ROUGHNESS EFFECTS ON THE SLIDING FRICTIONAL FORCE OF SUBMONOLAYER LIQUID-FILMS ON SOLID SUBSTRATES

The sliding frictional force of a liquid submonolayer in contact with a random rough surface in an oscillatory motion is considered. The fri ctional force is proportional to the square of the sliding velocity up silon, F-j similar to upsilon(2), with a proportionality factor that d epends an the particular roughness configuration. Analytic calculation s are performed for self-affine roughness characterized by the roughne ss exponent 0<H<1, the roughness amplitude Delta, and the correlation length xi. The proportionality factor is shown to decrease with increa sing H and decreasing ratio Delta/xi, following a power similar to Del ta/xi(H). [S0163-1829(98)01608-7].