Abstract
Adhesive boundary lubricated surfaces display different response under shear depending upon the experimental conditions. Particularly, the transition between different dynamic phases can be triggered by changing the velocity of sliding. Above some critical driving velocity, the sliding transits from a steady kinetic state to an "inverted" stick-slip regime where, in contrast to conventional stick-slip, the friction spikes point down rather than up. Here we report a second transition occurring at higher shear rates, with a second steady-state smooth sliding regime emerging from the inverted stick-slip regime. The new steady state exhibits a lower friction than the one of the first steady state at the onset of the transition to the stick-slip regime. A sequence of complex oscillatory sliding states with periodic and aperiodic patterns can be observed between the high-velocity smooth steady state and the highly periodic stick-slip regime.