The paper
peruses the frictional response of an important metal working lubricant
additive,
sodium oleate. Frictional
force microscopy is used to track the
response of the molecules self-assembled on steel substrate of 3-4 nm roughness
at 0 % relative humidity. The
friction-normal load characteristic emerges as
bell-shaped, where the peak friction and normal load at peak friction are both
sensitive to substrate roughness. The response at loads lower than that
associated with the peak friction is reversible while that at higher loads is
irreversible. We suggest that a new state of the surface material is created
when the normal loads are high.