FRICTION CONTROL IN THIN-FILM LUBRICATION

A novel method is proposed for controlling and reducing friction in th in-film boundary lubricated junctions, through coupling of small ampli tude (of the order of 1 Angstrom) directional mechanical oscillations of the confining boundaries to the molecular degrees of freedom of the sheared interfacial lubricating fluid. Extensive grand-canonical mole cular dynamics simulations revealed the nature of dynamical states of confined sheared molecular films, their structural characteristics, an d the molecular scale mechanisms underlying transitions between them. Control of friction in the lubricated junction is demonstrated, with a transition from a high-friction stick-slip shear dynamics of the lubr icant to an ultralow kinetic friction state (termed as a superkinetic friction regime), occurring for Deborah number values D-e = tau(f)/tau (osc) > 1, where tau(osc) is the time constant of the boundary mechani cal oscillations normal to the shear plane and tau(f) is the character istic relaxation time for molecular flow and ordering processes in the confined region. A rate and state model generalized to include the ef fects of such oscillations is introduced, yielding results in close co rrespondence with the predictions of the atomistic simulations.