Kinetics of adhesion on a viscoelastic sample by force microscopy

Indentation of the tip of an atomic force microscope is carried out under purely adhesive force, on a sample that is in a viscoelastic state. A characteristic size of the contact area is also measured by recording the tangential force while a small lateral modulation of the sample position is applied. Both the contact size and the penetration depth of the tip follow the compliance function of the material. It is shown that the kinetics of the adhesion can be described as the adhesive equilibrium of the tip on an elastic material whose compliance is the instantaneous value of the compliance function of the viscoelastic material. Implications for the analysis of the force-distance curves are discussed.