithmic in time, leading to the infamous strong sudden energy dissipation events, i.e. earthquakes. Interestingly, we find that similar ageing dynamics exist for nanoparticles, as evidenced by stick-slip movements of those objects. A complex interplay of ageing dynamics with thermally activated stick-slip friction explains the commonly observed friction peak at low temperatures [3].

[1] D. Dietzel et al., Physical Review Letters 111 (2013) 235502
[2] D. Dietzel et al., Physical Review Letters 101 (2008) 125505
[3] M. Feldmann et al., Physical Review Letters 112 (2014) 155503