In situ estimation of the chemical and mechanical contributions in local adhesion force measurement with AFM: the specific case of polymers

The atomic force microscope (AFM) was used to perform surface force measurements in contact mode to investigate surface properties of model systems at the nanoscale. Two types of model systems were considered. The first one was composed of a rigid substrate (silicon plates) which was chemically modified by molecular self-assembling (SAMs) to display different surface properties (hydroxyl, amine, methyl and ester functional groups). The second system consists of model polymer networks (cross-linked polydimethylsiloxane or PDMS) of variable mechanical properties, whose surfaces were chemically modified with the same groups as before with silicon substrates. The comparison of the force curves obtained from the two model systems shows that the viscoelastic or mechanical contribution dominates in the adhesion on polymer substrates. Finally, a relationship, which expresses the separation energy at a local scale as a function of the energy dissipated within the contact zone, on one hand and the surface properties of the polymer on the other, was proposed.