The viscosity of lubricating oils is generally dependent on temperature. To reduce this dependence, additives commonly known as viscosity index improvers have been developed. Their efciency is strongly controlled by the nature of their afnity with the base oil and their interactions with surfaces in the state of connement. A molecular tribometer derived from a surface force apparatus has been used to characterize the mechanical and tribological behavior of two semidilute polymer solutions. At large distances, two regimes can occur:

a. The polymer can be repelled from the wall and a depletion layer is built up. b. The polymer sticks to the wall and an adsorption layer is depicted.