Inverted stick-slip friction between two molecularly smooth adhesive surfaces sliding in a solution

Abstract

Sliding of adhesive boundary lubricated surfaces immersed in an aqueous surfactant solution has been studied with a Surface Force Apparatus (SFA). An unconventional stick-slip regime with “inverted” stick-slip events is observed. In contrast to the conventional scenario, the friction spikes point down (slip-stick) rather than up. The transition from smooth to (inverted) stick-slip sliding occurs above some critical sliding velocity, which is again different from normal stick-slip behavior where stick-slip spikes disappear, rather than appear, above the critical velocity. This unusual behavior has been characterized with respect of the driving velocity, the applied normal load, the temperature and the bulk surfactant concentration. A general model based on the kinetics of formation and rupture of adhesive links between two shearing surfaces as a function of the sliding velocity allows a quantitative interpretation of the results.