Active Control of Sliding Friction

Abstract

Reducing friction is strongly and endlessly demanded in a variety of engineering applications for saving energy and improving machine performance. Meanwhile, high friction is beneficial to many applications such as braking, traction driving and friction damping. It is desired that sliding friction can be controlled actively so that the magnitude of friction coefficient of a tribosystem in service is able to be manipulated timely in response to specific requirements of practice. For a class of the tribosystems including steel/steel, ceramics/steel and ceramics/silicon sliding contacts lubricated by aqueous solutions, it has been found that by imposing an external electric field friction coefficient can be indeed reduced or enhanced several times, depending on the polarity and magnitude of the applied electric field as well as the surfactants in the aqueous solution. Moreover, the change in friction coefficient is recoverable between the charged and non-charged states, and its response time to the external potential is in the order of sub-second. Both of the electrophoresis of surfactants and the electrolysis of water under electric fields are probably involved in the dramatic change of sliding friction.