MOLECULAR-DYNAMICS SIMULATION OF ULTRA-THIN LUBRICATING FILMS

Molecular dynamics simulation has been performed in the present study for a Lennard-Jones (LJ) fluid in Poiseuille flow to examine the rheol ogical behaviour of ultra-thin lubricating films. The results show tha t as two solid walls continuously approach each other, the effective v iscosity of the confined fluid increases and goes towards divergence; the critical pressure of the phase transition declines as the film thi ckness reduces; when the separation exceeds ten molecular layers, howe ver, the pressure curve slopes gently and tends to an asymptotic value -the bulk transition pressure of the lubricant; and an in-plane orderi ng structure will develop in the film, which originates from the wall- fluid interface and grows towards the middle of the film as the system pressure increases. It is concluded that the rheological performance of the lubricant may become film thickness dependent and a solid-liqui d transition may be induced when the film is molecularly thin.