Normal Contacts of Lubricated Fractal Rough Surfaces at the Atomic Scale

The friction of contacting interfaces is a function of surface roughness and applied normal load. Under boundary lubrication, this frictional behavior changes as a function of lubricant wettability, viscosity, and density, by practically decreasing the possibility of dry contact. Many studies on contacts with atomic scale roughness adopt simplified sinusoidal shapes for the roughness, comprising a deformable surface in contact with a rigid flat; however, roughness has a fractal nature. In this paper, molecular dynamics is used to simulate the three-dimensional contact between atomically rough fractal surfaces of nickel lubricated with different volumes of hexadecane molecules. Results show that the contact force on the solid surfaces decreases and changes in the surface RMS roughness diminish with increasing lubricant volume.