Superlow Friction of Graphite Induced by the Self-Assembly of Sodium Dodecyl Sulfate Molecular Layers

Two-dimensional (2D) layered materials usually exhibit superlow friction properties when the shear occurs between incommensurate interface lattices. In this work, we propose a new method, which is different from the traditional structure superlubricity, to achieve the superlow friction of graphite. This method involves attaching sodium dodecyl sulfate (SDS) molecular layers on the friction surfaces by self-assembly and sliding across the aqueous medium. The friction coefficient between graphite and silica can be reduced to approximately 0.005 at a maximal contact pressure of 31 MPa by this method. The mechanism of the superlow friction was investigated by using an atomic force microscopy and can be attributed to the extremely weak interaction between graphite and SDS molecules. It forms a shear plane of SDS molecules/graphite with extremely low shear strength and extremely low adhesion. This finding provides new insights into the molecular mechanisms underlying an efficient lubrication of 2D layered materials in liquid.